GIT Flashcards
GI system
- lips to anus (external)
- multiple associated structures (teeth, salivary glands, liver, LN)
- ingestion, digestion, absorption, elimination
- immune surveillance/barrier
- great species variation*
Gross layout
- mouth (oropharynx)
- esophagus
- stomach
- intestine
- rectum
- anus (cloaca)
Microscopic layout
- mucosa: epithelium, lamina propria, muscularis mucosa
- submucosa
- muscularis
- adventitia (serosa)
What is found in the muscularis mucosa?
Small band of smooth muscle
What is found in the submucosa?
Loose areolar CT where blood vessels travel
Mucosa
Stratified squamous lines the mouth and esophagus (rumen, reticulum, and omasum)
- changes to simple columnar deeper in the GIT
- lamina propria: accumulation of lymphocytes below the epithelial layer and BM
Submucosa
Varies in thickness
- thin up high and thicker in the lower intestine
Muscularis
Varies, have skeletal muscle in the esophagus and smooth muscle lower in the GIT
Serosa
Present as peritoneum in the abdomen
- adhered to other connective tissue in the cervical and mediastinum
Oral cavity
- lips (mucocutaneous junction)
- tongue: stratified squamous epithelium, skeletal muscle
- teeth
- tonsils: caudal portion of oropharynx
- salivary glands
Tongue
- stratified squamous epithelium (papillae and taste buds)
- voluntary striated muscle
- sublingual glands: produce saliva
Teeth
Crown: visible portion - enamel: outermost surface, only on the crown - dentin: dense CT - pulp: extends from crown to root Root - cementum - dentin - pulp - central canal/nerve
Tonsils
- location: palantine (swine), sublingual
- epithelium: crypts
- lymphoid nodules: vary with degree of antigen stimulation
Salivary glands
- add moisture/ emulsify
- begin digestion (CH2O)
- buffer, minerals
- antimicrobial
- major glands: parotid, mandibular, sublingual, zygomatic
Salivary gland components
- paired
- epithelial lined: lobules, acinus (-i), myoepithelium (characteristics of muscle, but is epithelium)
- ducts
- secretions: serous (water/protein), mucous, mixed (water and mucous based secretions)
Acini
Clusters of glands, separated by fine connective tissue
Mucous is ______
Proteinaceous, stains pink
Are salivary glands exocrine or endocrine?
Exocrine!
- secrete product into a duct before it reaches the target area
Esophagus
Muscular conduit - oropharynx to stomach - cervical - thoracic (extends to stomach) Stratified squamous epithelium - some submucosal glands Smooth and voluntary muscle
Adventitia of the esophagus
Does not have a discrete adventitia in the cervical region –> is attached to CT of trachea and cervical muscles
Does have an adventitia in the thoracic cavity and out into the abdomen
What are the 3 organs that cross the diaphragm
- aorta
- vena cava
- esophagus
Avian anatomy
Crop: esophagus
- stratified squamous, place for food storage, prone to infection
Proventriculus: chemical stomach
Gizzard: chew/grind food after it is treated with HCl
Monogastric stomach
- cardiac
- fundic
- pyloric
Ruminants
- rumen (paunch)
- reticulum (honeycomb)
- omasum (plies) - toward the right side of the animal
- abomasum (true/chemical stomach) - toward the right side
Rumen, reticulum, omasum
Stratified sqamous epithelium - many commensals - mostly fermentation - reducing environmnet - some absorption Omasum - water absorption
If you sterilize the rumen, then the cow cannot digest _____
Cellulose
Abomasum/stomach
- longitudinal folds (rugae)
- columnar epithelium with numerous goblet cells producing mucus and gastric pits
- regions: cardiac, fundus, pyloric
What are the mucus secreting regions of the stomach?
