Biology of Obesity: Adipose Tissue Function Flashcards
What determines the number of fat cells & their distribution
Genetics
When does they number of fat cells stay set?
In adulthood.
Can increase in number, but once developed stay forever.
Can you reduce they number of fat cells in your body?
No, you can shrink the cells but not decrease the number of them.
define cellulite
Fat deposited beneath the skin
Due to genetic deposition
functions of adipose tissue (7)
- cell membrane (structure/flexibility)
- energy production/energy reserve
- lipoproteins (transport & deliver)
- organ protection
- thermal regulation
- carrier for vitamins (ADEK)
- nerve insulation
where is fat stored
adipocytes, released when needed
how is fat stored inside of adipose
Triglyceride/triacylglycerol
What happens when energy is low
- insulin drops, epinephrine rises
-epiniphrine binds to the adipocyte and causes lipolysis
-increase in energy demand, the fatty acids and glycerol can leave the adipocyte and enter the blood
-uptake and oxidation in tissues (sk. muscle tissue) generate energy to meet increased demand
What happens after eating
-insulin keeps the fatty acids inside the adipocyte
-if eating frequently, and consume foods higher in carbohydrate then insulin levels stay high
what are the 2 types of adipose tissue
- white adipose tissue (WAT)-energy storing
- brown adipose tissue (BAT)- energy burning
amount and distribution of adipose tissue depends on what (3)
age, species, biological sex
characteristics and function of brown adipose tissue (3)
-many mitchocondrial (produce heat thermogenisis)
-more blood vessels (give colour)
-more metabolically active (relative to white)
who tends to have BAT opposed to WAT
infants, slender and younger women.
Lower amount in people with increased BMI & increased BF%
characteristics & function of WAT (4)
-actually yellow
-primary site for energy storage and release of hormones that modulate metabolism and insulin resistance
-provides cushioning & insulation
-subcutaneous and viscreal
characteristics & function of subcutaneous adipose tissue (SCAT) 4
-located just under the skin throughout the body
-represent the majority of our total body fat mass
-main source of energy
-general indication od substrate availibility for physical work. When depot becomes full fat must be stored eslewhere
characteristics & function of viscreal adipose tissue (VAT) 4
-located in and around viscreal organs
-stored fat as a result of SCAT depots being full
-genetics play a role in fat distribution patterns
-fat in this area is pro inflammatory
how does adipose tissue regulate metabolism
secretes hormones that are signals percieved by the brain as important indicators of energy stores (impacts appetite, food intake, nutrient absorption & energy expenditure)
what is caloric intake controlled by
appetite (hypothalamus)
what is calorie use controlled by
metabolic rate (thyroid hormones/ physical activity levels)
where are calories stored
adipose tissue
what is the role of the hypothalamus
directs bodily functions; the brains control centre for energy balance
define hedonic & homeostatic hunger
homeostatic- physical ques of hunger
hedonic- hunger from external ques (social/emotional/environmental/situational)
define appetite, satiety & satiation
appetite- desire for particualr food
satiety- feeling of being full after eating
satiation- feeling satisfied after eating
what happens during homeostatic regulation
-hypothalamus recieves signals from periphery
-input from GI, brain & adipokines
-output via motor neurons to GI, etc.
-this stimulates/inhibits hormone release from various areas of the body
hormones that stimulate feeding
-Ghrelin- released mainly from stomach. peaks before a meal. Stimulates appetite and eating
-Glucagon- Released from pancreas when blood glucose falls, indirectly activates feeding (glucagon increases, insulisn decreases and vice versa)
what 2 effects happen during short term regulation of food intake
- GI filling inhibits feeding
-distended stomach, stimulates stretch receptors, vagus nerve send inhibitory signals to hypothalamus to suppress feeding centres= reduced appetite - Food in mouth signals oral receptors, signals to hypothalamus= reduced appetite (less intense & shorter than GI filling)
what hormones suppress appetite (3). Where to they secrete from and what macronutrient stimulates their release?
- Cholecystokinin(CCK): released from duodenum in response to fats & proteins. Cause hypothalamus to reduce appetite.
- Glucagon like peptide 1 (GLP-1): Released from lower small bowel in response to carbohydrates. Stimulates insulin release. Lowers glucagon.
- Insulin: Released from pancreas when blood glucose rises.
what regulates long term regulation of food intake (2)
- Nutrients- more glucose, AA, fatty acids available= decreased appetite
- temperature regulation- cold= increased feeding, mediated by metabolic rate
feedback signals of long term (intermediate) regulation of food intake
- decreased blood glucose=increased appetite
-increased blood letoacids, signals hypothalamus satiety centre increases feeling of fullness
-adipose secretes hormones= more leptin released from adipose tisse to blood
-leptin binds to receptors in hypothalamus to suppress appetite and food intake and decrease insulin release from pancreas
What is leptin & its function
-hormone released from adipocytes
-regulates processes relevant to energy homeostasis (food intake, energy expenditure, activity, reproductive functions)
-role in defending against excessive body fat.
-extreme obesity happens when they fail to excrete leptin/don’t express the leptin receptor
what does leptin do in short term and long term body weight regulation? (starvation & increased energy)
starvation: loss of body fat, adipose is critically low, decrease in leptin results in increase of food intake and decrease in EE/cessation of reproductive function & somatic growth to conserve energy
consumption: increased energy consumption and accumulation of body fat stores, leptin increases with subsequent decrease in food and increase in sympathetic NS, tone & EE
Role of leptin in body weight regulation
tells the brain how much fuel in reserve
-as BMI/body weight drops so does leptin
what happens with leptin deficency
Mice & Humans- hyperphagia (abnormally excessive eating- very rare in humans), obesity, impaired thermogenisis, hyperinsulinemia, hyperlipidemia. Humans also have high plasma leptin (mice do not)
How can leptin be high in cases of obesity? (3)
-leptin resistence caused by hyperleptinemia
-possible that food intake is altering ability of the leptin to impact energy regulation
-possibly that leptin was designed primarily to detect periods of energy depletion (negative energy balance) rather than the other extreme.
“can we shed weight or shed fat?”
Talk about: liposuction, ozempic (GLP-1 agonist), lifestyle change.
- liposuction- Few metabolic health gains, could help to now improve on lifestyle change. Liposuction takes away the subcutaneous fat, not viscreal fat (will make no change metaboliczally)
- GLP-1 agonist- will also cause muscle loss, other medication side effects to deal with, cost
- Lifestyle change- shrinks existing fat cells.
can we shrink existing fat cells?
Yes, it is difficult because it is easy to add more to the fat cell to allow it to grow than it is to decrease the amount of fat in the cell.
what are 2 parts to Deposition of fat & what drives the deposition process
- De Novo Lipogenesis- making of new fat cell. Occurs in adipose tissue and liver
- Re-Esterification- storing fat that is already made
Insulin drives the process (inhibits lipolysis)
What are some ways to break chronically high levels of insulin (6)
- reduce amount of carbohydrates
- fasting/time restricted feeding
- fixing high cortisol levels
- improving sleep
- exercising
- all of the above
