Cardiovascular System III: The Cardiac Cycle, Hemodynamics, and Microcirculation

Vocabulary practice flashcards covering cardiac cycle phases, volumes, pressures, autonomic control, vascular anatomy, hemodynamics, arteriolar resistance, and Starling forces in capillary exchange.

Phonocardiogram

An instrument or graphic recording used to detect and display audible heart sounds, specifically the LUB-DUB sounds generated by valve closure.

Heart Murmur

An abnormal heart sound that typically results from defective heart valve function, such as valvular insufficiency or valvular stenosis.

Valvular Insufficiency

A condition in which a heart valve fails to close completely, allowing blood to leak backward.

Valvular Stenosis

A condition in which a heart valve fails to open completely, restricting forward blood flow.

First Heart Sound ($S_1$ or LUB)

The heart sound produced at the beginning of ventricular systole by the simultaneous closure of the atrioventricular (AV) valves.

Second Heart Sound ($S_2$ or DUB)

The heart sound produced during early ventricular diastole by the closure of the aortic and pulmonary semilunar valves.

Isovolumetric Ventricular Contraction

The phase of ventricular systole during which both the AV and semilunar valves remain closed as ventricular pressure builds rapidly without any change in blood volume.

Ventricular Ejection

The phase of ventricular systole occurring when ventricular pressure surpasses arterial pressure, forcing the semilunar valves open and rapidly pumping blood into the aorta and pulmonary artery.

Isovolumetric Ventricular Relaxation

The phase of early ventricular diastole during which all valves are closed, causing ventricular pressure to drop steeply while blood volume remains unchanged.

End-Diastolic Volume (EDV)

The volume of blood in a ventricle at the conclusion of diastole, representing the maximum potential volume of blood available to be ejected during systole.

End-Systolic Volume (ESV)

The volume of blood remaining inside a ventricle immediately after contraction and ventricular ejection are complete.

Stroke Volume (SV)

The actual volume of blood ejected from a ventricle during a single systole, typically corresponding to $40\text{--}60\%$ of the end-diastolic volume (EDV).

Cardiac Output (CO)

The volume of blood pumped by the heart into the circulation per minute, calculated as $\text{CO} = \text{HR} \times \text{SV}$.

Extrinsic Control of the Heart

Cardiovascular regulation mediated by mechanisms originating outside the heart, namely parasympathetic nerves (acetylcholine) and sympathetic nerves (norepinephrine and epinephrine).

Preload

The potential resting tension or force generated within ventricular walls due to cardiac muscle stretch by the end-diastolic volume (EDV) prior to contraction.

Afterload

The arterial resistance or pressure against which the heart ventricles must contract to open the semilunar valves and eject blood.

Tunica Intima

The innermost layer of a blood vessel, composed of an endothelium of simple squamous epithelial cells, loose connective tissue, and an internal elastic lamina in large arteries.

Tunica Media

The middle vessel layer, composed of circularly arranged smooth muscle and elastic fibers; it is substantially thicker in muscular arteries and arterioles.

Tunica Externa

The outermost vascular layer, composed primarily of supportive connective tissue and collagen fibers.

Arterial Pressure Reservoir

The ability of large, highly elastic arteries to expand during systole to store blood volume and recoil during diastole to maintain downstream driving pressure.

Mean Arterial Pressure (MAP)

The average driving blood pressure propelling blood through the systemic circulation during a cardiac cycle, calculated as $\text{MAP} = \text{CO} \times \text{TPR}$ or approximated as $\text{diastolic} + \frac{1}{3}(\text{systolic} - \text{diastolic}) \approx 93\,\text{mm\,Hg}$.

Total Peripheral Resistance (TPR)

The total resistance to blood flow throughout the systemic vascular network, governed predominantly by changes in arteriolar smooth muscle radius.

Vascular Tone

The baseline state of partial constriction continuously maintained by arteriolar smooth muscle through intrinsic myogenic activity and persistent sympathetic stimulation.

Alpha-1 ($\alpha_1$) Adrenergic Receptor

The receptor on vascular smooth muscle of most arterioles through which sympathetic norepinephrine and epinephrine stimulate vasoconstriction and elevate TPR.

Beta-2 ($\beta_2$) Adrenergic Receptor

The receptor located on arteriolar smooth muscle in cardiac and skeletal muscle that binds epinephrine to cause vasodilation during heightened activity or stress.

Capillary Endothelium

A single layer of simple squamous epithelial cells approximately $1\,\mu\text{m}$ thick that constitutes the wall of a capillary, lacking smooth muscle and connective tissue.

Capillary Pores (Fenestrations)

Narrow fluid-filled gaps between adjacent endothelial cells permitting the passage of water and small solutes (ions, glucose, amino acids) while excluding large plasma proteins.

Capillary Hydrostatic Pressure ($P_c$)

The outward fluid pressure exerted by blood against the inner capillary wall, measuring approximately $37\,\text{mm\,Hg}$ at the arteriolar end and $17\,\text{mm\,Hg}$ at the venular end.

Plasma Colloid Osmotic Pressure ($\pi_p$)

The inward osmotic pull of approximately $25\,\text{mm\,Hg}$ generated by impermeable plasma proteins (principally albumin) that retains and reabsorbs fluid into the capillary lumen.

Ultrafiltration

The bulk flow of protein-free plasma fluid out of the capillary into the interstitial space at the arteriolar end, driven by a net outward pressure of $11\,\text{mm\,Hg}$.

Capillary Reabsorption

The bulk movement of fluid from the interstitial space back into the capillary lumen at the venular end, driven by a net inward pressure of $9\,\text{mm\,Hg}$.

Edema

The excessive accumulation of fluid in interstitial spaces resulting from diminished plasma colloid osmotic pressure, elevated capillary blood pressure, or increased capillary permeability.