Secretion

Welcome to this lesson today on secretion. Today you will be taking a look at the process of secretion and its role in urine formation. Specifically you will learn about:

1. Urine Formation Overview
2. Secretion

1. Urine Formation Overview

Urine formation, as a whole, takes place within the kidneys and nephrons of the kidneys will filter blood and produce urine. There's three steps to urine formation that ensure only necessary products are excreted from the body; secretion is the third step in urine formation. First there is filtration, which occurs in the Bowman's capsule. Then there is reabsorption, which occurs primarily within the proximal tubule followed by secretion, which is the third step you'll learn about today.

2. Secretion

Tubular secretion starts at the proximal tubule, and then it'll occur at the other tubular parts of the nephron as it moves through. Substances such as hydrogen, potassium and urea at this point will move from the peritubular capillaries into nephron tubules, joining with forming urine.

• Tubular Secretion
• The third step in urine formation which is the process of secreting materials (wastes, acids) from peritubular capillaries into the nephron that weren’t filtered at the glomerulus.

In reabsorption, water and extra solutes that haven't been reabsorbed back into the blood will become a part of urine. Hydrogen, potassium, and urea from the peritubular capillaries will join with them, forming urine. Urine will then move toward the collecting duct, which will then move the formed urine into the ureters, and then the urinary bladder.

Secretion helps to maintain the body's acid base balance, and makes sure that substances don't build up in the blood. It starts at the proximal tubule and will work its way down through the Loop of Henley and distal tubule.

To better understand, take a look at the diagram below:

Here have the kidney and the kidney is where the nephrons are located. The nephrons produce urine and carry it to the collecting ducts. Collecting ducts moveurine to the renal pelvis of the kidney, which funnels it into the ureter. Ureters then, will funnel that urine down to the urinary bladder where it will be stored until it's excreted through the urethra. The urethra connects the urinary bladder to the outside, as urine is excreted. When urine is expelled from the urinary bladder through the urethra to the outside, we call that urination which is a reflex response.

• Urination
• A reflex that occurs when the urinary bladder fills to capacity and is stimulated to empty itself.

As the bladder fills with urine that it's storing, the tension across the muscles of the urinary bladder will increase, causing the internal sphincter to relax. The bladder will then contract, or shorten, forcing urine out through the urethra.

This lesson has been an overview on the third step of urine formation, called secretion.

Keep up the learning and have a great day!