Cardiovascular Physiology Quiz

The cardiovascular system is comprised of the heart, blood vessels, and blood. It is responsible for transportation (oxygen, nutrients, hormones, waste products), regulation (blood pressure, body temperature), protection (against infection and blood loss), and production/synthesis (blood cells).

Intrinsic regulation is controlled by the heart itself, while extrinsic regulation is controlled by external factors like the nervous and endocrine systems.

Cardiac muscle is striated, short branched, uninucleate, contains intercalated discs, and has larger t-tubules that overlap the Z-discs.

The heart has four chambers: two atria and two ventricles. The pulmonary system circulates blood to the lungs, while the systemic system circulates blood to the rest of the body.

Valves play a vital role in preventing backflow of blood. Atrioventricular valves prevent backflow to the atria and are supported by chordae tendinae, while semilunar valves prevent backflow into the ventricles.

The intrinsic conduction system is a network of specialized cells that coordinate heart contractions. It consists of pacemaker cells and conduction pathways, ensuring synchronized atrial and ventricular contractions.

Pacemaker cells are smaller than contractile cells, have fewer myofibrils, no organized sarcomere structure, and have an unstable membrane potential that spontaneously reaches threshold.

The pacemaker potential is the slow depolarization of the membrane potential in pacemaker cells, leading to a spontaneous action potential. It occurs due to the gradual influx of Na+ and Ca2+ ions, and the efflux of K+ ions through specific ion channels.

Sympathetic activity increases heart rate, conduction velocity, and contractility by increasing the activity of If channels, leading to a faster pacemaker potential and more rapid action potentials.

Parasympathetic activity slows down heart rate, conduction velocity, and contractility by increasing K+ permeability and decreasing Ca2+ permeability, leading to a hyperpolarized membrane and slower rate of action potentials.

Intercalated discs are highly convoluted and interdigitated junctions that connect adjacent cardiac muscle cells. They contain desmosomes, fascia adherens, and gap junctions, allowing for synchronized electrical activity.

Cardiac muscle cells have more mitochondria than skeletal muscle cells, less sarcoplasmic reticulum, larger t-tubules, and graded contractions.

The action potential of a contractile cell is longer in duration than a normal action potential due to the influx of Ca2+ ions. It has four phases: 4- resting potential, 0- depolarization, 1- temporary repolarization, 2- plateau, 3- repolarization.

The plateau phase of a cardiac muscle action potential is important because it prevents summation and tetanus, which would be fatal.

The longer refractory period in cardiac muscle prevents tetanus because it prevents summation of action potentials, ensuring the heart can relax between beats.

Excitation-contraction coupling in cardiac muscle begins with CICR (Ca2+ induced Ca2+ release) where Ca2+ from the extracellular fluid enters the cell via L-type Ca2+ channels, triggering the release of more Ca2+ from the sarcoplasmic reticulum.

The strength of cardiac muscle contraction is graded, meaning it depends on the amount of Ca2+ bound to troponin. This allows for fine-tuning of contractile force based on the filling of the heart chambers.

Relaxation of cardiac muscle occurs when Ca2+ is transported back into the SR and out of the cell via the NCX (Na+/Ca2+ exchanger). This decrease in intracellular Ca2+ levels stops myosin/actin interactions and allows the sarcomere to lengthen.

The cardiac cycle refers to the sequence of events as blood enters the atria, leaves the ventricles, and repeats. The intrinsic electrical conduction system coordinates this activity.

The intrinsic electrical conduction system, initiated by the SA node, transmits electrical signals through the atria and ventricles to synchronize contractions. This pathway includes the SA node, internodal pathways, AV node, Bundle of His, bundle branches, and Purkinje fibers.

An ECG (electrocardiogram) records the electrical activity of the heart, allowing visualization of the heart's electrical changes during the cardiac cycle. It provides valuable information about heart function and rhythm.

Systole refers to the contraction phase of the heart, while diastole refers to the relaxation phase. The cardiac cycle alternates between systole and diastole.

The cardiac cycle consists of five phases: rest, atrial systole, isovolumetric ventricular contraction, ventricular ejection, and isovolumetric ventricular relaxation. Each phase is defined by specific events and changes in pressure and volume.

The first heart sound ('lub') is produced by the closure of the AV valves during isovolumetric ventricular contraction, while the second heart sound ('dup') is produced by the closure of the semilunar valves during isovolumetric ventricular relaxation.

Stroke volume is the amount of blood pumped out of the left ventricle with each contraction. Normally, only about two-thirds of the blood in the ventricle is ejected.