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1. Major Functions of The Kidney

Regulation of osmolality of the body fluid

Regulating the volume of the extracellular fluid

Regulating concentrations of electrolytes of the

extracellular fluid Regulation of acid-base balance

Clearance of metabolic waste products (urea, uricacid, creatinine)

Production of special substances (erythropoietin,renin, prostaglandins, and thromboxane)

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2. Functional Anatomy

Overview of the kidney

Cortex

Medulla

outer medulla

inner medulla

Papilla

Minor calyx

Major calyx Renal pelvis

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The nephron is the basic unit of kidney structure andfunction

Renal corpuscleglomerulus

Bowman's capsule

Renal tubule

Cortical nephron (80%) Juxtamedullary nephron (20%) Structures of the renal tubule

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The juxtaglomerular apparatus

Macula densa (tubular epithelium)

Granular cells (smooth muscle cells of afferent arterioles)

renin

extraglomerular mesangial cells

Tubuloglomerular feedback hypothesis

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3. Urine Formation

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3. Urine Formation

Glomerular filtration

The glomerular filtration barrier capillary endothelium

glomerular basement membrane

podocyte cell layer

passage of macromolecules through the barrier are affected by pore size and

electrical charge

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Glomerular filtration rate (GFR)

GFR=Kf(PGC - PBS - pGC)

Kf =filtration coefficient - dependent upon fluidpermeability and surface area

The renal plasma clearance

Cx = Ux x V / Px (ml plasma/minute) Inulin clearance as a way to measure GFR

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Inulin clearance

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Renal blood flow

very high (20-25% CO = ~4ml/min/g)

relatively constant (BP 80-180 mmHg)

AutoregulationMyogenic

Tubuloglomerular feedback

Sympathetic activity

VasomediatorsConstrictors: endothelin, angiotensin II, NEP, EP,Thromboxane A2, adenosine.

Dilators: Nitric oxide, Ach, PGE2, PGI2, kinin.

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Paracrine signal: NaCl, NO,

adenosine etc. ?

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Tubular reabsorption

Active reabsorption (active transport)

sodium, glucose, phosphate

Passive reabsorption (passive transport)

urea, chloride, water

Reabsorption of glucose

Reabsorption of amino acids

Reabsorption of uric acid

Reabsorption of urea

Reabsorption of proteins

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Glucose moves in couple with Na+

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Passive reabsorption

of urea in proximal

tubule

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Tubular Transport of Electrolytes

Na+ reabsorption (actively transport by Na+/K+ -ATPase)

Na+ reabsorption in the proximal convoluted tubule

70% of Na+ transported in this segment

cotransported with sodium are glucose, amino acid,

phosphate, Cl- and water

Sodium reabsorption in the loop of Henle

20% sodium transported in the loop of Henle

cotransporter: Na+/K+/2Cl-

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Sodium reabsorption in the distal convoluted tubuleand collecting duct

- 9% sodium transported in these segments

- aldosterone stimulates sodium reabsorption by the collectingducts

Potassium is filtered, reabsorbed, and secreted in thekidney

The Principal cells of the collecting ducts secret K+

factors that facilitate secretion of K+

- Na+/K+ - ATPase in the basolateral membrane

- negative electrical potential (-50mV) in the lumen of collectiveducts than the basolateral side (0 mV)

- aldosterone increases uptake of K and the luminal membranepermeability to K+

Reabsorption of calcium, magnesium, and phosphate

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Principal cells & aldosterone

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Tubular reabsorption of water

Tubular reabsorption of water determines the urine flowrate and osmolality of urine

Mechanisms of tubular reabsorption of water

the loops of Henle act as countercurrent

multipliers (countercurrent theory)

countercurrent exchange in the vasa recta

Factors that influence the ability to form an osmotically

concentrated urine ADH

delivery of NaCl to ascending limb of LOH

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reabsorption of NaCl by ascending limb

delivery of fluid to medullary collecting ducts

medullary blood flow

urea

length of LOH

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4. Other Organs of the Urinary System

Ureters

Urinary bladder

Urethra

Micturition (urination)

stretch receptors initiate visceral reflex arc causing

relaxation of internal sphincter

external sphincter is voluntarily controlled except ininfants

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