The Alimentary System

Terminology

• Ampulla = a cavity, or the dilated end of a duct

• Concave = curves inward

• Convex = curves outwards

• Gastro = relating to stomach

• Hepato = relating to liver

• Vestibule = a chamber or channel communicating with or opening into another, in particular

Importance for Medical Professionals

• Understand procedures involving the abdomen (e.g., abdominal surgery, endoscopy)

• Support assessment and diagnosis

• Improve communication among clinicians

• Facilitate research

Content Overview

• Introduction

• Oral Cavity

• Salivary Glands

• Palate

• Tongue

• Esophagus

• Stomach

• Small Intestine

• Large Intestine

• Associated Glands

Introduction

• The alimentary tract is an epithelium-lined muscular tube from the mouth to the anal canal

• Glands along the epithelial lining provide enzymes and other materials required for digestion and absorption

• Larger glands located outside the tubular tract include:

  • The 3 pairs of salivary glands

  • Liver

  • Gall bladder

  • Pancreas

Introduction (Parts of Alimentary Tract)

• Cranial End to Caudal End sequence:

  • Mouth → Pharynx → Esophagus → Stomach → Small Intestine → Large Intestine → Anus

  • Included components in order: Oral cavity, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine, Anus

Introduction (Digestion of Food)

• Undigested food is expelled as fecal material

• Processes involved:

  • Mechanical: break down by teeth

  • Propulsion: movement down the tract

  • Chemical: exposure to digestive enzymes, breaking into smaller molecules

  • Absorption: nutrients cross the epithelial lining into blood capillaries

Oral Cavity

• Teeth (in each quadrant):

  • 2 incisors, 1 canine, 2 premolars, 3 molars

• 1st bicuspid, 2nd bicuspid, 1st molar, 2nd molar, 3rd molar (wisdom tooth), central incisor, lateral incisor, cuspid

• Roof: hard palate; soft palate; uvula

• Floor: tongue; mucous membrane

• Posterior mouth: continuous with oropharynx at oropharyngeal isthmus

• Lateral boundary: palatoglossal arch

Oral Cavity (More Details)

• Oral cavity proper vs vestibule (between teeth and cheeks)

• Dentition per quadrant: incisors (2), canine (1), premolars (2), molars (3)

Hard & Soft Palate

• Hard palate:

  • Thin horizontal bony plate of the skull formed by the palatine process of the maxilla and the horizontal plate of the palatine bone

• Soft palate:

  • Muscular, non-bony posterior part of the palate

  • Median part projects downward as the conical uvula

Muscles of the Soft Palate

• Tensor veli palatini

• Palatopharyngeus

• Palatoglossus

• Levator veli palatini

• Musculus uvulae

Oral Diaphragm (anatomical perspective)

• Key muscles/structures in the floor of the mouth region include:

  • Mylohyoid muscle

  • Geniohyoid muscle

  • Digastric muscle (anterior and posterior bellies)

  • Lingual nerve, hypoglossal nerve

  • Submandibular gland and duct

  • Sublingual gland

Salivary Glands

• Parotid gland

  • Largest gland

  • Serous (watery) secretion

  • Opens via Stensen’s duct (parotid duct)

  • Affected by mumps virus

• Submandibular gland

  • Mixed serous and mucous secretion

  • Opens via Wharton’s duct

  • Calculi more common in this duct

• Sublingual gland

  • Mucous secretion

  • Has multiple ducts

Tongue

• Features:

  • Apex (free) vs root (attached)

  • Dorsum (upper surface) with:

  • Sulcus terminalis

  • Foramen cecum

  • Papillae: filiform, fungiform, circumvallate

  • Lingual tonsil

  • Median and lateral glossoepiglottic folds

  • Vallecula

  • Ventral surface features: sublingual fold, frenulum, apex

• Taste zones and papillae:

  • Vallate (circumvallate) papillae with taste buds

  • Fungiform papillae with taste buds

  • Filiform papillae and non-tol taste buds

  • Foliate papillae (lateral sides)

• Muscles:

  • Extrinsic: Styloglossus, Palatoglossus, Genioglossus, Hyoglossus

  • Intrinsic: Longitudinal, Transverse, Vertical fibers

• Blood supply: Lingual artery; veins drain into the internal jugular vein

• Nerve supply:

  • General sensation: anterior 2/3 by lingual nerve; posterior 1/3 by glossopharyngeal nerve; posterior-most part by vagus

