The plasma protein that maintains oncotic pressure of blood is:?

SGPGI Nursing Officer-2022

Applied Physiology

Easy

Appeared in: SGPGI Nursing Officer-2022

Explanation

Albumin is the most abundant protein in the blood plasma, constituting about 60% of the total plasma proteins.
It is the primary contributor to colloid osmotic pressure (oncotic pressure), accounting for approximately 80% of this effect.
This osmotic force is crucial for retaining fluid within the capillaries, counteracting the hydrostatic pressure that pushes fluid out into the tissues.
A decrease in albumin concentration directly leads to a fall in oncotic pressure, resulting in fluid shifts and edema.

Option A: Globulins are primarily involved in the immune response (as antibodies or gamma globulins) and in transporting substances like lipids and hormones. While they contribute to oncotic pressure, their contribution is minor (about 20%) compared to albumin.
Option B: Fibrinogen is a soluble protein that is converted into insoluble fibrin threads during the blood clotting process. Its role is in hemostasis, not in maintaining oncotic pressure, to which its contribution is negligible.
Option D: Prothrombin is a zymogen (inactive enzyme precursor) involved in the coagulation cascade. It is converted to the active enzyme thrombin, which then acts on fibrinogen. It has no role in maintaining oncotic pressure.

Clinical Relevance

Nursing practice connection: Knowing Role of Plasma Proteins in Oncotic Pressure helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Low levels of albumin (hypoalbuminemia) cause a decrease in oncotic pressure, leading to fluid shifting from the blood vessels into the interstitial tissues. This is a key concept for nurses to understand the pathophysiology of edema.
Nurses must assess for signs of edema (e.g., pitting edema in the extremities, ascites, pulmonary edema) in patients with conditions known to cause low albumin, such as liver failure, nephrotic syndrome, and severe malnutrition.
What if? If a patient has chronic liver disease, their ability to synthesize albumin is impaired. This leads to low oncotic pressure and classic signs like ascites (abdominal swelling) and peripheral edema, which are critical findings for a nurse to monitor and manage.

How to Approach the Question

This is a factual recall question that tests your knowledge of basic physiology.
Identify the keywords in the question: 'plasma protein' and 'oncotic pressure'.
Mentally review the main types of plasma proteins and their primary functions.
Recall that Albumin's main role is maintaining oncotic pressure and transport.
Recall that Globulins are mainly for immunity and transport.
Recall that Fibrinogen and Prothrombin are essential for blood clotting.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 1 p. 168-170

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 619-621