lecture 15 - digestion Flashcards
serosa of the stomach forms:
part of the peritoneum
what promotes peristaltic movements
enteric reflexes
distention of the duodenum inhibits
gastric motility
this reduces teh rate of chyme expulsion from stomach
enterogastric reflex
prevents too much chyme from entering SI
rate of HCL is reduced and chyme digestion is increased
involved sympathetic motor impulses to inhibit gastric motility
all blood leaves liver in the
hepatic vein
functions of the small intestine
digestion adn abdorption of nutrients
length of SI
6.5m 2.5cm in diameter
3 sections of SI
duodenum
jejunum
ileum
digestion and absorption is facilitated by
large SA of the SI
circular folds of the SI
cannot strethc like rugae of stomach
folds of the mucosa and submucosa
increases SA, causes chyme to spiral
intestinal villi of the SI
finger like projections of the mucosas circular folds
lamina propria contains capillaries for them
covered in simple columnar epi
microvilli of the SI
finger like projections of the intestinal villis absorptive cells
mucosa of the SI
simple columnar epi
contains muscularis mucosae
has goblet cells and absorptive cells
contains enteroendocrine cells like
- S cells - secretin
- CCK cells - cholecsystokinin
- K cells - glucose dependent insulinotropic peptide
has paneth cells that secrete lysozyme and are phagocytic
what cells of the SI’s mucosa secrete lysozyme
paneth cells
lamina propria of the ileum contains:
mucosa assocaited lymphoid tissue (MALT)
- immune function
submucosa of duodenum contains:
duodenal glands that secrete alkaline mucus to neutralize gastric juices
muscular layer of the SI layers
outer longitudinal
inner circular
serosa of the SI forms:
part of the visceral peritoneum
intestinal juice
alkaline substance made of water, mucus, and bicarbonate
functions to provide liquid medium to aid in absorption
contains enzymes for digestion
pH = 6-7.4
carb digesting enzymes in intestinal juice
maltase, lactase, sucrase
protein digesting enzymes in intestinal juice
dipeptidase, aminopeptidase
nucleic acid digesting enzymes in intestinal juice
phosphatase, nucleosidases
what does the enterogastric reflex do (3)
stops too much chyme from entering SI
limits intestineal damage from acid
increases digestion time of chyme in stomach
segmentation
major movement type in SI
NO net movement of chyme
localized contraction in areas containing chyme ot mix and absorb
migrating motility complex
peristaltic movement stimulated by decreased distension
occurs after msot nutrient are absrobed
propels undigested onward
two movement types regulated by the myenteric plexus of the SI
segmentation
migrating motility complex
chyme entering teh SI contains:
partially digested carbs/ fats/proteins/nucleic acids
complete chemical digestion requires: (4)
pancreatic juice
bile
intestinal juice
microvillous border enzymes
overview of digestion of carbs in the body
salivary amylase in mouth breaks down polysaccharides to disacharides and oligosaccharides (glycogen/starch/etc)
pancreatic amylase in duodenum breaks down glycogen and starch to smaller oligosaccharides
microvillous border enzymes like maltase, sucrase, and lactase act on oligosaccharides ot produce monosaccharides like glucose and fructose
lactose intolerance is caused by
no lactase enzyme
this causes lactose to not be broken down, which allows bacteria to ferment the sugars, causing gas and diarrhea
overview of protein digestion
HCI in stomach denatures proteins, which pepsin hydrolyzes peptide bonds
digestive enzymes like trypsin from the pancreas split peptide bonds to create shorter peptide chains
microvillous border enzymes like dipeptidase break down peptides to single amino acids
overview of digestion of lipids
lingual lipase in the mouth breaks down triglycerides to fatty acids and monoglycerides
lingual and gastric lipase continue digestion of triglycerides to fatty acids and monoglycerides in the stomach
bile emulsifies triglyceride globules in the SI. here, pancreatic lipase splits triglycerides into fatty acids more
short and long chain fatty acids +monoglycerides are then absorbed
most lipid digestion occurs;
in the SI
this is due to pancreatic lipase, and bile
microvillous enzymes breakdown everything excpet:
triglycerides (lipids)
bile salts are (relation to water)
amphipathic
overview of nucleic acid digestion
pancreatic juice contains
- ribonuclease and deoxyribonuclease which digest their counterparts
nucleotides are further digested by microvillous border enzymes like nucleosidases and phophatases that digest nucleotides into pentose sugars, phosphate, and nitrogenous bases
carbs are absorbed as
monosaccharides
proteins are abrsorbed as
amino acids
absorptive epithelia cells role
control absorption
how is glucose and galactose absorbed
via secondary active transport with Na
how is fructose abso
via facilitated diffusion
how are amino acids absorbed
via active transport
how are di and tri peptides absorbed
via secondary active transport
how are short chain fatty acids absrobed
via simple diffusion
micelles
shrot chain fatty acids coated in bile salts
once in absorptive cells, what do fatty acid chains do?
