Digestive System

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Oral Cavity & Salivary Glands - Mouth Matters

Anatomy of Salivary Glands

  • Teeth: Types: Incisors, Canines, Premolars, Molars. Sets: Deciduous (20), Permanent (32).
  • Tongue: Muscular; taste (papillae: circumvallate, fungiform, foliate), speech, swallowing.
  • Palate: Roof of mouth. Hard (anterior, bony), Soft (posterior, muscular, uvula).

Salivary Glands:

GlandTypeDuct (Opens)Nerve Supply (Parasymp.)
ParotidSerousStensen's (opp. upper 2nd molar)Glossopharyngeal (IX)
SubmandibularMixedWharton's (sublingual caruncle)Facial (VII - Chorda Tympani)
SublingualMucousBartholin's/Rivinus (sublingual folds/caruncle)Facial (VII - Chorda Tympani)

Pharynx & Esophagus - Gullet Gateway

  • Pharynx:
    • Nasopharynx: Skull base to soft palate; Respiratory epithelium.
    • Oropharynx: Soft palate to epiglottis; Strat. Sq. Non-keratinized.
    • Laryngopharynx: Epiglottis to C6; Strat. Sq. Non-keratinized.
  • Esophagus: ~25cm muscular tube.
    • Constrictions (📌 C6, T4/5, T10): Cricopharyngeal, Aortic/Bronchial, Diaphragmatic.
    • Histology: Mucosa (Strat. Sq. Non-keratinized), Submucosa, Muscularis Externa (striated → mixed → smooth), Adventitia.
    • Sphincters: UES (cricopharyngeus), LES (physiological).
    • Blood: Inf. thyroid, aortic, L. gastric aa. Nerves: Vagus, sympathetic chain.
    • Porto-systemic anastomosis: Lower esophagus (L. gastric vein ↔ azygos vein).

⭐ Killian's dehiscence: Posterolateral muscular defect between thyropharyngeus & cricopharyngeus (parts of inferior constrictor); common site of Zenker's diverticulum.

Sagittal view of pharynx divisions Esophagus Constrictions and Measurements Esophageal wall histological layers

Stomach & Duodenum - Acidic Adventures

  • Stomach: J-shaped; parts: cardia, fundus, body, pylorus. Curvatures: lesser, greater.
    • Histology: Gastric glands with key cells:
      CellSecretion
      ParietalHCl, Intrinsic Factor
      ChiefPepsinogen
      Mucous NeckMucus
      G-cellsGastrin
    • Arterial: Celiac trunk. Venous: Portal vein. Lymph: Celiac nodes.
    • Nerve: Vagus (Parasympathetic), Celiac plexus (Sympathetic).
  • Duodenum: C-shaped; 4 parts (D1-D4).
    • Features: D1-Brunner's glands (alkaline mucus); D2-Major Duodenal Papilla (Ampulla of Vater); Ligament of Treitz (suspends Duodenojejunal flexure).

⭐ Arteries: Lesser curve supplied by Left & Right Gastric Arteries; Greater curve by Left & Right Gastro-omental Arteries.

Stomach and Duodenum Anatomy and Blood Supply

Small & Large Intestines - Absorption Arena

  • Small Intestine (SI): Primary nutrient absorption.

    • Jejunum vs. Ileum:

      FeatureJejunumIleum
      WallThicker, more vascularThinner, less vascular
      Plicae CircularesLarge, numerous, closely setSmaller, fewer, sparse distally
      Arterial ArcadesFewer (1-2 tiers), long vasa rectaMore (3-4+ tiers), short vasa recta
      Peyer's PatchesFew/AbsentNumerous, large
  • Large Intestine (LI): Water absorption, waste compaction.

    • Features: Taeniae coli (3 longitudinal bands), Haustra (sacculations), Epiploic appendages (fat tags).
    • Parts: Cecum, Appendix, Colon (Ascending, Transverse, Descending, Sigmoid), Rectum, Anal Canal.
    • Blood Supply: SMA (to splenic flexure), IMA (distal).
    • Watershed areas: Splenic flexure (Griffiths' point), Rectosigmoid junction (Sudeck's point).
    • Pectinate line (Anal Canal): Divides endoderm (above) from ectoderm (below) origin; changes innervation, blood supply, lymphatics.

Vasa Recta of Small Intestine

⭐ McBurney's point: Located one-third of the distance from the anterior superior iliac spine to the umbilicus, commonly corresponds to the base of the appendix (site of maximum tenderness in acute appendicitis).

Liver, Gallbladder & Pancreas - Accessory All-Stars

  • Liver: 4 lobes (R, L, Caudate, Quadrate); 8 Couinaud segments. Portal triad (Portal Vein, Hepatic Artery, Bile Duct). Histo: Hepatocytes, sinusoids (Kupffer cells), Space of Disse. Functions: Bile prod., metabolism. Couinaud liver segments & vasculature, biliary apparatus, and pancreatic ducts)
  • Gallbladder: Stores, concentrates bile. Calot's Triangle (boundaries: Cystic Duct, Common Hepatic Duct, Inf. Liver edge; content: Cystic Artery). 📌 Mnemonic: "3 C's" (Cystic Duct, Common Hepatic Duct, Cystic Artery).
  • Pancreas: Head, neck, body, tail. Exocrine: Acini (enzymes: amylase, lipase, proteases). Endocrine (Islets):
    CellHormone
    AlphaGlucagon
    BetaInsulin
    DeltaSomatostatin
    Ducts: Wirsung (main), Santorini (accessory).

⭐ Portal vein: formed by Splenic Vein & Superior Mesenteric Vein union.

High-Yield Points - ⚡ Biggest Takeaways

  • Meckel's diverticulum: Rule of 2s (2% population, 2 feet from ICJ, 2 inches long).
  • Gut arterial supply: Foregut by celiac trunk, Midgut by SMA, Hindgut by IMA.
  • Portal triad: Proper hepatic artery, portal vein, common bile duct in hepatoduodenal ligament.
  • Calot's triangle: Borders: cystic duct, common hepatic duct, liver edge; contains cystic artery.
  • GI wall layers: Mucosa, Submucosa (Meissner's plexus), Muscularis externa (Auerbach's plexus), Serosa.
  • Achalasia cardia: LES non-relaxation due to Auerbach's plexus loss in esophagus.

Practice Questions: Digestive System

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Stenson's duct of parotid gland opens opposite to:

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Flashcards: Digestive System

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Branches of the external carotid artery can be remembered with the mnemonic (Some Angry Ladies Fight Off PMS)S - _____A - Ascending pharyngeal arteryL - Lingual arteryF - Facial arteryO - Occipital arteryP - Posterior auricular arteryM - Maxillary arteryS - Superficial temporal artery

TAP TO REVEAL ANSWER

Branches of the external carotid artery can be remembered with the mnemonic (Some Angry Ladies Fight Off PMS)S - _____A - Ascending pharyngeal arteryL - Lingual arteryF - Facial arteryO - Occipital arteryP - Posterior auricular arteryM - Maxillary arteryS - Superficial temporal artery

Superior thyroid artery

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