The foot is a limb that is not given much importance when compared to other vital organs such as the brain or heart. However, the foot is a very complex mechanical structure that is made of 26 bones, 33 joints, and more than 100 muscles and ligaments. About a quarter of the bones in the human body and about a fifth of the joints are found in our two feet. That is why Leonardo da Vinci described the human foot as an engineering and artistic masterpiece.

A healthy person takes about 5,000 steps a day. Given a life of eighty years, a person takes about 150 million steps throughout their life. Assuming that each step is 75 cm, a person walks about 110,000 kilometers throughout his life. This corresponds to walking around the equator about 3 times. Apart from that, a typical person stands for around 2-4 hours a day. During all these activities, the human foot carries the entire body’s weight. In standing position, body weight is supported by two feet while activities such as walking and running are done by only one foot for a certain period of time. While standing, the feet carry 100% of their body weight, while walking, this rate rises up to 150%. While walking, the foot that needs to be lifted from the ground approaches the ground again with an acceleration in the same direction as gravity. Therefore, the impact force at the moment the foot touches the ground corresponds to 150% of a person’s body weight. In cases of severe effects such as running and jumping, this force easily increases up to 5 times the body weight and up to 10 times in some people. For a person weighing 70 kilograms, this force can be 105 kg (or about 1050 Newton) in walking, and easily 350 kg (or about 3500 Newton) in running or jumping. Assuming that a person walking for an hour takes 5,000 steps, the foot pulls a total of about 500 tons of load (5,000 steps x 105 kg). In running, this figure will increase approximately three times.

The foot has been created with a wonderful mechanical and construction design that is able to consistently sustain such high loads. The bones and muscles of the foot add two different belt designs to it. One of them, the structure called the longitudinal belt starts from the heel bone (calcaneus) and ends with its metatarsal bones (Figure 1). Some researchers claim that the long arch is divided into two parts as the inner (medial arch) and the outer arch (lateral arch). However, both structures resemble bridges built in arches. The second arch on the foot is called the transverse arch. This belt is perpendicular to the long belt from the right side of the foot to the left side and is shorter in length (Figure 2).

Therefore, the foot is a marvelous structure consisting of roughly two arches. This structure of the foot can be compared to arch bridges or a dam. The arch structure is known as the strongest structure against steep loads in construction areas due to the robustness of the designs against compression forces in cases of vertical loading. Therefore, hydroelectric dams are constructed in the form of arches or arcs in order to make the most resistant model against hydrostatic pressure.

The arch structure of the foot is very flexible and can also move up and down like a car suspension and acts as a shock absorption. If there was no such structure on the foot, the impact forces during walking and running activities would be higher and cause chronic foot pain. The flatfoot complication is a result of a damage in the arch structure in the foot which comes from birth or develops afterwards. Flatfoot patients are often unable to perform long-term activities and experience foot pain as well as complications in other organs of the body.

Our feet’s arch structure is not the only factor involved in shock absorption that is designed against mechanical forces. The layer of fat on the bottom of the foot also contributes to this process. In a healthy person, this fat layer, which has a height of 2.5 cm under the heel, drops to 5-7 mm in the front part of the foot. It also helps to distribute the vertical and horizontal forces caused by standing or walking evenly on the sole of the foot. At the same time, it serves as a source of heat insulation and helps protect our feet from hot or cold surfaces. In some diseases such as diabetes, in which this fat layer melts or decreases, wounds called foot ulcers can develop because the shock absorption and load distribution get damaged. Mechanical pressure is calculated by dividing the amount of mechanical force by the surface area on which it is applied, meaning that smaller surfaces areas are subjected to more pressure. This is why very tiny needles, despite weighing almost nothing, can pierce our skin and cause pain. Similarly, damage to the fat layer under the foot causes the forces applied under the foot to act on a limited surface area. For example, the reduction of fat in the area just below the heads of the metatarsal bones reduces the “cushioning” effect in this area and causes a pressure in high values. This extra pressure can cause tissue damage along with the aforementioned foot ulcers.

Such a situation that will cause pain in a normal person cannot be felt by many diabetics. If diabetes is not well controlled, neuropathy or a “lack of feeling” may occur as a complication. Dead nerve cells become unable to feel pain which can result in people not knowing about harm that is being done to their body. Diabetic patients who develop neuropathy would not feel fatty layer damage and accompanying high pressure values whereas a typical person normally would. Untreated foot ulcers can become infected and can turn into gangrene. Since the gangrenous foot has to be cut, diabetes unfortunately causes a large number of amputations. Such amputations are sadly quite frequent throughout the world due to diabetic neuropathy. Dr. Paul Brand, who studied diabetic foot ulcers, defined pain as a gift from God that no one wanted. Sometimes, what we do not like might be better for us (Qur’an 2:216); likewise, pain can cause a lot of trouble to people but it can also alert us of dangers and harm to our bodies.

Thus, foot care is very important in diabetics. The following three actions are recommended to patients; daily inspection of the foot; daily washing; and control of the inside of the shoes. The pest, pebble, or similar hard object in the shoe that can be very harmful for diabetics with loss of sensation would be removed this way. On the other hand, when such a hard object remains in the shoes, patients may step on them repeatedly without feeling it which will likely lead to an ulcer case.

With its pain that works like a health alarm, extraordinary mechanical loads it carries, heat insulation and shock absorbing features, the human foot is a wonder of art that calls for contemplation.

Enveloping our body like a piece of clothing, our skin is a miraculous organ that both forms a barrier against potential invaders and plays a crucial role in the maintenance of vital functions. It is a mirror that reflects our experiences, memories, and fate with the lines and marks on it. With a surface area of 1.72 square meters and a weight of approximately 9.6 kg, including the fatty tissue under it, the skin is the largest organ in our body and life cannot possibly be maintained without it.[1] It is through the skin that we learn knives cut, fire burns, and our mother has very soft hands. We don’t even realize, but the skin quietly carries out other numerous functions such as sweating toxins out of the body, maintaining body temperature, and synthesizing vitamin D.[2] Some of these functions are related to the sun and the protection of our body from it.

The sun emits all kinds of rays across the electromagnetic spectrum. The lethal ones among these rays are filtered by the atmosphere that envelops the Earth, so very few of these dangerous rays reach the land.[3] The rays that reach Earth are visible (wavelengths of 400-700 nm) and ultraviolet (wavelengths of 100-400 nm) rays. Ultraviolet radiation comes in three types: UVA, UVB, and UVC.

Having wavelengths of 320-400 nm, UVA rays make up 90% of the UV that reaches Earth’s surface. Regardless of whether it is cloudy or sunny, the same amount of these rays reaches Earth and penetrates as far as the lower layers of the human skin. UVA rays damage the connective tissue under the skin, causing the skin to get old and the formation of free radicals, which indirectly cause DNA damage, hence terminal skin cancers or melanoma. Rays that come in these wavelengths are also largely responsible for allergic reactions on the skin.

With wavelengths of 280-320 nm, UVB rays make up 5-10% of the UV radiation reaching Earth. These rays help with the synthesis of vitamin D but also cause sunburns and the synthesis of melanin in the skin. UVB rays also have a role in mutating genes that prevent growth of tumors, thus leading to the development of skin cancers other than melanoma.

With wavelengths of 100-280 nm, UVC rays are harmful to living things. When they reach the Earth’s atmosphere, UVC rays interact with the oxygen atoms here. This interaction leads to the formation of the ozone layer, which prevents UVC rays from almost never reaching the ground. These dangerous waves have been put into humankind’s service by being employed in the creation of the protective ozone layer.

Ultraviolet rays and the harmful effects of visible light on the skin

There are short-term and long-term effects of UV rays on the skin.

