The Kidneys

Last update by marcellus on 04/02/2012
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Describe sodium reabsorption in the proximal tubule

Answer:
1. Sodium enters the cell through membrane proteins, moving down its electrochemical gradient
2. Sodium is pumped out the basolateral side of the cell by Na+/K+ ATPase

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  • marcellus
    Answered in The Kidneys
    Describe sodium-linked glucose reabsorption in the proximal tubule
    1. Na+-dependent glucose transporters (SGLT) allow for reabsorption across the proximal tubule epithelium
    2. GLUT protein found in basolateral membrane allows for facilitated diffusion of Glucose into interstitial fluid
    3. Na+-K+-ATPase pumps Na+ back into interstitial fluid
  • marcellus
    Answered in The Kidneys
    Briefly overview Reabsoprtion
    1. Active transport of Na+ from the tubule lumen to the ECF creates a transepithelial electrical gradient in which the lumen is more negative than the ECF
    2. Anions then follow the positively charged Na+ out of the lumen
    3. The net movement of Na+ and anions from lumen to ECF dilutes the luminal fluid
    4. Increase the concentration of solutes in the ECF, so water leaves the tubule by diffusion and is reabsorbed
  • marcellus
    Answered in The Kidneys
    Describe the passive reabsorption of urea
    1. Urea moves across the epithelium by diffusion when there is a urea concentration gradient
    2. Reabsorption of Na+ creates an osmotic gradient where water movement creates a higher [urea] in the lumen -> creates a concentration gradient for urea to move into the extracellular fluid
    3. Once a urea concentration gradient is established, urea uses facilitated diffusion transporters to move out of the lumen into the extracellular fluid
  • marcellus
    Answered in The Kidneys
    Describe passive reabsoprtion in the distal convoluted tubule
    1. Concentration of ions and organic wastes are no longer similar to those in the blood plasma
    2. In the DCT a combination of secretion and reabsorption further alters the solute composition of the tubular fluid
    3. Na+ are reabsorbed in exchange for K+ by ion pumps stimulated by aldosterone
    - If pH of body fluids decrease H+ are secreted in exchange for Na+
  • marcellus
    Answered in The Kidneys
    Describe Secretion
    - Transfer of molecules from the ECF to the lumen of the nephron
    - Secretion relies heavily on membrane transport systems
    - The main role of secretion is to enhance excretion of a substance from the body
    - Secretion is an active process that involves moving substrates against a concentration gradient
  • marcellus
    Answered in The Kidneys
    Describe Secretion
    - Transfer of molecules from the ECF to the lumen of the nephron
    - Secretion relies heavily on membrane transport systems
    - The main role of secretion is to enhance excretion of a substance from the body
    - Secretion is an active process that involves moving substrates against a concentration gradient
  • marcellus
    Answered in The Kidneys
    Describe Excretion
    - Urine output is a result of filtration, reabsorption and secretion
    - Glucose, amino acids and other metabolites have been reabsorbed into the blood
    - Organic wastes are highly concentrated in the urine while the water and ions present is variable depending on the state of the body
  • marcellus
    Answered in The Kidneys
    Describe how excretion rate is calculated and what affects it
    - Excretion = Filtration - Reabsorption + Secretion
    - Excretion rate depends on
    - The filtration rate
    - Whether the substance is reabsorbed, secreted or both as it passes through the tubule
  • marcellus
    Answered in The Kidneys
    Describe what clearance is and how it is calculated
    - Clearance is the ability at which a solute disappears from the body by excretion or metabolism calculated by
    - Clearance = excretion rate of X/[X]plasma
  • marcellus
    Answered in The Kidneys
    What can we infer using a person's GFR?
    - If less of a substance is found in the urine than was filtered, net reabsorption has occurred
    - If more of a substance is found in the urine than was filtered, net secretion has occurred
    - If there is the same amount of substance found in the urine and what was filtered, only filtration has occured
  • marcellus
    Answered in The Kidneys
    Describe micturation and the factors that affect it
    - Micturation is the process of urinating
    - Urinary bladder can hold ~500mL of volume
    - Closure between bladder and urethra is controlled by sphincters
    - Sensory receptors are activated by stretch receptors -> PNS neurons fire -> smooth muscle contracts opening sphincters
The Kidneys
The Kidneys
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Kidney Physiology as part of Kinesiology 2610 taught by Stephen Cornish in Spring 2012 at the University of Lethbridge
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