Hunger, Thirst, Homeostasis Flashcards
Homeostatic systems
use our behavior to keep things balanced
Negative feedback
systems are the main homeostatic mechanisms
If a desired set point is deviated from, compensatory action begins
Hypovolemic thirst
stimulated by low extracellular/intravascular volume
Triggered by loss of water volume – concentration is not changed
Baroreceptors in blood vessels and heart detect the initial drop
Brain activates thirst and salt craving
Arteries constrict to raise BP
Osmotic thirst
stimulated by high extracellular solute concentration
Hypovolemia
causes release of vasopressin (antidiuretic hormone) – induces blood vessel constriction and reduces flow to the bladder
diabetes insipidus
vasopressin is not produced – kidneys send more urine to the bladder, resulting in chronic thirst
Angiotensin (II) Cascade
With decreased blood volume, kidneys release renin, which triggers formation of angiotensin II
angiotensin II:
1)blood vessels constrict
2)circumventricular organs trigger drinking
3)vasopressin is realeased
4)aldosterone is realeased
Circulating angiotensin II acts in the subfornical organ to send a signal to other brain sites to initiate drinking
Osmosensory neurons
reside in anterior hypothalamus (OVLT)
respond to rise in blood osmotic pressure
cell membranes shrink, opening mechanical-gated Na+ channels
in hypothalamus, respond to increased osmotic pressure causing the pituitary to release antidiuretic hormone
Diet
At the start of a diet, the basal metabolic rate will fall – to prevent losing weight
Glucose
the principal sugar used for energy
Glycogen
glucose stored for short term in the liver
Glycogenesis
converting glucose to glycogen, using pancreas hormone insulin
Lipids
fat tissue for longer-term storage
leptin
produced by fat cells and secreted it into the bloodstream
Defects in leptin production or sensitivity give a falsely low report of body fat, causing animals to overeat
Leptin inhibits secretion of AgRP
Ghrelin
Released by stomach endocrine cells (Appetite stimulant)
Rises during fasting; drops after eating
Some obese people have elevated ghrelin levels
Prader-Willi syndrome
genetic disease that causes a sense of never being full or satisfied
Ghrelin levels are elevated in Prader-Willi
Lateral hypothalamus (LH) lesions
refusal to eat
LH-lesioned animals stop eating, but will resume and stabilize their weight at a new, lower level
Ventromedial hypothalamus lesions
cause obesity
VMH-lesioned animals exhibit overeat until they become obese
Increased weight stabilizes - this weight is maintained even after food manipulations
NPY/AgRP neurons
produce neuropeptide Y and agouti-related peptide
stimulate appetite and lower metabolism -> weight gain
POMC/CART neurons
produce pro-opiomelanocortin and cocaine- and amphetamine-related transcript (CART)
inhibit appetite and raise metabolism -> weight loss
Anorexia Nervosa
Refusal to maintain body weight
Fear of weight gain
Body image disturbance
Amenorrhea
Restricting or Binge-Eating/Purging type
0.5% lifetime prevalence in women (.05% in men)
Other symptoms of anorexia
thinning of the bones
brittle hair and nails, dry and yellowish skin
mild anemia, muscle weakness and loss, lethargy
severe constipation
low blood pressure, slowed breathing and pulse
drop in body temperature
Bulimia
Recurrent binge eating
Recurrent inappropriate compensatory behavior
At least 2x/wk for 3 months
Eating Disorders Occur with Other Psychiatric Conditions
Women with Anorexia or Bulimia 40% Childhood anxiety disorders 20% Obsessive compulsive disorder 30% Abuse alcohol or drugs 90% Depression 246 Women with an Eating Disorder: 30% Attempted suicide 5% Died
Treatment of Obesity
Eat less: A daily deficit of 500 to 1000 calories is reasonable. This is the most important part of therapy and most difficult to do.
Modify behavior to avoid temptation to pig out. This means lifestyle change. Self-monitoring and social support are essential.
Exercise. A lot: Strenuous aerobic activity for over 200 minutes per week maintained for a long time with calorie restriction works.
treating obesity as an addiction
Obese people share several characteristics with addicts:
They have reduced numbers of dopamine D2 receptors and associated decrease in prefrontal metabolism
Peptides that induce eating target dopamine neurons
Anti-addiction drugs are somewhat effective in weight loss
Obesity and Reduced Metabolism
Basal metabolic rate (BMR):
energy required to fuel the brain/body and maintain temperature
75% of energy expenditure in average sedentary student
Of women on a diet, the 1/3 who failed to lose weight had low BMRs
Heredity accounts for 40% of a person’s BMR. But, spontaneous activity can increase it
Gastric bypass surgery
Weight loss averages 25% and is long-lasting (compared to 5%-10% with dieting and relapse within a year)
Reduces ghrelin and increases PYY and GLP-1, reducing hunger
Reduces mortality and has many health benefits
In a survey of students in grades 5-8, _____% were dieting and _____% were fasting.
30, 10
The anterior pituitary produces _____.
growth hormones
The posterior pituitary produces _____ and _____.
ADH, oxytocin
