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The Heart (The cardiac cycle: (1. Atrial contraction & ventricular…
The Heart
The cardiac cycle:
1. Atrial contraction & ventricular filling:
- Atria contract & ventricles relax
- Less atrial pressure & less arterial truck pressure
- AV valve opens and semilunar closes
2. Isovolumetric contraction:
- Atria relax
- Greater atrial pressure & less arterial trunk pressure
- AV valves closed & semilunar valves close
3. Ventricular ejection:
- Atria relax & ventricles contract
- Greater atrial pressure & greater arterial trunk pressure
- AV valves closed & semilunar open
4. Isovolumetric relaxation:
- Atria relax & ventricles relax
- Greater atrial pressure & less arterial trunk pressure
- AV valves closed & semilunar closed
5. Atrial relaxation & ventricular filling
- Atria relax & ventricles relax
- Less atrial pressure & arterial trunk pressure
- AV valves open & semilunar valves close
Anatomy:
Chambers:
- Right & left atrium: Receive blood
- Right & left ventricle: pump blood away
- Right side of the heart receives deoxygenated blood
- Left side of the heart receives oxygenated blood
Vessels:
- Superior & inferior vena cava: receives blood and drains to the right atrium
- Pulmonary trunk: splits into pulmonary arteries & carries deoxygenated blood to the lungs
- Pulmonary veins: deliver oxygenated blood from the lungs to the left atrium
- Aorta: delivers oxygenated blood to systemic circulation
Valves:
- Prevents the back flow of blood
- Right AV valve (tricuspid): between the right atrium & right ventricle
- Left AV valve (bicuspid/mitral): between the left atrium & left ventricle
- Pulmonary semilunar valve: between the right ventricle & pulmonary trunk
- Aortic semilunar valve: between the left ventricle & the aorta
Internal structures:
- Coronary sinus: returns deoxygenated to the right atrium
- Fossa ovalis: former location of the foramen ovale in a fetus to bypass blood circulation to the lungs.
- Papillary muscle: in the ventricles of the heart that contract and open the valves
- Chordae tendoneae: anchor the papillary muscle to the valves
- Septum: separates the two sides of the heart
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Conduction system:
- Sinoatrial node: located in the posterior wall of the right atrium. This is also called the pacemaker because this is where conduction begins, action potential is created here and spreads through gap junctions, moves to the
- Atrioventricular node: located in the floor of the right atrium, between the AV valve and the opening of the coronary sinus moves to the
- AV bundle: extends from the AV node through the septum divides into the
- Left & right bundles: which move to the
- Purkinje fibers: extend from the left & right bundles and continue through the walls of the ventricles and then the cycle starts over.
Autonomic control:
- The heart is regulated by the medulla
- Receives info from baroreceptors and chemoreceptors in the blood vessels & right atrium
- This doesn't initiate the heartbeat, just regulates
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Clinical terms:
- Cardiac output: amount of blood that is pumped by a single ventricle
- Stroke volume: volume of blood ejected by one beat
- Heart rate: number of beats per minute
- End diastolic volume: amount of blood remaining in the ventricle at rest
- End systolic volume: blood remaining in a ventricle at the end of contraction
- Venous return: volume of blood returned to the heart from the great veins
- Preload: stretch of the heart wall due to the load of the cardiac muscle
- Afterload: resistance in arteries to the ejection of blood by the ventricles & is the pressure of blood that has to be exceeded before blood is ejected from the chamber
- Frank-Starling Law: states that the as volume of blood entering the heart increases there is a greater preload