Reabsorption

Welcome to this lesson on reabsorption. In this lesson today, you will be discussing the role of reabsorption in urine formation. Specifically you will learn about:

1. Urine Formation Overview
2. Reabsorption

1. Urine Formation Overview

Urine formation's purpose is to make sure that only necessary products are excreted from the body. Urine formation takes place within the kidneys and the nephrons. Nephrons will filter blood and produce urine in a three-step process. The first step is filtration, then reabsorption, and then secretion. Though this is a three step process, this tutorial will focus primarily on the second step, reabsorption.

2. Reabsorption

Reabsorption is the second step in urine formation and reabsorption is also sometimes referred to as tubular reabsorption. In this step of urine formation water and solutes that have been filtered from blood in the first step, filtration, move throughout the rest of the nephron. Water and other solutes sometimes are very valuable and our body needs to retain them. These water and solutes need to be reabsorbed back into blood so the body can retain them.

So reabsorption takes place across the walls of the proximal tubules, primarily. The walls of the proximal tubule are very thin, about one cell thick. Solutes and water will leak out or be pumped out of nephron tubules and will then be reabsorbed into peritubular capillaries.

Peritubular capillaries interweave within the nephron and from there, they will return solutes to the bloodstream. Any remaining solutes that weren't reabsorbed from the nephron tubules into the bloodstream will become a part of urine.

• Tubular Reabsorption
• The second step in urine formation in which water and valuable solutes are reabsorbed from the nephron into the bloodstream.

• Peritubular Capillaries
• Capillaries associated with nephrons which allow water and solutes to be exchanged between the nephron and the blood during urine formation.

This step of reabsorption returns the vast majority of water and solutes, such as glucose, amino acids, and sodium back to the blood. Between 95 to 100% of those solutes get returned back into the blood because our body needs them. Any remaining solutes that do not get returned back to the blood will then become a part of urine.

So this lesson has been an overview on the reabsorption stage of urine formation.

Keep up the learning and have a great day!