Heart (continued)

Where is the heart located in relation to the body's midline?

1/3 to right, 2/3 to left

Where does the apex of the heart point?

inferiorly, anteriorly, to the left

What mainly forms the right border of the heart?

right atrium

What mainly forms the inferior border of the heart?

right ventricle

What mainly forms the left border of the heart?

left ventricle, left atrial auricle

What forms the superior border/base of the heart?

blood vessels entering and leaving the heart

What is the pericardium?

double walled sac surrounding the heart to protect it

What are the layers from outside to inside around the heart?

fibrous pericardium, parietal pericardium, pericardial space, visceral pericardium, myocardium

What is the fibrous pericardium?

tough outer sac that protects the heart

What is the parietal pericardium?

lines the inside of the fibrous pericardium

What is the visceral pericardium? (aka epicardium)

adheres directly to the heart and forms outer surface

What is the pericardial space?

space between parietal and visceral pericardium

What is found in the pericardial space?

thin layer of serous fluid

What is the function of pericardial fluid?

allows surfaces to slide with minimal friction as the heart beats

What type of cells make up the serous pericardium?

squamous mesothelial cells

What are the three layers of the heart wall?

epicardium, myocardium, endocardium

What is the myocardium?

cardiac muscle layer responsible for heart contraction

What is the endocardium?

lines the inside of heart chambers

What is the fibrous skeleton of the heart made of?

tough connective tissue

What are the mechanical functions of the fibrous skeleton?

supports valves, maintains the shape of valve openings, provides attachement for cardiac muscle

What is the electrical function of the fibrous skeleton?

acts as electrical insulator between atria and ventricles

Why does the electrical impulse normally have to pass through the AV node and AV bundle?

fibrous skeleton prevents direct electrical conduction between atria and ventricular muscle

Which fibrous rings are complete and which are incomplete?

mitral and aortic complete, tricuspid and pulmonary incomplete

What is present where the tricuspid and pulmonary fibrous rings are incomplete?

fatty connective tissue

What is the pathway of electrical conduction through the heart?

sa node, atrial muscle, av node, av bundle, left and right branches, purkinje fibres, ventricular muscle

Where is the SA node located?

right atrium

What is the function of the SA node?

initiates electrical impulse that causes atrial contraction

Why is the SA node called the heart's pacemaker?

depolarizes spontaneously, generating impulses

What is the intrinsic firing rate of the SA node?

60-100 impulses/min

What can influence the SA node and heart rate?

hormones and autonomic nervous system

What happens when the impulse spreads through the atrial muscle?

atria contract

What is the function of the AV node?

receives atrial impulses and conducts it slowly, creating a delay

Why is AV node delay important?

gives ventricles time to fill before they contract

Approximately how long is the AV node delay?

100ms

How fast does conduction occur through the AV node compared with the other parts of the conduction system?

very slow, 0.05 m/s

What is the function of the AV bundle (Bundle of His)?

carries impulse through fibrous skeleton towards ventricles

What does the AV bundle divide into?

right and left bundle branches

What are Purkinje fibres?

modified cardiac cells for rapid electrical conduction through ventricular walls

Why are Purkinje fibres important?

produce coordinated ventricular systole

How fast can conduction occur through the Purkinje system?

5 m/s, very fast

What is the cardiac cycle?

sequence of events that occur during one heartbeat

Approximately how long is one cardiac cycle at rest?

1 second at a resting heart rate of 60-70 beats/min

What determines the direction of blood flow through the heart?

pressure differences

What causes ventricular filling to begin?

ventricular pressure falls below atrial pressure

Which valve opens during ventricular filling on the left side?

mitral valve

Where does blood flow during ventricular filling?

left atrium to left ventricle

Approximately how much does the ventricle fill during passive ventricular filling?

80% of its capacity

What happens to ventricular volume during ventricular filling?

increases

What happens to the aortic valve during ventricular filling?

remains closed

What is the purpose of atrial contraction?

completes ventricular filling

What happens to atrial pressure during atrial contraction?

rises slightly

Which valve is open during atrial contraction on the left side?

mitral valve

What happens during isovolumetric ventricular contraction?

ventricles begin to contract, pressure rises while volume remains constant

Why does ventricular volume remain constant during isovolumetric contraction?

both inlet and outlet valves closed, so blood does not enter or leave

What causes the mitral valve to close?

rising ventricular pressure

What heart sound is produced when the mitral valve closes?

first heart sound s1

Why does the aortic valve remain closed during isovolumetric contraction?

ventricular pressure still below aortic pressure

What causes the aortic valve to open?

ventricular pressure becomes greater than aortic pressure

Where does blood flow during left ventricular ejection?

left ventricle to aorta

What happens to ventricular volume during ejection?

decreases as blood leaves the ventricle

What happens to ventricular and aortic pressure during the early part of ejection?

both increase

What happens later during ventricular ejection?

rate of ejection decreases, pressure decrease

What happens during isovolumetric ventricular relaxation?

ventricles relax, pressure falls rapidly while volume remains constant

Why does ventricular volume remain constant during isovolumetric relaxation?

mitral and aortic valves closed

What causes the aortic valve to close?

ventricular pressure falls below aortic pressure

What heart sound is produced when the aortic valve closes?

second heart sound s2

Why does the mitral valve remain closed initially during ventricular relaxation?

ventricular pressure still greater than atrial pressure

What happens after isovolumetric relaxation?

ventricular pressure falls below atrial pressure, mitral valve opens, ventricular filling begins again

What causes the first heart sound (S1)?

closure of av valves, including mitral valve

When does S1 occur?

start of ventricular systole

What causes the second heart sound (S2)?

closure of semilunar and aortic valves

When does S2 occur?

end of ventricular systole and start of ventricular relaxation

What is ventricular systole?

period when ventricles contract

What two stages make up ventricular systole?

isovolumetric ventricular contraction and ventricular ejection

What is ventricular diastole?

period when ventricles relax

What two stages make up ventricular diastole?

isovolumetric ventricular relaxation and ventricular filling