Blood Review

Overview of the Cardiovascular System and Blood

General Functions of Blood

• Transports oxygen, carbon dioxide, nutrients, hormones, and waste products.

• Maintains body temperature, pH balance, and proper osmotic pressure.

Normal pH Range of Blood

• The normal pH range of blood is approximately 7.35 to 7.45.

General Characteristics of Blood

• Its volume is about 5-6 liters in an average adult.

• Blood is approximately 7-8% of body weight.

Major Components of Blood

• Plasma: 55%

• Red Blood Cells (Erythrocytes): 45%

• White Blood Cells (Leukocytes): <1%

  • Buffy Coat (formed elements): Contains leukocytes and platelets.

Complete Cell in Blood

• The only formed element of blood that is a complete cell is the White Blood Cell (WBC).

Formed Elements of the Buffy Coat

• The formed elements that make up the buffy coat are Leukocytes and Platelets.

True Hematocrit vs. Clinical Hematocrit

• True hematocrit represents the proportion of blood volume occupied by red blood cells measured directly. Clinical hematocrit is often measured through centrifugation of whole blood samples.

Normal Erythrocyte Counts

• Normal erythrocyte counts for men are typically around 4.7 to 6.1 million cells per microliter, while for women it is 4.2 to 5.4 million cells per microliter.

Composition of Blood Plasma

Overall Composition of Plasma

• Composed of 90% water, 7% proteins, and 3% other substances.

Major Types of Plasma Proteins and Their Functions

• Albumin: Maintains osmotic pressure, produced in the liver.

• Globulins: Involved in immune response, produced in the liver and lymphatic tissue.

• Fibrinogen: Essential for blood clotting, produced in the liver.

Importance of Plasma Proteins on Colloid Osmotic Pressure

• Plasma proteins help maintain colloid osmotic pressure, which is vital for proper fluid distribution in tissues and prevents edema.

Hemopoiesis

Definition of Hemopoiesis

• The process of blood cell formation from stem cells, primarily occurring in the bone marrow.

Significance of Hemocytoblasts

• Hemocytoblasts are multipotent stem cells that can differentiate into all types of blood cells.

Multipotent Stem Cell

• A stem cell that can develop into multiple types of related cells.

Location of Hemopoiesis

• Hemopoiesis mainly occurs in the red bone marrow of long bones, pelvis, and sternum.

Erythropoiesis Process

• The process of producing red blood cells from stem cells, requiring erythropoietin (EPO).

• Reticulocytes are immature red blood cells that indicate the rate of erythropoiesis.

Leukopoiesis Process

• The process of producing white blood cells:

  • Lymphoid stem cells produce lymphocytes.

  • Myeloid stem cells produce other blood cells such as erythrocytes and platelets.

Thrombopoiesis and Megakaryocyte Role

• Thrombopoiesis is the production of platelets from megakaryocytes, which are large bone marrow cells that fragment to release platelets.

Erythrocytes

Structure of Erythrocytes

• Biconcave disks that lack a nucleus, which increases surface area for gas exchange.

Function of Erythrocytes

• Transport oxygen from the lungs to tissues and carbon dioxide back to the lungs.

Structure Dictating Function

• Their biconcave shape allows for flexibility and maximizes oxygen-carrying capacity.

Hemoglobin Structure and Function

• Hemoglobin is a protein in red blood cells that binds oxygen.

• Oxygen binds to the iron in the heme portion of hemoglobin.

Function of Erythropoietin (EPO)

Function of Erythropoietin (EPO) in Erythropoiesis

• Erythropoietin (EPO): A hormone produced primarily in the kidneys in response to low oxygen levels (hypoxia) in the blood.

• Role in Erythropoiesis: EPO stimulates the process of erythropoiesis, which is the production of red blood cells from stem cells in the bone marrow. When oxygen levels decrease, EPO secretion increases, encouraging the bone marrow to produce more red blood cells to enhance the oxygen-carrying capacity of the blood.

• Mechanism:

• EPO binds to receptors on erythroid progenitor cells in the bone marrow, promoting their proliferation and differentiation into mature red blood cells.

• EPO not only accelerates the maturation of proerythroblasts into erythrocytes but also stimulates the release of reticulocytes (immature red blood cells) into the bloodstream, thereby increasing the total number of circulating red blood cells.

• Homeostasis: As oxygen levels improve in the body, EPO production decreases, thereby maintaining a balance in red blood cell levels and preventing excess erythrocyte formation, which can lead to complications such as hypertension.

Hormonal Negative Feedback Loop in Erythropoiesis

Steps of the Hormonal Negative Feedback Loop in Erythropoiesis

1. Stimulus: Decrease in blood oxygen levels (hypoxia) triggers erythropoietin (EPO) release.

2. Receptor: Specialized cells in the kidneys detect low oxygen levels.

3. Control Center: The kidneys act as the control center by producing and releasing EPO into the bloodstream.

4. Effector: EPO stimulates erythroid progenitor cells in the bone marrow, promoting the production of red blood cells.

5. Restoration of Homeostasis: As red blood cell production increases, the oxygen level in the blood rises. Once the oxygen levels return to normal, the kidneys decrease EPO production, effectively restoring homeostasis.

