4-6

Abdominal Wall Surface Anatomy

The abdomen can be divided into 4 quadrants using the median sagittal and transumbilical planes or into 9 regions using the midclavicular lines plus subcostal and intertubercular planes

Anterolateral Abdominal Wall Layers

From superficial to deep: skin → subcutaneous tissue → external abdominal oblique → internal abdominal oblique → transversus abdominis → transversalis fascia → extraperitoneal fascia → parietal peritoneum

Three Flat Abdominal Muscles

External oblique, internal oblique and transversus abdominis form the muscular layers of the anterolateral abdominal wall, located outside semilunar line

Rectus Abdominis

Vertical paired muscle enclosed by the rectus sheath and separated at the midline by the linea alba; tendinous intersections create its segmented appearance (muscle part of abs), ABOVE arcuate line= rectus sheath on both sides, BELOW arcuate line= rectus sheath on anterior side, inferior epigastric vessels on other

Linea Alba

Fibrous midline raphe formed by fusion of the abdominal muscle aponeuroses (2 pack)

Linea Semilunaris

Curved lateral border of the rectus abdominis where the abdominal aponeuroses converge (11 line)

Arcuate Line

Inferior border of the posterior rectus sheath; below it all three aponeuroses pass anterior to rectus abdominis and the posterior surface is mainly covered by transversalis fascia

Abdominal Wall Innervation

Thoracoabdominal nerves T7–T11 plus subcostal nerve T12 and iliohypogastric/ilioinguinal nerves from L1 provide motor and cutaneous sensory innervation

Abdominal Wall Arterial Supply

Superior epigastric arises from the internal thoracic system; inferior epigastric arises from the external iliac system; intercostal arteries also contribute (just know highlighted)

Umbilical Folds

Five folds are present on the internal abdominal wall: one median two medial and two lateral umbilical folds

Patent Urachus

Failure of the urachus to completely close after birth; may cause persistent clear fluid drainage from the umbilicus (cyst in bellybutton)

Inguinal Ligament

Inferior rolled border of the external abdominal oblique aponeurosis extending from the ASIS to the pubic tubercle

Inguinal Canal

Passageway through the abdominal wall containing the spermatic cord in males or round ligament of the uterus in females, plus the ilioinguinal nerve and accompanying vessels/lymphatics

Hesselbach’s Triangle

Region associated with direct inguinal hernias and bounded by the rectus abdominis laterally the inferior epigastric vessels and inferiorly the inguinal ligament

• MDs don’t LIE

  • Medial= direct (H triangle), lateral= indirect (inguinal canal)

Diaphragm Openings

Caval opening is at T8 esophageal hiatus at T10 and aortic hiatus at T12; mnemonic: I 8 (IVC) 10 Eggs (esoph.) At 12 (aorta)

Posterior Abdominal Wall Muscles

Major muscles are quadratus lumborum, psoas major, psoas minor and iliacus; psoas major and iliacus combine to form iliopsoas

Oral Cavity Mucosa

Functions in protection secretion absorption immune defense and taste; generally lined by stratified squamous epithelium with regional differences in keratinization

Masticatory Mucosa

Located on gingiva and hard palate; keratinized or parakeratinized stratified squamous epithelium adapted to mechanical stress

Lining Mucosa

Located on lips cheeks floor of mouth inferior tongue and soft palate; generally nonkeratinized and adapted for flexibility

Specialized Mucosa

Located on the dorsal tongue and contains papillae and taste buds for taste sensation

Lip Histology

The lip has external skin vermilion zone and internal oral mucosa; skin is keratinized with hair follicles

Vermilion Zone

Thin epithelium over connective-tissue papillae that brings capillaries close to the surface and gives the lips their red appearance

Filiform Papillae

Most numerous tongue papillae; highly keratinized with backward-pointing projections for mechanical function and no taste buds

Fungiform Papillae

Mushroom-shaped papillae scattered among filiform papillae with taste buds on the upper surface

Foliate Papillae

Parallel folds on the lateral tongue with taste buds along their side walls; more prominent in infancy

Circumvallate Papillae

Large V-shaped papillae near the posterior tongue surrounded by a trench; taste buds are on lateral walls and von Ebner glands flush the trenches

Taste Bud

Barrel-shaped collection of sensory supporting and basal cells within stratified squamous epithelium that opens through a taste pore

Taste Bud Cell Types

Gustatory cells detect dissolved substances and communicate with sensory nerves; supporting cells maintain the environment; basal cells replace aging cells

Teeth

All teeth contain enamel dentin and cementum; humans have 20 primary teeth and 32 permanent teeth

Salivary Glands

Exocrine glands formed by secretory acini and branching ducts organized into lobules; major glands are parotid submandibular and sublingual

Serous vs Mucous Acini

Serous acini are dark-staining protein-secreting units with round nuclei and small lumens; mucous acini are pale mucin-secreting units with flattened basal nuclei and wider lumens

Mixed Acini

Secretory units containing both serous and mucous cells

Merocrine Secretion

Secretory product is released by exocytosis without loss of cellular material; this is the mechanism used by salivary glands

Salivon

Functional unit of a salivary gland consisting of an acinus intercalated duct and striated duct; myoepithelial cells help propel secretion

Salivary Duct Sequence

Saliva flows from acinus → intercalated duct → striated duct → interlobular/excretory duct → main duct