The short-term effects are sunburn, heat stroke, allergic reactions, suntan, and viral diseases such as herpes, which are usually felt shortly after exposure to the sun and can be triggered by suppression of the immune system. The long-term, accumulative effects are photo-aging (the skin getting wrinkly due to solar rays), sunspots, cataracts, and the development of skin cancers.[4]

On the other hand, our skin is not entirely unprotected against the dangerous effects of the sun. The keratin layer in the epidermis, the uppermost layer of the skin, absorbs or disperses light, so the amount of light penetrating into the layers below is significantly lowered. Beta-carotene in the skin along with some enzyme systems reduce free oxygen radicals released after exposure to the sun and thus eliminate solar damage. Likewise, melanin, which gives our skin its color, lies above the nuclei in skin cells and acts as an umbrella that protects the cellular DNA from solar radiation.[5]

Six subgroups of skin types have been determined according to color of the hair, eyes, and skin, as well as the skin’s reaction to solar rays. This classification is widely accepted for identifying risk groups and determining specific protection measures.[6]

Although the number of melanosomes, or melanin-producing cells in the human skin, is the same in all humans, the color of the skin is determined by the genetic differences in the type, amount, and size of melanin pigments. Melonosomes in Europeans are small and light, while those of Africans are larger and darker.[7]

The importance of protection from the sun

The frequency of skin cancer has been increasing, which is precipitated by the fact that the ozone layer has gotten thinner and people are not well informed about UV protection. Many people take beach vacations and sunbathe, do mountain sports, have tanned skin, work in open air professions (such as construction workers, lifeguards, and tour guides), and they do so without much care.

For protection, we should first know that harmful effects of solar rays accumulate over time. The damage caused by the sun is stored in the body, just like change we save in a piggy bank. Unfortunately, we accumulate 40-50% of the total damage we are exposed to in a lifetime in the first quarter of life – that is, during childhood and our teenage years.[8] The skin’s natural protection mechanisms are not fully developed during these periods, nor is our understanding of protection. A research study carried out in Australia has shown that the rate of malign melanoma seen in young people can be reduced by 73% through effective solar protection methods.[9]

The major reason for wrinkles, the primary and fundamental indication of aging skin, is not in fact our age but the sun. UVA and UVB rays break down the connective tissue below the skin, disrupt the skin’s repair mechanisms, and cause skin aging (or photo-aging). Therefore, photo-aging takes place faster and earlier in people who work outside.[10]

{Picture: Photo-aging visible on one side of a truck driver’s face}[11] 

It’s imperative that we begin teaching children and adolescents about UV protection: having suffered five sunburns in childhood and early youth increases the risk of developing melanoma by 80%.[12] Children shouldn’t spend long hours in the midday, summer sun. 

Solar damage isn’t just more likely in children and teenagers, but also in people with skin type 1 or 2 (light skin), red hair, and/or colored eyes (blue); people, especially light-skinned people, with many skin moles; people whose family members have or had skin cancer; those who have a skin disorder triggered by the sun (lupus, dermatomyositis, rosacea); and people who have innate light sensitivity (albino, xeroderma pigmentosum, etc.). All these groups must be particularly careful about protecting themselves from the sun.

What are some ways to protect ourselves from UV Rays? Well, because UV radiation bombards the Earth most intensely at noon during the summer, staying indoors is greatly recommended between the hours of 10:00 am and 4:00 pm.  Additionally, the reflection rate of solar rays is higher by the seaside and in snowy environments.[13]

Wearing appropriate clothes is still the most effective and the least expensive method of sun protection. Clothing can have a solar protection factor (SPF) of 15-30. The level of protection is determined by the type of fabric, number of pores, and type, color, and thickness of weaving. The best clothes are made from cotton, silk, and denim and are unbleached and woven tightly. Wet clothes are more permeable. The use of wide hats, sunglasses, and umbrellas are also important for protection.

In addition to these measures, sun protection creams should also be used. The idea that protection creams will prevent the synthesis of vitamin D, voiced frequently lately, should not prevent the use of sun protection because the solar rays we receive during the day from the face and hands are sufficient for the synthesis of vitamin D. A person should pick a sun cream appropriate for their skin and apply it in sufficient amounts 20 minutes before going out. Babies should be protected through natural means, and physical sun protection should be used for children and pregnant women. A person should reapply sun protection products every two or three hours while outside, and, if planning to swim, they should choose water resistant products.

Besides physical protection that blocks, scatters, or reflects solar rays, there are also skin-absorbable chemical protections with cosmetically accepted formulations that eliminate light by absorbing it.

Generally speaking, a good sun protection should protect against both UVA and UVB rays. It should be cosmetically acceptable, non-toxic, water and perspiration resistant, and at the appropriate SPF (sun protection factor) level. However, because reapplication is required every two to three hours, protection above SPF 50 is the same. Therefore, it is no use buying a more expensive, higher protection product.[14] For people with type 3 skin (darker white skin with gold tone), SPF 30 is sufficient. For light skinned people, children, and pregnant women, however, SPF 50 is recommended.

SPF is the number indicating by how many more times a sunscreen protects the skin against UVB than the skin itself. Skin type is very important in sunscreen choice. The natural protection period of a person with type 1 skin is 5-10 minutes, while it may go up to 90 minutes for a person with type 6 skin. In other words, a light-skinned person gets a sunburn in 5-10 minutes of exposure, while a dark-skinned person may not get one at all. Therefore, these people should not choose products at the same SPF level. For example, if the skin’s self-protection duration is five minutes, a sunscreen with a SPF of 30 provides the same protection for 150 minutes.

Apart from sun protection creams, oral products can also help with sun protection. For example, oral zinc intake is proven to prevent cellular and DNA damage caused by UV radiation. Vitamin C is effective at preventing UVA rays due to its antioxidant properties and vitamin E at preventing UVB rays. In addition, the intake of beta carotene (a precursor of vitamin A) and bioflavonoids (also called vitamin P which generally has effects similar to vitamin C), found in orange and red fruit, protects against UV damage. Polyphenolic compounds in green tea also display protective properties against UV radiation.[15]

Finally, we should remember that using a sun protection product is a small part of our attitude toward your overall protection from the sun. Considering the role of the ozone layer in filtering the sun’s harmful rays, we should protect the perfect balance in the universe and re-evaluate our responsibilities and future actions for the maintenance of this balance.

Notes

[1] livescience.com.

[2] Gilchrest BA. “Sun exposure and vitamin D sufficiency,” Am. J Clin Nutr. August 2008, Vol. 88 # 2 570S-577S.

[3] Understanding UVA and UVB. skincancer.org.

[4] sciencelearn.org.nz.

[5] “The Protective Role of Melanin against UV Damage in Human Skin.” Photochem Photobiol. 2008; 84(3):539-549.

[6] laserdocs.co.uk/easy-way-to-find-out-your-fitzpatrick-skin-type/

[7] Ibid.

[8] Adele CG, Sarah C Wallingford and Penelope M. “Childhood exposure to UV radiation and harmful skin effects: Epidemiological evidence.” Prog Biophys Mol Biol. December 2011, 107(3): 349-355.

[9] Green AC, Williams GC, Logan V, Srutton GM. “Reduced Melanoma after Regular Sunscreen Use: Randomized Trial Follow-Up,” Journal of Clinically Oncology. 20 January 2011, Vol. 29 # 3:257-263.

[10] Fitzpatrick’s Dermatology in General Medicine.

[11] www.nejm.org/doi/full/10.1056/NEJMicm1104059.

[12] Markovic SN, Erickson LA, Rao RD, et al. “Malignant Melanoma in the 21^st Century, part 1: Epidemiology, risk factors screening, prevention and diagnosis.” Mayo Clin Proc, 2007; 82: 364-380.

[13] Skin cancer prevention and early detection. www.skincancer.org.

[14] www.dermnetz.org.

[15] Halliwell B. “Free radicals, antioxidants and human disease.” Lancet 1994; 344-:721-724.

In our previous article where we discussed the mind-boggling complexity of our eyes’ retinas. We learned about the ten separate layers of cells, but we did not elaborate on the intricacies of their creation. We also learned how the substance in the cone cells, called rhodopsin, is destroyed on exposure to light and then regenerated in the dark. We thus touched on the wisdom behind the existence of both night and day.

The destruction of rhodopsin is caused by the generation of electricity after its contact with light. This electric impulse is transmitted from cones and rods to either horizontal or bipolar (having two poles) cells. The section between these two different layers of cells is called the outer plexiform layer, where horizontal cells receive electric impulses from rods and cones, and carry them to neighboring bipolar cells. The horizontal cells are also charged with transmitting electricity horizontally between rod and cone cells. The signals make it possible for shapes to be carried to the central nervous system in an appropriate contrast. Other signals are blocked so that the borders of the place of contact with light can be clarified in the brain, which does not receive an excessive load of signals. If it were not for these cells, it would be harder to perceive borders because the line of difference between two different colors would not become clear.