recombine to triglycerides and together with phospholipids, cholesterol, and proteins, they form chylomicrons
chylomicrons (what are thye, where do they go)
absorbed fatty acids that have been recombined
exit intestinal cells via exocytosis into. lymphatic capillaries
where do chylomicrons travel
in lympahtic system
enterohepatic circulation
bile salt is secreted by hepatocytes, released in duodenum, reabsorbed by the ileum, and resecreted into bile
absorption of Na
via diffusion and secondary active transport
absorption of water by SI and LI
SI - 8L
LI - 90% of the last L
absorption is by osmosis
alcohol absorption
metabolized in stomach byb alchohol dehydrogenase
absorbed in stomach and small I
metabolized in liver
large intestine functions
completion of absorption of water/ions/vitamins
formation of feces
3 sections of LI
cecum, colon, rectum
LI length
1.5m 6.5cm wide
mucosa of the LI
has no villi or folds
intestinal glands are lined with simple columnar epi
lamina propria contains lympahtic nodules
contains muscularis mucosae
large intestine cells in mucosa
absorptive cells - for water
gobelt cells - mucus secretion
LI submucosa made of
areolar CT
muscular layer of LI
contains external longitudial and inner circular muscle layers
teniae coli
formed by thickened portions of longitudinal muscle in the LI
haustra
folds that give teh LI a pouch like appearance
caused by contractions
cecum
bottom of the opening to LI
gastroileal reflex
intensified peristalsis in ileum immerdiately after a meal
trigger when stomach distended
migrating motility complex intensifies and chym is forced into the LI
haustral churning
when chyme is mixed and porpelled in the LI
ileocecal valve is closed
gastrocolic reflex
initiated. by food entering stomach
increased colon motility
mass peristalsis
strong peristaltic waves that push contents of LI to rectum
what enzymes are secreted in the LI
none
bacterial fermentation in the LI
undigested carbs = release of hydrogen, CO2, and methane gas
breakdown of undigested protein to amino acids, breakdown of amino acids to things like hydrogen sulphide
breakdown of bilirubin that makes feces brown due to released pigments
what vitamins do bacteria produce that are absorbed in the colon
B and K
feces
dead epi cells, undigested food, and bacteria
defecation
elemination of feces from the recetum
defecation reflex is controlled by
the ANS
mass peristalsis fills rectum, stretching of rectum walls triggers this reflex
how is defecation sensed
mechanoreceptors send impulse to cord, motor impulses from cord travl through PSNS nerves to rectum/anus.
contraction of longitudinal muscle forces feces into anal canal
relaxation of internal sphincter allows feces to more to external sphincter
voluntary relaxation of external anal sphincter completes defecatio
diarrhea
increase in freq, vol, and fluid content of feces
caused by increase motility of intestines, decreased absorption
constipation
infrequent of difficult defecation
caused by decreased motility of intestines, and excessive water reabsorption
treat with fibre, water, and exercise
