In: Anatomy and Physiology
If someone is over-hydrated, how can the body respond to correct the fluid/electrolyte imbalance? Include which hormone(s) would be secreted/or inhibited to correct the imbalance, and describe exactly how these hormones fix the imbalance.
When someone is over hydrated then in that case blood volume increases. Atrial Natriuretic Peptide (ANP) is secreted from cardiac muscle cells in atria when it senses atrial stretch due to increase in blood volume. Increase in blood volume causes increase in blood pressure. On sensing this, ANP causes vasodilation of afferent arteriole of glomerulus apparatus this causes increase in renal blood flow and increase in glomerulus filteration rate. ANP also causes vasoconstriction of efferent arteriole of glomerulus apparatus which increases glomerulus filteration volume. All these effect of ANP along with inhibition of reabsorption of water in renal tubules leads to increase in excretion of water and urine volume thereby leading to diuresis. ANP also acts on collecting duct of nephron to reduce reabsorption of Na+ which enhances sodium excretion. ANP also acts on proximal tubule and inhibit Na+/H+ exchange and also inhibits reabsorption of Na+/Cl- in distal tube, both these actions of ANP also enhances sodium excretion. Hence the diuresis and naturesis caused by ANP reduces the blood volume and controls over hydration.
Secondly in condition of over hydration, RAAS system does not get active and renin is not secreted from juxtaglomerular cells and due to which angiotensin II is not produced due to which Anti diuretic hormone (ADH) secrettion from posterior pituitary does not happen and because of which water reabsorption does not take place in renal tubules. Moreover in the absence of angiotensin II, aldosterone is also not produced from adrenal cortex due to which sodium does not gets reabsorbed from renal tubules. Hence, inhibition of ADH and aldosterone causes diuresis and naturesis due to which excess water is removed from body and over hydration is controlled.