6- small intestine Flashcards
which is smallest and largest
duodenum
jejunum
ileum
small: duodenum
longest: ileum
what is ferritin
a protein complex that acts as a storage form of iron
what is transferrin
plasma protein that carries iron
what do absorptive/enterocytes do
absorb
brush border enzymes
what do most cells from the stem cells end up becoming
absorptive cells
what do goblet cells do
secrete mucous
what is the role of ileum
digest and absorb (less important)
secrete intrinsic factor for B12 and absorbs bile acid
what do paneth cells do
secrete antibacterial proteins
what are the major cell types in villus
goblet, endocrine and absorptive cells
what are the major cell types in crypts
stem and paneth cells
what is a brush border
small microvilli projections of epithelial cells that cover the villi, major absorptive surface of the small intestine
what kind of molecules do brush border enzymes break down
carbs and peptides
what do brush border enzymes durn maltose and limit dextrins into
glucose
why do brush border enzymes need to break these sugars down to glucose
because the intestine can only absorb monosaccharides
how does glucose/ galactose get from the intestinal lumen into epithelial cells
2ary cotransport with sodium
how does glucose/ galactose get from the epithelial cells into the blood
facililated transport
how does fructose get from the intestinal lumen into epithelial cells
facilitated diffusion
how does fructose get from the epithelial cells into the blood
facilitated diffusion
why does lactose intolerance cause diarrhea
decrease water absorption in gut because lactose produces an osmotic gradient
how does glucose/ galactose get from the epithelial cells into the blood
facilitated transport
how do small peptides get absorbed into epithelial cell
2 active coupled to H+
what happens once small peptides enter the cytosol
they are hydrolyzed by peptidases into amino acids
how to amino acids enter the blood
facilitated diffusion
what happens once fatty acids enter the enterocyte and why
ER processes them back into triglycerides
what are chylomicrons
proteins that were packed by Golgi and secreted via exocytosis
what does the ER do to the triglycerides
triglycerides that aggregated and coated with amphipathic proteins
what are chylomicrons and what do they contain
extracellular fat droplets
triglycerides, phospholipids, cholesterol and far soluble vitamins
what does the ER do to the triglycerides
triglycerides that aggregated and coated with amphipathic proteins
what happens once the triglycerides are coated with amphipathic proteins
packaged in Golgi and secreted via exocytosis
where do large chylomicrons go
into the lymphatic system
what do lymphatics enter the systemic circulation
the thoracic duct
are capillaries or lacteals more leaky
lacteals
thats why chylomicrons can fit
what does lipoprotein lipase on endothelial cells of blood vessels release
triglycerides from chylomicrons as monoglycerides and free fatty acids which can be taken up by tissues
how is iron transported into the enterocyte
2 active
what happens once iron is in the enterocyte
incorporated into ferritin
what happens to iron that is not stored
it is released into the blood and is attached to transferring
what happens to iron bound to ferritin
it sheds after a few days
what happens where there are ample iron stores
ferritin is upregulated so there is a reduced absorption of iron
what happens when there are depleted stores of iron
less ferritin made so that more iron is absorbed
what happens where there are ample iron stores
ferritin is up-regulated so there is a reduced absorption of iron
where does majority of the water in the intestines come from
organs that drain into the intestine (liver, pancreas)
how much fluid is handled in the GI tract daily
8-9 L
what happens to most of the fluid in the GI tract
reabsorbed in the small intestine
where is water absorption happening
in the villi
where is secretion happening
crypts
how does water get across epithelium
paracellular transport (tight junctions) due to osmotic gradient
which are important electrolytes for water transport
Na
Cl
HCO3
what electrolytes are important for water absorption
what kind of transport
Na gradients generated in secondary active nutrient uptake (glucose and amino acids)
what electrolytes are important for water secretion
what kind of transport
Cl- gradient made by secondary active transporter
triggered by cAMP production
what causes cholera
increases cAMP in crypt epithelium, which activates Cl- secretion into lumen and water follows
what is the most common motion in the small intestine
segmentation
what is the MMC and what does it replace
replaces segmentation, it is the migrating myoelectrical complex
a pattern of peristaltic activity
overlapping waves
what is the purpose of MMC
push any undigested material and bacteria into the small intestine
what is motilin
intestinal hormone released by small intestine cells that initialy MMC
what inhibits motilin
eating
