Regulation of ECF Volume - Pt 1 Flashcards
What are the major ECF and ICF osmoles?
ECF - Na+ and Cl-
ICF - K+
What is regulation of ECF volume equal to?
Regulation of body Na+
What is the distribution of total body water?
ECF - 14l (1/3) with 3l in plasma and interstitial fluid is 11l
ICF - 28l (2/3)
Total 42l
What does changes in Na content of the ECF lead to?
Changes in ECF volume and will affect volume of blood perfusing the tissues - effecting circulating volume and BP
What is regulation of Na basically dependant on?
High and low pressure baroreceptors
Describe the renal response to decreased ECF volume (hypovolaemia)
Increase salt and H2O loss (vomiting, diarrhoea or excess sweating) - Decreases PV, venous pressure, VR, atrial P, EDV, SV, CO then BP which decreases carotid sinus baroreceptor inhibition of sympathetic discharge
What does increase sympathetic discharge lead to?
Increase vasoconstriction, total peripheral resistance and increase BP towards normal
By increased renin and renal constriction
What does decreased atrial pressure and carotid sinus baroreceptor discharge lead to?
Increase ADH release - may cause hypo-osmolarity
What does increased renin lead to?
Increased angiotensin II - increased proximal tubule NaCl and H2O reabsorption
Increased aldosterone - increased distal tubule NaCl and H2O reabsorption
What is the effect of sympathetic discharge specifically on the kidneys?
Increased renal VC nerve activity then increased renal arteriolar constriction and an increase in renin
What is the effect of increased renin specifically on the kidneys?
Increased angiotensin II - decreased peritubular capillary hydrostatic pressure (increased oncotic pressure) and increased Na reabsorption from proximal tubule so less Na excreted
What are changes in proximal tubule Na reabsorption due to?
Changes in rate of uptake by peritubular capillaries determined by oncotic pressure
greater absorptive forces in peritubular capillaries
What happens to oncotic pressure when NaCl and H2O is lost?
Oncotic pressure forces increase even more than normal so can reabsorb 75% of the filtrate in the proximal tubule
How does GFR remain largely unaffected?
Autoregulation maintains GFR and VC of afferent and efferent means little effect on GFR until volume depletion causes decrease MBP
What 2 things mainly maintain GFR?
Construction of afferent due to to sympathetic VC coupled with angiotensin II mediated constriction of efferent arterioles