Cardiovascular System

it is a medium-sized artery that draw blood from an elastic artery and branch into 'resistance vessels' including small arteries and arterioles

• they are afferent vessels 
• they carry blood to the heart

they are exchange vessels

they connect the smallest arteries and veins

thin walls allow exchange of dissolved gases, nutrients and wastes between blood and surrounding tissue

they receive blood under great pressure from the heart [ventricles] after cardiac contraction after cardiac contraction [systole]

[the aorta and arteries have elastic walls and the ability to expand in diameter to stop them] rupturing on receipt of blood following ventricular contraction

during ventricular relaxation the artery walls return to normal size [by elastic recoil]

veins receive their blood at low pressure from capillaries

veins have valves to prevent black flow of blood

muscular contraction assists blood flow through veins

blockage by atherosclerosis and altered compliance

dysfunctional or damaged valves- varicose veins

• coronary arteries 
• coronary veins

atherosclerosis can reduce blood flow and can cause coronary ischaemia

can be removed surgically or with a stent

contractile cells are the cells which contract and move blood through the heart

the atria contracted followed by the ventricles

it contracts spontaneously without neural or hormonal stimulation

located on the junction between atria and ventricles on the floor of the right atrium [pacemaker cells]

located on junction between atria and ventricles on the floor of the right atrium

internodal pathways connect the nodes and spread the stimulus through the atrial myocardium

the bundle of his transmits the electrical impulses from the AV node to the point of the apex of the fasicular branches via the bundle branches

purkinje fibres transmits impulse to ventricular myocardium and ventricular contraction begins

• an ECG is a recording of the electrical events in the heart 
• records the:
• P waves
• QRS complex 
• T wave

the depolarisation of the atria and atrial contraction

• ventricle depolarisation.
• electrical signal is strong because the ventricular muscle is much bigger.
• it is more complex also because of the pathway through which the impluses spreads in the ventricles

• ventriclular repolarisation.
• atrial repolarisation takes place during vent depolar and is masked by the QRS

it indicates an enlarged heart

coronary ischaemia

PR interval goes from start of atrial depolarisation to start of QRS because the R can be difficult to see in abnormal ECGs

it can be an indication of disease

increased time due to the damage of conducting pathways/AV nodes

• increased time due to electrolyte disturbances, medication, coronary ischaemia
• QT interval time taken for vent to depol and then repolar. measured from end of PR interval