Bipolar cells have two opposite poles. They are created as one of two types, in accordance with their functions: one amplifies generated electric impulses, while the other inhibits the transmission of excessive impulses from around the perceived object to the brain. Bipolar cells provide the contrast necessary for making borders clear. They make clear vision possible, and yet most people have never heard of this wondrous gift inside their retinas!

How is contrast enabled?

Thanks to an innate ability, our brain does not occupy itself with regions that have the same color or the same light. It will not be stimulated much if, for example, a wall is completely white or a car is bright red all over. If, however, there are other colors on the wall, say, a white moon or star on a red background, then there will be more stimulation in the brain. Suppose we place the shape of a crescent on the wall. The stimulated parts of the brain will lie along the sharp ends of the crescent, not in the inside or outside of it. The stimulation in the brain is less associated with non-contrasting regions than contrasts in view. The higher the contrast, i.e. the greater the difference between light and dark areas, the greater the degree of stimulation.

Amacrine cells in the inner plexiform layer of the retina enable horizontal transmission. There are up to 30 different types of these cells, and they carry out at least five to six functions. For instance, one type of Amacrine cell transmits electric impulses from cones and rods to bipolar cells, then to other Amacrine cells, then to ganglion cells, and finally to the brain.

Another type of Amacrine cell responds strongly to the onset of the visual signal, while another to its completion. One other type reveals the difference in light intensity regardless of direction, while still others respond to the movement of a light point in a certain direction in the retina, causing a perception in the brain as to the direction of the light.

Further research may reveal yet more functions. Amacrine cells might have such functions as regulating the intensity of electric impulses specific to each wavelength and generating different levels of impulses for moving or stationary objects.

The function of the ganglion cells in the innermost layer of the retina is to help ensure that the electric impulse generated and corrected in the retina is eventually transmitted to the brain. Three distinct ganglion cells are identified in the retina. These cells are represented with the letters W, X, and Y. W cells are assigned the task of transmitting signals from rod cells, which produce black and white visual signals in the dark. Making up about 40 percent of all ganglion cells, they have diameters of less than 10 micrometers and transmit signals at a speed of 8 m/sec. It is evident that these cells are assigned the task of perceiving objects in the dark as rough, vague shapes.

X cells, on the other hand, transmit electric impulses to the brain, creating precise color pictures of objects. Making up 55 percent of ganglion cells, they have midsize diameters (10-15 micrometers) and transmit signals at a speed of 14 m/sec.

The largest of ganglion cells (with diameters as long as 35 micrometers), Y cells are assigned the task of transmitting instant changes in sight. Making up only 5 percent of ganglion cells, they send signals at speeds of 50 m/sec.

Sending intense signals in split seconds, Y cells inform the central nervous system immediately in case of a threat or an unusual encounter. When our body or eyes face a threat, these cells help protect us by warning the brain to move away from the threat or close our eyelids rapidly. If it were not for these cells, we would not be able to reflexively close our eyes and thus protect them. It’s incredible to ponder how complex these systems are – and how perfectly they’ve been created.

Between layers of cells there also lie layers of network that house neurons and their connections (synapses). These cells too have subgroups trained to carry out specific tasks. All of these cells are built according to certain specifications so that they can transmit stimuli to the brain when they receive light. Extremely severe visual problems develop when even a single layer of these types of cells is missing. Every one of the layers in our eyes is immensely special, and it is hard to imagine them to have been randomly placed there. It should be born in mind that this article simply skipped numerous elements of the retina and their chemical functions. Taking the precise measurements and mechanisms into account, we can only feel greater awe and love in the face of the incredible art devoted to the creation.

The first article can be found at https://fountainmagazine.com/2018/issue-126-november-december-2018/retina-the-mind-boggler

The eye is a miracle as it is. Even though we have a rough understanding of its basic anatomy, we are confronted with a much more complex miracle when we venture into the intricacies of its anatomy and the physiology of the act of seeing. We have theories about the many details – such as the perception and representation of mental images and their storage in the memory – but we still do not exactly know how the act of seeing works.

One of the most mysterious layers of the eye, the retina has an elaborate structure with a slew of functions. Not every eye surgeon dares touch the retina, which houses the most sensitive and special cellular layers. It is a three dimensional, crescent-shaped structure located in the back of the eye and is made up of ten super thin layers of cells that span the exterior part of the eye abutting the veins and its interiors.

Retinal layers

The ten layers that form the retina are:

1. Pigment (coloring matter) layer
2. Layer of rods and cones
3. External limiting membrane
4. Outer nuclear layer comprising rod and cone cells
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Ganglion layer
9. Nerve fiber layer
10. Inner limiting membrane

These layers are incredibly sensitive and elaborate, and studying their intricate structure give a sense of awe.

Light for sight

Light first arrives at and penetrates through the cornea, the living glassy layer at the outermost layer of the eye. It then goes through the frontal fluid (aquesous humor) and the aperture called the pupil (pupilla). It hits the internal wall of the retina (the inside of the crescent) after passing through the lens in the eye and then the optic fluid filling up the chamber in the back. This alone is an interesting fact because it is much later that the light that gets to the retina reaches the layer of sensitive cone and rod cells, which perceive light. As these cone and rod cells are lined one after another for their protection, light reaches this outer layer of the retina after the ganglion cells, retinal layers and nuclear layers. Such an alignment leads to a reduction of acuity in the peripheral regions of the retina.

We have theories about the many details – such as the perception and representation of mental images and their storage in the memory – but we still do not exactly know how the act of seeing works

The central pit (fovea centralis)

The inner layers at the center of the retina, on the other hand, are drawn to the sides to prevent any loss in visual acuity. Resembling a pit, this section is much thinner than the periphery of the retina, so the layers that are likely to obstruct the passage of the light, and hence reduce visual acuity, are aligned specifically to allow light to directly hit cone and rod cells. Besides, cone cells, which are in charge of exact, colored sight, exist in this region, whereas rod cells, which are in charge of rough and uncolored (black and white) sight, do not.  The central pit where visual acuity is at its highest is for keen, colored, and exact sight. Why then is the rest of the retina not created for acute sight and why is this small section equipped with this ability?

As it turns out, if the entire retina had the ability to see keenly then it would not be possible for the eye to focus on a spot and accurately distinguish it from surrounding objects. If we could see the entire page of a book at a glance, for example, the lines would mix up in our brain. We would not be able to understand what we are reading. We normally start reading from the top of the written page and continue line by line as we focus on and take in each word. Our brain then can focus and perceive a single word accurately by restricting keen perception of the surrounding area.

The retinal pigment layer

The color black is known to absorb, not reflect, light. Thanks to such absorption, the layer made up of black pigments (melanin) or dyes prevents the reflection of light, which is crucial for visual acuity. This black substance functions like the black dye in the bellows of old cameras. If there were not any layer to absorb light, light would scatter off the wall inside the eyeball, thereby obscuring the sharpness between light and dark spots, which is essential for the formation of a clear image, and producing a blurry image due to the overall illumination of the retina.

People who lack this melanin pigment as a result of a genetic defect (Albinism disorder) have white hair, and they are oversensitive to light because the colored iris layer of the eye does not contain the melanin pigment, which refracts light. When an albino person enters a bright area, the light that hits the retina is reflected in all directions through the pigment-lacking retina and the white surfaces of the rigid layer underneath (sclera). Therefore, a ray of light that would normally stimulate a few cones or rods is scattered everywhere, stimulating all or most of the light receivers. As a result, visual acuity in albinos can only be between 20/100 and 20/200, even with the help of the best optical correction, which is a low value compared to 20/20 in normal sight. The joke that rabbits do not wear glasses because they eat carrots is based on the high concentration of vitamin A in this pigment, or black dye, layer of the eye. Indeed, vitamin A is a crucial factor for the health of these pigments.

Layer of rods and cones

Composed of 127 million light-sensitive receivers (photoreceptors), the retina is 0.2 mm thick at the yellow spot (macula lutea), where the image forms most clearly, and 0.1 mm thick at the edges of this area. The 120 million cylindrical rods in the retina are in charge of black and white sight (at twilight), and the 7 million tapered cones, of colored, colored and exact sight. The more common cylindrical rods are 50 µm (microns) in length and 1-5 µm in thickness. The less common cones are 40 µm (microns) in length and 3-5 µm in thickness.

