Gastrointestinal Flashcards
Typical hollow organ layers
Esophagus - describe structure
Muscular tube connecting pharynx to stomach
Mucosal lining:
- SSNKE
- lamina propria
- muscularis mucosae
Submucosa:
- loose CT
- esophageal glands
Muscularis externa
- inner circular/outer longitudinal
- upper 1/3 = skeletal muscle
- middle 1/3 = skeletal/smooth mixed
- lower 1/3 = smooth muscle
Adventitia
- located in thorax
Serosa
- located in abdominal cavity
ID organ and layers
Esophagus
ID organ and describe
X-section of esophagus
The plexus in the esophagus is located where and called what
Submucosal layer, Meissner’s Plexus
Esophageal glands and ducts
Glands are submucosal and mixed seromucous
Ducts are stratified cuboidal
ID Tissue and describe
Muscularis externa is the outer third of the esophagus. The outer cells run logitudinally and the inner are circular. Between is the myenteric (Auerbach’s) plexus.
ID Tissue and describe
muscularis externa (outer section of esophagus) – longitudinal section
Note the mix of longitudinal and circular muscle cells
Gastroesophageal junction
AKA squamocolumnar junction
Gastro-esophageal reflux disease (GERD)
Results from chronic acid reflux at which point the formally SSNKE esophageal lining is replaced by the cuboidal lining as in the stomach (metaplasia)
Can lead to invasive carcinoma
Three regions of the stomach
Cardia
Fundus
Pyloris
Stomach- Cardiac region
- short pits
- short glands
cells:
- mostly mucous
- enteroendocrine
Stomach - Fundic region
Thick mucosa
- short pits
- long glands
Cells:
- Enteroendocrine cells
- Chief cells
- parietal cells
- surface epithelium
Smooth muscle cells are elongated into the mucosa
Location of cells in the fundic region of the stomach
Parietal cells
eosinophilic cells (due to abundant mitochondria) found in the fundic region of the stomach
They secrete HCL and intrinsic factor (vitamin B12 absorbs in the gut)
Chief cells
(zymogenic) found in fundic region of stomach
very basophilic
- secrete pepsinogen, lipase, chymosin
Stomach - pyloric region
- long pits
- short glands
cells:
- mostly mucous
- enteroendocrine
*
Pyloric sphincter
is thickened inner circular muscular layer of the stomach
Sections and characteristics of the small intestine
duodenum
jejunum
ileum
Characteristics:
- villi/microvilli
- plica circulares
- goblet cells
- crypts (intestinal glands)
Sections and characteristics of the large intestine
cecum
appendix
colon
Characteristics:
- no villi
- many goblet cells
- crypts
- teniae coli
ID organ and describe
Small intestine
Duodenum
First part of the small intestine
contains Brunner’s glands which secrete alkaline mucous to neutralize acid chyme (this submucosa gland is diagnostic of the small intestine)
Villi: specializations for digestion and absorption
(in small intestine)
How does the epithelium in the small intestine control absorption?
With terminal bars
Lymphatic capillary in intestinal villi
Central lacteal
Absorbs lipids into the lymphatic
Crypts
invaginations into mucosa
AKA Crypts of Lieberkuhn
Contains:
- goblet cells (no microvilli on goblet cells)
- paneth cells
- enteroendocrine
- stem cells
How can you tell a cross section of a villi and crypt apart?
