Digestion and Absorption Class 11 Notes For NEET PDF Download

Digestion is the process of breaking down complex food particles into simpler forms to absorb nutrients.
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Digestion and Absorption Class 11 Notes For NEET PDF Download
Digestion and Absorption

Digestion and Absorption

Digestion is the process of breaking down complex food particles into simpler forms to absorb nutrients.

The digestive system of humans comprises an alimentary canal. There are various glands associated with it.


Structure of  Alimentary canal

✓ Mouth: Mechanical breakdown of food; begins chemical digestion of carbohydrates 

✓ Esophagus: Peristalsis pushes food to stomach 

✓ Stomach: Mixes food; enzymatic digestion of proteins 

✓ Small intestine: Final enzymatic breakdown of food molecules; main site of food and water absorption 

✓ Large intestine: Absorbs water and minerals 

✓ Salivary glands: Secrete saliva, which contains enzymes that initiate breakdown of carbohydrates 

✓ Liver: Produces bile, which emulsifies fat 

✓ Pancreas: (behind the stomach) Produces and releases digestive enzymes and bicarbonate ions into small intestine



Mouth 

Mouth


Tongue: Freely movable muscular organ attached to the floor of the oral cavity by the frenulum. 

Teeth: 

  • Primary dentition (20 teeth): I 2/2, C 1/1, M 2/2 = 10 
  • Permanent dentition (32 teeth): I 2/2, C 1/1, P 2/2, M 3/3 = 16 Mouth 

Types of teeth 

Thecodont Dentition -  It means teeth are placed in the jaw sockets. 

Heterodont Dentition - Different kinds of teeth are present. 

  • Incisors (I) -For cutting 
  • Canines (C)- For tearing 
  • Premolars (PM) -For mastication 
  • Molars (M) -For mastication 

Diphyodont Dentition

Milk [decidual] teeth: 20 in number. Develops at 6-7 months of birth. They are replaced by permanent teeth at the age of 6-7. 

Permanent teeth: 32 in number. 


Stomach

Stomach


  • Stomach: Thick-walled, J-shaped organ 
  • Located on the left side of the body beneath the diaphragm. 
  • Has four main regions: the cardia, fundus, body, and pylorus 

Mechanical Digestion: 

  • The stomach stores food, mixes it with gastric juice, and churns it into liquefied chyme. Gastric Glands 
  • Contains hydrochloric acid, pepsin. → Parietal cells secrete HCl → Chief cells secrete pepsinogen → Mucus protects the stomach lining from gastric juice. 
  • Hydrochloric acid in the gastric juice kills microorganisms and denatures proteins. 
  • The protein-splitting enzyme pepsin begins protein digestion.

Small Intestine

  • It’s the longest part of the gut. 
  • 7 m long and 2.5 cm diameter 
  • Consists of duodenum, jejunum, and ileum 
  • Duodenum (C shaped first part) 
  • Jejunum (middle part) 
  • Ileum (terminal part) 

Receives 

  • Chyme from stomach 
  • Digestive enzymes and bicarbonate from pancreas 
  • Bile from liver and gallbladder Small Intestine 

Villi: Finger-like Villi are seen at the mucosa. Each villus has a brush-border columnar epithelial layer provided with microvilli. Villus consists of a capillary network and a small lymph vessel (lacteal). 


LARGE INTESTINE

LARGE INTESTINE


  • 1.5 m long. It has 3 parts: Caecum, Colon & Rectum.
  • Caecum: It is well-developed in herbivores but very small in man.
  • Colon: The colon consists of ascending colon, transverse colon, and descending colon.
  • Rectum: Pelvic colon leads to the rectum that opens out by anus.
  • The anus is guarded by an anal sphincter (circular voluntary muscles). 

Function: Bacteria in the large intestine convert proteins to amino acids, break down amino acids, and produce some B vitamins and vitamin K. Absorbing some water, ions, and vitamins.


SALIVARY GLANDS

SALIVARY GLANDS



Salivary glands secrete saliva. 

The function of Saliva: 

✓ It is 99.5% water and 0.5% solutes 

✓ Slightly Acidic in nature pH-6.8 

✓ Ions like sodium, potassium, chloride, bicarbonate, and phosphate. 

✓ Mucus, Immunoglobulin A, bacteriolytic enzyme lysozyme, 

✓ Salivary amylase (Ptyalin) 

✓ 1000- 1500 ml of saliva is secreted per day SALIVARY GLANDS 

Types of Salivary Gland 

Parotid Gland 

✓ Near ear, Largest gland 

✓ Secretes saliva into the oral cavity via a parotid duct 

✓ Called Stenson’s duct 

Submandibular Gland 

✓ Called Submaxillary gland 

✓ Present at the Floor of the mouth 

✓ Release their secretion through Submandibular ducts 

✓ Called Wharton’s duct 

Sublingual glands 

✓ Smallest salivary gland 

✓ Present beneath the tongue, release their secretion through sublingual ducts Also called Ducts of Rivinus



Liver Largest gland

Liver Largest gland


Structure 

✓ Covered by a fibrous capsule called Glisson's capsule. 

✓ It has four lobes: left, right, caudate, and quadrate. 

✓ Hepatic lobules are structural and functional units 

✓ The liver produces bile, which emulsifies fat; the gallbladder stores the 

Bile Composition: 

✓ Has no enzymes, Contain bile pigments (bilirubin and biliverdin) 

✓ Bile salts, cholesterol & phospholipids.

Function 

✓ Detoxifies blood, Stores iron and vitamins A, D, E, K, and B12. 

✓ Makes plasma proteins, Stores glucose as glycogen after a meal, and breaks down glycogen to glucose, Produces urea after breaking down amino acids  



PANCREAS: Second largest gland. 

PANCREAS: Second largest gland.


Exocrine Part: 

✓ Produces pancreatic juice 

✓ A clear, colorless liquid consisting mostly of water, some salts, sodium bicarbonate, and enzymes 

✓ Slightly alkaline pH (7.1–8.2) 

✓ Bicarbonate neutralizes acidic chyme from the stomach 

Exocrine Gland 

✓ Carbohydrate digesting enzyme → pancreatic amylase, 

✓ Fat digesting enzyme → pancreatic lipase 

✓ Protein digesting enzyme → trypsin, chymotrypsin, and carboxypeptidase. 

✓ Nucleic acid→ Ribonuclease and deoxyribonuclease