Cardiovascular System I – The Heart

Practice flashcards covering heart anatomy, electrical activity, the cardiac cycle, cardiac output, and heart nourishment based on Week 6 Integrated Physiology lecture materials.

Cardiovascular system

A system consisting of the heart, blood vessels, blood, and lymph.

Pulmonary circuit

One of the two circuits of the circulatory system that carries blood between the heart and the lungs.

Systemic circuit

One of the two circuits of the circulatory system that carries blood between the heart and the rest of the body systems.

Apex

The lowest, pointed part of the heart.

Base

The upper part of the heart.

Parietal pericardium

The outer layer of the pericardium that forms a tough, fibrous sac.

Epicardium

The outer layer of the heart wall, also known as the visceral pericardium.

Myocardium

The middle layer of the heart wall composed of cardiac muscle tissue.

Endocardium

The inner layer of the heart wall consisting of endothelium and areolar tissue.

Tricuspid valve

The right atrioventricular (AV) valve located between the right atrium and right ventricle.

Bicuspid valve

The left atrioventricular (AV) valve located between the left atrium and left ventricle.

Semilunar valves

The valves located at the exits of the ventricles, specifically the pulmonary and aortic valves.

Chordae tendineae

Tendon-like strands that connect the papillary muscles to the AV valve flaps to prevent eversion.

Papillary muscles

Muscles located in the ventricles that contract to pull on the chordae tendineae, preventing the AV valves from opening backward.

Contractile cells

Cardiac muscle cells that make up $99\%$ of the heart's muscle tissue and perform the mechanical work of pumping.

Autorhythmic cells

Specialized cardiac cells (pacemaker cells) that initiate and conduct action potentials but do not have a resting potential.

Sinoatrial (SA) node

The heart's primary pacemaker that sets the heart rate at approximately $70\,mph$ (or beats per minute) under normal conditions.

Atrioventricular (AV) node

The tissue where the electrical impulse is delayed for approximately $150\,msec$ allowing the atria to contract before the ventricles.

Purkinje fibers

Specialized conducting fibers in the ventricles that transmit impulses at $225\,msec$ to trigger ventricular contraction.

Ectopic focus

An abnormal pacemaker that takes over heart rhythm by firing faster than the SA node, often at speeds like $140\,mph$.

P wave

The component of an ECG representing atrial depolarization.

QRS complex

The component of an ECG representing ventricular depolarization while atria are simultaneously repolarizing.

T wave

The component of an ECG representing ventricular repolarization.

PR segment

The part of an ECG recording that corresponds to the AV nodal delay.

ST segment

The interval in an ECG during which the ventricles are contracting and emptying.

TP interval

The interval in an ECG during which the ventricles are relaxing and filling.

Systole

The phase of the cardiac cycle characterized by contraction and emptying.

Diastole

The phase of the cardiac cycle characterized by relaxation and filling.

Isovolumetric ventricular contraction

The phase where all heart valves are closed and ventricular pressure increases markedly while volume remains constant.

Isovolumetric ventricular relaxation

The phase where all valves are closed and ventricular pressure falls sharply while volume remains constant.

Dicrotic notch

A small fluctuation in aortic pressure seen on a pressure graph when the aortic valve closes.

"Lub" (1st heart sound)

The first heart sound produced by the closing of the AV valves.

"Dup" (2nd heart sound)

The second heart sound produced by the closing of the semilunar valves.

Cardiac output (CO)

The volume of blood pumped per minute, calculated as $C.O. = S.V. \times H.R.$

Stroke volume (SV)

The volume of blood pumped out of a ventricle per beat, calculated as $SV = EDV - ESV$.

End-diastolic volume (EDV)

The volume of blood in the ventricle at the end of diastole, typically around $120\,mL$ to $135\,mL$.

End-systolic volume (ESV)

The volume of blood remaining in the ventricle at the end of systole, typically around $50\,mL$ to $65\,mL$.

Ejection fraction

The percentage of the end-diastolic volume that is pumped out, defined as $\frac{SV}{EDV} \times 100$.

Frank-Starling Law of the Heart

The intrinsic control principle stating that increased venous return results in increased stroke volume due to stretching of the heart muscle.

Vagal tone

The constant background parasympathetic influence on the heart via the vagus nerve.

Baroreceptors

Pressure-sensitive receptors located in the carotid sinus and aortic arch that send neural signals to the medulla.

Adenosine

A paracrine chemical that causes vasodilation to increase coronary blood flow in response to increased oxygen demand.

Coronary circulation

The specialized system of blood vessels that nourishes the heart muscle, where $70\%$ of flow occurs during diastole.