Life processes are the essential elements of living organisms without which individuals cannot survive. Different species exhibit their ability to participate in a variety of life processes, however, in the human beings, the most common life processes are the respiration followed by digestion( nutrition), locomotion, circulation, and excretion. Digestion deals with the amount, nature and type of food intake. This article is an attempt to explain the essence of digestion and why do we call digestion process as the life process.
Digestion - a life process in human beings
Digestive system assists in the process of an individual`s nutrition. The digestive system is also known as the GI system( Gastrointestinal System) or Gut. Gut is an irregular, long cavity that begins with the mouth and continue to the pharynx, stomach, small intestine, large intestine, rectum and anus. Digestive system has many accessory glands that help in the process of digestion. It is also known as an alimentary canal lined with a continuous channel having mucus membranes, circular and longitudinal muscles, connective tissues along with a rich nerve and blood supply. Gut has the capacity to produce the movement of food in a wavy fashion known as the peristaltic movement . Peristalsis is the result of neuromuscular reflex action producing contractions and relaxations of the muscular layer.
Anatomy of the digestive system
Mouth or buccal cavity
Mouth is otherwise known as the oral cavity or the buccal cavity; the first part to receive food. Mouth helps in chewing and providing the consistency of the food that helps in the easy movement in a forward direction. Mouth gives a place for teeth, tongue, lips, and oral glands that assisting in receiving, chewing, cutting, grinding and softening the food. Mouth also provides an opportunity to enjoy the taste of the food through their taste buds aligned against the tongue at various spots.
The roof of the mouth gives space for the maxillary process that holds the upper teeth, and the floor of the mouth is known as mandibulum that holds lower teeth. Based on the age at which the tooth erupts and fall off, they are classified into 2 types; milk teeth and the permanent teeth. Milk teeth appear for the first time during infancy and fall off between the age group of 6 to 9 years . The permanent teeth will replace the temporary milk teeth forever. Permanent teeth erupt within a few days of loss of milk teeth. Based on the structure and function, there are 4 sets of teeth; they are, Molar, Premolar, Canine, and Incisors. There are 32 permanent teeth; 16 on the upper jaw and 16 on the lower jaw. Molars are otherwise known as the chewing teeth and premolars are the grinding teeth. On the other hand, canines help in piercing and tearing of food . The incisors are helpful in cutting and biting the food.
Glands in the mouth
Oral glands assist in the process of digestion by releasing the digestive juices along with the saliva. There are different types of glands in the mouth; salivary glands, sublingual glands, parotid glands and the submandibular glands.
Food pipe( oesophagus)
The food after biting, chewing, cutting and grinding into a paste with the help of teeth, it will slowly be engulfed (swallowed) by the action of smooth muscular tube known as food pipe (oesophagus). Food pipe runs on the frontal region (visible side) of the neck where one can see the throat movement while the food is being swallowed. Oesophagus is a soft elastic pipe-like structure, flexible and active while it senses the food moving along the length of the tube. It produces a forward and downward movement that will push the food. The food at this stage is known as the bolus (small lumps). The bolus finally reaches the stomach for further digestion process.
The stomach is a strong, rough muscular pouch made up of elastic and rough walls. The shape of the human stomach resembles the fruit - pear. The stomach is the junction between the small intestine and the oesophagus. It is acidic in nature because of the secretion of hydrochloric acid (Hcl). Hcl, help to kill the bacteria entering through the food. Hcl also assists in the digestion of proteins by releasing the protein digestion enzymes such as the pepsin. Enzymes found in the stomach will bring the complex form of food into simpler units known as amino acids.
The small intestine is a very long, coiled and elastic structure found in the form of colonic loops. It is continued from the tail end of the stomach to reach till the colon (large intestine). It is supported by abdominal muscles measuring about 7 to 8 meters long. The small intestine is divided into duodenum, jejunum, and ileum. Intestine is surrounded by many accessory organs such as liver, gallbladder, pancreas and some other glands to assist in the process of digestion. The liver is the largest accessory organ, and it is called as the largest than all other glands in the body. The liver is a vital organ help in removing the toxins out of the body through detoxification process. Small intestine help in the digestion of carbohydrates, fats, vitamins, and minerals. Intestine help in the absorption of digested food through finger-like projections known as villus. the undigested or partly digested food moves into the large intestine with the help of peristalsis.
The large intestine is a wider and shorter part of the intestine measures about 1.5 meters. After the digestion of food in the small intestine, the food enters into the large intestine where undigested food and salt get further processed and the remaining waste material is passed onto the rectum and anus in the form of faecal matter.
Physiology of digestion
Digestion is a continuous process in which different nutrients (carbohydrates, proteins, lipids/fats, vitamins, and minerals.) undergo digestion and absorption at different segments of the gut. Digestion of carbohydrates- simple starch, begins in the buccal cavity with the help of salivary juice containing salivary amylase ( enzyme). The digestion and partial absorption of protein take place in the stomach. As the food moves into the small intestine, bile juice and the pancreatic juices come in contact to help further digestion of food. The bile juice is secreted from the liver and gall bladder whereas the pancreatic juice is released by the pancreas. These juices are released into the duodenum of the small intestine through pipe-like structures called bile duct. The small intestine is the segment where the majority of digestion and absorption process gets completed. The digested, simple units of food will enter the villus of the small intestine which in turn move the simple form of digested nutrients into the bloodstream. In the large intestine, the majority of water and some salts are absorbed. After the digestion in the large intestine, the remaining waste products are transferred into the rectum and anus - found at the distal part of the intestine.
What happens to the nutrients after they get absorbed from the intestine?
Cellular metabolism is the next step once the nutrients enter the bloodstream. The nutrients will get converted into ATP. ATP (Adenosine triphosphate) is the chemical name given to energy in our body. It helps in carrying out all our day to day chores by releasing essential energy. The process of respiration is used to make an ATP molecule from ADP and inorganic Phosphate. Endothermic processes in the cell then use this ATP to drive the reactions. When the terminal phosphate linkage in ATP is broken using water, the energy equivalent to 30.5 kJ/mol is released.