Faal Ginjal Kebidanan

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The Kidney Function

Laboratorium FisiologiFakultas Kedokteran Universitas Brawijaya


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Clinical Case:

A 10 year boy has some symptoms: dark red urine andswollen/puffy face. This patient also complains about pain duringswallowing, high fever and respiratory tract inflammation. Now, all

symptomps are relieved.

From physical analysis: increased blood pressure and edema on face

and foot.

From blood analysis: increased creatinin and urea and reducedplasma albumin. Also foundproteinuria and gross hematuria.


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Based on those anamneses and physical analysis, this patient is

suspected to suffer glumerulonephritis, a disease of immune system

with failure of glumerulus. This disease is self-relieved, with loss

of signs and symptomps. Some patients can have worse outcome,

the diseases becomes persistent and develop as permanent renal

failure.These signs and symptoms are the effect of glumerolus function

failure leading to renal failure.

Human kidney plays important roles on maintainingvolumeand

composition ofextracelluler fluid. This organ maintains internalbody environments. As a result, failure of structure and function of

this organ will dysharmonize humanbody homeostasis.


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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 Blood Flow (RBF)

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:

Glomerular Filtration Rate (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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Arterial Pressure

Glomerular hydrostatic

pressure

Macula Densa

Na Cl

Proximal Na Cl

reabsorption

Efferent Arteriolar

resistance

Afferent Arteriolar

resistance

Angiotensin II

Renin

GFR

KEMBALI
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Reabsorption Secretion

Tubular reabsorption includes Passive & Activemechanism.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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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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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 5


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Factor affecting urinaryconcentrating ability are:

Anti Diuretic Hormone

The length of Henles loop. Tubule fluid and blood flow

Urea.


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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 5


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