The alimentary canal is the continuous muscular tube extending from the mouth to the anus through which food is ingested, digested, absorbed, and egested. It is important for NEET Biology because NTA frequently tests enzyme secretion sites, nutrient absorption mechanisms in the small intestine, the role of bile in fat digestion, and peristaltic movements.
Mouth
Ingestion and mechanical digestion by teeth; saliva mixes with food to form bolus. Salivary amylase begins starch digestion.
Salivary glands
Three pairs — parotid, sublingual, and submandibular — secrete saliva containing salivary amylase (ptyalin) and lysozyme.
Oesophagus
Muscular tube that transports food from pharynx to stomach by peristaltic movements. No digestion or absorption occurs here.
Stomach
J-shaped muscular organ with fundic, cardiac, and pyloric regions. Secretes HCl, pepsinogen, and mucus. Pepsin digests proteins.
Liver
Largest gland; produces bile which is stored in the gall bladder. Bile emulsifies fats, aiding lipase action.
Gall bladder
Stores and concentrates bile produced by the liver. Releases bile into the duodenum through the common bile duct.
Pancreas
Mixed gland secreting pancreatic juice containing trypsinogen, lipase, amylase, and nucleases into the duodenum.
Duodenum
First C-shaped part of small intestine; receives bile and pancreatic juice. Major site of chemical digestion.
Jejunum
Middle portion of small intestine. Primary site for absorption of sugars, amino acids, and fatty acids through villi.
Ileum
Final part of small intestine; absorbs vitamin B12, bile salts, and remaining nutrients. Contains Peyer's patches.
Large intestine
Absorbs water, electrolytes, and some vitamins. Includes ascending, transverse, descending, and sigmoid colon.
Rectum
Stores faeces temporarily before defecation. The rectal walls expand to accommodate waste material.
Anus
Terminal opening of the alimentary canal controlled by internal (involuntary) and external (voluntary) sphincters.
Enzyme secretion sites
Salivary amylase (mouth), pepsin (stomach), trypsin and lipase (pancreas via duodenum). Know precursor forms — pepsinogen activated by HCl, trypsinogen activated by enterokinase.
Absorption in small intestine
Villi and microvilli increase surface area. Amino acids and monosaccharides absorbed into blood capillaries; fatty acids and glycerol into lacteals as chylomicrons.
Role of bile in fat digestion
Bile salts emulsify large fat globules into smaller micelles, increasing surface area for lipase. Bile is not an enzyme — it contains no digestive enzymes.
Peristalsis
Involuntary wave-like contractions of smooth muscle that push food through the alimentary canal. Controlled by the myenteric plexus (Auerbach's plexus) in the gut wall.
Solve previous year NEET questions on alimentary canal, enzymes, and nutrient absorption.
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