Atrial natriuretic factor is released by
A) Heart
B) Brain
C) Kidney
D) Pancreas

Hint: Several factors contribute to the release of Atrial natriuretic factor in response to increased atrial pressure. These include vasoconstrictors, atrial tachycardia, and increased consumption of salt in the diet among others.

Complete Answer:
- The atrial natriuretic factor or peptide is a molecule that helps regulate atrial volume. This polypeptide hormone is secreted by the cells of the atrium in response to increased stretch of the heart wall. The correct answer is A.
- The brain also releases a similar natriuretic peptide hormone which regulates atrial pressure. Brain-type natriuretic factor is released both by the brain and the atrium. However, this is a different peptide from ANP. Option B is incorrect.
- The role of the kidneys in regulating blood volume is partially regulated by the heart. ANF stimulates sodium excretion and glomerular filtration rate, both of which will work towards decreasing blood volume. The kidneys also respond to aldosterone and ADH to regulate urine production and thereby decrease overall blood volume helping lower blood pressure. Answer C is therefore incorrect.
- ANP is involved in regulating the function of the exocrine pancreas. It has been seen that there is an ANP-like hormone produced by the pancreas. However, the quantities of this are very small as compared to the ANP from the heart. Therefore, option D is incorrect.

Hence the correct answer is option A.

Note: The functioning of the body through the actions of hormones is done through several feedback mechanisms. Each hormone can affect a specific organ resulting in a particular response, which in turn can increase or decrease the production of that hormone.