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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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