Physiology of Obesity/Adipose Tissue

Question 1

differentiate between white fat and brown fat

Answer 1

brown fat is prominent in neonates and important for thermoregulation

white fat is a storage depot for body fuels, visceral fat is metabolically active, and is heterogeneously secreted based on body location

Question 2

describe adipose tissue

Answer 2

1. fat is stored as adipose tissue, a specialized energy organ
2. excess consumed calories are stored in adipocytes
3. lipids are more readily stored and have a greater energy yield (ATP) than other nutrients when broken down

Question 3

how are fatty acids stored? how are they transported? what can they be converted to for use?

Answer 3

stored in adipose tissue as triglycerides, a concentrated energy source with 3 fatty acids each

fatty acids are not water soluble so need special transport systems for travel through blood and lymph

can be converted to ketone bodies for use

Question 4

what are the 3 phased of fuel metabolism?

Answer 4

1. absorptive phase/digestion
2. nutrient utilization/post-absorptive
3. energy deficiency/food deprivation

Question 5

describe the absorptive phase of fat metabolism (4)

Answer 5

1. liver converts glucose to glycogen and triglycerides for storage
2. glucose is converted to fatty acids through glycolysis, and IRREVERSIBLE! process!!
3. fatty acids are then transported to adipose tissue for storage, or to other tissues like muscle for energy
4. since fatty acids are insoluble in blood, insulin activates lipoprotein lipase, which packages fatty acids into VLDL for transport from the liver to adipose tissue for storage

Question 6

describe the nutrient utilization phase of fat metabolism (5)

Answer 6

1. this phase is fundamentally defined as the movement of fuels out of the storage depot for immediate use
2. in this phase, the liver switches from glucose utilization to glucose production in response to decreased insulin production
3. muscles mobilize amino acids to support liver gluconeogenesis (not as important for exam bc muscle not fat)
4. fatty acids are released from adipose tissue, stimulated by hormone sensitive lipase (activated by lack of insulin)
5. fatty acids are released into blood as NEFAs bound to albumin, where they will either be used directly for energy by tissues or by the liver for ketone body production

Question 7

describe the feed deprivation phase of fat metabolism (4)

Answer 7

1. glucose and amino acids are conserved
2. fats and ketone bodies are utilized for energy production via rapid mobilization of adipose tissue fatty acids in the form of NEFAs
3. most NEFAs go to the liver, but some NEFAs can be metabolized by other tissues
4. once in the liver, NEFAs are either (3)
   a. oxidized for energy production (small amount)
   b. esterified into triglycerides for storage in the liver
   c. used to produce ketone bodies that will be sent throughout the body for energy

Question 8

describe ketone body formation

Answer 8

1. occurs in the liver
2. promoted by low glucose availability and high fatty acid supply
3. ketone bodies are transported to peripheral tissues for use
4. ketone bodies will be excreted in the urine if levels get high in blood

Question 9

describe fed state and fasted state

Answer 9

fed state: fatty acids and glucose being deposited into adipose tissue for storage
fasted stage: fatty acids and glycerol being mobilized from adipose tissue for use

Question 10

what are adipokines? name 2

Answer 10

cells within adipose tissue; leptin and adiponectin

Question 11

describe leptin, including its 6 actions

Answer 11

1. leptin is released from adipose tissue proportionally to circulating insulin levels and inversely to circulating glucocorticoid levels
2. release of leptin increases with increased adipose mass
3. inflammatory cytokines also increase leptin production

functions are:
1. body weight control
2. energy balance
3. metabolic regulation
4. reproduction
5. increased cytokine production
6. bone and cartilage growth

Question 12

describe adiponectin, including its 4 functions

Answer 12

circulating levels of adiponectin are inverse to fat mass, so decreased adiponectin with increased fat mass

functions are:
1. insulin-sensitization
2. enhanced insulin secretion
3. anti-inflammatory
4. may increase energy expenditure by CNS

Question 13

what are the big 3 inflammatory cytokines? describe their role generally

Answer 13

TNF-alpha, IL-1beta, and IL-6

still discovering role but thought to encourage inflammatory response of tissues

Question 14

what is the big issue with too much fat, generally?

Answer 14

too much white fat is SUPER pro-inflammatory and bad; if in a chronic inflammatory state, can result in arthritis, renal, cardiovascular, pancreatic, hepatic disease or behavioral changes