The concentration of the cones increases toward the center of the retina and decreases toward the edges, to be outnumbered by the rods. In the cytoplasm of the cones and rods are stored substances that are sensitive to light (photosensitive) which break up when light contacts them and produce electricity in the cones and rods. In rods this chemical is called rhodopsin. In cones, on the other hand, are three substances corresponding to the colors red, green, and blue that are sensitive to the wavelengths of colored light. To be more exact, there are three separate cone cells that include one of these three substances. Chemically, the photosensitive substances in the cones are a little different from rhodopsins.

The destruction of rhodopsin by light energy

Rhodopsin, along with the color substances, fills up about 40% of rods and cones. They are made up of a protein called scotopsin and a molecule called retinene that is derived from vitamin A. When light energy is absorbed by rhodopsin or the color substances, rhodopsin starts to fade in as fast as one trillionth of a second. The underlying reason for this is that the electrons in the retinene (vitamin A) part of rhodopsin is activated by light, which alters the shape of the retinal molecule at a mind-boggling speed (one trillionth of a second). Extremely complicated and precise chemical and physical changes then take place. It is very difficult to monitor all of these biochemical changes, and they require specialization [1].

The regeneration of the rhodopsin destroyed by light

Rhodopsin destroyed by light is regenerated in the dark. Only in the twentieth century did we manage to partially identify the mechanism by which molecules with very specific geometric shapes decay at incredible speeds only to be regenerated later. It is wondrous that such knowledge and power are present in the cell allowing the light energy to destroy the molecule and the regeneration process is launched. The circulation between destruction and regeneration of the molecule continues throughout a lifetime [2]. Vitamin A is assigned a crucial task in the generation of rhodopsin in the dark. All-trans retinal is converted in the retina into all-trans retinol, which is then converted into 11-cys retinol with the help of an isomerase enzyme. Finally, 11-cys retinol is converted into 11-cys retinal, which in turn combines with scotopsin to form rhodopsin. Vitamin A is present both in the cytoplasm of rods and in the pigment layer of the retina. In this way, vitamin A is kept in reserve to be used for generations of new retinal. If, on the other hand, there is an excess of vitamin A in the retina, the excess amount is converted into retinal, by which the amount of light-sensitive pigment in the retina is lowered.

Night blindness

Night blindness appears in anyone who suffers a serious deficiency of vitamin A. Because there is a lack of vitamin A to be converted into retinal, rhodopsin amounts decrease dramatically. This disease is called night blindness as it is noticeable only in the dark or at night and does not affect sight during the day, due to the reduction of light for proper seeing. In daylight, however, cones can still be stimulated despite a similar decrease in color pigments. Night blindness typically only appears in people that have a low vitamin A diet because huge reserves of vitamin A are normally stored in the liver to be used for the eyes.

The human retina contains 400,000 light receptive cells per square millimeter. For comparison, this number is 680,000 in the retina of the owl, which needs to perceive even the slightest glow when hunting in the night. As another example, with 397,000 such cells the amount in the cat’s retina is almost the same as ours.

An average of 130 sight cells in the retina are connected to a ganglion (nerve node) cell. Constituting the nerve of sight, or the optic nerve (nervus opticus), every nerve fiber is connected to a ganglion cell. It takes about 15-60 seconds for the retinal optic nerves to adapt from dark to light, while it takes as long as 30-45 minutes to adapt from light to dark. The visual range of optic cells, i.e. the lowest and highest amount of light the eye can perceive, is between 10^-7 and 10⁶ nanometers. Light that is below or above this range is invisible to us because of its insufficient or overwhelming wavelength.

All the colors we see in the world are named according to the wavelengths absorbed and reflected by optic cells. The spectrum of the optic cells lies between red and violet, which is the limit of visible light for humans. Light with a wavelength of 400 nm is perceived as violet, while light with a wavelength of 760 nm is perceived as red. Our eyes cannot see infrared and ultraviolet light. Some animals, however, are known to see light beyond these limits. For example, we know that bees can see certain shades of ultraviolet light, which helps them find flowers to pollenate.

Clearly, it is not an easy job to elaborate on the divine art manifested in such a small area as the retina. Complicated structures and reactions that require specialization even to comprehend keep taking place smoothly every moment we look around. At least we can be thankful for this amazing gift of vision given to us free of charge so that we can recognize the universe.

Notes

[1] It causes the cys form of the molecule to change into the all-trans form. Although the all-trans form has the same chemical structure as the cys form, its chemical structure is different in that it is a flat rather than angular molecule. With the impact of light photons, the position of the molecule in space changes, yet its chemical composition remains the same. Because the position of the reactive regions of all-trans retinal no longer fit in with the reactive regions on scotopsin protein, the molecule is pulled off. The product that forms at that moment is batorhodopsins, which is a partly destroyed combination of all-trans retinal and scotopsin. An extremely unstable compound, batorhodopsin turns into lumirhodopsin in nanoseconds, into metarhodopsin I in microseconds, into metarhodopsin II in about one millisecond, and finally into decomposed products, scotopsin and all-trans retinal much more slowly (in seconds).

[2] The first step in the reformation of rhodopsin is the recycling of all-trans retinal into 11-cys retinal, which requires ATP energy and is catalyzed by retinal isomerase enzyme. Once created, 11-cys retinal combines with scotopsin to form rhodopsin.

How can animals in the wild hunt during the night as if it were day? A remarkable biological feature acts as a pair of “natural” night vision goggles.

Animals can move and even hunt in the pitch-dark of the night. How do these animals see comfortably in the dark? How are their eyes different from ours?

Anatomically, the eye consists of three layers called the Tunica fibrosa (outer layer), the Tunica vasculosa (mid layer), and the Tunica nervosa (retina). The outer layer of the eye is composed of the sclera and cornea; the middle section of choroidea, corpus ciliare, and the iris; and the inner section of the retina.

Light rays reflected off objects first pass through the eye’s translucent layer (the cornea), then into the black round part located in the front of the eye (pupillae, or pupil), and later go through the lenses. The colored section around the pupil, covered by smooth muscles, is in charge of regulating the amount of light entering the eye. The real and inverted image of an object is projected on the retina by the refraction of light through the lens; the image is transmitted to the optical center of the brain as a result of nerve cell stimulation via the optical nerves. Sight happens as a result of these causal chains.

Now, there is a twist to all this: the optical center in the brain accepts spots that do not emit light as black. For humans, this means a loss of sight. Black objects are not visible because they absorb and keep all the light reaching them.

How could these animals, without night vision goggles, see in pitch blackness despite having the same optical mechanisms as humans?

The answer to this question was hidden in an anatomic structure (tapetum lucidum) located in the eyes of some vertebrates. This special structure, lacking in humans, monkeys, squirrels, birds, red kangaroos, and some other mammals, is found in equines, ruminants, and many carnivores. This structure is located in the cytoplasm of the choroidea layers in between the innermost light sensitive ocular layer and sclera, and it acts like a biological reflector. With its crystalline composition of varying colors from golden yellow to white, tapetum lucidum is a wonder of creation. The eyes of these animals shine when a light source is projected due to the aforementioned structure.

The primary task of this formation is to reflect the light which is projected to the rear section of the eye again without absorbing it. This happens due to the crystalline makeup. Thus, lower light levels are enhanced by the repeated reflection in the eye, and sight is enabled for animals. The second job of Tapetum lucidum is to elevate the sensitivity of the retina to light in order to transmit signals with no stimulation strength to the optical center.

This reminds us of night vision goggles. Night vision cameras are electro-optical devices that strengthen the light that is present. Light enters this device through the lens and hits the charged cathode, which has a lot of high energy. The energy load hits the phosphorous screen where the image is focused after passing through the vacuum inside the charger. The image is an enhanced picture on the phosphorous screen and it is not visible directly through the object. Tapetum lucidum however, is such an artistic work that it cannot even be compared with the night vision systems of technology. While the lifespan of a night vision system is only 2,500–4,000 hours (104–167 days), animals with Tapetum lucidum can benefit from this for a lifetime. The newest night vision systems, with a maximum optic range of 30-120 meters, cannot provide sight under light conditions one fourth of the moon’s illumination strength, whereas animals with Tapetum lucidum can see objects hundreds of meters away in much dimmer light.

