Cardiovascular Responses — Hypovolaemia Hormones

Reduced venous return

• Reduced right atrial stretch
  • Reduced atrial natriuretic peptide

ANP

• Dilates afferent arteriole, constricts efferent arteriole
  • Increased glomerular capillary hydrostatic pressure
    • Increased glomerular filtration
• Inhibits glomerular capillary mesangial cell constriction
  • Increases filtration coefficient by increasing surface area available for diffusion and osmosis

ADH

Reduced CO → reduced MAP → increased signalling of carotid sinus and aortic arch baroreceptors

• Stimulates release of vasopressin (ADH)

ADH

• Induces systemic vasoconstriction
  • Vascular smooth muscle cell V₁ receptors → IP₃ second messenger → increased intracellular calcium
• Increased renal water resorption
  • Distal tubule and collecting duct V₂ receptors
    • Via cAMP
  • Expression of aquaporin 2
    • Water channels

RAAS

Renin

• Release stimulated (from juxtaglomerular cells) by:
  • Sympathetic nerve stimulation (β₁-adrenoreceptors)
  • Reduced afferent arteriolar pressure
  • Reduced flow of Na⁺ and Cl^– in macula densa

Angiotensinogen —renin–> angiotensin I —ACE–> angiotensin II —secreted from zona glomerulosa of adrenal gland —> aldosterone

Angiotensin II

• Systemic vasoconstriction
• Constrict afferent and efferent renal arterioles, constricts mesangial cells -> reduces GFR

Aldosterone

• Stimulates collecting principal cell Na/K ATPase -> sodium resorption, potassium secretion (and so indirectly causes water retention)

Others

• Stimulation of aortic and carotid baroreceptors, cardiopulmonary mechanoreceptors, chemoreceptors
  • Sympathetic activation
  • Release of adrenaline from adrenal medulla
    • Peripheral vasodilation
    • Increased inotropy, chronotropy
• Cortisol release increased
• Erythropoetin released within 24 hours after haemorrhage

Sakurai 2016

Answer by Sakurai