  • Special sensation (taste): anterior 2/3 by chorda tympani; posterior 1/3 by glossopharyngeal; posterior-most by vagus

Epiglottis and Related Structures

• Epiglottis lies adjacent to palatopharyngeal and palatoglossal arches; lingual and palatine tonsils nearby

• Taste zones and papillae near dorsum of tongue

Muscles of the Tongue (Detailed)

• Extrinsic:

  • Styloglossus: elevates and retracts tongue (upward and backward)

  • Palatoglossus: closes oral cavity from oropharynx

  • Genioglossus: protrudes tongue

  • Hyoglossus: depresses tongue

• Intrinsic:

  • Longitudinal, Transverse, Vertical fibers; alter shape of tongue

• Innervation note: Hyoglossal nerve supplies intrinsic and most extrinsic muscles except Palatoglossus (innervated by pharyngeal plexus via the cranial part of the accessory nerve)

Tongue Blood Supply & Nerve Supply (Summary)

• Arterial: Lingual artery

• Venous drainage: Lingual veins to internal jugular vein

• General sensation and taste mapping as above

Esophagus

• Connects throat to stomach (gullet)

• Muscular tube with mucous membrane

• Length: $25 ext{ cm}$

• Begins at the cricoid cartilage (C6) and ends entering the right side of the stomach

• Relations by region:

  • Neck: anterior to trachea and recurrent laryngeal nerve; posterior to prevertebral muscles and vertebral column

  • Thorax: anterior to trachea, left recurrent laryngeal nerve, left bronchus, left atrium; posterior to vertebral column, thoracic duct, azygos vein, posterior intercostal arteries, descending thoracic aorta; lateral to mediastinal pleura, azygos vein (right)

  • Abdomen: anterior to left lobe of liver; left vagus nerve is related to the stomach; posterior to left crus of the diaphragm and right vagus nerve

• Esophageal constrictions (important for endoscopy)

  • 1st constriction: 1st at about $15 ext{ cm}$ from upper incisors; cricopharyngeal sphincter (C6)

  • 2nd constriction: $23 ext{ cm}$ from upper incisors; crossed by aortic arch and left main bronchus

  • 3rd constriction: $40 ext{ cm}$ from upper incisors; where it pierces the diaphram; LES at this level

• Esophageal muscle layers: inner circular and outer longitudinal

• Spatial muscle composition by region: upper part is striated; middle is mixed; lower part is smooth

Esophagus (Blood Supply, Lymphatics, Nerves)

• Arterial supply by region: inferior thyroid (neck), descending thoracic aorta and left gastric (thorax/abdomen)

• Venous drainage: azygos (thorax), left gastric vein (abdomen) and portal system via left gastric veins

• Lymphatics: deep cervical (neck), superior/posterior mediastinal (thorax), along left gastric vessels and celiac (abdomen)

• Nerve supply: neck via recurrent laryngeal and sympathetic trunks; thorax via vagal trunks, esophageal plexus, sympathetic trunks, greater splanchnic nerves; abdomen via anterior/posterior gastric nerves and sympathetic trunk

Stomach – Location & Anatomy

• Location: intraperitoneal organ in the upper abdomen; graphic region landmarks: epigastric, left upper quadrant, right upper quadrant, and surrounding regions

• Capacity: newborn approx. $30 ext{ ml}$; adult $1000 ext{ to } 1500 ext{ ml}$

• Parts: cardiac region, fundus, body, pylorus

• Shape variations (empty to distended): empty, moderately filled, distended

• Shape variants by built: hypertonic, orthotonic, hypotonic, atonic

stomach (Functions & Orifices)

• Functions: storage of ingested food, enzymatic digestion, absorption of water, glucose, and alcohol; secretion of gastrin hormone; typical gastric retention time $ext{RT} ext{ ≈ } 3 ext{ to } 4 ext{ hours}$

• Cardiac orifice: about $2.5 ext{ cm}$ to the left of the midline; no true anatomical sphincter; opposite T11 vertebra

• Pyloric orifice: contains pyloric sphincter; prepyloric vein (branch of right gastric vein); opposite L1 vertebra

• Curvatures: lesser curvature (right border) with angular notch and lesser omentum; greater curvature (left border) with pre-pyloric notch and gastro-splenic/gastro-phrenic ligaments; greater omentum

• Surfaces:

  • Anterior surface: peritonealized; relations: anterior abdominal wall, left costal margin, left pleura and lung, diaphragm, left lobe of liver

