Q.(a) Explain the heart's role in secreting a hormone that regulates renal function ? What hormone is this ? OR

The heart secretes the hormone Atrial Natriuretic Factor (ANF, also called Atrial Natriuretic Peptide, ANP) from its atrial muscle when the atrial walls are stretched by excess blood volume; ANF acts on the kidneys and blood vessels to lower blood volume and blood pressure.

Although the heart is primarily known as a pumping organ, specialised muscle cells in the walls of the atria (the upper chambers of the heart) also function as endocrine cells. When blood volume increases (for example, due to excess fluid or high blood pressure), the atrial walls are stretched more than normal. This mechanical stretching directly stimulates the atrial muscle cells to secrete a peptide hormone called Atrial Natriuretic Factor (ANF), also known as Atrial Natriuretic Peptide (ANP).

Once released into the blood, ANF has several coordinated effects that work to reduce the excess blood volume and pressure that triggered its release:

• It causes vasodilation (relaxation/widening) of blood vessels, which directly lowers blood pressure.

• It acts on the kidneys to increase the excretion of sodium ions (natriuresis) and, following the sodium, water as well (diuresis), reducing overall blood volume.

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