Histology of gastrointestinal system Flashcards
Layers of the mucosa
Epithelium- mucus secreting
Layers of the mucosa
Lamina Propria-MALTS for immune survailence ( lymphocytes, plasma cells)
Layers of the mucosa
Muscularis mucosae-Causes movement of mucosa. Innervated by parasympathetic
Submucosa
Very vascular
Tunica muscularis
Smooth muscle. Inner=circular m. outer=longitudinal m. Between layers is a parasympathetic myenteric plexus
Tunica externa
known as tunica adventitia
mucosa structure
stratified squamous in oral cavity, pharynx, esophagus, anal canal. Stomach has secretory glands. small intestine has villi and large intestine has mucus glands
Muscularis mucosae
extend into lamina propria and villi
Tunica muscularis function
peristalsis which is inherent but regulated by ANS, hormones, environmental influences.
Esophagus
upper 1/3 & lower 1/3 have seromucous glands. Upper 1/3 of tunica muscularis contains skeletal muscle, middle 1/3 is mixed, lower 1/3 is smooth muscle.
Esophageal sphincter
Physiologic and involved contraction of diaphragm, Aboral peristalsis, Intra abdominal pressure
Stomach
Mechanical and chemical functions
muscle layers in the stomach
innermost is oblique, inner (middle) circular, outer is longitudinal
Gastric glands
1-7 glands that empty into lumen at a single gastric pit. Glands are straight tubular with base, neck , isthmus opening into it
Parietal cells
Large, round , eosinophilic cytoplasm. tubulovesicular system, Short microvilli, Carbonic acid is produced in cells which dissociates into hydrogen and bicarbonate ions. Vesicles of tubulovesicular system may bud off into canaliculi so that HCL is produced in lumen of canaliculi
Chief cells
basophilic cytoplasm, secrete pepsinogen
pepsinogen
stored in zymogen granules and cleaves to become pepsin in low ph
Stem cells
replace all kinds of gastric cells by migrating up and down gland
Neuroendocrine cells
secrete hormones, serotonin
Pyloric region of stomach
mucus secreting pyloric glands to protect duodenum from low ph. Circular layer of tunica muscularis is thick which forms the pyloric sphincter
Pyloric region of stomach
also has neuroendocrine cells called G-cells which secrete gastrin into the blood stream
gastrin
increases secretion from parietal and chief cells and enhances gastric motility
duodenum
villi becomes shorter progressing towards ileum. Brunners glands are specific to duodenum
Brunners glands
contain columnar mucus- secreting cells. Secrete lysozyme, May excrete IgA from plasma cells in lamina propria
Histopathalogy note
Alcian blue stains acidic mucin but does not stain alkaline mucin.
Small intestinal villi
simple columnar epithelium ( enterocytes). These have up to 3000 microvilli per cell
goblet cells in small int. villi
mucus secreting
paneth cells of small int. villi
At base of crypts with eosinophyilic granules
what do secreted materials do?
kill off pathogens which have survived the acidic environment
other cells in small intestine
neuroendocrine cells, stem cells, intraepithelial lymphocytes
Lacteal
lymphatic vessels of lamina propria
brush border of microvilli
stains PAS-Positive due to glycocalyx
Duodenum secretions
enterokinase, activates trupsin from trypsinogen in pancreas
secretin
promotes secretion of pancreatic juices
Cholycystokinin- pancreozymin (CCK)
promotes pancreatic secretions, stimulates gall bladder secretions
duodenal papilla/ major duodenal papilla
intersection of bile duct and pancreatic duct. Entry way into duodenum
Jejunum & Ileum
devoted to absorption of water and nutrients. increasing number of peyers patches and goblet cells
protein digestion in stomach
Denatured by HCL, Hydrolyzed into polypeptide fragments by pepsin
Protein digestion in small int.
Pancreatic enzymes, Membrane bound enterocytes, each amino acid is absorbed by a different carrier
Carbohydrate digestion
Salivary and pancreatic amylase( converts starch into glucose and maltose)
Digestion of lipids
fats emulsified by bile, pancreatic lipases break down triglycerides
digestion of lipids
subunits are absorbed by enterocytes and reconstituted before being transfered to lymphatics via lacteals in lamina propria
digestion of lipids
triglycerides in smooth ER are coated with proteins and phospholipids to form chylomicrons which are released into intercellular clefts.
Chylomicrons
basically a travel vesicle for triglycerides. They are sent to the liver after they’re done
Large intestine
besides H20 & electrolytes, it absorbs fat soluble vitamins produced by bacteria living in large int.
large int. composition
straight tubular glands with absorptive cells, goblet cells, stem cells.
teniae coli
longitudinal layer of tunica muscularis
Anus
stratified squamous epithelium