This isn’t the only example of how masterfully and diverse eyes can be. Damseflies have over 30,000 simple eyes, called ommatids; eagles can see their prey from thousands of feet above them.

By the principle that “certain things are appreciated best in their absence,” if we imagine a dark night in which we are unable to see anything and cannot even step a foot safely, we can perhaps understand that Tapetum lucidum is a great blessing for these animals.

Reference

Veterinary Ophthalmology (2004) 7, 1,11–22. Comparative morphology of the tapetum lucidum (among selected species), F. J. Ollivier,* D. A. Samuelson, D. E. Brooks, P. A.Lewis, M. E. Kallberg and A. M. Komáromy.

In the northern hemisphere, where annual average rainfall is around 100 kg per square meter in cold and dry regions, boreal forests, with needle-leaf trees, dominate. The southern hemisphere is dominated by savanna; bushes and meadows occupy millions of hectares.. In these regions, natural fires can be the most important factor of ecosystem changes. When looking at the results of these fires, it sometimes seems they were preprogrammed as to when, where, and how they spread.

Examples of fire dependent ecosystems

The cone of the Jack Pine species (Pinus banksiana), which is widely distributed throughout North American forests, requires absolute forest fire in order to release its seeds. The cone of this species can remain on the trees without releasing seeds for years because of climate and the resin layer covering it. Seeds preserved in the cones wait for the next fire; the cone’s scales open with the heat generated during such a fire. The seeds then start their journey towards a piece of soil that they can grow into. Here the role of fire is very important, not only for the dispersal of seeds but also in preparation of germination. The high humidity and low temperatures in the forests of these regions delays the decomposition of fallen leaves. This layer of dead material over the mineral soil is another hindrance for seeds to meet the soil. When scales of the cones open with the help of forest fire, this thick layer of dead leaves is also removed, having burned down to create fertile new soil.

Another example of fire benefiting plants is the chaparral vegetation of the North American forest. This type of plant cover is composed of short, perennial wooden plants and annual non-woody plants. During the hot, dry weather of summer, this vegetative cover becomes particularly vulnerable to fire. A dark black cover composed of unburned parts, frames, and ashes of the plants is left behind. This sight, which is saddening at first, actually hides various beauties in it, and these beauties only emerge after a series of events.

Golden eardrops (Dicentra chrysantha), which is a member of the perennial Chaparral family, is deeply affected by fire. The seed of this plant requires a fire event in the germination season and should be exposed to smoke for at least 10 minutes.

The positive effects of forest fires can also be seen in the healthy survival of an ecosystem. Due to its thick bark, the widely distributed Ponderosa pine (Pinus ponderosa), of North America, is minimally affected by the low, medium level cover fires that happen every five to twenty years. The weak and unhealthy individuals in this dense forest get burned as a result of natural forest fires, leaving healthy, thick barked trees. This way, possible epidemics of harmful forest organisms, via these unhealthy trees, is prevented. In the meantime, due to periodic fires, dead cover, or fallen and dead trees are removed, thus preventing bigger fires.

In the eastern Mediterranean, brutia pine, yellow pine, black pine, aleppo pine, and stone pine can are widely distributed. Among these, brutia pine is spread across a wide area, especially in most fire sensitive regions. It is created with a thicker bark around the trunk compared to other pines. This species can be minimally impacted from low and medium level cover fires. On the other hand, seeds in the cones of brutia pine are thrown far away by the heat of the fire, reaching fertile germinating grounds, thus helping to spread the forest.

References

• Fuller, M. 1991. Forest Fires: An Introduction to Wildland Fire Behavior, Management, Firefighting, and Prevention, SD421.F84, Wiley & Sons, Inc., NY, pp. 238.
• Keeley, J. E. 2007. “Chaparral and Fire,” Fremontia, Volume 35:4, pp. 16-21.
• Bond, W. J., Wilgen, B.W. 1996. Fire and Plants, SE18HN, UK, Chapman & Hall, UK, pp. 259.

Distribution and density of the hairs in our body is coded in our genes. This program is activated after birth and hair roots are formed at around 8th-10th week of pregnancy. The hairs that cover the fetus are thin, short, and weak. The growth of hairs is completed in the 22nd week. Number of hairs in a fetus does not change much according to gender. Later on in a person’s life, hairs can become dense or rare, owing to factors such as race, age, gender and hormonal state. There are hair roots covering almost all over our body except for the soles, palms, forehead, the areas under the eyes, on and behind the ears.

A hair is made up of the hair root and the hair shaft on it. A hair root is surrounded with two layers. The duty of these layers is to prevent harm to the hair shaft and let the hair grow in the right direction. A hair root is a multilayered structure where every layer has a different function. The papilla is in the base of the hair root and it basically serves to send nourishment to hair cells. The upper layer of the hair shaft is the hard substance called keratin. The innermost layer, which can be seen as the spinal cord of a hair, does not exist in every hair shaft. The second layer, known as the cortex, constitutes most of the hair shaft. The color of hair is mostly determined by the pigment in this layer. The outermost layer is the upper skin of the hair.

Hairs in different parts of the body have their peculiar forms of and limits to growing. Under the control of hormones, hair roots cause hairs of different properties—such as thickness and color—to form. The hairs in moustache, armpits, between the legs, beard, and on the head grow fast and continually. On the other hand, the hairs on our arms, chest, back, legs and including those in the eyebrows grow very slowly and they know their limits. If the person does not own functional testicles, there may be no hair in certain areas of the body except for the hair on his head.

Most of us are apt to think that certain stories make our hair curl; actually, hair erector muscles are the unsung heroes of those stories. Under every hair in the body, there is an erector muscle that makes it move. These muscles have important functions for the body.

Firstly, it helps the oil glands carry out their function. The oil sacks are located on the surface of a hair. The sizes of these sacks are around 0.2-2 millimeters. Sacks are in the form of clusters. Oil glands are also placed all over the body, accept for the soles and palms. They are the natural “lubricants” for the skin and hairs; they protect the skin from the damage of drying up. Every gland under the skin has a channel. There are alveoli that open to every channel. When the hair muscle is stimulated, the hairs become erect and the connected gland start secreting a substance called sebum. The glands empty their contents to the body of the hair.

Regulating the acidity (pH) level of the skin is among the duties of the hair erector muscle and it produces a protective gel. The oily secretion forms a thin layer of gel; as it serves protecting the skin from heat and cold, it is given an antibacterial effect as well. The natural coating of the skin prevents reproduction of harmful germs. The pH level of the skin is 5-6 and it does not allow bacteria to grow. If this substance is not secreted from the skin, the pH acidity shifts toward alkali, moisture level of the skin increases; the fat layer and then the natural coating is damaged. Thus, germs find a suitable environment to reproduce.

Hair erector muscles are also given a role in adjusting body heat. The hairs in the human body are not related to heat isolation. When the body is exposed to cold environments, the mechanisms that increase body heat are activated. When sympathetic nervous system stimulates hair erector muscles, they contract, hairs bristle, and the body heat is tampered through the reduced heat release. Sometimes, even the invisibly small hairs erect and goose bumps appear on the skin. The purpose is to form a screen for heat. They also allow for perspiration in hot weather and help the body to cool down. In addition, hair erector muscles serve as touching receptors as well. The receptors in hairs easily detect objects on the body surface. Hairs that are activated by touch stimulate the nerve tissue in their base. In a way, they keep a round the clock watch for the body; as tiny and unsung heroes.

They say that perfection is hidden in details, which is also very true for hairs. And perhaps, the secret to appreciation lies in recognizing details, and appreciating their perfection.

I am the barrier between your body and the outer world and I am responsible for this area. I can sense every change in the outer world, including heat, cold, humidity, pressure, various radiations, and the effects of many harmful chemicals and physical phenomena. When I become aware of the presence of something that is harmful, I warn your organs to act according to these changing conditions. That is why everybody knows me primarily as a sense organ.

