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Gastrointestinal Block > L03- Histology (eso, stomach, intestine) > Flashcards

L03- Histology (eso, stomach, intestine) Flashcards

1
Q

General histological layers of GIT (Overview)

A

(from internal to external)

A. Mucosa

  • epithelium
  • lamina propria
  • muscularis mucosae

B. Submucosa

C. Muscularis Externa

  • internal circular layer
  • external longitudinal layer

D. External Layer (Serosa or adventitia)

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2
Q

GIT Epithelial lining

A
  • Innermost layer of mucosa layer
  • esophagus - non-keratinizing stratified squamous epithelium
  • stomach - protective simple columnar epithelium (predominantly mucus-secreting)
  • intestines - simple columnar epithelium (absorptive cells & mucus-secreting cells)
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3
Q

GIT Laminar propria

A
  • Middle layer of mucosa layer
  • loose connective tissue
  • accommodates the mucosal glands (epithelial invagination)
  • lymphatics and fenestrated blood capillaries
  • unencapsulated lymphoid nodules and plasma cells (for protection)
  • Function: supports, protects and nourishes the epithelium
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4
Q

GIT Muscularis mucosae

A
  • Outermost layer of mucosa layer
  • thin layers of smooth muscle (inner circular & outer longitudinal)
  • for local movement and folding of the mucosa (controlled by submucosal/Meissner’s plexus and some paracrine hormones)
  • modulates the height of villi in small intestine
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5
Q

GIT Submucosa

A
  • Layer external to mucosa and internal to muscularis externa
  • loose connective tissue
  • with larger blood vessels and lymphatics
  • submucosal plexus of autonomic nervous system (ANS) ganglion cells and nerve fibres

i.e. Meissner’s plexus
• from vagus nerve (parasympathetic) control muscularis mucosa and glandular secretion (secretomotor)

• contains mucus-secreting glands in duodenum and esophagus only

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6
Q

GIT Muscularis externa

A
  • External to submucosa, internal to adventitia/serosa
  • two layers of smooth muscle: inner (circular) and outer (longitudinal)
  • regulate the luminal diameter of the intestine
  • moves luminal contents along the tract (peristalsis)
  • peristaltic waves coordinated by Auerbach’s (myenteric) plexus (between the circular and longitudinal muscle layers) and by paracrine hormones
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7
Q

GIT external layer

A
  • Serosa or adventitia
  • Serosa - visceral peritoneum (mesothelium + connective tissues); presents in most part of GI tract
  • Adventitia - loose connective tissue in esophagus and retroperitoneal segement of intestines
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8
Q

Retroperitoneal segments of GIT

A

1) Esophagus
2) Duodenum (distal second and third segments)
3) Ascending Colon
4) Descending Colon

[note: the above have adventita for external layer but not serosa]

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9
Q

Meissner’s plexus

A

aka Submucosal plexus

Location: Submucosa

Source: parasympathetic input only (from vagal nerve CNX)

Function: Secretomotor - control muscularis mucosa (local movement and folding of the mucosa) and glandular secretion

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10
Q

Auerbach’s Plexus

A

aka Myenteric plexus

Location: Muscularis externa, between the internal circular muscle layer and external longitudinal muscle layer

Source: Both sympathetic and parasympathetic input

Function: provides motor innervation to both layers of the tunica muscularis; thus regulating luminal diameter and creating peristaltic movements

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11
Q

Esophagus histological overview

A
  • muscular walls to convey chewed food from pharynx to the stomach
  • stratified squamous nonkeratinizing epithelium to withstand abrasion
  • esophagela cardiac glands (simple tubular, mucous) in lamina propria (near stomach) and submucosal esophageal glands proper eases the passage of ingested food
  • substantial muscularis mucosae
  • muscularis externa:

o striated muscle in the upper third
o smooth muscle in the lower third
o mixed in the middle third

  • physiologic muscular sphincters at two ends of esophagus: pharyngoesophageal and the gastroesophageal sphincters
  • adventitia as the outermost layer (since retroperitoneal)
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12
Q

esophagela cardiac glands

A
  • located in lamina propria of mucosa of esophagus
  • found near the cardia of stomach
  • simple tubular, mucous gland
  • eases the passage of ingested food
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13
Q

esophageal gland proper

A
  • Located in submucosa of esophagus
  • eases the passage of ingested food
  • compound gland, long excretory duct, mucous gland
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14
Q

Stomach histological overview

A
  • break down of ingested food; beginning of digestion (chyme: partially digested food from stomach)
  • gastric mucosa (simple columnar epithelium) raised into folds (rugae)
  • mucosal simple tubular glands: HCl, mucus, digestive enzymes, hormones
  • no submucosal glands except in region close to duodenum
  • three muscular layers in muscularis externa:
o innermost (oblique);
 o middle (circular),
 o outermost (longitudinal)

