Functional Anatomy of Digestive System

Oral Cavity & Pharynx - Mouthful Marvels

• Salivary Glands: Parotid (Stensen's), Submandibular (Wharton's), Sublingual (Rivinus).
• Teeth (Function): Incisors (cutting), Canines (tearing), Premolars & Molars (grinding).
• Tongue: Papillae: Filiform (touch), Fungiform, Circumvallate, Foliate (taste). Taste buds present.
• Muscles of Mastication: 📌 MaTe MeLa: Masseter, Temporalis, Medial & Lateral pterygoids (CN V3).
• Swallowing (Deglutition):

⭐ Tongue Innervation (Sensory): Ant. 2/3: Lingual (general, V3), Chorda tympani (taste, VII). Post. 1/3: Glossopharyngeal (general & taste, IX). Motor: Hypoglossal (XII) except Palatoglossus (X).

Esophagus & Stomach - Gut's Gateway Grub

• Esophagus: Muscular tube; non-keratinized stratified squamous epithelium.
  • Constrictions (4): Cricoid, Aortic arch, L. main bronchus, Diaphragmatic hiatus. 📌 Cars Are Big Danger.
  • Sphincters: UES; LES (physiological, pressure 10-25 mmHg). ↓LES tone → GERD.
• Stomach: J-shaped; regions (Cardia, Fundus, Body, Antrum, Pylorus); rugae for expansion.
  • Gastric Glands & Cells:

    Cell	Secretion(s)	Stimulants
    Parietal	HCl (pH 1.5-3.5), Intrinsic Factor	ACh, Gastrin, Histamine
    Chief	Pepsinogen, Gastric Lipase	ACh, Gastrin, Secretin
    Mucous Neck	Mucus, Bicarbonate	Vagal, Prostaglandins
    G-cells	Gastrin	Peptides, AAs, Vagal

  ⭐ Left gastric artery (from celiac trunk) supplies stomach's lesser curvature, a common site for ulcers and bleeding.

Small Intestine - Absorb All Action

Primary site for digestion & absorption. 📌 "Dow Jones Industrial" (Duodenum, Jejunum, Ileum).

Comparative Features:

• Plicae circulares (valves of Kerckring): ↑ 3x
• Villi: ↑ 10x
• Microvilli (brush border): ↑ 20x (Total ↑ ~600x)

Key Cells:

• Enterocytes: Absorption (brush border enzymes)
• Goblet cells: Mucus
• Paneth cells: Lysozyme, defensins (crypts)

Carbohydrate Absorption Pathway:

⭐ Duodenum is the primary site for iron (Fe²⁺ via DMT1) and calcium absorption.

Large Intestine Complex - Colon Cleanup Crew

• Parts: Cecum, appendix, colon (ascending, transverse, descending, sigmoid), rectum, anal canal.
• Hallmarks: Taeniae coli (3 muscle bands), haustra (sacculations), epiploic appendages (fat sacs).
• Microscopy: Abundant goblet cells; no villi.
• Supply: Arterial: Superior Mesenteric Artery (SMA), Inferior Mesenteric Artery (IMA). Innervation: Enteric NS, Vagus (proximal), Pelvic splanchnics (S2-S4, distal parasympathetic).
• Roles: Water/electrolyte absorption. Bacterial Vit K, B synthesis. Feces formation, storage, expulsion.

⭐ Exam Favourite: Watershed areas prone to ischemia: Griffith's point (splenic flexure: SMA-IMA junction) & Sudeck's point (rectosigmoid junction: IMA-superior rectal artery).

Defecation Reflex Pathway:

Accessory Digestive Organs - Gland Grandeur Guides

• Liver: Portal triad (Bile Duct, Hepatic Artery, Portal Vein 📌 DAVE). Functional unit: hepatic acinus (vs classic lobule). Synthesizes bile.

  ⭐ Portal triad contents: Portal vein, Hepatic artery, Bile duct.

• Gallbladder: Stores & concentrates bile. Cholecystokinin (CCK) stimulates contraction & bile release.
• Pancreas (Exocrine): Acini secrete enzymes; ducts secrete bicarbonate ($HCO_3^-$).
  • Regulation: Secretin → ↑$HCO_3^-$; CCK → ↑enzymes.

Pancreatic Enzymes:

High‑Yield Points - ⚡ Biggest Takeaways

• Meissner's plexus (submucosal) governs secretions/blood flow; Auerbach's plexus (myenteric) controls motility.
• Interstitial Cells of Cajal (myenteric plexus) are pacesetter cells generating slow waves.
• Brunner's glands (duodenum) secrete alkaline mucus to neutralize chyme.
• Peyer's patches (lymphoid aggregates) are most numerous in the ileum.
• Taeniae coli contraction forms haustra in the large intestine.
• Sphincter of Oddi controls bile/pancreatic juice flow into the duodenum.
• G cells (gastric antrum) secrete gastrin, stimulating HCl secretion.