  • Posterior surface: peritonealized except bare area; relations (stomach bed): lesser sac, left crus of diaphragm, left suprarenal gland, left kidney, splenic artery, pancreas, transverse mesocolon, spleen

• Subdivision diagram: Cardia, Fundus, Body, Pylorus; pyloric antrum and pyloric canal; esophagus to cardia; pylorus to duodenum

• Interior surface: mucous membrane with folds (rugae), gastric pits, and the gastric canal (of Magenstrasse)

• Stomach musculature layers: outer longitudinal, middle circular, internal oblique (within the stomach region)

• 3-layer schematic: Esophagus → Muscularis externa layers (longitudinal, circular, oblique) with region-specific muscle tissue composition

Stomach – Arterial, Venous, Lymphatic & Nerve Supply

• Arterial supply:

  • Left gastric artery (principal; branch of celiac trunk)

  • Right gastric artery (branch of common hepatic)

  • Left gastro-epiploic artery (branch of splenic)

  • Right gastro-epiploic artery (branch of gastroduodenal)

  • Short gastric arteries (branches of splenic)

• Venous drainage:

  • Right & left gastric veins drain to portal vein

  • Short gastric and left gastro-epiploic veins drain to splenic vein

  • Right gastro-epiploic vein drains to SMV (superior mesenteric vein)

• Lymphatic drainage:

  • Follows arteries to gastric, gastro-omental, and short gastric nodes

  • Final pathway to the celiac lymphatic nodes

• Nerve supply:

  • Sympathetic: from lateral horn T6–T9

  • Parasympathetic: vagal trunks (anterior and posterior)

  • Gastric and hepatic branches, including nervi of Latarjet (gastric lesser curvature) and Nerve of Grassi (branches from posterior vagal trunk near gastro-oesophageal junction)

Stomach – Glands

• Cardiac glands: mucus secretion

• Fundic & body glands: zymogenic (chief) cells secrete pepsin; oxyntic cells secrete HCl via proton pump; mucus neck cells

• Pyloric glands: mucus secretion and gastrin production

Small Intestine

• Extends from the pylorus to the ileocecal junction

• Parts: Duodenum, Jejunum, Ileum

• Development: derived from foregut and midgut

• Blood supply: celiac trunk and superior mesenteric arteries

• Innervation:

  • Sympathetic: greater and lesser splanchnic nerves

  • Parasympathetic: vagus nerve (secretomotor to these regions)

• Lymphatics and venous drainage accompany arterial supplies

Duodenum

• 4 parts:

  • 1st part: proximal 5 cm, freely movable

  • 2nd part: vertical, about 7.5 cm

  • 3rd part: horizontal, about 12.5 cm

  • 4th part: ascending portion about 2.5 cm

• Interior features: circular folds (plicae circulares; valves of Kerckring) except the first part; duodenal cap (bulb) is smooth-walled

• Relations and adjacent structures summarized in sectional diagrams

Duodenum – Blood Supply & Veins

• Superior pancreaticoduodenal artery (branch of gastroduodenal)

• Inferior pancreaticoduodenal artery (branch of superior mesenteric)

• Veins: superior pancreaticoduodenal vein to portal vein; inferior pancreaticoduodenal vein to superior mesenteric vein

Jejunum & Ileum

• Mobile parts of the small intestine suspended by the mesentery (the Mesentery)

• Length: $6 ext{–} 8 ext{ m}$ total; within about $15 ext{ m}$ of mesentery

• Mesentery extends from L2 to sacroiliac joint; supplied by branches of the superior mesenteric artery

• Lymphatics drain to nodes along the superior mesenteric artery

• Proximal 2/5 is the jejunum (≈ $2.5 ext{ m}$); distal 3/5 is ileum (≈ $3.5 ext{ m}$); no clear boundary between them

• Jejunum lies in the umbilical region; ileum lies in the pelvis and hypogastric regions; position varies with body position

• Parasympathetic supply is secretomotor; sympathetic reduces secretions and motility

Jejunum vs Ileum – Key Differences

• Location: Jejunum mainly left upper quadrant; Ileum mainly right lower quadrant

• Lumen: Jejunum wider; Ileum narrower

• Wall: Jejunum thicker; Ileum thinner

• Plicae circulares: Jejunum many large folds; Ileum fewer and more widely spaced; absent in distal ileum

• Arterial arcades: Jejunum has one or two arcades; Ileum has longer arterial arcs with more arcades

• Fat in mesentery: More near root (jejunum) vs more distributed along intestine in ileum

• Peyer’s patches: Present in ileum (not in jejunum)

