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functions of adipose tissue:
Largest repository of energy (triglycerides) in the body
Source of water
Shapes the surface of the body
Pads act as shock absorbers (soles, palms, orbits of eyes)
Thermal insulation of the body
Fills spaces and keeps organs in place
Secretory organ (hormonal - leptin - circulating satiety factor)
- predominant form in humans
- one large fat droplet in cytoplasm
- found everywhere but eyelids, penis
- human fetus
- hybernating mammals
- lose during first decade of life
- brown because so many brown mitochondria
- numerous lipid droplets
mesenchymal cell --> lipblast --> can go into either brown or white fat
white adipose tissue that is right under the skin, thermal insulation
- secreted by adipocytes
- inhibits food intake
- increases metabolism
- increases loss of body weight
- closely packed
- thickest part of cytoplasm is right around the nucleus, contains golgi mitochondria, poorly developed rER
- rim of cytoplasm around lipid droplet = sER
- individual cells cells surrounded by reticular fibers (secreted by the adipocyte)
are adipocytes membrane bound?
no! because they are already lipids!
what separates hydrophilic cytoplasm ringfrom hydrophobic fat?
vimentin intermediate filaments
short term weight regulation:
- appetite and metabolism controlled on daily basis
- Ghrelin - appetite stimulant (hypothalamus), produced by gastric epithelia. mutation here makes you obsessed with food!
- peptide YY (PYY) - an appetite suppressant, produced by small intestine
long term weight regulation
- leptin - produced by adipocytes, targets the hypothalamus, regulates amount of adipose tissue in the body, related to obesity
- insulin- pancreatic hormone, enhances conversion of glucose into triglycerides in adipocytes, acts on hypothalamus
- synthesized in liver
- VLDL = left over glucose
- more lipid at surface area
- diff apolipoproteins
- higher proportion of cholesterol to triglycerides
- chylomicronsformed in intestinal epithelial cells
- triglycerides (and a little cholesterol) surrounded by apolipoproteins, cholesterol and phospholipids
- shipped in packages so not randomly floating in blood
- synthesized by adipocyte and transferred to capillary cell membrane
- HYDROLYZES triglycerides into free fatty acids (transferred to fat cell through transporters)
- ex: VLDL - IDL - DL (as broken down)
- - excessive accumulation of fat in unilocular tissue cells that become larger than
excessive accumulation of fat related to an increase in the number of adipocytes
why is brown fat brown?
- to produce heat
how does breakdown of brown fat occur?
nerve impulse (sympathetic nervous system) releases norepinephrine into adipose tissue, activates hormone - sensitive lipase (cleaves triglycerides into fatty acids - go to mitochondria - go to TCA makes NADH and FADH2 which go into the ETC and pump out a lot of H+
how does norepinephrine target hormone sensitive lipase in brown fat?
norepinephrine - adenylate cyclase -turns ATP into cAMP (secondary messenger which targets hormone sensitive lipase)
how does norepinephrine stimulate hormone sensitive lipase in white fat?
norepinephrine - g coupled proetin - adenylase cyclase - turns ATP into cAMP - targets protein kinase A - phosphorylates hormone sensitive lipase and gets the whole thannngg goin!
how is heat produced by nonshivering thermogenesis?
UCP-1 = uncoupling protein!! what makes proton gradient produce heat instead of energy (ATP)
- normally what happens is you have a proton gradient between membrane of mitcohondria, the H+s flow from the innermembrane space back to the matrix through ATP synthase making ATP.... but brown multilocular tissue has a protein UCP-1!! that allows the H+s to travel though it when they are going down gradient and produces heat not ATP
how does heat get transferred to the rest of the body?
there are blood vessels all through the adipose tissue
what is the protein that aids in storage of fats? and what is the protein that stimulates break down of fats?
- lipoprotein lipase
- hormone sensitive lipase