Anatomy and Physiology of Blood

Anatomy & Physiology of Blood

Section 1: Plasma and Formed Elements

Learning Outcomes

  • 17.1: List the components of the cardiovascular system, and describe several important functions of blood.
  • 17.2: Describe the important components and major properties of blood.
  • 17.3: Explain the origins and differentiation of the formed elements.

Module 17.1: Blood Overview

  • Blood is a vital fluid component of the cardiovascular system, which consists of:
    • Heart: Pumps blood and maintains blood pressure.
    • Blood Vessels:
    • Arteries: Carry blood away from the heart.
    • Capillaries: Permit exchange between blood and interstitial fluids.
    • Veins: Return blood to the heart.

Functions of Blood

  • Transport:

    • Gases: Oxygen from lungs to tissues, carbon dioxide from tissues to lungs.
    • Nutrients: From the digestive tract or storage in adipose or liver.
    • Hormones: From glands to target tissues.
    • Waste Products: Transported to kidneys for excretion.

  • Regulation:

    • pH and Ion Composition: Blood absorbs and neutralizes acids. Diffusion between blood and interstitial fluid balances ion concentration.

  • Fluid Loss Restriction: Blood uses enzymes and substances to initiate clotting at injury sites, forming a temporary patch.

  • Defense: Blood transports white blood cells and antibodies to combat toxins and pathogens.

  • Temperature Stabilization:

    • Blood absorbs heat generated in one area and distributes it. Blood flow is directed closer to the skin during high temperatures and towards vital organs during low temperatures.

Summary of Functions

  • Transport dissolved gases, nutrients, hormones, and metabolic wastes.
  • Regulate pH and ion concentrations of interstitial fluids.
  • Restrict fluid losses at injury sites.
  • Defend against pathogens and toxins.
  • Stabilize body temperature.

Review

  • Components of the Cardiovascular System: Heart, blood vessels, blood.
  • Functions of Blood: Transport, regulation, restriction of fluid loss, defense, temperature stabilization.

Section 2: Blood Composition

Module 17.2: Blood Structure

  • Blood as a connective tissue: Comprises plasma and formed elements.
  • Whole Blood Composition:
    • Plasma: Liquid matrix (~55% of total volume).
    • Formed Elements: Cells and cell fragments (~45% of total volume).
    • Blood Volume:
    • Males: 5–6 liters (5.3–6.4 quarts)
    • Females: 4–5 liters (4.2–5.3 quarts)

Properties of Whole Blood

  • Temperature: Average ~38°C (100.4°F).
  • Viscosity: Blood is approximately five times as viscous as water due to protein interactions in the plasma.
  • pH Level: Slightly alkaline, ranging from 7.35 to 7.45 (average 7.4).

Plasma Composition

  • Plasma Components: 55% total volume; similar to interstitial fluid but varies in certain solutes.
    • Primary Differences: Presence of respiratory gases and dissolved proteins (plasma proteins cannot cross capillary walls).

Formed Elements

  • Components:
    • Platelets: <0.1% of formed elements; involved in clotting.
    • White Blood Cells (WBCs, leukocytes): <0.1%; five classes with different functions related to immunity.
    • Red Blood Cells (RBCs, erythrocytes): 99.9% of formed elements; crucial for oxygen transport.

Blood Components with Percentages

  • Plasma Proteins (7%):
    • Albumins: ~60% of plasma proteins; regulate osmotic pressure.
    • Globulins: ~35%; include antibodies and transport proteins.
    • Fibrinogen: ~4%; involved in clot formation.
  • Plasma Solutes: Water (92% of plasma), electrolytes, organic nutrients, organic wastes.

Hematocrit and Formed Element Composition

  • Hematocrit: Percentage of whole blood volume contributed by formed elements (average 45%; males 47%, females 42%).

Review

  • Blood Components: Plasma and formed elements.
  • Define: Hematocrit as the packed cell volume.
  • Analyze plasma protein variations during infections.

