Physiology of Blood: Composition & Functions

What are the primary components that make up human blood?

Human blood, a specialized connective tissue, circulates throughout the body, delivering essential substances and removing waste. It comprises a liquid matrix, plasma, and various cellular elements. These formed elements include different types of blood cells, each with distinct, vital roles. Understanding these primary constituents is crucial for comprehending blood's diverse functions, from oxygen transport to immune defense and clotting mechanisms, all working in concert to sustain life and physiological balance.

• Plasma (Liquid Portion): Extracellular matrix, primarily water, carrying dissolved substances.
• Blood Cells: Cellular components including red blood cells, white blood cells, and platelets.

What is plasma, and what are its key constituents and functions?

Plasma is the liquid, extracellular matrix of blood, making up approximately 55% of its total volume. This yellowish fluid is predominantly water, serving as an indispensable solvent and transport medium for nutrients, hormones, electrolytes, and metabolic waste. Plasma also contains crucial proteins like albumin, globulins, and fibrinogen, along with dissolved organic molecules. These components contribute to plasma's vital roles in maintaining osmotic pressure, regulating pH, transporting lipids, facilitating immune responses, and initiating blood clotting, ensuring systemic stability.

• Composition: Primarily water (92%), proteins (7%), and dissolved organic molecules (1%).
• Proteins: Albumin (60%), Globulins (36%), Fibrinogen (4%).
• Functions of Plasma Proteins: Essential for osmotic balance, transport, immunity, and coagulation.
• Site of Synthesis: Most plasma proteins are synthesized in the liver.

What are red blood cells, and how do they facilitate gas transport?

Red blood cells, or erythrocytes, are the most abundant cellular components in blood, primarily responsible for oxygen and carbon dioxide transport. These unique cells lack a nucleus and mitochondria, maximizing their capacity to carry hemoglobin, the iron-containing protein that binds gases. Their distinctive biconcave disk shape and flexibility enable them to navigate narrow capillaries, efficiently delivering oxygen to tissues and collecting carbon dioxide for removal via the lungs. This continuous gas exchange is fundamental to cellular respiration and overall metabolic function.

• Characteristics: Biconcave disk shape, flexible, 120-day lifespan, formed in bone marrow.
• Function: Primarily oxygen and carbon dioxide transport.
• Hemoglobin: Iron-containing protein responsible for gas binding.
• Production: Regulated by erythropoietin, primarily in bone marrow.
• Destruction: Old or damaged cells removed by macrophages in spleen and liver.

What are white blood cells, and what roles do they play in immunity?

White blood cells, or leukocytes, are crucial components of the immune system, defending the body against infections, foreign invaders, and abnormal cells. Unlike red blood cells, they possess a nucleus and can leave the bloodstream to patrol tissues, actively seeking out threats. Leukocytes are diverse, categorized into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (monocytes, lymphocytes), each specializing in different aspects of immune response, from phagocytosing pathogens to coordinating complex immune reactions, providing robust protection.

• Granulocytes: Basophils, Neutrophils, Eosinophils, with granular cytoplasm.
• Agranulocytes: Monocytes and Lymphocytes, lacking visible cytoplasmic granules.
• Site of Formation: Produced in bone marrow and lymphatic tissues.
• Functions: Phagocytosis, allergic reactions, inflammation, specific immune responses.

What are platelets, and how do they contribute to blood clotting?

Platelets, also known as thrombocytes, are small, irregular-shaped cell fragments derived from megakaryocytes in the bone marrow. Despite their small size, they are indispensable for hemostasis, the process that stops bleeding following vascular injury. Upon damage, platelets rapidly adhere to the exposed collagen, aggregate to form a temporary plug, and release factors. These factors initiate the complex coagulation cascade, ultimately leading to the formation of a stable fibrin web that reinforces the platelet plug and seals the damaged vessel, preventing excessive blood loss.

• Characteristics: Small, anucleated cell fragments.
• Function: Primarily initiating blood clotting (hemostasis).

How does the body achieve hemostasis, the process of stopping bleeding?

Hemostasis is a finely tuned physiological process that prevents excessive blood loss following vascular injury, maintaining blood volume and pressure. It involves a rapid, coordinated series of events, beginning with immediate vasoconstriction, where the injured blood vessel narrows to reduce blood flow. This is swiftly followed by the formation of a temporary platelet plug at the injury site. This plug then provides a crucial surface for the intricate coagulation cascade, a series of enzymatic reactions culminating in the formation of a stable fibrin web, which reinforces the plug and seals the wound.

• Vessel Constriction: Immediate narrowing of blood vessels to reduce flow.
• Platelet Plug Formation: Platelets adhere to injury site, aggregate to form temporary seal.
• Fibrin Web Formation: Fibrin strands create meshwork, stabilizing platelet plug.
• Coagulation Cascade: Complex enzymatic reactions leading to fibrin production.

What is anemia, and how does it affect the body?

Anemia is a common medical condition characterized by a deficiency in healthy red blood cells or insufficient hemoglobin, leading to reduced oxygen-carrying capacity of the blood. This critical reduction means that tissues and organs throughout the body do not receive adequate oxygen for normal metabolic functions. Anemia can result from various underlying factors, including insufficient red blood cell production, increased red blood cell destruction, or significant blood loss. Symptoms often include persistent fatigue, generalized weakness, shortness of breath, and pallor, significantly impacting daily life.