Anatomy & Physiology II: Chapter 18

The heart

Describe the size and shape of the heart?

Approximately the size of a clenched fist and cone shaped

Where is the heart located in the thorax?

In the mediastinum at the midsternal line between the lungs

What structures protect the heart?

Sternum & ribcage

Where is the apex of the heart located?

Inferior portion of the heart pointing left

Where is the base of the heart located?

Superior portion of the heart formed primarily by the left atrium

What are the two coverings of the heart?

Fibrous pericardium and serous pericardium

What is the function of the fibrous pericardium?

Anchors and protects the heart and prevents overfilling

What is the function of the serous pericardium?

Reduces friction via serous fluid in the pericardial cavity

What is pericarditis?

Inflammation of the pericardium causing chest pain and impaired heart pumping

What are the three layers of the heart wall?

• Epicardium

• Myocardium

• Endocardium

What is the function of the epicardium?

Protection and reduction of friction

What is the function of the myocardium?

Cardiac muscle contraction to pump blood

What is the function of the endocardium?

Smooth lining that reduces friction and prevents clot formation

Which chamber has the thickest myocardium?

Left ventricle

Why does the left ventricle have the thickest myocardium?

It pumps blood to the entire body at high pressure

Which chambers have the thinnest myocardium?

Right atrium & left atrium

Why is myocardium thinner in the right ventricle than the left ventricle?

It only pumps blood to the lungs

What are the four chambers of the heart?

• Right atrium

• Right ventricle

• Left atrium

• Left ventricle

Which chambers receive blood?

Right atrium & left atrium

Which chambers pump blood?

Right ventricle and left ventricle

Which side of the heart contains deoxygenated blood?

Right side

Which side of the heart contains oxygenated blood?

Left side

Which vessels connect to the right atrium?

Superior vena cava & inferior vena cava

Which vessel connects to the right ventricle?

Pulmonary trunk

Which vessels connect to the left atrium?

Pulmonary veins

Which vessel connects to the left ventricle?

Aorta

Which systemic vessels carry deoxygenated blood?

Superior & inferior vena cava

Which pulmonary vessels carry deoxygenated blood?

Pulmonary arteries

Which systemic vessels carry oxygenated blood?

Aorta

Which pulmonary vessels carry oxygenated blood?

Pulmonary veins

What fetal remnant is found in the interatrial septum?

Fossa ovalis

What was the function of the foramen ovale in the fetus?

Allowed blood to bypass the lungs by flowing between the atria

What is the function of heart valves?

Ensure one way blood flow

Where is the tricuspid valve located?

Between the right atrium & right ventricle

Where is the bicuspid (mitral) valve located?

Between the left atrium & left ventricle

Where is the pulmonary semilunar valve located?

Between the right ventricle & the pulmonary trunk

Where is the aortic semilunar valve located?

Between the left ventricle & the aorta

What causes heart valves to open?

Pressure differences between chambers

What causes heart valves to close?

Backflow of blood

What structures anchor the AV valves?

Chordae tendineae and papillary muscles

Into which chamber does blood enter the heart from the systemic circuit?

Right atrium

From which chamber does blood exit the heart into the pulmonary circuit?

Right ventricle

Into which chamber does blood enter the heart from the pulmonary circuit?

Left atrium

From which chamber does blood exit the heart into the systemic circuit?

Left ventricle

Trace the pathway of deoxygenated blood through the heart

Systemic tissues to right atrium to right ventricle to pulmonary trunk to lungs

Trace the pathway of oxygenated blood through the heart

Lungs to pulmonary veins to left atrium to left ventricle to aorta to systemic tissues

Which vessels supply blood to the heart tissue?

Coronary arteries

Which vessel drains blood from the heart tissue into the right atrium?

Coronary sinus

What are the branches of the left coronary artery?

Circumflex artery & anterior interventricular artery

What are the branches of the right coronary artery?

Right marginal artery & posterior interventricular artery

What are anastomoses?

Merging blood vessels that provide backup blood supply

What is angina pectoris?

Chest pain caused by temporary myocardial ischemia

What is a myocardial infarction?

Prolonged ischemia causing death of cardiac muscle tissue

How are cardiac muscle cells similar to skeletal muscle cells?

They are striated & use actin & myosin

How are cardiac muscle cells different from skeletal muscle cells?

They are involuntary branched and connected by intercalated discs

What is the specialized connection between adjacent cardiac myocytes?

Intercalated discs

How do intercalated discs allow the heart to beat as a syncytium?

They allow rapid electrical & mechanical coupling between cells

What is the role of desmosomes in cardiac muscle?

Provide mechanical strength

What is the role of gap junctions in cardiac muscle?

Allow ions to flow between adjacent cells

What are the two types of cardiac cells?

Contractile cells & conducting pacemaker cells

What are the phases of a cardiac contractile cell action potential?

• Depolarization

• Plateau

• Repolarization

What causes the plateau phase of the action potential?

Calcium influx

How does the plateau phase prevent tetanus?

It prolongs the refractory period

What is a pacemaker potential?

An unstable resting membrane potential in pacemaker cells

Is the pacemaker potential stable?

No

What ion movement causes the pacemaker potential?

Slow sodium influx & reduced potassium efflux

How do pacemaker action potentials differ from contractile cell action potentials?

Pacemaker depolarization relies on calcium & lacks a plateau phase

What is the pacemaker of the heart?

Sinoatrial (SA) node

Where is sinus rhythm generated?

Sinoatrial (SA) node

Where does the electrical signal pause before reaching the ventricles?

Atrioventricular (AV) node

What structure conducts impulses from atria to ventricles?

Bundle of His (AV bundle)

What structures conduct impulses through the ventricular myocardium?

Bundle branches & Purkinje fibers

Trace the cardiac conduction pathway?

SA node to AV node to AV bundle to bundle branches to Purkinje fibers

What is an arrhythmia?

An abnormal heart rhythm

What can cause arrhythmias?

Ischemia electrolyte imbalances or damage to the conduction system

What is fibrillation?

Rapid uncoordinated cardiac contractions

Why is fibrillation dangerous?

It prevents effective pumping of blood

What does an ECG represent?

Electrical activity of the heart

What electrical event occurs during the P wave?

Atrial depolarization

What electrical event occurs during the QRS complex?

Ventricular depolarization

What electrical event occurs during the T wave?

Ventricular repolarization

What electrical event occurs during the PR segment?

Delay at the AV node

What electrical event occurs during the ST segment?

Ventricular contraction plateau phase

What are the four phases of the cardiac cycle?

• Ventricular filling

• Isovolumetric contraction

• Ventricular ejection

• Isovolumetric relaxation

What is systole?

Contraction phase

What is diastole?

Relaxation phase

During ventricular filling are the AV valves open or closed?

Open

During ventricular filling are the semilunar valves open or closed?

Closed

During isovolumetric contraction are all heart valves open or closed?

All valves closed

During ventricular ejection which valves are open?

Semilunar valves

During isovolumetric relaxation are all heart valves open or closed?

All valves closed

What is end diastolic volume EDV?

Volume of blood in the ventricle at the end of ventricular filling

When does EDV occur?

End of ventricular filling

What is end systolic volume ESV?

Volume of blood remaining in the ventricle after contraction

When does ESV occur?

End of ventricular ejection

What causes the S1 heart sound?

Closure of AV valves

What causes the S2 heart sound?

Closure of semilunar valves

What causes a heart murmur?

Turbulent blood flow due to valve abnormalities

What is stroke volume?

Amount of blood pumped by one ventricle per beat

What factors affect stroke volume?

• Venous return

• Preload

• Afterload

• Contractility