Life processes are the essential phenomenon of living organisms without which we cannot survive. Different species exhibit their ability to survive by various means and the life processes are one of the most important aspect of survival. Although every life process is important but they are not the same among different species . Some of the most common life processes in human beings includes respiration, digestion(nutrition), locomotion, circulation, and excretion. Digestion deals with the process of converting complex food products into simpler nutrients with the help of the mechanical and chemical action of the digestive system. In this post let us understand the importance of digestion and why the digestion process in one of the important life process.
Digestion in human beings
Nutrition and digestion is one of the priority processes next tot he respiration and heart beats. Hungry for a day or two can make the individual sick and might even die. Our digestive system assists in the process of cutting, chewing, grinding, mixing, swallowing, digestion( mechanical and chemical ) and absorption of food. It is also known as the GI system( Gastrointestinal System) , alimentary canal, or Gut. Gut is an irregular cavity begins from the mouth and continue to the pharynx, stomach, small intestine, large intestine, rectum and ends at the anus. Human digestive system includes primary organs and a number of accessory glands that aid in the process of digestion. The alimentary canal is lined with a continuous channel of mucus membranes , submucosa, , circular and longitudinal muscles, connective tissues along with a very rich supply of nerves and blood vessels. Gut has the capacity to move the food in a wavy fashion and the movement is called peristaltic movement. Peristalsis is aided by the action of neuromuscular system through their alternative contractions and relaxations.
Anatomy of the digestive system
Mouth is otherwise known as the oral cavity or the buccal cavity and it is the first part to receive food. Parts of the mouth helps in cutting, tearing, chewing, grinding of the food to bring it to a paste of smoother consistency which is easy to swallow. Mouth accommodates teeth, tongue, lips, and oral glands with each one them performing their unique roles. Mouth also provides an opportunity to enjoy the taste of the food with the help of its taste buds that are scattered across various surfaces of the tongue. Mouth also has numerous glands that secrete saliva and other essential enzymes such as salivary amylase which aids in the digestion of carbs. It is also one of the component of speech and expressions. The roof of the mouth provides space for the maxillary process that holds the upper teeth, and the floor of the mouth that accommodates the lower jaw and teeth is known as mandibulum. Teeth in human beings are of 2 types and they are classified based on the age at which they erupt and fall off as well as the functions performed by different teeth . Our teeth can be milk teeth and the permanent teeth. Milk teeth appear for the first time during infancy and lost when the child reaches the age of 6 to 9 years. Similarly, permanent teeth erupt within a few days after the loss of milk teeth. Based on the structure and functions, 4 sets of teeth found in human beings are , Molars, Premolars, Canines, and Incisors. 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. Furthermore,our total number of teeth is 32 where 16 of them lie on the upper jaw and 16 on the lower jaw.
Glands in the mouth
Oral glands assist in the process of digestion by releasing many digestive enzymes along with the saliva. Glands in our mouth includes ; salivary glands, sublingual glands, parotid glands and the submandibular glands. Parotid glands are located on the inner sides of the cheeks, whereas the submandibular glands are found at the floor of the mouth and sublingual glands are found under the tongue. These glands plays important role in the digestion of carbohydrates with the help of an enzyme called salivary amylase.
2. Food pipe( oesophagus)
The food after being cut into small pieces undergoes chewing and grinding with the help of teeth and the food turns into a fine paste called bolus. Bolus is slowly engulfed (swallowed) by the action of smooth muscular tube known as food pipe (oesophagus). Food pipe is located just beside the tracheal channel (windpipe) that is closely linked with the respiratory system. 3 major segments of the oesophagus are oropharynx, nasopharynx and laryngopharynx. Oesophagus is a soft elastic pipe-like structure, flexible and active while it senses the food moving along the length of the tube. The longitudinal and circular muscles below the mucus layer generates forward and downward movement that transfers the food into the stomach.
Stomach is divided into fundus, body and tail with little difference in the thickness and cell types at each level. It is a strong and rough muscular pouch made up of many layers. As stomach is highly acidic, the inner walls are very thick, elastic and very strong. The shape of the human stomach resembles pear fruit. 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 that enter 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 tube-like canal present in the form of loops called intestinal segments. It is continued from the tail end of the stomach to reach till the initial segment of large intestine (ascending colon) where small intestine and the large intestine gets combined with the help of ileocaecal valve. Small intestine is supported by many abdominal muscles from outside. In adults, the small intestine measures about 7 to 8 meters long and it is divided into 3 major segments ;duodenum, jejunum, and ileum. Our intestine is surrounded by a number of accessory organs such as liver, gallbladder, pancreas as well as many intestinal glands that assist in the process of digestion. The liver is the largest accessory organ, and it is one of the vital organs essential for detoxifying our body system. It is also important to store fat-soluble vitamins A,D,E and K. Liver helps in the digestion of carbohydrates, fats, vitamins, and minerals. Our intestine has many finger-like projections called villus. Villus has a rich blood supply through tiny capillaries that help in absorbing the simpler nutrients . 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 undergoes further processing and the residual waste material is passed on to the rectum and anus where wastes are excreted 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 that contains 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 in 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 ; first segment of the small intestine. Bile juices are released through pipe-like structures called bile duct. The small intestine is the segment where the majority of digestion and absorption is completed. The digested, simple units of food will enter the villus of the small intestine which aid in the transfer of 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 leftover waste products are transferred into the rectum and anus - found at the distal part of the intestine.
Fate of nutrients
Once the nutrients enter the bloodstream, cellular metabolism begins. Inside the cytoplasm of each cell, nutrients are converted into ATP (Adenosine triphosphate) ;the chemical name given to energy in our body. ATPs release energy necessary for all our day-to-day chores . The formation of ATP is mediated by the process of respiration in th epresence of ADP and inorganic Phosphate. The 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 along with carbon dioxide. The carbon dioxide released after the metabolism enters the veins to reach the heart. Our lungs recieves the carbondioxide rich blood to purify.