In humans and many animals, nutrients are transported via the rhythmic beats of the heart, which acts like a pump. In plants, no organ is present to pump water and nutrients. Despite this, nutrients are transported non-stop through their bodies. How?

This movement is enabled via perfectly planned biochemical and physical laws. Nutrients that are obtained from the environment or synthesized in cells are transported in their own vascular channels. Minerals, vitamins, fructose, and hormones are delivered by these vessels to cells, sometimes hundreds of meters away.

The different parts of trees have different mechanisms for keeping them healthy. The rigid, long, powerful support tissue (sclerenchyma) and the ground vascular capillaries (parenchyma) assist with the support and transport of materials in the trunk. Thick and meter wide trunks, made of hard, lengthy fibers can withstand winds and storms for thousands of years due to their special architecture, which delivers organic materials to the entire organism.

The process begins in the roots, which have very critical tasks, as well as morphological and physiological specifications. The root tip advances deep into the soil, using its regenerative, cone-shaped, protective tissue (the calyptra). Damaged and lost cells at the tip are replaced. The upper tissue layer has absorbent hairs (Epidermic cells) that take in water and minerals from the soil after differentiating according to their genetic program.

After being absorbed through the roots, nutrients and water are taken into the plant’s “vessels.” These vessels are lifeless ligneous ducts that can quickly transport water and many minerals via long and sturdy channels (xylem). Living channels with filter-like porous walls (phloem) slowly transport organic materials to the necessary tissues. In these porous cells, the nuclei and some membranous organelles are eliminated to facilitate material transport.

Nearby companion cells help support metabolism. This kind of cooperation and communication are routinely observed in the natural world, showing an incredible compassion between cells and organisms through electromagnetic, ionic, and nuclear forces of molecules.

The xylem and phloem vessels feature the finest forms of the arts of endurance, decoration, distribution, architecture and design, and they are produced from reproductive and differentiating cells (called Meristem tissue). They exist in tree trunks that are hundreds of meters high, and also in tiny ferns. The roots of perennial plants are as robust as the columns holding up a sea platform. This architectural feature helps support the plant’s body in the best way.

Another part of the process, and one of the most important features of plants, is the synthesis of organic food material with the help of sun rays and photosynthesis. The transport of nutrients generated via photosynthesis inside the vascular tissue is fascinating. Elements of the vascular tissue carry out different tasks; cooperation is once again key: the porous channels carry organic material and the ligneous tubes carry water. Vascular bundles transport these nutrients from one leaf towards the root cell via diffusion, active transport, and fluidic pressure. Bark, on the outer part of a tree’s trunk, is merely protective – much as skin is for humans.

There are assimilation cells in charge of photosynthesis in plant leaves. Traveling on these cells, water and solute material transit towards the major vascular bundles via cytoplasmic (the symplast) or cell wall channels (the apoplast). Conversely, the cells providing nutrients to photosynthetic, organic food synthesizing cells and demanding tissues, are source cells. By utilizing carbon dioxide, water, or nitrous salts together with energy coming from light, various foods are produced in the source cells. With the help of many chloroplast organelles, as well as the chlorophyll and enzymes inside the source cells, the organic materials which have been produced are conducted to companion cells. These nutrients pass into sieved, porous channels from the companion cells.

As nutrients pass into the semi-empty, living, porous parts of the cell walls, their fluid absorbing capacity also improves. By releasing some water from the neighboring lifeless, ligneous channel bundles, water pressure forms in the porous cells. The nutrient flow is maintained at a stable and sized speed thanks to the finest architecture of and rigidity found in the system.

Fructose, sucrose and other important nutrients easily pass towards the tissue cells from the porous cells as the fluid pressure grows. When necessary, the right amount of food is stored in preparation for winter or harsh weather.

The last part of the process enables the transfer of nutrients. Through active transport, diffusion, and pressure flow, the required organic nutrients can be transferred everywhere. The cells that enable the transfer are the pool cells. They generate a great osmotic pressure density at the roots.

During the processing of food, possible harmful substances like mud, or carbon dioxide taken from the air, are processed and converted into wonderful nutrients. Some of these nutrients are even converted into food for people and animals. In the pool cells, many delicious fruits like pomegranates, oranges, grapes, and cherries are produced. While plants consume the mud and carbon dioxide themselves, they offer the best of food to humans and animals in a beautiful program of art and creation.

