February 9, 2010

Hypothalamus- autonomic nervous system. Controls parasympathetic (gut control, decreases heart rate) and sympathetic (epinephrine, raises blood pressure and heart rate).

Hormone-> any chemical released into the extracellular environment which is usually the blood plasma = hormones then act on selective cells to alter homeostasis. Selective cells express receptors for the hormones.

Homeostasis= physiological equilibrium. Or, as defined by our professor: efficient reaction to the env. to maintain cellular function (life!)

Hormones released by the hypothalamus, plus the neural connections, provide motivation for a variety of bhv.
A) Temp= set point = balance ----------->
B) Fluid Balance
C) Energy Balance- appetite

Temp --> set point => HOT- hyperthermia or COLD- hypothermia both used in homeostasis.

endoderms=> internal temp regulation (e.g. sweating, panting, licking nose, spreading of wings/ears, all an evaporation process.

Vasodilation- the increase of blood flow to peripheral tissue. Blood flow is the primary mechanism for temp set point. To regulation temp through metabolism, the hypothalamus uses TRH (Thyroid Releasing Hormone)

TRH->Thyroid->T3 +T4+hyroxine-> cells increase metablolism

Brown fat is an uncoupling protein.

Fever=>disease increase Temp=> increase the fluid in the interstital space.

Interstital space= extracellular environment increases immune response.

Hyperthermia = death

Hypothermia = loss of conciousness -> death

Fluid balance pertains mostly to water

Intracellular 67%
Extracellular 33%

A)Interstitial fluid ----- 25%
B)Blood --------------- 7%
C) Cerebral Spin. Fluid - 1%

hormones usually travel in blood stream, but ultimately most go to interstitial fluid -> cells

Within the Hypothalamus fluid balance is regulated by osmosis (diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration, also called diffusion). In this example, the water cannot pass through the lining of this tube, but can pass through the Na+ and K+ channels easier.

Kidneys work by moving Na+ and H2O to make urine. Sooo..... where Na+ goes, H2O follows.

Kidneys regulate or retain H2O based on hormones from hypothalamus, Neuropeptide vasopressin (ADH)

ADH- anti-diuretic hormone. Diuretic increases urine volume. Why release ADH in terms of blood volume? Capillaries shrink to increase blood pressure.

ADH causes the kidney to release Renin= a protein that is an enzyme that acts as a circulating hormone angiotensinogen (At) -> to make At I another At converting enzyme (ACE). Both AtI and At I. (ACE inhibitors are the best of blood pressure meds)

At II is going to
1) increase blood pressure by reducing capillary volume
2) initiate feedback loops (i.e. reflex arc)
a)brain-subfornical organ (SFO): situated on the ventral surface of the fornix, at the foramen of Monro, is one of the circumventricular organs of the brain.
b) adrenal gland- Aldosterone-> retains Na+

In relation to thirst:
Hypothalamus-> bloodstream (ADH)-> Kidney-> Feedback (brain)-> hypothalamus indicating "You need a drink"

SFO is a circumventricular organ (CVO)- a location where blood/brain barrier contains a window of various thickness different CVO's have different permeability to hormones.

AtII H2O Balance CVO monitor whats in our blood
1) Hypothalamus 1) hormones
2) Motor Output 2) chemicals (sugar, H2O, etc.)

CVO= area portrema with in the medulla (on the floor of the VI ventrical) ->Blood -> CSF
Area postrema connects to the nucleus tractus solitarius (NTS).

See fig 9-10 for Neural Connectivity of the Hypothalamus