MP

Respiratory, Abdominal Wall & Digestive Anatomy – Lecture Review

Respiratory Tract (Continuation from Previous Lecture)

Trachea

  • Begins inferior to the larynx; reinforced by C-shaped hyaline‐cartilage rings

    • Cartilage is incomplete posteriorly ➔ open part of “C” closed by a fibro-muscular membrane

  • Maintains patency for airflow; posterior membrane allows slight esophageal expansion during swallowing

  • Bifurcates at the carina (\text{C A R I N A}) into right & left primary bronchi

Bronchi

  • Primary (Main) bronchi

    • Right: wider, shorter, and more vertical ➔ most common site of aspirated foreign bodies

    • Left: narrower, longer, more oblique ➔ less frequent aspiration pathway

  • Secondary (Lobar) bronchi

    • Supply individual lung lobes

    • Right lung: 3 secondary bronchi (superior, middle, inferior)

    • Left lung: 2 secondary bronchi (superior, inferior)

  • Tertiary (Segmental) bronchi

    • 8\text{–}10 per lung (variable); supply bronchopulmonary segments

Bronchioles & Functional Divisions

  • Bronchioles = smallest conducting airways (no cartilage)

  • Terminal bronchioles

    • Final part of conducting division (air conduction only)

  • Respiratory bronchioles

    • First part of respiratory division (walls thin enough for gas exchange)

    • Lead to → alveolar ducts → alveolar sacs → individual alveoli

    • All four distal structures (respiratory bronchiole, duct, sac, alveolus) permit gas exchange

Lungs: Gross Features

External Morphology

  • Apex: pointed, projects superior to 1st rib

  • Base: broad; rests on diaphragm

Hilum / Root Structures (medial view)

  • Contain bronchi, pulmonary arteries, pulmonary veins (+ smaller nerves & lymphatics)

  • LEFT lung (superior → inferior): Pulmonary artery / Bronchus / Pulmonary veins

  • RIGHT lung:

    • Bronchus = posterior-superior

    • Pulmonary artery = anterior-superior

    • Pulmonary veins = inferior

Lobes & Fissures

  • Right lung: 3 lobes (superior, middle, inferior) separated by

    • Oblique fissure (superior & middle vs. inferior)

    • Horizontal fissure (superior vs. middle)

  • Left lung: 2 lobes (superior, inferior) separated by one oblique fissure

    • Superior lobe possesses lingula (tongue-like projection — presumed evolutionary remnant of a middle lobe)

    • Cardiac notch accommodates heart’s leftward projection

Abdominal Wall & Pelvic Musculature

Functions

  • Support & retain abdominal viscera

  • Increase intra-abdominal pressure for defecation, micturition, parturition, sneezing, etc.

Lateral Abdominal Wall (3 layers)

Layer

Fiber direction

Relative depth

External oblique

“Hands-in-pockets” (inferomedial)

Superficial

Internal oblique

Superomedial ((90^\circ) to external)

Intermediate

Transversus abdominis

Transverse / horizontal

Deep

  • Aponeuroses of these muscles form the rectus sheath around rectus abdominis

Rectus Abdominis Complex

  • Two vertical muscle bands lateral to linea alba (midline fibrous raphe)

  • Interrupted by 2–3 tendinous intersections ➔ visible “six-/eight-pack”

Inguinal Region

  • Inguinal ligament: rolled inferior border of external-oblique aponeurosis (ASIS → pubic tubercle)

  • Inguinal canal (superior to ligament)

    • Males: transmits spermatic cord

    • Females: transmits round ligament of uterus

Inguinal Hernias

  • Indirect: sac enters deep inguinal ring → canal (lateral; follows cord/round-lig.)

  • Direct: protrudes medial to canal through weakened abdominal wall; does not traverse canal

Posterior Abdominal Wall

  • Quadratus lumborum: quadrilateral muscle lateral to psoas major; ipsilateral trunk flexion

Pelvic Diaphragm

  • Muscular floor of pelvis; supports pelvic viscera

  • Components:

    • Levator ani (pubococcygeus + iliococcygeus)

    • Coccygeus (ischiococcygeus)

Digestive System Overview

Alimentary Canal vs. Accessory Organs

  • Alimentary canal: continuous muscular tube (oral cavity → anus) carrying food bolus

  • Accessory organs: secrete substances aiding digestion (salivary glands, liver, gallbladder, pancreas, etc.)

Abdominal Quadrants (surface anatomy)

  • Lines: vertical (xiphoid → pubic symphysis) & horizontal (through umbilicus)

  • Right Upper (RUQ): liver, gallbladder, right kidney

  • Left Upper (LUQ): stomach, spleen, left kidney

  • Right Lower (RLQ): cecum, appendix, right ovary (♀)

  • Left Lower (LLQ): sigmoid colon, left ovary (♀)

Histological Layers of Alimentary Canal

  1. Mucosa: epithelium + lamina propria in direct contact with food

  2. Submucosa: connective tissue, vessels, glands

  3. Muscularis externa

    • Usually 2 smooth-muscle layers: inner circular & outer longitudinal

    • Exception: stomach has 3 layers (adds inner oblique)

  4. Serosa / Adventitia: outermost covering (visceral peritoneum or connective tissue)

Peritoneum & Mesenteries

  • Parietal peritoneum: lines abdominal wall

  • Visceral peritoneum: covers organs

  • Mesentery: double layer connecting visceral to parietal peritoneum; conveys vessels & nerves, prevents organ torsion

