Nutrition is the process of intake of food by an organism and its utilization for energy. This is a vital process which helps living beings to obtain their energy from various sources. The food which we eat undergoes a lot of processing before the nutrients present in them are utilized to generate energy. Humans and other animals have specialized organs and system for this. Let’s go through nutrition in humans and the human digestive system in detail.
Human Digestive System
A human digestive system is a group of organs working together to convert food into energy and basic nutrients to feed the entire body. The food we take in is digested and utilized by our body and the unused parts of the food are defecated. Human digestive system is the sum of the gastrointestinal tract (GIT; also called alimentary canal) and accessory organs (tongue, liver, pancreas, etc). These two parts together help in digestion in humans.
The alimentary canal is the long tube through which the food that we eat is passed. It begins at the mouth (buccal or oral cavity), passes through the pharynx, esophagus or food pipe, stomach, small intestines, large intestines, rectum and finally ends at the anus. The food particles get digested gradually as they travel through various compartments of the alimentary canal. Accessory organs are organs which participate in the digestion process but are not actually a part of GIT. They stimulate the digestion by releasing certain enzymes.
Nutrition in Human beings
Mouth and the Buccal Cavity
Food begins its journey through the digestive system in the mouth, also known as the buccal cavity or the oral cavity. The mouth has many accessory organs such as the tongue, teeth, and salivary glands, which help in the digestion of food. Teeth grind the food into small pieces. Salivary glands secrete saliva which contains an enzyme called the salivary amylase. This enzyme breaks down starch content and moistens the food, before the tongue and other muscles push the food into the pharynx.
The pharynx passes the chewed food from the mouth to the esophagus. The flap of tissue known as the epiglottis present in pharynx prevents food from entering into the wide pipe
Esophagus or Food Pipe
The esophagus is a muscular tube connecting the pharynx to the stomach. It carries swallowed masses of chewed food along its length and pushes it down to the stomach.
The stomach is a thick-walled muscular bag that is located on the left side of the abdominal cavity. It is the largest part of the human digestive system. Stomach acts as a storage tank for food so that the body has time to digest large meals properly. It receives food from the food pipe at one end and opens into the small intestine at the other end. The inner walls of the stomach consist of the gastric glands which secrete mucus, hydrochloric acid, and digestive enzymes. These continue the digestion of food that began in the mouth.
Mucous protects the lining of the stomach while acid kills bacteria that enter the body along with the food. Hydrochloric acid also makes the medium in the stomach acidic, which helps the digestive enzymes like pepsin to act. The digestive enzymes break down proteins into simpler substances.
The small intestine is the longest part of the human digestive system. It is a highly coiled long, thin tube which is about 7.5 meters in length. The length of the small intestine depends on the diet of the organism. A major proportion of digestion takes place in the small intestines. All types of nutrients are digested here with the help of secretions which it receives from the liver and the pancreas. The walls of the small intestine also secrete juices for digesting food.
The liver releases bile juice which alkalizes the acidic food received from the stomach and also emulsifies the fat content. The pancreatic juice digests the proteins and lipids. Finally, the intestinal secretions convert the carbohydrates into glucose, proteins to amino acids and fats into fatty acids and glycerol.
Once the food is broken down into the simple particles, it is ready to be absorbed by the body. The villi, finger-like projections present on the walls of the small intestine, absorb the digested food by increasing the surface area. The absorbed food is then transported to different parts of the body through the blood vessels for cell activities.
The large intestine is a long, thick tube which is about 1.5 meters long. The large intestine absorbs water and small amounts of nutrients from the undigested food with the help of many symbiotic bacteria residing in it. The remaining waste passes into the rectum, where it remains as semi-solid feces. Feces exit the body through the anus via time-to-time excretion. This process is called Digestion.
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