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)
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)
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
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
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
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
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
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]
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
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
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)
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
13
Q
esophageal gland proper
A
- Located in submucosa of esophagus
- eases the passage of ingested food
- compound gland, long excretory duct, mucous gland
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)
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
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)
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
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)
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)
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)
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
Parietal cells
- 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
Chief cells
- 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
Types of enteroendocrine cells
1) Enterochromaffin-like (ECL) cells
- Secretes histamine
2) D-cells
- Secretes somatostatin
3) G-cells
- Mainly in pyloric glands
- Secretes gastrin
28
Enteroendocrine cells of fundic gland
* 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
Stem cells at gastric glands
- 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
Glands of stomach comparison
**_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
Location of secretory vesicles in stomach secretory cells
**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
Fundic gland histological slide recognition
33
Small intestine function
completes digestion process
absorbs nutrients
produces a variety of GI hormones
34
Digestive features of small intestine histology
**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
Absorption features of small intestine
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
Villi of small intestine
* 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
Intestinal glands in small intestine
Crypts of Lieberkühn: main cell types - goblet cells, paneth cells
38
Peyer's patches
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
Cell types in small intestine
1) small crypt base columnar cells (stem cells)
2) Villous columnar cells
3) Goblet cells
4) Paneth cells
5) Enteroendocrine cells
40
Stem cells in small intestine
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
Villous columnar cells
- 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
Goblet cells in small intestine
* in both villi and crypts
* increase in number from duodenum to ileum
43
Paneth cells
* 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
Enteroendocrine cells of small intestine
* 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
Duodenum histological slide recognition
46
Regional variations in small intestines
47
Large intestine histological features
**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
Anal canal
* 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
Hemorrhoids
Chronic congestion of anal venous plexus ⇒ dilate and varicosed ⇒ anal mucosa bulges (internal hemorrhoids) ⇒ protrude under the anal skin (external hemorrhoids)
50
Appendix
* blind-end appendage of the cecum
* microscopically resembles large intestine
* prominent lymphoid nodules extending deep into submucosa (confluent and surround the entire lumen)
51
Appendicitis
* appendicitis: obstruction of lumen ⇒ bacterial infection ⇒ perforate ⇒ peritonitis
* (appendectomy : removal of the inflamed appendix)
