Download Hypothalamus and Homeostasis

Hypothalamus and
Homeostasis
PSY391S
March 13, 2006
John Yeomans
Hypothalamus Functions
• “We are the accumulation of mechanisms that
allowed our ancestors to survive and reproduce
their genes” (Sagan)
• Hypothalamus is an accumulation of tiny nuclei
for survival and reproduction.
• Hormones and neural signals to and from
viscera.
• Motivated behaviors to respond to internal
challenges.
• Homeostasis maintains internal environment.
Reproduction changes environment.
Hormonal and Neural Signals
• Hypothalamus controls pituitary hormones
acting on many organs.
• Hypothalamus receives hormonal inputs
by way of circumventricular organs.
• Hypothalamus coordinates neural and
hormonal signals for visceral control
(Autonomic NS) and motivated behaviors.
• Hypothalamus receives neural inputs from
descending limbic/olfactory systems and
ascending taste/visceral systems.
Posterior Pituitary
Hormones to Brain
• Blood-brain barrier (glia surrounding brain
vessels) prevents entry of large molecules
in most brain regions.
• Leaky capillaries in 6 tiny nuclei near
ventricles allow entry of hormones.
• Circumventricular organs have receptors
for many circulating hormones (e.g. leptin,
angiotensin II, gonadal hormones).
Circumventricular Organs
Subcommissural
organ
Arcuate N.
Posterior Pituitary
Endotherms
• Birds and mammals control body
temperature near 37ºC.
• Advantages: Constant physiology, better
brain function, bigger brains, and
adaptation to extreme environments.
• Costs: More insulation needed (fat,
feathers, fur), more energy needed, more
internal controls.
Temperature Control Systems
Temperature
Hypothalamus maintains
temperature best.
Fluid Regulation
• Body made up of ~65% H2O, for cell
chemistry, and for movement of nutrients
and cells (e.g. blood and lymph).
• Salt concentration maintained at 0.9%.
• Intracellular and extracellular
compartments separated by
semipermeable membranes that control
ions and other chemicals.
Water and Salt Regulation
Thirst
Water Loss:
respiration,
sweating,
urination,
defecation,
bleeding.
Salt loss.
Water Intake:
drinking,
feeding,
Salt content.
Renin-Angiotensin
14 AA
Blood
Kidney
10 AA
8 AA
7AA
Adrenals
Neural control
of blood pressure
Behavioral control
of water and salt.
Hormonal control of
blood pressure and tonicity
Vasoconstriction &
H20 reuptake in kidney
Energy Sources
•
•
•
•
•
•
•
Carbohydrates-->Glucose
Proteins-->Amino acids
Fats-->Fatty acids
These are stored in the body:
Fat cells (long-term) 80-90% of total
Muscle and liver glycogen (starch)
Blood glucose, fatty acids and amino
acids. (short-term)
• Ketones used if blood glucose low.
Insulin and Glucagon
• Pancreas hormones made by beta and
alpha cells of Islets of Langerhans.
• High blood glucose activates insulin; low
blood glucose activates glucagon.
• Insulin activates transport of glucose into
body cells (not brain).
• Glucagon converts glycogen into glucose.
• This keeps blood glucose levels stable.
Brain Energy
• Uses glucose and O2 only (Ketones in
starvation).
• Does not need insulin so always gets
glucose.
• Brain uses over 20% of glucose and O2.
• Fainting helps brain get these when blood
pressure drops.
Feeding and Obesity
John Yeomans
PSY391S
March 15, 2006
Hypothalamus and Feeding
Brain Lesions and Stimulation
• LH and PVN lesions--> less eating;
VMH and arcuate lesions--> more eating.
• LH stimulation-->eating; VMH-->aversion.
• PVN-->NPY and NE increases feeding;
5HT decreases feeding.
• Therefore, LH and PVN for feeding, VMH
for satiety.
ob/ob or db/db mice
-
(-/-)
(+/+)
Leptin and Obesity
• ob/ob and db/db mice are obese, and eat
fats as if starving.
• ob/ob mice have mutation in leptin gene.
• Leptin is peptide produced in fat cells in
proportion to size.
• db/db mice have mutation in leptin
receptor gene.
• Leptin receptors in arcuate n. and LH.
Short-Term Feeding Signals
• Taste and smell (accept or reject).
• Stomach--ghrelin, distension, vomiting
(area postrema).
• Intestines, pancreas, gall bladder-hormones (CCK, insulin, PYY3-36),
• Liver-->vagus to N. Solitary Tract, area
postrema-->parasympathetic and
sympathetic.
• Hypothalamus--hormone receptors, neural
systems, motivated behaviors.
Human Obesity
• Starvation-->hunger, depression and poor
health. Exercise healthier, but harder.
• Surgery--liposuction, stomach resection.
Still hungry.
• Leptin insensitivity. Leptin is high, but
hypothalamus doesn't respond.
• Serotonin (fenfluramine, SSRIs) works, but
has side effects.