With the help of a labelled diagram of human digestive system, explain what happens to the food we take in.
Answers
Answer: DIGESTION: There is a need of converting large and non diffusible food molecules into smaller and diffusable molecules. This is achieved through the process of digestion.
Explanation:
ALIMENTARY CANAL: The digestive system of human consists of a long tube that extends from mouth to anus. This tube is called Alimentary Canal. It main sections are Oral Cavity, pharynx, oesophagus, stomach, small intestines and large intestines.
ORAL CAVITY: Oral cavity is the space behind mouth and has very important functions: FOOD SELECTION ( when food enters the oral cavity, it is tasted and felt) CHEWING OR MASTICATION (alsoThe third and four function of oral cavity is LUBRICATION and CHEMICAL DIGESTION( the chewing process stimulates the three pairs ofase a juice called saliva. Saliva adds water snd mucous to food which act as a lubricant to ease the passage of food through oesphagus. Saliva also contains an enzyme salivary amylase wch helps in the semi digestion of starch.)
During the process of chewing lubrication and semi digestion, the pieces of food are rolled up by the tongue into small slippery spherical mass called bolus.
After food being swallowed, food enters a tube called oesophagus which connects pharynx to stomach.
STOMACH ( THE REAL DIGESTION STARTS):
When food enters the stomach, gastric glands releases gastric juice, and the food is broken down through a process of churning.
SMALL INTESTINE:
Duodenum comprises of the first 10 inches (25 cm) of small intestine and it is the part of alimentary canal where most of the digestive process occurs. Here, food is further mixed with 3 different secretions:
Bile from liver helps in the digestion of lipids through emulsification i.e. by keeping the lipid
droplets separate from one another.
2. Pancreatic juice from pancreas contains enzymes trypsin, pancreatic amylase and lipase
which digest proteins, carbohydrates and lipids respectively.
3. Intestinal juice from intestine walls contains many enzymes for the complete digestion of all
kinds of food.
Next to the duodenum is 2.4 meters long jejunum. It is concerned with the rest of the digestion of proteins, carbohydrates and lipids of our bite.
Next 3.5 metre long part is of small intestine is ileum.There are circular folds in the inner wall of ileum. These folds have numerous finger-like projections called villi (singular: villus). Villi increase the surface area of the inner walls and it helps alot in the absorption of digested food.
Each villus is richly supplied with blood capillaries and a vessel of lymphatic system, called lacteal.
The walls of villus are only single-cell thick. The digested molecules i.e. simple sugars and amino acids are absorbed from intestine into the blood capillaries present in villi.Blood carries them away from small intestine via the hepatic portal vein and goes to liver for filtering. Here, toxins are
removed and extra food is stored. From liver, the required food molecules go towards heart via the hepatic vein. Fatty acids and glycerol, present in small intestine, are absorbed into the lacteal of villus. Lacteal carries them to the main lymphatic duct, from where they enter in bloodstream.
Large intestine - Absorption of water and defecation
After the digested products of our bite have been absorbed in blood, the remaining mass enters
large intestine. It has 3 parts; caecum (or pouch that forms the T-junction with small intestine), colon
and rectum. From colon, water is absorbed into blood.As water is absorbed, the solid remains of
food are called faeces.
Faeces mainly consists of the undigested material. Large number of bacteria,sloughed off cells of
alimentary canal, bile pigments and water are also part of faeces. Faeces are temporarily stored in rectum, which opens out through anus. Under normal conditions
when the rectum is filled up with faeces, it gives rise to a reflex and anus is opened for defecation.
This reflex is consciously inhibited in adults but in infants it is controlled involuntarily. During
growth, child learns to bring this reflex under voluntary control.