Chap014_Blood

Chapter 14: Blood

Overview

• Blood is the only type of connective tissue with a liquid matrix (plasma).

• Functions:

  • Transports vital substances.

  • Regulates processes for homeostasis.

  • Maintains stability of interstitial fluid.

  • Distributes heat.

• Blood volume varies based on:

  • Body size.

  • Fluid concentration.

  • Electrolyte concentration.

  • Amount of adipose tissue.

• Average adult blood volume:

  • 4-5 liters for females.

  • 5-6 liters for males.

Blood Cells

• Formed elements in blood:

  • Red blood cells (RBCs).

  • White blood cells (WBCs).

  • Platelets (cell fragments).

• Blood cells primarily form in red bone marrow.

Composition of Blood

• Cellular Components:

  • Erythrocytes (RBCs): 4.2 to 6.2 million cells/mm³.

  • Leukocytes (WBCs): various types with specific roles.

  • Platelets: crucial for hemostasis.

• Blood Smear Analysis:

  • Identifies various blood cells:

    • Erythrocytes.

    • Neutrophils (50-70%).

    • Eosinophils (2-4%).

    • Basophils (<1%).

    • Lymphocytes (20-30%).

    • Monocytes (2-8%).

Blood Composition

• Whole blood:

  • Plasma: 46-63%.

  • Formed elements: 37-54%.

• Plasma Composition:

  • Water (92%).

  • Proteins (7%): Albumin, Globulin, Fibrinogen.

  • Electrolytes and other solutes.

Plasma Electrolytes

• Cations:

  • Sodium: 135-145 mEq/L.

  • Potassium: 3.5-5.0 mEq/L.

  • Calcium: 4.0-5.5 mEq/L.

  • Magnesium: 1.5-2.5 mEq/L.

• Anions:

  • Chloride: 95-105 mEq/L.

  • Phosphate: 2.5-30 mEq/L.

  • Sulfate: 1.0 mEq/L.

Key Points

• Main Proteins:

  • Albumin, Globulin, Fibrinogen.

• Main Electrolytes:

  • Sodium and Chloride.

• pH: 7.4 (range 7.35 to 7.45).

• Hematocrit:

  • Men: 40.7-50.3%.

  • Women: 36.1-44.3%.

Erythrocytes - Red Blood Cells (RBCs)

• Functions:

  • Transport oxygen and remove carbon dioxide.

  • Buffer blood pH via carbonic anhydrase.

• Structure:

  • Biconcave disks allowing reversible deformability.

  • High surface area to volume ratio enhances oxygen transport.

  • Composed of hemoglobin (95% of RBC protein).

• Lifespan: Approximately 120 days.

Erythropoiesis

• Regulated by erythropoietin produced by kidneys in response to hypoxia.

• Developmental stages:

  • Stem cell (hemocytoblast).

  • Proerythroblast,

  • Various erythroblast stages leading to reticulocyte formation.

Nutritional Requirements

• Adequate iron, proteins, vitamins (Folate, B12) required for erythropoiesis.

Red Cell Destruction

• Processed in the spleen, liver, bonemarrow.

• RBCs undergo phagocytosis and are broken down into bilirubin.

• Lifespan of RBCs: About 120 days.

Anemia

• Common types and symptoms:

  • Low hematocrit and hemoglobin levels.

  • Symptoms: fatigue, dizziness, paleness, shortness of breath.

  • Causes include dietary deficiencies, chronic blood loss, and inherited disorders like Sickle Cell Anemia.

Sickle Cell Anemia

• Genetic disorder affecting hemoglobin leading to sickled cells.

• Symptoms include recurrent pain, risk of vascular occlusion.

• Treatment includes stem cell transplant.

Hemostasis

• Key process to prevent blood loss involving:

  • Platelets, vessel walls, plasma proteins.

• Stages:

  • Primary (platelet plug formation).

  • Secondary (fibrin clot formation).

Platelets

• Formed from megakaryocytes.

• Function:

  • Secrete vasoconstrictors, promote clot formation, and temporary plug formation.

• Lifespan: About 10 days.

Fibrinolysis

• Breakdown of clots involving plasminogen and tissue plasminogen activator.

Blood Types Characteristics

Blood Type A

• Antigens: A antigens present on the surface of red blood cells

• Antibodies: Anti-B antibodies in the plasma

• Compatibility: Can receive blood from types A and O; can donate to types A and AB.

Blood Type B

• Antigens: B antigens present on the surface of red blood cells

• Antibodies: Anti-A antibodies in the plasma

• Compatibility: Can receive blood from types B and O; can donate to types B and AB.

Blood Type AB

• Antigens: A and B antigens present on the surface of red blood cells

• Antibodies: No anti-A or anti-B antibodies in the plasma

• Compatibility: Can receive blood from all types (universal recipient); can donate to type AB only.

Blood Type O

• Antigens: No A or B antigens on the surface of red blood cells

• Antibodies: Anti-A and anti-B antibodies in the plasma

• Compatibility: Can receive blood from type O only; can donate to all types (universal donor).

Key Points:

• Understanding blood types is essential for transfusions to avoid adverse reactions.

• Rh factor (positive/negative) is also important in determining compatibility.

Coagulation Cascade

Intrinsic Pathway:

• This pathway is activated by damage to the blood vessel and involves several clotting factors already present in the bloodstream. It typically involves a series of activations leading to the formation of thrombin.

Extrinsic Pathway:

• Initiated by external trauma to a blood vessel that exposes tissue factor (TF) to the bloodstream. This pathway activates factor VII, which, in turn, activates factor X, ultimately leading to thrombin generation.

Fibrinogen to Fibrin (Clot Formation):

• Fibrinogen: A soluble protein produced in the liver that circulates in the plasma.

• Conversion to Fibrin: Thrombin, an enzyme that is activated during the coagulation cascade, cleaves fibrinogen to convert it into fibrin.

• Fibrin: A fibrous protein that forms a stable meshwork, reinforcing the platelet plug during clot formation and effectively sealing the site of injury to prevent further bleeding.

This coagulation cascade involves both intrinsic and extrinsic pathways converging to ensure effective clotting and healing in response to vascular injury.