Water Excretion

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Lecture 5

• Water Excretion

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Department of Physiology Seminar
Dr. Randy Seeley Professor Department of
Psychiatry Obesity Research Center Genome
Sciences Institute University of
Cincinnati School of Medicine Cincinnati,
Ohio will present How Obesity Went to Our Heads
Novel Aspects of the CNS Regulation of Energy
Balance 1200 p.m. Friday, April 20, 2007 Room
1059, Life Science III
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Quiz

• NEXT FRIDAY WILL COUNT FOR EXTRA CRDIT ON
  TEST!!!
• 20 point quiz
• Your exam score will be multiplied by 0.9
• The points you earn on the quiz will be added to
  that adjusted score.
• Whichever is HIGHER is your score.
• Bottom line, the quiz can only HELP YOU!

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Cartoon of Sodium Handling
Cortex
Medulla
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(No Transcript)
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• 1. Describe where, how much, and by what
  mechanism water is reabsorbed in the nephron.

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Normal routes of water gain and loss in adults
1.
Vander

• Intake ml/day
• Beverage 1200
• Food 1000
• Metabolism 350
• TOTAL 2550
• Output
• Insensible loss (skin/lungs) 900
• Sweat 50
• Feces 100
• Urine 1500
• TOTAL 2550

These values vary, as well as the concentration
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Comparison of Sodium and Water Reabsorption
Along the Tubule
1.

• Segment Sodium Water
• Proximal Tubule 65 65 (isosmotic)
• Descending thin
• Limb of Henles loop - 10
• Ascending thin and thick
• Ascending limb of Henles loop 25
  impermeable
• Distal Convoluted tubule 5 impermeable
• Collecting-duct 3 depends on hydration
• (3 to gt24)

Vander
ADH dependent
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1.
Water Permeability
Fig. 37-8
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1.
Fig. 34-2
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Urine Osmolality

• Plasma Osmolality 290 mOsmol
• Urine Osmolality 50-1200 mOsmol
• When urine osmolality plasma isosmotic
• More dilute hyposomotic
• More concentrated - hyperosmotic

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• 4. Explain how the kidney produces hyposmotic
  and hyperosmotic urine.
• (we skip 2 3 for now, to be cont...next
  lecture)

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4.
TFTubular fluid P Plasma
TF/Posmol
Fig. 37-1
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Water Loading
4.
Drink Water
Plasma Osmolality
Activation of osmoreceptors in anterior
hypothalamus
ADH secretion from Post. Pituitary
Water permeability in late DT and CT
Water Reabsorption
Urine Osmolality
Urine Volume
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Water Deprivation
4.
Drink Water
Plasma Osmolality
Activation of osmoreceptors in anterior
hypothalamus
ADH secretion from Post. Pituitary
Water permeability in late DT and CT
Water Reabsorption
Urine Osmolality
Urine Volume
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• 5. Describe the source, regulation of release,
  and mechanism of action of ADH.
• (ADH, AVP, Vasopressin)

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ADH (antidiuretic hormone)

• Produced in supra-optic and paraventricular
  nuclei of the hypothalamus.
• Stored in posterior pituitary and released.
• Regulation of release
• Increased osmolality (1)
• Decreased plasma volume (10)
• Pain, stress
• Ethanol

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Actions of ADH
5.

• Increases the permeability of collecting duct to
  water
• V2 receptors
• Vasoconstrictor at high concentrations
• V1 receptors

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ADH Mechanism of Action
5.
Receptor binds, causes vesicles to fuse and
insert aquaporins (water channels) into the
membrane.
Fig. 37-9