The Heart and Vascular System

Comprehensive vocabulary flashcards covering the anatomy and physiology of the heart, the cardiac cycle, cardiodynamics, blood vessels, capillary dynamics, and cardiovascular regulation.

Pulmonary Circuit

The division of the cardiovascular system driven by the right side of the heart that transports deoxygenated blood to the lungs for gas exchange and returns oxygenated blood to the heart.

Systemic Circuit

The division of the cardiovascular system driven by the left side of the heart that distributes oxygenated blood to all peripheral tissues and returns deoxygenated blood to the heart.

Pericardium

A double-walled protective sac enclosing the heart composed of a superficial fibrous pericardium and an inner two-layered serous pericardium.

Cardiac Tamponade

A potentially fatal condition resulting from fluid accumulation in the pericardial cavity (often due to pericarditis), which compresses the heart and restricts normal ventricular filling.

Epicardium

The outermost serous layer of the heart wall, identical to the visceral layer of the serous pericardium.

Myocardium

The middle muscular layer of the heart wall made up of concentric layers of branching cardiac muscle tissue.

Endocardium

The innermost layer lining the heart chambers and valves, consisting of an endothelial layer of simple squamous epithelium continuous with the blood vessel endothelium.

Fibrous Skeleton of the Heart

A network of dense connective tissue that anchors heart valve cusps, provides structural support, and electrically isolates the atria from the ventricles.

Intercalated Discs

Specialized cell-to-cell junctions interconnecting cardiac myocytes that feature desmosomes to transfer mechanical tension and gap junctions to propagate electrical action potentials.

Auricle

An expandable, pouch-like flap on the anterior surface of each atrium that increases atrial volume capacity.

Coronary Sulcus

A deep groove on the heart's exterior surface marking the boundary between the atria and the ventricles.

Pectinate Muscles

Prominent parallel muscular ridges situated on the anterior atrial wall and internal surfaces of the auricles.

Trabeculae Carneae

Irregular muscular ridges along the inner luminal surface of the ventricles.

Moderator Band

A muscular band found specifically in the right ventricle that carries part of the conducting system to the papillary muscles to coordinate contraction.

Chordae Tendineae

Fibrous collagenous cords connecting the cusps of atrioventricular valves to papillary muscles, preventing valve cusps from everting into the atria during ventricular systole.

Semilunar Valves

Three-cusped pocket-like valves (aortic and pulmonary) that lack chordae tendineae and prevent backflow of blood from the great vessels into the ventricles during diastole.

Fossa Ovalis

An oval depression located on the interatrial septum, representing the sealed remnant of the fetal foramen ovale.

Aortic Sinuses

Small dilations situated at the base of the ascending aorta that prevent aortic semilunar valve cusps from adhering to the aortic wall and give rise to the coronary arteries.

Plateau Phase

A prolonged period of depolarization (~$175\,\text{msec}$ at ~$0\,\text{mV}$) in cardiac contractile cells caused by slow calcium ion ($\text{Ca}^{2+}$) influx balancing potassium ion ($\text{K}^+$) outflow.

Absolute Refractory Period

A prolonged interval in cardiac muscle during which the membrane cannot respond to further stimulation, preventing tetanic contractions and summation.

Automaticity

The intrinsic ability of pacemaker cells in the cardiac conducting system to depolarize spontaneously and generate action potentials without neural stimulation.

Sinoatrial (SA) Node

The primary cardiac pacemaker situated in the posterior wall of the right atrium that sets resting heart rate with an intrinsic depolarization rate of $80\text{--}100\,\text{action potentials/min}$.

Atrioventricular (AV) Node

A specialized group of conducting cells in the floor of the right atrium that delays electrical transmission by approximately $100\,\text{msec}$ to ensure atria finish contracting before ventricles excite.

Purkinje Fibers

Specialized, large-diameter conducting cells that rapidly relay electrical impulses from the bundle branches throughout the ventricular myocardium.

Ectopic Pacemaker

An abnormal site of excitable cardiac tissue outside the regular conducting pathways that fires rapidly and overrides the normal rhythm set by the SA node.

P Wave

The ECG deflection representing atrial depolarization produced by the electrical activation spreading from the sinoatrial node across the atria.

QRS Complex

The large spike seen on an ECG produced by ventricular depolarization, which masks concurrent atrial repolarization.

T Wave

The deflection on an ECG that represents ventricular repolarization.

P-R Interval

The duration on an ECG measured from the start of atrial depolarization (P wave) to the beginning of the QRS complex, reflecting conduction through the AV node.

End-Diastolic Volume (EDV)

The maximum volume of blood in a ventricle following the completion of ventricular diastole and atrial systole, normally averaging about $130\,\text{mL}$.

End-Systolic Volume (ESV)

The residual volume of blood left inside a ventricle after ventricular contraction and ejection have completed, typically about $50\,\text{mL}$.

Stroke Volume (SV)

The volume of blood pumped out by one ventricle in a single beat, mathematically defined as $\text{SV} = \text{EDV} - \text{ESV}$ (typically about $80\,\text{mL}$).

Cardiac Output (CO)

The volume of blood pumped through each ventricle per minute, calculated as $\text{CO} = \text{HR} \times \text{SV}$.

Isovolumetric Ventricular Contraction

The early phase of ventricular systole in which ventricular pressure rises with all heart valves closed, yielding an increase in tension without a change in chamber blood volume.

