8.6: Blood Plasma — Read — Invisible Network

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Plasma consists primarily of water, accounting for about 92 percent, along with a complex mixture of substances. These include both organic and inorganic components, such as nutrients, gasses, electrolytes, hormones, antibodies, antigens, and waste products, either dissolved or suspended, each present in varying concentrations. Nonprotein solutes make up roughly one percent of the total plasma volume, while approximately seven percent consists of proteins. Serum, on the other hand, is the liquid portion of blood remaining after coagulation, essentially plasma without the clotting factors. It is commonly used in diagnostic tests as it provides valuable information about the body's biochemical and metabolic state.

Plasma Proteins

Plasma proteins can be broadly classified into three main groups. Albumin is the most abundant plasma protein and is synthesized by the liver. It primarily acts as a transport vehicle for fatty acids and steroid hormones. Since lipids are hydrophobic, they require binding to albumin for transportation in the watery plasma. Albumin also plays a crucial role in maintaining osmotic pressure within blood vessels, which helps regulate blood volume and pressure. Typically, albumin constitutes around 54 percent of the total plasma protein content, with clinical levels ranging from 3.5 to 5.0 g/dL of blood.

Globulins are the second most prevalent group of plasma proteins and consist of three main subgroups: alpha, beta, and gamma globulins. Alpha and beta globulins serve as carriers for substances like iron, lipids, and fat-soluble vitamins (A, D, E, and K) to deliver them to cells. Additionally, they contribute to osmotic pressure. Gamma globulins, also known as immunoglobulins or antibodies, are crucial components of the immune system and are produced by specialized WBCs called plasma cells. Globulins account for approximately 38 percent of the total plasma protein volume, with clinical levels ranging from 1.0 to 1.5 g/dL of blood.

Fibrinogen is the least abundant of the plasma proteins and, like albumin and certain globulins, is synthesized by the liver. It plays a vital role in the blood clotting process. Fibrinogen comprises about seven percent of the total plasma protein volume, with clinical levels ranging from 0.2 to 0.45 g/dL of blood.⁴

**Table 1** | Major Blood Components |
Component and % of Blood	Subcomponent and % of Component	Type and % (where appropriate)	Site of Production	Major Function(s)
Plasma 46-63%	Water 92%	Fluid	Absorbed by Intestinal Tract or Produced by Metabolism	Transport Medium
	Plasma Proteins 7%	Albumin 54-60%	Liver	Maintain Osmotic Concentration, Transport Lipid Molecules
		Globulins 35-38%	Alpha Globulins - Liver	Transport, Maintain Osmotic Concentration
			Beta Globulins - Liver	Transport, Maintain Osmotic Concentration
			Gamma Globulins (Immunoglobulins)- Plasma Cells	Immune Responses
		Fibrinogen 4-7%	Liver	Blood Clotting
	Regulatory Proteins <1%	Hormones and Enzymes	Various Sources	Regulate Various Body Functions
	Other Solutes 1%	Nutrients, Gasses, and Wastes	Absorbed by Intestinal Tract, Exchanged in Respiratory System, and Produced by Cells	Numerous and Varied
Formed Elements 37-54%	Erythrocytes 99%		Red Bone Marrow	Transport Oxygen and Carbon Dioxide
	Leukocytes <1%	Granular Leukocytes: Neutrophils, Eosinophils, Basophils	Red Bone Marrow	Nonspecific Immunity
		Agranular Leukocytes: Monocytes and Lymphocytes	Lymphocytes: Bone Marrow and Lymphatic Tissue	Specific Immunity
		Agranular Leukocytes: Monocytes and Lymphocytes	Monocytes: Red Bone Marrow	Nonspecific Immunity
	Platelets <1%		Megakaryocytes in the Red Bone Marrow	Blood Clotting

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Plasma Proteins