Blood: Components and Functions

• Blood is a specialized fluid in animals, essential for delivering nutrients and oxygen to cells and for transporting metabolic waste away from cells.
• In vertebrates, blood consists of blood cells suspended in blood plasma.
• Blood volume in adults averages about 5 liters.

Blood Components

• Blood comprises plasma and blood cells.

Plasma

• Plasma, the liquid component of blood, constitutes roughly 55% of blood volume.
• Plasma’s main components include:
  • Water (92%)
  • Proteins (7%) such as albumin, globulins, and fibrinogen
  • Dissolved solutes (1%) like electrolytes, nutrients, waste, and gases
• Plasma proteins’ functions:
  • Albumin maintains osmotic pressure, which prevents water from diffusing out of the blood into tissues.
  • Globulins encompass antibodies and transport proteins.
  • Fibrinogen is important in blood clotting.

Blood Cells

• Blood contains three primary cell types: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Red Blood Cells (Erythrocytes)

• Red blood cells (RBCs) represent the most abundant type of blood cell.
• RBCs specialize in oxygen transport via hemoglobin.
• Hemoglobin, a protein found in RBCs, binds to oxygen.
• The biconcave disc shape of RBCs enhances surface area for oxygen diffusion.
• RBCs lack a nucleus and organelles, which allows more space for hemoglobin.
• Erythropoiesis, occurring in bone marrow, produces RBCs.
• Erythropoietin, a hormone produced by the kidneys, stimulates erythropoiesis.
• A red blood cell’s lifespan is approximately 120 days.
• The spleen and liver remove old or damaged RBCs from circulation.

White Blood Cells (Leukocytes)

• White blood cells (WBCs) participate in immune defense.
• The main types of WBCs consist of neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
• Neutrophils, being the most numerous WBCs, are phagocytic and destroy bacteria and pathogens.
• Lymphocytes include T cells, B cells, and natural killer (NK) cells.
  • T cells mediate cell-mediated immunity.
  • B cells produce antibodies.
  • NK cells kill infected or cancerous cells.
• Monocytes transform into macrophages, which are phagocytic cells engulfing pathogens, debris, and foreign substances.
• Eosinophils defend against parasites and mediate allergic reactions.
• Basophils release histamine and other inflammatory mediators, contributing to inflammation and allergic reactions.
• Bone marrow and lymphatic tissues produce WBCs.

Platelets (Thrombocytes)

• Platelets, small cell fragments, participate in blood clotting.
• Megakaryocytes in bone marrow produce platelets.
• Platelets adhere to damaged sites from blood vessel damage, forming a platelet plug.
• Factors released by platelets activate the coagulation cascade, resulting in a fibrin clot.

Blood Types

• Blood type depends on the presence or absence of specific antigens on red blood cell surfaces.
• The ABO and Rh systems represent the two primary blood group systems.

ABO Blood Group System

• The ABO system encompasses four main blood types: A, B, AB, and O.
• Blood type depends on the presence or absence of A and B antigens on RBCs.
• Type A individuals have A antigens on RBCs and anti-B antibodies in their plasma.
• Type B individuals have B antigens on RBCs and anti-A antibodies in their plasma.
• Type AB individuals have both A and B antigens on RBCs, possessing no anti-A or anti-B antibodies in their plasma and are known as universal recipients.
• Type O individuals lack both A and B antigens on RBCs, possessing both anti-A and anti-B antibodies in their plasma and are known as universal donors.
• Compatible blood transfusions are necessary to prevent immune reactions.
  • Incompatible transfusions cause the recipient's antibodies to attack the donor's RBCs, leading to agglutination and hemolysis.

Rh Blood Group System

• The Rh system relies on the presence or absence of the RhD antigen on RBCs.
• Individuals possessing the RhD antigen are Rh-positive (Rh+).
• Individuals lacking the RhD antigen are Rh-negative (Rh-).
• Rh incompatibility can occur during pregnancy if an Rh-negative mother carries an Rh-positive fetus.
  • The mother's immune system may produce anti-Rh antibodies, which can cross the placenta and attack the fetal RBCs, potentially leading to hemolytic disease of the newborn (erythroblastosis fetalis).
  • RhoGAM (Rh immunoglobulin) can prevent this by administering it to the mother during pregnancy and after delivery.

Blood Disorders

• Numerous blood disorders can affect various blood components.

Anemia

• Anemia involves a deficiency of red blood cells or hemoglobin.
• Common symptoms include fatigue, weakness, and shortness of breath.
• Types of anemia:
  • Iron-deficiency anemia stems from a lack of iron needed for hemoglobin production.
  • Vitamin-deficiency anemia results from a lack of vitamin B12 or folate needed for RBC production.
  • Aplastic anemia arises from bone marrow damage, reducing the production of all blood cells.
  • Hemolytic anemia results from premature RBC destruction.
  • Sickle cell anemia, a genetic disorder, causes abnormally shaped RBCs, which leads to chronic anemia and other complications.

Leukemia

• Leukemia involves a cancer of the blood or bone marrow, characterized by abnormal white blood cell proliferation.
• Leukemia can be acute or chronic based on its rate of progression.
• Types of leukemia: acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), and chronic myeloid leukemia (CML).

Lymphoma

• Lymphoma comprises a cancer affecting the lymphatic system, including lymph nodes, the spleen, and the thymus.
• Lymphoma is divided into Hodgkin lymphoma and non-Hodgkin lymphoma.

Thrombocytopenia

• Thrombocytopenia involves a platelet deficiency, increasing the risk of bleeding.
• Decreased platelet production, increased platelet destruction, or splenic sequestration can cause thrombocytopenia.

Hemophilia

• Hemophilia represents a genetic disorder impairing blood clotting.
• A deficiency of clotting factors, like factor VIII (hemophilia A) or factor IX (hemophilia B), causes hemophilia.