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8.11 Chapter Summary

Posted12/11/2024
Updated28/12/2024
ByBMF
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1. Mammalian Circulatory System: Closed Double Circulation

Definition

  • Closed Circulatory System: Blood is confined within vessels, allowing efficient transport.
  • Double Circulation: Two distinct circuits:
    • Pulmonary Circulation: Heart → lungs → heart
    • Systemic Circulation: Heart → body → heart

Components

  • Heart: Central pump with four chambers (left/right atria and ventricles).
  • Blood: Fluid connective tissue transporting gases, nutrients, hormones, waste.
  • Blood Vessels: Network including arteries, arterioles, capillaries, venules, veins.

2. Main Blood Vessels: Pulmonary and Systemic Circulations

Pulmonary Circulation

  • Pulmonary Artery:
    • Function: Carries deoxygenated blood from the right ventricle to the lungs.
    • Features: Thicker walls to handle high pressure from the heart.
  • Pulmonary Vein:
    • Function: Returns oxygenated blood from the lungs to the left atrium.
    • Features: Thinner walls compared to arteries, contains valves to prevent backflow.

Systemic Circulation

Aorta:

  • Function: Largest artery, distributes oxygenated blood from the left ventricle to the body.
  • Features: Elastic walls to accommodate pressure from ventricular contraction.

Vena Cava:

  • Function: Large veins (superior and inferior) that return deoxygenated blood from the body to the right atrium.
  • Features: Thinner walls, contain valves to prevent backflow.

3. Identification and Structure of Blood Vessels

Microscopic Identification

  • Arteries:
    • Structure: Thick muscular and elastic walls, narrow lumen.
    • Identification: Larger diameter, more muscular layers.
  • Veins:
    • Structure: Thinner walls, larger lumen, valves present.
    • Identification: Less muscular, presence of valves visible under microscope.
  • Capillaries:
    • Structure: Single endothelial cell layer, very thin walls.
    • Identification: Smallest diameter, no valves, site of gas and nutrient exchange.

Plan Diagrams

Transverse Section (TS):

  • Arteries: Thick tunica media with elastic fibers.
  • Veins: Thinner tunica media, presence of valves.

Longitudinal Section (LS):

  • Arteries: Clearly defined layers (intima, media, externa).
  • Veins: Presence of valves, thinner wall structure compared to arteries.

4. Structure-Function Relationships of Blood Vessels

Muscular Arteries

  • Structure: Thick tunica media with smooth muscle.
  • Function: Regulate blood flow by vasoconstriction and vasodilation.

Elastic Arteries

  • Structure: High elasticity due to abundant elastic fibers.
  • Function: Expand and recoil with each heartbeat, maintaining blood pressure.

Veins

  • Structure: Thinner walls, larger lumen, valves to prevent backflow.
  • Function: Return deoxygenated blood to the heart; valves assist against gravity.

Capillaries

  • Structure: Extremely thin walls (single cell layer).
  • Function: Facilitate exchange of gases, nutrients, and wastes between blood and tissues.

5. Recognition and Drawing of Blood Cells

Red Blood Cells (Erythrocytes)

  • Appearance: Biconcave discs, no nucleus.
  • Function: Transport oxygen and carbon dioxide via hemoglobin.

Monocytes

  • Appearance: Largest white blood cells, kidney-shaped nucleus.
  • Function: Phagocytosis of pathogens and debris, precursor to macrophages.

Neutrophils

  • Appearance: Multilobed nucleus, granular cytoplasm.
  • Function: Phagocytose bacteria and fungi, first responders to infection.

Lymphocytes

  • Appearance: Large nucleus with scant cytoplasm.
  • Function: Adaptive immunity, include B cells and T cells.

Drawing Tips

  • Use clear labeling for each cell type.
  • Show distinct features (e.g., nucleus shape, granules).
  • Accurate proportions to differentiate cell sizes.

6. Water: Main Component of Blood and Tissue Fluid

Composition

  • Water Content: Approximately 90% of blood plasma and tissue fluid.

Properties Related to Transport

Solvent Action:

  • Role: Dissolves transport molecules (e.g., ions, nutrients, gases).
  • Importance: Facilitates movement of substances throughout the body.

High Specific Heat Capacity:

  • Role: Maintains stable body temperature by absorbing and releasing heat.
  • Importance: Protects the body from rapid temperature changes, ensuring optimal enzyme function.

7. Functions and Formation of Tissue Fluid

Functions of Tissue Fluid

  • Nutrient Delivery: Supplies cells with nutrients from blood.
  • Waste Removal: Collects metabolic wastes from cells for excretion.
  • Gas Exchange: Facilitates oxygen delivery and carbon dioxide removal.

Formation of Tissue Fluid

Process:

  • Filtration: Blood pressure forces plasma out of capillaries into interstitial spaces.
  • Exchange: Nutrients and gases move between blood and cells via tissue fluid.
  • Reabsorption: Osmotic pressure draws excess fluid back into capillaries.

