Bio-302 Lecture 6 - Blood Vessels

Overview of the Cardiovascular System

• The cardiovascular system consists of the heart and blood vessels, playing a crucial role in transporting blood throughout the body.

Anatomy & Physiology: Chapters 20-21

• Understand the structure and function of the cardiovascular system, focusing on blood vessels.

Page 1: Introduction to the Cardiovascular System

• Introduction to key concepts of cardiovascular anatomy and physiology.

Page 2: The Electrocardiogram (ECG)

• Understanding One Cardiac Cycle

  • Phases of the cardiac cycle: Atrial Diastole, Atrial Systole, Ventricular Diastole, and Ventricular Systole.

  • Key Events

    1. Atrial contraction begins.

    2. Atria eject blood into ventricles.

    3. AV valves close after atrial systole.

    4. Isovolumetric ventricular contraction occurs.

    5. Ventricular ejection takes place.

    6. Semilunar valves close.

    7. Isovolumetric relaxation occurs.

    8. AV valves open for passive atrial filling.

Page 3: Contractile Cells in the Heart

• Types of Cardiac Cells:

  • Contractile cells form the bulk of atrial and ventricular walls.

  • They differ from skeletal muscle fibers; they maintain prolonged depolarization to enable maximal contraction.

• Refractory Periods:

  • Blue = Absolute Refractory Period

  • Pinkish Orange = Relative Refractory Period

Page 4: Action Potentials in Cardiac Cells

• Three steps of action potential in cardiomyocytes:

  1. Rapid depolarization due to sodium influx.

  2. Plateau phase from calcium influx balancing sodium efflux.

  3. Repolarization occurs as potassium exits, following calcium closure.

  • Long refractory period prevents premature contractions.

Page 5: Pacemaker Cells

• Pacemaker cells rest at -60 mV due to HCN channels that allow spontaneous depolarization, critical for initiating action potentials.

• Autorhythmicity determines heart rhythm and ensures continuous contraction without skipping beats.

Page 6: Sinoatrial Node Functions

• The Sinoatrial (SA) node sets the base heart rate (approx. 90 bpm).

• The Atrioventricular (AV) node can maintain heart rate (~50 bpm) in absence of SA node input.

• The AV node acts as a gatekeeper to slow electrical impulses to the ventricles, preventing excessive rapid heart rates.

Page 7: Autonomic Control of Heart Rate

• The cardiac plexus innervates the heart via sympathetic and parasympathetic divisions:

  • Sympathetic Division: Increases heart rate release of norepinephrine (tachycardia).

  • Parasympathetic Division: Decreases heart rate via acetylcholine (bradycardia).

Page 8: Reflexes Regulating Cardiac Activity

• Baroreceptors monitor blood pressure and respond to changes with appropriate cardiac activity adjustments.

• Declines in BP typically elicit an increase in cardiac output to meet tissue demands.

Page 9: Regulation Summary

• Summary of heart rate regulation mechanisms involving autonomic nervous system pathways and hormonal influences.

• Key players include cardiac centers in the medulla, vagus nerve control, sympathoadrenal system, etc.

Page 10: Homeostasis in Blood Pressure

• Cardiac output adjustments maintain blood pressure:

  • When blood pressure fluctuates above or below normal, corresponding cardiac center reflex responses occur.

Page 11: Cardiovascular Endocrinology

• The heart releases natriuretic peptides to regulate blood pressure in response to increases in circulatory volume.

Page 12: Chemoreceptor Activation

• Chemoreceptors regulate heart rate by monitoring blood pH and CO2 levels, activating the cardioacceleratory center when necessary.

Page 13: Cardiac Work Measurement

• Cardiac work can be analyzed through pressure-volume graphs, where the area under the plot represents work done by the heart during circulation.

Pages 14-28: Blood Vessels and Circulation

• Circuits:

  • Pulmonary Circuit: Involves pulmonary arteries/veins.

  • Systemic Circuit: Comprised of systemic arteries and veins.

• Vasculature Characteristics:

  • A closed circulatory system featuring arteries, veins, and capillaries.

  • Functionality of blood vessels differs; arteries carry blood away, while veins return it, and capillaries enable exchange of materials.

Page 29: Capillary Permeability

• Capillary Types:

  • Continuous: Least permeable, found in various body regions.

  • Fenestrated: More permeable, ideal for hormone access.

  • Sinusoidal: Most permeable, allowing extensive cell traffic; found in liver and lymphatic organs.

Page 30: Capillary Network Functionality

• Capillary beds function as interconnected loop systems, adapting blood flow as needed through sphincter control.

Pages 31-38: Characteristics of Veins

• Veins serve as capacitance vessels and maintain blood flow through valves and muscle contractions.

• Describe the structure of venules and larger veins in comparison with arteries, with a focus on tunica layers and overall functionality.

Page 39: Blood Pressure Management

• Understand the variations in blood pressure across blood vessels and potential issues caused by excessive pressure.

Page 40: Summary of Vascular Parameters

• Review parameters such as blood flow velocity and total cross-sectional area across various vessel types focusing on pressures and capacities.

Page 41: Blood Distribution Dynamics

• Overview of blood distribution within the cardiovascular system, outlining various segments and their percentages in overall blood volume.

Pages 42-48: Regulation of Circulation

• Discuss autoregulation mechanisms, including vasodilation and vasoconstriction cues, along with nervous and endocrine controls involved in circulation regulation.

Page 49: Capillary Filtration Dynamics

• Review the dynamics of capillary filtration, emphasizing factors driving the movement of fluids and solutes across capillary walls, focusing on hydrostatic and osmotic pressures.

Conclusion

• A comprehensive understanding of the cardiovascular system's anatomy and physiology, including the functioning of the heart, blood vessels, and regulatory mechanisms is critical for medical and health-related fields.