However, in addition to being a sense organ, I have many other important duties; however, if I were to list them here, this article would take up the entire magazine. In order to ensure your good health I have to carry out my duties, be they aesthetic, protective or metabolic, perfectly. Even if you only examine my appearance, you will see how beautiful I am. You should visit an anatomy laboratory one day and watch the medical students performing an autopsy. Examine the cadaver whose skin has been pulled back to allow the students to study the internal organs. Look, if you can! Although the body is miracle, if the skin is not present, it would lose its splendor and become ugly and horrible. The beauty and meaningful existence of all the other organs are only complete with me. Our Lord God Almighty has created me and dressed you with me as a garment that fits each part of your body. He has lined your palms and soles with a thick outer lining made of keratin; this enables you to walk and use some hand tools easily. If on the foot or hand I were as thin as I am in the lip area, then I would easily get punctured and injured while walking or using a tool. God has created special joints where your fingers and toes join the feet and hands. These joints allow your fingers, hands and feet to move in many different ways. In order to protect your head from the sun and cold God has changed some of my cells into hair and has given it the ability to grow constantly. God also protects your eyes with special hairs that we call eyelashes and eyebrows. With these He also completes the beauty of your face. However, these do not grow constantly like the hair on our heads. Just think, otherwise you would have to trim both your eyebrows and eyelashes everyday in order to see. The special hairs in your nose and ears help prevent the entry of harmful particles, like dust or harmful microorganisms. You may think “How important is that? Just a few strands of hair?” Of course, hair is not the most important thing of all, but is life nothing more than staying alive? Of course not! There is also an aesthetic aspect to life. We can understand this if we look at a person who has no eyebrows or eyelashes! Certainly, God has made human beings beautiful creations and the hair is an important part of this beauty. As with everything He does, the significance of the hair is much more meaningful than when first seen.

In addition to my aesthetic beauty, I should also tell you about my protective functions. My first and most vital job is to balance the level of liquid in your body and to prevent its loss. The liquid level and the amount of minerals inside your body are very important. If it were not for me your kidneys would not be able to regulate the level of these liquids. It is for this reason that people who have burns that take up two-thirds of their skin or more cannot live; the water loss in their bodies is too great. In burn care centers, they try to control the loss of liquids using very sensitive devices; however, with serious burns this is usually unsuccessful. My protective functions are not limited to liquids; I also protect your body from all kinds of bacteria, funguses and viruses. As you know, your skin can get inflamed and infected from even a thorn. If the skin becomes damaged or broken over a large area you could face serious infections. This is because if I am not present many microorganisms will invade your body and make you ill.

Your body is very sensitive to heat and cold. The temperature of your inner body normally should be between 370C and 38 0C (96.8 0F and 98.6 0F); if it increases above this temperature, then you are unwell. If you remain for a long time in cold conditions and your inner body temperature falls off, many of your organs, especially the lungs, stomach, and kidneys are damaged and cannot work properly. You could die if the temperature is too low for too long. And in contrast, if you stay too long in the heat and your inner body temperature increases, your nervous system can be damaged, as the brain is very sensitive. Then your heart and other organs will start to fail, which eventually results in death. Indeed, human beings live everywhere, from the deserts to the poles and everywhere people are able to maintain an inner core temperature that is constant between 96.8 0F and 98.6 0F. I play a very important part in this system. Although the main control center is the brain, it acts according to stimuli that I send and I carry out important functions when the brain responds to these stimuli. Later, I will tell you how I can both warm and cool you.

Before telling you about my other functions, I would also like to tell you about my structure, which appears quite basic from the outside. Of course, I am not simply a cover that wraps your flesh. First of all, I am a living organ that is being nourished, that grows, that is repaired and which is very flexible. As I get rid of dead cells, I replace them with new ones; I am aware of everything that happens in my surroundings and I allow you to feel the world around you. I consist of two major layers: the epidermis (outmost layer) and the dermis (the inner level). The visible layer, the epidermis, consists of cells that gradually die off and stiffen. Those cells are toughened with a protein called keratin which is absorbed inside their structure; everyday I shed dead skin cells. This is part of the “dirt” that is removed from your body with every shower. This outer layer contains bacteria, funguses or other parasites that have been transmitted from the outside world and which may cause diseases. These parasites are removed as the dead skin cells are shed. The innermost layer (stratum germinativum) of the epidermis has a great capacity for cell division and it constantly produces new cells from the bottom to the outermost level. These cells start out life as cylinders, but as they move towards the outer surface they become cubical and then flatten out. At the same time keratin is being produced in those cells, and as a result they stiffen and start to die off. When the cells arrive at the outermost level, they are already dead. Some of those dead cells do not fall off. They accumulate and combine to make up the structures that we call nails and calluses. In this way the cells protect those areas that are most sensitive or most often used.

You will be surprised to see what great biological activities take place in the epidermis. Even when a person dies, this layer does not die right away. After death the nails and beard continue to grow. This occurs because of the activities in the germinative epithelium, which makes up the basal layer of the epidermis.

Beneath the epidermis is the dermis, a relatively thick layer. This is the layer which keeps the skin lively and firm and which produces the color. Many works of arts are present in this layer to complete my splendid structure. This layer consists of connective tissue with fiber bundles that is made of collagen protein. As people get older, their skin dries up and starts to lose its collagen proteins. Once the fibers start to decrease, I lose my firmness, and then I start to wrinkle. Although people are not happy with wrinkles, which are inevitable, I don’t think this is something to worry about; wrinkles are also a sign of maturity and experience. In the structure of my dermis there are other parts that have very important functions: The sweat glands, which are in the shape of coiled tubes, spread throughout the body act as ventilators; in addition, the hair follicles, the sebaceous gland, which helps to nourish and moisturize the hair, the chromatophores (pigment-containing cells) that determine the skin color, the hair muscles that give your hair flexibility and the blood vessels that nourish me are all important. I also have special receptor cells that can sense temperature, pressure and pain and there are nerve endings scattered among these cells.

In different parts of the body I am more sensitive to particular sensations. My sense receptors (corpuscles) vary in shape and you human beings have named them after the scientists who discovered them. There is Pacini’s corpuscle, Meissner’s corpuscle, Ruffini’s corpuscle and Krause’s corpuscle. Each of those receptors is thought to be receiving independent stimuli, but this has not been proven by experiment yet.

Do you ever wonder why you and your friends have so many different skin tones? This is the result of the work of the chromatophores (cells that contain pigment) which are located in the dermis, at the point closest to the epidermis. These cells, which have a number of branches, move in relation to the intensity of the light, and their branches can stretch and shrink back. These movements cause the pigment granules (melanin granules) to disperse within the cell or aggregate towards the center. This is how they can lighten or darken the skin color, causing you to get a “tan.” The seasons, the length of the day and the intensity and duration of the sunlight all affect the movement of these cells. These cells darken your skin color during the summer and lighten it during the winter. But, why is this necessary? This is a wonderful physiologic mechanism that has so many amazing purposes and meanings. I am sure you have noticed that people who live in Northern Europe and North America have a lighter complexion than those who live in the more southerly regions of the earth. This is because the countries in these northern regions are exposed to a less intense sunlight for a shorter time. The further north you go the more rainy and cloudy it is. However, sunlight also plays a very important role in the synthesizing of vitamin D in your body. The molecule known as 7-dehydrocholesterol can be converted into vitamin D only with sunlight. Vitamin D is a fat-soluble vitamin that is highly important for calcium absorption and bone metabolism. If you do not have enough exposure to the sun, then vitamin D cannot be produced; this could result in disorders like rickets (most common), as well as several other bone diseases and skeletal complications. However, it is interesting that sunlight is a two-edged sword. Neither too much nor too little sunlight is good for you. Too much exposure to the sunlight damages my health, causing such diseases as skin cancer and eye disorders. Our Lord God Almighty has made all parts of the earth suitable for human life. He knows well, of course, what people need in order to be able to live in places that have less sunlight and in other places that have a great deal of sunlight. In order to allow people to benefit from the sunlight everywhere, He has given the necessary qualities to my chromotaphores and the melanin granules that they contain. In places that have less sunlight, my chromotaphores synthesize less melanin. The melanin disperses throughout the cells or the cells move downwards, and my color lightens. This allows more sun absorption and this sunlight is used for vitamin D production. In sunny places, however, people are more exposed to the ultraviolet rays of the sun as well as other forms of radiation. This is why the risk of my cells becoming mutant and cancerous is greatly increased. In order to avoid such a situation, more melanin is synthesized in people who live in sunny places. The melanin in the chrotaphores gathers towards the center of the cell and my color darkens. Thus, excess sunlight is absorbed by my melanin pigments thanks to their special structure and function. This prevents other sensitive cells from becoming damaged and cancerous.

