The document summarizes the human digestive system and the process of digestion. It describes the steps of digestion from ingestion to defecation. The main parts of the digestive system include the mouth, esophagus, stomach, small intestine, large intestine and accessory organs like the liver, pancreas and salivary glands. Digestion involves both mechanical and chemical breakdown of food by enzymes from these organs. Nutrients are then absorbed in the small intestine and transported to the liver and cells before undigested waste is excreted during defecation.

1. Physiology of digestion
Human digestive system
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3. Steps of digestion
1. Ingestion
2. Mastication and mixing
3. Propulsion3. Propulsion
4. Chemical digestion and absorption
5. Defecation
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4. Digestive system = alimentary canal + accessory glands
Parts of Alimentary canal:-
- Mouth
- Pharynx
- Oesophagus
- Stomach
Accessory glands:-
- Salivary glands
- Pancreas
- Liver
Digestive enzymes:-- Stomach
- Small intestine
- Large intestine
Digestive enzymes:-
- Amlolytic enzymes
(breaks carbohydrate)
- Proteolytic enzymes
(breaks protein)
- Lipolytic enzymes
(breaks fats)
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5. Digestion:- The physical, chemical
and physiological processes of
handling food and converting it
into simple soluble molecules thatinto simple soluble molecules that
can be absorbed by body cells are
is called as digestion.
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6. Digestion in mouth
• In mouth three process occur chewing, salivation and
swallowing.
• Teeth:- Teeth help in chewing food and masticate the food.
• Tongue:- help in mixing food with saliva.
• Functions of saliva:-
- Food particles are moistened by saliva. Mucin in saliva- Food particles are moistened by saliva. Mucin in saliva
smoothens the food particle making it easy to swallow.
- Amylase enzyme in saliva starts partial conversion of starch
into maltose.
- Saliva stimulates the secretion of gastric juice.
- Lysozyme in saliva kills bacteria and protects teeth against
caries.
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7. Swallowing of food
• Swallowing :- Its an unconditional reflex action by which food
bolus is transferred from the mouth via oesophagus into the
stomach.
• The bolus is pushed towards oesophagus by alternate wave of
contraction and relaxation of oesophagus muscles. Thiscontraction and relaxation of oesophagus muscles. This
movement is called peristalsis.
• No digestion occurs in the oesophagus.
• The opening of stomach is controlled by oesophageal
sphincter muscular ring. It opens up during swallowing
action.
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8. Digestion in stomach
• Stomach:- Hollow muscular pouch like sac lined by protective
mucous membrane. Mucus protect stomach tissues against self
digestion.
• Secretory gland in stomach produce gastric juices.
• Constituent of gastric juice:-
- enzymes named pepsin and renin – pepsin acts on protein and
converts proteoses into peptones. Renin converts milk protein into
casein.casein.
- hydrochloric acid 0.4 to 0.6% - destroys bacteria. Provides acidic
medium for pepsin to act on proteoses.
- small quantity of water and minerals.
● mechanical and chemical digestion of food converts food bolus into
partially digested pulpy mass of food called chyme.
- food remains in stomach for 3 hours. Then it is passed to small
intestine by opening of pyloric sphincter.
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9. The small intestine
• Small intestine is divided into 3 parts
(1) Duodenum, (2) jejunum, (3) ileum
• Duodenum:- It is short, folded, upper region of
the small intestine measuring 25 cm. The bile
duct pours bile juice and pancreatic duct pours
pancreatic juice into the duodenum. By common
bile duct.
pancreatic juice into the duodenum. By common
bile duct.
• Jejunum:- The duodenum continues downwards
as a short region about 25 meters in length. No
chemical digestion takes place here.
• Ileum:- The ileum is a long, narrow highly coiled
tube about 3.6 metres in length. In adult it
secrets 2 to 3 litres of intestinal juice.
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11. Bile juice and pancreatic juice
• Role of bile juice:-
bile:- is a yellowish green fluid
having sodium bicarbonate and
bile pigment bilirubin and
biliverdin.
- Bile is produced in liver and
stored in the gall bladder.
- Functions of bile:-
• Pancreatic juice:-it contains
three types of enzymes
1. Amylopsin:- converts starch
into maltose.
2. Trypsin:- digest remaining
proteins, proteases, and
peptones into peptides and
amino acids.- Functions of bile:-
1. Provide alkaline medium in
intestine for the enzymes to
function in small intestine.