Meckel’s Diverticulum (Ileal diverticulum)

• Slight bulge in the ileum present at birth; vestigial remnant of omphalomesenteric (vitelline) duct

Large Intestine

• Extends from the ileocecal junction to the muco-cutaneous (pectinate) line of the anal canal

• Subdivisions: caecum & appendix; colon (ascending, transverse, descending, sigmoid); rectum; anal canal

• Functions: water absorption, bacterial synthesis of vitamins, storage of feces until defecation

Large Intestine – Anatomy & Features

• Caecum: beginning of the large intestine; asymmetrical sac with taeniae coli; appendix about 2 cm below the ileocecal junction; caecum covered by peritoneum on all sides; size roughly $6 ext{ cm} imes 7.5 ext{ cm}$ (length × breadth)

• Appendicular artery as arterial supply; end arteries; lymph to superior mesenteric nodes

• Taeniae coli: 3 thick bands from longitudinal muscle; haustrations; appendices epiploicae (fat-containing pouches) present except in caecum, appendix, rectum

• Caecum relations: anterior abdominal wall; right iliopsoas; ileum; ileocecal junction; vermiform appendix

• Ascending colon: extends to right colic (hepatic) flexure; length ~ $15 ext{ cm}$; breadth ~ $5 ext{ cm}$; retroperitoneal on posterior surface; marginal artery of Drummond via ileocolic and right colic branches

• Transverse colon: from hepatic to splenic flexures; hangs by the transverse mesocolon; length ~$50$ cm; breadth ~ $5 ext{ cm}$; forms a U-shaped loop; suspended by transverse mesocolon; relations above and below described; arterial supply via middle colic arteries (right 2/3) and left colic (left 1/3); venous drainage via portal system and SMV; lymph to superior/inferior mesenteric nodes

• Descending colon: from left colic flexure to left pelvic brim; length $25 ext{ cm}$; breadth $3.5 ext{ cm}$; retroperitoneal; phrenicocolic ligament connects to diaphragam; arterial supply via left colic and sigmoid branches of IMA

• Sigmoid colon: from left iliac fossa to rectosigmoid junction (S3 level); length $40 ext{ cm}$; breadth $3.5 ext{ cm}$; 3 parts (vertical, horizontal, oblique); sigmoid mesocolon suspends; relations with ILIAC vessels, ureter, nerves; arterial supply via 3–4 sigmoid arteries from IMA; venous drainage via inferior mesenteric veins; lymph to inferior mesenteric nodes; function as a fecal reservoir

• Rectum: lower dilated part; pelvic cavity; taeniae coli absent; no mesentery; continuation of sigmoid; curves related to sacrum; begins at the rectosigmoid junction; length $12 ext{ cm}$; upper part width $4 ext{ cm}$; peritoneal relations differ by anterior surface coverage between zones; recto-vesical pouch (males) and rectouterine pouch of Douglas (females)

• Anal canal: terminal part of the alimentary tract; extends from ano-rectal junction to anal orifice; length $3.8 ext{ cm}$; lateral walls approximated when empty; major relations include perineal body and structures in front and ischio-rectal fossae behind and sides

• Interior of anal canal divided by pectinate line and Hilton’s line into: upper, intermediate, lower zones; pectinate line marks muco-cutaneous junction; surface anatomy includes anal columns, valves, papillae, and sinuses

• Sphincters: Internal (involuntary; thickening of circular muscle; upper 3/4; autonomic supply) and External (voluntary; from pudendal nerve branches; pubo-rectalis sling)

Anal Canal – Detailed Zones & Pectinate Line

• Upper area (≈ 15 mm): anal columns (Morgagni), anal valves (Ball’s valves), anal papillae, anal sinuses; ducts open into sinuses; glands at the floor of sinuses

• Intermediate area (≈ 15 mm): pecten/transitional zone; stratified squamous non-keratinized epithelium; bluish color due to internal venous plexus; located between pectinate line and Hilton’s line

• Lower area (≈ 8 mm): true skin; perianal skin has corrugation

• Hilton’s line marks lower end of internal sphincter and attachment of intermuscular septum

Associated Glands of GIT

• Pancreas: retroperitoneal; head, body, tail; both endocrine and exocrine roles; ducts empty via ampulla of Vater into second part of the duodenum through the sphincter of Oddi

• Liver: the largest gland; right side under the diaphragm; four lobes (left, right, caudate, quadrate); falciform ligament attachment; porta hepatis (hilus) as entry point; relationship to gall bladder

