Digestion and Absorption - Notes | Class 11 | Part 2: Digestive Glands

II. Digestive (Associated) Glands

• They secrete digestive juices.
• They include salivary glands, gastric glands, intestinal glands, pancreas, & liver.

a. Salivary Glands

• 3 pairs. They are:
  • Parotids (2): Largest salivary gland. Seen in cheeks.
  • Submaxillary/Submandibular (2): Seen in lower jaw.
  • Sublingual (2): Below the tongue.
• 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).

b. Gastric Glands

Tubular glands found on the inner wall. They consist of:

1. Mucus neck cells: Secrete mucus. Mucus and bicarbonates protect the stomach wall (mucosal epithelium) from HCl and prevent autodigestion.
2. Chief (zymogen or peptic) cells: Secrete proenzymes like pepsinogen & prorennin and some lipase.
3. 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.

c. Liver

• Largest gland (1.2 - 1.5 kg). Reddish brown.
• Situated in abdominal cavity, just below the diaphragm.
• Bilobed (large right lobe & small left lobe). Each lobe is formed of hepatic lobules (structural & functional units).
• A lobule has many hepatic cells arranged as cords around a central vein. They secrete alkaline bile juice.
• Liver lobule is covered by Glisson’s capsule.
• Bile is transported from liver to duodenum as follows:

  Bile → hepatic duct → gallbladder → cystic duct → common bile duct → common hepato-pancreatic duct → duodenum.

• Hepato-pancreatic duct is guarded by sphincter of Oddi.
• Bile has no enzymes but contains bile pigments (bilirubin & biliverdin), bile salts, cholesterol, and phospholipids.

d. Pancreas

• Second largest gland. Seen near duodenal loop.
• It is a cream-coloured heterocrine gland, i.e., it has both exocrine and endocrine parts.
• The exocrine part has a pancreatic duct that opens into duodenum along with bile duct (hepato-pancreatic duct).
• Exocrine part secretes alkaline pancreatic juice. It contains inactive protease enzymes (trypsinogen, chymotrypsinogen & procarboxypeptidases), amylases, lipases, & nucleases.

e. Intestinal Glands

• Simple tubular glands. 2 types:
  1. Crypts of Lieberkuhn: Consists of mucus-secreting Goblet cells and enzyme-secreting Paneth cells.
  2. Brunner (duodenal) glands: Confined to submucosa of duodenum. Secrete mucus only.
• Intestinal glands secrete alkaline intestinal juice (succus entericus). It contains enzymes (maltase, lactase, sucrase, dipeptidase, lipases, nucleotidases, nucleosidases, etc.).
• The bicarbonate and mucus provide alkaline medium and protect intestinal mucosa.

Select a Topic 👇

Topic 1: Alimentary Canal Topic 2: Digestive Glands Topic 3: Digestion and Absorption of Food Topic 4: Disorders of Digestive System

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