Histology digestion

What are the three primary germ layers in the week-3 embryo?

Ectoderm (dorsal), mesoderm (middle), and endoderm (ventral)

Which germ layer forms the gut tube and respiratory lining?

Endoderm

Which germ layer gives rise to muscles, bones, and connective tissues?

Mesoderm

Which germ layer forms the skin, sensory organs, and central nervous system?

Ectoderm

Into which three regions does the mesoderm differentiate?

Paraxial, intermediate, and lateral plate mesoderm

What cavity forms within the lateral plate mesoderm around day 19?

Intraembryonic coelom

What do the two layers of lateral plate mesoderm become?

Parietal (somatic) mesoderm lining body walls and visceral (splanchnic) mesoderm covering organs

What adult membranes derive from parietal and visceral mesoderm?

Parietal mesoderm → body-wall serous membranes

During week 4 folding, what tube forms from yolk-sac endoderm?

Primitive gut tube

Which structure becomes the anterior body wall during lateral folding?

Fusion of parietal mesoderm + ectoderm (lateral body folds)

What suspends the gut tube from the posterior wall?

Dorsal mesentery

Which embryonic structure separates thoracic from abdominal cavities by day 22?

Septum transversum

What folds divide the thorax into pericardial and pleural cavities?

Pleuropericardial folds

Which membranes complete the diaphragm by week 7?

Pleuroperitoneal membranes plus septum transversum

From which somites do diaphragm muscle cells arise?

Somites 3, 4, and 5

Which arteries supply the embryo’s foregut, midgut, and hindgut?

Foregut → celiac artery

What are the derivatives of the foregut?

Pharynx, esophagus, stomach, duodenum (proximal), liver, gallbladder, and pancreas

How is the respiratory tract separated from the foregut?

By formation of the tracheoesophageal septum, creating lung bud anteriorly and esophagus posteriorly

What embryonic rotation does the stomach undergo?

90° clockwise around its longitudinal axis, then a second rotation in a frontal plane

What adult peritoneal structures derive from the ventral mesogastrium?

Falciform ligament and lesser omentum (hepatogastric and hepatoduodenal ligaments)

What adult peritoneal structures derive from the dorsal mesogastrium?

Greater omentum, gastrosplenic ligament, and splenorenal ligament

How do the liver and gallbladder originate embryologically?

As the hepatic diverticulum (liver bud) from the ventral foregut

Which embryonic buds form the pancreas?

Dorsal pancreatic bud (body/tail/head) and ventral bud (uncinate + part of head) that fuse after duodenal rotation

Why does the midgut herniate physiologically into the umbilical cord?

Because its rapid elongation outpaces the size of the embryonic abdominal cavity

How many degrees and in which direction does the midgut loop rotate overall?

270° counterclockwise around the SMA (90° during herniation + 180° on return)

What do the cranial and caudal limbs of the primary intestinal loop become?

Cranial limb → jejunum and ileum

How is the cloaca divided into urogenital and anorectal parts?

By growth of the urorectal septum, separating the cloaca into the urogenital sinus (anterior) and rectum/anal canal (posterior)

From which germ layer and arch does the anterior two-thirds of the tongue develop?

Ectoderm of the first pharyngeal arch

Which nerve supplies general sensation to the anterior two-thirds of the tongue?

Lingual nerve (branch of V₃, trigeminal)

Which nerve carries taste from the anterior two-thirds of the tongue?

Chorda tympani of facial nerve (VII) via lingual nerve

Which arches give rise to the posterior one-third of the tongue?

Second, third, and fourth pharyngeal arches

Which nerve supplies general and special sensation to the posterior one-third of the tongue?

Glossopharyngeal nerve (IX)

What embryonic structure suspends the stomach and later becomes greater omentum?

Dorsal mesogastrium

What is the foramen cecum a remnant of?

Proximal thyroglossal duct at the tongue’s terminal sulcus

During tooth development, what are the bud, cap, and bell stages?

Sequential morphogenetic phases of the enamel organ shaping the future tooth

Which sheath guides root formation of the developing tooth?

Hertwig’s epithelial root sheath (HERS)

What adult structures arise from the dental follicle?

Cementum, periodontal ligament, and alveolar bone

When do deciduous and permanent teeth begin to develop?

Deciduous teeth at weeks 6–7

What are the four main histologic layers of the colon wall?

Mucosa, submucosa, muscularis propria (externa), and serosa (or adventitia)

Which cells line the colonic surface epithelium?

Simple columnar enterocytes (absorptive cells) and mucus-secreting goblet cells

What are the crypts of Lieberkühn in the colon?

Straight, unbranched tubular glands extending from the luminal surface down to the muscularis mucosa

Where in the colonic mucosa are goblet cells most concentrated?

In the deeper portions of the crypts near the muscularis mucosa

What is the lamina propria?

Loose connective tissue between crypts, containing immune cells (plasma cells, lymphocytes, eosinophils, macrophages)

What does the muscularis mucosa consist of?

A thin layer of smooth muscle at the deepest part of the mucosa

What structures are found in the colonic submucosa?

Dense irregular connective tissue, blood vessels, lymphatics, and Meissner’s (submucosal) plexus

What is the function of Meissner’s plexus?

Innervates mucosal goblet cells and muscularis mucosa to regulate secretion and local motility

How is the muscularis propria of the colon organized?

Inner circular smooth-muscle layer and outer longitudinal layer arranged as three teniae coli

What plexus lies between the two muscle layers of the colon?

Auerbach’s (myenteric) plexus, which controls peristalsis

What are the four universal layers of the GI tract?

Mucosa, submucosa, muscularis propria, and outer serosa or adventitia

What type of epithelium lines the esophageal mucosa?

