13 January 2014

Digestion in Humans : Science

Digestion in Humans : NCERT / CBSE Notes

Human Digestive System : 

The human digestive system contains alimentary canal and associated glands. Digestive system of man consists of MouthBuccal CavityOesophagusPharynxStomach Duodenum,Small IntestineLarge Intestine (colon)Rectum and Anus.
Human Digestive System, NCERT Notes, CBSE Notes

  • Mouth and Buccal Cavity is bounded by upper lip and lower lip.
  • Food is entered into the Buccal Cavity through mouth is called Ingestion.
  • The food is crushed and chewed in the Buccal Cavity with the help of the teeth and tongue.
  • The Buccal Cavity leads into pharynx.
  • The different teeth present in the Buccal Cavity are incisorscaninespremolars and molars.

Salivary glands

Salivary glands are present inside the Buccal Cavity.They secrete saliva. This saliva plays an important role in breaking down complex components like starch,which is further simplified into sugars.
  • A flap-like valve called the epiglottis closes the windpipe. It prevents the entry of food particles into tracheae.
  • Movement of food inside the esophagus in the stomach is by peristalsis movement.
  • Stomach is u-shaped and it is the widest part of the alimentary canal.
  • Food is digested inside the stomach with the help of gastric juice secreted by the gastric glands present in the stomach.
Liver is the largest gland in our body. It produces bile juiceBile plays an important role in the digestion of fats.
  • Pancreas is the Mixed gland. It acts as a both endocrine and exocrine gland.
  • The pancreas secretes the pancreatic juice that helps to digest carbohydrates, proteins and fats. The pancreatic juice converts carbohydrates into simple sugars and glucose, proteins into amino acids, and the fats to fatty acids and glycerol.
Intestines : The inner walls of the small intestine have millions of small finger like projections called the VilliDue to their presence the surface area for digestion as well as absorption of digested food increases by eight times.
  • Energy needed for various activities is obtained from glucose.
  • This process of utilisation of absorbed food, such as glucoseamino acidsfatty acids and glycerol is called as Assimilation.
The undigested and unabsorbed food then enters the large intestine. The food then travels upward in the ascending colon of the large intestine. The function of the large intestine is to absorb the water and salts from the undigested food material. The undigested semi solid waste that passes into the Rectum is called faeces
  • It is then removed through the anus at intervals in a process called Egestion.
Mouth : The internal part of the mouth contains the teeth and the tongue. Each tooth is rooted in a separate socket in the gums.
  • The mouthoesophagusstomachsmall intestine and large intestine form the alimentary canal, also known as the digestive tract.
  • The glands that secrete juices are the salivary glands, the gastric glands, the liver, the pancreas and the intestinal glands.
  • The digestive tract, along with the associated glands, forms the digestive system.
  • Bacteria in the mouth break down the sugars from leftover food, and release acids. The acids damage the teeth, causing tooth decay.
  • The buccal cavity is bounded in the front by the upper and the lower lips, at the top by the roof of the mouth, at the bottom by the tongue, and on the sides by the cheeks
  • Food is taken in through the mouth, a process known as ingestion.
  • Incisors act like scissors,and are used for biting food. Canines are sharp and pointed, and are used to pierce or tear food. Premolars and molars, or the principal grinders, help in chewing and grinding food.
  • The salivary glands secrete saliva, a transparent fluid that helps break down complex components into simpler forms.
  • The taste buds, located in different areas of the tongue, help detect different tastes.
  • The oesophagus is the food pipe that carries food from the throat to the stomach. The oesophagus is also known as the gullet, and is about 25 centimetres long.
  • When you swallow food, a flap-like valve, called the epiglottis, closes the windpipe.

Stomach : The stomach is the widest part of the alimentary canal. Its walls are thick and very muscular. It is closed off at each end by a ring of muscular valves.
  • Digestion in the stomach occurs with the aid of hydrochloric acidmucous and digestive juices.
  • The ‘C’ shaped tunnel, called the duodenum, is the upper part of the small intestine.
  • The liver secretes a yellowish green watery fluid called bile. It is temporarily stored in a sac called the gall bladder. It has a narrow tube-like structure called the bile duct, which opens into the duodenum.
  • The pancreas secretes pancreatic juice that helps digest carbohydrates, proteins and fats. The pancreatic juice converts carbohydrates into simple sugars, glucose and proteins into amino acids, and fats into fatty acids and glycerol.
  • Bile breaks the larger fat molecules into tiny droplets, thereby increasing their surface area, which helps digest fats easily.
  • The pancreatic duct that arises from the pancreas joins the bile duct.
Absorption The inner walls of the small intestine have millions of small finger-like projections, called the villi. The surface of the villi allows amino acids and glucose to reach the blood capillaries, and allow fatty acids and glycerol to reach the lymph vessels, a process called absorption.
Assimilation : The process of utilisation of absorbed food such as glucose, amino acids, fatty acids and glycerol is known as assimilation.
  • Undigested food, which contains a lot of water and salts, is absorbed by the walls of the large intestine.
  • Food travels upwards in the ascending colon of the large intestine, then moves towards the transverse colon, and then back downwards towards the descending colon.
The undigested semi-solid waste that passes into the rectum is called faecesFaeces are temporarily stored in the rectum, and are removed through the anus at intervals by a process called egestion.

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