Capillary Network:

  • Dense network allows efficient exchange between blood and tissues.
  • High surface area and thin walls maximize transport efficiency.

8. Role of Red Blood Cells (RBCs) in Transporting O₂ and CO₂

a. Hemoglobin

  • Structure & Function:
    • Hemoglobin is a protein within RBCs composed of four globin chains, each containing an heme group.
    • Each heme group binds one O₂ molecule, allowing each hemoglobin molecule to carry up to four O₂ molecules.
  • Oxygen Transport:
    • In the lungs, high partial pressure of O₂ (pO₂) facilitates O₂ binding to hemoglobin.
    • In tissues, lower pO₂ promotes O₂ release.

b. Carbonic Anhydrase

  • Enzyme Function:
    • Catalyzes the reversible conversion of CO₂ and H₂O to carbonic acid (H₂CO₃).
  • Role in CO₂ Transport:
    • Enhances the efficient conversion of CO₂ into a transportable form within RBCs.

c. Formation of Hemoglobinic Acid

  • Process:
    • CO₂ reacts with water (H₂O) to form carbonic acid (H₂CO₃) via carbonic anhydrase.
  • Significance:
    • Carbonic acid dissociates into bicarbonate ions (HCO₃⁻) and hydrogen ions (H⁺), facilitating CO₂ transport in plasma.

d. Formation of Carbaminohemoglobin

  • Process:
    • CO₂ binds directly to the amino groups on hemoglobin, forming carbaminohemoglobin.
  • Significance:
    • Approximately 20-30% of CO₂ is transported bound to hemoglobin, aiding in its removal from tissues.

9. Chloride Shift

Description:

  • Exchange Mechanism:
    • To maintain electrical neutrality, bicarbonate ions (HCO₃⁻) produced from CO₂ transport exit RBCs into plasma.
    • Simultaneously, chloride ions (Cl⁻) from plasma enter RBCs.

Importance:

  • Maintains Ionic Balance:
    • Prevents accumulation of negative charges inside RBCs.
  • Facilitates Efficient CO₂ Transport:
    • Ensures continued conversion of CO₂ to bicarbonate, enhancing CO₂ carriage in blood.

10. Role of Plasma in CO₂ Transport

Mechanisms:

  1. Dissolved CO₂:
    • ~5-10% of CO₂ is transported dissolved directly in plasma.
  2. Bicarbonate Ions (HCO₃⁻):
    • Majority (~60-70%) of CO₂ is transported as bicarbonate ions in plasma.
    • Formed via the action of carbonic anhydrase within RBCs.
  3. Carbamino Compounds:
    • ~20-30% of CO₂ is carried bound to hemoglobin as carbaminohemoglobin.

Significance:

  • Efficient Transport:
  • Plasma facilitates the bulk transport of CO₂ from tissues to lungs.
  • Buffering Capacity:
  • Bicarbonate ions help maintain blood pH balance.

11. Oxygen Dissociation Curve of Adult Hemoglobin

Description:

  • Graph Representation:
    • Plots hemoglobin saturation with O₂ against pO₂.
    • S-Shaped (Sigmoidal) Curve:
      • Reflects cooperative binding of O₂ to hemoglobin.

Phases:

  1. Steep Sloping (Low pO₂):
    • High affinity for O₂; small increases in pO₂ lead to significant O₂ binding.
  2. Plateau (High pO₂):
    • Saturation point; hemoglobin is nearly fully loaded with O₂.

Key Features:

  • Cooperative Binding:
  • Binding of one O₂ molecule increases affinity for the next.
  • Bohr Effect:
  • Shift in the curve due to changes in pH and CO₂ levels.

12. Importance of the Oxygen Dissociation Curve

In the Lungs (High pO₂):

  • Maximal O₂ Loading:
    • High pO₂ in alveoli ensures hemoglobin becomes saturated with O₂.

In Respiring Tissues (Low pO₂):

  • Efficient O₂ Release:
    • Low pO₂ facilitates the release of O₂ from hemoglobin to tissues where it’s needed for metabolism.

Overall Significance:

  • Adaptability:
    • The curve allows hemoglobin to pick up O₂ in the lungs and release it in tissues efficiently.
  • Facilitates Gas Exchange:
    • Ensures oxygen delivery matches tissue demand based on varying pO₂ levels.

13. Bohr Shift (Bohr Effect)

Description:

  • Definition:
    • A rightward shift of the oxygen dissociation curve caused by increased CO₂ concentration and decreased pH (more H⁺ ions).

Mechanism:

  • Lower pH and Higher CO₂:
    • Promote release of O₂ from hemoglobin.
    • CO₂ binds to hemoglobin, stabilizing the T (tense) state, reducing O₂ affinity.

Importance:

  • Enhanced O₂ Delivery to Tissues:
    • In active tissues producing more CO₂ and H⁺, the Bohr shift facilitates greater O₂ unloading.
  • Adaptive Response:
    • Aligns O₂ delivery with metabolic activity and needs of tissues.

