Biology Chapter: Plasma Composition and Proteins

Plasma Composition

• Plasma comprises water (90%), organic compounds (9%), inorganic compounds (1%), and other organic compounds (2%).
• Key plasma proteins include albumin (7%), globulin (2.7%), and fibrinogen (0.3%).

Plasma Proteins

• Plasma contains over 300 different proteins.
• Many illnesses affect plasma protein levels.
• Most proteins are produced in the liver.
• A normal adult's plasma contains roughly 70 g/L of protein.
• Plasma protein concentration in humans is about 6-8.3 g/dL.
• Plasma proteins include simple proteins and conjugated proteins, such as glycoproteins and various lipoproteins.

Learning Objectives

• Students will learn about plasma composition and plasma proteins.
• Students will grasp the difference between plasma and serum.
• Students will understand plasma protein separation techniques.
• Students will familiarize themselves with individual plasma proteins and their functions.
• Students will learn about clinical abnormalities linked to plasma proteins.

Patient Case

• A 50-year-old woman, experiencing unconsciousness, anemia, and edema, had a blood sample taken for lab analysis.

Blood Composition

• Plasma makes up approximately 55% of blood.
• White blood cells and platelets account for less than 1% of blood.
• Red blood cells constitute about 45% of blood.

Functions of plasma Proteins

• Transport: Transferrin carries iron; ceruloplasmin transports copper; albumin transports fatty acids, bilirubin, calcium and many drugs; transcortin transports cortisol and corticosterone; retinol-binding protein transports retinol; haptoglobin transports free hemoglobin; thyroxine-binding globulin transports thyroxine.
• Osmotic Regulation: Plasma proteins maintain blood volume and fluid content in the interstitial fluid.
• Blood clotting: Clotting factors like fibrinogen participate in blood clotting mechanisms. Excess or deficiency may lead to disease states like hemophilia.
• Anticoagulant activity: Plasmin breaks down thrombin and dissolves clots.
• Buffering: Plasma proteins help regulate the body's acid-base balance.

Clinical Significance of Albumin

• Albumin is crucial for maintaining colloidal osmotic pressure.
• Low albumin levels cause fluid retention in tissues (edema).
• Albumin transports fatty acids, preventing them from crossing the blood-brain barrier.
• Bilirubin is bound to albumin; medications can displace albumin's bilirubin binding, causing problems in newborns.
• Albumin synthesis decreases in liver disease or starvation, leading to edema

Synthesis of Albumin

• The liver synthesizes about 12 g of albumin daily.
• This represents 25% of total hepatic protein synthesis.
• Albumin is initially synthesized as a preproprotein.
• A signal peptide and a hexapedide are removed, completing the synthesis pathway.

Other Plasma Proteins: Globulins

• Globulins, separated by half-saturation with ammonium sulfate, have molecular weights ranging from 90,000 to 1,300,000.
• Electrophoresis separates globulins into alpha-1, alpha-2, beta, and gamma globulins.
• Alpha and beta globulins are produced by the liver.
• Gamma globulins are generated in plasma cells and lymphoid tissues.
• Gamma globulin levels rise in infections, liver disease, and various malignancies.
• Specific examples of globulins include alpha-1 antitrypsin, alpha-1 acid glycoprotein, and alpha-1 fetoprotein.

Alpha-1 Antitrypsin

• Also known as alpha-1-antiprotease.
• A single-chain protein with 3 oligosaccharide chains.
• It is the primary component (>90%) of the alpha-1 fraction.
• Produced by hepatocytes and macrophages.
• It's a key inhibitor of serine proteases, like elastase.
• Deficiency leads to proteolytic lung damage (emphysema), often exacerbated by smoking.

a2-Macroglobulin

• Synthesized by hepatocytes and macrophages.
• Acts as a general protease inhibitor, crucial for in vivo anticoagulation.
• Increased levels are frequently seen in nephrotic syndrome.

Ceruloplasmin

• A copper-containing alpha-2-glycoprotein.
• It carries about 90% of the copper in plasma.
• Synthesized by the liver, as apoceruloplasmin, and copper attachment leads to its active form.

Other Properties

• The most clinically important α₂-globulins are haptoglobins, ceruloplasmin, and α₂-macroglobulins.

Other Proteins (β-globulins)

• Key examples in this group are Transferrin, C-reactive protein, hemopexin, complement C1q and B lipoprotein (VLDL).

Critical Clinical Conditions

• Nephrotic syndrome: Low molecular weight proteins (and higher) are lost in the urine, affecting various protein levels in the blood.
• Cirrhosis: Impaired liver function reduces the synthesis of many plasma proteins, including albumin.
• Chronic Infections.
• Leukemias/Lymphoma: Certain types show elevated levels of abnormal plasma proteins.
• Multiple myeloma: Characterized by an abnormal immunoglobulin (light chain) in the urine called Bence Jones protein.

Abnormal Electrophoretic Patterns

• Nephrotic syndrome: Low molecular weight proteins lost in urine.
• Cirrhosis: Decreased albumin, increased globulin.
• Chronic infections, leukemias, and lymphomas: Elevated gamma globulins.
• Rheumatoid arthritis: Elevated gamma and alpha-2 globulin.
• Multiple myeloma: Characteristic spike (M band) due to monoclonal immunoglobulin.
• Alpha-1-antitrypsin deficiency: Thin or missing alpha-1 band.

Prealbumin (Transthyretin)

• A transport protein for thyroid hormones and retinol (vitamin A).
• Migrates faster than albumin in electrophoresis.
• Separated by immunoelectrophoresis.
• Lower levels may indicate liver disease, nephrotic syndrome, acute phase reaction, or malnutrition.
• Short half-life (2 days).

Fibrinogen

• Also called clotting factor 1, and it represents 4-6% of total plasma protein.
• Synthesized by the liver and has 6 polypeptide chains linked by disulfide bonds, essential in blood clotting mechanisms.
• Elevated levels accompany inflammation and some cancers(acute phase proteins).

Negative Acute Phase Proteins

• Albumin, transthyretin (prealbumin), RBP and transferrin can decrease during inflammatory processes.

Cryoglobulins.

• Proteins that precipitate at low temperatures causing obstructions in blood vessels.

General Plasma Protein Function summaries

• Transport: Transport various substances, including hormones, metals, lipids, and drugs.

This quiz covers the essential aspects of plasma composition including its percentage breakdown and the various proteins present in plasma. Students will learn about the roles of plasma proteins, techniques for separation, and how plasma differs from serum. Understanding these concepts is crucial for recognizing clinical implications related to plasma protein levels.