small bowel and large intestine

Question 1

what does the large intestine reabsorb

Answer 1

ions, water

Question 2

where are most ions and water reabsorbed

Answer 2

proximal colon, where chyme is more fluid

Question 3

how are Na+ and Cl- absorbed

Answer 3

exchange mechanisms

Question 4

how is water absorbed

Answer 4

follows ions by osmosis

Question 5

how is K+ absorbed

Answer 5

moves passively into lumen via gap junctions

Question 6

result of water entering colon exceeding 4500mL/day

Answer 6

diarrhoea

Question 7

what 2 cells are abundant in large intestine

Answer 7

enterocytes, goblet cells

Question 8

where are stem cells located in large intestine, and their fate

Answer 8

at bottom of colonic crypts, which migrate up and differentiate before being sloughed off after a few day (possess some memory)

Question 9

features of large intestine mucosa

Answer 9

smooth, no villi so small SA vs small intestine as no glucose or amino acid absorption in colon

Question 10

features of enterocytes in large intestine

Answer 10

short, irregular microvilli for reabsoprtion of salt

Question 11

function of goblet cells in large intestine

Answer 11

secrete mucous to facilitate passage of increasingly dry luminal contents as more and more water reabsorbed

Question 12

abudance of goblet cells in large intestine

Answer 12

increases along length; within crypts

Question 13

function of mucous

Answer 13

cover bacteria and particulate matter to protect laminal surface from infection and/or abrasion

Question 14

what stimulates goblet cell secretion

Answer 14

ACh from local nerves

Question 15

why are paneth cells absent in large intestine

Answer 15

commensal bacteria present, and paneth cells may destroy bacteria; don’t need same degree of protection

Question 16

why are enteroendocrine cells fewer in number in large intestine

Answer 16

regulation of digestion and absorption in small intestine very complicated so more required there

Question 17

features of glycocalyx in large intestine

Answer 17

doesn’t contain digestive brush border enzymes

Question 18

what are basic colonic contractions and why are they used

Answer 18

kneading process that provide minimal propulsion (5-10cm/hour), allowing chyme to stay in colon for long time to promote absorption

Question 19

what contraction does proximal colon elicit and why

Answer 19

antipropulsive to impede propulsion and keep food in region for longer

Question 20

contractions in transverse and descending colon and why

Answer 20

localised segmental contractions of circular muscle (Haustral contractions), shuffling contents forwards and backwards; short propulsive movements every 1/2 hour (increase after meal)

Question 21

how often does coordinated mass movement in colon occur

Answer 21

between 1 and 3 times a day

Question 22

purpose of mass movement

Answer 22

peristaltic wave that propels contents up to 3/4 length of large intestine in a few seconds

Question 23

what promotes mass movements

Answer 23

indigestible high-fibre food

Question 24

what are faeces

Answer 24

indigestible waste of chyme that entered large intestine

Question 25

when is the afferent sensation of needing to defaecate perceived

Answer 25

suddenly following mass movement

Question 26

when is the internal anal sphincter relaxed

Answer 26

in defecation reflex (spinal reflex via sacral spinal cord - same as voluntary activity)

Question 27

ejection of faecal waste

Answer 27

distension of rectal wall detected by pressure receptors → signials sent via myenteric plexus → peristaltic waves initiated in descending, sigmoid colon and rectum → internal anal sphincter relaxes

Question 28

when does sensation subside until

Answer 28

next mass movement

Question 29

what can last few centimeters of rectum (“social”) distinguish between

Answer 29

gas, liquid and solid (difficult to tell difference between gas and oil)

Question 30

amount of faeces produced by healthy adult per day

Answer 30

150g (2/3rds is water)

Question 31

solid components of faeces

Answer 31

cellulose, bacteria (smell), cell debris, bile pigments/salts (give healthy brown colour)