  • Retroperitoneal organs (posterior to parietal peritoneum): kidneys, ureters, aorta, IVC, parts of duodenum, pancreas (head/neck), ascending & descending colon, etc. (mnemonic “SAD PUCKER”) – focus: kidneys, ureters, aorta, IVC

Foregut Structures

Oral Cavity & Salivary Glands

  • Mechanical breakdown by teeth; food bolus mixed with saliva (amylase begins carbohydrate digestion)

  • Paired major glands

    • Parotid (extra-oral; anterior to ear) ➔ parotid duct pierces cheek

    • Submandibular (partly intra- & extra-oral; beneath mandible)

    • Sublingual (entirely intra-oral; beneath tongue; many small ducts – “gleeking”)

Pharynx (shared airway/foodway)

  • Nasopharynx (respiratory only)

  • Oropharynx & Laryngopharynx (respiratory + digestive) ➔ propel bolus to esophagus

Gut Divisions

  • Foregut: distal esophagus, stomach, proximal duodenum, liver, gallbladder, pancreas, spleen

  • Midgut: distal duodenum → proximal 2/3 transverse colon

  • Hindgut: distal 1/3 transverse colon → rectum

Esophagus

  • Muscular conduit; no digestion/absorption

  • Passes diaphragm at T10 ("I 8 10 Eggs A 12" mnemonic)

  • Proximal \tfrac{1}{3} skeletal muscle, middle mixed, distal \tfrac{1}{3} smooth muscle

Stomach

  • J-shaped reservoir; mechanical/chemical digestion

  • Regions: cardia → fundus (gas bubble) → body → pyloric canal (pyloric sphincter regulates gastric emptying)

  • Curvatures: greater (left) & lesser (right)

  • Internal rugae permit expansion

  • 3 smooth-muscle layers (adds inner oblique) for churning

Peritoneal Folds of Stomach

  • Greater omentum: apron-like double layer hanging from greater curvature; can migrate to wall-off infection

  • Lesser omentum: spans lesser curvature → liver (hepatogastric + hepatoduodenal parts)

Pancreas

  • Retroperitoneal (except tail); posterior to stomach, transversely oriented

  • Endocrine (~1 %): islets of Langerhans secrete insulin & glucagon ➔ regulate blood glucose

  • Exocrine (~99 %): acini produce pancreatic juice (enzymes, bicarbonate)

    • Secreted via main pancreatic duct → joins duodenum (with bile) at hepatopancreatic ampulla

Liver

  • Largest gland; RUQ beneath diaphragm

  • Major functions: (1) produce bile (lipid emulsification) (2) metabolic & detox “first-pass” of portal blood

  • Four lobes

    • Right (large) & Left (small) — divided anteriorly by falciform ligament

    • Quadrate (inferior, adjacent gallbladder)

    • Caudate (superior, adjacent IVC)

  • Ligaments/attachments

    • Coronary ligament: suspends superior surface to diaphragm (crown-like)

    • Falciform ligament: liver → anterior abdominal wall; inferior free edge forms round ligament (ligamentum teres — obliterated fetal umbilical vein)

  • Porta hepatis (hilum): entry/exit for

    • Common hepatic duct (bile out)

    • Proper hepatic artery (oxygenated blood in)

    • Hepatic portal vein (nutrient-rich, deoxygenated blood in)

Gallbladder & Biliary Tree

  • Pear-shaped sac on posteroinferior liver surface (stores & concentrates bile)

  • Duct system

    • Right & Left hepatic ducts → common hepatic duct (bile from liver)

    • Cystic duct (two-way) connects gallbladder ↔ common hepatic duct

    • Cystic + common hepatic merge as common bile duct → joins pancreatic duct → duodenum

    • Bile flow options:

    • Liver → common hepatic → common bile → duodenum

    • Liver → common hepatic → cystic → gallbladder (storage) → cystic (reverse) → common bile → duodenum

Midgut & Hindgut (Preview)

  • Midgut: distal duodenum, jejunum, ileum, cecum & appendix, ascending colon, proximal \tfrac{2}{3} transverse colon

  • Hindgut: distal \tfrac{1}{3} transverse colon, descending & sigmoid colon, rectum, anal canal

  • Detailed anatomy to be covered in next lecture segment

Key Numerical / Mnemonic References

  • Diaphragmatic openings: T8 (IVC), T10 (Esophagus), T12 (Aorta) – “I 8 10 Eggs A 12”

  • Bronchial segmentation: 3 lobar bronchi (R) vs 2 (L); 8\text{–}10 tertiary bronchi per lung

  • Retroperitoneal mnemonic: SAD PUCKER (Suprarenal, Aorta/IVC, Duodenum – 2/3, Pancreas, Ureters, Colon – asc/desc, Kidneys, Esophagus, Rectum)

Clinical Correlations & Practical Points

  • Right main bronchus predisposes to aspiration pneumonia/foreign‐body obstruction

  • Inguinal hernias: distinguish indirect (through canal) vs direct (through abdominal wall)

  • Greater omentum’s “policeman of abdomen” role in containing infections

  • Portal blood detoxification underscores hepatic vulnerability to toxins/first-pass drug metabolism

  • Gallstones may lodge in cystic duct or hepatopancreatic ampulla, causing biliary colic or pancreatitis

(End of current lecture content — next session will continue with small intestine onward)