Comprehensive Notes on Cardiac Circulation and Vascular Physiology and Vascular Anatomy

Mechanisms of Cardiac Circulation

  • Vena cava: Transports deoxgenatedc blood from various parts of the body back to the heart.
  • Right atrium: Receives blood and contracts to move it into the right ventricle.
  • Tricuspid valve: Opens to allow the flow of blood from the right atrium to the right ventricle.
  • Right ventricle: Contracts to pump blood toward the lungs.
  • Pulmonary valve: Opens to facilitate blood movement from the right ventricle to the pulmonary system.
  • Pulmonary arteries: Carry blood to the lungs.
  • Pulmonary veins: Return oxygenated blood back from the lungs into the heart.
  • Left atrium: Contracts to push oxygenated blood into the left ventricle.
  • Mitral valve: Opens to allow blood flow into the left ventricle.
  • Left ventricle: Contracts to drive blood into the systemic circulation for the body.
  • Aortic valve: Opens to allow blood to exit the heart into the aorta.
  • Aorta: Sends blood throughout the body.

The Cardiac Conduction System

  • SA node (Sinoatrial node):
    • A group of cardiac muscle cells located in the right atrium.
    • Sends electrical impulses every 0.8 seconds0.8\text{ seconds} to the wall of the atrium to trigger contraction.
    • Functions as the primary pacemaker regulating the rate of heart contractions.
  • AV node (Atrioventricular node):
    • A group of specialised cardiac cells located in the septum between the atriums.
    • Delays the electrical impulse before it reaches the muscle cells, causing the ventricles to contract.

Phases of the Cardiac Cycle

  • The Cardiac cycle consists of 3 phases3\text{ phases} totaling 0.8 seconds0.8\text{ seconds} at a rate of 70 beats / min70\text{ beats / min}.
  • The cycle is aurally represented by the LUB/DUB sounds.
  • Phase 1: Auricular systole
    • Atriums contract.
    • The SA node initiates an electrical impulse to the muscle cells of both atria to contract.
    • The Tricupid and bicsupid valve are opened.
    • Semilunar valves are closed, and blood flows into the ventricles.
    • During this phase, P waves are formed on the ECG.
  • Phase 2: Ventricular systole
    • Ventricles contract, resulting in a heart contraction.
    • The SA node impulse leads to the AV node impulse, which carries electrical signals to the ventricles via specialised fibers, causing them to contract.
    • Tricupid and bicuspid valves are closed.
    • Semilumar valves (SL valves) are opened, and blood flows into the pulmonary arteries and the aorta.
    • QRS waves are formed on the ECG.
    • Produces long, low "LUB" sounds, which are formed by the closing of both AV valves.
  • Phase 3: Atrioventricular diastole
    • Heart relaxation occurs, where both atriums and ventricles are relaxed.
    • Blood fills both atriums via the pulmonary valve and vena cava.
    • SL valves are closed while AV valves are open.
    • This phase lasts 0.4 seconds0.4\text{ seconds}.
    • T waves are formed on the ECG.
    • Produces the "DUB" sound, which is formed by the closing of the SL valves.

Valve Failure and Retrograde Blood Flow

  • When a valve fails to contract, it results in the wrong flow back (retrograde flow) of blood.
  • Deoxygenated blood flow back:
    • Tricupisd failure: Blood flows from the RV back to the RA.
    • Pulmonary valve failure: Blood flows from the PA back to the RV.
  • Oxygenated blood flow back:
    • Bicupid failure: Blood flows from the LV back to the LA.
    • Aortic valve failure: Blood flows from the Aorta back to the LV.

Cardiovascular Diagnostics and Blood Pressure

  • ECG (Electrocardiogram): A graph that shows changes in the electrical activity of the heart as a result of contractions.
  • Electrocardiography: The process of measuring and recording the electrical activity of the heart during both the contraction and relaxation phases of the atria and ventricles.
  • Pulse:
    • A series of pressure waves within an artery caused by the contraction of the ventricles.
    • As the heart contracts, blood surges through the arteries, causing their elastic walls to expand and stretch, which produces the pulse.
    • Produced specifically when the LV contracts.
    • Pulses are produced only in arteries; there is no pulse in veins.
  • Blood pressure:
    • A force that blood exerts against the inside walls of blood vessels (specifically arteries).
    • Produced as a result of both ventricles contracting.
    • Measurement is typically taken in the arteries that supply blood to the arm.
  • Diastolic Pressure:
    • Occurs when ventricles relax.
    • Normal range is 70 to 80 mmHg70\text{ to }80\text{ mmHg}.
    • During this time, AV valves are open but SL valves are closed.
    • A defect in SL valves affects diastolic pressure.
  • Systolic Pressure:
    • Occurs when ventricles contract.
    • Normal range is 110 to 120 mmHg110\text{ to }120\text{ mmHg}.
    • During this time, AV valves are closed but SL valves are opened.
    • A defect in AV valves affects systolic waves.
  • Hypertension: Blood pressure that is higher than normal, which places a strain on the walls of the arteries and increases the chance of bursting blood vessels.
  • Hypotension: Blood pressure that is lower than normal.

Classification and Structure of Blood Vessels

  • Systematic blood vessels pathway: Arteries rightarrow\\rightarrow arterioles rightarrow\\rightarrow capillaries rightarrow\\rightarrow venules rightarrow\\rightarrow veins rightarrow\\rightarrow vena cava.
  • Pulmonary blood vessels pathway: Pulmonart artery rightarrow\\rightarrow pulmonary arterioles rightarrow\\rightarrow pulmonary capillaries rightarrow\\rightarrow pulmonary venules rightarrow\\rightarrow pulmonary veins.
  • Arteries:
    • Function: Carry blood away from the heart.
    • Content: Usually oxygenated blood, with the exception of pulmonary arteries which carry deoxgyenated blood.
    • Key features: Thick, elastic, and contain no valves.
    • Wall Layers:
      • Inner: Endothelial layer (epitheal tissue).
      • Middle: Smooth muscle.
      • Outer: Connective tissue.
    • Elastic support: Provides the strength needed to handle high blood pressure without bursting; the stretching of these walls creates pulses.
  • Arterioles: The smallest arteries that branch off to connect main arteries to the capillaries.
  • Capillaries:
    • Structure: Walls are only one cell layer thick.
    • Diameter: The diameter is narrow enough that red blood cells pass through in a single file.
    • Function: Enables fast diffusion of gases and nitruents within the surrounding tissue.