Cardiovascular, Respiratory, and Renal Physiology: Leukocytes, Cardiac Function, Blood Vessels, and Fluid Regulation

Vocabulary practice flashcards detailing key terminology, physiological processes, cellular structures, and regulatory mechanisms from human anatomy and physiology lectures.

Leukocyte

A white blood cell (WBC) that serves as a major component of the body's defences against disease, protecting against pathogens and mutated cells, cleaning debris, and typically numbering between $5000\text{ to }10,000\text{ per }\mu\text{L}$.

Diapedesis

The process (also known as emigration or extravasation) by which leukocytes squeeze between adjacent endothelial cells in a blood vessel wall to exit the circulation and enter surrounding body tissues.

Positive Chemotaxis

The phenomenon in which leukocytes move toward the source of specific chemical signals released by injured cells, infected cells, or other leukocytes.

Granular Leukocytes

A category of leukocytes characterized by abundant, highly visible granules within their cytoplasm, including neutrophils, eosinophils, and basophils.

Neutrophils

The most abundant leukocytes ($50\text{--}70\%$ of total WBCs), measuring $10\text{--}12\,\mu\text{m}$ with light lilac granules and a lobed nucleus (two to five lobes), which act as rapid-responding phagocytes against bacteria.

Polymorphonuclear Leukocytes

A term ('polys') used to describe older neutrophils due to the increasing number and variable shapes of their nuclear lobes.

Eosinophils

Granular leukocytes representing $2\text{--}4\%$ of total WBCs, measuring $10\text{--}12\,\mu\text{m}$ with two- to three-lobed nuclei and reddish-orange granules that contain antihistamine molecules and compounds toxic to parasitic worms.

Basophils

The least common leukocytes ($<1\%$ of total WBCs), measuring $8\text{--}10\,\mu\text{m}$ with large dark blue-to-purple granules that secrete histamine to intensify inflammation and heparin to oppose blood clotting.

Agranular Leukocytes

Leukocytes that contain fewer, less-obvious cytoplasmic granules and simple nuclei without distinct lobes, consisting of lymphocytes and monocytes.

Lymphocytes

The second most common leukocyte class ($20\text{--}30\%$ of total WBCs) and the only formed element arising from lymphoid stem cells, comprising natural killer (NK) cells, B cells, and T cells.

Natural Killer (NK) Cells

A subset of lymphocytes that provide generalized, non-specific immunity by recognizing and destroying cells lacking 'self' cell-surface markers, including cancer cells and virus-infected cells.

Monocytes

Large agranular leukocytes ($12\text{--}20\,\mu\text{m}$, $2\text{--}8\%$ of WBCs) with indented or horseshoe-shaped nuclei that differentiate into phagocytic macrophages upon migrating into body tissues.

Leukopenia

A clinical condition characterized by an abnormally low number of leukocytes, leading to an increased susceptibility to infectious diseases.

Leukocytosis

An excessive proliferation and elevated count of leukocytes in the blood, frequently indicating infection or inflammation.

Platelets

Small, membrane-enclosed cytoplasmic fragments of megakaryocytes ($2\text{--}4\,\mu\text{m}$ in diameter, $150,000\text{ to }160,000\text{ per }\mu\text{L}$) essential for haemostasis and tissue repair.

Megakaryocyte

A large bone marrow cell ($50\text{--}100\,\mu\text{m}$) with an enlarged multi-lobed nucleus that extends platelet-precursor cytoplasmic extensions through bone marrow capillaries to release $2000\text{ to }3000\text{ platelets}$ over its lifespan.

Thrombopoietin

A glycoprotein secreted primarily by the liver and kidneys that stimulates the proliferation of megakaryoblasts into mature megakaryocytes.

Thrombocytopenia

A disorder defined by an insufficient number of circulating platelets, impairing blood clot formation and leading to excessive bleeding.

