Na+ Reabsorption in PCT: Fig. 18.4
Urea & Water Reabsorption : Fig. 18.5
• Antidiuretic Hormone
ADH (9 amino acids)
• Also called vasopressin
• 8 Arginine or 8 Lysine Vasopressin
• Released from posterior pituitary
• In response to osmoreceptors in hypothalamus
• Acts on Collecting Duct to increase water permeability
• Causes decreased P
& increased
blood volume
ADH on DCT & CD: Fig 18.10
Control of Blood Osmotic Pressure
• Increased P ---> stimulate hypothalamus
osmoreceptors
• release of ADH into blood
• Acts on CD to increase water permeability
• Water diffuses from filtrate / urine into medulla and blood (vasa
recta)
• Why does water pass from urine / filtrate medullary space and blood?
• Can you draw & explain the Plasma
- ADH homeostatic feedback loop?
Medullary Osmotic Gradient: Fig 18.6
MULTIPLIER - COUNTERCURRENT EFFECT
Medullary Osmotic Gradient & Vasa Recta: Fig 18.8
ADH Dependent H2O Permeability and Reabsorption
Water Reabsorption in DCT & CD: Fig 18.9
COUNTERCURRENT MECHANISMS
• Multiplication
• Exchange
• Loops of Henle in Juxtamedullary Nephrons
Diuretics
• Osmotic, including water and non-reabsorbed solutes
• Na+ - K+ ATPase inhibitors
• Caffeine and theophylline
• Furosamide
• Alcohol - Inhibits ADH release
Increased renal BF, GFR & vasa recta BF
The Urinary Bladder: Fig 17.22
Regulation of Potassium Excretion
Two mechanisms:
[K+]plasma
Aldosterone - Secreted from adrenal cortex
Regulation of Aldosterone
• Stimuli
• Elevated [K+]plasma
• Angiotensin II (via renin
from juxtaglomerular cells)
• Released from adrenal cortex
Action of Aldosterone
Acts on renal tubules to synthesize more Na+ - K+
ATPase
Increases Na+ reabsorption & K+ secretion
and excretion
Atrial Natriuretic Peptide (ANP)
Increases Na+ excretion by decreasing Na+ reabsorption
Decreases Aldosterone secretion
Decreases Renin secretion = more water & Na+ excretion
Released in response to artial stretch
due to increased blood volume and BP
Blood Volume Regulation
Decreased blood or extra-cellular fluid volume ---> increased renin
----> Increased renin & aldosterone
Increased blood or extra-cellular fluid volume ---> increased ANP
Calcium – Phosphate Relationships
Increased [Ca++]plasm a must be accompanied by
a decreased [HPO4-2]plasma
Parathyroid Hormone (PTH)
Parathyroid hormone (PTH) increases Ca++ reabsorption and
decreases HPO4-2 reabsorption
Increases HPO4-2 excretion and decreases Ca++
excretion
PTH - Released in response to decreased plasma Ca++