Fluid balance Flashcards
Baroreceptors
- Low + high pressure
Sensory receptors that detect changes in blood pressure.
Indication of changes in the effective circulating volume (ECV).
Low pressure receptors located:
- Large systemic veins
- Atria
- Pulmonary vessels
HIGH pressure detectors:
- Carotid sinus
- Aortic arch
- Real afferent arteriole
Location of low pressure baroreceptors
- Large systemic veins
- Atria
- Pulmonary vessels
Location of high pressure baroreceptors
- Carotid sinus
- Aortic arch
- Real afferent arteriole
ADH
Anti-diuretic hormone/ Vasopressin.
Regulates water balance by influence water absorption at the collecting duct.
Short half life: 10-15 mins
Mechanism:
- Acts on V2 receptors on the basal membrane of CD principal cells.
- Causes the insertion of Aquaporin-2 on the apical membrane
Plasma osmolality
The osmotic pressure in the plasma
- The high the osmolarity, the more concentrate plasma is.
Changes in osmolarity detected by chemoreceptors.
Chemoreceptors
Detects changes in plasma osmolarity in hypothalamus.
When osmolarity rises:
Efferent pathways + effector:
- ADH—-> Kidneys
- Thirst—-> Brain= drinking behaviour
Effect: Increased water absorption and water intake.
Efferent pathways and effector of baroreceptors.
- Short and long term effect.
Efferent pathways:
- ADH
- RAAS
- ANP
- SNS
Effectors:
Short term: heart, blood vessels
Long term: kidneys
Effect:
Short term: blood pressure
Long term: Na+ excretion
Angiotensin II effects
Increases Na+ and water reabsorption
Stimulates aldosterone secretion from the adrenal cortex
Stimulates thirst at the hypothalamus.
Increases ADH secretion at posterior pituitary gland.
Vasoconstriction of renal and other systemic vessels
Renal cell hypertrophy- long term
- More protein synthesis of Na+ transporters
ANP
- Site of release
- Trigger of release
- Action
Atrial natriuretic peptide
- Decreases blood pressure by increasing Na+ excretion in the kidneys
Released from the atrial myocytes
Trigger of release: Stretching of the atria caused by an increase in ECV.
Action:
- Decreases blood pressure by increasing Na+ excretion in the kidneys
- Renal vasodilation= increased Na+ excretion
Mechanism of ANP
- ANP stimulates renal vasodilation which increases renal blood flow.
- Increased renal blood flow increases GFR.
- Increased GFR increases Na+ secreted—-> This is detected by the macula densa.
- Macula densa inhibits renin release from juxtaglomerular cells= inhibiting RAAS
Volume regulation pathway- ADH.
- Decreased ECV
- Decreased ECV is detected by peripheral baroreceptors.
- This is signaled to the hypothalamus.
- Stimulates the release of ADH from the posterior pituitary gland into circulation.
- ADH stimulates increased water absorption from the kidney into the blood= Increase in ECV.
Volume regulation pathway- ADH.
- Increased plasma osmolarity
- Increased osmolarity is detected by chemoreceptors in the hypothalamus.
- This stimulates ADH release from the posterior pituitary gland into circulation.
- ADH increases water absorbed from the kidneys into blood= increases ECV, decreases plasma osmolarity.
Volume regulation pathway- RAAS
- Decreased ECV
- Decreased ECV is detected by renal baroreceptors and macula densa.
- RAAS system is activated by the release of renin from juxtaglomerular cells.
- Angiotensin II and Aldosterone are released into circulation.
- This reduces Na+ excretion and increases Na+ absorption in the kidney which increases water absorption = Increase in ECV
Volume regulation pathway- ANS
- Decreased ECV
- Low ECV is detected by peripheral baroreceptors: liver, aortic arch, carotid sinus, atria, pulmonary vessels, CNS
- Low pressure is signaled to the hypothalamus= activation of sympathetic NS.
- Sympathetic NS activates RAAS and directly affects renal haemodynamics.
- Both actions reduces Na+ excretion and increases Na+ absorption in the kidneys= Increased ECV.
Peripheral baroreceptors that detect changes in ECV- locations [6]
Liver
Cardiac atria
CNS
Aortic arch
Carotid sinus
Pulmonary low pressure receptors
