Digestion in grain-eating birds

The digestive system of the chicken, which is a representative of the world of birds, is comprised of organs lined up in straight line succession: a beak, mouth, gullet, craw, front stomach (with gland), gizzard, small intestine, caecum, large intestine, cloacae and anus. In addition, enzymes secreted from the pancreas, liver and gallbladder also have digestive duties. Ending in a sharp point, the beak was created especially to be able to pick up single pieces of feed. Chickens do not have assisting organs like the palate, cheek, tongue or teeth that are normally found in the mouth, the first door of digestion in most animals. Ruminating animals like cows, sheep, goats and camels use the tongue instead of a beak for taking food into their mouths, and then their teeth are used to begin the breakdown of food. In chickens, however, this breakdown is initiated with the bottom and top beak. In ruminants there are taste buds in different shapes on the tip, sides and middle of their tongues which also function as the organ for the sense of taste. Since such taste buds are not found in chickens, there is also no perception of taste like that experienced in ruminating animals.

The structure and function of the gullet, or food pipe, has similar characteristics in chickens and other animals. However, just as in all birds that eat single seeds and grains, there is another digestive organ in chickens in the shape of a bag opposite to where the gullet expands. Called a craw, this tiny pouch is a place for the storage, wetting and softening of feed, and it serves the purpose of bringing food to the consistency needed for further digestion; consequently, it lightens the burden of the stomach (just like when we leave food that is difficult to cook, like chick peas or beans, standing in water overnight before we cook it).

A chicken’s stomach is composed of two different sections, the front stomach and the gizzard. The feed the chicken eats passes from the gullet and the craw to the front stomach, where digestive secretions are made. The food is stored here briefly and mixed with the special fluids of the stomach. Found in this secretion are both the pepsin enzyme, which starts the digestion of proteins, and hydrochloric acid, which is secreted to generate the pH level that makes this enzyme effective (and which also helps in the dissolution of minerals). These two important secretions are produced by different glands in the stomach. Like the craw, the gizzard, which comes after the front stomach, is the place where mechanical digestion, which is particular to all birds that eat grains, takes place. The gizzard is called the stomach with muscles because it is comprised of a pair of thick and strong muscle layers. As a result of these muscles constricting strongly, feed is broken down mechanically and ground up. While gathering feed, the chicken usually also swallows small pieces of sand, stone and limestone as if it knows how its digestive system works. Although many of us think that chickens swallow stones because they cannot distinguish them from feed, it is obvious that there is a purpose why they are doing it. If these stones, which are like “mill stones” for the digestive tract, are not found in the gizzard, the feed is not fully ground; consequently, it will pass to the small intestine in a form that will not be fully beneficial to the body.

Depending on its characteristics, the feed eaten can stay in the gizzard for a few minutes or several hours. The small intestine, which comes after the stomach, is comprised of the duodenum (twelve-finger intestine), the jejunum and the ileum. The small intestine is similar in grain-eating birds to those of other animals. The duodenum empties the secretions coming from the pancreas and the bile coming from the gall bladder. The digestion and absorption of the feed actually takes place in the small intestine due to these secretions. Final digestion and the absorption of carbohydrates and protein are effected by bacteria found at the point where the small intestine ends, in the 10-15 centimeter-long, V-shaped caecum.

The large intestine and the cloacae are found in the advanced sections of the digestive system. The role of the large intestine, which is twice as large in diameter as the small intestine, is to temporarily store the waste from the digested food and to maintain the balance of water in the body. The cloacae is a small orifice with a structure formed by the widening of the large intestine towards the anus and where the digestive, defecation and reproduction tracts open up.

While giving grain-eating birds the above mechanisms in order to nourish them, God equipped ruminating animals with different oral, dental, gastric and intestinal structures as well as different digestive strategies.

Digestion in ruminating mammals

While secreting saliva is essential for ruminating animals, it is not necessary for chickens because of differences in their digestive system. As a result of the secretion of saliva the fodder of ruminants is softened and dryness of mouth is prevented. Ptyalin (or alpha amylase), which is found in saliva, has antibacterial properties that protect animals from infections in addition to playing a role in digestion. The mother cows constantly licking their newborn calves is both an expression of compassion and also of wisdom in protecting the newborn from probable infections (Similarly, animals like dogs and cats licking their wounds and thus speeding up healing is no coincidence, but a sign of universal wisdom and mercy). This wisdom shows that saliva, of which cows secrete 90-180 liters and sheep 5-8 liters per day, is not a waste.

