digestion and absorption Flashcards
where does most absorption take place
in the small intestine
absorption in the stomach
absorbs some non polar substances such as alcohol and aspirin
what do enteroendocrine cells secrete
various hormones including gastrin (G cells)
processing time of different types of food
carbohydrates empty fastest followed by high protein foods
meals with high triglyceride content remain in the stomach the longest
small finger like projcections that protrude from the mucosal lining to increase nutrient absorption surface area
vili
hair like projections that aid in the absorption of nutrients
microvili
what does the mucosal epithelal cell layer of the small intestine house
enterocytes
brush border
goblet cells
crypt cells
enterocytes
absorptive cells
brush border
microvilli covered cells expressing digestive enzymes
goblet cells
secrete mucus
crypt cells
epithelial stem cell which replenish dead/ sloughed off cells
most nutrients consumed as macromolecules
must be enzymatically broken down (chemical digestion) before absorption
most carbs in diets
polysaccharides
starch and cellulose
from plant products (pasta and breads)
glycogen
from animals and animal products
cellulose
dietary fibre is not a substrate of digestive enzymes and therefore cannot be digeseted
structure of starch
branched
structure of glycogen
super brancehd
structure of cellulose
fibre that is packed and rows and column
disaccharides
sucrose (sugar) and lactose
monosaccharides
glucose and fructose (absorbable forms of carbs)
what digests polysaccharides
salivary and pancreatic amylase
salivary amylase
inactivated by the acids in the stomach
pancreatic amylase
continues polysaccharide digestion in the small intestine
what do amylases do
reduce starch or glycogen to either maltose (glycose disaccharide) or short branched polysaccharide called limit dextrins
digestion of carbs to monosaccharides
completed by brush border enzymes boundot the apical membranes of absorptive cells lining the small intestine
brush border enzymes
dextrinase and glycoamylase
sucrase
lactase
maltase
dextrinase and glgycoamylase
breaks down limit dextrins and straight chain glucose polymers into glucose monomers
sucrase
hydrolyzes sucrose into glucose and fructose
lactase
hydrolyzes lactose to glucose and galactose
maltase
hydrolyzes maltose to two glucose molecules
how is fructose absorbed
by facilitated diffusion
gluctose and galactose digesiton
enter epithelial cells via active cotransport with sodium
2 Na ions enter for each glucose transported. excess Na is pumped out by the basolateral sodium pump which required ATP for energy
how do sports drinks use Na linked glucose transport
provide energy to high preformance athletes
monosaccharides enter the bloodstream thorugh facilitated diggusion across the basolateral membrane. they then travel to the liver for processing
protein digestion
must be digested into small peptides and amino acids prior to absorption
enzymes for protein digestion
to protect the secretory cells from digestive enzymes, the enzymes are stored in these cells in an inactive form, called zymogens
secreted zymogens are converted into active enzymes by proteolytic activation
expopeptidases
cleave off individual amino acids from one end of the polypeptide
digestion of small peptides into amino acisd
endopeptidases
break bonds in the middle of the polypeptide to produce shorter polypeptides
endopeptidases example
pepsinogen
pepsinogen
is secreted by chief cells in the stomach
it is partially activated by hydrogen ions secreted in the parietal cells in the stomach
the pancreas secretes several zymogens into the duodenum
what are the zymogens being secreted into the duodenum
trypsin, chymotripsin,
what does enterokinase do
converts trypsinogen to trypsin
trypsin then activates other zymogens
exopeptidases example
caboxypeptidases (procarboxypeptidases) and aminopeptidase
caboxypeptidases (procarboxypeptidases) and aminopeptidase
finish protein digestion by cleaving amino acids from the carboxyl and amino ends of a polypeptide chain respectivel
amino acid and small peptide absorption
small peptides and amino acids are actively transported into the intestinal epithelial cells by cotransport with ions
amino acids are then tranported across the basolateral membrane by facilitated diffusion and diffuse into the blood
most dietary lipids are
triglycerides (90%)
lipids and mizing
dont mix with stomach contents bc they are hydrophobic and cant be reached by digestive enzymes
bile salts
facilitates the action of digestive enzymes by emulsifying fat globules down into smaller droplets (micelles)
bile salt synthesis and secretion
synth in hepatocytes and secreted in the bile
lingual lipase
saliva and stomach
gastric lipase
gastric lumen
pancreatic lipase
small intestine
what happens when lipids interact with lipase
monoglycerides and fatty acids are liberated through the action of lipase and they retain their association with bile acids and complex with other lipids to form structures called micelles
fate of lipid containing chylomicrons
transported into the lymphatic vessel underlying the epithelial cell layer (lacteal)
large numbers of absorbed chylomicrons appears milky and the lymphatics are easy to see in the small intestine
vitamin digestion
consumed in their absorptive form and do not undergo digestion
the mechanism of absorption of vitamins depends on whether the vitamin is hydrophobic or hydrophilic
hydrophobic/ fat soluble vitamins
ADEK
absorbed with lipids therfore bile salts can help absorption of these vitamins
water soluble vitamins
are absorbed by active transport or facilitated diffusion
folate, thiamine, riboflavin, niancin, pantothenic acid, biotin, vitamin B6, bitamin B12, vitamin C
mineral absorption
occurs by active transport
80% of sodium enters the GI tract through secretions and 20% is ingested
calcium absorption
regulated based on the bodys needs
enhanced by the homrones 1,25 OH vitamin D3 which increases the amount of calcium binding protien therefore calcium absorption is dependent upon sufficient dietary vitamin D
iron absorption
both in the redduced inorganic form Fe2+ and when bound to heme
water absorption
passive: driven by an osmotic gradient across the mucosal epithelium created by the transport of solutes (mainly sodium) from the lumen to the interstitial fluid
sources of water
drinking water (2l/day)
secretions from the stomach, intestine, acessory glands (7l/day)
fact about water
approx 70% of the water that is initially present in the duodenum is typically absorbed by the time chyme reaches the colon
