240 ^|

A Handbook of Biology

3

Muscularis externa : Outer to sub-mucosa. Smooth muscle

layer (inner circular & outer longitudinal muscles).

4

Serosa : Outermost fibrous layer. It is made of thin mesothelium,

with some connective tissues. Epithelium of visceral organs

DÏGËSTÏVË (ÅSSØÇÏÅTËD) GLÅÑDS



They secrete digestive juices. They include salivary glands, gastric

glands, intestinal glands, pancreas & liver

Salivary glands : 3 pairs. They are



Parotids (2) : largest salivary gland. Seen in cheeks. Stenson’s duct is the

major duct



Sub-maxillary/sub-mandibular (2): Seen in lower jaw. Wharton’s duct

is the submaxillary duct



Sub-lingual (2) : Below the tongue. Duct of Rivinus connects the

sublingual gland to the floor of the buccal cavity



Salivary glands secrete saliva. It contains 99.5% water, mucin (mucus),

enzymes like salivary amylase (Ptyalin) and lysozyme and electrolytes

(Na⁺, K⁺, Cl^-, HCO3

- etc).

Gastric glands : Tubular glands found on the inner wall. They consists of :

Mucus neck cells: Secrete mucus. Mucus and bicarbonates protect the

stomach wall (mucosal epithelium) from HCl and prevents autodigestion.

Chief (zymogen or peptic) cells: Secrete proenzymes like pepsinogen &

pro-rennin and some lipase

Oxyntic (parietal) cells: Secrete HCl & Castle’s intrinsic factor (for

absorption of vitamin B12). Gastric glands secrete acidic (pH 1.8-2.0)

gastric juice. (NEET – I 2016) Small amounts of lipases are also secreted

by the gastric glands.