GIS03 Histological features of digestive tract Flashcards
1
Q
4 distinct histological layers of GI tract
A
- Mucosa
- Epithelium
- Lamina propria (support + nourish epithelium)
—> loose CT
—> lymphatics + fenestrated blood capillaries
—> unencapsulated lymphoid nodules + plasma cells (protection)
- **Muscularis mucosae (smooth muscle)
—> local movement + folding of mucosa (controlled by **Meissner’s / Submucosal plexus)
—> modulate height of villi - Submucosa
- dense irregular
- larger blood vessel, lymphatics
- **Mucus-secreting gland (duodenum + esophagus)
- **Meissner’s / Submucosal plexus (ANS ganglion + nerve fibres)
—> continuous with myenteric plexus
—> control Muscularis mucosae and secretion (Secretomotor function) - Muscularis externa
- 2 smooth muscle layers: Longitudinal (outer) + Circular (inner) + Innermost oblique (stomach)
- regulate diameter
- peristalsis
- coordinated by ***Auerbach’s / Myenteric plexus (between circular and longitudinal) + Paracrine hormones - Serosa / Adventitia
- Serosa (mesothelium + CT): visceral peritoneum (Intraperitoneal organ)
- Adventitia (loose CT): oesophagus + Retroperitoneal organs
2
Q
2 types of plexus
A
- Submucosal plexus (Meissner’s plexus)
2. Myenteric plexus (Auerbach’s plexus)
3
Q
- Esophagus epithelium
- Stomach epithelium
- Intestine epithelium
A
- Stratified squamous non-keratinizing (prevent abrasion)
- Simple columnar (predominantly mucus-secreting)
- Simple columnar (absorptive + mucus-secreting)
4
Q
Esophagus
A
- Muscular to move food from pharynx to stomach
- Epithelium: ***Stratified squamous non-keratinizing
- To ease passage of food:
—> **Esophageal cardiac glands (simple tubular, mucous) in Lamina propria near cardia of stomach
—> **Submucosal esophageal gland (ease passage of food) - Muscularis mucosae: substantial
- Muscularis externa:
—> Striated (upper 1/3)
—> Striated + Smooth (middle 1/3)
—> Smooth (lower 1/3) - 2 muscular sphincter:
—> Pharyngoesophageal (upper esophageal spincter UES) —> Cricopharyngeus
—> Gastroesophageal (lower esophageal spincter LES) - Adventitia (outermost)
5
Q
Stomach histology
A
- Breakdown ingested food, begin digestion (Chyme: partially digested food)
- Gastric mucosa:
—> epithelium: **Simple columnar (raised into **Rugae)
—> mucosal gland: Simple tubular (HCl, mucus, enzymes, hormones) - Muscularis externa:
—> Oblique (innermost)
—> Circular (middle)
—> Longitudinal (outermost) - Serosa (smooth outermost layer)
6
Q
Division of stomach
A
- Cardia
- simple columnar
- mucosal cardiac gland: coiled
- ***secretory cells: mucus + lysozyme
- few parietal cells: HCl - Fundus
- **simple mucous cells
- **multiple cell types
- mucosa:
—> Gastric pits (出d) (foveola, tiny epithelial recesses —> opening to gastric glands): **mucous columnar cells
—> **Gastric gland (入d) (fundic gland, straight + branched at base): ***HCl, mucus, enzymes, electrolytes, water - Body
- ~fundus - Pylorus
- **Pyloric glands:
—> deeper gastric pits
—> shorter gland, more branched
—> fewer parietal and chief cells
—> proximal region: HCl + mucus
—> other region: mucus
—> fewer enteroendocrine cells: **Gastrin + **Serotonin + **Somatostatin
- outlet: substantial circular muscularis externa (Pyloric sphincter)
7
Q
Gastric glands
A
- branched mucosal gland in **lamina propria
—> Isthmus (uppermost opening, germination)
—> Neck (mainly **Parietal cells: acidophilic, germination)
—> Base (mainly ***Chief cells: basophilic) - secretions regulated by ***Vagus nerve (parasympathetic) + Paracrine hormones (paracrine cells in stomach, duodenum)
—> Gastrin (stimulate HCl)
—> Urogastrone (inhibit HCl)
—> Somatostatin (inhibit gastrin)
8
Q
***Gastric gland cell types
A
- Mucous neck cells
—> middle part (neck)
—> ***mucus-secreting, mitotic - Parietal cells (Oxyntic)
—> upper and middle part
—> **acidophilic, large, pyramidal
—> **Gastrin + H2 + M3 ACh receptors
