1. This document describes the physiology and biochemistry of digestion. It defines digestion as the breakdown of complex organic food into simpler organic molecules, which can occur intracellularly or extracellularly. 2. The main parts of the human digestive system are described, including the mouth, esophagus, stomach, small intestine, large intestine, and associated digestive glands. 3. The key digestive glands discussed are the salivary glands, gastric glands of the stomach, liver, pancreas, and intestinal glands. Their secretions and functions in digestion are summarized.

1. Physiology and biochemistry
By: Hukam Chand
AP Zoology
GC Drang at Narla

2. Definition: Breakdown of complex organic
food into simpler organic molecules.
Two types:
1. Intracellular- Within the cells eg. Amoeba.
2. Extracellular-Outside the cell in a cavity
eg. Man.
Both types of digestion are seen in
coelenterates.

3. Digestive system
Alimentary
canal
• Foregut-mouth
and buccal cavity.
• Midgut- pharynx
to colon.
• Hindgut- Rectum
and anus.
1. Mouth- A transverse slit
bounded by movable lips.
2. Buccal cavity- Palate (Hard
and soft), Tongue, teeth.
3. Hard palate for mastication
whereas soft palate is with uvula
which closes internal nares
during swallowing .
4. Tongue- Attached to floor by
frenulum, and consists of three
types of papillae (Circumvallate,
fungiform and filiform).

4. 5. Teeth- Thecodont, diphyodont and heterodont type.
Human tongueV. S. Of teeth

5. Pharynx- Common passage
for air, food and water.
Oesophagus- narrow
muscular tube which opens
in the stomach.
Stomach- Most distensible
part of gut. Three parts
(Cardiac, Fundic and Pyloric).
Inner mucosa raised into
gastric rugae (increases area
for digestion).
Stomach

6. • Small intestine- largest part
of alimentary canal. It
consists of three parts
(duodenum, jejunum and
ileum). It is the main region
where digestion and
absorption takes place.
• Large intestine- it consists
of caecum, colon and
rectum. Colon helps to
conserve water and
minerals. It also helps in the
formation of faeces.

7. Digestive glands
• Salivary glands- three (Parotid,
submaxillary and sublingual).
Secrete saliva (1-1.5l/day),
enzyme ptyalin which works at
Ph 6.8 in the presence of Cl.
Gastric
glands-
Present in
mucosa of
stomach.
Gastric juice
(2-3l/day),
works at 1.2-
1.8 pH.
• Chief or peptic-
pepsinogen,
prorennin, etc.
• Oxyntic or
parietal- HCl, CIF.
• Goblet- mucus
• Argentaffin-
Serotonin
• G cells- Gastrin
hormone

8. LIVER
• Largest gland, exocrine, about
1.5Kg, covered by Glisson’s
capsule. Secretes non-enzymatic
bile juice which is stored by pear
shaped gall bladder.
• Functions: Secretes bile,
regulates blood sugar by
glycogenesis and glycogenolysis,
controls lipogenesis, secretes
heparin, detoxification and
deamination, phagocytosis by
Kupffer’s cells, haemopoiesis, etc.

9. PANCREAS
• Second largest,
heterocrine gland, about
60 gms.
• Exocrine part consists of
lobules(acini) which
secrete Pancreatic juice
(enzymes like
trypsinogen,
chymotrypsinogen, etc).
• Endocrine part have
islets of Langerhans,
which consists of
following cells:
alpha (Glucagon), beta
(Insulin), delta
(Somatostatin), etc.

10. Intestinal glands
• Numerous, microscopic and
are of two types.
1. Crypts of Lieberkuhn- secrete
digestive enzymes and
mucus. Paneth cells (secrete
enterocrinin) and Argentaffin
cells.
2. Brunner’s gland- present in
submucosa of duodenum,
secretes mucus and little
enzymes.
• Secretion of both called
intestinal juice or succus
entericus. About 2-3 l/day.
Works at 8.3pH.