Urine is formed via glomerular filtration, reabsorption, and secretion in the nephron. Glomerular filtration is the initial process where plasma is filtered from the renal bloodstream into Bowman's capsule through small pores in the glomerular capillaries. The glomerular filtration rate measures the volume of filtrate produced per unit of time and is a key indicator of kidney function. Filtration occurs due to Starling forces and other factors that allow plasma and solutes but not cells to pass through the glomerular membrane into the filtrate.

1. Urine Formation
Glomerular Filtration
Dr. Amir Bahadur

2. Body Fluids Composition

3. Urine Formation
a)Filtration (Glomerular)
b)Re-absorption
c)Secretion

4. DIAGRAMS/ FIGURES

5. Renal Corpuscle
Glomerulus+ Bowman’s Capsule

6. CUT through NEPHRON

8. a). Glomerular Filtration
Concepts of following are necessary
Renal Blood Flow (RBF)
Renal Clearance
Glomerular Filtration Rate (GFR)

9. 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

10. 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

11. 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

12. 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

13. 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

14. Starling Forces

15. 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

16. GFR---other factors
• Pores/ fenestrations in capillaries
endothelium
• Negative charge on basement membrane of
bowman’s capsule
FILTRATE is plasma and solutes without cells.