glomerular function

7/31/2019 Glomerular Function

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GLOMERULAR FUNCTION


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Internal structure of the kidney


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Blood supply of the kidney : 21% of the cardiacoutput = 1200 ml/mnt


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Arcuate artery

Arcuate vein

Thin ascending limbof the loop of Henl

Thick ascending limbof the loop of Henl

Distal convoluted tubule

Proximal convolutedtubule

Collecting duct

Descending limbloop of Henl

Vascular supply to the nephron

Vasa recta

Glomerulus Afferent arterioleEfferent arteriole


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Proximalconvoluted

tubule

Capsulespace

Efferent arteriole

PedicelPodocyte

Endotheliumof glomerulus

Afferent arteriole

Juxtaglomerularcell

Parietal layer of glomerular capsule

Structure of the Bowmans (glomerular) capsule


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Stellate cells called mesangial cells are locatedbetween the basal lamina and the endothelium.

They are similar to cells called pericytes, whichare found in the walls of capillaries elsewhere inthe body.

Mesangial cells are especially common betweentwo neighboring capillaries, and in these locationsthe basal membrane forms a sheath shared by both capillaries (Figure 38 2).


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The mesangial cells are contractileand play a role in the regulation of glomerular filtration.

Mesangial cells secrete theextracellular matrix, take up

immune complexes, and areinvolved in the progression of glomerular disease.


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Formation of Urine

Involves three main processes: 1.Filtration 2.Reabsorption 3.Secretion


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Filtration membrane

Is composed of three layers:

1. fenestrated glomerular endothelium

2.basement membrane

3.filtration slits are formed by the pedicels of the podocytes

Substance are filtered are on the basis of size and/or electrical properties


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Glomerular Filtration Membrane

Insert fig. 17.8


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Glomerular Filtration Membrane Endothelial capillary pores are large fenestrae. 100-400 times more permeable to plasma, H 20, and dissolved solutes

than capillaries of skeletal muscles. Pores are small enough to prevent RBCs, platelets, and WBCs from

passing through the pores.


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Glomerular Filtration Membrane Filtrate must pass through the basement membrane:

Thin glycoprotein layer. Negatively charged.

Podocytes: Foot pedicels form small filtration slits. Passageway through which filtered molecules must pass.


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The filtration barrier - podocytes

fenestratedendothelium

fenestratedendothelium

primary process

podocyte cell body secondary

process

(pedicel )

filtration slit

basallamina

podocyte

pedicel filtrationslit basal

lamina


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The filtration barrier - pedicelsBowmans

space

capillary

pedicel

filtrationslit


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Common component of the glomerular filtrate Organic molecules: glucose,amino acids Nitrogenous waste: urea, uric acid, creatinine Ions: sodium, potassium, chloride

Rumus tekanan filtrasi

Kf, the glomerular ultrafiltration coefficient, is the product of theglomerular capillary wall hydraulic conductivity (ie, its permeability)and the effective filtration surface area.

PGC

is the mean hydrostatic pressure in the glomerular capillaries, PT

the mean hydrostatic pressure in the tubule (Bowmans space), GC the oncotic pressure of the plasma in the glomerular capillaries, andT the oncotic pressure of the filtrate in the tubule (Bowmans space).


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Forces affecting filtration

Glomerular hydrostatic pressure (blood pressure) promotesfiltration=55 mmHg

Capsular hydrostatic pressure opposes filtration=15 mmHg

Glomerular osmotic pressure opposes filtration=30 mmHg Net filtration pressure =

55 (15+30) =10 mmHg


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Glomerular filtration rate

The total amount of filtrate formed by the kidney perminutes

Sekitar 20% dari renal plasma flow

Nilai GFR ditentukan oleh: (1) keseimbangan antaratekanan hidrostatis dan osmotik (2) filtrationcoefficient kapiler (Kf) yaitu permeabilitas dan area

permukaan filtrasi GFR normal 125 ml/min, atau 180 L/day.


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Autoregulation Mechanism

To counteract changes in GFR

Myogenic mechanism Increased systemic pressure: Autoregulation: afferent arteriole diameter decreased

(constricted) to maintain the GFR Decreased systemic pressure: Autoregulation: afferent arteriole diameter increased

(dilated) to maintain the GFR


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Qualities of agents to measure GFR Inulin: (Polysaccharide from Dahalia plant)

Freely filterable at glomerulus Does not bind to plasma proteins Biologically inert Non-toxic, neither synthesized nor metabolized in kidney Neither absorbed nor secreted Does not alter renal function Can be accurately quantified Low concentrations are enough (10-20 mg/100 ml

plasma)


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Creatinine: End product of muscle creatine metabolism Used in clinical setting to measure GFR but less

accurate than inulin method Small amount secrete from the tubule

Para-aminohippurate (PAH):

An organic anion not present in body Freely filtered, secreted but not reabsorbed by

nephron Non-toxic, neither synthesized nor metabolized in

kidney Low concentrations are enough (10 mg/100 ml plasma) RPF = Clearance PAH = UPAH.V / PPAH


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Solute Clearance:Rate of removal from the Blood

Figure 19-16: Inulin clearance


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Concept of clearance

Where,Cx = Clearance of substance X (mg/min)Ux = Urine concentration of X (mg/ml)Px = Plasma concentration of X (mg/ml)V = Urine flow rate of X (ml/min)

GFR = C x =P x

Ux . V

Qx extracted = Qx excreted

Px . Cx = Ux . V

Effective renal plasma flow =GFR

ERBF = C x =1 - Hct ERPF

Renal blood flow = RBF = Extraction ratio ERBF

Effective renal blood flow =

Extraction ratio (0.9) = APAH

APAH - V PAH

Hct=hematocrit

VPAH = vein plasma PAHAPAH = arterial plasma PAH


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glomerular function

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