Blood Composition and Functions

• Blood is a vital bodily fluid in humans and animals
• Delivers essential substances like oxygen and nutrients to cells
• Transports metabolic waste away from cells

Blood Composition

• Consists of plasma and cells, including red blood cells, white blood cells, and platelets
• Volume is about 5 liters in an adult human
• Denser and more viscous than water
• Slightly alkaline, pH between 7.35 and 7.45

Plasma

• Makes up about 55% of blood volume
• Straw-colored liquid
• 92% water
• Contains dissolved substances:
  • Proteins (albumin, globulins, fibrinogen)
  • Glucose
  • Electrolytes (Na+, Cl-, K+, etc.)
  • Hormones
  • Dissolved gases (O2, CO2)
  • Waste products (urea, creatinine)

Red Blood Cells (Erythrocytes)

• Most abundant blood cells
• Responsible for transporting oxygen
• Biconcave discs, increasing surface area for gas exchange
• Mature RBCs lack a nucleus and organelles
• Primary component is hemoglobin, an iron-containing protein that binds to oxygen
• Produced in bone marrow through erythropoiesis
• Erythropoietin, released by kidneys, stimulates RBC production
• Lifespan of about 120 days
• Old or damaged RBCs are removed by the spleen and liver

White Blood Cells (Leukocytes)

• Involved in immune defenses
• Protect against infection and foreign invaders
• Less numerous than RBCs
• Five main types:
  • Neutrophils
  • Lymphocytes
  • Monocytes
  • Eosinophils
  • Basophils

Neutrophils

• Most abundant WBC
• Phagocytic cells
• Ingest and destroy bacteria and fungi
• First responders to infection

Lymphocytes

• Include B cells (produce antibodies), T cells (coordinate immune response and kill infected cells), and natural killer (NK) cells (kill infected or cancerous cells)
• Important in adaptive immunity

Monocytes

• Differentiate into macrophages in tissues
• Phagocytic cells that ingest pathogens, dead cells, and debris
• Activate lymphocytes and other immune cells

Eosinophils

• Defend against parasitic infections
• Involved in allergic reactions

Basophils

• Release histamine and other mediators
• Promote inflammation
• Involved in allergic reactions

Platelets (Thrombocytes)

• Small, cell fragments
• Derived from megakaryocytes in bone marrow
• Crucial role in blood clotting (hemostasis)
• Aggregate at the site of blood vessel injury
• Form a temporary plug and activate the coagulation cascade

Hemostasis

• Process of stopping bleeding
• Involves:
  • Vasoconstriction (reducing blood flow to the injured area)
  • Platelet plug formation
  • Blood coagulation (formation of a fibrin clot)
• Coagulation cascade involves clotting factors activating each other
• End result is conversion of fibrinogen to fibrin
• Fibrin forms a mesh to stabilize the platelet plug
• Clot retracts over time
• Dissolved by the enzyme plasmin

Blood Functions

• Transport:
  • Oxygen from lungs to tissues
  • Carbon dioxide from tissues to lungs
  • Nutrients from the digestive system to tissues
  • Hormones from endocrine glands to target organs
  • Waste products from tissues to kidneys and liver
• Regulation:
  • Body temperature (by distributing heat)
  • pH (through buffers)
  • Fluid and electrolyte balance
• Protection:
  • White blood cells protect against infection
  • Antibodies neutralize pathogens
  • Blood clotting prevents blood loss

Blood Groups

• Classified based on antigens on red blood cell surfaces
• The ABO blood group system:
  • A
  • B
  • AB
  • O
• Rh blood group system:
  • Rh-positive (Rh+)
  • Rh-negative (Rh-)
• Blood transfusions must be compatible
• Incompatible transfusions can lead to agglutination (clumping) and hemolysis (destruction) of red blood cells

Blood is a crucial fluid composed of plasma and cells, including red blood cells, white blood cells, and platelets. Plasma, making up 55% of blood volume, is mostly water and contains proteins, glucose, and electrolytes. Red blood cells are responsible for transporting oxygen.