Physiology: Circulation, Respiration, and Renal

Flashcards covering key physiology concepts related to muscle, circulation, and the heart, including anatomy, electrical activity, and mechanics.

Sarcomere

The contractile unit of a muscle fiber, consisting of overlapping thick (myosin) and thin (actin) filaments.

Myofibril

A long, cylindrical organelle within a muscle fiber, composed of many sarcomeres linked end to end.

Muscle fiber (muscle cell)

A single muscle cell, containing multiple myofibrils and surrounded by a sarcolemma.

Tropomyosin

A rod-shaped molecule composed of two intertwined polypeptides that partially covers the myosin-binding sites on actin monomers, preventing cross-bridge contact in relaxed muscle.

Troponin

A globular protein composed of three subunits (I, T, C) that interacts with both actin and tropomyosin, holding tropomyosin in its blocking position until Ca2+ binds to it.

Troponin C (Ca2+-binding subunit)

The subunit of troponin to which Ca2+ binds, leading to a conformational change that moves tropomyosin away from myosin-binding sites on actin.

T-tubules (transverse tubules)

Invaginations of the muscle plasma membrane (sarcolemma) that extend into the muscle fiber, in intimate contact with the sarcoplasmic reticulum.

Sarcoplasmic reticulum (SR)

An intracellular organelle in muscle cells that stores and releases Ca2+ to initiate muscle contraction.

Dihydropyridine (DHP) receptor

A modified voltage-sensitive Ca2+ channel in the T-tubule membrane that acts as a voltage sensor, inducing a conformational change to open ryanodine receptors.

Ryanodine receptor

A protein embedded in the sarcoplasmic reticulum membrane that forms a Ca2+ channel, releasing Ca2+ into the cytosol when activated by the DHP receptor.

Sliding-filament mechanism (muscle contraction)

The process by which overlapping thick and thin filaments in each sarcomere move past each other, propelled by cross-bridge movements, causing muscle shortening without changing filament length.

Cross-bridge cycle

A series of events involving myosin heads binding to actin, pulling the thin filaments (power stroke), detaching, and reattaching to a new site, continuing as long as Ca2+ is bound to troponin.

Action potential (motor neuron)

An electrical signal initiated in a motor neuron that propagates to its axon terminals, leading to muscle contraction.

Acetylcholine (ACh)

A neurotransmitter released from axon terminals of motor neurons that diffuses to the motor end plate of muscle fibers.

Nicotinic receptors

Receptors on the motor end plate that bind ACh, increasing permeability to Na+ and K+ and producing the end-plate potential.

End-plate potential (EPP)

A depolarization of the muscle fiber membrane at the motor end plate caused by the influx of Na+ exceeding K+ efflux, triggering a muscle action potential.

Ca2+-ATPase (muscle)

An active transport pump that decreases cytosolic Ca2+ concentration by transporting Ca2+ back into the sarcoplasmic reticulum after muscle contraction.

Cardiovascular system

A closed-loop system consisting of blood, blood vessels, and the heart, responsible for carrying nutrients, hormones, oxygen, removing waste, producing immune cells, and maintaining fluid and temperature balance.

Hematopoietic stem cell (multipotent uncommitted)

A type of stem cell in the bone marrow that can differentiate into all types of blood cells.

Erythropoietin

A hormone, primarily produced by the kidneys, that stimulates the production of erythrocytes (red blood cells).

Anemia

A decrease in the oxygen-carrying capacity of blood due to a reduced number of erythrocytes, diminished hemoglobin concentration, or a combination of both.

Sickle-cell disease

A genetic mutation altering hemoglobin, causing abnormal hemoglobin molecules to form fiber-like polymers at low oxygen levels, distorting erythrocytes into sickle shapes, leading to capillary blockage and erythrocyte destruction.

Platelets (blood components)

Colorless, nonnucleated cell fragments in the blood, produced when cytoplasmic portions of megakaryocytes pinch off, involved in blood clotting.

Pulmonary circulation

The circuit that carries oxygen-poor blood from the right ventricle to the lungs and then returns oxygen-rich blood to the left atrium.

Systemic circulation

The circuit that carries oxygen-rich blood from the left ventricle through all body organs and tissues (except the lungs) and then returns oxygen-poor blood to the right atrium.

Hemodynamics

The study of the principles governing blood flow, pressure, and resistance within the circulatory system.

Blood pressure

The force exerted by the blood against the vessel walls, measured in millimeters of mercury (mmHg).

