Lecture 31 - GI pt 2 Flashcards
function of SI
digestion and absorption of all nutrients
key structural features of SI
highly adapted to max surface area - very long (15-18 ft) -folds of mucosa/submucosa -mucosa has fingerlike projections (villi) -epithelial cells have microvilli SA is DOUBLE A TENNIS COURT WOOOW
villi
fingerlike projections, site of absorption of nutrients and fluids
- lamina propria rich in blood vessels, nerves, lymphatics
- central core in lamina propria contains fibers of muscularis mucosae and a central lacteal
crypts
invagination continuous with villi, site of SECRETION, stem cells located near base of crypt; cells mature and differentiate as they migrate up the crypt.
paneth cells
only in SI, only at base of crypt. right next to stem cells – provides protection so that stem cell portion of small bowel is protected
lamina propria has
veins, arteries, and lymphatic channel (lacteal)
lacteals
things from outside world dont have to work hard to get in here
Columnar (absorptive) cells
-also known as enterocytes
-tall, eosinophilic cells with basal nuclei
-numerous microvilli on apical surface (~3,000 per cell)
microvilli form a striated border (“brush border”) covered by a glycocalyx
Subcellular Features of Enterocytes:
1) microvilli: each microvillus has a core of actin filaments
2) junctional complexes: attachment to adjacent enterocytes prevents direct access of luminal contents into inter-cellular spaces
3) intercellular clefts: space between cells; at base of cells
4) numerous mitochondria and vesicles
where does fat first go
intercellular cleft into chylomichrons into lymphatics
where are goblet cells found
in SI and colon - through villus but mostly crypt
mucous cells in other places have a different name
paneth cells
almost only in SI
pyramidal cells confined to base of crypt
bright pink (eosinophilic) granules in cytoplasm
secrete lysozyme, defensins (anti-bacterial)
important for protecting stem cell compartment
Enteroendocrine cells
in SI
Pyramidal, pale cells sparsely distributed in crypts
Secrete several hormones (secretin, CCK, somatostatin, enteroglucagon, peptide YY, etc…)
stem cells found
at base of cryot
duodenum main function
neutralizes acidic chyme that exits the stomach
brunner’s glands
unique to duodenum
located in submucosa
cells contain alkaline mucus with basal nuclei
where are most minerals absorbed
duodenum
jejenum function
responsible for absorption of most nutrients (proteins, carbohydrates, lipids, vitamins)
ileum function
- absorption of many nutrients
- distal main site of absorption of vitamin B12 and bile acids
- Peyer’s patches are prominent (lymphoid aggregates)
peyers patches
lymphoid aggregate, prominent in ileum
bands of muscle in colon
tinae coli
function of colon
- Absorption of water (solidify stool; prevent dehydration)
- Propulsion of feces
structural features of colon
Mucosa: flat (crypts only; no villi); mostly goblet cells
Muscularis propria: thick; outer layer arranged as three longitudinal bands called “tenia coli”
colon cell types
goblet, columnar (absorptive), enteroendocrine, paneth, stem cells at base of crypts
goblet cells in colon
most prominent
- round, clear cytoplasm containing mucus; basal nuclei
- mucus serves as cytoprotection, lubrication
columnar cells in colon
similar to small intestine enterocytes but less numerous; poorly developed brush border
absorb water and electrolytes
Enteroendocrine cells in colon
Rare in colon (mainly cecum and rectum); neurosecretory granules
paneth cells in colon
Rare in colon; mainly cecum and ascending colon
what controls continence
anal canal
anal canal structural features
Mucosa: stratified squamous epithelium
Sphincter mechanism
sphincter mechanism of anal canal
Internal anal sphincter: smooth muscle (involuntary control)
External anal sphincter: skeletal muscle (voluntary control)
