Transport maximum

Transport maximum (also known as Tm) is the maximum rate at which a substance can be reabsorbed by the kidneys. This is a crucial concept in physiology, particularly in the study of renal physiology.

Overview

The kidney is responsible for filtering waste products from the blood and excreting them in the urine. One of the ways it does this is through a process called reabsorption, where substances are taken back into the body from the filtrate. However, there is a limit to how much of a substance the kidneys can reabsorb. This limit is known as the transport maximum.

Mechanism

The transport maximum is determined by the number of available transporter proteins in the renal tubules. These proteins bind to the substance that needs to be reabsorbed and carry it back into the body. When all the transporter proteins are occupied, the substance will start to appear in the urine, as it can no longer be reabsorbed. This point is known as the transport maximum.

Clinical significance

The concept of transport maximum is particularly important in conditions such as diabetes mellitus, where the blood glucose levels are high. Normally, all the glucose in the filtrate is reabsorbed back into the body. However, in diabetes, the glucose levels exceed the transport maximum for glucose reabsorption, leading to glucose appearing in the urine (a condition known as glycosuria).

See also

• Renal physiology
• Reabsorption
• Diabetes mellitus
• Glycosuria

References

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