Explain two different ways the kidneys response to decreased blood flow and blood pressure ?

1. Renin-angiotensin-aldosterone system (RAAS): When the kidneys detect decreased blood flow and blood pressure, they release an enzyme called renin into the bloodstream. Renin then converts angiotensinogen, a protein produced by the liver, into angiotensin I. Angiotensin I is then converted into angiotensin II by an enzyme called angiotensin-converting enzyme (ACE), which is primarily produced by the lungs. Angiotensin II is a potent vasoconstrictor, meaning it causes blood vessels to constrict, increasing blood pressure. It also stimulates the release of aldosterone from the adrenal glands, which promotes the reabsorption of sodium and water in the kidneys, further increasing blood volume and blood pressure.

2. Sympathetic nervous system activation: The kidneys also respond to decreased blood flow and blood pressure by activating the sympathetic nervous system. This results in the release of norepinephrine and epinephrine, which are hormones that cause blood vessels to constrict, increasing blood pressure. The sympathetic nervous system also stimulates the release of renin from the kidneys, further activating the RAAS pathway described above. Additionally, the sympathetic nervous system can directly affect the kidneys by reducing blood flow to the renal cortex and medulla, which helps to conserve water and sodium in the body.

1. Renin-angiotensin-aldosterone system (RAAS):
- Decreased blood flow and pressure in the afferent arteriole of the glomerulus stimulates the release of renin from the juxtaglomerular (JG) cells.
- Renin converts angiotensinogen (produced by the liver) into angiotensin I, which is then converted to angiotensin II by angiotensin-converting enzyme (ACE) in the lungs.
- Angiotensin II constricts blood vessels (increasing blood pressure) and stimulates the release of aldosterone from the adrenal glands.
- Aldosterone promotes sodium reabsorption in the collecting tubules of the nephrons, increasing water reabsorption and thus blood volume.

2. Sympathetic nervous system:
- Decreased blood flow and pressure activate the sympathetic nervous system, which releases norepinephrine and epinephrine.
- Norepinephrine and epinephrine constrict blood vessels, increasing systemic vascular resistance (SVR) and thus blood pressure.
- They also stimulate the heart to increase cardiac output, further raising blood pressure.
- In addition, sympathetic activation increases reabsorption of sodium and water in the proximal tubules of the nephrons, contributing to fluid retention and increased blood volume.