Module 17.3: Hemopoiesis

Hemopoiesis: Overview

  • Process of formed elements production occurs in red bone marrow via hemocytoblasts (hematopoietic stem cells).
  • Hemocytoblasts differentiate into:
    • Lymphoid stem cells: Produce lymphocytes (white blood cells).
    • Myeloid stem cells: Yield red blood cells and other white blood cells.

Lymphoid Stem Cells

  • Differentiate into lymphocytes.
  • Mature in red bone marrow or migrate to lymphoid tissues (thymus, spleen, lymph nodes).
  • Hormones like colony-stimulating factors stimulate blood cell formation during immune responses.

Myeloid Stem Cells

  • Differentiate into other formed elements:
    • Monoblasts evolve to monocytes.
    • Myeloblasts develop into granulocytes (neutrophils, eosinophils, basophils).
    • Megakaryocytes form platelets.
    • Proerythroblasts transition to red blood cells.

Erythropoietin (EPO)

  • Hormonal response to low tissue oxygen levels (hypoxia).
  • Stimulated by conditions like anemia or reduced kidney blood flow.
  • Promotes stem cell and red blood cell (RBC) development in red bone marrow.

Review

  • Hemocytoblasts: Define as progenitor cells for blood formation.
  • Platelet Origins: Discuss their production and function.
  • Lymphoid vs. Myeloid Cells: Compare the produced cell types.

Section 3: Structure and Function of Formed Elements

Module 17.4: Hematology

  • Definition: Study of blood and blood-forming tissues.
  • Importance: Provides critical health information and detects conditions like anemia and infections.
  • Dyscrasias: General term for blood disorders.
  • Blood tests: To determine blood type and evaluate RBC, WBC, and platelet counts.

Complete Blood Count (CBC)

  • Measures:
    • RBC count
    • WBC count
    • Erythrocyte indices (hemoglobin levels)
    • Hematocrit
    • Differential count to identify specific white blood cell types.

Red Blood Cell Tests

  • Assess morphology (number, size, shape) and maturity of circulating RBCs.

Review

  • Hematology: Define and explain its significance.
  • CBC Elements: Discuss its components.
  • Condition Indications: Understand what a depressed hematocrit reflects.

Module 17.5: Red Blood Cells

  • RBCs: Most numerous formed elements within blood, crucial for gas transport.
  • Count: Approx. 260 million RBCs per drop; around 25 trillion in an adult.
  • Typical RBC Values:
    • Males: 4.5–6.3 million RBCs/µL.
    • Females: 4.2–5.5 million RBCs/µL.

Morphology & Functionality

  • Shape: Biconcave disc; enhances gas exchange through increased surface area.
  • Stack Formation: RBCs can form rouleaux (stacks) for efficient transport through vessels.
  • Flexibility: Capable of navigating narrow capillaries.

Characteristics of Red Blood Cells

  • Lack of organelles, including nuclei and ribosomes, leads to limited lifespan (<120 days).
  • Function purely for the transport of respiratory gases, primarily through hemoglobin.
  • Hemoglobin content per blood: 14–18 g/dL for males, 12–16 g/dL for females.

Hemoglobin Structure

  • Comprised of two alpha and two beta chains; contains heme groups with iron that bind oxygen.
  • Each RBC features approx. 280 million hemoglobin molecules capable of transporting over 1 billion oxygen molecules.
  • Oxygenated (oxyhemoglobin) blood is bright red, while deoxygenated blood (deoxyhemoglobin) is darker.

Review

  • Evaluate RBC functional aspects, hemoglobin structure, and differences between oxyhemoglobin and deoxyhemoglobin.

Module 17.6: RBC Production and Recycling

  • RBCs replaced consistently with ~1% replaced daily; ~3 million produced every second.
  • Erythropoiesis: Formation in red bone marrow.
  • Life cycle includes:
    • Hemolysis (rupture or engulfment by macrophages) results in hemoglobin degradation.
    • Erythropoiesis involves several steps leading from erythroblasts to reticulocytes and finally to mature RBCs.
  • Breakdown of RBCs by macrophages:
    • Iron is recycled and stored or transported via transferrin.
    • Heme is converted to biliverdin and bilirubin; bilirubin excretion happens through the liver and contributes to jaundice if accumulated.

