Lecture 22 -- review questions Flashcards
what is bile?
fluid made and released by liver, stored in gallbladder
helps with digestion by breaking down fats into fatty acids
what is bile made of?
1) bile salts (which are made by bile acids)
2) proteins
3) bilirubin
4) cholesterol
5) lecithin (phospholipid)
“boys poop brown colored liquid”
what are the main components of bile?
bile acids (make up bile salts)
what are bile salts made of?
bile acids that are often bonded to glycine or taurine to increase water solubility (=conjugated bile acids)
what is the role of bile salts in the digestive process?
break down fat
large fat globules –> smaller fat droplets
where is bile produced? from which molecule?
liver
cholesterol
what are conjugated bile salts?
made up of bile acids that are bonded to glycine or taurine to increase water solubility
what is the only way for the body to get rid of cholesterol?
bile salts are produced from cholesterol in the liver
liver synthesizes bile salts from cholesterol to replace the bile lost in feces
what percentage of bile salts are lost in the feces?
20%
in what part of the intestine are bile salts recycled (= taken back to the liver)?
ileum
what is the role of emulsification?
bile salts in duodenum break large fat globules into smaller fat droplets
–> increase surface area available to lipase enzymes
what are micelles?
aggregates of bile salt that forms a polar outer shell and a hydrophobic inner core
long chain FAs, cholesterol, and other hydrophobic molecules dissolve in the core
what are triglycerides composed of?
1 triglyceride = 1 glycerol molecule + 3 fatty acids
3 fatty acid chains linked by a glycerol
which enzyme is mainly responsible for digesting triglycerides in the small intestine?
pancreatic lipases
what is the function of micelles in the absorption of lipids?
micelles incorporate the lipid digestion products and enable these lipid digestion products to be transported to the small intestinal surface (plasma membrane of enterocytes) for absorption
why do the lipids need to be transported in the core of the micelles to the enterocytes?
lipids are hydrophobic —> must be kept in the core of a hydrophilic bile salt shell of the micelle in order to diffuse across the water layer adjacent to the enterocyte surface in order to reach the surface of the enterocyte
what happens to the fatty acids and monoglycerides once inside of the enterocyte?
FAs and monoglycerides pass by simple diffusion into the enterocyte (intestinal epithelial cell)
within the cell, FAs and monoglycerides are converted to TGs
proteins coat the TGs and other fatty substances to form chylomicrons
which lipoprotein does it form inside of enterocyte?
chylomicrons
are lipids absorbed into the blood or lymph? Through which structure?
chylomicrons are too large to penetrate endothelium of capillary
lymph
lacteals
what is chyle?
fatty, milk-white intestinal lymph
will chylomicrons always be in the lymphatic system (until degradation), or will they be transferred to the blood circulation at one point?
will be transferred to blood circulation at one point
carried thru lymphatic system to general circulation
where is fat absorbed? (organ of the alimentary canal)
small intestine
what are lipoproteins?
tiny droplets w/ a core of cholesterol and TGs and a coating of proteins (apolipoproteins) and phospholipids
coating has 2 purposes:
- enables lipids to remain suspended in the blood
- recognition marker for cells that absorb them
what molecules can you find at the core and the surface of lipoproteins?
core:
- cholesterol
- TGs
coating:
- proteins (apolipoproteins)
- phospholipids
what is the classification of lipoprotein based on? (ie which characteristic?)
density
4 major categories
what do VLDL, LDL, and HDL stand for?
VLDL – very low density lipoprotein
LDL – low density lipoprotein
HDL – high density lipoprotein
what is the most abundant component of chylomicrons?
triglycerides
what is the most abundant component of VLDL?
triglycerides
what is the most abundant component of LDL?
cholesterol
what is the most abundant component of HDL?
protein
which lipoprotein contains the most cholesterol?
LDL
which lipoproteins contain the most triglycerides: HDL, LDL, or VLDL?
VLDL
what is apolipoprotein, and where can you find it?
a protein that coats lipoproteins
surface of lipoproteins
what is the function of lipoprotein lipase, and where is it found?
removes TGs from lipoproteins
breaks down TGs into fatty acids and glycerol
found in surface of endothelial cells
the removal of TGs from chylomicrons by lipoprotein lipase on the vascular endothelial surface results in which molecule?
fatty acids
glycerol
where do chylmicron remnants go?
liver for disassembly
where is VLDL produced?
liver
what is the function of VLDL?
Does VLDL carry fat synthesized by the liver?
where?
bring more TGs to the body’s cells (including adipose tissue for storage)
yes; VLDLs do carry fats synthesized by the liver
carry them to the body’s cells
what converts VLDL to LDL?