Intercalated Duct

Small duct lined by simple cuboidal epithelium that receives secretion from acini and contributes bicarbonate secretion and chloride absorption

Striated Duct

Intralobular duct lined by simple columnar cells with basal infoldings and mitochondria; actively modifies saliva through ion transport

Excretory Duct

Large duct located within connective-tissue septa between lobules with a larger lumen and taller or stratified epithelium

Myoepithelial Cells

Contractile cells between secretory epithelial cells and basement membrane that help squeeze secretions from acini into ducts

Secretory IgA

Primary antibody isotype in secretions that protects mucosal surfaces by preventing microbial attachment and neutralizing toxins

Parotid Gland

Largest major salivary gland; almost entirely serous and produces about 30% of saliva with much of the salivary amylase

Submandibular Gland

Mixed gland but strongly serous-predominant; produces about 60% of saliva and has well-developed striated ducts

Sublingual Gland

Smallest major salivary gland; produces about 5% of saliva and is predominantly mucous with serous demilunes

Salivary Gland Histology Comparison

Parotid is predominantly serous and dark; submandibular is mixed but serous-predominant; sublingual is mixed but mucous-predominant and pale

Von Ebner Glands

Serous glands associated with circumvallate papillae that secrete into taste trenches to rinse away tastants and allow new stimuli to reach receptors

GI Tract Basic Organization

The GI tract is a hollow tube organized into mucosa submucosa muscularis externa and serosa or adventitia

Mucosa

Consists of epithelium lamina propria and muscularis mucosae; functions in protection absorption and secretion

Submucosa

Dense irregular connective tissue containing larger blood and lymphatic vessels the submucosal plexus and glands in certain regions

Muscularis Externa

Usually contains inner circular and outer longitudinal smooth muscle with the myenteric plexus between them; primarily responsible for motility

Serosa vs Adventitia

Serosa consists of connective tissue plus mesothelium and visceral peritoneum; adventitia is connective tissue only and attaches organs to surrounding structures

Meissner’s Plexus

Submucosal enteric plexus that regulates mucosal and submucosal activity including secretion and local blood flow

Auerbach’s Plexus

Myenteric enteric plexus between muscularis externa layers that coordinates smooth-muscle activity and peristalsis

Esophageal Histology

Esophagus is lined by nonkeratinized stratified squamous epithelium and contains prominent muscularis mucosae plus mucous glands in the submucosa

Esophageal Muscularis Externa

Upper third contains skeletal muscle

Esophageal Glands

Esophageal glands proper are mucous glands in the submucosa that lubricate the lumen

Gastroesophageal Junction/Z-Line

Abrupt transition from nonkeratinized stratified squamous epithelium of the esophagus to simple columnar gastric epithelium

Lower Esophageal Sphincter

High-pressure region involving distal esophageal and diaphragmatic muscle that helps prevent reflux of gastric contents into the esophagus

Stomach Histology

Stomach has simple columnar surface epithelium with gastric pits and glands; rugae are folds of mucosa and submucosa that allow expansion

Stomach vs Small Intestine

Stomach has gastric pits and glands but no villi; its rugae allow expansion after meals

Cardiac Region of Stomach

Contains shallow gastric pits and mucus-secreting cardiac glands near the esophageal opening that help protect against refluxed acid

Fundic/Body Glands

Long straight branched tubular glands containing mucous cells parietal cells chief cells enteroendocrine cells and stem cells

Pyloric Region

Characterized by very deep gastric pits and shorter highly branched or coiled mucus-secreting glands

Gastric Pits

Invaginations of the surface simple columnar epithelium; shallowest in the fundus/body and deepest in the pylorus

Surface Mucous Cells

Line the gastric surface and pits and produce protective mucus that shields the epithelium from gastric acid

Mucous Neck Cells

Located within gastric glands and contribute mucus to the protective gastric barrier

Parietal Cells

Large eosinophilic cells that secrete HCl and intrinsic factor; concentrated in the upper and middle portions of fundic glands

Chief Cells

Basophilic cells concentrated toward the base of gastric glands that produce pepsinogen for protein digestion

Enteroendocrine Cells

Scattered cells within gastric glands that release signaling molecules basally toward connective tissue and blood to regulate secretion motility and digestion

Gastric Juice Components

Mucus protects the mucosa

HCl Function

Produces a gastric pH around 1–2

Intrinsic Factor

Glycoprotein secreted by parietal cells that binds vitamin B12 and is required for B12 absorption

Parietal Cell HCl Secretion

Stimulation causes intracellular tubulovesicular membranes containing proton pumps to fuse with the canalicular membrane

Parietal Cell Stimulation

Gastrin acetylcholine and histamine stimulate parietal cells to increase HCl secretion; mnemonic GAH

Chief Cell Activation

Low gastric pH converts secreted pepsinogen into active pepsin

PAS Stain

Periodic acid–Schiff stain highlights carbohydrate-rich structures such as mucin glycogen and basement membranes; gastric mucus therefore stains strongly magenta

Histologic Gastric Cell Recognition

Parietal cells are large eosinophilic or pink cells with many mitochondria while chief cells are darker basophilic or purple cells rich in RER and zymogen granules

Gastric Hormone Distribution

Gastrin is concentrated mainly in the stomach and proximal small intestine; CCK secretin GIP and motilin are primarily associated with the small intestine while VIP and somatostatin have broader GI distributions