Step 1

The cells that make up the human body require sufficient amounts of nutrients and energy to perform their essential physiological functions. This requirement of nutrients and energy is met up by the dietary intake of food and water. The conversion of complex molecules such as proteins and carbohydrates present in the food into the simpler molecules so that they are readily absorbed into the body, is the task of the human digestive system. The human digestive system, also known as the gastrointestinal tract, comprises the tract formed by organs through which the consumed food moves and subsequently digested and absorbed. This tract forms a tube or canal, in which all the parts of the digestive system are connected to each other. Both the ends of the canal are opened for ingestion and egestion. The canal which holds the parts of the digestive system is also referred to as the alimentary canal.

Step 2

The digestive system of the humans consists of the following parts: mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus. The five major processes that can explain the functions of the digestive system are: ingestion, propulsion, digestion, absorption, and excretion.

Ingestion: The process of ingestion refers to the consumption of food or entry of food into the alimentary canal. The mouth or the oral cavity is the first and foremost part of the human digestive system which comes in the direct contact of the food. The ingested food is grinded and chewed, masticated and mixed with saliva and its enzymes, with the help of teeth and tongue movements. The food mixed with salivary juices is called bolus.

Propulsion: The process of propulsion refers to the forward movement of food through the digestive tract. The bolus moves down from mouth to the pharynx and esophagus through deglutition and peristaltic movements, to reach the stomach. The deglutition or swallowing is a complex reflex mechanism that involves moving food through the oral cavity and pharynx. The peristalsis refers to the alternating waves of contraction and relaxation of smooth muscles of the alimentary wall, occurring in a symmetrical manner in the esophagus, stomach, and intestine to propel the food forward.

Digestion: The digestion may be defined as the conversion of complex molecules present in the food into the simpler molecules so that they are readily absorbed into the body. The process of digestion can be further categorized as physical/mechanical digestion and chemical digestion. In chemical digestion, the chemical properties of the food are altered through the chemical reactions mediated by digestive enzymes and other secretions in the stomach and intestine. In mechanical digestion, the physical characteristics of the food are altered through mechanical movements in the digestive system. The mechanical digestion involves chewing of food in the mouth, churning of food in the stomach, and segmentation in the small intestine.

Absorption: The nutrients obtained after digestion enter into the bloodstream through the process of absorption. This absorption of nutrients primarily takes place in the small intestine. The absorption in the small intestine takes place through the presence of small finger-like projections called villi. These villi increase the surface area for absorption. Most of the nutrients are directly absorbed into the bloodstream from the cells of the epithelium layer lining luminal surface of the small intestine. The large intestine also participates in absorption of water and remaining nutrients.

Excretion: The solid wastes that are left after the absorption into intestines are removed through rectum and anus during the excretion process. The last part of the digestive system, that is the large intestine, stores the waste material remaining after absorption in the form of feces. The feces are removed from the rectum in a process called defecation. The mass movements are a type of intestinal motility in which intense and prolonged peristaltic contractions trigger the process of defecation by the sudden distension of the rectum.

State which digestive functions occur in the differentregions of the digestive tract.

Public Answer

State which digestive functions occur in the different
regions of the digestive tract.