Chapter 19-The Kidney

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Chapter 19-The Kidney
2014-04-13 17:33:06
Chapter 19 Kidney

The Kidney
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  1. Functions of Kidney
    • • Kidneys maintain fluid and electrolyte balance
    • • Kidney function can be broken down into six general areas
    • 1. Regulation of extracellular fluid volume and blood pressure
    • 2. Regulation of osmolarity
    • 3. Maintenance of ion balance
    • 4. Homeostatic regulation of pH
    • 5. Excretion of wastes
    • 6. Production of hormones
  2. What are the gross structures of theurinary system?
    • 1. Kidney
    • 2. Ureter
    • 3. Urinary bladder
    • 4. Urethra
    • • These structuresare located in theabdominal cavity
  3. How is the kidney constructed?
    • • Interior of kidney is organized into two layers
    • 1. Cortex is outer layer
    • 2. Medulla is innerlayer
    •     • Nephron is thefunctional unit
    • • 80% nephrons are located mostly in the cortex (cortical nephron)
    • • 20% have most of their structure in the medulla(juxtamedullary neuron)
    • • Vascular organizationis important tofunction of nephron
    • – Renal arteriestakes blood to the cortex
    • – Renal vein collects blood filtered by the kidney
  4. Supply of blood in the nephron
    • • An afferent arteriole carries blood from an artery to:
    • – capillaries that supply the nephron
    • – each capillary is folded into a ball called a glomerulus

    A glomerulus continues as an efferent arteriole (Supply of blood in the cortex)

    A glomerulus issituated inside Bowman’s Capsule of a nephron

    • Blood flows from efferent arteriole into branching capillaries called peritubular capillaries.

    • Blood from the peritubular capillaries eventually collects in a venule
  5. Structure of the nephron
    • The nephron consists of a folded tube

    • • At one end of the tube is the renal corpuscle consisting of
    •     1. Glomerulus
    •     2. Bowman’s capsule

    • Fluid flows out of glomerulus into Bowman’s capsule

    • From Bowman’s capsule fluid flows into proximal tubule

    • • Then fluid flows through the loop of Henle consisting of:
    •   1. Descending limb
    •   2. Ascending limb

    • Fluid in Ascending Limb flows into distal tubule

    • Then the fluid joins fluid from other nephrons flowing through the collecting duct

    • The distal tubule and the collecting duct comprise the distal nephron

    • A collecting duct extends from the cortex through the medulla and drains into the renal pelvis

    • Fluid in pelvis empties into ureter
  6. Nephron function
    • Three processes take place in the nephron:

    1. Filtration: fluid moving from blood into lumen of tubule;this is filtrate

    2. Reabsorption: return of substances infiltrate back to blood

    3. Secretion: adding substances taken from blood to filtrate
  7. • How does nephron modify fluid volume and osmolarity?
    • Bulk filtration takes place in glomerulus (A).

    • Bulk reabsorption of isotonic fluid takes place in proximal tubule (B).

    • Dilute urine is formed in loop of Henle (C).

    • Final regulation of salt and water balance occurs in distal tubule (D)

    • Urinary excretion (NOT secretion) of any substance XYZ is:

    Amount XYZ excreted =Amount XYZ filtered – Amount XYZ reabsorbed + Amount XYZ secreted
  8. Process of filtration
    • • Hydrostatic pressure of glomerulus drives filtration
    •     – Mean arterial blood pressure is glomerular hydrostatic pressure
    •     – fluid driven out of glomerulus into Bowman’s capsule

    • • Glomerular hydrostatic pressure is opposed by
    •    – Glomerular oncotic (osmotic) pressure
    •    – Tubular hydrostatic pressure
    • • Net filtration pressure is the glomerular hydrostatic pressure minus the osmotic and tubular pressures

    • • Net filtration pressure drives the flow of fluid out of the glomerulus into the nephron
    • • The volume of fluid that flows into Bowman’s capsule per unit time is called glomerular filtration rate (GFR)
  9. Regulation of GFR
    • • GFR is normally 180L/day\
    • • Arteriole resistance changes control GFR
    • • Increase afferent resistance reduces hydrostatic pressureand GFR

    • • Arteriole resistance is controlled by autoregulation
    •    – (MAP) Pressure increase causes afferent arteriole to increase resistance
    •    – (MAP) Pressure decrease causes afferent arteriole to decrease resistance
  10. Reabsorption
    • • Net movement of filtered substances back into capillary
    • • Glucose is normally reabsorbed completely

    • • How much glucose can be reabsorbed?
    • • The higher the blood glucose, the faster the filtration rate
    • • Reabsorption rate increases with filtration rate of glucose until amaximum is reached
    • • The rate at saturation is the Transport Maximum (Tm)

    • • The maximum plasma glucose concentration that can be filtered is the Transport Maximum
    • • Renal Threshold: glucose concentration above transport maximum
    •      – results in net excretion of glucose 
    •      – Typically no glucose is excreted by kidney
    • • Diabetic: blood glucose > renal threshold and excretes glucose
  11. Secretion
    • • Net movement of non‐filtered substances into renal tubule
    • • Active transport required for secretion
    • • K+ and H+ are important ions that are secreted
    • • Organic compounds are secreted
  12. Excretion
    • • Excretion is defined as:Excretion =filtration –reabsorption +secretion
    • • Excretion is measured by a clearance rate
    • • Clearance is the rate a solute disappears from blood supply to kidney
  13. How to get rid of Glucose?
    • • Glucose is not cleared by the kidney
    • • Excretion rate =clearance rate
    • • Glucose is filtered at 100 ml/min
    • • All filtered glucose is reabsorbed
    • • Clearance = 100ml/min – 100 ml/min
    • • Excretion of glucose is0 ml/min
    •       – Except diabetic

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