Blood: Structure, Function, and Laboratory Analysis

Blood

Formed Elements (ID and Function)

The formed elements of blood are specialized cells and cell fragments that perform essential functions in the circulatory system. They are suspended in plasma and include erythrocytes, platelets, and leukocytes.

• Erythrocytes (Red Blood Cells): Responsible for transporting oxygen from the lungs to tissues and facilitating carbon dioxide removal. They contain the protein hemoglobin, which binds oxygen.

• Platelets (Thrombocytes): Cell fragments derived from megakaryocytes. Platelets are crucial for blood clotting and wound repair.

• Leukocytes (White Blood Cells): Defend the body against infection and foreign substances. Types include:

  • Lymphocyte: Key role in immune response; includes B cells and T cells.

  • Monocyte: Engulf and digest pathogens and debris; differentiate into macrophages.

  • Neutrophil: Most abundant; phagocytize bacteria and fungi.

  • Eosinophil: Combat parasitic infections and modulate allergic responses.

  • Basophil: Release histamine during allergic reactions; involved in inflammation.

Example: Neutrophils increase in number during bacterial infections, while eosinophils are elevated in parasitic infections and allergies.

Plasma

Plasma is the liquid component of blood, making up about 55% of its volume. It serves as a transport medium for nutrients, hormones, and waste products.

• Albumin: The most abundant plasma protein; maintains osmotic pressure and transports substances.

Example: Low albumin levels can lead to edema due to decreased osmotic pressure.

Blood Typing

Blood typing is essential for safe transfusions and is based on the presence or absence of specific antigens on the surface of erythrocytes.

• ABO Antigens & Rh Factor: ABO system classifies blood into four main types (A, B, AB, O) based on antigen presence. The Rh factor determines if blood is positive (+) or negative (-).

• Antibody Reactions for Each Blood Type: Antibodies in plasma react against incompatible antigens, leading to agglutination.

• Blood Donor and Recipient Compatibility: Transfusions require matching donor and recipient blood types to prevent immune reactions.

Blood Type	Antigens on RBC	Antibodies in Plasma	Can Receive From	Can Donate To
A	A	Anti-B	A, O	A, AB
B	B	Anti-A	B, O	B, AB
AB	A and B	None	A, B, AB, O	AB
O	None	Anti-A, Anti-B	O	A, B, AB, O

Example: Type O negative is considered the universal donor, while AB positive is the universal recipient.

Hematocrit (HCT)

Hematocrit is the percentage of blood volume occupied by red blood cells. It is a key indicator of oxygen-carrying capacity and overall health.

• Interpretation of HCT: Normal ranges vary by age and sex; low HCT may indicate anemia, while high HCT can suggest dehydration or polycythemia.

• Common Causes of Variation in HCT: Blood loss, nutritional deficiencies, chronic diseases, and altitude can affect hematocrit levels.

Example: Athletes training at high altitude may have increased hematocrit due to enhanced erythropoiesis.

Additional info:

• Blood is classified as a connective tissue due to its cellular components suspended in plasma.

• Hemoglobin concentration and oxygen saturation are also important laboratory measures related to blood function.