Renin is a protease renin secreted by the paraglomerular apparatus and is mainly influenced by the small renal artery pressure and the sodium content in the primary urine. If there is a decrease in small renal artery pressure, or after a decrease in sodium content, it will activate an increase in the secretion of renin by the glomerular collateral organ, leading to activation of the renin-angiotensin-aldosterone system, which may eventually lead to an increase in sodium-preserving blood volume and an increase in blood pressure effect. Increased renin secretion is seen in patients with decreased renal artery pressure due to shock, and in patients with decreased renal artery pressure due to conditions such as hypotension, which can also lead to increased renin secretion after hyponatremia.