Urine FormationGlomerular Filtration
Dr. Amir Bahadur
Body Fluids Composition
Urine Formation
a)Filtration (Glomerular)b)Re-absorptionc)Secretion
DIAGRAMS/ FIGURES
Renal CorpuscleGlomerulus+ Bowman’s Capsule
CUT through NEPHRON
a). Glomerular Filtration
Concepts of following are necessary
Renal Blood Flow (RBF)Renal ClearanceGlomerular Filtration Rate (GFR)
Renal Clearance
• Volume of plasma cleared of any substance in per unit time
• C= UV/P C is renal clearance U is urine concentration V is volume of urine Plasma concentration
RENAL BLOOD FLOW
• 25% of cardiac output• Increased with increased pressure difference
between renal artery and vein and reduced renal vascular resistance
• Decreased--- vice versa • Vaso-dilators and vaso-constrictors effect
RBF• Auto-regulated over wide range of pressures
RBF---Auto Regulation
i. Myogenic mechanism---- afferent arteriole stretch, resistance increased, RBF reduced and maintained.
ii. Tubulo-glomerular Feedback----- increased RBF, increased fluid in DCT, macula densa detects increased pressure, vascular resistance increased, RBF and maintained
RBF---- Auto regulation
iii. Neural Regulation: Sympathetic flow, vasoconstriction of afferent arterioles, regulate RBF
iv. Hormonal Regulation: JG cells, renin, angiotensin II, vasoconstriction of efferent arteriorles
Glomerular Filtration Rate (GFR)
• Filtrate through glomerulus in unit time • Important predictor of nephron function• Normal is 120mL/min• Many factors causing changes in GFR but
kidneys optimize.• Starling forces at bowman’s capsule & other
factors for filtration
Starling Forces
GFR---Starling Forces
• Glomerular hydrostatic pressure• Glomerular oncotic pressure• Bowman’s hydrostatic pressure• Bowman’s oncotic pressure
Net filtration is in to the bowman’s capsule
GFR---other factors
• Pores/ fenestrations in capillaries endothelium
• Negative charge on basement membrane of bowman’s capsule
FILTRATE is plasma and solutes without cells.