Plasma osmolality

Plasma osmolality refers to the measure of the concentration of solutes per kilogram in the blood plasma. It is a crucial aspect of homeostasis, as it influences water distribution between body compartments and helps maintain the balance of the body's electrolytes.

Overview

Plasma osmolality is typically determined by the concentration of sodium, glucose, and urea in the blood. It is usually measured in milliosmoles per kilogram (mOsm/kg). The normal range for plasma osmolality is between 275 and 295 mOsm/kg.

Function

The primary function of plasma osmolality is to control the balance of water and solutes in the body. It plays a significant role in maintaining the body's homeostasis. When the plasma osmolality increases, it triggers the release of antidiuretic hormone (ADH) from the pituitary gland. ADH then acts on the kidneys to conserve water and reduce urine output, thereby decreasing the plasma osmolality.

Measurement

Plasma osmolality can be measured directly using osmometry or estimated using a formula. The most commonly used formula is:

Osmolality (mOsm/kg) = 2 x ([Na+] + [K+]) + [Glucose] + [Urea]

Where:

[Na+] and [K+] are the concentrations of sodium and potassium in the blood.

[Glucose] and [Urea] are the concentrations of glucose and urea in the blood.

Clinical Significance

Abnormal plasma osmolality can indicate various medical conditions. High plasma osmolality (hyperosmolality) can be caused by dehydration, diabetes, and certain types of drug toxicity. Low plasma osmolality (hypo-osmolality) can be due to overhydration, liver disease, or certain hormonal disorders.

See Also

• Osmolality
• Osmosis
• Homeostasis
• Antidiuretic hormone
• Pituitary gland

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