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.