Stratified squamous nonkeratinized epithelium

What glands are unique to the esophageal submucosa?

Mucous-secreting submucosal (esophageal) glands

How does the muscle composition of the esophagus change along its length?

Upper third—striated (skeletal) muscle

What is the lower esophageal sphincter (LES)?

A functional sphincter without distinct histologic thickening that prevents acid reflux

What is Barrett esophagus?

Metaplasia of lower esophageal squamous epithelium to mucus-secreting simple columnar cells due to acid injury

What are the three layers of the gallbladder wall?

Mucosa, tunica muscularis, and external adventitia or serosa

What distinguishes gallbladder mucosa from intestinal mucosa?

No crypts—only mucosal folds (rugae) lined by simple columnar epithelium with abundant goblet cells

How is the gallbladder muscular layer arranged?

Bundles of randomly oriented smooth muscle that contract to expel bile

What covers the gallbladder serosa?

Loose connective tissue with mesothelial (simple squamous) covering

What is Glisson’s capsule?

The fibrous connective-tissue capsule enveloping the liver

What is the functional unit of the liver?

The hepatic lobule—hexagonal plates of hepatocytes radiating around a central vein

What three structures make up the portal triad?

Branch of hepatic artery, branch of portal vein, and bile ductule

How do hepatocytes and sinusoids interact?

Hepatocytes form one-cell-thick plates separated by sinusoidal blood channels for nutrient exchange and bile secretion into canaliculi

What stain highlights reticulin fibers in a liver lobule?

Reticulin stain, used to detect thickened trabeculae in hepatocellular carcinoma

What cells form pancreatic exocrine acini?

Pyramid-shaped serous cells with basally located nuclei and apical zymogen granules

What are centroacinar cells?

Extensions of intercalated ducts into the center of acini, unique to the pancreas

Describe the ductal progression in the pancreas.

Centroacinar → intercalated ducts (simple cuboidal) → intralobular ducts (stratified cuboidal) → interlobular ducts (simple/stratified columnar)

What are the islets of Langerhans?

Clusters of endocrine cells (α, β, δ, PP cells) that stain paler and produce insulin, glucagon, somatostatin, and pancreatic polypeptide

Which cell type predominates in the islets?

β-cells (≈70%), secreting insulin

How does the small intestine’s villus morphology change from duodenum to ileum?

Tall, slender villi in duodenum/jejunum

What are Peyer’s patches?

Aggregates of lymphoid follicles in the ileal lamina propria

What glands are unique to the duodenal submucosa?

Brunner’s glands, secreting alkaline mucus to neutralize gastric acid

What cell type at the base of intestinal crypts provides innate immunity?

Paneth cells, with eosinophilic granules containing antimicrobial peptides

What are the two muscle layers of the small-intestinal muscularis externa?

Inner circular and outer longitudinal smooth muscle, with Auerbach’s plexus between them

What histologic feature distinguishes the stomach body/fundus mucosa?

Gastric (fundic) glands with parietal (acid-secreting) and chief (pepsinogen-secreting) cells

How many muscle layers are in the stomach wall?

Three: inner oblique, middle circular, and outer longitudinal

What cells line the surface and pits throughout the stomach?

Mucus-secreting simple columnar epithelium

Which gastric region has the deepest pits and branched glands?

Pylorus, with deep pits and coiled pyloric glands containing G cells (gastrin-secreting)

What are the four general functions of the digestive tract?

Intake of food/liquid, mastication, motility & secretion, chemical digestion & absorption, hormone release, and elimination of waste

What are the three types of oral mucosa?

Masticatory (keratinized/parakeratinized), lining (non-keratinized), and specialized (taste buds)

Where is parakeratinized epithelium found in the oral cavity?

On gingiva, hard palate, and dorsal tongue—superficial cells retain pyknotic nuclei

Which minor salivary glands are found in oral lining mucosa?

Scattered glands in lips, cheeks, and alveolar mucosa within lamina propria

Name the three major paired salivary glands and their secretions.

Parotid (serous), submandibular (mixed), and sublingual (mucous/mixed)

What enzyme is produced by serous acini in salivary glands?

Amylase (plus lipase, lysozyme, and IgA transport)

What are the three parts of a tooth?

Crown, neck, and root

What tissues comprise the periodontium?

Cementum, periodontal ligament, alveolar bone, and gingiva

What is enamel composed of and how thick is it?

96% mineral (hydroxyapatite), 2% organic, 2% water

What are Striae of Retzius?

Incremental growth lines in enamel parallel to surface, reflecting metabolic rhythm

Where are dental papilla and dental sac located in the tooth germ?

Papilla under enamel organ gives rise to dentin/pulp

Which cells form predentin and later dentin?

Odontoblasts at the pulp–dentin interface

What is the function of Hertwig’s epithelial root sheath?

Guides root formation and induces odontoblast differentiation

What are the four layers common to the entire GI tract?

Mucosa, submucosa, muscularis propria, and serosa/adventitia

How does esophageal muscle change along its length?

Upper third–striated

What epithelium lines the esophagus?

Non-keratinized stratified squamous

Which glands in the esophageal submucosa lubricate the mucosa?

Esophageal (cardiac) mucous glands

Which nerve plexus in the esophagus controls peristalsis?

Auerbach’s (myenteric) plexus between muscle layers

What histologic change defines Barrett esophagus?

Metaplasia of squamous epithelium to mucus-secreting simple columnar

Name the three muscle layers of the stomach.

Inner oblique, middle circular, and outer longitudinal

What cells line gastric pits and secrete mucus?

Mucous neck cells (and surface mucus cells)

Which gastric gland cells secrete HCl and intrinsic factor?

Parietal cells

Which gastric gland cells secrete pepsinogen?

Chief (zymogenic) cells