Overview Faal Ginja.ppt

8/14/2019 Overview Faal Ginja.ppt

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The Kidney FunctionBy

M. Rasjad Indra


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Main function

Excretion of metabolic waste products &foreign chemicals

Regulation of: water & electrolyte balances.

body fluid osmolarity & electrolyteconcentration.

acid-base balance.

arterial pressure.

Secretion, metabolism, and excretion ofhormones

Gluconeogenesis


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Renal Blod Flow

1200 ml/minute or 20-25% of cardiac out put

Both kidney weigh: 300 gr or 0.5% b.w. Blood flow per grams of kidney tissue: 4 ml /

minute => 1200 ml / 300 gr, why?

Blood flow is highest in the renal cortex, why? RBF & GFR change relatively little if arterial blood

pressure between 80 - 180 mmHg, why?


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The nephron ~ Functional Unit

Each kidney contains about 1 million nephrons

The kidney cannot regenerate new nephrons.

After age 49 the number usually decrease 10 %

every 10 years.

Regional differences in nephron structure:

Cortical nephrons: they have short loops.

Juxtamedullary nephrons: they have long loops. Urine formation results from: Glumerular filtration,

tubular reabsorption, and tubular secretion.

Urinary excretion rate = Filtration rate- Reabsorption rate + Secretion rate


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Ke Counter Current
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Two capillary beds: The glomerular & Peritubularcapillaries

Are arranged in series

Separated by the efferent arterioles

Regulate the hydrostatic pressures in both sets of capillaries.

Hydrostatic pressure: The glomerular (high ~ 60 mmHg) => for filtration.

The peritubular (low ~ 13 mm Hg) => for reabsorption.

By adjusting the resistances of afferent and efferent arterioles

The kidneys regulate the hydrostatic pressure of the glomerular &

peritubular capilaries.

Changing the rate of filtration and / or tubular reabsorption.

Response to body homeostatic demands.

KEMBALI


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Urine formation startwith the filtrationof plasma inthe glomeruli:

GFR determined by: The balance of hydrostatic & colloid osmotic forces across the

glomerular membrane

The glomerular filtration coefficient (Kf)

Net Filtr.Pressure= PG- PB- G+ B.

GFR= Kfx Net Filtration Pressure

Glomerular filtration is rather non selective: Proteinare mostly retained in the plasma

Low-molecular weightsubstance are freely filtered(excepts that are bound to the plasma protein).

Negative charged large molecules are filtered less easilythan positively charged molecules of equal molecules size

Glomerular Filtration


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Macula densa

Juxtaglomerular cells


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Reabsorption Secretion Tubular reabsorption includes Passive & Active

mechanism.1.Across the tubular epithelial cells into interstitiel

2.Through the peritubular capillary membrane back intothe blood

Active transport (against electrochemical gradient& requires energy.1.Primary active transport

Expl: Sodium transport in luminal membrane prox. Tub.

2.Secondary active reabsorption Expl.: Glucose & amino acid reabs.

Secondary active Secretion: Expl: Hydrogen ion: Counter-transportwith sodium

reabsorption in luminal membrane


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Glucose:Allof the filtered are activelyreabsorbed and sodium dependent.

Urea & Chloride arepassively reabsorb.

Active absorb. of Na+--> the driving forcefor tubular reabsorb. of water, glucose,amino acids, chloride and phosphate.

Some organic compoundsare secreted

from the blood into the tubular urine.


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Transport Maximum

Transport maximum for substances that are activelyreabsorbed:

Glucose 320 mg/min.

Phosphate 0.10 mM/min.

Sulfate 0.06 mM/min.

Amino acid 1.5 mM/min. Uric acid 15 mg/min.

Lactate 75 mg/min

Plasma protein 30 mg/min

Transport maximum for substances that are actively

secreted:

Creatinin 16 ng/min

Para-aminohipuric acid 80 ng/min


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Constituent Filtered Reabsorbed Excreted

Water 167.5 liters 166 liters 1.5 liters

Sodium 24,000 mmoles 23,900 mmoles 100 mmoles

Potasium 720 mmoles 630 mmoles 90 mmoles

Chloride 19,500 mmoles 19,400 mmoles 100 mmoles

Bicarbonate 4,500 mmoles 4,498 mmoles 2 mmolesPhosphate 6 g 5 g 1 g

Glucose 150 g 150 g 0 g

Urea 50 g 25 g 25 g

Uric acid 8 g 7.2 g 0.8 g

Creatinine** 1.5 g 0 g 1.8 g


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Reabsorption of glucose

Glucose is cotransport with sodiumacross the luminal cell membrane(uphill)

the energy from:

the sodium gradient, how?

the electrical gradient

Glucose leave the cell membrane to

peritubular capillary blood byfacilitated difussion


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Glucose Threshold

The ability to reabsorb is limited

At normal plasma glucose levels(65-90 mg/dl) => completelyreabsorb.

At 180-200 mg/dl => glucose firstappear in the urine (threshold).

Tubular transport maximum (Tm)for glucose: the maximal rate ofglucose reabsorption.


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Sodium (Na+):

Most filteredsodium is reabsorbed. The proximal tubules: 70%.

The loop of Henle: 20%

The distal tub. and collecting duct: 9%

The quantity of Na+excreted =>importantrole in body sodium balance.


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CountercurrentMechanism

Loop of Henle (countercurrent multipliers)&Vasa recta (countercurrent ex-changers)

Loops of Henle: establish an osmotic gradientin the medulla.

The descending limb: water permeable

The ascending limb:

Active sodium transport

Low water permeability The vasa recta: remove water from the

medulla.

Ke Slide 8


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The collecting ducts:

Final regul. of Na

+

excretion.AldosteroneandADH:increase Na+and

water reabs. by the collecting duct.

Potasium (K+):

Filtered, reabsorband secreted

The cortical collecting tubules:important site of K+ secretion.


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Ke Slide 4


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Clearance(CX)= UXx V (ml plasma/ minute)

PX

The Inulin clearance (CIN

)= GFR .....Why ?

Endogenous Creatinine Clearance also = GFR ..... Why ?

Clearance Ratio = Cx

CInulin

PAH clearance (CPAH)=Effective Renal Plasma Flow (ERPF) Renal Plasma Flow (RPF) = CPAH EPAH =PPAH-VPAH(Extraction Ratio)

EPAH PPAH

Renal Blood Flow (RBF) = RPF

1-Hematocrit Excretion Rate = Uxx V

Reabsorption Rate = Filtered Load Excretion Rate

= (GFR x Px) (Uxx V)

Secretion Rate = Excretion Rate Filtered Load

The Clearance Concept (CX) to Quantify Kidney Function


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Inulin:

Not be reabsorbed or secreted by the kidney

Not be metabolized, synthesized, or stored

Pass through the glomerular filtration

barrier unhindered

Nontoxic

Be able to measure in plasma and urine

Clearance Inulin ~ GFR

PAH is avidly secreted by tubules that it is almost completely

cleared from all of the plasma in one passage of blood through

the kidneys

Clearamce PAH ~ ERPF

uteplasmaml

plasmamlxmg

uteurineXmlurinemlxmgCx min/)(

)(/)(

min/)()(/)(


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Urea Recirculation in RenalTubules


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The two ureters are muscular tubesthat carry the urine from the

kidneys to the bladder. The urinary blader functions as a

reservoir for urine and is

periodically emptied (micturition).

MICTURITION

A complex act involving autonomicand somatic nerves, spinal reflexes,and higher brain centers.


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Ke slide 4

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