Major Functions of The Kidney

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• 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, uric
  acid, creatinine)
• Production of special substances (erythropoietin,
  renin, prostaglandins, and thromboxane)

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• 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 and function
• Renal corpuscle
• glomerulus
• 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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• Urine Formation

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• 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)
• GFRKf(PGC - PBS - pGC)
• Kf filtration coefficient - dependent upon
  fluid permeability 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)
• Autoregulation
• Myogenic
• Tubuloglomerular feedback
• Sympathetic activity
• Vasomediators
• Constrictors 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
  tubule and collecting duct
• 9 sodium transported in these segments
• aldosterone stimulates sodium reabsorption by the
  collecting ducts
• Potassium is filtered, reabsorbed, and secreted
  in the kidney
• 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 collective ducts than the basolateral
  side (0 mV)
• aldosterone increases uptake of K and the luminal
  membrane permeability 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 flow rate 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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• 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 in infants

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