Pyloric and fundus
Cardiac and pyloric region
Mostly mucus
Torus pyloricus
Structure found only in pigs
- tumor like area near the pylorus
Fundic region
Majority of stomach
Glandular secretions
Gastric glands
- simple branched tubular glands
- mucus (goblets)
- pepsin from chief cells (deeper in gland) and zymogen granules
- HCl from parietal cells
- intrinsic factor (glycoprotein) from parietal cells
- enteroendocrine secretions into the LP
Small intestine
- principal site digestion/absorption (species variation)
- 3 major portions: duodenum (medium), jejunum (long), and ileum (short)
- mesentary: support and contains vessels (incl. lymph nodes)
Small intestinal mucosa
Villus - finger-like projections - crypts - shorter/lower Columnar epithelium - microvilli Lacteal (most prominent in the jejunum) Lamina propria
SI microscopic anatomy
- mucosa: columnar epithelium with brush border (microvilli on top of villi)
- submucosa: glands, loose areolar CT
- muscularis
- serosa: simple squamous on CT base
Muscularis
Inner circular layer
Outer longitudinal layer
- contracts, allows for peristalsis
SI cell types
- enterocytes: enzymes, H2O, absorption, tight junctions, brush border
- goblet cells
- paneth cells
- enteroendocrine cells
- M cells
Microscopic features
Lamina propria/submucosa
- submucosal glands in the duodenum
- submucosal plexus
- myenteric plexus
- GALT: dome sites and M cells
Villous length
Duodenum: tall villi, deep crypts
Jejeunum: middle, middle, middle
Ileum: short villi, shallow crypts, MALT
Ileum has ________ attachment
Antimesenteric
Large intestine/cecum
- species variation (hind gut fermenter)
- mostly straight tubular crypts
- no villi
- many goblets
- no paneth cells
- lymphoid tissue
If there is no villi, then you are in the _____ or _____
Stomach; large intestine
Large intestine/cecum functions
- more lymphoid tissue (GALT)
- absorption (water, nutrients)
- elimination
- mucocutaneous junction
Pancreas
Exocrine (duct)
- digestive enzymes: acini, proteases, lipases
Endocrine (ductless)
- metabolic hormones: islets, insulin, glucagon, somatostatin
Exocrine portion of the pancreas
Serous gland Zymogen granules - trypsinogen - chymotrypsinogen - proteases, peptidases - lipases - amylolytic enzymes - nucleolytic enzymes Bicarbonate (ductules) Neural and hormonal control
Acinus
“clusters of grapes”
- lined by simple cuboidal that dump contents into duct that ends up in the small intestine
- serous gland: product is water and mostly proteinaceous
Endocrine portion of pancreas
- islets
- mostly blood glucose control: glucagon, insulin, somatostatin
Liver
Largest gland in the body
Metabolism
Bile production: gall bladder for storage (digestion)
Liver metabolism
- carbohydrates
- lipids
- protein production (serum)
- protein catabolism (NH3)
- vitamins, minerals
- toxins, pharmaceuticals
Liver gross
- anterior abdomen
- lobes
- dual blood supply
- -> hepatic artery (25%)
- -> portal vein: GI, pancreas, spleen drainage (75%)
Liver histologic
Constituents - parenchyma - CT stroma - vessels - perisinusoidal spaces Lobules - classic (functional) - portal (exocrine) - acinar
Portal triads
Surround central veins
What are the 3 structures within a portal triad
- hepatic artery
- portal vein
- bile duct
Hepatocytes
Cuboidal Anastomosing plates/cords High metabolic activity - mitochondria - ER (rough, smooth) - golgi - lipid droplets - glycogen
Other cells of the liver
- discontinuous endothelium
- kupffer cells
- stellate cells
Bile ducts are lined by ____
Cuboidal epithelium
Bile canaliculi
Tiny white spots between adjacent hepatocytes
Liver blood flow
Portal triad
- hepatic artery, portal vein, and bile duct
Sinusoids: incomplete endothelium
Central vein
Biliary tree
- bile canaliculus
- bile flow opposite blood flow
- ductules –> bile ducts
Gall Bladder
- species variation
- stores/concentrates bile
- high cuboidal epithelium –> tight junctions, irregular microvilli
- no muscularis mucosa/submucosa
- smooth muscle
- serosa (visceral peritoneum
What animals do not have a gall bladder?
Killer whales, white tailed deer, rats, and horses
