Adipose Tissue Flashcards
What tissue gives structure to adipose tissue?
Reticular tissue
High density of reticular fibers (type 3 collagen)
Adipose tissue characteristics
Highly vascularized
Found: subcutaneous areas, body cavities, surrounding organs and tissues (nerves, vessels)
Adipose tissue fxn
reservoir for lipid storage:
Structural components for cells (lipids)
Energy sources for cells (fatty acids)
Provides lipid molecules for steroid hormone production
Temperature insulation (due to poor thermal conduction of adipose tissue Protection of underlying structures
Unilocular Fat
Yellow Fat-most common type
Single lipid droplet fills the majority of cellular cytoplasm
–nucleus and cytoplasm are “squeezed” into the periphery of adipocytes
Multiocular Fat
“brown fat”-limited amount in adults
infants and animals that hibernate
lipids of brown fat are broken down for production of heat–controlled by sympathetic nervous system
Brown Fat cytoplasm: multiocular
numerous lipid droplets
many mitochondria
central nucleus
Heat production of multiocular fat
catabolism of fatty acids from lipid droplets is uncoupled from ATP synthesis
Thermogenin
- Transmembrane protein of mitochondria
- Allows shunting of energy away from ATP production and into heat production
- All energy for metabolism of fatty acids from multilocular adipose tissue is given off as heat
Lipid Transport
Lipids need special systems to be transported within the water-based blood and tissue fluid- transported attached to proteins
This configuration allows them to be “soluble” in the plasma and allows cells to control entry and exit of lipid molecules
Major lipoprotein groups (modes of lipid transport)
VLDL, LDL, HDL, IDL and chylomicrons
Chylomicron
Small particles formed in the intestine: transported in plasma (to liver, fat cells)
Chylomicrons are triglycerides packaged with:
Cholesterol, phospholipids, and proteins
Lipid storage
Most stored fatty acids have their origin in dietary fats
During digestion, triglycerides are split into monoglycerides and fatty acids in the GI tract for transport to adipocytes-(Transported in the blood as chylomicrons)
Adipocytes also receive lipids from:
Triglycerides synthesized in the liver and transported in the form of VLDL
Conversion of glucose to fatty acids and glycerol; these are then formed into triglycerides for storage
Triglycerides are transported in the blood as?
Chylomicrons & VLDL
FFA bound to proteins
Lipoprotein lipase
Enzyme within endothelial cells of capillaries
Breaks down lipoproteins and releases:
FFA (free fatty acids)
Glycerol
Excess glucose is also processed by?
Adipocytes
Insulin stimulates the uptake of glucose
Insulin stimulates adipocyte synthesis of FFAs from glucose
Then stored within the lipid droplet of adipocyte
Lipid storage IN the adipocyte:
FFAs diffuse from the capillary into the adipocyte
Once inside the adipocyte, FFAs are repackaged with glycerol to re-form triglycerides
Triglycerides are stored in droplet(s) within the cytoplasm of the adipocyte
Release of lipids from adipocytes
Lipids are mobilized from adipocytes in response to:
Hormonal stimuli that promote triglyceride release
Growth hormone (GH)
Thyroid hormone (T3/T4)
Glucocorticoids (cortisol)
Neurogenic stimuli
Norepinephrine (NE) from sympathetic nerve endings stimulates triglyceride release
Liberation of triglycerides from adipocytes into the blood is driven by:
hormones and the sympathetic nervous system
serves to increase lipids/FFAs for cell energy
Hormone sensitive lipase (HSL)
Becomes active when triglyceride release from adipocytes is stimulated
HSL hydrolyzes triglycerides into FFAs and glycerol
FFAs and glycerol diffuse into capillaries for distribution
FFAs are bound to albumin for transport in the blood
What hormones activate HSL?
Thyroid Hormone
Growth Hormone
Epinephrine/Norepinephrine – sympathetic system
Cortisol
Are lipids mobilized uniformly?
Fats in subcutaneous, mesenteric, and retroperitoneal areas are mobilized first
Adipose tissue in hands, feet, and retro-orbital fat pads resist long periods of starvation
Leptin
Protein produced by adipocytes
Regulates metabolism, energy intake and production
Leptin acts mainly in the hypothalamus to?
Decrease food intake (decreases hunger)
Increase energy utilization (liberate FFAs)
General regulation of the amount of adipose tissue in the body
Types of Obesity
Exogenous - caloric intake > caloric expenditure
Endogenous - metabolic cause - < 1% of all cases
Most at risk for obesity
minorities
low income
low education
Consequences of obesity
Hypertension Coronary artery disease Dyslipidemia Stroke – cerebrovascular accident (CVA) Type II diabetes Gall bladder disease Osteoarthritis (OA) Sleep apnea Cancer
Normal body fat content
Males = 11-15% Females = 21-28%
Chronic Activity and Lipid Mobilization
Increased sensitivity of adipocytes to norepinephrine and epinephrine
Allows for greater, more efficient mobilization of fats when stimulated by sympathetic nervous system
Increased use of lipids by chronically trained muscle
Increase capillary/muscle fiber ratio
Increase # of mitochondria
Increase in oxidative enzymes which allow for increased aerobic capacity