Dicrotic Notch

A small rebound dip and rise in aortic pressure following semilunar valve closure caused by the elastic recoil of the aortic wall.

Preload

The extent of stretch on myocardial ventricular fibers prior to contraction, determined primarily by the end-diastolic volume (venous return).

Afterload

The arterial pressure/tension that a ventricle must overcome in order to force open a semilunar valve and eject blood.

Frank-Starling Principle

The intrinsic cardiac rule stating that an increased end-diastolic volume stretches cardiac myocytes, causing an increase in the force of contraction and resulting stroke volume.

Atrial (Bainbridge) Reflex

A sympathetic reflex triggered by stretch receptors in the right atrial wall in response to elevated venous return, causing an acceleration of heart rate to clear excess blood volume.

Tunica Interna (Intima)

The innermost tunic of a blood vessel wall, composed of a simple squamous endothelial lining resting on a thin layer of connective tissue and an internal elastic membrane in arteries.

Tunica Media

The middle layer of a blood vessel wall dominated by smooth muscle cells and elastic tissue, regulated by the sympathetic nervous system to adjust vessel caliber.

Tunica Externa (Adventitia)

The outermost fibrous connective tissue sheath of a blood vessel that blends into surrounding structures and stabilizes the vessel position.

Vasa Vasorum

Tiny networks of blood vessels embedded in the walls of large arteries and veins that deliver nutrients and oxygen to the tunica media and tunica externa.

Elastic Arteries

Large, low-resistance conducting vessels (such as the aorta and pulmonary trunk) with elastic fibers throughout all three tunics that dampen pressure fluctuations generated by ventricular systole.

Arterioles

Small resistance vessels possessing a thin or incomplete tunica media that regulate systemic blood pressure and capillary bed perfusion through vasoconstriction and vasodilation.

Continuous Capillaries

Capillaries featuring an intact endothelial lining held together by tight junctions, permitting diffusion of water, small solutes, and lipid-soluble materials while blocking blood cells and plasma proteins.

Fenestrated Capillaries

Porous exchange vessels featuring small windows (fenestrations) through the endothelial cells that permit rapid filtration of fluids and medium-sized solutes (found in kidneys, endocrine organs, and intestine).

Sinusoids

Discontinuous capillaries with large intercellular gaps and an incomplete basement membrane, allowing free exchange of large plasma proteins and formed elements (found in liver, bone marrow, and spleen).

Precapillary Sphincter

A band of smooth muscle at the origin of a true capillary that regulates blood flow into the capillary bed.

Vasomotion

The cyclical opening and closing of precapillary sphincters (occurring roughly $10\,\text{times/min}$) that causes intermittent, pulsing blood flow through capillary beds.

Capacitance Vessels

A designation for veins due to their high distensibility and ability to act as blood reservoirs containing $60\text{--}65\%$ of the total blood volume at low pressures.

Venoconstriction

Sympathetic contraction of smooth muscle in medium-sized systemic veins that mobilizes the venous reserve to increase blood volume and pressure in the arterial system.

Peripheral Resistance (PR)

The opposition to blood flow caused by friction between blood and vessel walls throughout the systemic circuit, primarily determined by vessel diameter, vessel length, blood viscosity, and turbulence.

Mean Arterial Pressure (MAP)

The average arterial driving pressure across the cardiac cycle, calculated by adding diastolic pressure to one-third of the pulse pressure ($\text{MAP} = \text{diastolic pressure} + \frac{1}{3}\,\text{pulse pressure}$).

Capillary Hydrostatic Pressure (CHP)

The physical fluid pressure exerted by blood inside capillary walls (ranging from $35\,\text{mm\,Hg}$ at the arterial end to $18\,\text{mm\,Hg}$ at the venous end) that drives filtration outward into the interstitial fluid.

Blood Colloid Osmotic Pressure (BCOP)

The osmotic force exerted by non-diffusible plasma proteins (averaging approximately $25\text{--}26\,\text{mm\,Hg}$) that draws water and small solutes back into the capillary from the interstitial space.

Net Filtration Pressure (NFP)

The overall pressure governing fluid movement across a capillary wall, calculated as the difference between net hydrostatic pressure and net colloid osmotic pressure: $\text{NFP} = (\text{HP}_c - \text{HP}_{if}) - (\text{OP}_c - \text{OP}_{if})$.

Autoregulation

Immediate, local physiological adjustments of precapillary sphincters and peripheral resistance in response to tissue chemical changes (e.g., low $\text{O}_2$, elevated $\text{CO}_2$, low $\text{pH}$) without altering cardiac output.

Vasomotor Center

A cluster of sympathetic neurons within the medulla oblongata that continuously innervates arteriole smooth muscle to maintain resting vasomotor tone.

Baroreceptor Reflex

An autonomic homeostatic mechanism mediated by stretch receptors in the carotid sinuses, aortic arch, and right atrium that adjusts heart rate and vascular tone to counter changes in blood pressure.

Ductus Arteriosus

A fetal vascular shunt connecting the pulmonary trunk directly to the aorta, which bypasses the nonfunctional fetal lungs and constricts at birth.

Aneurysm

A localized abnormal dilation or ballooning in the wall of an artery caused by a weakness in the vessel's elastic connective tissue, presenting a risk of rupture.