Filtration

Welcome to this lesson on filtration. In this lesson today, you will be learning about filtration and its role in urine production. Specifically, you will learn about:

1. Urine Formation Overview
2. Filtration

1. Urine Formation Overview

So there's three steps to urine formation. Filtration's the first step, followed by reabsorption and then secretion. These steps of urine formation occur in the nephrons, which are found in the kidneys. So these nephrons filter blood, and they filter water and solutes out of the blood, and then help to form urine. But today, you’re going to be focusing on this first step of filtration.

2. Filtration

Filtration is the first step in urine production and this process of urine formation ensures that only necessary products are excreted from the body. Filtration only occurs within a specific part of the nephron, Bowman's capsule. During filtration blood enters the capillaries within Bownman's capsule, called the glomerulus or glomeruli, through the afferent arteriole, which is narrow compared to other blood vessels within the body. Because of this, blood is delivered towards the nephron through the afferent at a high pressure due to the more narrow diameter these arterioles have. This high pressure will force water and solutes from the blood, from the blood in these afferent arterioles, into the Bowman's capsule of the nephron.

The solutes that are forced out of the blood include: glucose, sodium, urea, vitamins, amino acids, et cetera. Water and solutes that are pushed out of the blood would then flow into the proximal tubule where the next stage of urine formation occurs, reabsorption.

Larger solutes in the blood, such as blood cells or platelets, will actually end up staying in the blood, and follow the arteriole as it weaves around the nephron.

• Filtration
• The first step in urine formation in which solutes and water are forced out of blood and into the bowman's capsule of a nephron.
• Bowman's Capsule
• A section of a nephron where afferent arterioles deliver blood to the nephron for water and solutes to be filtered out.
• Glomerulus
• A tangle of blood vessels in the bowman's capsule where water and solutes are forced out of blood and into the bowman's capsule to begin the next stage of urine formation.

So this lesson has been an overview on filtration as the first step in urine formation.

Keep up the learning and have a great day!