Small Intestine Function

Question 1

Function of small intestine (5)

Answer 1

1) Mix digestive secretions with food
2) Propel chyme along intestine
3) Digest + absorb (nutrients + constituents of digestive secretions)
4) Regulate gastric function (synthesising and secreting hormones)
5) Defend body against micro-organisms

Question 2

Which part does the most digestion? Most absorption?

Answer 2

Duodenum (digestion)

Jejunum (absorption)

Question 3

Secretions received from other organs (3)

Answer 3

Bile (Lipid Digestion)
Pancreatic Enzymes
Alkaline Juices (HCO3-)

Question 4

Bile?

Answer 4

Bile secreted from gallbladder → common bile duct (response to CCK)

Question 5

Pancreatic enzymes + alkaline juice?

Answer 5

secreted from pancreas into pancreatic duct (response to CCK + secretin)

Opens out into duodenum (major duodenal papilla)

Question 6

SPHINCTER OF ODDI?

Answer 6

Secretions into S.I regulated by sphincter of Oddi

Question 7

Activation of pancreatic enzymes

Answer 7

Active enzymes (pancreatic lipase + pancreatic amylase)
Inactive enzymes (trypsinogen + chymotrypsinogen)

Brush border enzyme enterokinase coverts: trypsinogen→ trypsin (active form)

Trypsin activates chymotrypsinogen

Question 8

Carb products formed from digestion (3)

Answer 8

Glucose
Galactose
Fructose

Question 9

function of brush border enzymes

Answer 9

hydrolyse compounds into glucose / galactose / fructose

Question 10

brush border enzymes (3)

Answer 10

(lactose, sucrase, trehalase)

Question 11

Bile acid digestion (lipids)

Answer 11

Emulsification of fat goblets into small chunks (micelles)

Larger surface area

Question 12

3 major lipid digestion enzymes

Answer 12

Pancreatic Lipase, Phospholipase A2, Cholesterol Ester Hydrolase

Question 13

What are micelles hydrolysed into (4)

Answer 13

Fatty acids
Monoglycerides
Cholesterol
Lysolecithin

Question 14

Lipid absorption

Answer 14

Products from digestion released at apical membrane
Diffuse into enterocyte

Products re-esterified to form original lipids, triglycerides, cholesterol, phospholipids

Packaged tightly inside apoproteins (form chylomicrons)

Too large to enter circulation so enter lymphatic system (via lacteals)

Question 15

What controls secretions? (3)

Answer 15

Enteric Nervous System
Hormones
Enterotoxins

Question 16

Enteric Nervous system (seretonin + prostoglandins)

Answer 16

Mechanical stimulation of enterochromaffin cells = release of serotonin

Serotonin stimulates sensory neurons = activates secretomotor neurones - terminates at enterocytes

Mechanical stimulation of mucosa = releases prostaglandins (group of lipids) = stimulates secretomotor neurones

Question 17

Hormones involved in controlling secretion (2)

Answer 17

Guanylin + Histamine

Question 18

Guanylin action (+ consequences)

Answer 18

Stimulates guaylin receptor on apical border of enterocyte
= increased activity on guanylate cyclase
= elevated intracellular concentration of cyclic guanosine monophosphate
= increased opening of K+ channels (basolateral layer) + Cl- channels (luminal membrane) = increased fluid secretion

Question 19

Histamine action

Answer 19

Antigen-antibody reactions at mast cells + stimulation of cells by substance P (during axon reflexes) = histamine release
Histamine stimulates secretion by histamine receptors in enterocytes

Question 20

Enterotoxins

Answer 20

Bacterial toxins

Stimulate enterocytes directly by enteric reflexes

Question 21

MMC’s (definition + function)

Answer 21

Propulsive waves

MMC’s prevent reflux of bacteria from large intestine back to the terminal ileum

Question 22

Segmentation? (WHAT + WHY)

Answer 22

Mixes chyme with secretions + brings mixture into contact with mucosa

Contractions of circular muscle layer in short intervals along the intestine

Intestine between contracted regions = relaxed

Question 23

Segmentation pros + cons

Answer 23

Chyme only propelled short distance from contraction = not effective for propelling chyme

Effective for breaking up unstirred layer of fluid next to epithelial cells = easier nutrient absorption

Question 24

Peristalsis (what + why)

Answer 24

Propels chyme along small intestine

REPEATED contraction of circular muscle layer on oral side of chyme bolus
Relaxation on aboral side

Contraction pushes bolus into the adjacent area of intestine ready to receive it

Question 25

Intestino - intestinal inhibitory reflex

Answer 25

If a region of intestine becomes distended (swollen) or obstructed - contraction in adjacent regions are inhibited
Depends on activation of sympathetic nerves via coeliac ganglion + spinal chord

Question 26

Gatro-ileal reflex

Answer 26

Caused by increase in gastric activity (food digesting in stomach)
Propulsive activity of terminal ileum is increased
Contents emptied into caecum via relaxed ilea-caecal sphinchter
Gastrin + CCK (duodenal hormone) increase contractive activity in ileum
Ileo-caecal sphincter relaxes