Digestive physiology review Flashcards
What is mechanical digestion
breakdown of large food particles into smaller food particles
- Teeth
- Stomach churning
- Sm. Intestine segmentation
What is chemical digestion
enzymatic breakdown of organic macromolecules into smaller molecules (monomers)
*Chemical bonds are broken
what do enzymes do
- lower energy requirement for rxn. to take place (catalyst proteins)
- allow rxn’s to take place quickly even @ body temperature
- Very Specific: Bind to substrates & produce products
what are the reactants in an enzymatic reaction called
substrates
what are the factors that affect the rate of enzyme catalyzed reaction
1) Ph
2) Temp
3) Soln. conc.
what is a catabolic reaction
large macromolecules/polumers are broken down into smaller monomers.
These are EXERGONIC/EXOTHERMIC (energy is released when the bonds are broken & it can be used to make ATP)
Explain protein, amino acid & peptides
- Protein = very long polymer of amino acids
- Peptides= a couple amino acids linked together
- Amino acid = singular. R= the variable. There is 20 different ones
Explain complex carbohydrate/polysaccharide, disaccharides, and monosaccharides/simple sugar
- Complex carbohydrate/polysaccharide: Starch or glycogen (many monosaccharides all linked together)
- Disaccharides: Sucrose, maltose, lactose (2 monosaccarides)
- Monosaccaride/simple sugar: just one. Glucose, fructose, galactose
explain a lipid triglyceride & glycerol & fatty acids
Triglyceride = glycerol + 3 fatty acids unsaturated or saturated
saturated =no double carbon bond
unsaturated = double carbon bond
Where can protein be digested into peptides and by what
1) stomach by pepsin
2) Duodenum by trypsin
3) sm. intestine by chymotrypsin
4) in sm intestine by carboxypeptidase
How is protein digested into peptides in the stomach
by pepsin, secreted by chief cells, activated by HCL.
how is protein digested into peptides in the duodenum
by trypsin, secreted by the pancreas
how is protein digested into peptides in the sm. intestine
by chymotrypsin, secreted by the pancreases & bu carboxypeptidase, secreted by the pancreas.
how are peptides digested into amino acids in sm intestine.
by peptidases secreted by the sm. intestine brush boarder enzymes.
What is so special about trypsin, chymotrypsin & carboxypeptidase
1) these proteases/peptidases are secreted by the pancreases as inactive proenzymes (can’t digest proteins).
2) Trypsinogen is activated by enteropeptidase (brush boarder enzyme)
3) Chymotrypsinogen & procarboxypeptidase are concerted by trypsin
how are complex carbs digested into tri/disaccharaides in the mouth
by salivary amylase secreted by the salivary glands
how are complex carbs digested into disaccharides in the sm. intestine
by pancreatic amylase secreted by the pancreas
how are disaccharides digested into monosaccharides in the sm intestine.
by Disaccharidases secreted by brush border
how are triglycerides digested into fatty acid & monoglycerides in the mouth
by lingual lipase secreted by the tongue
how are triglycerides digestied into sm. drops in digestive solution in the duodenum
by bile secretion by the liver
how are triglycerides digested into fatty acids & monoglycerides in the small intestine
by pancreatic lipase secreted by the pancreas
how are nucleic acids digested into nitrogenous bases & sugar in the sm. intestine
by nucleases & nucleosides secreted by the pancrease& sm/ intestine
where does absorption of nutrients take place
mainly the ileum & the jejunum (across the brush boarder)
How are sugars (monosaccarides) & amino acids transported across brush boarder of sm. intestine
1) By cotransport (move molecules into cell even where conc. is more high)
2) By facilitated delusion (b/c some can only move down their gradient)
the products of protein & carbohydrate digestion enter…
the capillaries in the lamina propria & then the hepatic portal vein & then the liver
How do lipids cross the brush boarder
1) Monoglycerides & fatty acids (lipid soluble) diffuse across the brush border w/ no transporter needs
2) The are NOT h20 soluble so they must be coated in proteins &phospholipds to be transported into blood/lymph: called chylomicrons
step by step process of fat digestion to being put into blood
1) Fatty acids & monoglycerides emulsion by bile
2) Now micelles (bile coated droplets containing fatty acids/ monoglyceride)
3) Fatty acids & monoglycerides diffuse across cell membrane.
4) reassemble into triglycerides, then combine w/ cholesterol, phospholipids & proteins to form chylomicrons
5) chylomicrons leave sm. intestine cell by exocytosis
6) they are to large to go into blood vessels, so they are picked up by lacteals to the cisterna chyli to thoracic duct to veins
What do the chylomicrons do once they’re in blood?
LIPOPROTEIN LIPASE in endothelium of capillaries breaks down triglycerides
-Fatty acids go to adipose to be stored as triglycerides, muscle to be used as energy & liver to be processed
what breaks down triglycerides in capillaries once their in blood
lipoprotein lipase
what is a micelle
bile coated droplet containing fatty acids & monoglycerides) product of emulsification
What are lipoproteins
proteins made in the liver
they transport lipids to & from the liver & tissues
there is Low density & high density
Low Density lipoproteins
LOWSY (lots of lipid, less protein)
- transports lipids from LIVER to TISSUES via:
- Receptor mediated endocytosis (pulls lipids into cells)
- Can be deposited in endothelium (Plaque deposited that sits under the endothelium & causes atherosclerosis)
- increased risk of heart attack & stroke
what are high density lipoproteins
HEALTHY (less lipid, more protein)
-Transports lipids from cells to liver - can be excreted in bile ( made form cholesterol)
what are the LDL & HDL steps in the liver
1) Liver removes fatty acids from chylomicrons, adds cholesterol to from LDL
2) LDL enters circulation
3) Receptor mediated endocytosis of LDL
4) Cells use cholesterols to synthesize cell membrane, hormones, etc.
