CVS Physiology

• The jugular venous pressure (JVP) reflects what is happening on the right side of the heart as there are not valves between internal jugular vein and the right side of the heart
• On a JVP waveform:

  A = Atrial contraction

  C = Ventricular contraction

  V = Venous filling of atria
• Cardiac output mL/min = Heart rate (bpm) x SV (mL/beat)
• The average cardiac output is 5.25L/ min
• Stroke volume is regulated by:

  1. Preload
  2. Contractility
  3. Afterload
• Intrinsic control of blood vessels means they can automatically adjust their vascular tone by dilating or constricting in response to changes in the environment. Some of these changes include temperature, cytokines, hypoxia and CO2
• Baroreceptors are located in the aortic arch and carotid sinus
• The baroreceptor reflex is part of the extrinsic control of blood pressure
• An increase in arterial pressure increases baroreceptor activity. This leads to an increase in parasympathetic nervous system activity and a decrease in sympathetic nervous system activity. This leads to a decrease in heart rate and systemic vasodilation. Decrease in contractibility.
• The sympathetic nervous system causes vasoconstriction via norepinephrine and epinephrine
• The Renin Angiotensin Aldosterone System (RAAS) is activated by increased sodium concentration, decreased renal blood flow or stimulation by the SNS
• RAAS:

  1. Juxtaglomerular cells of kidneys increase renin production
  2. Liver releases angiotensin
  3. Renin + Angiotensin = increase in Angiotensin I
  4. ACE from lungs convert Angiotensin I to Angiotensin II
  5. Vasoconstriction of arterioles
  6. Increased Aldosterone = increased sodium and water reabsorption and therefore increased blood volume
• The Sinoatrial node lies between the superior vena cava and right atrium
• SAN generates impulses automatically by spontaneous depolarization of its membrane. The most important being a small influx of sodium ions.
• Action potentials in the SAN trigger depolarization of the atrial then ventricular myocytes
• Depolarization conducts slowly through the AVN. AVN continues as the His bundle - conducting the impulse rapidly towards the ventricles
• His bundle splits into the right bundle branch and main left bundle branch. Purkinje fibres then carry the impulse throughout the ventricles leading to their contraction
• The first heart sound, S1, is made by the closure of the mitral and tricuspid valves. Their closure is prompted by the beginning of ventricular systole.
• The second heart sound, S2, is made by the closure of the aortic and pulmonary valves at the start of ventricular diastole.
• S3 is a third heart sound that may be heard just after S2 during diastole. it occurs due to rapid ventricular filling. May be normal in children and young adults but can be a sign of heart failure
• A fourth heart sound, S4, may be heard just before S1 during late diastole. it is due to rapid ventricular filling during atrial systole. It can represent a non compliant ventricle due to pathologies such as hypertrophic cardiomyopathy and aortic stenosis