Summary of RBC Recycling Process

  • From macrophages to liver for processing; via intestines for waste management.

Review

  • Discuss implications of liver disease on bilirubin metabolism.

Section 4: Blood Typing and Clinical Implications

Module 17.7: Blood Typing Basics

  • Blood types defined by surface antigens (A, B, Rh).
  • ABO Blood Group: Based on A/B antigens; plasma contains antibodies against non-self antigens.
  • Agglutination: Clumping of RBCs due to immune response against foreign antigens.

Rh Blood Group

  • Presence/absence of Rh antigen (Rh+ vs Rh-);
  • Important for transfusions; incompatibility leads to serious reactions.

Blood Typing Tests

  • Solutions mixed with blood samples; agglutination indicates the presence of specific antigens.
  • Safe transfusion needs compatible blood types to prevent reactions.

Genetics of Blood Type

  • Anti-A/B antibodies develop without exposure; Rh-negative individuals may develop anti-Rh antibodies if sensitized by Rh-positive blood.

Review

  • Define significance of surface antigens, common blood types, and compatibility in transfusions.

Module 17.8: Hemolytic Disease of the Newborn

  • Condition caused by maternal anti-Rh antibodies attacking fetal RBCs.
  • Commonly seen in Rh- women carrying Rh+ fetuses; sensitization occurs during first delivery, poses risk in subsequent pregnancies.
  • Prevention: RhoGAM injection prevents sensitization by destroying fetal RBCs that cross the placenta.

Overview

  • The clinical significance related to fetal-maternal blood type compatibility.

Review

  • Define and explain RhoGAM necessity and implications for mothers with Rh- status.

Section 5: White Blood Cells and Clotting Mechanisms

Module 17.9: White Blood Cells (WBCs)

  • Functions: Defend the body against disease; five primary types of leukocytes: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils.
  • Shared Properties:
    • Short lifespan in circulation; migrate to inflamed sites.
    • Positive chemotaxis leads them to areas of infection.
    • Phagocytosis capabilities in certain types (neutrophils, eosinophils, monocytes).

Types of White Blood Cells

  • Granulocytes: Neutrophils (50–70%), Eosinophils (2–4%), Basophils (<1%).
  • Agranulocytes: Monocytes (2–8%), Lymphocytes (20–40%).

White Blood Cell Counts

  • Normal levels approximately 7000 WBCs per µL; differential count can indicate infections.

Review

  • Identify WBC types and their respective functions.

Module 17.10: Hemostasis (Clotting Process)

  • Definition: Mechanism to halt blood loss from damaged blood vessels; includes vascular, platelet, and coagulation phases.

Vascular Phase

  • Begins shortly after injury; endothelial cells respond, releasing chemicals that trigger smooth muscle contraction.

Platelet Phase

  • Involves adhesion of platelets to damaged sites; results in platelet aggregation.

Coagulation Phase

  • Initiated by exposing blood to tissue factor, leading to fibrinogen conversion into fibrin, which forms clots.

Fibrinolysis

  • Dissolution of clots after tissue repair is complete; initiated by plasminogen.

Review

  • Define hemostasis and detail the phases involved.

Module 17.11: Blood Disorders

  • Diagnosis: Commonly obtained through venipuncture; examines blood for signs of disorders.
  • Types of Disorders:
    • Nutritional, congenital, infectious, and degenerative disorders.

Notable Blood Disorders

  • Iron Deficiency Anemia: Common in women; results in small, less effective RBCs.
  • Sickle Cell Anemia: A genetic condition resulting in abnormal hemoglobin.
  • Hemophilia: A bleed disorder affecting clotting factors.
  • Leukemia: Cancer of blood-forming tissues, often presenting immature WBCs in circulation.

Review

  • Compare types of anemia and leukemia classifications.