The whole process is really quite miraculous when you look at the entire things:

Water and dissolved minerals are received from the soil by the absorption of the epidermis cells. By transpiration, the pull between the hydrogen atoms of the water molecules (cohesion) enables the transport of liquids in the ligneous tubes all the way to leaf tips. Water molecules in the capillary shaped ligneous tubes rise quickly, with a physical force. Water and salts obtained from the soil are, in a way, pumped to all organs with the assistance of the fluidic osmotic pressure in the roots. The transport of water to higher levels is better facilitated by a different attraction force (adhesion) between the vascular bundles and water molecules. In time, the pool cells take in and store organic nutrients with the help of their receptor structures, thus lowering the density of the porous channels. Due to the osmotic balance principle, the excess waters are returned back to the ligneous tubes. The material transport speeds up during the day because of transpiration and photosynthesis, and it slows down during the night.

We vessels can be divided into three main groups in terms of structure and function. The ones with thicker walls, which bring every organ the blood they need from the heart, are the arteries. The pressure inside us is higher and we easily carry blood to the organs. The ones with thinner walls, lower pressure, and larger inner space are called veins. As a matter of fact, both arteries and veins have a three-layered structure that is very suitable for holding a fluid like blood. Since our walls are strengthened with both connective tissue and smooth muscle layers, we bear the pressure coming from the heart and help blood proceed by contracting and relaxing. Since arteries are directly subjected to the strong pressure from the heart, our walls were created in a thicker and stronger form. Since the veins return blood to the heart and thus have lower pressure, we have valves that close after blood passes, so it does not flow backward due to gravity. This is a serious challenge for the blood passing through your legs. Varicose veins might develop due to weight gain from pregnancy or obesity, which increases pressure on the legs, or to hours of standing, walking, or running on hard surfaces.

Capillaries are the most delicate blood vessels, with walls made of a single layer of epithelium, which enables us to exchange substances between blood and tissues. As blood vessels, our total length is about 120,000 kilometers. Try to imagine if a fisherman’s net were made from a rope of this length and how wide it would be! And yet, such a vast network of blood vessels is located in your body, and capillaries take blood to every part, without neglecting an area as tiny as the head of a pin.

The well-being of your organs is directly related to us. If our interiors begin to narrow, because of fatty cholesterol plaque for instance, then we begin to lose our flexibility. This means malnutrition for that organ, since a lesser amount of blood than expected can come. If a blood clot sticks to our wall and blocks the blood flow, the relevant organ may be in terrible trouble. If other arteries supply blood to that organ, then it can handle this, but if a main artery is blocked and if secondary channels do not exist or are insufficient, you experience infarction. Taking this into consideration, you need to be careful what you eat and lead a physically active life. When you get old, if sufficient blood does not pass through us in your brain, failures with brain activities appear and you go senile. As the walls of veins and arteries have a rich network of nerves, we let the suitable amount of blood flow according to the need of the organ we’re serving, under the control of the autonomous nervous system. While blood vessels that are connected to an organ not currently requiring much blood contract to reduce the amount supplied, those that are connected to currently more active organs expand. And dear Peter, the greatest blessing here is that none of these activities require any conscious effort from you; everything works smoothly without your even being aware.

This wonderful network of ours finds its value in the vital fluid we carry. If it weren’t for blood, we would have no value at all, and such a perfect means of distribution would be unnecessary. Even the duty of the heart is to make this fluid circulate throughout the body. Now, let us step aside and allow blood to have the floor.

The muscle cells are responsible for the strength and tone of the vessels. Today, we know that the role of the endothelial layer goes beyond a simple physical barrier. In addition, there are twenty-five different substances secreted by the endothelial cells that play a role in blood clotting, cell proliferation, the regulation of vessel permeability, and the functioning of the immune system. The endothelial cells are 10-15 &μm wide and 20-25 μm long. They are located in the inner vessel wall in a single-cell layer. The total endothelial area in the body of an adult is around 5000-6000 m², and it weighs around 2.5 kg. Endothelial cells during inflammation Capillaries consist of an endothelial structure; they can only be seen under a microscope, but their total length is nearly 96,000 km. The blood brought by the arteries is conveyed to the vein through capillaries. At this stage, the gas, liquids, and nutrients are brought out through the vessels and the cells and tissues around are supplied with oxygen and nutrients. In return, the liquids that they discharge and other waste matter are conveyed to the vein through capillaries. This matter-exchange, which occurs both inside and outside of the capillaries, is regulated thanks to the permeability of the endothelial cell layer and the pressure balance of the capillary system. During cardiac failure and inflammation, liquid release is increased due to a pressure imbalance and the liquid retrieval is not sufficient to make up for the amount lost. This results in swelling in the area in question. Here, we need to underline that inflammation, which appears with symptoms such as edema, redness, fever, and pain, is not a harmful process. On the contrary, it is a miraculous defensive mechanism granted to our body; inflammation protects the body against serious damage. For instance, the inflammation that forms around a bee sting prevents the venom from spreading throughout the body. The endothelial cells are given an important role in the inflammation as well. The chemical molecules secreted by the endothelial cells in the inflamed spot cause the vessels to react by enlarging and thus perfusion is increased. Later, the endothelial layer becomes ready for leukocytes to settle; these are used in neutralizing the substance that caused the inflammation in the first place.