The stomachs of ruminants are comprised of four sections; the first three are the rumen, the reticulum and the omasum. These three sections are called the front stomach. The section that does the real work is called the abomasum. Because the nutritional value of grass is very low in comparison with meat, it is obvious that a large bodied ruminant will need a lot of grass. Consequently, the capacity of rumen being 150 liters is a wise and fitting design. In addition, the cellulase enzyme that digests the cellulose walls in plant cells is not produced in the tissues of any mammals. The possessor of infinite knowledge and power, God placed high concentrations of bacteria, protozoa, yeast and fungus-all of which can produce the cellulase enzyme needed to break down cellulose-in the rumen of ruminating mammals. The rumen acts as a fermentation factory because of these microorganisms. Breaking down the cellulose-rich food consumed by ruminants, these microorganisms both fulfill their own nutritional needs and help to meet the host’s energy, protein and vitamin (especially B12) needs within a symbiotic relationship. I wonder where the microorganisms in the rumen learned about this synthesis and assistance mechanisms!

What a magnificent engineering wonder is the “sulcus esophagus,” a semi-duct structure in the shape of a canoe that extends from the end of the food pipe in newborn ruminants to the abomasum where the essential stage of digestion takes place. Due to this structure, milk drunk reaches the last stage of the stomach without passing through the rumen, for there is no matter like cellulose in the content of milk that needs to be broken down. Consequently, there is no need for the milk to go to the rumen. If it were not like this, the milk would go directly to the rumen where it would be ruined by microorganisms, lose its nutritional quality and be like a bribe given in vain to the microorganisms in the rumen.

Modern medical practice has come back to the conclusion that diet is the key to good health and investment in good dietary advice will lead to a reduction in treatment costs, Emphasis on diet is a principle universal to almost all forms of traditional medicine. You can find sound advice on diet everywhere from Europe to China. The Prophet of Islam, upon whom he peace, set out the dietary principles that led to great advances in Arab and Islamic medicine. He said:

The stomach is the well of the body and the veins drink from it. If it is healthy, the veins pass on good health, if it is sick the veins pass on poison.

The term himya is used to mean both diet and precaution. Harith, ‘the doctor of the Arabs’, said: himya is the source of every cure and the stomach is the home of every illness’. To understand what is meant by himya we should recall the incident when the Prophet and his cousin, Ali, were invited to eat at the house of Umm al Mandari. Muhammad, upon whom be peace, began to eat and then stopped and said to Ali: ‘You are recovering.’ He gave him some barley and chard saying, ‘This is better for you’.

Himya has three functions: 1) it is used as a cute; 2) it is used to maintain good health; 3) it is used alongside cures to aid recovery

Diet and balance

In our previous article, we described the concept of mizaj, balance. Cures are prescribed according to the type of imbalance. Certain foods are classified as ‘moist’, others as ‘dry’. They match their opposites. The simplest example can he found in the Prophet’s advice: ‘Fever is from the fire, put it out with water.’ Another example would he rubbing olive oil on dry skin. One may say that these ideas are common sense and not really medical principles.. However, developing from these ‘simple’ examples came the system of medicine which went on to set the foundations for modern medical practice. Al-tibb al-Nabawi influenced surgeons and physicians like Ibn Sina and al-Hazen. It appears that in the rapid advancement of science many forgot these basic simple ‘common sense’ truths. Now we find ourselves again returning to the idea of a balanced diet.

Diet is normally described in terms of the three macronutrients, namely proteins, fats and carbohydrates. The structural parts of all body cells are made of proteins. It is these which stop them from collapsing. They are also vital in the functioning of the cells. Every protein consists of a string of building blocks called amino acids. The human body needs about 22 amino acids to make its necessary proteins. Fourteen of these can be manufactured by the body. The remainder have to be obtained through our food.The US National Academy of Sciences recommends 0.8 gms of protein per kilogram of body weight. The concept of balance is very important. It has until recently been commonly accepted that red meat is an ideal source of high-quality protein. A recent British report has been interpreted as suggesting that a vegetarian diet actually optimizes health. The reason for this is that taking in large amounts of ‘first grade’ protein from meat inevitably leads to an increased intake of harmful animal fat. This was clearly understood by the Companions of the Prophet. He told them; ‘The lord of all foods for the people of this world and the next is meat’ (related by Ibn Majah). ‘Umar also warned them: ‘Be careful of meat for it has harm like the harm found in wine.’ Another Companion of the Prophet said: ‘Do not make your insides a graveyard for animals.’ Balance is vital. ‘Second grade’ proteins found in grains and legumes are just as effective when combined with ‘first grade’ meat proteins. The different types of meat and their contribution to mizaj, can he found in Ibn al Qayum’s al – Tibb al-Nabawi. It corresponds to the now widely accepted view that red meat is vital but must be balanced with fowl and vegetables.