Haemostasis

The physiological process by which the body arrests blood loss from a damaged blood vessel, comprising vascular spasm, platelet plug formation, and coagulation.

Vascular Spasm

The initial, dramatic contraction of smooth muscle layers in the wall of a damaged blood vessel triggered by endothelins and pain receptors to reduce blood flow.

von Willebrand Factor

A glycoprotein released by endothelial cells that stabilizes the growing platelet plug by aiding platelet adhesion to exposed collagen fibers.

Coagulation

The cascade-like formation of a gelatinous blood clot consisting of an insoluble mesh of fibrin that traps formed elements and platelets.

Extrinsic Pathway

A rapid coagulation sequence initiated within seconds when damaged extravascular tissues release Factor III (tissue factor / tissue thromboplastin), which complexes with Factor VII and $\text{Ca}^{2+}$ to activate Factor X.

Intrinsic Pathway

A longer coagulation cascade initiated within minutes when Factor XII (Hageman factor) contacts negatively charged surfaces, leading sequentially to the activation of Factors XI, IX, and VIII, which form an enzyme complex to activate Factor X.

Common Pathway

The terminal stage of coagulation where activated Factor X (prothrombinase) converts prothrombin (Factor II) to thrombin, which then converts soluble fibrinogen (Factor I) into insoluble fibrin strands.

Fibrinolysis

The enzymatic degradation and removal of a blood clot during healing, in which plasminogen is converted into the active protease plasmin.

Plasmin

The active fibrin-digesting enzyme formed from plasminogen that breaks down the structural fibrin mesh of a healed clot.

Thrombus

An aggregation of platelets, red blood cells, and white blood cells trapped within a fibrin mesh that forms inside an intact or slightly damaged blood vessel.

Embolus

A piece of a thrombus or other mass that breaks free from a vessel wall and circulates through the bloodstream, capable of obstructing distant vessels.

Pericardium

The membranous sac defining the pericardial cavity and surrounding the heart, consisting of an outer fibrous pericardium and an inner serous pericardium (parietal and visceral layers).

Cardiac Tamponade

A life-threatening condition in which fluid or blood accumulates within the pericardial cavity, exerting pressure that restricts full ventricular relaxation and severely reduces cardiac output.

Myocardium

The thick, middle layer of the heart wall composed largely of cardiac muscle cells arranged in a swirling, figure-8 pattern supported by collagenous fibers and blood vessels.

Endocardium

The innermost layer of the heart wall, composed of simple squamous endothelium continuous with the lining of the blood vessels, which lines the chambers and covers the heart valves.

Tetralogy of Fallot

A congenital heart defect characterized by four anomalies: pulmonary infundibular stenosis, overriding aorta, ventricular septal defect, and right ventricular hypertrophy.

Chordae Tendineae

Tough, collagenous strings ('heart strings') that connect the cusps of atrioventricular valves to papillary muscles, preventing valve inversion during ventricular systole.

Moderator Band

A specialized band of cardiac muscle covered by endocardium in the right ventricle that reinforces the ventricular wall and conducts electrical impulses directly to the inferior papillary muscle.

Autorhythmicity

The unique intrinsic property of cardiac muscle cells that allows them to initiate their own action potentials at a regular, fixed rate without nervous or endocrine input.

Intercalated Disc

A specialized intercellular junction linking adjacent cardiomyocytes, composed of desmosomes and gap junctions that allow mechanical adherence and rapid ionic conduction for synchronous contraction.

Sinoatrial (SA) Node

A specialized clump of conductive myocardial cells located in the superior and posterior wall of the right atrium that sets the sinus rhythm and serves as the primary pacemaker of the heart.

Atrioventricular (AV) Node

A secondary cluster of conducting cells in the inferior right atrium that delays the electrical impulse by approximately $100\text{ ms}$ before passing it to the atrioventricular bundle, ensuring atrial emptying.

