Digestion

Mechanical: Mastication (Chewing) by teeth. Tongue rolls food into a Bolus.

Chemical: Salivary glands secrete Saliva containing:

• Amylase (Ptyalin): Digests Starch → Maltose.
• Bicarbonate: Stabilizes pH.
• Mucus: Lubrication.

J-shaped bag with Cardiac and Pyloric sphincters. Food becomes Chyme.

• Gastric Juice (Secreted by Gastric Glands):
  • Mucous cells: Secrete Mucus (Protection).
  • Parietal (Oxyntic) cells: Secrete HCl (pH 2-3, Kills bacteria, Activates Pepsinogen).
  • Chief (Zymogen) cells: Secrete Pepsinogen (Inactive). HCl converts it to Pepsin (Active) which digests Proteins → Peptides.

Longest part. Divided into 3 regions:

1. Duodenum: Receives secretions:
   • Bile (from Liver): Emulsifies fats (Physical digestion), Neutralizes acid. No enzymes.
   • Pancreatic Juice (from Pancreas): Contains Amylase (Starch), Lipase (Fats), Trypsin (Proteins). Bicarbonate neutralizes Chyme.
2. Jejunum: Further digestion by Intestinal juice (Succus entericus).
3. Ileum: Major absorption site. Contains Villi (finger-like projections) to increase surface area. Villi have blood capillaries (for Glucose/Amino acids) and **Lacteals** (for Fatty acids/Glycerol).

No digestion. Absorbs water and salts. Stores undigested waste as Feces in Rectum, eliminated via Anus (Defecation).

Largest gland.

• Digestion: Secretes Bile.
• Metabolism: Deamination (removes Amino group), Urea formation (Urea Cycle).
• Storage: Glycogen, Vitamins (A, D, E, K), Iron.
• Detoxification: Neutralizes toxins.

• Ulcer: Sore in gut lining (Peptic/Duodenal). Causes: Excess acid, *Helicobacter pylori* infection, Smoking, NSAIDs (Aspirin).
• Obesity: Excess body fat. Causes: Overeating, hormonal imbalance. Risk of Heart disease, Diabetes.
• Bulimia Nervosa: Eating disorder. Binge eating followed by self-induced vomiting (Purging). Physiological and psychological effects.