GI Histology Flashcards
Functions of the GI system
major components
- ingestion, propulsion and digestion of food
- absorb nutrients
- reabsorb fluid
- excrete waste (bile & undigested material)
- protection
Components
- alimentary canal (long hollow tube)
1. esophagus
2. stomahc
3. small intestine
4. large intestine
- pancreas (exo and endocrin function)
- hepatobililary tract
Layers of the Alimentary Canal
4 main layers
all areas have
1. mucosa: the inner most layer to line the tube
2. submucosa
3. muscularis externa/propria
4. serosa/adventitia
Mucosa Layer
layers
function
Mucosal Layers
- innermost: epithelium
- lamina propria: connective tissue
- muscularis mucosae: thin smooth muscule
function
- secrete enzymes fo digestion
- absorption
- barrier
- secrete mucus
Submucosa layer
layers
function
Submucosa Layers
- made of connective tissue, adipose tissue, vessels & glands, and meisner’s plexus (sensory (Para and symp.) stimulation)
Function
- support the canal
- produce enzymes
Muscularis Externa/Propria Layer
types of muscle
function
Muscularis Externa/Propria
inner layer: circular smooth muscle
outer layer: longitudinal smooth muscle
except: the upper 1/3 of esophagus is skeletal muscle
except: the stomach also has oblique layer (3rd)
function
- propulsion of food
Serosa/Adventitia
layers
function
mesentery v mesothelium
Serosa: (visceral peritoneum): thin layer of connective tissue surrounded by mesothelium: forming the mesentery (cover organ)
Adventisa: loose connective tissue (anchor to wall)
Function
- support (blood vessels, nerves, cushion GI tract)
- storage of fat
Mesetery: a double layer of visceral peritoneum which anchors organs to the abdominal wall
Mesothelium: simple squamous epithelium which lines the cavity
Esophagus
- function & overview
- histology
- barretts esophagus
function
- muscular tube for food to pass, via parastalsis from pharynx to stomach
Sphincters
- upper esophageal: skeletal muscle ; swallow
- lower esophageal: smooth muscle; prevent backflow ( gerd)
Histology (innermost lining to out)
- non-keratinized stratified squampus epithelium
- lamina proper
- muscualris mucosae
the mucosa layer ^^
- submucosa
- muscularis proper (upper 1/3 = skeletal muscle, lower 2/3 = smooth muscle) circular and longitundial
- adventita
Barrett Esophagus
- a change from normal squamous epithelium to columnar and goblet cells from the intestinal lumen
- a metaplasia: due to GERD; can increase the risk for cancer
- “salmon pink patches”
Stomach
- Function and Overview
- Layers
- Histology
Function & Overview
- food storage
- production of chyme
Layers
- Mucosa: columnar epithelium with gastric pits
1. Foveolar epithelial cells: protection
2. Gastric pits (the opening on the surface)
2. Gastric Glands
3. Parietal cells: secrete HCL, and intrinsic factor for B12
4. Chief Cells: secrete pepsinogen (for pepsin)
5. Enteroendocrine cells: secrete hormones (gastrin(stimulate) and somatostatin (stop)) for the acid to start or stop
- submucosa layer
- muscularis layer
1. inner oblique
2. middle circular
3. outer longitudinal - serosa
Small Intestine
overview and function
histology
specifics
Small Intestine
- duodenum
- jejunum
- illeum
- receives the bile and pancreatic secretions
- major site of digestion and absorption
Histology
- contain plicae circulares to increase surface area for absorbtion
- each PC contines villi : the fingerlike projections
- on the villi are the following cell types
1. enterocytes (absorptive cells) = columnar cells with apical microvilli on each cell making a brush boarder
2. Goblet cells = secrete mucin
3. Paneth cells = secrete antimicrobial enzymes
Specifics
- the Duodenum = Brunner Glands : locatedin the submucosa which secrete alkaline mucus (offset the stomach)
- the Illeum = Peyer’s Patches: aggregated Lymphoid tissue in the mucosa and submucosa
Large Intestine (Colon)
Overview and Function
histology
specifics
Colon
- major site of water reabsorbtion
- absorbs major vitamins: thiamine, riboflavin, Vit. K) from the colonic bacteria
- stoarge until excretion
Specifics
- contain taenia coli: long ribbons of smooth muscle which contract lengthwise
- the taenia coli create haustra: outpouching of the colon into segments whnet he taenia coli contract
Histology
- Mucosa = simple columnar with lots of goblet cells = mucus!!
1. the goblet cells and the columnar cells are aligned perfectly like “test tubes” in a rack & called colonic crypts
- submucosa
- muscularis propria= inner circular * outer longitundial (taneai coli)
- Serosa: for the transverse colon and the sigmoid
- adventitia: for the acending//decending & rectum
Pancrease
overview and function
Exocrine specifics
Endocrine specifics
chronic pancreaitis
Overview
- release of exocrine or endocrine hormones/secretions
- exocrine: go through a duct to the SI
- endocrine: go to the blood stream directly
Exocrine Function
- majority of the pancrease works with the exocrine function
- ductal cells: secrete bicarb
- Acinar cells: secrete, lipase, amylase, protease
Endocrine Function
- islet of Langerhan : pale cells which secrete…
1. glucagon
2. insulin
3. somoatostatin
4. pancreatic polypeptide hormone
In Chronic Pancreatitis
- the acnir cells are replased by fiberosis and chronic inflammation
- the islets and ductal cells are distorted
- alcohol is the MC cause
Hepatobilliary Tract
overview and function
hepatic blood flow
histology
cirrhosis
Overview
- includes the liver, gallbladder & bile ducts
- responsibel for the production and transportation of bile
Hepatic Blood
dual blood supply
- Hepatic Artery: oxygenated blood to the liver
- Portal Vein: the deoxygenated blood frmo the spleen, pancreas & GI Tract come here first
- then the blood all leaves through the hepatic vein carrying the filtered blood to the IVC
Histology of the Liver
- hepatocytes in cord arrangement
- at the center is teh central vein
- the the edges is the portral triads: hepatic artery, lymph and portal vein
- space between each cord = sinusoid
Hepatocytes
- polygonal cells with lots of cytoplasm and rounded nucli
Flow of Blood
- from the protal veins on the triad to teh central vein
Flow of lymph
- from the central vein to the bile duct on the triads
Cirrhosis
- mc due to alcohol
- nodules of hepatocytes separated by fiberosis and chronic inflammation
What is bile
components
function
flow
- thick fluid from the hepatocytes, secreted into the biliary tract & stored in teh gallbladder
made of…
- cholesterol and lipids
- bile salts (to digest fats)
- bilirubin (the breakdown of hemoglobin)
function
- aid to brekadown fat
- elmiamte waste (hemoglobin adn excess cholesterol)
flow
- from the liver
- doen the R and L hepatic ducts
- to common hepatic duct
- then if stored = up the cystic duct to gallbladder
- when needed: down the cystic duct and out the commong bile duct to the sphincter of odi in the duodenum
