Human A&P 202 Review: Osmolarity of Body Fluids

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I'm posting Human A&P 202 topics, to help me review for nursing school; hopefully they will be helpful for students currently taking BIO202.

Osmolarity of Body Fluids

Na+ and K+ regulation are crucial to overall body homeostasis. Their regulation is the primary job of aldosterone (a mineralocorticoid). Changes is Na+ concentration lead to changes in blood volume, blood pressure and rising levels of K+ lead to aldosterone secretion by the adrenal cortex. The regulation of a number of ions including K+, H+, HCO3- and Cl- is coupled to that of Na+. Aldosterone reduces excretion of Na+ from the body. It targets the distal parts of the kidney tubules, where it stimulates Na+ reabsorption and water retention along with the elimination of K+.

The renin-angiotensin mechanism influences both blood volume and blood pressure by regulating the release of aldosterone and therefore Na+ and water reabsorption by the kidneys. Specialized cells in the kidneys release renin into the blood when blood volume/pressure declines. Renin initiates a cascade that produces Angiotensin II; an aldosterone stimulator.

Fluctuation blood levels of K+ directly influence the zona glomerulosa cells in the adrenal cortex. Increased K+ stimulates aldosterone release.

Atrial natriuretic peptide hormone is secreted by the heart when blood pressure rises, fine tunes blood pressure and sodium-water balance of the body. It blocks renin and aldosterone secretion, consequently ANP'S overall influence is to decrease blood pressure by allowing Na+ and water to flow out of the body in urine.

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From: Human Anatomy & Physiology- Elaine N. Marieb & Katja Hoehn

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