Mastering Water Intake and Body Fluid Control

Fluid Regulation and Hormones

• The organ that detects plasma hyperosmolarity and informs AVP-secreting cells in the hypothalamus is the circumventricular organ.
• The hormone responsible for increasing water permeability in the collecting ducts of nephrons is vasopressin (AVP).
• The hormone synthesized in the heart atrial that leads to the excretion of NaCl by the kidney is atrial natriuretic peptide (ANP).

Diabetes Insipidus

• The typical symptom of diabetes insipidus, a condition characterized by impaired secretion of AVP, is excessive thirst and polyuria.

Hypovolemia Response

• The main reaction of the body to hypovolemia (loss of blood volume) is the stimulation of vasopressin (AVP) secretion.

Hormone Regulation

• The hormone that acts on the SFO to stimulate AVP secretion is angiotensin II.
• The hormone that stimulates aldosterone in the adrenal cortex, which helps retain NaCl by the kidney, is angiotensin II.
• The main effect of the renin-angiotensin system in response to a drop in blood pressure is the vasoconstriction of arterioles and the stimulation of aldosterone secretion.

Thirst Response

• The stimulus that initiates the thirst response in the body is the detection of plasma hyperosmolarity by the circumventricular organ.

Fluid Movement

• The channels in the plasma membrane that regulate the movement of water are aquaporins.
• The movement of fluids in the body is from an area of high hydrostatic pressure to an area of low hydrostatic pressure.
• The direction of fluid flux in the body is determined by the difference in hydrostatic pressure between the capillary and the interstitial fluid.
• The role of interstitial fluid in the body is to facilitate the exchange of nutrients and waste between the capillary and the cells.

Fluid Composition

• The main difference between intracellular fluid (ICF) and extracellular fluid (ECF) is the concentration of electrolytes and solutes.
• The hydrostatic pressure of blood is determined by the pumping action of the heart and the resistance of the blood vessels.

Blood Pressure Regulation

• The main force affecting the distribution of fluids across capillary and tissue is the hydrostatic pressure of blood.
• The colloidal osmotic pressure of blood affects fluid movement in the body by attracting water into the capillary and opposing the hydrostatic pressure.
• The role of hydrostatic pressure in fluid movement in the body is to push fluid out of the capillary and into the interstitial fluid.
• The role of osmotic pressure in fluid movement in the body is to attract fluid back into the capillary and balance the hydrostatic pressure.