Cardiovascular Physiology Overview

Cardiovascular Physiology Study Notes

• Parasympathetic Stimulation:

  • Slows heart rate by increasing potassium permeability in SA node cells.
  • Decreases potassium permeability in AV node cells.
  • Does not affect sodium permeability in SA node cells.

• ECG (Electrocardiogram) QRS Complex:

  • Represents ventricular depolarization.

• Cardiac Output:

  • Approximately 5 liters per minute at rest.
  • Left ventricle output generally equals right ventricle output.
  • Varies with physical activity, not constant.
  • Highest when heart rate is maximal.

• Left Ventricular Pressure Peak:

  • Highest during isovolumetric contraction.

• Blood Flow Regulation:

  • Primarily influenced by vascular radius.
  • Affected by blood viscosity and plasma protein concentration, less so erythrocyte count.

• Atrioventricular Valve Closure:

  • Occurs at the onset of isovolumetric contraction.

• Stroke Volume:

  • Influenced by intrinsic regulatory mechanisms (Frank-Starling mechanism).
  • Varies with preload.
  • Not a fixed value.

• Absolute Refractory Period (Cardiomyocytes):

  • Prevents tetanic contractions.
  • A time interval during which cardiomyocytes cannot be excited, even by strong stimuli.
  • Mostly due to potassium ion outflow.
  • Duration is only several milliseconds in the ventricular myocardium.

• Capillary Fluid Filtration:

  • Decreases with decreased capillary hydrostatic pressure and increased plasma colloid osmotic pressure.
  • Increased capillary permeability raises the filtration.

• Cardiac Cycle:

  • Ejection period begins with semilunar valve opening.
  • Atrial cycle is shorter than ventricular cycle.
  • Ventricular pressure changes during isovolumetric contraction.
  • Ventricular filling occurs when atrioventricular valves are open.

• Atrial Pressure Difference:

  • Pulse pressure.

• Angiotensin II:

  • A vasoconstrictor acting on vascular smooth muscle (ATI receptors).

• Vasodilators:

  • Prostacyclin and nitric oxide are vasodilators.
  • Serotonin is not a vasodilator.
  • Bradykinin is a vasodilator.

• Vasopressin:

  • A potent vasoconstrictor, not a hypotensive agent.
  • Affected by hypovolemia.

• Venous Return:

  • Influenced by skeletal muscle activity (contractions hinder), and breathing (inspiration increases).
  • Not increased by standing position (initially, but adjustment occurs).

• Baroreceptors:

  • Stretch receptors located in major arteries (major blood vessels).
  • Activated by changes in blood pressure.

• Mitral Valve Opening:

  • Occurs at the end of isovolumetric relaxation.

• Atrial Systole Importance:

  • Greatest importance for ventricular filling at rest and during bradycardia (slow heart rate).

• First Heart Sound:

  • Begins slightly before the Q wave of the ECG.
  • Primarily due to atrioventricular valve closure.

• Electrical Axis of Heart:

  • Varies depending on conditions (expiration, pregnancy, hypertrophy).

• Coronary Blood Flow:

  • Primarily regulated by local factors.
  • Reduced by hypoxia, not significantly by sympathetic stimulation.
  • Minimal during diastole.

• Autoregulation (Brain Blood Flow):

  • Maintains constant blood flow despite blood pressure changes within a vital range (60-160 mmHg).
  • Blood flow does not depend on volume limitations.

• Blood Velocity (Smallest):

  • Blood velocity is smallest in capillaries due to their large total cross-sectional area.

• Venous Blood Flow:

  • Influenced by respiration and skeletal muscle contraction.
  • Venous valves help maintain flow direction.
  • More influential during expiration, less influenced by skeletal muscle contraction.

• Kidney's Role in Blood Pressure Regulation:

  • Regulates blood volume through urine production in response to various factors.
  • Maintains circulating blood volume.

• Venous Return to Heart:

  • Affected by gravity and skeletal muscle activity.
  • Valves aid in one-way flow.

• Sympathetic Nervous System Activity:

  • Typically produces vasoconstriction in many vessels.
  • Affects coronary vessel dilation.
  • Primary regulator of brain circulation.

• Arterial Baroreceptors:

  • Respond to blood pressure changes, not directly to the limbic system.
  • Essential in short-term pressure regulation; mechanoreceptors.

• Vascular Resistance:

  • Laminar blood flow resistance influenced by vessel diameter, length, and blood viscosity; the Reynolds number.
  • Number of blood cells doesn't directly factor in laminar resistance.

• Elastic Vessels:

  • Aorta and large arteries; act as pressure reservoirs during cardiac systole.

• Poiseuille's Law (Laminar Blood Flow):

  • Blood flow is directly proportional to the fourth power of the vessel radius, not the second power.

• Pulse Pressure:

  • Highest in the aorta, influenced by stroke volume.
  • Decreases with greater aortic compliance.

• Capillary Permeability:

  • High permeability is seen in capillaries in endocrine glands, and also in the skin.

• Pulmonary Arterioles:

  • Exhibit lower resistance than systemic arterioles.
  • Dilate in hypoxia.

• Capacitance Vessels:

  • Veins, due to their high compliance, are capacitance vessels.

• Cardiac Excitation Conduction:

  • Conducted by the excitatory-conductive system.

• Action Potential Plateau:

  • AV node cells have the longest action potential plateau.

• Mean Electrical Axis:

  • The mean direction of atrial and ventricular depolarization, which varies based on bodily conditions.

• Parasympathetic Inotropic Effect:

  • Reduces heart contractility by affecting N-cholinergic receptors, decreasing cAMP production, reducing adenylyl cyclase activation.

• PQ Interval:

  • Represents excitation conduction time from the SA node to the ventricles.
  • Lengthens with parasympathetic stimulation; not fixed (but usually, under 0.2 seconds).

This quiz covers key concepts in cardiovascular physiology, including blood flow regulation, cardiac output, and the electrocardiogram. It explores the effects of parasympathetic stimulation and the mechanics of heart contractions. Perfect for students studying physiology or preparing for exams.