(tip: which molecules are removed from VLDL thru their journey in the circulation?)
lipoprotein lipase removes TGs from VLDL and converts them to FAs and glycerol
what is the function of LDL?
deliver cholesterol to the body’s cells
what is the function of HDL?
pick up excess cholesterol from tissues and deliver to the liver for use or disposal
what is lipolysis?
breakdown of fats by hydrolysis to release FAs
what happens to the glycerol and fatty acid products obtained upon the action of lipase in the adipose tissue? (metabolic pathways)
glycerol is converted to a glycolysis intermediate
FAs undergo beta-oxidation to generate acetyl-CoA
which part of TG molecules enters glycolysis?
glycerol
what is beta oxidation?
process that converts FAs to generate acetyl-CoA to use for the citric acid cycle to generate ATP and NADH and FADH2 which are used for the electron transport chain
why do fats have glucose-sparing and protein-sparing effects?
as long as enough fat is available to meet the energy needs of the tissues, protein isn’t catabolized for fuel and glucose is spared for consumption by cells that can’t use fat (e.g. neurons)
how is glycolysis related to lipid metabolism?
TG –> broken down by lipoprotein lipase into glycerol
glycerol –> converted to a glycolysis intermediate –> degraded to pyruvate
pyruvate gets converted to acetyl-CoA for the citric cid cycle –> help synthesize ATP
what causes ketone bodies to form?
when body is rapidly oxidizing fats, excess ketone bodies accumulate –> pH imbalance (ketoacidosis)
ketosis can be a serious risk in extreme low-carb diets
what does Acetyl-CoA stand for?
acetyl coenzyme A
what is lipogenesis?
synthesis of triglycerides from excess carbs and amino acids
can our body synthesize triglycerides from glucose?
yes;
excessive amounts of carbs and amino acids are converted to TGs by lipogenesis and stored
diets that are high in carbs generate excess acetyl-CoA that can be converted into fatty acids
glucose –> glycerol –> TGs
glucose –> pyruvic acid –> acetyl-CoA –> fatty acids –> TGs
is Acetyl-CoA converted to glycerol or fatty acids?
fatty acids
diets that are high in carbs generate excess acetyl-CoA that can be converted into fatty acids
what 4 hormones influence the short-term regulation of feeding behavior?
do they regulate satiety or hunger?
ghrelin –> hunger
amylin –> satiety
CKK (cholecystokinin) –> satiety
peptide YY (PYY) –> satiety
where and when is ghrelin released?
secreted when stomach is empty
signal to being a meal
causes hypothalamus to secrete GH-RH (to take advantage of nutrients about to be absorbed)
also stimulated party by gastric peristalsis
where is peptide YY secreted?
enteroendocrine cells in ileum and colon
sense that food has arrived
where is amylin synthesized?
B-cells in the pancreas
what is the most important long-term regulator of feeding behavior and appetite?
leptin
insulin
what 2 hormones tell your brain how much fatty tissue the body has, contributing to maintaining energy balance?
leptin and insulin
does leptin inhibit or promote appetite?
inhibit
fat cells empty –> no leptin signal –> we eat
fat cells full –> leptin signal –> we stop eating
when the adipocytes are full of stored lipids, do they inhibit or stimulate leptin release?
when the adipocytes are lacking lipid stores, do they inhibit or stimulate leptin release?
leptin makes you stop eating
full –> leptin release –> stop eating
empty –> no leptin release –> start eating
what is leptin insensitivity?
receptor defect where the body doesn’t respond to leptin
leptin signals when fat cells are full –> you’re supposed to stop eating
if body doesn’t respond to leptin, will keep eating, even when fat cells are full –> this causes obesity
a common factor in obesity
how does leptin stimulate lipolysis?
leptin stimulates sympathetic nerve fibers in adipose tissue to secrete Noradrenaline
–> stimulates lipolysis
what hypothalamic nucleus receives input from hormones regulating the feeding behavior?
arcuate nucleus of the hypothalamus
in the arcuate nucleus, there are 2 sets of neurons that, when stimulated, have different outcomes:
which hormones stimulate or inhibit each of these set of neurons and what are the outcomes related to the feeding behavior (hunger, satiety)?
which neurotransmitters are released in these neurons (at the arcuate nucleus level)?
Neuropeptide Y-secreting neurons –> promotes hunger and food intake –> releases Neuropeptide Y (NPY) neurotransmitters (this is a potent appetite stimulant)
- stimulated by: ghrelin
- inhibited by: PYY, CCK, insulin
melanocortin-secreting neurons –> satiety and inhibits eating –> releases melanocortin neurotransmitter (inhibits eating)
- stimulated by leptin