Goblet cell number increases from…
…proximal to distal intestine
Paneth Cells
Found in crypts of small intestine
- highly eosinophilic granules of antimicrobial products:
- lysozyme
- alpha-defensins
Enteroendocrin cells
secrete basally into ECM, fenestrated capillaries (FC). Found throughout GI tract, including in crypts of intestine
Two types:
Open type regulated by luminal contents
Closed type regulated by neural & paracrine mechanisms
Stem cells
Generate all 4 types:
- enterocyte*
- goblet cell*
- enteroendocrine
- paneth
*Turnover 5-6 days; this rapid rate renders the cells susceptible to many cancer therapies that target rapidly dividing tumor cells
Jejunum
second part of the small intestine; contains plicae circulares or infolding of submucosa
Ileum
Distal portion of the small intestine
Contains the Peyer’s Patch: masses of lymphocytes
Most cells in masses of lymphocytes are enterocytes, but there are scattered M cells
Microfold “M” Cell
Found scattered on Peyer’s Patch in ileum of small intestine
M Cells have deep invagination that allow immune cells (T cells, B cells, macrophages, etc) to get as close to the gut lumen as possible
By pinocytosis, they sample the environment
Deep to the submucosa layer of the small intestine is the…
muscular externa; has inner circular/outer longitudinal layers with myenteric plexus between two muscle layers
Note: small intestine also has Meissner’s pexus (submucosal)
Serosa
AKA visceral peritoneum
covers most of small intestine and large intestine
Colon
- no villi
- many crypts (IGs)
- abundant goblet
cells
- few/no Paneth cells
- enteroendocrine
- tenia coli
Teniae Coli
Found in colon in three bands; longitudinal smooth muscle
Surrounding the colon are two structures
Serosa (visceral peritoneum) and adventitia
Appendix
Smooth surface, no microvilli
is part of lymphoid system with masses of lymphocytes (dark staining masses)
lots of crypts
has muscularis externa, but no tenia coli (in that way it’s more like small intestine)
ID organ and describe
ID letters
Liver functions
Metabolic
- Uptake, storage, metabolism & distribution of important nutrients and vitamins
- Degradation & conjugation of metabolites and potential toxic substances (endogenous & exogenous)
- Iron recycling (especially after splenectomy)
Exocrine
- Production & secretion of bile (containing bile salts, phospholipids, and cholesterol)
Endocrine
- Synthesis & secretion into the blood of most plasma proteins: e.g., albumin, α-, β-globulins
ID organ and describe tissue
highly cellular organ; plates of hepatocytes
function aspects are lobules; corners have portal triads
at center of lobule is central vein
Structure of liver lobule
portal vein is carry O2 poor/nutrient rich blood from gut to liver
O2 rich blood from aorta mixes with that blood
bile is working its way out
Liver sinusoids
- discontinuous/fenestrated endothelium
- overlie perisinusoidal space (Disse)
- contain reticular fibers (slow blood flow)
Cells of the liver
- polyhedral hepatocytes
- Kupffer cells (in the sinusoid, stain darkly)
- Ito (stellate) cells
- store Vit. A
- are activated upon damage (generating scar tissue)
Exocrine function of liver: Bile
Exocrine product is bile which is made by hepatocytes
Channel between adjacent hepatocytes (plates of hepatocytes) to form bile canuliculi which connects outwards to bile duct (in portal triad)
Three types of liver lobules
Cells that are in the middle of the liver acinus recieve most nutrient rich and O2 rich blood
Centrilobular necrosis
Zone 3 first to go!
Gall Bladder
- storage of bile
- concentration of bile (done by epithelium cells)
- no muscularis mucosa or submucosa
- simple columnar epithelium (no goblet cells)
- “false glands” *
- Rokitansky-Aschoff sinuses
- cholecystokinin (CCK) stimulates muscularis contraction
- secretin stimulates bicarbonate secretion from bile duct cells
ID organ and describe tissue
Gall bladder
- storage of bile
- concentration of bile
- no muscularis mucosa or submucosa
- simple columnar epithelium (no goblet cells)
- “false glands” *
- Rokitansky-Aschoff sinuses
- cholecystokinin (CCK) stimulates muscularis contraction
- secretin stimulates bicarbonate secretion from bile duct cells
Rokitansky-Aschoff sinuses
Found in gall bladder, continuous with lumen
cholecystokinin (CCK)
stimulates muscularis contraction of gall bladder
secretin
stimulates bicarbonate secretion from bile duct cells
Cholelithiasis
gall stones
Pancreas
Exocrine:
- lobular organ partitioned by septa
- serous acini
- zymogen granules containing inactive digestive enzymes
- ducts to covey secretions and deliver bicarbonate-rich fluid
- acini controlled by CCK
- ducts controlled by secretin
Endocrine:
- Islets of Langerhans (arrows)
- rich network of fenestrated capillaries
- produces and secretes insulin, glucagon, somatostatin
ID organ and describe tissue
Pancreas; tissue has serous acini
serous acini: lots of zymogen present in apical end of cell, basally located nuclei. Basophilia with lots of RER
Islets of Langerhans
Important in endocrine function of panceas
Number of different cell types make a number of different hormones
ID Tissue and describe
Interlobular ducts of pancreas
embedded within collagen (stains blue)
typically have simple cuboidal epithelium
ID Tissue and describe
Intralobular duct of pancreas
lighter staining nuclei
ID Tissue and describe
intralobulat duct of pancreas
if nucleus is in plane of section, looks like it’s in the lumen of the acinus
this is called a centroacinar cell
Cystic fibrosis