• serosal covering (continuation of mesogastrium, peritoneal in nature)

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15
Q

Stomach divisions

A

1) Cardia - where esophagus enters the stomach
2) Fundus - uppermost part of stomach
3) Body
4) Pylorus - where stomach joins the duodenum

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16
Q

Stomach division histological overview

A

_A. Cardia _

  • epithelium changed drastically from the stratified squamous type (in esophagus) to simple columnar type (in cardiac region)
  • (exceptionally) a few submucosal glands in area near the duodenum
  • mucosal cardiac gland
  • secretory cells: mucus and lysozyme
  • few parietal cells (low HCl)
  • esophageal sphincter - a physiological sphincter

B. Fundus and body of stomach

  • Surface epithelial lining - simple mucous columnar cells (not goblet cells)
  • Gastric pit (foveola) - tiny epithelial recess lined by mucous columnar cells, where gastric glands open into
  • Gastric (fundic) gland : straight, branched at the base; secretes gastric juice (water, HCl, mucus, digestive enzymes, electrolytes)

_C. Pylorus _

• pyloric glands:

  • deeper pits
  • shorter gland
  • more branched
  • proximal region (secret HCl and mucus)
  • other regions (entirely mucous secreting)
  • fewer enteroendocrine cells
  • secretion of serotonin, gastrin, somatostatin

• substantial circular middle layer of the muscularis externa at the outlet of stomach (pyloric sphincter - an anatomical sphincter)

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17
Q

Cardia histological overview

A
  • epithelium changed drastically from the stratified squamous type (in esophagus) to simple columnar type (in cardiac region)
  • mucosal cardiac gland
  • (exceptionally) a few submucosal glands in area near the duodenum
  • secretory cells: mucus and lysozyme
  • few parietal cells (low HCl)
  • esophageal sphincter - a physiological sphincter
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18
Q

Fundus histological overview

A
  • Histologically similar to stomach body
  • Surface epithelial lining - simple mucous columnar cells (not goblet cells)
  • Gastric pit (foveola) - tiny epithelial recess lined by mucous columnar cells, where gastric glands open into
  • Gastric (fundic) gland : straight, branched at the base; secretes gastric juice (water, HCl, mucus, digestive enzymes, electrolytes)
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19
Q

Stomach body histological overview

A
  • Histologically similar to fundus
  • Surface epithelial lining - simple mucous columnar cells (not goblet cells)
  • Gastric pit (foveola) - tiny epithelial recess lined by mucous columnar cells, where gastric glands open into
  • Gastric (fundic) gland : straight, branched at the base; secretes gastric juice (water, HCl, mucus, digestive enzymes, electrolytes)
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20
Q

Pylorus histological overview

A

• pyloric glands

  • deeper pits
  • shorter gland
  • more branched
  • proximal region (secret HCl and mucus)
  • other regions (entirely mucous secreting)
  • fewer enteroendocrine cells
  • secretion of serotonin, gastrin, somatostatin

• substantial circular middle layer of the muscularis externa at the outlet of stomach (pyloric sphincter - an anatomical sphincter)

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21
Q

Fundus in radiography

A
  • Darker in X-ray
  • Because fundus is the uppermost part of stomach where ususally air accumulation occur
22
Q

Gastric glands histological overview

A

Nature: simple branched mucosal gland in lamina propria of mucosa

Divisions (upper to lower):

  • Isthmus (opening into the gastric pits)
  • Neck
  • Base

Cell types:

1) Undifferentiated cells in neck and isthmus
2) Mucous neck cells
3) Parietal (oxyntic) cells
4) Enteroendocrine cells
5) Chief (zymogenic) cells

23
Q

Regulation of fundic glands

A

Regulated by vagus nerve and by several hormones (cells in gastric and duodenum):

1) Gastrin: stimulates HCl secretion
2) Somatostatin: inhibits release of gastrin
3) Urogastrone: inhibits HCl secretion

24
Q

Mucous neck cells

A
  • cells in gastric glands
  • in the neck region
  • mucus-secreting and mitotic
25
Q

Parietal cells

A
  • cells of gastric glands
  • aka oxyntic cells
  • large, acidophilic, pale-staining, pyramidal
  • concentrated in the upper and middle part of gastric glands
  • intracellular channels (canaliculi)

i) HCl production
ii) lined by numerous mitochondria and sER (active transport of H+ions)
iii) account for acidophilic in H & E staining

