Blood Functions and Composition

Blood Functions

• Transports gases, nutrients, waste products, and regulatory molecules
• Regulates pH and osmosis
• Maintains body temperature
• Protects against foreign substances
• Forms clots

Blood Composition

• Plasma: 55% of total blood volume
  • Pale, yellow liquid surrounding cells
  • 91% water, 7% proteins, 2% other substances
• Formed elements: 45% of total blood volume
  • Solid structures (cells and fragments)
  • Erythrocytes (RBCs), Leukocytes (WBCs), Thrombocytes (Platelets)

Plasma Proteins

• Albumin: 58% of plasma proteins
  • Maintains water balance (osmotic pressure).
• Globulins: 38% of plasma proteins
  • Part of the immune system.
• Fibrinogen: 4% of plasma proteins
  • Involved in clot formation
  • Activated clotting factors convert fibrinogen to fibrin, which forms threadlike proteins for blood clots.

Plasma vs Serum

• Plasma: Liquid portion of unclotted blood
  • Contains albumin, globulin, and fibrinogen
  • Obtained using anticoagulants
• Serum: Liquid portion of clotted blood
  • Contains only albumin and globulin

Hematopoiesis

• Process of producing formed elements in blood
• Occurs primarily in red bone marrow in adults
• Derived from a single cell population (hemocytoblasts/stem cells)
• Different cells differentiate into different cell lines (myeloid & lymphoid)
• Important for the production of all formed elements in blood.

Erythrocytes (RBCs)

• Disk-shaped with thick edges/biconcave shaped (thicker than the center)
• Increases surface area which allows gases to move in and out quickly.
• Lose their nucleus and most organelles during development to accommodate hemoglobin for oxygen transport.
• Live for 120 days (males) and 110 days (females).
• Unable to divide
• Transports oxygen from lungs to tissues.

Hemoglobin

• Main component of erythrocytes.
• Transports 98.5% of oxygen in the body and carbon dioxide.
• Oxygenated: Bright red
• Deoxygenated: Dark red
• Each hemoglobin molecule consists of 4 protein chains (globin) and 4 heme groups. Each heme contains an iron atom, critical for oxygen transport.

Oxyhemoglobin

• Hemoglobin with oxygen attached

Carboxyhemoglobin

• Hemoglobin with carbon monoxide attached.

Carbon Monoxide

• Gas produced by incomplete combustion.
• Binds to iron in hemoglobin 210 times more readily than oxygen and does not tend to unbind.
• This makes hemoglobin bound to carbon monoxide incapable of transporting oxygen.

Leukocytes (WBCs)

• Lack hemoglobin
• Larger than erythrocytes (RBCs)
• Contains a nucleus
• Can leave the blood and travel through tissues (ameboid movement).
• Fights off infections; Removes dead cells and debris (phagocytosis).

Granulocytes (types of leukocytes)

• Neutrophils: Lilac granules; most common type. Phagocytes, remain in blood for 10-12 hours, then move to tissues, increased in bacterial infections
• Eosinophils: Orange-red granules; involved in parasitic infections and allergies, destroys parasites, reduces inflammation.
• Basophils: Least common; granular leukocytes; involved in allergic reactions; releases histamine and heparin (prevents clot formation)

Agranulocytes (types of leukocytes)

• Lymphocytes: Small granules; part of the immune response; increased in viral infection; several types (T cells and B cells)
• Monocytes: Largest; increased in chronic infections; produce macrophages (phagocytes)

Platelets

• Minute fragments of cells (cytoplasm surrounded by a cell membrane)
• Produced in the red bone marrow from megakaryocytes.
• Small fragments break off and enter the blood as platelets.
• Important role in preventing blood loss.

Blood Loss Prevention (Hemostasis)

• Vascular spasm: Temporary constriction of blood vessels (smooth muscle contraction).
• Platelet plug formation: Accumulation of platelets.
• Blood clotting (coagulation): Transformation of blood from liquid to gel.
  • Clot is a network of threadlike proteins called fibrin (traps blood cells and fluid).
  • Depends on clotting factors.

Clotting Factors

• Proteins in plasma, only activated following injury, made in the liver, requires vitamin K.

Clotting Steps

• Injury activates clotting factors.
• Prothrombinase is formed and acts on prothrombin to convert it into thrombin.
• Thrombin converts fibrinogen to fibrin.
• Fibrin forms a clot.

Anticoagulants

• Heparin and antithrombin inactivate thrombin.
  • Prevents clots from forming.

Blood Grouping

• ABO blood groups are determined by antigens on surface of red blood cells.
  • Type A: has Anti-B antibodies
  • Type B: has Anti-A antibodies
  • Type AB: has neither Anti-A or Anti-B antibodies
  • Type O: has both Anti-A and Anti-B antibodies
• Rh blood groups are determined by Rh antigens on the surface of red blood cells; 95-85% are Rh+
• Incompatibility during transfusion or pregnancy can result in agglutination or hemolysis of red blood cells

Blood Tests

• Complete Blood Count (CBC): Provides information about RBC count, hemoglobin, hematocrit, and WBC count
• Red blood cell count: measures RBCs
• White blood cell count: measures WBCs
• Hemoglobin: measures hemoglobin in blood.
• Hematocrit: percentage of RBCs in blood.
• Differential white blood count: determines percentage of each type of leukocytes

Clotting Disorders

• Von Willebrand disease: Most common inherited bleeding disorder.
• Hemophilia: Genetic disorder where clotting is abnormal or absent, sex-linked.
• Septicemia: blood poisoning.