homeostasis Flashcards
Walter Canon and homeostasis
named process by which body maintains a constant internal state
homeostasis
maintenance of an internal environment; tendency to keep the body variable within a set range
set point
single value body aims to maintain
allostasis
adaptive way body changes its set point depending on the situation; maintaining stability via physiological/behavioral processes
- adaptive in short term, usually a reflection in food, water, and shelter availability
- achieved through alterations in HPA axis hormones, ANS, cytokines, or other systems
hunger
motivation to find and inject food
satiety
cessation of eating
energy acquisition
feeding/eating
energy expenditure
burning calories via exercise/metabolism
adipose tissue
excess energy stored as fat
metabolism in a well fed state
- food is broken down into glucose, fatty acids, amino acids
- insulin released from the pancreas to facilitate the transport of glucose (lowers blood glucose levels and stores it)
- excess glucose is converted to glycogen and stored (process occurs in liver, glucose–> glycogen)
glycogen
stored form of sugar in the liver
lipogenesis
creation of fat
glucagon
released from the pancreas to facilitate release of glucose from the liver to increase blood sugar levels
how to raise blood sugar levels without eating
- decrease insulin, increase glucagon
- gluconogenesis: production of glucose from amino acids in the liver
- lipolysis: fat breakdown
- glycogenolysis: breakdown of stored glycogen in liver
type 1 diabetes
insulin dependent diabetes
**B cells of the pancreas are destroyed by the immune system–> no insulin produced at all, so no storage of glucose at all
type 2 diabetes
tissues develop an INSENSITIVITY to insulin (insulin is being produced, but not really doing its job anymore)
- no glucose take-up–> hyperglycemia
- cells insensitive to insulin–> energy deficit–> increase in insulin release
- adipose tissue LAST to become insulin-resistant–> take-up of glucose–> lipogenesis
- **with increasing energy deficit and lipogenesis–> increased appetite, increased food intake, and weight gain
effects of type 1 and 2 diabetes
difficulty moving glucose out of the blood into the tissues
- hyperphagia: elevated appetite
- hyperglycemia: high blood glucose levels
- increased thirst and urination
hyperinsulinemia
too much insulin
- increased glucose uptake, inhibited lipolysis–> decreased breakdown of fats, low blood sugar
- obesity results, people hungry, cannot lose body fat, eating frequently
orexigenic
increases food intake: ghrelin, NPY, AgRP,
anorexigenic
decreases food intake: leptin, insulin, CCK, POMC/CART, a-MSH
leptin
concentrations in proportion of body fat
- elevated leptin: signals hypothalamus that fat stores are high, decreases eating
- lower leptin: signals hypo that fat stores are low, increases eating
anorexia
loss of appetite
aphagia
absence of feeding
high leptin and insulin
feeding inhibitory pathway–> stimulation of CATABOLIC pathway–> decreased eating, increased energy use
low leptin and insulin
feeding stimulatory pathway–> ANABOLIC pathway–> increased eating, decreased energy use
Hypothalamus, feeding stimulatory and inhibitory pathway, PVN/hypothalamic nuclei, hormones
hypothalamus has a feeding stimulatory and inhibitory circuit, both send signals to the PVN and other nuclei of the hypothalamus to modulate feeding behavior
- feeding stimulatory and inhibitory circuits are modulated by hormonal signals that cross the BBB
- leptin, insulin, ghrelin
feeding stimulatory circuit: NPY and AgRP
- NPY: stimulates PVN to evoke feeding behavior–> increased motivation to eat
- AgRP: promotes feeding by BLOCKING melanocortin type 4 receptor (appetite inhibitor)
**under fed state: low levels of L and I–> activation of NPY and AGRP neurons–> increase food intake
once L and I levels are restored, NPY and AGRP inhibited
feeding inhibitory circuit: POMC and CART
increased CART–> decreased food intake
-POMC–> produces a-MSH (acts through melanocortin type 4) to decrease appetite
**elevated leptin and insulin activates POMC/CART–> secrete products into PVN and LHA–> decrease food intake
ghrelin
increases food intake
- opposite effects of L and I
- associated with NPY and AGRP (increase food intake)
adiposity signals communicate with autonomic circuits to mediate food intake
- stomach distention information
- CCK released from duodenum–> signals that food has been digested