Human Circulatory System, Cardiac Anatomy, and Physiology

Comprehensive vocabulary flashcards covering the anatomy of the human heart, blood composition, vascular histology, cardiac conduction, electrocardiogram waves, and hemodynamic parameters.

Haematopoiesis

The production of blood cells, which takes place in the red bone marrow of spongy bones such as the pelvis, sternum, ribs, and vertebrae.

Erythropoietin (EPO)

A hormone that stimulates red blood cell production; the kidneys are the primary source in adults, with additional contribution from the liver.

Plasma

The yellowish liquid component of whole blood (approximately $90\%$ water and $55\%$ of total blood volume) that transports blood cells, nutrients, electrolytes, hormones, proteins, and metabolic wastes.

Erythrocytes (Red Blood Cells)

Biconcave formed elements lacking a nucleus that transport oxygen from the lungs to body tissues using haemoglobin, with an average lifespan of $120\,\text{days}$.

Platelets

Non-nucleated cell fragments derived from megakaryocytes in the red bone marrow that initiate clot formation and reduce blood loss.

Haemostasis

The physiological process of arresting blood loss from an injured vessel through platelet adhesion, aggregation, and the generation of a reinforcing fibrin mesh.

Epicardium

The outermost protective layer of the heart wall.

Myocardium

The thick middle layer of cardiac muscle responsible for pumping; it is thickest in the left ventricle to overcome systemic vascular resistance.

Endocardium

The inner endothelial lining of the heart chambers and valves that is in direct contact with circulating blood.

Pericardium

The protective double-layered sac enclosing the heart, containing serous fluid that lubricates and reduces friction during contractions.

Cardiac Tamponade

A life-threatening medical emergency caused by fluid accumulation and elevated pressure in the pericardial space that compromises ventricular filling.

Intercalated Discs

Specialized cell junctions connecting cardiomyocytes, featuring gap junctions for rapid electrical conduction and desmosomes for mechanical adhesion.

Tricuspid Valve

The atrioventricular (AV) valve positioned between the right atrium and right ventricle that prevents backflow into the right atrium during ventricular systole.

Mitral (Bicuspid) Valve

The atrioventricular (AV) valve situated between the left atrium and left ventricle that prevents backflow into the left atrium during ventricular contraction.

Chordae Tendineae

Fibrous cords connecting the cusps of atrioventricular valves to papillary muscles, preventing valve inversion or prolapse during ventricular contraction.

Papillary Muscles

Muscular projections from the ventricular walls that contract to tense the chordae tendineae during systole.

Coronary Sinus

The venous channel that collects deoxygenated blood from the coronary veins of the myocardium and empties directly into the right atrium.

Tunica Intima

The innermost layer of an artery or vein, composed of an endothelial lining that offers a low-friction surface for blood flow.

Tunica Media

The middle layer of blood vessels composed of smooth muscle and elastic fibres, which regulates vessel diameter and systemic blood pressure.

Tunica Externa (Adventitia)

The outer connective tissue sheath of blood vessels, rich in collagen, which anchors and provides structural support to the vessel.

Pulse Pressure

The arithmetic difference between systolic pressure and diastolic pressure ($\text{Pulse Pressure} = \text{Systolic} - \text{Diastolic}$).

Sinoatrial (SA) Node

The primary physiological pacemaker of the heart, located in the right atrium, which spontaneously initiates rhythmic cardiac electrical impulses.

Atrioventricular (AV) Node

A node in the cardiac conduction pathway that introduces a brief electrical delay, ensuring the atria fully contract and empty before ventricular contraction begins.

Purkinje Fibres

Specialized conduction myofibres that rapidly distribute electrical impulses throughout the ventricular myocardium to coordinate synchronized ventricular contraction.

Autorhythmicity

The intrinsic capacity of cardiac tissue to generate rhythmic action potentials independently of external neural stimulation.

P Wave

The ECG deflection representing atrial depolarisation, with a normal duration of $0.08\text{ to }0.10\,\text{sec}$.

QRS Complex

The ECG waveform representing ventricular depolarisation, normally lasting $0.06\text{ to }0.10\,\text{sec}$.

T Wave

The ECG waveform indicating ventricular repolarisation, with an expected duration of $0.35\text{ to }0.45\,\text{sec}$.

PR Interval

The time recorded on an ECG from the start of the P wave to the start of the QRS complex, typically measuring $0.12\text{ to }0.20\,\text{sec}$.

ST Segment

The flat, isoelectric segment on an ECG between ventricular depolarisation and repolarisation.

First Heart Sound (S1 / "LUB")

The heart sound produced by the closure of the atrioventricular (tricuspid and mitral) valves at the onset of ventricular systole.

Second Heart Sound (S2 / "DUB")

The heart sound caused by the closure of the semilunar (aortic and pulmonary) valves at the beginning of ventricular diastole.

Stroke Volume (SV)

The volume of blood pumped out by one ventricle per single heartbeat, averaging approximately $70\,\text{mL/beat}$ at rest in an adult.

Cardiac Output (CO)

The volume of blood pumped by a ventricle each minute, defined by the formula $\text{CO} = \text{HR} \times \text{SV}$ (approximately $5\,\text{L/min}$ at rest).

Preload

The mechanical stretch and end-diastolic volume filling the ventricles immediately before myocardial contraction.

Afterload

The vascular resistance or pressure that the ventricular myocardium must overcome to eject blood into the aorta or pulmonary trunk.

Cardiac Reserve

The difference between an individual's maximum cardiac output and their resting cardiac output.

Pulmonary Circulation

The circulatory route moving deoxygenated blood from the right ventricle through the pulmonary trunk to the lungs, returning oxygenated blood via pulmonary veins to the left atrium.

Systemic Circulation

The circulatory circuit delivering oxygenated blood from the left ventricle through the aorta to body tissues and returning deoxygenated blood via the venae cavae to the right atrium.

Hepatic Portal Vein

A large vessel that channels nutrient-rich venous blood from the digestive organs to the liver before it returns to systemic venous circulation.