Question

what roles do kidneys play in blood pressure maintenance? Include the following in the answer: urine, Na+, renin, angiotensin 2, blood volume, osmotic pressure, and aldosterone

Answer 1

- In case of deceased blood pressure due to low blood volume as a result of dehydration or hemorrhage or deceased plasma sodium concentration, the juxtaglomerular cells (JG cells) of kidneys secrete a hormone called renin.
- Renin converts angiotensinogen produced by liver to angiotensin I which is converted into angiotensin ll by angiotensin converting enzyme (ACE).
- Angiotensin ll is a potent vasoconstricter which constricts the vascular smooth muscles and increase the blood pressure, bringing it back to normal range.
- Angiotensin ll also stimulates zona glomerulosa of adrenal cortex to secrete aldosterone. Aldosterone increases the reabsorption of water and sodium from renal tubules into the circulation thus increasing the blood volume and bringing back the blood pressure to normal range. Aldosterone also increases the excretion of potassium ions from the renal tubules.
- When the osmotic pressure of the blood is increased, there is increased production of antidiuretic hormone (ADH) from the hypothalamus and increased release of ADH from posterior pituitary gland into the blood stream (ADH is produced by hypothalamus and stored in the posterior pituitary gland from where it is released into the blood stream when required).
- ADH acts on the distal tubules and collecting ducts of nephrons and increases the reabsorption of water from the renal tubules into the circulation thus increasing the fluid volume of plasma and bringing back the osmolarity of plasma to normal level. This increased water reabsorption from the tubules leads to the production of a hypertonic urine.
- Thus, the renin-angiotensin-aldosterone system (RAAS) and antidiuretic hormone (ADH) helps in regulating the blood pressure by increasing the reabsorption of water and sodium from the tubules into the circulation and producing a hypertonic urine.