Topic 47 - The maintenance of Isosmosis; ADH- mechanism Flashcards
1
Q
Words to include
A
- Blood volume ↓
- Fluid intake ↓
- Dehydration
- Concentration of dissolved salts ↑
- Osmotic pressure ↑
- Receptors in hypothalamus (reacts to the shift in osmotic pressure)
- Posterior lobe of pituitary
- ADH release
- Posterior lobe of pituitary
- Hypothalamic thirst center (responds to ADH release)
- Water intake
- EC hyperosmosis
The role of ADH maintaining isosmosis
- Vasopressin = antidiuretic hormone (ADH)
-
Ensures:
-
Isosmosis & water conservation
- V2 receptor effect
- cAMP mediated
- V2 receptor effect
- Smooth muscle contraction
- V1 receptor
- IP3 mediated
- V1 receptor
-
Isosmosis & water conservation
- Hyposomitc urine
- Ø endocrine mechanisms
- ADH readjust isosmosis
- Ø endocrine mechanisms
- Damage to hypothalamic ADH secreting locus
- Hyposmotic urine
- Diuresis ↑ → extra H2O load
- Blocked by ADH
- Hydropenia
- Blood-ADH increase
ADH mediated H2O transport
- Hypothalamus
- Nucl. supraopticus
- Nucl. paraventricularis
- Neurohypophysis
- Osmotic concentration of blood ↑
- Water retention
- Collecting ducts
- V2 receptor
- AQP-2 water channels
- Luminal side
- Transparent to water
- Reabsorbed according to osmotic gradient
- Transparent to water
- Blood pressure ↑
- Ø ADH production
- Baroreceptors
- Ø ADH production
- Aquaporine-1
- Aquaporine-2
ADH mechanism of action
- Level of action:
- Connecting part of distal tubule
- Collecting duct
- H2O permabilty
Hyperosmosis
- Substances not reabsorbed after filtration
- Mannit
- Glucose
- Substances reabsorbed after filtration
- Sodium
- Hyperosmosis
- Hyperosmotic isovolemia (EC and IC balance)
- Hypothalamic osmoreceptor activity ↑
- Blood ADH level ↑
- AQP-2 expression ↑ (distal tubule)
- Free water clearance, water retention
- Isosmotic hypervolemia
Hyposmosis
- ADH inhibition → no H2O retention → hypovolemic isoosmosis
Figure
- ADH secretion from neurohypophysis
- Hyperosmosis of plasma (EC) +
- Primary factor
- Osmoreceptors (hypothalamus) +
- Stress +
- Pain +
- Baroreceptors (arcus aortae, sinus aorticus) ÷
- Blood pressure ↑
- Stress, volume receptors (left atrium, lungs) ÷
- ANP production (central and atrial) ÷
- External effects
- AQP-2 expression
- Water retention
- Bleeding
- V1 receptor stimulation
- Vessel contraction
- V1 receptor stimulation
- ACTH-like
- Corticoid production ↑
- Renal effects +
- AQP-2 expression
- Water retention
- AQP-2 expression
- DCT and collecting duct
- AQP-2 expression
- Water retention
- AQP-2 expression
2
Q
The maintainance of isosmosis
A
- When blood volume is reduced as a result of decreased fluid intake or injury, the body gets dehydrated
- Concentration of salts dissolved in the blood increases
- Causing a rise in osmotic pressure
- Receptors in the hypothalamus react to the shift in osmotic pressure
- Trigger posterior lobe of the pituitary to activate release of ADH
- At the same time, the thirst center in hypothalamus responds by stimulating the sensation of thirst → water intake
- Adequate stimulus is the EC hyperosmosis
Hyperosmosis
- Can be created by:
- Substances which can not be reabsorbed after filtration
- Eg. Mannit and glucose
- Substances which can be reabsorbed after filtration
- Eg. Na+
- Substances which can not be reabsorbed after filtration
- Hyperosmosis
- EC and IC getting balance: hyperosmotic isovolemia
- Hypothalamic osmoreceptor activity ↑
- Blood ADH level ↑
- Distal tubule: AQP-2 expression ↑
- Free water clearance, water retention
- Isosmotic hypervolemia
Hyposmosis
- ADH inhibition → no H2O retention → isosmotic hypovolemia
- In case of reduced salt intake or primary salt loss the osmotic concentration of EC ↓
3
Q
ADH
Define ADH
A
- Vasopressin = antidiuretic hormone (ADH)
- It is a hormone made by the hypothalamus and stored in the posterior pituitary gland
- Role:
- It tells the kidneys how much water to conserve
- Regulates and balances the amount of water in blood
4
Q
ADH
The role of ADH maintaining isosmosis
A
ADH effects on the kidney:
- Ensures isosmosis and water conservation
- Effect via V2 receptor (cAMP mediated)
- Smooth muscle contraction effect
- Effect via V1 receptor (IP3 mediated)
- The most important effect of ADH is to conserve body water by reducing the loss of water in urine
- A diuretic is an agent that increases urine formation
- ADH stimulates water reabsorption by stimulating insertion of aquaphorins (water channels) into the membranes of the kidney tubules. These channels transport water through tubular cells and back into blood
-
Result:
- Plasma osmolarity of urine ↓
- Osmolarity of urine↑
-
Result:
- Experimentally perfused kidney produces hyposmotic urine
- Reason:Ø endocrine mechanisms → ADH readjusts isosmosis
- Damage to hypothalamic ADH secreting locus
- Results: Hyposmotic urine
- Increased diuresis → extra H2O load can be promptly blocked by ADH
-
Hydropenia
- Result: immediate blood-ADH increase
ADH effect on the vascular system
- High concentration of ADH cause vasoconstriction of arterioles → arterial pressure ↑
5
Q
ADH
Mechanism of action
A
- Level of action:
- Connecting part of distal tubule
- Collecting duct
- Result: H2O permability
6
Q
ADH
ADH mediated H2O transport
A
- ADH is produced in the hypothalamus
- Nucl. supraoticus
- Nucl. paraventricularis
- Gets to neurohypophysis
- Released when osmotic concentration of the blood ↑
- Above 300 mosmol/l, plasma osmolarity ADH production ↑
- Result: water retention
- V2 receptors of the collecting ducts stimulate the apperance of aquaphorpine-2, water channe proteins
- The luminal side becomes transparent to water
- Water according to the osmotic gradient is reabsorbed
- ADH production is inhibited by increase in blood pressure
- Through baroreceptors
7
Q
ADH
- Give example of an pathological condition*
- Ikke nødvendig å kunne*
A
-
Diabetes insipidus, can arise from two situations
- Hypothalamic diabetes: Deficiency in secretion of ADH from the posterior pituitary
- Nephrogenic diabetes: The kidney is unable to respond to ADH
- Symptoms: excessive urine production
8
Q
ADH
Mechanism, figure
A