Part 4.7 Digestion Flashcards
hepatocytes aggregate into ___
lobules.
functional unit of liver
hepatic lobules.
T/F Digestion occurs in small intestine
true. tripsogen secretion from pancreas is responsible for short chain polypeptide breakdown
the ____ of _____ secrete the succus entericus, and is the nusery site for new epithelial cells of the small intestine
crypts of lieberkuhn. they make cells via mitosis and they crawl up the villi pole
enzymes from the ____ do most of the digestion in the lumen of the small intestine
enzymes from the pancreas. small intestine duodenum also secrete things but they are mainly alklaine solution (brunner glands) or secretion of water (for hydrolysis) and mucus. others include enterokinases that are locked within the small intestinal wall and are not secreted into the lumen
fats need to be in the form of ____ in order to be absorbed
micelles
purpose of brush border enzymes. examples?
enzymes of the small intestine that are secreted by the small intestine but do not leave the wall.
1) enterokinases: activates more pancreatic trypsinogen
2) disaccharidases: maltase, sucrase, lactase hydrolyse respective disaccharides 3) aminopeptidases. hydrolyse peptide fragments into aminoacids.
T/F Brush border enzymes are species dependent
true. dependent on diet. ex/ birds do not have lactase disaccharidase because they do not drink milk. they do have an esterase which hydrolyse esters in ripening fruit.
long term dietary changes can alter the length of intestines and density of transporter. and example of this is acclimatization response of omnivores to a high carb diet, what happens to the intestine?
there is an upregulation of glucose transporters in the brushboarder enzymes.
T/F: types of transporters and size of intestine is closely matched to diets of species
true. for example, herbivores have a lot of carb transporters
what is the small intestine reserve capacity?
small intestine portions can be lost and we can still absorb nutrients. Except for the ileum. if you remove the ileum, you need B12 supplementation.
sodium is absorbed in the small intestine both ___ and ___
passively and actively.
on the brushboarder of the lumen, there is a ____ for sodium, and drags along a product of digestion with it (is this passive or active). Outline the process of Na+ absorption
cotransporter for digesta and sodium. driven by chemical gradient. there are more nutrients and Na+ in the lumen, allowing the cotransporter to let Na+ into the cells. This portion is passive, because it follows the chemical gradient of the digesta
once the epithelial cells contain sodium taken from the lumen, a ___-___ATPase pump sodium into the interstitial space and ultimately into the plasma.
once the epithelial cells contain sodium (via the brushboarder cotransporter), an Na+-K+ATPase pump sodium into the interstitial space and ultimately into the plasma.
how is Na+ passively transportered? Actively?
Passively:
1) through leaky tight junctions 2) through Gi-Na+ cotransporter.
actively transported via Na+-K+ atpase.
purpose for sodium active transport in the small intestine.
for water absorption. Na+ creates an OSMOTIC PRESSUE in the INTERSTITIAL FLUID so water is absorbed. 2) for cotransport of glucose and amino acids.
ourline carb absorption in the small intestine
1) dissacharidases in brushborder break down disaccharides into monosaccharides
2) monosaccharides abssrobed via cotranport (with sodium)
3) Ms’s then enter the interstitial fluid and then the blood via CARRIER_MEDIATED DIFFUSION - or through leaky tight junctions.
outline the process of protein absorption in the small intestine
1) exogenous and endogenous protein get broken down by pepsin (stomahc) and pancreatic enymes
2) aminopeptidases in brushborder of SI break things into AAs
3) AA and glc co transport process allow them to be aborbed into epithelium
**some intracellular peptidases break down any remaining peptides in the epithelial cell into AAs
4) carrier-mediated diffusion on basolateral membrane of the epithelial cell allows them to move into intersitium and capillaries.
T/F endogenous proteins account for over 50% of daily protein absopriton
true. in addition to food, we digest ourselves. we have proteins from digestive enzymes that are reabsorbed, proteins from mucosal cells. and traces of plasma proteins that leak into the lumen. beneficial historically when we didn’t eat as much meat.
purpose of intercellular peptidases
sometimes, larger polypeptide chains rather than single AAs enter the epithelial cell via the Na+-AA cotransporter. these intercellular peptidases break down any residual protein chains that were not broken down by the aminopeptidases on the brush border.
oultine fat absorption in the small intestine
1) bile emulsifies fat into droplets for lipase
2) lipase forms micelles of monoglycerides and free fatty acids
3) micelles can enter brushborder cells via PASSIVE diffusion- they do not need cotransporters into epithelial cells because they are hydrophobic.
4) when in the epithelial cells, they are re-synthesized into triglycerides and packaged into CHYLOMICRONS.
5) chylomicrons leave the cell by exocytosis and enter the central lacteal (lymph vessels of mammals) or capillaries in birds
when in the epithelial cells, FFA micelles are re-synthesized into triglycerides and packaged into ______
when in the epithelial cells, FFA micelles are re-synthesized into triglycerides and packaged into CHYLOMICRONS.
what is a chylomicron
tryglyceride coated with water soluble lipoprotein
chylomicrons leave the epithelial small intestine cell by exocytosis and enter the ____ ____ (of mammals) or capillaries in birds
CENTRAL LACTEAL. however, some free fatty acids sneak out of epithelial cell and end up in blood supply without being formed into a chylomicron or going into central lacteal
where are bile salts reaborbed
in the ileum of the small intestine
once the products of digestion (except for fat that is in the central lacteal) are in the plasma, where is this blood delivered? Why?
to the liver via the hepatic portal vein. digestive processing and detoxification before entering the vena cava and general circulation
most fat (in the form of chylomicrons) do not go into the liver because they are part of the central lacteal of the villi and not in the blood vessels. What happens instead? Purpose of not going directly to the liver.
doesn’t go directly to the liver but enters the lymphatic system. some is taken by adipose cells before ever reaching the liver. eventually, some fat makes its way into the liver and are processed into LIPOPROTEINS. fat dilution via direct entry into adipocytes or by being retained in the lymphatic system avoids the liver from being overwhelmed with too much fat for it to process.
3 purposes of large intestine
1) water reaborption
2) holding and propelling feces
3) symbiotic microbes for fermentation (in some species that rely on high-cellulose diets –> primarily done in the cecum)
specialized portion of the cecum in humans for immune function
the veriform appendix.
human colon is divided into three sections:
1) ascending 2) transverse 3) descending branch
ileum connects to large intestine via _____ valve
ileocecal valve.
omnivores and herbivores tend to have enlarged _____ for microbial digestion
enlarged colon/cecum for microbial digestion/fermentation because of their high-cellulose diets.
Glucose and galactose are both absorbed by secondary active transport, in which symport carriers, such as the ___ –_____ cotransporter (SGLT) on the luminal membrane transport both of them from the lumen into the interior of the intestinal cell. Recall that the operation of these carriers, which do not directly use energy themselves, depends on the Na+ concen- tration gradient established by the energy-consuming baso- lateral Na+/K+ pump, which is pumping Na+ out of the cell, constantly keeping the ICF lower in Na+ than the lumen
Glucose and galactose are both absorbed by secondary active transport, in which symport carriers, such as the sodium–glucose cotransporter (SGLT; see Figure 14-25b) on the luminal membrane transport both the monosaccharide and Na+ from the lumen into the interior of the intestinal cell. Recall that the operation of these carriers, which do not directly use energy themselves, depends on the Na+ concen- tration gradient established by the energy-consuming baso- lateral Na+/K+ pump
