Flashcards in MCP 9 Deck (20)
how to define and measure obesity?
waist to hip ratio
waist to height ratio
body shape index
why is obesity a problem?
-risk factor for development of type 2 diabetes mellitus
-obstructive sleep apnea
- joint diseases, gallbladder disease, reproductive disorders, 20% of cancer deaths
genetic causes of obesity
polygenic: product of many genes are involved in controlling body weight
environmental causes of obesity
diet, exercise. consequence of industrial revolution
regulation of weight around a set point. set point is determined by genetic factors and can be reset by environmental factors leading to weight gain.
1. a signal that monitors fat stores: leptin (made by adipocytes)
2. a sensor: brain cells in hypothalamus express leptin receptors
3. effector systems: hypothal centers influence energy intake and expenditure by releasing effector molecules
wild type ob gene
encodes a protein, leptin, produced and released by adipocytes. highly conserved in many vertebrate species. ob mutation results in truncated inactive protein. ob/ob mice behave as if starved, causing an increase in weight and body fat
wild type db gene
encodes for the leptin receptor. db/db mice dont produce the receptor. mutation results in a defective receptor
injections of leptin into ob/ob mice
decreased feeding and body weight, increased energy expenditure
how does leptin work?
acts on CNS to trigger food intake and energy utilization. reduces production of orexigenic effectors made by AgRP neurons. increases production of anorexigenic effectors by POMC neurons
integration of short, medium, and long term signals
ghrelin, cholecyskinin, and PYY act as short and medium term signals to influence appetite and energy expenditure. agonists and antagonists of these signals may be developed as potential drugs for weight control
in most obese people, the leptin level is high, suggesting that the person is insensitive to leptin. leptin resistance limits the wide use of leptin as a drug to treat obesity
5 main components of energy expenditure
1. resting energy expenditure, or BMR
2. energy expended in digesting, metabolizing, and storing food
3. volitional exercise: mechanical work and thermal effect
4. nonexercise activity thermogenesis
5. adaptive thermogenesis
facultative. shivering in response to cold exposure. non-shivering is subject to regulating by brown fat tissue
white fat cells
for fat storage and body insulation
brown fat cells
for heat production. rich in mitochondria and express high levels of uncoupling protein, UCP1.
beige fat cells
white adipose tissue that has been partially converted to brown fat. increased number of mitochondria and UCP1
dissipates energy during thermogenesis in brown fat tissue. leaks protons of the electrochemical gradient without being coupled to ATP production. process is called adaptive thermogenesis, or non-shivering thermogenesis. the energy is released as heat without being coupled to ATP synthesis
BAT presence inversely correlates with BMI. UCP1 promotes re entry of protons into mitochondrial matrix, generating heat. fatty acid-proton symporter is activated by fatty acids. UCP1 expression can be controlled in many ways
polygenic inheritance of tendency to obesity
40-70% of body variation is due to genetic factors. a few families with defects in leptin, leptin receptor, and MC4R receptor identified. no common mutations identified yet.