Final answer:
Angiotensin II is the hormone secreted by the kidney that causes blood vessels to narrow, leading to an increase in blood pressure. It is part of the renin-angiotensin-aldosterone system, working alongside aldosterone and ADH to regulate blood pressure and fluid balance.
Step-by-step explanation:
The hormone secreted by the kidney that influences vasoconstriction and raises blood pressure is angiotensin II. Angiotensin II is a very potent vasoconstrictor, causing the blood vessels to narrow, thereby increasing blood pressure. It is part of the renin-angiotensin-aldosterone system (RAAS) which tightly regulates blood pressure and fluid balance in the body. When blood pressure falls, renin is released by the kidneys, which converts angiotensinogen from the liver into angiotensin I. Angiotensin converting enzyme (ACE), primarily in the lungs, then converts angiotensin I to angiotensin II. This hormone not only causes vasoconstriction but also stimulates the release of aldosterone from the adrenal cortex, leading to increased sodium and water reabsorption in the kidneys, which further elevates blood pressure.
In addition to increasing blood pressure through vasoconstriction, angiotensin II and aldosterone work together to preserve vascular volume. Aldosterone leads to the reabsorption of sodium ions and water, increasing blood volume, and consequently, blood pressure. Moreover, angiotensin II can signal the release of anti-diuretic hormone (ADH) from the hypothalamus, which also promotes water retention and blood pressure increase.