• Gall Bladder: stores and concentrates bile (up to ~10-fold); bile released into duodenum via cystic duct and common bile duct; stimulates fat emulsification; gallstones can block ducts

Liver – Microscopic Anatomy (Brief)

• Hepatic lobule with central vein; plates of hepatocytes; sinusoids with fenestrated endothelium; Kupffer cells; portal triad (portal vein, hepatic artery, bile duct)

• Bile canaliculi drain into bile ducts; bile flows towards the portal triad

Bile & Gall Bladder (Bile Composition)

• Bile components: bile salts, bilirubin (bile pigment), cholesterol, phospholipids, electrolytes

Pancreas (Self-Notes)

• Retroperitoneal; head, body, tail; endocrine (islets of Langerhans) and exocrine (acinar cells secreting pancreatic juice)

• Pancreatic ducts lead to the duodenum via the Ampulla of Vater and Sphincter of Oddi

Self Practice (Review Prompt)

• Differences between Jejunum and Ileum (Key Points to Compare):

  • Lumen diameter; wall thickness; circular folds; length and arterial branching; fat in mesentery; presence of Peyer’s patches

  • Jejunum: wider lumen, thicker wall, many large circular folds, shorter arterial arcade, more fat near root; Peyer’s patches absent

  • Ileum: narrower lumen, thinner wall, fewer circular folds, longer arcade network, fat distributed along the mesentery; Peyer’s patches present

Summary – Practical Landmarks & Clinical Relevance

• The stomach’s “rule of 2’s”: two ends (cardiac & pyloric), two surfaces (anterior and posterior), two orifices (cardiac and pyloric), two incisurae (cardiac notch and angular notch), two curvatures (greater and lesser), two omenta, two sphincters (cardio-esophageal and pyloric), two vagal nerves, two sets of arteries (gastric and gastro-epiploic), two canals, and an approximate volume of $2 ext{ pints}$ when distended

• Caecum and appendix are critical surgical landmarks; the appendix is a vestigial organ with variable positions (e.g., retrocaecal, pelvi, splenic) and a surface point of reference called McBurney’s point

• Porto-systemic anastomoses (e.g., superior rectal vein to inferior mesenteric vein; portal vs systemic venous drainage) are clinically important for understanding varices and collateral circulation

• The pectinate line marks the boundary between endoderm (above) and ectoderm (below) in the anal canal; this has implications for embryology and nerve supply (autonomic above; somatic below)

Key Formulas & Data (LaTeX)

• Stomach capacity (adult): $1000 ext{ to } 1500 ext{ ml}$

• Stomach capacity (newborn): $30 ext{ ml}$

• Esophagus length: $25 ext{ cm}$

• Cardiac orifice offset: $ext{approximately } 2.5 ext{ cm left of midline}$; vertebral level $T11$

• Pyloric sphincter location: vertebral level $L1$

• Duodenum total length approximation (sum of parts): $5 ext{ cm} + 7.5 ext{ cm} + 12.5 ext{ cm} + 2.5 ext{ cm} \, = ext{ about } 27.5 ext{ cm}$

• Jejunum vs Ileum: Jejunum length approx $2.5 ext{ m}$; Ileum approx $3.5 ext{ m}$ within a total small intestine length ~$6 ext{–}8 ext{ m}$ under the mesentery

Note on Relations & Surgical Relevance

• Precise anatomical relationships (e.g., between duodenum, pancreas, and transverse colon) are essential for surgical planning (e.g., resections, anastomoses)

• Understanding the ileocecal region (caecum and appendix) helps in diagnosing obstruction and appendicitis

• Knowledge of the rectum and anal canal anatomy (sphincters, Hilton’s line, pectinate line, and hemorrhoidal plexuses) is essential for proctology and anorectal surgery

Quick Reference Tables (Condensed)

• Major glands: Parotid (serous), Submandibular (mixed), Sublingual (mucous)

• Stomach regions: Cardia, Fundus, Body, Pylorus; curvatures: Greater, Lesser; orifices: Cardiac, Pyloric

• Small intestine parts: Duodenum (4 parts), Jejunum, Ileum; Meckel’s diverticulum is a vestigial omphalomesenteric duct remnant

• Large intestine divisions: Caecum (with appendix), Ascending, Transverse, Descending, Sigmoid; Rectum; Anal canal with pectinate line

This set of notes consolidates the key points from the provided transcript, with emphasis on anatomy, physiology, relations, and clinical relevance for exam preparation.