For the benefits of undergraduate students.

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.