The second of the macronutrients are fats. They are composed of fatty acids, long molecules of carbon, hydrogen and oxygen. They produce more than twice the amount of energy of proteins or carbohydrates and also carry vitamins A, D, E and K. They are vital for growth and repair, as well as for insulating the body and maintaining a regular temperature. They cushion vital organs. There are several kinds of fat. They differ according to their degree of saturation. Saturated fats produce high levels of blood cholesterol. Cholesterol is a complex waxy substance that is essential to the walls of body cells, the production of vitamin D, hormones, bile acids and nerve tissues. The liver produces cholesterol naturally and does not need any from the diet. Therefore, any added will be excess and lead to imbalance. High cholesterol levels have been associated with high risk of heart attack. A simple way to reduce cholesterol levels would be to moderate the use of eggs and organ meats such as liver.

Carbohydrates are the third of the macronutrients. They provide the body with energy help control the breakdown of protein, and protect the body against toxins. Carbohydrates are of two types. Monosaccharides are simple single molecule sugars. An example is glucose. Polysaccharides are more complex molecules and are broken down into two or more sugars.An example is starch. They arc found in fruits, vegetables and grains. They have a high nutritive value and provide vitamins, minerals, proteins and fibre. Polysaccharides take longer to digest and are therefore more effective in keeping away hunger. Barley has been a vital ingredient in Arab medicine dating back to the Messenger as well as an important part of his own and his followers’ diet.

Digestion

A pillar in al-Tibia al-Nabawi is that illness can be related to diet and digestion. The Messenger laid special importance on position while eating as well as going to toilet. He emphasized the importance of oral hygiene and exercise. The ‘stomach’ mentioned in the saying of the Prophet quoted earlier is generally understood to refer to the whole digestive system. We are being told to keep our whole body in order. Looking carefully after our diet and digestion means looking after our whole body and ultimately our minds and inner selves. Optimum digestion means optimum health.

Digestion begins with the mouth and the teeth. Food is broken down by chewing and is moistened with saliva which stimulates the rest of the digestive process.It is then swallowed as holus. This should take a few minutes. Problems associated with this process include the interaction of bacteria and sugar or other carbohydrates. This breaks down the protective enamel and causes tooth decay. We are told to use siwak, a simple tooth stick, when we make ritual ablution. It is said to he purifying for the mouth, pleasing to the Lord and it makes the devil angry. In al-Tibia al-Nabawi, oral hygiene is not only for good health, it is a part of worship. The Messenger, upon whom he peace said, ‘Prayer with siwak is better than 70 prayers without it.’

The bolus passes to tile stomach via the muscular oesophagus. Reflux of stomach acid during this process leads to heartburn. This, according to al-Tibb al-Nabawi, can he avoided by sitting in a relaxed position while eating. The Messenger said: ‘I do not eat while leaning,’ and ‘I sit as a slave sits and I eat as a slave eats’. He used to sit and eat on the floor with his thigh resting on his foot, with due respect to his Lord and also to those he was eating with,

After the bolus has passed from tile oesophagus it enters the gallbladder. The gallbladder stores bile made by the liver and releases it into the duodenum. Gallstones are the main prob1em associated with the gallbladder. This can he avoided by himya, correct balanced diet. A diet low in animal fats reduces the risk of gallstones.

The bolus passes into the stomach which is a muscular sac that mixes acid fluid with food which then passes into the intestines. The stomach was described by the Messenger as ‘the well of the body’. It is very important that the well is kept clean. Dieticians are now beginning to fully realize the damage that is done to the stomach through smoking, alcohol and irritant foods. Fasting to ‘give the stomach a rest’ is now a common treatment. The role of fasting in Islam is well known. The obligation to fast-for one month a year benefits the Muslim’s body, mind and soul. The commended regular fasting throughout the year is either three days in the middle of the month, or on Mondays and Thursdays.

There are two intestines in the digestive system. The first, called the duodenum or small intestine, is a tube that receives strong alkaline juices from the pancreas and gallbladder which break down fats and neutralize stomach acid . The most common illness related to the small intestine is duodenal ulcers. These are commonly caused by alcohol, smoking and stress.

The passage of food takes four hours in the stomach, about four and a half in the small intestine and finally about twelve hours in the large intestine. The large intestine is a tube in which food and fluid are absorbed. Food residue is formed into faeces.

The final stage of digestion, i.e. the removal of waste, is just as important as the first. The Prophet recommended we sit or squat to avoid constipation. He was very particular about keeping the private areas clean and therefore free of infection, the use of water and performing ablution afterwards. This is not detached from worship. The prayer that he, upon him he peace, said when he completed this final act of digestion sums up the approach of al-Tibb al-Nabawi. Al-Tibb is looking after one’s health, physical and spiritual and, at the same time, remembering the source of all food and all health. He used to say:

All praise belongs to God who took out from me that which harms me and left in me that which benefits me’.