Cardiovascular Physiology Quiz

Cardiovascular Physiology

• Heart Structure:
  • Blood enters the right atrium via the superior vena cava, inferior vena cava, and coronary sinus; blood enters the left atrium via four pulmonary veins.
  • Valves: Ensure one-way blood flow by preventing backflow.
  • Chambers: Four chambers (right atrium, right ventricle, left atrium, left ventricle) with specific roles in the cardiac cycle.
  • Systemic Circulation: Left side of the heart pumps oxygenated blood to body tissues (except lungs).
  • Pulmonary Circulation: Right side of the heart pumps deoxygenated blood to lungs for oxygenation.
  • Heart Valves:
    • Atrioventricular Valves: Located between atria and ventricles;
      • Left AV valve - bicuspid
      • Right AV valve - tricuspid
    • Semilunar Valves: Aortic and pulmonary valves, critical for blood ejection from the heart.

Cardiac Electrophysiology

• Pacemaker Potential: Governed by HCN (hyperpolarization-activated cyclic nucleotide-gated) ion channels; initiates spontaneous action potentials in pacemaker cells.

• Cyclic AMP (cAMP): Modulates HCN channel currents, impacting automaticity and heart rate.

• Electrocardiogram (ECG):

  • Measures heart's electrical activity via electrodes on limbs and chest.
  • Produces 12 tracings from various lead combinations.
  • Used to detect abnormalities in conducting pathway, heart enlargement, heart damage, and cause of chest pain.

• ECG Waves and Cardiac Events:

  • P Wave: Atrial depolarization (contraction).
  • QRS Complex: Ventricular depolarization (contraction).
  • T Wave: Ventricular repolarization (relaxation).

The Cardiac Cycle

• Phases of the Cycle:

  • Atrial depolarization (P wave), atrial systole.
  • Ventricular depolarization (QRS complex), ventricular systole.
  • Ventricular repolarization (T wave), ventricular diastole.
  • Cycle repeats.

• Cardiac Output (CO):

  • Volume of blood ejected per ventricle in a minute.
  • CO = Heart Rate (HR) x Stroke Volume (SV).
  • At rest, CO is typically ~5 L/min at HR 70 bpm and SV 70 mL.

Heart Sounds

• Auscultation: Listening to heart sounds.
• Heart Sounds: Caused by blood turbulence and closing heart valves.
  • S1 ("lubb"): AV valve closure.
  • S2 ("dupp"): Semilunar valve closure.
  • S3 and S4: Less audible sounds from blood turbulence in filling phases.

Athletic Heart Adaptations

• Hypertrophy: Increased cardiac chamber volume and SV, up to 200 mL/beat.
• Lower Resting Heart Rate: Enhanced cardiovascular health, often below 70 bpm in trained athletes.

Factors Affecting Stroke Volume (SV)

• Preload: Ventricular stretch before contraction; influenced by venous return.
• Contractility: Heart muscle's inherent ability to contract; influenced by physiological / pharmacological factors.
• Afterload: Pressure the ventricles must overcome to eject blood; inversely related to SV.

Preload

• Frank-Starling Law: Increased preload leads to stronger heart contractions, thus enhancing SV. Preload also depends on duration of diastole and venous return.

Contractility

• Factors influencing contractility:
  • Positive inotropic agents: Increase contractility (noradrenaline).
  • Negative inotropic agents: Decrease contractility (acidosis).

Afterload

• Resistance ventricles must overcome to eject blood; influenced by systemic vascular resistance and blood pressure.
• Higher afterload leads to lower stroke volume.

Regulation of Heart Rate

• Mechanoreflexes: Receptors relaying information about body position to the cardiovascular centre; ↑ heart rate with exercise.
• Chemoreceptors: Monitor blood chemistry (O2, CO2, pH); affect heart rate and respiration in response to changes in blood chemistry.
• Baroreceptors: Monitor blood pressure; crucial for maintaining blood pressure homeostasis.
• Sympathetic Regulation: Noradrenaline released from sympathetic nerves, increasing heart rate and contractility.
• Hormonal Influence:
  • Acetylcholine slows heart rate.
  • Adrenaline and noradrenaline significantly increase heart rate and myocardial contractility during stress.
  • Thyroid hormones enhance cardiac contractility, increasing heart rate.
• Ion Concentrations: Changes in Na+, K+, and Ca2+ levels affect heart rate and contractility

Haemodynamics and Blood Flow Dynamics

• Blood Flow: Driven by pressure differences between heart and blood vessels. Blood flows through narrow arterioles, capillaries, and venules, encountering resistance.
• Capillary Networks: Extensive network of small vessels that connects to body cells, facilitating exchange of oxygen, nutrients, and waste products.
• Blood Distribution During Activity: Venoconstriction reduces blood volume in reservoirs, assisting in maintaining blood pressure during increased muscular activity.
• Vascular Compliance: Tendency of vessels to expand in response to pressure increases; venous system has high compliance, acting as a blood reservoir.

Blood Pressure

• SBP: Systolic Blood Pressure - peak pressure.
• DBP: Diastolic Blood Pressure - lowest pressure.
• MAP: Mean Arterial Pressure - average pressure.
  • MAP = DBP + 1/3 (SBP - DBP)
• Pulse Pressure: Difference between systolic and diastolic pressure; reflects stroke volume and vascular compliance.

Blood Flow Rate

• Vessel Diameter: Critical for flow rates; wider vessels lead to slower flow for optimal exchange. Smaller vessels have increased cross-sectional area, leading to decreased velocity.

Pressure, Flow, and Resistance

• Blood flow calculated using Darcy's Law: Q = ΔP/R. factors determining blood flow are pressure difference and resistance.

Vascular Resistance

• Vessel Lumen Size: Narrower lumen increases resistance.
• Blood Viscosity: Higher viscosity (e.g., dehydration) increases resistance.
• Vessel Length: Longer vessels increase resistance.

Summary of Blood Pressure Regulation

• Systems such as Baroreceptors, Chemoreceptors, Renin-Angiotensin System, and Atrial Natriuretic Peptide (ANP) regulate blood pressure through diverse mechanisms.

Renin-Angiotensin System

• Renin initiates a cascade, producing angiotensin II, a potent vasoconstrictor, increasing systemic blood pressure; also affects kidney salt and water retention.

Atrial Natriuretic Peptide (ANP)

• Reduces blood volume by promoting sodium and water excretion and vasodilation.

Capillary Blood Distribution During Activity

• Venoconstriction is responsible in reducing blood volume stored in blood reservoirs during intense muscle activity.