—> intracellular channels (canaliculi): **HCl production, numerous mitochondria + **sER (active transport of H+ —> acidophilic), numerous microvilli (interdigitating + long)
—> secrete **Gastric intrinsic factors: **B12 absorption (deficient: impaired RBC production in myeloid tissue: pernicious anaemia)
3. Chief cells (Zymogenic) —> lower half —> ***Zymogen granules: enzyme precursors: Pepsinogen (—> pepsin in acidic pH) + Rennin / Chymosin + Lipase —> extensive ***rER (***basophilic) —> prominent Golgi —> basal nucleus
- Enteroendocrine cells
—> small number + great variety
—> produce peptide hormones (***Motilin + Serotonin)
—> diffuse neuroendocrine system
—> Paraneuron (neurotransmitter secreting cells)
—> Amine precursor uptake and decarboxylation (APUD) system - Undifferentiated cells (neck + isthmus)
—> germination region
—> high mitotic rate
—> epithelium replaced in 4-6 days
9
Q
- Gastrin
- Urogastrone
- Somatostatin
A
- Stimulate HCl
- Inhibit HCl
- Inhibit gastrin
10
Q
Motilin
A
Smooth muscle motility
11
Q
Small intestine function
A
- Complete digestion process
- Pancreatic digestive enzymes (alkaline pancreatic secretion —> counteract gastric acidity)
- Bile: emulsification of fat, augment pancreatic lipase
- Mucus from:
—> **Goblet cells of mucosal epithelium
—> **Mucosal glands in lamina propria: **Crypts of Lieberkuhn / intestinal crypts in small and large intestine
—> **Submucosal glands: ***Brunner’s glands in duodenum - Absorb nutrients
- Plicae circulares (2-3 fold increase SA)
- Intestinal villi (10 fold increase SA)
- Microvilli (20 fold increase SA) - Produce variety of GI hormone
12
Q
Small intestine special features
A
- Villi
—> **Fenestrated blood capillaries network —> absorption of nutrients
—> **Lacteals / lymphatic capillaries —> absorption of fat (monoglycerides + free fatty acids —> sER lipid synthesis in villus columnar cells —> lipid vesicles —> fuse with lateral borders of villus columnar cells —> liberate lipid content into intercellular spaces —> ***Chylomicron —> enter lacteals in lamina propria —> reach blood via Thoracic duct)
—> Smooth muscle cells extend into villi from muscularis mucosae —> modulate height of villi
—> lymphocytes, plasma cells, eosinophils in lamina propria - Intestinal glands (crypts of Lieberkuhn: **Goblet cells + **Paneth cells)
- Peyer’s patches
—> aggregated lymphoid nodules, prominent in **ileal walls, extend into submucosa
—> **Gut-associated lymphoid tissue (GALT): mucosal immunity
—> **M cells (Antigen presenting epithelial cells) overlying Peyer’s patches —> ingest foreign antigen —> deliver to macrophage / lymphocyte —> B cells develop into **IgA plasma cells —> secrete IgA onto epithelium —> primary defence
13
Q
Regional variations in small intestines
A
- Plicae circulares
duodenum (numerous) > jejunum > ileum - Villi
duodenum: Broad, tongue-like
jejunum: narrow
Ileum: narrow - Submucosal gland
duodenum: ***Brunner’s gland
jejunum: absent
Ileum: absent - Lymphoid nodules
duodenum: present
jejunum: present
Ileum: extensive as ***Peyer’s patches - Outermost layer
duodenum: adventitia (mostly retroperitoneal)
jejunum: serosa
Ileum: serosa
14
Q
***Small intestine cell types
A
Derived from small crypt base columnar cells / stem cells, villi epithelial cells renewed every 5-6 days
-
**Villous columnar cells
- **absorption (microvilli, striated / brush border)
- brush border of enzymes: **Disaccharidases + **Peptidases
- junctional complexes: tight junction + adhering junction - Goblet cells
- in villi and crypts
- increase from duodenum to ileum -
**Paneth cells
- lower part of **crypts
- large acidophilic zymogen granules
- extensive rER + prominent Golgi apparatus
- major source of **Lysozyme (antibacterial enzyme)
- secrete **TNFalpha + ***Defensins
- support stem cell development - Enteroendocrine cells
- crypts
- GI hormones: **Secretin + **Cholecystokinin-pancreozymin
15
Q
Large intestine components
A
- Colon
- Rectum
- Anal canal
- Appendix