  • numerous interdigitating and long microvilli
  • mucous coating to protect the gastric lining
  • Receptors for gastrin, histamine H2 and acetylcholine M3 receptors
  • secrete gastric intrinsic factor (for vit. B12 absorption in small intestine) - if deficiency, will lead to impaired erythrocyte production in myeloid tissue i.e. pernicious anaemia
26
Q

Chief cells

A
  • cell of gastric gland
  • aka zymogenic cell or peptic cell
  • concentrated at the lower half of the gland
  • many zymogen granules

~ enzyme precursors: pepsinogen and the precursor of rennin and lipase
~pepsinogen is converted to pepsin by acid pH

  • extensive rER for protein production (basophilic), basally located nucleus
  • prominent Golgi complex
27
Q

Types of enteroendocrine cells

A

1) Enterochromaffin-like (ECL) cells
- Secretes histamine
2) D-cells
- Secretes somatostatin
3) G-cells

  • Mainly in pyloric glands
  • Secretes gastrin
28
Q

Enteroendocrine cells of fundic gland

A
  • Cell of gastric glands
  • small number (with great variety)
  • produce peptide hormones
o motilin (smooth muscle motility)
 o serotonin
  • Can be considered as paraneuron: neurotransmitter secreting cells (some GI peptides and amines are neurotrasmittor)
  • belongs to APUD cells system (amine precursor uptake and decarboxylation)
  • referred to as the diffuse neuroendocrine system (DNES)
29
Q

Stem cells at gastric glands

A
  • Undifferentiated cells
  • at neck and isthmus of gastric glands
  • germination region
  • high rate of mitosis
  • epithelium replaced in 4 to 6 days
  • replace all cells in glands, pits and luminal surface
30
Q

Glands of stomach comparison

A

Cardiac gland

  • shorter glands
  • secretory cells: mucus and lysozyme
  • few parietal cells (low HCl)

Gastric (fundic) gland :

  • straight
  • Longer glands
  • branched at the base
  • secretes gastric juice (water, HCl, mucus, digestive enzymes, electrolytes)

Pyloric glands:

- deeper pits

- shorter gland

  • more branched
  • proximal region (secret HCl and mucus)
  • other regions (entirely mucous secreting)
  • fewer enteroendocrine cells
  • secretion of serotonin, gastrin, somatostatin
31
Q

Location of secretory vesicles in stomach secretory cells

A

For exocrine cells:

  • secretory vesicles concentrated on apical/luminal surface
  • e.g. Chief cell, neck mucous cell

For endocrine cells:

  • secretory vesicles concentrated on basment lamina/basal surface (for secretion into underlying cells and bloodstream)
  • e.g. enteroendocrine cells
32
Q

Fundic gland histological slide recognition

A
33
Q

Small intestine function

A

completes digestion process

absorbs nutrients

produces a variety of GI hormones

34
Q

Digestive features of small intestine histology

A

1) digestive enzymes in small intestine are from pancreas:

o pancreatic secretion is alkaline – counteract gastric acidity

o bile from liver – augment pancreatic lipase

2) mucus secretion in small intestine:

o from submucosal (Brunner’s) glands in duodenum

o from mucosal glands in lamina propria of mucosa in GI tract (crypts of Lieberkühn or intestinal crypts in small and large intestines)

o from goblet cells of the mucosal epithelium

35
Q

Absorption features of small intestine

A

Absorptive surface expanded by :

1) plicae circulares: approx. 2-3 X surface area
2) intestinal villi : approx. 10 X surface area
3) microvilli: approx. 20 X surface area

Collectively increased the surface area by 400 to 600 folds

36
Q

Villi of small intestine

A
  • made of tall absorptive columnar cells with abundant goblet cells and occasional enteroendocreine cells interspersed between them
  • contain a profuse network of fenestrated blood capillaries — absorption of nutrients.
  • absorption of fats by lymphatic capillaries known as lacteals located in centre of villi - [Absorbed products of fat in forms of monoglycerides and free fatty acids ⇒ lipid synthesis in the sER of the villous columnar cells ⇒lipid containing vesicles ⇒ fuse with the lateral borders of villous columnar cells ⇒ liberate their lipid content into the intercellular spaces between cells (chylomicrons) ⇒ enter the lacteals in lamina propria ⇒ reach blood chiefly via the thoracic duct]
  • smooth muscle cells extend into villi from muscularis mucosae (modulate the height of villus)
  • numerous cell types (lymphocytes, plasma cells and eosinophils) in lamina propria
37
Q