Balancing blood pressure

The layer of smooth muscle cells is stimulated with chemicals secreted by the endothelial cells and the tone of the vessels are controlled through the constriction and relaxation of the vessels. Therefore, an important duty in the regulation of blood pressure is given to these cells. During aninfection, bacteria circulate in the blood stream and the blood pressure falls extremely low. Tissue nutrition is upset (septic shock) and an excess of muscle-relaxing substance is released by the endothelial structure. Veins and arteries become too relaxed and there is a considerable drop in blood pressure (hypotension). On the other hand, with problems like atherosclerosis, the endothelial cells cannot fulfill their duty and due to a deficiency in nitrogen oxide, they become immune to the stimulus to relax the muscles. The resulting problem in this situation is hypertension.

Endothelial cells prevent hemorrhage

In order for a hemorrhage to stop the vessels that are bleeding need to narrow down. This is very important in the first stages of blood loss, particularly when there is a problem with blood clotting. When a hemorrhage begins, the endothelial cells are ordered to excrete a substance called endothelin. This starts the narrowing down of the bleeding vessels. Endothelin is not excreted in normal vessels. When the umbilical cord of a newborn is cut, it prevents the baby from losing blood.

Endothelial cells in blood clotting

The duty of endothelial cells can prevent or facilitate blood clotting, depending on the situation. First of all, they prevent the blood cells from adhering to the vessel walls and prevent clotting inside the vessels. Imagine water flowing through a pipe. The speed of the flow is greater in the center and lower at the periphery. Therefore, in the long run, some residue forms inside the pipe. In the veins and arteries, the flow of blood near the walls is also slower. To prevent the formation of any residue, both the endothelial cells and the blood cells are created with negative loaded surfaces and the blood cells are pushed towards the center. In addition, a substance called prostocyclin (PGI2) is excreted and the thrombocytes change their structure. As a result, residue formation and clotting is prevented along the vessel walls. In a case of any long term damage to the endothelium (e.g. due to smoking, diabetes, or hypertension), the relevant protection mechanism fails, and clotting inside the vessels results in thrombosis. Some serious cases can even necessitate the amputation of a limb. The endothelial cells can also facilitate clotting when necessary. In case of bleeding due to a wound, they function contrarily and help the blood to clot to prevent blood loss.

Endothelial cells in the bone marrow, the liver, and spleen

As a divine blessing, the endothelial cells form a looser layer in these organs and vessel permeability is increased. Thanks to this increase, matter Exchange with blood is easily realized; blood reaches these organs, which are responsible for the constant control of the contents of the blood, easily.

Endothelial cells in the brain and eyes

The endothelial cells in organs like the brain and eyes are very closely integrated forming a barrier between the blood and the organs. This is to such an extent that the major nutrients of the brain, like glucose and oxygen, pass without any obstacles, but several chemicals, including medication, are blocked by the selective-permeability of this protective mechanism. Research has proven that various substances injected into the bloodstream reach almost all the tissues except for the brain. Thanks to the efficient protective mechanism that has been given to these minute cells, the brain is saved from a great deal of negative effects. Even a single cell is not left to chance and nothing happens randomly. As can be seen throughoutthe universe, opposites are made to work hand in hand in the human body as well in a splendid harmony for the continuation of life.

References

• Vinay Kumar, Abul K. Abbas, Nelson Fausto, Richard Mitchell, Robbins Basic Pathology, W.B. Saunders; 8th edition, 2007. Hall, John E., Arthur C. Guyton, Textbook of Medical Physiology,