Blood flow

The volume of blood moved per unit time, measured in milliliter/minute.

Resistance (blood flow)

A measure of how difficult it is for blood to flow between two points at a given pressure difference, representing the friction that impedes flow.

Blood viscosity

A determinant of resistance, referring to the friction between molecules of a flowing fluid, affected by water volume and the number of red blood cells.

Total blood vessel length

A determinant of resistance; longer vessels lead to greater resistance.

Inside radius of the tube (resistance)

The most important determinant of changes in resistance in blood vessels, where a smaller radius (vasoconstriction) increases resistance and a larger radius (vasodilation) decreases it.

Atria (heart chambers)

The upper chambers of the heart through which blood flows from veins to the ventricles; atrial contraction aids ventricular filling.

Ventricles (heart chambers)

The lower chambers of the heart whose contractions produce the pressures that drive blood through the pulmonary and systemic vascular systems.

Arteries

Low-resistance tubes conducting blood to various organs with little pressure loss, also acting as pressure reservoirs.

Arterioles

Major sites of resistance to blood flow, responsible for regulating blood flow distribution to organs and participating in arterial blood pressure regulation.

Capillaries

Major sites of nutrient, gas, metabolic end product, and fluid exchange between blood and tissues.

Veins

Low-resistance, high-capacitance vessels carrying blood back to the heart, with capacity adjusted to facilitate flow.

Pericardium

A protective sac surrounding the heart, consisting of fibrous and serous layers, with a pericardial cavity containing fluid.

Pericardial fluid

A lubricating fluid within the pericardial cavity that reduces friction between heartbeats.

Epicardium

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

Myocardium (heart wall)

The middle, thickest layer of the heart wall, composed of cardiac muscle cells arranged in layers that encircle the blood-filled chambers.

Endocardium

The innermost layer of the heart wall, lining the cardiac chambers.

Right AV (tricuspid) valve

The valve located between the right atrium and right ventricle, preventing backflow of blood into the right atrium during ventricular contraction.

Left AV (bicuspid) valve (Mitral valve)

The valve located between the left atrium and left ventricle, preventing backflow of blood into the left atrium during ventricular contraction.

Pulmonary semilunar valve

The valve located between the right ventricle and the pulmonary artery, preventing backflow of blood into the right ventricle during ventricular relaxation.

Aortic semilunar valve

The valve located between the left ventricle and the aorta, preventing backflow of blood into the left ventricle during ventricular relaxation.

Intercalated disk

Specialized cell junctions that connect branching cardiac muscle fibers end to end, containing desmosomes and gap junctions.

Right coronary artery

An artery that supplies blood to the right side of the heart, dividing into marginal and posterior interventricular branches.

Left (main) coronary artery

An artery that supplies blood to the left side of the heart, dividing into circumflex and anterior descending branches.

Sympathetic postganglionic fibers (heart)

Nerve fibers that innervate the entire heart and release norepinephrine, increasing heart rate and contractility.

Parasympathetic fibers (heart)

Nerve fibers that terminate mainly on special cells in the atria and release acetylcholine, decreasing heart rate.

Beta-adrenergic receptors (heart)

Receptors on cardiac muscle cells (SA node, AV node, atrial and ventricular muscle) that bind norepinephrine and epinephrine, increasing heart rate and contractility.

Muscarinic receptors

Receptors on cardiac cells (SA node, AV node, atrial muscle) that bind acetylcholine, decreasing heart rate and conduction rate.

Conducting system (heart)

A network of specialized cardiac cells that do not contract but initiate the heartbeat and rapidly spread action potentials throughout the heart via gap junctions.

Sinoatrial (SA) node

The normal pacemaker for the entire heart, initiating action potentials that spread through the myocardium.

Atrioventricular (AV) node

A part of the cardiac conducting system that conducts action potentials from the SA node to the bundle of His, introducing a 0.1-second delay to allow atrial contraction before ventricular.

Bundle of His

Conducting-system fibers in the interventricular septum that transmit depolarization from the AV node to the bundle branches.

Purkinje fibers

Large-diameter, rapidly conducting cells in the bundle branches that quickly spread action potentials to myocytes throughout the ventricles.

Pacemaker potential

The slow, spontaneous depolarization of SA node cells that brings the membrane potential to threshold, initiating an action potential and providing automaticity.

Automaticity (heart)

The capacity for spontaneous, rhythmic self-excitation, characteristic of pacemaker cells like those in the SA node.

