Renal lecture 2
• Regulation of salt and water balance
• Anti-diuretic hormone
• Renin- angiotension-aldosterone
Control of water and salt balance
-hormonal control of salt and water reabsorption
-Role of renal system in maintaining blood pressure
-Renin-angiotensin-aldosterone system
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Classification of Body Fluids
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Water Steady State
• Amount Ingested = Amount Eliminated
• Pathological losses
vascular bleeding (H20, Na+)
vomiting (H20, H+)
diarrhea (H20, HCO3-).
Daily Salt Balance
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Salt Balance
• Very important in regulating ECF volume
• Salt input occurs by ingestion
– Often not well controlled
• Salt balance maintained by outputs in
urine
– Salt also lost in perspiration and in feces
• Kidneys keep salt constant in ECF
– Glomerular filtration rate (GFR)
– Tubular reabsorption of sodium
Osmolarity
• Hypertonicity
– Cells shrink
– Causes
• Insufficient water intake
• Excessive water loss
• Diabetes insipidus
– Symptoms and effects
• Shrinking of neurons
– Confusion, irritability, delirium, convulsions, coma
• Circulatory disturbances
– Reduction in plasma volume, lowering of blood pressure, circulatory
shock
• Dry skin, sunken eyeballs, dry tongue
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Osmolarity
• Hypotonicity
– Cells swell
– Causes
• Inability to excrete a dilute urine (renal failure)
• when water is rapidly ingested
• When excess water is retained in body due to inappropriate
secretion of vasopressin
– Symptoms and effects
• Swelling of neurons
– Confusion, irritability, lethargy, headache, dizziness, vomiting,
drowsiness, convulsions, coma, death
• Weakness (due to swelling of muscle cells)
• Circulatory disturbances (hypertension and edema)
Baroreceptor Reflex
Influence on the GFR in
Long-term Regulation of
Arterial Blood Pressure
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Water Reabsorption:
Vasopressin/anti-diuretic hormone
Vasopressin (Anti-Diuretic Hormone; ADH)
•
ADH is synthesised within the
Paraventricular Nucleus of the
hypothalamus.
hypothalamus
Paraventricular
nucleus
pituitary
•
ADH is stored in the
posterior pituitary.
• ADH exerts a
pressor effect
(i.e., ↑BP)
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Control of Vasopressin/ADH release
•
Left atrial receptors
Monitor pressure of blood flowing through (reflects ECF volume)
Upon detection of major reduction in arterial pressure, receptors stimulate vasopressin
secretion and thirst
•
Osmoreceptors
Monitor osmolarity of plasma in CNS and stimulates vasopressin secretion
•
Angiotensin II
Stimulates vasopressin secretion and thirst when renin angiotensin-aldosterone
mechanism is activated to conserve Na+
Vasopressin (Anti-Diuretic Hormone; ADH)
hypothalamus
1. Dehydration or salt ingestion
2. ↑ Blood osmolarity
3. Stimulates osmoreceptors
in the hypothalamus
pituitary
↓ BP
5a. Causes vasoconstriction
4. Triggers ADH release
from the pituitary
→ ↑ TPR
5b. Promotes water retention by the kidney
→ ↑ BP
→ ↑ Blood Volume
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How does ADH work?
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DIABETES INSIPIDUS
Kidneys stop conserving water
Thirst
Dehydration
Damage to hypothalamus
Low ADH
Urine Excretion
• Depending on the bodyʼs state of hydration, the kidneys secrete
urine of varying concentrations.
• Too much water in the ECF establishes a hypotonic ECF.
• A water deficit establishes a hypertonic ECF.
• A large, vertical osmotic gradient is established in the
interstitial fluid of the medulla (from 100 to 1200 mosm/liter to 1200
mosm/liter). This increase follows the hairpin loop of Henle deeper
into the medulla.
• This osmotic gradient exists between the tubular lumen and the
surrounding interstitial fluid.
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Countercurrent Multiplier
Figure 19.7 Pg 542 (3rd Edition Germann & Stanfield)
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Sodium Reabsorption:
Aldosterone
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Regulation of Sodium Reabsorption and Balance
• Na+ reabsorption in the proximal tubule is unregulated
Therefore, regulation of GFR can contribute to Na+ regulation
• Na+ reabsorption in the distal tubule is under hormonal control
Aldosterone (increases Na+ reabsorption)
Atrial Natriuretic Peptide (decreases Na+ reabsorption)
RAAS
• Renin-angiotensin-aldosterone system
• Most import and best known hormonal
system involved in regulating Na+
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Factors Stimulating Renin Release
afferent
arteriole
macula densa
distal
tubule
JG cells (stretch sensitive)
RAAS
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steroid
Aldosterone
distal tubule
adrenal
gland
Na+
K+
adrenal
cortex
adrenal
medulla
Aldosterone
renin
angiotensin
system
collecting
duct
How does aldosterone work?
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Roles of Angiotensin II
Increase Blood Pressure
RAAS
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• At the end of this lecture you should:
Understand the role of ADH in the control of water balance/plasma
volume and thus blood pressure
Be familiar with the RAAS
Understand the role of aldosterone in salt balance
Know the actions of angiotensin II
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