What are Plasma
Proteins?
- Plasma
proteins are proteins present in the plasma (fluid part of blood).
- They form
about 6–8% of plasma.
- Synthesized
mainly in the liver, except immunoglobulins (made by plasma
cells).
Types of Plasma
Proteins
There are three main types:
|
Plasma Protein |
% of Total |
Site of Synthesis |
|
Albumin |
~60% |
Liver |
|
Globulin |
~36% |
Liver & plasma cells |
|
Fibrinogen |
~4% |
Liver |
Mnemonic: "A-G-F" =
Albumin → Globulin → Fibrinogen (in decreasing order of %)
1. Albumin
- Most abundant
plasma protein (~60%)
- Synthesized
by liver
- Molecular
weight: ~69,000 Da
Functions of Albumin
- Maintains colloidal
osmotic pressure (pulls water into blood vessels)
- Acts as carrier
protein (for hormones, bilirubin, drugs, etc.)
- Acts as a buffer
to maintain pH
Mnemonic: “COB”
C – Carrier
O – Osmotic pressure
B – Buffer
2. Globulins
Divided into:
- α1, α2, β globulins
– made by liver
- γ-globulins
(immunoglobulins) – made by plasma cells
Functions of Globulins
- Transport
substances (lipids, vitamins, metals)
- Immunity –
γ-globulins = antibodies (IgG, IgA, etc.)
- Maintain osmotic
pressure
Mnemonic: “TIE”
T – Transport
I – Immunity
E – Exert osmotic pressure
3. Fibrinogen
- Least
abundant but vital for blood clotting
- Large
protein (~340,000 Da)
- Synthesized
in the liver
Function:
- Gets
converted into fibrin during coagulation → helps in clot
formation
Mnemonic: "F = Fibrin = Formation of clot"
Other Proteins Present
in Plasma (Minor ones):
- Complement
proteins – immunity
- Lipoproteins –
transport of lipids
- Enzymes –
metabolic activities
- Hormone-binding
proteins – transport hormones
Normal Values of Plasma
Proteins:
|
Component |
Normal Range (g/dL) |
|
Total proteins |
6–8 g/dL |
|
Albumin |
3.5–5 g/dL |
|
Globulins |
2–3.5 g/dL |
|
Fibrinogen |
0.2–0.4 g/dL |
Clinical Importance:
|
Condition |
Effect on Plasma Proteins |
|
Liver disease (cirrhosis) |
↓ Albumin, ↓ Fibrinogen |
|
Nephrotic syndrome |
Loss of albumin in urine |
|
Chronic infections |
↑ Globulins |
|
Malnutrition |
↓ All plasma proteins |
Super Mnemonic Summary
for Functions:
“TOPIC”
- T –
Transport (Albumin, Globulins)
- O – Osmotic
pressure (Albumin, Globulins)
- P –
Protection (Immunoglobulins, Complement)
- I –
Immunity (γ-globulins)
- C –
Clotting (Fibrinogen)
FAQs – Frequently Asked Questions
Q1. What are plasma
proteins?
Ans: Proteins present in plasma, mainly albumin, globulin, and fibrinogen,
performing transport, immune, and clotting functions.
Q2. Which is the most
abundant plasma protein?
Ans: Albumin (~60%)
Q3. What is the
function of fibrinogen?
Ans: It helps in blood clot formation by converting into fibrin.
Q4. Where are plasma
proteins synthesized?
Ans:
- Albumin,
globulin (α, β), fibrinogen – liver
- γ-globulins
(antibodies) – plasma cells
Q5. What happens to
plasma proteins in liver disease?
Ans: ↓ Albumin and ↓ fibrinogen → leading to edema and bleeding tendency
