Nutrition
Nutrition: It is the process by which organisms obtain food and energy for growth, repair and maintenance of the body.
Human Digestive System
Peristalsis
Peristalsis: It is the rhythmic wave-like antagonistic contractions of the longitudinal and circular muscles to mix and propel the contents of the alimentary canal.
Digestion: It is the process of breaking down large, complex and insoluble food molecules into small, simple and soluble molecules. Digestion involves the physical breakdown of food substances which mechanically breaks down food into smaller pieces to increase surface area to volume ratio for digestive enzymes to work on. Digestion is also a chemical process involving breaking of bonds with the acid of enzymes.
Absorption: It is the process by which digested food molecule are taken into the blood capillaries for amino acids and glucose and into the lacteal for fats. This takes place in the villi in the ileum/small intestine. The digested food molecules move into the villi of the ileum by diffusion or active transport.
Assimilation: It is the distribution and use of products of digestion as an energy source and conversion into other nutrients needed for growth and repair of body parts.
Deamination: It is the process by which amino groups are removed from amino acids and converted to urea.
Ingestion: Food is taken into the body.
Digestion: Large food molecules are broken down into smaller soluble molecules.
Absorption and assimilation: The digested food molecules are absorbed into the cells. These food molecules are converted into new protoplasm or used to provide energy.
Egestion/Defaecation: Undigested food is removed from the body.
Excretion: Removal of waste, e.g. in urine, sweat
The pharynx
The pharynx connects the buccal cavity to the oesophagus (gullet) and larynx (voice-box). The pharynx also leads to the trachea (windpipe), which in turn leads to the lungs. The pharynx is thus a part of both the digestive system and respiratory system.
Both food and air must pass through the pharynx when they enter the body. Normally, air passes into the trachea while food passes into the oesophagus. During breathing, the larynx is lowered and the glottis is open. During swallowing, the larynx is raised and the glottis is covered by theepiglottis. Thisprevents foodparticles fromentering the trachea.Food particles thenpass down theoesophagus byperistalsis.Occasionally, smallparticles of food or water may get into the larynx or trachea.This automaticallyinduces violentcoughing to force the food particles or water out and to prevent choking.
When the circular muscles contract, the longitudinal muscles relax.The wall of the gut constricts, that is, it becomes narrower and longer.Food in the gut is squeezed or pushed forward.
When the longitudinal muscles contract, the circular muscles relax.The wall of the gut dilates, that is, it becomes wider and shorter. This widens the lumen for the food to enter.
The stomach
Food passes from the oesophagus to the stomach, which is a distensible muscular bag. Food in the stomach is digested by gastric juice secreted by the gastric glands. The pyloric sphincter, at the place where the stomach joins the small intestine, contracts so that the entrance to the small intestine closes. When it relaxes, the entrance open and food from the stomach into the small intestine.
The small intestine
Food passes from the stomach to the small intestine. The small intestine consists of the duodenum, jejunum and ileum. It is about 6 m long in an adult. Most of the water is absorbed in small intestine.
The large intestine
The small intestine leads to the large intestine. It consists of the colon and the rectum. It is about 1.5 m long. The large Intestine absorb excess water and mineral salts from undigested food materials.
The liver
The liver is made up of five lobes. The cells of the liver secrete bile.
The gall bladder
The gall bladder stores bile temporarily.
The pancreas
The pancreas secretes pancreatic juice, which helps digest food.