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GIS > GIS03 Histological features of digestive tract > Flashcards

GIS03 Histological features of digestive tract Flashcards

1
Q

4 distinct histological layers of GI tract

A
  1. 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
  2. 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)
  3. 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
  4. Serosa / Adventitia
    - Serosa (mesothelium + CT): visceral peritoneum (Intraperitoneal organ)
    - Adventitia (loose CT): oesophagus + Retroperitoneal organs
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2
Q

2 types of plexus

A
  1. Submucosal plexus (Meissner’s plexus)

2. Myenteric plexus (Auerbach’s plexus)

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3
Q
  1. Esophagus epithelium
  2. Stomach epithelium
  3. Intestine epithelium
A
  1. Stratified squamous non-keratinizing (prevent abrasion)
  2. Simple columnar (predominantly mucus-secreting)
  3. Simple columnar (absorptive + mucus-secreting)
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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)
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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)
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6
Q

Division of stomach

A
  1. Cardia
    - simple columnar
    - mucosal cardiac gland: coiled
    - ***secretory cells: mucus + lysozyme
    - few parietal cells: HCl
  2. 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
  3. Body
    - ~fundus
  4. 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)
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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)
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8
Q

***Gastric gland cell types

A
  1. Mucous neck cells
    —> middle part (neck)
    —> ***mucus-secreting, mitotic
  2. 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
  1. 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
  2. Undifferentiated cells (neck + isthmus)
    —> germination region
    —> high mitotic rate
    —> epithelium replaced in 4-6 days
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9
Q
  1. Gastrin
  2. Urogastrone
  3. Somatostatin
A
  1. Stimulate HCl
  2. Inhibit HCl
  3. Inhibit gastrin
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10
Q

Motilin

A

Smooth muscle motility

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11
Q

Small intestine function

A
  1. 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
  2. Absorb nutrients
    - Plicae circulares (2-3 fold increase SA)
    - Intestinal villi (10 fold increase SA)
    - Microvilli (20 fold increase SA)
  3. Produce variety of GI hormone
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12
Q

Small intestine special features

A
  1. 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
  2. Intestinal glands (crypts of Lieberkuhn: **Goblet cells + **Paneth cells)
  3. 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
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13
Q

Regional variations in small intestines

A
  1. Plicae circulares
    duodenum (numerous) > jejunum > ileum
  2. Villi
    duodenum: Broad, tongue-like
    jejunum: narrow
    Ileum: narrow
  3. Submucosal gland
    duodenum: ***Brunner’s gland
    jejunum: absent
    Ileum: absent
  4. Lymphoid nodules
    duodenum: present
    jejunum: present
    Ileum: extensive as ***Peyer’s patches
  5. Outermost layer
    duodenum: adventitia (mostly retroperitoneal)
    jejunum: serosa
    Ileum: serosa
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14
Q

***Small intestine cell types

A

Derived from small crypt base columnar cells / stem cells, villi epithelial cells renewed every 5-6 days

  1. **Villous columnar cells
    - **    absorption (microvilli, striated / brush border)
    - brush border of enzymes: **Disaccharidases + **Peptidases
    - junctional complexes: tight junction + adhering junction
  2. Goblet cells
    - in villi and crypts
    - increase from duodenum to ileum
  3. **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
  4. Enteroendocrine cells
    - crypts
    - GI hormones: **Secretin + **Cholecystokinin-pancreozymin
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15
Q

Large intestine components

A
  1. Colon
  2. Rectum
  3. Anal canal
  4. Appendix
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16
Q

Large intestine functions

A
  1. Complete absorption
  2. Retrieve water from luminal contents
  3. Produce protective mucus, GI hormone (NO digestive enzymes)
  4. House bacteria producing vitamin B12 + vitamin K
  5. ***NO villi
  6. ***Numerous crypts
  7. Surface epithelium: tall absorptive ***columnar cells with striated border, goblet cells, enteroendocrine cells (renewed every 6 days from lower parts of crypt)
  8. ***Paneth cells rare and absent
  9. ***NO submucosal gland
  10. Caecum + Colon: longitudinal muscle: 3 longitudinal bands (Teniae coli) —> continuous contraction —> Sacculation / **Haustra coli (*absent in appendix)
  11. Appendix epiploica: bag of fat along colon only
  12. Retroperitoneal segments of colon and rectum: adventitia, remainder serosa
17
Q

Anus

A

Internal anal sphincter: circular smooth muscle of muscularis externa —> Inferior hypogastric plexus

External anal sphincter: circular band of skeletal muscle (***voluntary control of defecation) —> Inferior rectal nerve (Pudendal nerve)

Inferior part of anal canal: simple columnar epithelium —> stratified squamous non-keratinizing epithelium —> keratinizing epidermis of skin

18
Q

Haemorrhoid

A

Anal canal mucosal lining lacks crypts
—> raised into **anal columns (longitudinal ridges)
—> joined to form **anal valves
—> **discontinuous muscularis mucosae terminate at anal valve (contain a **plexus of small veins: anastomosis between portal venous system and systemic venous system)
—> chronic congestion
—> dilate and varicosed
—> anal mucosa bulges (internal haemorrhoids)
—> protrude under anal skin (external haemorrhoids)

19
Q

Appendix

A
  • Blind-end appendage of caecum
  • microscopically resembles large intestine
  • prominent ***lymphoid nodules extending deep into submucosa (confluent and surround the entire lumen)
  • Appendicitis: obstruction of lumen —> bacterial infection —> perforate —> peritonitis
  • appendectomy: removal of inflamed appendix

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