Purkinje Fibres

Myocardial conductive fibres that rapidly propagate the action potential from the apex of the heart upward through the ventricular contractile myocardium in approximately $75\text{ ms}$.

Prepotential Depolarisation

The spontaneous, slow rise in membrane potential from $-60\text{ mV}$ to $-40\text{ mV}$ in cardiac conductive cells caused by a continuous influx of $\text{Na}^+$ ions through voltage-gated channels.

P Wave

The first major deflection on an ECG tracing, representing the depolarization of the atria prior to atrial contraction.

QRS Complex

The prominent waveform on an ECG that represents rapid ventricular depolarisation while masking concurrent atrial repolarisation.

T Wave

The ECG wave representing the repolarisation of the ventricles, marking the onset of ventricular diastole.

Cardiac Output (CO)

The volume of blood pumped by each ventricle in one minute, mathematically calculated as heart rate multiplied by stroke volume ($\text{CO} = \text{HR} \times \text{SV}$).

Stroke Volume (SV)

The amount of blood ejected by each ventricle during a single contraction, determined by subtracting end systolic volume from end diastolic volume ($\text{SV} = \text{EDV} - \text{ESV}$).

Frank-Starling Mechanism

The physiological principle stating that within physiological limits, the force of heart contraction is directly proportional to the initial stretch (preload) of the muscle fibres.

Afterload

The tension or resistance against which the ventricles must pump blood to force open the semilunar valves and eject stroke volume.

Bainbridge Reflex

An autonomic reflex (atrial reflex) in which increased venous return stretches the walls of the atria, stimulating baroreceptors to signal the cardiac centre to increase sympathetic output and elevate heart rate.

Vasa Vasorum

Minute blood vessels embedded within the outer tunics of large arteries and veins that supply nutrients and remove waste from the cells of the vessel walls.

Tunica Media

The middle layer of a blood vessel wall, composed of circular smooth muscle and elastic fibres, which regulates lumen diameter through vasoconstriction and vasodilation.

Sinusoid Capillaries

The least common and most permeable capillaries, featuring large intercellular gaps, fenestrations, and an incomplete basement membrane that allow passage of plasma proteins and entire cells.

Precapillary Sphincters

Rings of smooth muscle located at the origin of capillaries branching from a metarteriole that regulate blood perfusion into capillary beds.

Type II Alveolar Cells

Cuboidal cells interspersed among type I alveolar cells that synthesize and secrete pulmonary surfactant, reducing alveolar surface tension.

Respiratory Membrane

The ultra-thin ($0.5\,\mu\text{m}$) anatomical barrier comprising the type I alveolar epithelium, capillary endothelium, and their fused basement membranes across which gas diffusion occurs.

Dalton's Law

A physical gas law stating that in a mixture of nonreactive gases, each gas exerts its own independent partial pressure, and the total pressure is the sum of these partial pressures.

Henry's Law

A physical principle stating that the concentration of gas dissolved in a liquid is directly proportional to the gas's solubility and its partial pressure above the liquid.

Bohr Effect

The physiological phenomenon in which lower (more acidic) blood pH promotes the dissociation of oxygen from haemoglobin molecules.

Haldane Effect

The relationship in which lower oxygen saturation of haemoglobin enhances its affinity to bind and transport carbon dioxide.

Chloride Shift

The exchange of bicarbonate ($\text{HCO}_3^-$) moving out of red blood cells for chloride ($\text{Cl}^-$) entering the cells, which maintains electrical neutrality during carbon dioxide transport.

Antidiuretic Hormone (ADH)

A hormone produced in the hypothalamus and released by the posterior pituitary that stimulates the insertion of aquaporin water channels into renal collecting duct membranes to promote water reabsorption.

Aldosterone

A mineralocorticoid hormone secreted by the adrenal cortex that enhances sodium and water reabsorption while promoting potassium excretion in the distal convoluted tubules and collecting ducts.