Why is digestion necessary

All animals require a supply of water, oxygen, simple sugars, amino acids, fatty

acids, vitamins, other organic and inorganic molecules.

• In nature these substances are available in the form of

• Proteins• Starches• Fats• Vitamins• Minerals.

• All of these substances need to be broken down in to simple molecules so that they can pass through cell membranes and are used by body.

• These simple molecules are • amino acids• sugars • fatty acids

Describe what happens to a meal having fats/CHO/Proteins when its in stomach.

Digestion in stomach

Cardiac sphincter

• It is a special ring of muscles at the junction of oesophagus and stomach.

sphincter

• sphincter• a circular band of voluntary or involuntary

muscle that encircles an orifice (opening) of the body or one of its hollow organs.

• When sphincter muscles contract , the entrance to stomach closes and stops moving back of stomach contents back into oesophagus (food pipe).

• This sphincter opens when a wave of peristalsis comes down the food pipe.

• per·i·stal·sis• the progressive wave of contraction and

relaxation of a tubular muscular system

Location of stomach

Location of stomach

• Stomach is situated on the left side of abdomen under diaphragm

• (in direction or location) from front to back in the median plane or in a plane parallel to the median.

Stomach wall

• 3 layers• Outer layer of connective tissue• Middle layer of smooth muscles• Inner layer( mucosa) of connective tissue with

many glands.

Middle layer

• Outer longitudinal• Inner circular muscles

• These muscle layers help in churning (mixing ,tossing and turning) and mixing of food with stomach secretions.

• This mixture is called chyme

Mucosa

• It has various tubular gastric glands which are composed of 3 kinds of cells.

Mucous cells

• They secrete mucus• Mucous is thick secretion that covers the

inside of stomach and stops digestion of lining of stomach wall

Parietal cells

• Also called oxyntic cells• They secret HCl.• HCl is secreted in concentrated forms.• It adjusts the pH of stomach contents ranging

from 2-3 so that pepsin can act on proteins.• It also makes food soft • It kills microorganism taken along with food

Zymogen cells

• They secrete pepsinogen.• Pepsin is an enzyme.• Its inactive form is called pepsinogen.• Pepsinogen gets converted to pepsin only in

acidic environment or after getting exposed to some already activated pepsin.

• Pepsin hydrolyses protein to produce peptones and polypeptides.

Gastric juice

• Secretions of all these cells is called gastric juice.

Digestion of carbohydrates

• In the MouthThe process of digesting carbohydrates begins in the mouth. Our saliva contains an enzyme called amylase that starts breaking down the more complex carbs into simpler types.

• In the StomachEnzyme activity continues in the stomach, but slows down significantly as digestive acids are released into the stomach by the glands.

• The secretion of gastric juice is regulated by • 1. smell• 2.sight• 3.quality

• Chyme finally goes to duodenum through relaxed pyloric sphinter.