GFR 1 Composition Similar to plasma no proteins

GFR 1. Composition: Similar to plasma (no proteins no RBCs), less Ca++ and fatty acids (because partially bound w/proteins) 2. Glom. Capill. Membrane: 3 layers, endo, basement , and epith (podocyts) 500 x more filtration: a) small holes (fenestra) in endothelium b) Basement w/collagen and Proteoglycan (-) c) Slit - pores in podocytes (epithelium (-))

Filtration fraction (FF) = the fraction of the renal plasma flow that is filtered about 20% of plasma flow FF= GFR/Renal plasma flow

Filterability depends on size and charges GFR = Kf x Net filtration pressure Kf: Filtration coefficient is a measure of the product of the hydraulic conductivity and surface area of glom capill. ml/min/mm. Hg Net filtration pressure = Glomerular hydrostatic pressure = Bowman's capsular pressure = Glomerular oncotic pressure 60 - 18 -32 = 10 mm. Hg

Kf: a measure of the product of the hydraulic conductivity and surface area of glomerular capillaries Kf = GFR / Net filtration pressure Kf=125 /10 =12. 5 ml/min/mm. Hg Kf= 4. 2 ml/min/mm. Hg/100 gm of kid Kf=0. 01 ml/min/mm. Hg/100 gr in other tissues

Factors affect GFR • 1. ^Glomerular capillary filtration coefficient ^ GFR. • Chronic uncontrolled hypertension & DM decrease coefficient and GFR (increase thickness of glomerular cap basement memb) • 2. ^Bowman's capsule hydrostatic pressure decreases GFR stones

3. ^ Glomerular capillary colloid osmotic pressure decreases GFR: 28 to 36 average 32 mm. Hg and this pressure is determined by: a. Arterial plasma colloid osmotic pressure b. Fraction of plasma filtered (filter. Fraction)

4. ^Glomerular capillary hydrostatic pressure increases GFR : this pressure is determined by: a. Arterial pressure b. Afferent arteriolar resistance c. Efferent arteriolar resistance this has biphasic effect: Moderate ^GFR Severe decreases GFR

Renal blood flow and GF Controled by Renal blood flow: 1200 ml/min 21% C. O 1 -2% in vasa recta O 2 consumption by the kid mainly related to active Na reabsorption by renal tubules. • 1. Sympathetic N. S : Strong activation decreases GFR and flow as hemorrhage and CNS ischemia • Moderate activation : little effect (normal person)

RENAL BLOOD FLOW = RAP-RVP / Total renal vascular resistance

2. Hormonal and autacoid: a. Norepinephrine , epinephrine, endothelin constrict renal blood vessels and decreases GFR b. Angiotensin II constricts efferent arterioles ^GFR - ^Na and H 2 O reabs. (not the afferent) c. Endothelial - Derived Nitric oxide decreases resistance and ^ GFR d. Prostaglendins, bradykinin cause vasodilators

3. Autoregulation of GFR and Renal blood flow : • Arterial pressure 75 - to 160 mm. Hg changes GFR very few%. • 180 L/day if pressure ^ by 25% so GFR - 225 L/day. If reabsorption constant so urine 46. 5 L/day. • Autoregulation and ^ or adaptive changes in reabsorption will not cause significant increase in urine output (pr. Diuresis) or (pr. Natriuresis).

Tubuloglomerular feedback: 1. Afferent arteriolar feedback mechanism 2. Efferent arteriolar feedback mechanism Juxtoglomerular complex: Macula densa cells ( prox distal tubule) Juxtaglomerular cells (in the wall of eff & aff arterioles) decrease [Na. Cl] stimulate macula densa : • 1. Dilates afferent • 2. Releases renin(from glom. Cells) ang. I- Ang. II Constricts efferent.

4. Myogenic autoregulation : When arterial pressure ^---) contracts vessels & prevent increase renal blood flow. 5. Other factors : 1. A. ^ Protein intake ^ blood flow and GFR ^ a. a reabsorption w/Na decreases Na autoreg by stimulate macula densa to dec aff art and so incr RBF & GFR B. ^Blood glucose: same mechanism.