2. Emulsify fat that is break fats
into small droplets.
3. Various metabolic waste gets
eliminated from the blood
stream by bile juice.
amino acids.
3. Steapsin (lipase):- splits
emulsified fats into fatty acid
and glycerol.
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12. Role of liver
• Liver is the largest gland of the body.
• Structure of liver:- It is reddish brown in colour, having larger right
lobe and smaller left lobe. Each lobe has thousands of lobules
penetrated by the branches of the hepatic and portal veins.
Functions of liver:-
- It produce bile which is essential for lipid metabolism.
- It converts and stores excess glucose into glycogen.
- From access amino acid nitrogen is freed in the liver and is- From access amino acid nitrogen is freed in the liver and is
converted into urea which is eliminated as part of urine.
- Liver produces RBC in embryo. And in adult the RBC are destroyed
in the liver.
- Toxic metabolites are made harmless in liver.
- Fibrinogen is produced in liver.
- Heparin, an anticoagulant is produced in liver.
- Liver stores nutrients ( fats, glucose), vitamins (A,D,E,K) and traces
elements ( iron, copper).
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13. Digestion in ileum
Enzymes in ileum:-
1. Erepsin:- converts proteoses, peptones and
peptides into amino acid.
2. Maltase:- breaks down maltose into glucose.
3. Sucrase:- converts glucose into gucose and3. Sucrase:- converts glucose into gucose and
fructose.
4. Lactase:- converts lactose into glucose and
galactose.
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14. Absorption of nutrients
• Complex food substances are
broken down by the enzymes
in digestive tact.
• These broken simple soluble
food substances are absorbed
by the cells of the villi and
passed into the blood.passed into the blood.
• From the blood these food
substances are passed into the
liver first and then circulated
in entire body.
• Refer function of liver slide no
12 to know what liver does to
absorbed molecules of food.
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15. Adaptation in ileum for the role of absorption.
• Ileum is long coiled which
provides larger surface area in
contact with food.
• The ileum is narrow so the food
passed slowly through it. Which
helps in better absorption of
food.
• Inner wall of ileum is single celled
which makes it easy for absorbed
• Carbohydrates are absorbed in
the form of glucose, fructose and
galactose.
• Proteins are absorbed in the form
of amino acids and simple
peptides.
• Glycerol is water soluble and is
readily absorbed.• Inner wall of ileum is single celled
which makes it easy for absorbed
food molecules to be passed into
blood stream.
• Inner lining of ileum is having
projections called villi which
increase the surface area to
absorb molecules.
• Food remains in small intestine
for 4 hours.
readily absorbed.
• Fatty acids are absorbed only
after they form compound with
bile salts.
• Salts and vitamins are absorbed
in small intestine.
• Water and minerals are absorbed
in stomach, small intestine and
large intestine.
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16. Assimilation
• From the blood the absorbed nutrients are used by body
and new cells are formed in the body is called assimilation.
• The nutrients are first carried to the liver by hepatic portal
vein. Then transported to heart for circulation in the body.
• Liver converts following things:-
1. Excess glucose form the intestine is converted into
glycogen by liver. This glycogen is stored in the adiposeglycogen by liver. This glycogen is stored in the adipose
tissues in the body under the skin.
2. Excess fatty acids are used to produce cholesterol.
3. Excess of nitrogen formed as a result of formation of new
proteins from amino acids is converted into urea and is
allowed to enter in blood stream to be filtered by kidney.
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18. Egestion
Undigested food contains :-
- cellulose
- Left over gastric juice
- Bile contents
- Dead cells of gut lining
- Dead and decaying bacteria
All these components give brown
faecal matter.
• Structure of large intestine
consists of 3 main parts:-
1. caecum:- the junction of small
intestine and large intestine is
called caecum.
2. Colon:- It measure 5cm in width
and 1.5 m in length.
- It runs up from caecum then
horizontally across the liver andfaecal matter.
The semi-solid mass moves in large
intestine by peristalsis.
Defaecation:- the periodical
elimination of faeces from the
body is known as defaecation.
Function of colon:-
- Water absorption.
- Useful bacteria produce vitamin K
- Formation of faeces.
horizontally across the liver and
finally down the left side.
3. Rectum:- rectum is 15 cm long
and it ends in a 5 cm long anal
canal. Anus is guarded by
sphincter muscles. Through
anus the faecal matter is
thrown out of the body.
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