Fate of Erythrocyte Destruction Products

• Components are recycled: iron is reused for new hemoglobin production, and heme is broken down mainly into bilirubin for excretion.

Definition of Anemia

• A condition where there is a deficiency in red blood cells or hemoglobin, leading to insufficient oxygen transport.

ABO & Rh Blood Grouping

Definition of Antigen

• A molecule capable of inducing an immune response, found on the surface of red blood cells.

Role of Surface Antigens on RBCs

• Surface antigens determine the blood group type based on their presence or absence (A, B, AB, O).

ABO Blood Types Characteristics

Rh (D) Antigen Presence

• The presence of Rh antigen classifies blood as Rh positive; absence classifies it as Rh negative.

Blood Donation Compatibility for Rh Types

• Rh Positive: Can receive from Rh+ and Rh- but can only donate to Rh+.

• Rh Negative: Can only receive from Rh- but can donate to Rh+ and Rh-.

Anti-Rh Antibody Development

• Anti-Rh antibodies develop only in Rh negative individuals following exposure to Rh positive blood (e.g., during pregnancy or transfusion).

Consequences of Incorrect Blood Transfusion

• Incorrect transfusion can lead to agglutination (clumping) and hemolytic reactions, which can be life-threatening.

Universal Donor and Recipient

• Universal Donor: Type O- (no A/B antigens, Rh negative)

• Universal Recipient: Type AB+ (no antibodies against A, B, or Rh antigens)

Erythroblastosis Fetalis

• A hemolytic disease in newborns that occurs when an Rh- mother carries an Rh+ fetus, causing the mother to produce anti-Rh antibodies that attack the fetal blood cells in subsequent pregnancies.

Leukocytes

Common Characteristics of Leukocytes

• They have nuclei, lack hemoglobin, and are involved in immune responses.

Diapedesis and Chemotaxis

• Diapedesis: The movement of leukocytes out of the bloodstream into tissues.

• Chemotaxis: Movement of cells towards sites of injury or infection guided by chemical signals.

Granulocytes vs. Agranulocytes

Five Types of Leukocytes (most to least abundant)

1. Neutrophils

2. Lymphocytes

3. Monocytes

4. Eosinophils

5. Basophils

Structure and Function of Each Leukocyte

Functions of T Lymphocytes, B Lymphocytes, and Natural Killer Cells

• T Lymphocytes: Cell-mediated immunity

• B Lymphocytes: Antibody production

• Natural Killer Cells: Attack virus-infected and tumor cells

Brief Description of Leukemia

• A type of cancer characterized by excessive production of abnormal white blood cells.

Thrombocytes

Platelet Structure Differences

• Platelets are not whole cells but fragments of megakaryocytes.

Function of Platelets

• Essential for blood clotting and maintaining hemostasis.

Hemostasis and Coagulation of Blood

Distinction between Hemostasis and Coagulation

• Hemostasis: The overall process to stop bleeding.

• Coagulation: The specific process of blood clotting involving protein cascades.

Phases of Hemostasis

1. Vascular Phase: Vascular spasm (endothelial cell response)

2. Platelet Phase: Platelet plug formation (involves platelets adhering to the injury)

3. Coagulation Phase: Fibrin clot formation (conversion of fibrinogen to fibrin)

Vascular Phase & Endothelial Cells Role

• Endothelial cells release substances that promote vasoconstriction to reduce blood flow and blood loss.

Platelet Plug Formation Steps

• Platelets adhere to exposed collagen, become activated, and aggregate to form a temporary plug.

Formation of Insoluble Fibrin Clot

• Fibrinogen is converted to fibrin by thrombin, which weaves through the platelet plug, stabilizing it.

Intrinsic vs. Extrinsic Clotting Mechanisms

• Intrinsic: Triggered by damage to blood vessels; uses factors already in the blood.

• Extrinsic: Triggered by external tissue damage; involves tissue factor from damaged tissues.

Common Pathway of Coagulation

• Both pathways converge at factor X, leading to fibrin formation. Leads to final step.

Positive Feedback in Hemostasis

• Platelets release substances that attract more platelets, enhancing the clotting process.

Role of Calcium Ions in Clotting

• Calcium ions are essential for several steps in the clotting cascade, particularly in activating clotting factors.

Fibrinolysis Process

• Fibrinolysis involves the breakdown of fibrin in a clot by plasmin, which helps restore normal blood flow.

Importance of Fibrinolysis

• Prevents excessive clotting and allows for remodeling of tissues after injury.

Thrombus, Embolus, and Embolism

• Thrombus: A stationary clot within a blood vessel.

• Embolus: A clot that has broken loose and travels through the bloodstream.

• Embolism: The obstruction of a blood vessel by an embolus.