Small Intestine Function Flashcards
Function of small intestine (5)
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
Which part does the most digestion? Most absorption?
Duodenum (digestion)
Jejunum (absorption)
Secretions received from other organs (3)
Bile (Lipid Digestion)
Pancreatic Enzymes
Alkaline Juices (HCO3-)
Bile?
Bile secreted from gallbladder → common bile duct (response to CCK)
Pancreatic enzymes + alkaline juice?
secreted from pancreas into pancreatic duct (response to CCK + secretin)
Opens out into duodenum (major duodenal papilla)
SPHINCTER OF ODDI?
Secretions into S.I regulated by sphincter of Oddi
Activation of pancreatic enzymes
Active enzymes (pancreatic lipase + pancreatic amylase) Inactive enzymes (trypsinogen + chymotrypsinogen)
Brush border enzyme enterokinase coverts: trypsinogen→ trypsin (active form)
Trypsin activates chymotrypsinogen
Carb products formed from digestion (3)
Glucose
Galactose
Fructose
function of brush border enzymes
hydrolyse compounds into glucose / galactose / fructose
brush border enzymes (3)
(lactose, sucrase, trehalase)
Bile acid digestion (lipids)
Emulsification of fat goblets into small chunks (micelles)
Larger surface area
3 major lipid digestion enzymes
Pancreatic Lipase, Phospholipase A2, Cholesterol Ester Hydrolase
What are micelles hydrolysed into (4)
Fatty acids
Monoglycerides
Cholesterol
Lysolecithin
Lipid absorption
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)
What controls secretions? (3)
Enteric Nervous System
Hormones
Enterotoxins
Enteric Nervous system (seretonin + prostoglandins)
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
Hormones involved in controlling secretion (2)
Guanylin + Histamine
Guanylin action (+ consequences)
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
Histamine action
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
Enterotoxins
Bacterial toxins
Stimulate enterocytes directly by enteric reflexes
MMC’s (definition + function)
Propulsive waves
MMC’s prevent reflux of bacteria from large intestine back to the terminal ileum
Segmentation? (WHAT + WHY)
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
Segmentation pros + cons
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
Peristalsis (what + why)
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
Intestino - intestinal inhibitory reflex
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
Gatro-ileal reflex
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
