lecture 8 Flashcards
3 components of the cardiovascular system
○ Heart
§ Acts as a pump
§ Establishes the pressure gradient
○ Blood vessels
§ Passageways that blood is distributed from heart to rest of blood
○ Blood
Transport medium that materials are dissolved or suspended in to transported on
describe the heart + which ventricle is thicker?
- Muscular pump
- 4 chambers and 4 valves
- Left + right atria (funnel blood into ventricles)
- Left + right ventricles (main pumping chambers)
- The left ventricle is thicker then the right ventricles because LV pumps blood to the whole body, so deals with more pressure to push blood to the rest of the body (heart is a muscle, more u use it, bigger it gets)
Myocardium is too thick for enough blood to diffuse from heart chambers to myocardial cells so the heart needs its own blood supply
describe the pulmonary circulation
○ Right side of the heart
○ Carries blood from heart and lungs
Low pressure
systemic circulation
○ Left side of heart
○ Carries blood between heart and other body systems
○ High pressure
Note: NO side of the body pumps more blood, is a closed circuit
describe the cardiac cycle: diastolic vs systolic
- Events that occurs in 1 heart beat
- Diastole- relaxation of heart muscles
- Systole- contraction of heart muscles
Note: the atrium and the ventricles beat at different times, atirum bits slightly earlier to pump the blood into the ventricle first
steps of the cardiac cycle
- Late diastole
§ Passive filling of ALL chambers via ventricles
§ Both chambers relaxed
2. Atrial systole
§ Atrial contraction, forces a small amount of blood into ventricles
§ Because the pressure into ventricles is higher then in the atrium causing valves to open
§ Is not a NECESSARY step- could survive without it
3. Isovolumic ventricular contraction
§ 1st phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves
§ Due to pressure icnreasing, causing atrium and ventricle valves to shut, so no blood is entering/leaving, so there is a consistent (same) amount of blood in the ventricle at that time
§ At this point the pressure in the ventricles is less then the arteries
4. Ventricular ejection
§ As ventricular pressure rises + exceeds pressure in the arteries, the semilunar valves open + blood is ejected
§ Ventricles contract till pressure is higher in ventriculus then in arteries, causing blood to flow out of semilunar valves- ventricular ejection
§ AV valve before is closed so no back flow
5. Isovolumic ventricular relaxation
§ As ventricles relax, pressure in ventricles falls, blood flows back into cusps of semilunar valves + snaps them closed
§ So volume in ventricle remains the same, due to pressure being higher in atrium then in arteries
§ The pressure is low enough to close semilunar valves but not high enough to open AV valves, until pressure does, then cycle repeats
The whole cycle depends on the pressure on the right side being higher then on the left side, and if the pressure decreases, valves close, if pressure increases, valves open
heart sounds
- 2 sounds in a heathly person
- S1
○ AV valves closing - S2
Semilunar valves closing
- S1
describe the electrical acitivty of the heart
- Heart beats rhythmically as a result of action potential it generates itself (autorhythmicity)
The action potential preceds mechanical events
2 types of cardiac muscle cells
○ Contractile cells
§ 99% of cardiac muscle
§ Do mechanical work of pumping
§ Normally do not initiate own action potential
○ Autorhythmic cells
§ 1% of cardiac muscle
§ Do NOT contract
Specialised for initiating + conducting action potentials responsible for contraction fo working cells
function of AV node
AV node delays the impulse approx. 0.1 second (so atrium can pump slightly before ventricle)
describe the SA node
- Node of auto rhythmic (pacemaker) cardiomyocytes embedded in right atria wall
- Auto rhythmicity = 70-80 bpm
- Auto rhythmicity can be modulated by nerves + hormones
Fires the most rapidly, so controls the heart rate, is the pacemaker
describe the internodal pathways
- Within atria connect SA with AV node
50msec delay for action potential to travel from SA ndoe to AV node causing atrial contraction
describe cardiac fibrous tissue
- Atria and ventricles are separated by a layer of dense electrically nonconductive fibrous tissues
Acts as insulation + ensures electrical signals follows a particular pathway, otherwise wont contract properly
describe the AV node
- The node of autorhythmic cardiomyocytes imbedded within floor of the right atrium
- Authorhythmicity = 40-60bpm
- Gateway for electrical signal arising from SA to enter ventricles
- Delays the action potential by 0.1s (because takes 0.1sec for signal to pass through AV node)
- Autorythmicity = 40-60bpm
- Delay is important so atria can contract fully first before ventricles
Is autorthyythmic in case something is wrong with SA node, will have AV node to stimulate heart beat
describe the bundles of His
○ Carries impulses towards heart apex
○ 2 branches lcoated within interventricular septum
○ Left bundle much larger- because left side has more muscle to stimulate
Autorhythmic at 20-40 bpm