During hot weather, in order to balance your inner body temperature, the blood vessels that pass through the skin expand and more blood is carried through the skin. I give off the water in my blood through my sweat glands. While this warm water called “sweat” spreads over my surface and evaporates, an important amount of heat is released into the air. Thus, your inner body temperature does not increase and you remain cool inside. Thanks to the work of my sweat glands, I can also get rid of some nitrogenous waste and thus support your kidneys. During cold weather, however, the activities of my sweat glands decrease, and this helps you to stay warm. The blood vessels narrow so that the blood in me is reduced. More warm blood is channeled into your body so that your important inner organs do not become cold. The muscles of my hairs contract and the hairs straighten, thickening the layer of hair that covers me. It feels like you are covered with a blanket. If your body temperature falls off significantly, my receptors stimulate the muscles that lie under me and these muscles produce heat by vibrating. That is why you shiver from cold! Women have fewer hairs on their body. Do you think this is unfair? Of course not! Unlike men, women’s bodies are created in such a way that they can store a greater percentage of fat among the tissues under the skin. This hypodermic fatty tissue not only protects women from cold, but it is also used as extra storage for nutrients that they use when breastfeeding. It also helps protect women’s muscles and bones against bumps and shocks from the outside. So, this tissue works both as a temperature isolator and as a “shock absorber.” There is nothing unfair about this. And, it proves that God gives each of His creation exactly what they need and deserve.

Some people say that the skin is a mirror of the body’s health; this is true. The fact that I am visible and can be examined easily makes me the first organ to display symptoms of many diseases that lie below. Abnormalities that appear on me are usually a sign of metabolism disorders, ulcers and other glandular disorders in the body. For example, if your liver is being affected by a poisonous substance, this shows up as red spots on the hands. But not only physical ailments affect, me; I am also affected by your spiritual condition. Of course, the opposite can happen, too. That is, diseases on the skin can affect your inner organs.

I have mentioned before that my ability to renew and repair myself is very great. God willing, I can repair mild burns, bruises and cuts easily under normal circumstances. However, if the bruise goes as deep as my basal layer, there might be a scare there to remind you in the future and to give thanks to God for your health. In addition, in diseases like diabetes, my ability to renew and repair myself is weakened and I cannot easily heal. In such cases, you have to take the utmost care to keep me clean so that I do not get infected.

Well Peter, I think that I have said enough about myself. I will not continue to go on about the many symptoms of diseases that can be seen on me, including, allergies, itchiness, and infections. However, it is important for you to know that I can demonstrate hundreds of different conditions that are caused by a great range of factors, such as genetically transmitted diseases, immune system disorders, and bacterial, viral, and fungal infections. But don’t worry! As you can see, the majority of people live a healthy life despite these risks. The Creator has provided your body with a protective mechanism and has taught you how to take care of yourself. My job here is to indicate the Creator and how He has made me a flawless work of art that demonstrates deep meanings behind its complexity. Rather than continuing to give you a lecture on dermatology, it would be better if you were to live according to God’s consent. If you do so, you will be protected from diseases; even if you do become ill, you will have greater patience and moral strength. You will also be more thankful to God for your health.

We photons are the envoys of the sun. Our duty is to carry the energy that was stored in the sun during the creation of the universe to the earth. In the sun’s center, during the nuclear reaction called fusion, four hydrogen nuclei form one helium nucleus. The mass of four hydrogen nuclei is 4 x 1,6726 x 10 ^-24 grams (i.e. 6,6904 x 10 ^-24 grams); the mass of one helium nucleus is 6,6447 x 10 ^-24 grams. It is clear that the mass of one helium nucleus is a little smaller than the mass of four hydrogen nuclei. If we calculate the difference: 6,6904 x 10 ^-24 g – 6,6447 x 10 ^-24 g = 0,0457 x 10 ^-24 g. This small mass difference is transformed into great energy by order of the Creator, and in this way we and our relatives, neutrinos, are created.

Our Lord has created us as the fastest particles in the universe. We cover 300,000 kilometers in a second. Although we move so fast, the sun’s center is very dense. The density is about 150 times greater than the density of water (1 g/cm3). Thus, as soon as we move, we crash into the hydrogen and helium nucleuses around us. They swallow us, but then they immediately set us free; then yet another strike waits for us immediately. In every collision, our energy is reduced a little, and we divide into several light particles with lower energy levels. Most of our lives-perhaps 100 thousand years-is spent in these collisions.

If we left the center of the sun without any collisions, the earth would be blasted to pieces in a moment when we hit it. As a result of the collisions, we, who have a high energy level in the beginning, are converted into low energy level light particles.

So many of us are created in the sun that at every second a four-million-ton mass is converted into energy. In the sun, which is 5 billion years old, approximately a hundred times the mass of the earth has been converted into energy up to today.

While we are created in the center of the sun, we reach the outer layer of the sun, the photosphere, by passing slowly through the layers from the center to the surface of the sun. On leaving the surface, our energy decreases, our number increases, and our temperature goes down to 5,800 degrees C. You may consider this temperature very high, but you should not forget that our temperature in the beginning was 15 million degrees C.

We pass the 700,000 kilometers from the center of the sun to the photosphere layer in 100,000 years. The photosphere’s density is so low that it is only one percent of the atmosphere’s density at sea level. We leave this layer fast without any collisions. To reach the earth, there is 150 million kilometers of space ahead of us. Here we show our speed, which we did not have a chance to display earlier because of the collisions we have inside the sun. We travel the 150-million-kilometer distance in 8.5 minutes and reach the earth. There are some of us with extremely high energy levels who can cause damage on earth. The ozone layer is responsible for picking them off. The non-dangerous ones among us reach the face of the earth by traveling through the 100-kilometer-deep atmosphere in 1/10000 of a second. Finally, it is time to deliver the energy we have carried to you.

Every photon has a duty. Some of us heat the earth; some of us vaporize the water in the seas to bring the merciful rains. We have many other duties as well as these. Perhaps our most important duty is to be swallowed by the chlorophyll in plant leaves, so as to provide the energy in the food you eat and in the oxygen you breathe.

Possibly the energy that you have used while reading this essay was obtained from a bean you ate in your lunch. Do not forget that we brought from the sun’s center both the energy in the bean you ate and the energy in any plant that was food for any animal whose meat you have eaten.

We also carried the energy that was in the gas of the truck that brought these pages to you. If our brothers that came to the earth a million years ago had not brought energy to the plants at that time, could those plants have been transformed into oil or coal by decaying underground?

Our Lord gave us light particles a mission to carry the energy that is stored in substances so that the energy will be a source of life for you. We fulfill our duties without any error so that you might think and learn a lesson from these facts.

In your next meal, consider looking at the blessings on your plate from the following perspective: “I am about to eat energy that was heated approximately 100,000 years ago at 15 million degrees C in an oven in the sun’s center and later cooled and made appropriate for the bodies of human beings.”

The four main functions required for life, namely the digestive, respiratory, circulatory, and excretory systems are all found in plants but performed by different organs. If these functions are non-existent the dynamism or the essence of existence that we call life will disappear and death is inevitable. If these four functions (digestion, circulation, respiration, and excretion) are in working order, it means an organism is alive but only at the level of plant life. To reach the animal level of life, in addition to the four main functions, functions like senses, nervous and muscular systems are also required.

If these functions fail, life continues, but at the level of plant life. We sometimes hear people saying “in a vegetative state.” When you hear this, people are usually talking about a person who has lost the use of the animal functions. He or she may be unable to see, feel, hear, or move. Intelligence, comprehension, will power, conscience and the many other special aspects of human beings cannot be compared with the essential functions of living; these are additional characteristics of being human which accompany the animal system of functions and emerge in relation to a person’s spirituality. This obviously does not mean that those who have lost their abilities are less human and they do not have any rights; on the contrary, it means to say that they are not responsible any more.