Intestinal glands in small intestine

A

Crypts of Lieberkühn: main cell types - goblet cells, paneth cells

38
Q

Peyer’s patches

A

Peyer’s patches: aggregated lymphoid nodules

  • particularly prominent in ileal walls, extended to submucosa
  • Not encapsulated, therefore is not lymph nodes
  • Gut-associated lymphoid tissue (GALT): mucosal immunity
  • Antigen presenting epithelial cells (M cells) overlying the aggregated lymphoid nodules ⇒ ingest the foreign antigen ⇒ deliver them to underlying APS macrophages or lymphocytes ⇒ B-cells develop into IgA producing plasma cells ⇒ IgA is secreted onto the free surface of epithelia ⇒ primary defence against mucosal infection
39
Q

Cell types in small intestine

A

1) small crypt base columnar cells (stem cells)
2) Villous columnar cells
3) Goblet cells
4) Paneth cells
5) Enteroendocrine cells

40
Q

Stem cells in small intestine

A

All the cell types are believed to be derived from the small crypt base columnar cells (stem cells). Epithelial cells on villi are renewed about every 5 to 6 days.

41
Q

Villous columnar cells

A
  • Epithelial cells on villi are renewed about every 5 to 6 days
  • Microvilli - striated/brush border (to increase absorptive surface)
  • produce enzymes: disaccharidases and peptidases (to complete digestions of carbohydrates and proteins), enzymes are integral membrane glycoprotein of the cell membrane) – brush border enzymes
  • junctional complexes
  • tight junctions (sealing)
  • adhering junctions
42
Q

Goblet cells in small intestine

A
  • in both villi and crypts
  • increase in number from duodenum to ileum
43
Q

Paneth cells

A
  • found at the base of crypts of small intestines (more distal part)
  • large acidophilic zymogen granules
  • extensive rER and prominent Golgi apparatus
  • major source of antibacterial enzyme:
  • TNFa (proinflammatory)
  • Lysozyme (degrade bacteria wall)
  • Defensins (increase permeability of bacterial membrane)

• support stem cell development

44
Q

Enteroendocrine cells of small intestine

A
  • secretes GI hormones including secretin and cholecystokinin-pancreozymin)
  • belongs to APUD cells system (amine precursor uptake and decarboxylation)
  • referred to as the diffuse neuroendocrine system (DNES)
45
Q

Duodenum histological slide recognition

A
46
Q

Regional variations in small intestines

A
47
Q

Large intestine histological features

A

Function:

  • completes absorption and retrieves water from the luminal contents
  • produces abundant protective mucus, some GI hormones, no digestive enzymes secreted
  • houses bacteria that produce vitamin B12 and vitamin K

A. Mucosa

  • no villi
  • numerous crypts (long and straight)
  • surface epithelium: tall absorptive columnar cells with a striated border, goblet cells (increase in no. from ascending colon to rectum), enteroendocrine cells
  • Paneth cells: rare and usually absent
  • epithelium replaced about every 6 days by new cells arising from lower parts of the crypts.

B. Submucosa

• no submucosal gland

C. Muscularis Externa

• in cecum and colon, external longitudinal muscle arranged mostly as three longitudincal bands (teniae coli) ⇒ continuous contraction ⇒ sacculation of the colon (haustra coli, absent in appendix)

D. Outermost Layer

  • presence of applendix epiploica - pouches of the peritoneum filled with fat - along the colon and upper part of the rectum.
  • retroperitoneal segments of the colon and rectum have an adventitia, remainder covered by serosa
48
Q

Anal canal

A
  • mucosal lining of the anal canal lacks crypts
  • inferior part of anal canal: simple columnar epithelial lining changes to stratified squamous non- keratinizing ⇒ keratinizing epidermis of skin.
  • raised into longitudinal ridges (anal columns) joined to form anal valves
  • discontinuous muscularis mucosa, teminate at anal valve
  • contain a plexus of small vein (anastomosis between the portal venous system and the systemic venous system)
  • at anus, circular smooth muscle (muscularis externa) – internal anal sphincter
  • external anal sphinter: circular band of skeletal muscle (provide voluntary control of defecation)
49
Q

Hemorrhoids

A

Chronic congestion of anal venous plexus ⇒ dilate and varicosed ⇒ anal mucosa bulges (internal hemorrhoids) ⇒ protrude under the anal skin (external hemorrhoids)

50
Q

Appendix

A
  • blind-end appendage of the cecum
  • microscopically resembles large intestine
  • prominent lymphoid nodules extending deep into submucosa (confluent and surround the entire lumen)
51
Q

Appendicitis

A
  • appendicitis: obstruction of lumen ⇒ bacterial infection ⇒ perforate ⇒ peritonitis
  • (appendectomy : removal of the inflamed appendix)

Gastrointestinal Block (24 decks)

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