Given a text passage, come up with an appropriate title for it. The title should accurately represent what the main focus of the passage is. The title of a passage may be present in the first few sentences of the passage and/or be referred to multiple times in the passage. The title should be 1-5 words long.
Q: Atrial natriuretic peptide ( ANP ) or Atrial natriuretic factor ( ANF ) is a peptide hormone which reduces an expanded extracellular fluid ( ECF ) volume by increasing renal sodium excretion . ANP is synthesized , and secreted by cardiac muscle cells in the walls of the atria in the heart . These cells contain volume receptors which respond to increased stretching of the atrial wall due to increased atrial blood volume . ANP is one of a family of nine natriuretic peptides : seven are atrial in origin .
A:
Atrial natriuretic peptide