14. External and Internal Structure of the Mammalian Heart

External Structure

  • Shape & Location
    • Shape: Approximately the size of a clenched fist, slightly cone-shaped.
    • Location: Situated in the mediastinum, between the lungs, slightly left of the midline.
  • Surfaces
    • Base: Upper, broader part; connects to the great vessels (aorta, superior and inferior vena cava, pulmonary arteries and veins).
    • Apex: Lower pointed end; directed downward, forward, and to the left.
  • Great Vessels
    • Aorta: Main artery distributing oxygenated blood to the body.
    • Superior & Inferior Vena Cava: Large veins returning deoxygenated blood from the body.
    • Pulmonary Arteries: Carry deoxygenated blood to the lungs.
    • Pulmonary Veins: Return oxygenated blood from the lungs to the heart.

Internal Structure

Chambers

  • Atria (2): Right and left; receive blood entering the heart.
  • Ventricles (2): Right and left; pump blood out of the heart.

Valves

Atrioventricular (AV) Valves:

  • Tricuspid Valve: Between right atrium and right ventricle.
  • Bicuspid (Mitral) Valve: Between left atrium and left ventricle.

Semilunar Valves:

  • Pulmonary Valve: Between right ventricle and pulmonary artery.
  • Aortic Valve: Between left ventricle and aorta.

Septum

  • Interatrial Septum: Separates right and left atria.
  • Interventricular Septum: Separates right and left ventricles.

Walls

  • Endocardium: Inner lining.
  • Myocardium: Thick muscular middle layer responsible for contractions.
  • Pericardium: Outer protective sac.

15. Differences in Wall Thickness

Atria vs. Ventricles

  • Atria:
    • Wall Thickness: Thin (1-2 mm).
    • Reason: Receive blood and contract to fill ventricles; lower pressure requirements.
  • Ventricles:
    • Wall Thickness: Thick (4-5 mm for left, 3 mm for right).
    • Reason: Pump blood out of the heart; higher pressure generation needed.

Left Ventricle vs. Right Ventricle

Left Ventricle:

  • Wall Thickness: Thicker (~5 mm).
  • Function: Pumps oxygenated blood into the aorta for systemic circulation; requires greater force.

Right Ventricle:

  • Wall Thickness: Thinner (~3 mm).
  • Function: Pumps deoxygenated blood into the pulmonary artery for pulmonary circulation; lower pressure needed.

16. The Cardiac Cycle

Phases of the Cardiac Cycle

  1. Diastole (Relaxation Phase):
    • Ventricles: Relax and fill with blood from the atria.
    • Blood Pressure: Lower pressure.
    • Valves: AV valves open; semilunar valves closed.
  2. Systole (Contraction Phase):
    • Ventricles: Contract to pump blood out.
    • Blood Pressure: Higher pressure.
    • Valves:
      • AV Valves: Close to prevent backflow (first heart sound).
      • Semilunar Valves: Open to allow blood ejection.

Blood Pressure Changes

  • During Diastole:
    • Pressure: Decreases as ventricles relax.
    • Valves: AV valves open, semilunar valves closed.
  • During Systole:
    • Pressure: Increases as ventricles contract.
    • Valves: AV valves close, semilunar valves open.

Valve Operations

AV Valves:

  • Open during diastole to allow ventricular filling.
  • Close during systole to prevent backflow into atria.

Semilunar Valves:

  • Open during systole to allow blood ejection.
  • Close during diastole to prevent blood from returning to ventricles.

17. Roles of the Sinoatrial Node, Atrioventricular Node, and Purkyne Tissue

Sinoatrial (SA) Node

  • Location: Upper part of the right atrium.
  • Function: Acts as the heart’s natural pacemaker.
    • Initiates electrical impulses that set the rhythm of the heart.
    • Causes atrial contraction (atrial systole).

Atrioventricular (AV) Node

  • Location: Lower part of the right atrium near the septum.
  • Function:
    • Receives impulses from the SA node.
    • Delays the electrical signal to allow ventricular filling.
    • Transmits impulses to the Purkyne fibers.

Purkyne Tissue (Purkyne Fibers)

  • Location: Network of fibers in the ventricular walls.
  • Function:
    • Conducts electrical impulses rapidly throughout the ventricles.
    • Ensures coordinated and efficient ventricular contraction (ventricular systole).

Sequence in the Cardiac Cycle

  1. SA Node generates an impulse → atria contract.
  2. AV Node receives the impulse, delays it.
  3. Purkyne Fibers distribute the impulse → ventricles contract.

Key Terms to Remember

  • Systole: Phase of ventricular contraction.
  • Diastole: Phase of ventricular relaxation.
  • Atria: Upper chambers receiving blood.
  • Ventricles: Lower chambers pumping blood.
  • Valves: Prevent backflow; ensure unidirectional blood flow.
  • SA Node: Heart’s pacemaker.
  • AV Node: Electrical relay station.
  • Purkyne Fibers: Conduct electrical impulses in ventricles.

Practice Questions 1

Practice Questions 2

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