Endocrine, Blood, and Cardiovascular Systems Lecture Notes

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How is Angiotensin I converted into Angiotensin II, and where does this conversion primarily occur?

Angiotensin I is then converted to Angiotensin II by Angiotensin-Converting Enzyme (ACE), which is primarily found in the endothelial cells of the lungs (but also present in other tissues).

What are the specific effects of Angiotensin II on blood volume and blood vessel diameter?

Angiotensin II has several key effects:

1. Blood Vessel Diameter: It causes potent vasoconstriction of arterioles, which directly increases total peripheral resistance and thus blood pressure.
2. Blood Volume: It stimulates the adrenal cortex to release aldosterone and the posterior pituitary to release antidiuretic hormone (ADH). It also directly promotes sodium reabsorption in the renal tubules. These actions lead to an increase in blood volume.

What are the specific effects of Aldosterone on blood volume and blood vessel diameter?

Aldosterone primarily affects blood volume by increasing the reabsorption of sodium (and subsequently water) and the excretion of potassium in the renal tubules (distal convoluted tubule and collecting duct). This leads to an increase in blood volume and, consequently, increased blood pressure. It does not directly affect blood vessel diameter.

What are the specific effects of Antidiuretic Hormone (ADH) on blood volume and blood vessel diameter?

Antidiuretic Hormone (ADH), also known as vasopressin, has two main effects:

1. Blood Volume: Its primary role is to increase the reabsorption of water in the renal collecting ducts by inserting aquaporins. This reduces urine output and directly increases blood volume.
2. Blood Vessel Diameter: At high concentrations (e.g., during severe dehydration or hemorrhage), ADH can also cause potent vasoconstriction of systemic arterioles, which contributes to an increase in blood pressure and helps maintain perfusion.