AV conduction disorder

A malfunction of the AV node that reduces or eliminates the transmission of action potentials from the atria to the ventricles, potentially leading to the bundle of His or Purkinje network becoming ventricular pacemakers.

Electrocardiogram (ECG)

A tool for evaluating the electrical events within the heart by measuring the currents generated in the extracellular fluid by simultaneous changes in many cardiac cells.

P wave (ECG)

The component of the ECG that corresponds to current flow during atrial depolarization.

QRS complex (ECG)

The component of the ECG that results from ventricular depolarization.

T wave (ECG)

The component of the ECG that results from ventricular repolarization.

L-type calcium channels (cardiac)

Voltage-gated calcium channels in the plasma membrane of cardiac cells that open slowly, allowing extracellular calcium to enter and contributing to the plateau phase of the action potential and triggering Ca2+ release from the SR.

Refractory period (heart)

A long period during which cardiac muscle cannot be re-stimulated, preventing tetanic contraction and ensuring adequate time for ventricular filling.

Cardiac cycle

The recurring sequence of atrial and ventricular contractions and relaxations, divided into systole (contraction/ejection) and diastole (relaxation/filling).

Systole

The period of ventricular contraction and blood ejection in the cardiac cycle.

Diastole

The alternating period of ventricular relaxation and blood filling in the cardiac cycle.

Isovolumetric ventricular contraction

A brief phase during early systole when ventricular pressure increases, closing AV valves, but aortic/pulmonary valves remain closed because ventricular pressure is still below arterial pressure.

Ventricular ejection

The phase during systole when ventricular pressure exceeds aortic/pulmonary pressure, forcing semilunar valves open and blood flows out of the ventricles.

Isovolumetric ventricular relaxation

A brief phase during early diastole when the ventricles relax, ventricular pressure decreases below aortic/pulmonary pressure, closing semilunar valves, but AV valves remain closed because ventricular pressure is still higher than atrial pressure.

Ventricular filling

The phase during diastole when ventricular pressure drops below atrial pressure, opening AV valves and allowing blood to flow from the atria into the ventricles.

End-diastolic volume (EDV)

The amount of blood in the ventricle at the end of ventricular diastole (just before contraction).

End-systolic volume (ESV)

The amount of blood remaining in the ventricle after ejection (at the end of systole).

First heart sound ('lub')

Occurs when the atrioventricular (AV) valves close at the beginning of ventricular systole.

Second heart sound ('dup')

Occurs when the semilunar valves close at the beginning of ventricular diastole.

Stenotic valve

A narrowed heart valve that causes turbulent blood flow (a murmur) due to increased resistance.

Insufficient valve

A leaky heart valve that causes turbulent backflow of blood (a murmur).

Cardiac output (CO or Q̇)

The volume of blood pumped out of each ventricle per unit time, calculated as heart rate multiplied by stroke volume (HR × SV).

Heart rate (HR)

The number of times the heart beats per minute.

Stroke volume (SV)

The volume of blood each ventricle ejects during each contraction, calculated as the difference between end-diastolic volume and end-systolic volume (EDV - ESV).

Chronotropic effects

Influences on heart rate, where parasympathetic activity decreases it and sympathetic activity increases it.

Sympathetic stimulation (heart rate)

Increases heart rate by increasing the slope of the pacemaker potential in SA nodal cells, causing faster depolarization.

Parasympathetic stimulation (heart rate)

Decreases heart rate by decreasing the slope of the pacemaker potential in SA nodal cells, causing slower depolarization.

Preload (SV)

Refers to changes in the end-diastolic volume, which is a major factor influencing stroke volume.

Ventricular contractility

The strength of ventricular contraction at any given end-diastolic volume, increased by sympathetic neurotransmitters like norepinephrine and epinephrine.

Afterload

The arterial pressure against which the ventricles must pump blood; an increased afterload tends to reduce stroke volume by making it harder for contracting muscle fibers to shorten.

Norepinephrine (ventricular contractility)

A sympathetic neurotransmitter that acts on beta-adrenergic receptors to increase ventricular contractility and speed up contraction/relaxation.

Epinephrine (myocardial contractility)

A hormone from the adrenal medulla that binds to beta-adrenergic receptors, increasing myocardial contractility in the same way as norepinephrine.

Echocardiography

A noninvasive method for measuring cardiac function, using ultrasound to create 2D or 3D images of the heart.

Cardiac angiography

An invasive method for measuring cardiac function, involving high-speed x-ray videography after injecting contrast material.