The focal points of sensory functions of sight, hearing, touch, taste, and smell are found within the head in the brain, which is the command center of our body and the most complex form of existence we know of in the universe. The brain is connected to the nervous system which communicates with all the organs in the human body. This is why the head is so precious; it is a very sensitive part of the body and has to be protected like a jeweler guards precious stones. If you tread on a nail, it may hurt for a while, but with treatment the wound can be cured. But if a nail were to penetrate someone’s head, this could damage any of the sensory functions or, God forbid, could even result in death.

As you have probably understood from our introduction, the head is firstly the center of animal functions then the focus point of the addition of the human senses. When you mention the head we are the first thing that comes to mind: the eyes. Did we hear you ask why? It’s because we are what you are reading these words with right now, and because you can see the beautiful creations of the universe with us-that’s why.

If my Creator had not created us and positioned us in the two cavities on your head, you would have no knowledge of the beauties of light, color, insects, flowers, roses or birds. You would be afraid to walk without us because you would have no idea where you are about to tread. The effect of sight can only be sent through us to your brain and reflected into your mind. The development of human knowledge would have been very delayed if God had not created us or the other sense organs because the only way to gain knowledge is through healthy sense organs. The sense organs are the only way of detecting and recognizing the characteristics of objects.

You need us to realize that water is transparent, apples are red, quinces are yellow and violets are purple, you need us to recognize your mothers, fathers and friends. You need us to eat, drink, read and write and so you do not bump into walls. What do you think will happen if we close our lids for ten seconds and you try to walk down the street? Try it if you want!

You see-it was harder than you thought. You were scared in case you bumped into something or fell over. Look, Peter, just take a deep breath and give praise to our Creator while our lids are closed tight, for you could not tolerate being in the dark for a mere ten seconds, so what if you never saw the light? Just think sometimes about people who are not as fortunate as you, who cannot see for one reason or another. Give praise to our Creator for not giving you such a trial, and pray for the patience of those friends who have been deprived of sight.

Yes, now we have come to our characteristics and delicate creation, so pay attention. When Darwin saw God’s magnificent skill in our creation, he realized that we could not have been just a coincidence or a self-made creation, and it was impossible for us to be a creation of unconscious nature. Due to the guilt he felt inside, he found it necessary to say that the idea that “the evolution of complex organs like the brain and the eye could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.”

There is no artificial optical device that can match the esthetics or precision of our creation. Our operating principles depend on the optical laws God Almighty has determined for the light. As a matter of fact, just by looking at our structure, human beings worked out the rules of optics, you made the simplest of cameras, and you went on to produce the most magnificent photographic cameras possible. But whatever you do, never try to compare one of us to those cameras you have invented or you may become rather embarrassed. Your cameras are a simple toy compared to us. From the time of the invention of the old, wooden box cameras that had to be covered with a black cloth up to the modern digital cameras of the present, 175 years have passed. Many people worked for years to bring cameras to such a perfect state. Can anyone claim that the old camera made of a wooden box and a lens evolved by itself and turned into the high-quality, digital cameras of today? With all the knowledge accumulated by hundreds of scientists over the years, can this invention really be called a coincidence? So, can we be a coincidence? Could the eyes of mollusks or insects make themselves evolve and transform into the eyes of humans? Of course not! But to understand this a little better you must pay attention to our structure.

We are globe-shaped and look like covered capsules with a multi-layered structure which is quite solid and supple (Figure 1). Each of us is approximately 24mm in diameter. We have an outer layer made of something called sclera (hard coating). We are protected by a strong cover made up of dense ligament fibers, and beneath this is the choroid layer (a layer of blood vessels), where the blood vessels nourishing us go into; this layer covers us completely like a network of vessels. In the middle of the eye is the retina which is a layer of film. It is located in the most precious place where our actual receivers of light reside. There are other layers which each have their own duty beneath these layers, but we won’t go into too much detail.

We each have a main casing that is round and has a dome-shaped surface which slightly protrudes. The center of the hard coating, the cornea, is transparent so that it will allow light to pass through. On the outer part of the transparent area is what they call the white of the eye, and the whole areas seen from the front is covered in a clear membrane (the conjunctiva) with mucus cells. This keeps us lubricated. So as to focus light rays, our cornea section is more curved than other sections. There is a tiny chamber behind this curved front and this is actually where the lens, which separates the main chamber, is found. In the front chamber between our lens and cornea is a transparent liquid, the iris, which gives us our color. The black hole in the center of the iris is called the pupil. The iris, which has a special structure of muscles, works like a curtain contracting and expanding our pupil in response to the brightness of light. If the light is powerful, it contracts to protect the retina from any damage, whereas if the light is dim, the iris expands the pupil to allow more light into the retina.

The fibers (zonules) that hold the lens suspended in place and the cluster of muscles (corpus ciliare), which changes our lens according to the focus distance, are in front of a layer of blood vessels. Our lens, which plays a role in focusing, changes shape and adjusts according to whether the focus point is near or at a distance by thinning and thickening. We do this with the help of the fibers that keep the lens suspended.

Behind the lens is a larger chamber filled with a jellylike, transparent liquid (vitreous humor). The pressure and consistency of the jellylike liquid ensure that we keep our round shape. There are photoreceptive cells in the shape of rods and cones which are sensitive to light in the dark chamber behind our retina. The visual images formed by the rays which pass through the cornea and lens to the retina are upside-down. There is a small pit in my retina where almost every cell has a light receptor cell. This is where your sharpest vision is formed, but that doesn’t mean that it is where you actually perceive the object you are looking at. Sight is what happens when a group of cells in the brain’s visual center is stimulated, and the images on our lens are comprehended. It is unbelievable how fast is the effect of the chemical and electro events on our light receptor cells. The effect of light is conveyed to your brain through the stimulation of electric signals in our receptors’ optic nerve where the actual vision is produced in the brain, so in a way we are just the means of vision.

Because we are such delicate and sensitive organs, our Creator placed us in the cavities within the bone structure of your head for protection. We fit in the very strong and secure structure comprising your chin bone, cheek bones, forehead bone, orbital bone (just around us, your eyes), nasal bone and occipital bone (at the rear and bottom of your skull), but this is not our only protective mechanism. We have top and bottom eyelids that we close to protect ourselves from oncoming dangers. The frequent blinking of our eyelids prevents our cornea from becoming dirty, just like the windscreen wipers of a car. Our eyelids are not just simple folds of skin, they are a secretion system of glands which continuously lubricate the inner part of your lashes and seize dirt and dust, turning them into harmless particles. When you feel emotion, the secretion produced by the tear glands between us and the nose fills the tear ducts, passes through the two canals, and gives us a good wash. But when you cry too much, the excess secretion empties through another canal, which also washes your nose.

As this system is complex, it can also go wrong sometimes. If you consider our many parts and our millions of cells you will clearly see the possibility that any one of our components may fail. However, our Creator has formed the eyes in most people’s heads without any defect or failure, so we can serve you with vision of the universe.

The Creator gives us something called illness so we are reminded of our weakness, a defect or failure which arises as an act of wisdom. Some illnesses, like diabetes, deficiency of vitamin A or atherosclerosis, may have a negative effect on us and even render us useless. We eyes also have some defects which occasionally appear, such as not being able to see at a distance, or close up. Focus defects are easily remedied with spectacles or lenses, but faults in the sensitive light receptor cells in the retina are more difficult to amend. The pressure of the liquid in our larger chamber must be correctly balanced. If this pressure increases too much, we will give you a great deal of pain due to what doctors call glaucoma. If we lose our transparency, your vision will become clouded by what is called a cataract. Apart from this, there are many viruses and bacteria that can cause infections and diseases, but the cells of your immune system are like soldiers who, with the Creator’s help, protect you from those bacteria and viruses.

Look, Peter! It would take pages and pages for us to explain ourselves to you, but we don’t really want to confuse you with even more anatomical information. Our whole aim is to explain the reasons for the creation of our parts, to astonish you with the wisdom and fine art of the Divine, so you will contemplate the wonders of creation and give praise to the Almighty for the blessings he has bestowed upon you. If we have been successful in achieving this, that would be the greatest reward we could ask for.

Irfan Yilmaz is a professor of biology at Dokuz Eylul University, Izmir, Turkey.