Snapshot
- A 30-year-old man presents with increased frequency in urination and persistent thirst despite drinking a lot of water. He reports drinking > 15 L of water per day without relief of his symptoms. Urine studies show low urine osmolality and low urine sodium. Administration of vasopressin causes relief of symptoms. The physician tells this patient that he is missing a key hormone that plays an important role in both maintaining serum osmolarity and blood pressure. (Central diabetes insipidus)
Introduction
- Mean arterial pressure (MAP) is maintained by
- baroreceptors
- chemoreceptors
- renin-angiotensin-aldosterone system
- antidiuretic hormone (ADH)
- atrial natriuretic peptide (ANP)
- Baroreceptors
- located in the carotid sinus and aortic arch
- via glossopharyngeal nerve and vagus nerve
- works to maintain arterial pressure at a constant
- responds to ↑ or ↓ in arterial pressure
- located in the carotid sinus and aortic arch
- Chemoreceptors
- located in carotid sinus, aortic arch, and medulla
- works to maintain PO
2, PCO
2, and pH
- peripheral chemoreceptors respond to a ↓ partial pressure of oxygen (PO
2), ↓ pH, and ↑ PCO
2
- central chemoreceptor respond to ↑ or ↓ in PCO
2 or pH
- Renin-angiotensin-aldosterone system
- works to maintain MAP by controlling blood volume
- renin is secreted in response to ↓ arterial pressure
- renin converts angiotensinogen → angiotensin I
- angiotensin-converting enzyme (ACE) converts angiotensin I → angiotensin II
- angiotensin II
- induces aldosterone secretion
- increases thirst
- induces secretion of ADH secretion
- acts on arterioles to ↑ total peripheral resistance (TPR)
- aldosterone increases Na+ reabsorption in the kidney
- ADH
- regulates serum osmolarity and blood pressure
- increases water reabsorption in the kidney
- ANP
- works to decrease blood volume when an ↑ atrial pressure
- a diuretic released by the atria in response to ↑ atrial pressure and blood volume
- vasodilation → ↓ TPR
- inhibits renin secretion
- increased Na+ and water excretion