ch 23 digestive system p3 Flashcards
small intestine
extends from pyloric sphincter to ileocecal valve
3 subdivisions of small intestine
duodenum, jejunum, ileum
duodenum
1st portion of small intestine, digestive juices of liver and pancreas empty into duodenum via major duodenal papilla (shortest)
jejunum
connects duodenum to ilium, middle portion, slower rate of digestion and absorption
ileum
last portion of the small intestine, joins small to large intestine at ileocecal valve.
circular folds of small intestine
permanent folding of submucosa and mucosa, ribbed to move chyme slowly and increase absorptive capacity. very efficient
villi
projections of mucosa, increase SA of small intestine so absorption can go faster. each villi center has blood supply n lacteal.
villi are largest where
duodenum. becomes smaller in jejunum and ileum. duodenum does the most nutrient absorption, leaflike in small intestine
microvilli
villi on villi, creates brush border. many enzymes on surface completes digest process. these enzymes found here complete digestion of carbs n proteins
intestinal crypts
tubular glands in small intestine wall, contain different cells that secrete products. similar to gastric glands in stomach. different cells in there secrete dif products
cells of villi and crypts
enterocyte, goblet cells, enteroendocrine cells, paneth cells, stem cells
enterocytes of small intestine
simple columnar cells with microvilli, mostly made of these, absorbs nutrient in villi and secretes intestinal juice in crypts
does intestinal juice have a function
no just a carrier fluid
goblet cells of small intestine
mucus secreting cells, must protect membrane
enteroendocrine cells of small intestine
release many hormones to control bile pancreatic and intestinal juice secretions
paneth cells of small intestine
release defenses and lysozyme, immune defense there
stem cells of small intestine
continuously dividing cells that replenish mucosa, can replace any other cells when cells get damaged
digestive roles of small intestine
has enzymes for digestion, the digestive enzymes are mostly imported from accessory organs liver and pancreas. the brush border enzymes produced by small intestine breakdown macro to monomers.
regulates chyme, too much acidic chyme is hypertonic to blood plasma
solute concentration in chyme vs blood
chyme has higher solute concentration than blood, small intestine and chyme and blood interact, chyme in small intestine may cause water to leave circulation and enter small intestine
what effect would a large amount of acidic chyme entering small intestine have on Blood volume
damage walls of small intestine, blood volume would decrease and could lead to hypovolemic shock.
segmentation in small intestine
contractions in small intestine slows movement of chyme, contractions push chyme back ad forth into next pocket.
what cells initiate contractions and how in small intestine
pacemaker cells, cells in duodenum depolarizes faster than ileum and allows for forward movement. back and forth motion mixes chyme with bile and pancreatic juices to increase absortopton
duodenum and pacemaker cells
pacemakers depolarize faster in duodenum, contracts more and more with each segmentation. a unidirectional movement
small intestine after a meal
parasympathetic enhances segmentation, chyme is slowly moved to increase digestion and absorption.
small intestine between a meal
motion released when absorption has already occurred. long peristaltic waves begun in small intestine, waste and shit is moved to large intestine.
what happens as soon as new meal incomes
motion decreases, segmentation starts again
ileocecal valve control
ileum has unusable stuff, so it’ll go to large intestine for excretion. the valve controls the passage of materials from small to large intestine.
ileocecal relaxes due to
gastroileal reflex- increases segmentation by making segment increase waste away
gastrin- hormone increases small intestine motility and relaxes ileocecal valve so undigested material passes
large intestine
has 3 structures seen no where else in alimentary canal,
teniae coli- bands of smooth muscle tissue from longitudinal layers pulls on wall of colon making small pockets
haustra- the pockets formed from teniae coli, gives colon segmented appearance.
epiploic appendages- idk what they do maybe immune defense bc they have immune cells
haustra functions
contractions of individual haustra aid motility in colon, independent of its neighbors and has circular and longitudinal layer
6 subdivisions of large intestine
cecum, appendix, colon, sigmoid colon, rectum, anus
cecum
sac like structure on bottom making up first part of large intestine. water and salt not absorbed is there a bit.
appendix
not true part of alimentary canal, prevents bacteria from large to small, bacteria dies but we keep good bacteria as a reserve there. its a lymphoid organ, so immune system a bit. appendix is tiny so stuff can get stuck there, bacteria can’t leave and reproduce and may get stuck then we remove it
colon parts
ascending - up R side of abdominal cavity
transverse - crosses R to L abdomen
descending- travels down L side of abdominal cavity
sigmoid colon
point where colon enters pelvis
rectum
temporary feces holding site, has rectal valves which prevent feces from being passed with gas
anus and its sphincters
opens to exterior of body, end of alimentary canal. has 2 sphincters
internal- smooth muslce, not voluntary a reflex
external- skeletal muscle, voluntary and tells us when to poop
microaantomy of large intestine
simple columnar epithelia, but anal canal is stratified squamous epithelia. abundant crypts are packed with the goblet cells, which secrets mucous which helps poop friction
does digestion occur in large intestine
NO, all digestion occurs before it meets large intestine. there’s no villi, brush border, or circular folds which is needed for digestion
bacterial flora of large intestine
1000 plus types of symbiotic bacteria that comes into body through anus, or survives harsh stomach conditions
importance of bacterial flora
vitamin synthesis- B complex which have coenzymes to speed up process, vitamin K synthesized by gut bacteria (blood clots)
fermentation- bacteria can ferment indigestible carbs and mucin, produces short chain fatty acids to fuel the body cells. 500 mL gas per day, more carbs more gas.
digestive processes in large intestine
slow, sluggish contraction in haustra. not much goes on just moves stuff. allow mixing of residue to increase water absorption.
mass movements in large intestine
forces residue towards rectum, promotes drying out of feces and last of water is removed, fiber strengthens movement and softens feces. new food in old out
defecation
pooping, initiated by stretching of rectal walls. sigmoid colon and rectum contract o internal sphincter relaxes. allows opening of external anal sphincter (voluntary), if not allowed reflex ends and begins again in a few minutes. more intense each time
