List the hormones secreted by the atrium.

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Hint: The hormone secreted by atria is responsible for the reduction of blood volume in the atrium as well as regulation of ECF volume and blood pressure. These are secreted by the myocardiocytes in the wall of atria.

Complete answer:
The cardiac atria of humans secrete a specific peptide hormone known as Atrial natriuretic peptide (ANP) or atrial natriuretic factor (ANF). In humans, this secretion is encoded by the NPPA gene. It is synthesized and secreted by cardiac muscle cells present in the wall of the atria. The main function of this hormone is to cause a reduction in expanded ECF volume by increasing the renal sodium excretion.

Additional Information:
The atrium is the upper chamber of the human heart that receives the blood from the exterior and sends it to the ventricle. There are two of these- one on the right side and the other on the left side of the heart. The left one receives blood from lung circulation whereas the right one receives from venous circulation.
Cardiac muscle cells are myocardiocytes are the myocytes that constitute the cardiac muscle and are the source of the ANP hormone. The volume receptors in these cells respond to the increased stretch of the atrial wall by increased blood volume.
There are three types of natriuretic peptides present in our body- ANP, BNP, and CNP. Among these, ANP is responsible for ECF volume regulation. The reduction of blood volume caused by ANP may result in secondary effects like the reduction of ECF volume, improved cardiac ejection fraction, decrease in blood pressure, serum potassium increase, etc.

Note: Other natriuretic peptides BNP and CNP also have considerable importance in our bodies. BNP is secreted by the heart ventricle as a response to increased ventricular blood volume. This hormone is responsible for a decrease in cardiac output and an overall decrease in Central venous pressure as well as a reduction in blood volume that follows natriuresis and diuresis. On the other hand, CNP is synthesized and secreted by the endothelium in response to stimuli like shear stress or certain pro-inflammatory cytokines but it doesn't work as a natriuretic peptide-like ANP or BNP.