Digestive System part 3 Flashcards
what is the absorbable unit of carbs in the small intestine?
monosaccharides: glucose, fructose, galactose
what is the absorbable unit of lipids in the small intestine?
free fatty acids, glycerol and monoglycerides
what is the absorbable unit of proteins in the small intestine?
primarily single amino acids, dipeptides and tripeptides
glucose and galactose absorption in the small intestine
- pass through apical surface by secondary active transport using Na+ conc. gradient
- glucose and galactose compete for the same protein channel
- cross basolateral surface by way of facilitated diffusion
fructose absorption in the small intestine
passes through apical and basolateral surfaces via facilitated diffusion
amino acid absorption in the small intestine
- pass through apical surface via active transport or secondary active transport with Na+
- pass through basolateral surface via simple diffusion
dipeptide and tripeptide absorption in the small intestine
- pass through apical surface by way of secondary active transport with H+
- pass through basolateral surface via simple diffusion
small short chain FAs (10-12C) absorption in the small intestine
- simply diffuse through apical and basolateral surfaces
long chain fatty acids (>12C) and monoglycerides
- bile salts surround long chain FAs and form a micelle which picks up and drops off into other side of apical cell surface by simple diffusion
- TG are surrounded by chylomicrons (proteins that are too big to enter capillaries) so they enter the lymphatic system through a lacteal of a villus
- then travel through thoracic duct (central lymphatic vessel) to junction of left internal jugular and subclavian veins
where do absorbed nutrients go once past basolateral surface of intestinal cells? (all nutrients but lipids)
they are taken up by a villus blood capillary
to hepatic portal vein
to the liver
fluid ingested/secreted into GI system/day
9.3 L
fluid absorbed by GI system/day
8.3 L
fluid excreted in feces
100ml
large intestine
1.5 m long, 6.5 cm wide
4 major regions
ascending and descending colon are retroperitoneal
ileocecal sphincter
valve that controls movement of chyme into LI
cecum
where SI opens into LI, like a pocket for contents from SI
veriform appendix
- don’t know exact function, contains lymphatic tissue so thought to have some immune function
- also may aid in microbe formation: repopulation of env’t of colon after a change
4 regions of the colon
from start to end: ascending transverse descending sigmoid
sigmoid colon
S shaped, brings chyme back to midline region of the body
right colic flexure
located just below liver
ascending colon turns to transverse colon
left colic flexure
located just below spleen
transverse colon turns to descending colon
omental appendices
small lipid filled pouches that attach to teniae coli
rectum
15cm long
thicker muscle layer here than the rest of the GI tract
contains simple columnar epithelium
anal canal
final 2-3 cm of GI tract
thickened muscle walls form sphincters
contains stratified squamous epithelium for protection
internal vs external anal sphincters
internal: made of smooth muscle so involuntary
external: skeletal muscle, allows it to be voluntary
anal columns
folds in mucous membrane of anal canal where arteries and veins are found
- hemorrhoids are a result of swollen, enlarged, or inflamed veins here
types of cells found in large intestine (in glands)
absorptive cells
goblet cells
absorptive cells in LI
take up water primarily, some ions, some cells have microvilli surface
goblet cells in LI
secrete mucous, also help move chyme here
muscular layer in LI
- internal circular layer found everywhere
- outer layer of thickened longitudinal muscle found in 3 bands known as the teniae coli
teniae coli
when it contracts, it forms pockets called haustra
- it’s always slightly contracted
gastroileal reflex
when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room
haustral churning
hasutrum fills and once distended, contracts to move contents to the next haustrum
– fills cecum and initiates contraction from one haustrum to another
peristaltic waves in LI
3-12 contractions/min
alternating circular and longitudinal muscle contractions
mass peristalsis
in LI, strong peristaltic wave from transverse colon (initiated by gastrocolic reflex) pushes contents into rectum
gastrocolic reflex
when stomach fills, mass peristalsis moves contents of transverse colon into rectum
chemical digestion in LI
- no enzymes secreted, only mucous
- bacteria ferment things
- bacteria also produce vitamins K and B in colon which get absorbed with water and ions in LI
what do bacteria ferment in LI
- undigested carbohydrates produce hydrogen, CO2, methane gases
- digestion of AAs; indoles and skatoles give odor to feces
- decomposition of bilirubin to stercobilin which makes feces brown
feces
produced after 3-10 hours in LI from chyme when 90% of water is reabsorbed
- composed of dead epithelial cells, metabolic byproducts, undigested food (ex. cellulose), bacteria (live and dead; makes up 30% of dry feces weight)
defecation reflex
- gastrocolic reflex caused by filling of stomach moves feces into rectum which initiates defecation reflex
- stretch receptors signal sacral spinal cord
- parasympathetic nerves contract longitudinal muscles of descending/sigmoid colon, rectum and internal anal sphincters relax
- external anal sphincter is voluntarily controlled
phases of digestion
describe regulation of movement through GI system
- cephalic phase
- gastric phase
- intestinal phase
cephalic phase
preps mouth and stomach for food before or just as our food is eaten: preps mouth and stomach for food, initiated by sight, smell, thought and taste
- neural centres use facial & glossopharyngeal nerves to stim. salivation and vagus nerve to stimulate gastric juice release in stomach
gastric phase
once bolus reaches stomach causes an increase in both gastric secretion and motility
- receives both neural (feedback loop via parasympathetic and ENS) and hormonal regulation (gastrin), promotes gastric emptying
intestinal phase
once chyme enters SI, inhibits gastric emptying to promote digestion of our food
- neural (feedback loop: enterogastric reflex) and hormonal regulation (secretions of secretin and cholecystokinin aka CCK)
secretin
release is stimulated by acidic chyme entering SI
- stim release of pancreatic juice and decreases gastric secretions
- all in an effort to reduce acid coming into SI
cholecystokinin (CCK)
release is stimulated by AA and fat in chyme entering SI
- stm secretion of pancreatic juice, contraction of gallbladder to release bile and then relaxes hepatopancreatic ampulla so secretions can enter SI
- decreases gastric emptying by contraction of pyloric sphincter
- stimulates hypothalamus so the brain has feelings of satiety and we feel full
