Regulation of ECF Volume and Osmolarity

Regulation of ECF Volume and Osmolarity

Na+ and Cl- are most abundant ions in ECF consequently. Increase NaCl content of ECF causes changes in ECF volume.
Two control system operate in association to regulate ECF, Na+ concentration and osmolarity.
1. Osmosodium Receptor (ADH feedback system):
Osmoreceptor located in supraoptic nuclei of hypothalamus are sensitive to slight increase in osmolarity of interstitium. Thus when there is low osmolarity (low solute content). There will be osmosis of water into these receptor causing their swelling, decrease rate of ?????? discharge causing posterior pituitary to stop releasing ADH eventually causing decrease permeability of distal tubule, collecting tubule, collecting duct ? decrease water reabsorption, increase secretion of diluted urine and reverse is true.
2. Thirst:
Any factor cause increase dehydration causes thirst sensation, most common cause increase osmolar concentration of ECF which causes osmosis of fluid from neural cells of thirst center.
3. Atrial Natriuretic Factor (Peptide):
Hormone secreted by right atrium whenever blood pressure in right atrium increase. It exert hormonal influence on kidney. Its release causes:
1. Inhibition of rennin and aldosteron secretion.
2. Dilate arteries and veins, reducing peripheral vascular resistance, lower blood pressure.
3. Inhibition of ADH secretion, lead to production of large volume of diluted urine.