5) Cholesterol not used is picked up by HDL in the blood
Explain the carb/starch absorption pathway
1) Oral (salivary amylase)
2) sm. intestine (pancreatic amylase)
- it is now disaccharides & trisaccharides
3) Facilitated cotransport diffusion of monosaccharides into brush border
4) facilitated diffusion of monosaccharides into capillaries
explain lipid absorption pathway
1) Oral (lingual lipase )
2) sm. intestine (emulsified by bile from liver)
- pancreatic lipase
- now monoglycerides & fatty acids
3) diffuse into brush border -reassembled into triglyceride
4) Packaged into chylomicrons
5) Into lacteals by exocytosis
Explain the protein absorption pathway
1) stomach (pepsin enzyme) = peptides
2) Sm. Intestine (trypsin, chymotrypsin, carboxypeptidase, elastase) all from pancreas
-product = peptides & amino acids
3) Intestinal mucosa secretes peptidases
=amino acids now
4) facilitated diffusion cotransport into mucosa
5) facilitated diffusion cotransport of amino acid into capillary
what happens to the absorption of vitamins
1) water sol. (B,C) -> facilitated diffusion
- Except b12 must be bound to intrinsic factor
2) Fat sol. (ADEK) diffuse w/ lipids (in chylomicrons)
What i s pernicious anemia
defect in gene that codes for intrinsic factor. Cannot absorb B12 need for cell division
Explain the absorption of ions/electrolytes
- Transporter required (H2O soluble & charged)
- facilitative diffusion of active transport
- Na+ with amino acids is cotransported
- Ca2+ transported is activated by vit. D3 & parathyroid hormone
- Iron = active transport enhanced by vit C/acids
How is water absorbed
By osmosis (92% in sm. intestine) (6-7% in lrg intestine)
- only about 150ml in feces per day
- no absorption in stomach
How is digestion regulated
by hormones & Autonomic nervous system (enteric plexuses = neurons in GI tract)
what are the 3 phases for digestion regulation
1) Cephalic phase
2) Gastric Phase
3) Intestinal phase
what happens in the cephalic phase
occurs b4 food enters stomach
-sight/smell/taste/thought -> hypothalamus -> parasympathetic system -> increase saliva & gastric juice
what happens in the gastric phase
activated by the arrival of food/protein in the stomach
1) Chemoreceptors trigger gastrin secretion by the G cells in the gastric gland
2) Stretch receptors trigger parasympathetic vagus nerve
3) both of these increase gastric juice & increase gastric motility
What happens in the intestinal phase
1) Activated by the arrival of chyme in the duodenum
2) The chemo & stretch receptors cause:
- duodenal endocrine secretion of hormones
- parasympathetic activation -> increases intestinal motility
what are the 2 main duodenal endocrine hormones secreted in the intestinal phase
1) Secretin
2) cholecytoskinin
what does secretin do
1) Increases pancreatic sodium bicarbonate secretion
2) increase bile secretion by liver
3) decreases gastric secretion
4) decreases gastric motility
what does cholecystokinin do
1) Increases pancreatic enzyme secretion
2) increases gallbladder contraction
3) relaxes hepatopancreatic sphincter
4) increases pancreatic sodium bicarbonate secretion
5) decreases gastric secretion
6) decreases gastric motility
What is glucose dependent insulinotropic peptide and when is it secreted
- secreted when sugars&fats enter duodenum
- Stimulate insulin secretion
- stimulate lipogenesis in adipocytes
what is vasoactive intestinal peptide
stimulated intestinal glands to increase sodium bicarbonate & H20 secretion
-it dilates the intestinal blood vessels to increase blood flow
explain control of defecation
-mass movements (twice a day)
-initiated by arrival of food in stomach/intestine (gastrocolic/duodenocolic reflexes)
-under parasympathetic control
-and conscious control of skeletal muscles
Transit time: 24-48hr
distesion of the rectum causes…
relaxation of internal smooth muscle. sphincter & defecation
Where are the satiety centres
the hypothalamus
it recieves signals from stretch receptors in GI tract, blood chemoreceptors, hormones, energy storage tissues, the brain (emotions) and gut bacteria
explain short term appetitive decrease
Stretch receptors, Increased blood glucose, increase insulin, increased blood amino acids & increased Cholecystokinin DECREASE APPETITE
explain short term appetite increase
Ghrelin (hormone secreted when stomach lining is empty) increases appetite
explain long term regulation of appetite
Lectin (secreted by adipose)
increased adiopose, increased leptin, = decreased apeitite
-obesity leads to lectin resistance
peristalsis in the small intestine begins …
when chyme enters the duodenum
glucose & sodium are
cotrasported together
secreted by intestinal gland & by acinar cells
sodium bicarbonate
