Lecture 31 - GI pt 2

Question 1

function of SI

Answer 1

digestion and absorption of all nutrients

Question 2

key structural features of SI

Answer 2

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

Question 3

villi

Answer 3

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

Question 4

crypts

Answer 4

invagination continuous with villi, site of SECRETION, stem cells located near base of crypt; cells mature and differentiate as they migrate up the crypt.

Question 5

paneth cells

Answer 5

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

Question 6

lamina propria has

Answer 6

veins, arteries, and lymphatic channel (lacteal)

Question 7

lacteals

Answer 7

things from outside world dont have to work hard to get in here

Question 8

Columnar (absorptive) cells

Answer 8

-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

Question 9

Subcellular Features of Enterocytes:

Answer 9

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

Question 10

where does fat first go

Answer 10

intercellular cleft into chylomichrons into lymphatics

Question 11

where are goblet cells found

Answer 11

in SI and colon - through villus but mostly crypt

mucous cells in other places have a different name

Question 12

paneth cells

Answer 12

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

Question 13

Enteroendocrine cells

Answer 13

in SI
Pyramidal, pale cells sparsely distributed in crypts
Secrete several hormones (secretin, CCK, somatostatin, enteroglucagon, peptide YY, etc…)

Question 14

stem cells found

Answer 14

at base of cryot

Question 15

duodenum main function

Answer 15

neutralizes acidic chyme that exits the stomach

Question 16

brunner’s glands

Answer 16

unique to duodenum
located in submucosa
cells contain alkaline mucus with basal nuclei

Question 17

where are most minerals absorbed

Answer 17

duodenum

Question 18

jejenum function

Answer 18

responsible for absorption of most nutrients (proteins, carbohydrates, lipids, vitamins)

Question 19

ileum function

Answer 19

• absorption of many nutrients
• distal main site of absorption of vitamin B12 and bile acids
• Peyer’s patches are prominent (lymphoid aggregates)

Question 20

peyers patches

Answer 20

lymphoid aggregate, prominent in ileum

Question 21

bands of muscle in colon

Answer 21

tinae coli

Question 22

function of colon

Answer 22

• Absorption of water (solidify stool; prevent dehydration)

- Propulsion of feces

Question 23

structural features of colon

Answer 23

Mucosa: flat (crypts only; no villi); mostly goblet cells

Muscularis propria: thick; outer layer arranged as three longitudinal bands called “tenia coli”

Question 24

colon cell types

Answer 24

goblet, columnar (absorptive), enteroendocrine, paneth, stem cells at base of crypts

Question 25

goblet cells in colon

Answer 25

most prominent

• round, clear cytoplasm containing mucus; basal nuclei
• mucus serves as cytoprotection, lubrication

Question 26

columnar cells in colon

Answer 26

similar to small intestine enterocytes but less numerous; poorly developed brush border
absorb water and electrolytes

Question 27

Enteroendocrine cells in colon

Answer 27

Rare in colon (mainly cecum and rectum); neurosecretory granules

Question 28

paneth cells in colon

Answer 28

Rare in colon; mainly cecum and ascending colon

Question 29

what controls continence

Answer 29

anal canal

Question 30

anal canal structural features

Answer 30

Mucosa: stratified squamous epithelium

Sphincter mechanism

Question 31

sphincter mechanism of anal canal

Answer 31

Internal anal sphincter: smooth muscle (involuntary control)

External anal sphincter: skeletal muscle (voluntary control)