Cardiovascular System 1

Cardiovascular System 1

• Heart Enclosing Structures: The heart is enclosed by a double-walled sac called the pericardium. The fibrous pericardium protects the heart, anchors it to surrounding structures, and prevents overfilling. The serous pericardium reduces friction between the heart and surrounding structures. A lubricating serous fluid fills the pericardial cavity between the layers.

• Pulmonary and Systemic Circuits: The pulmonary circuit involves the right side of the heart, carrying deoxygenated blood to the lungs for gas exchange. The systemic circuit involves the left side of the heart, pumping oxygenated blood to the rest of the body.

• Atrioventricular and Semilunar Valves: Atrioventricular (AV) valves (tricuspid and mitral) prevent backflow into the atria during ventricular contraction. Semilunar (SL) valves (aortic and pulmonary) prevent backflow from the arteries into the ventricles after blood ejection. AV valves open during relaxation, and SL valves close.

• Sinoatrial (SA) and Atrioventricular (AV) Nodes: The SA node is the heart's pacemaker, initiating electrical impulses triggering heartbeats. The AV node delays the impulse slightly, allowing the atria to fully contract before passing the signal to the ventricles. This coordinated signal ensures ventricular contraction.

Cardiac Cycle and Blood Flow

• Cardiac Cycle Phases: The cardiac cycle includes four phases: ventricular filling (atria contract, filling ventricles); isovolumetric contraction (ventricles contract, valves closed); ventricular ejection (semilunar valves open, blood pumped); and isovolumetric relaxation (ventricles relax, decrease pressure without changing blood volume).

• Influences on Stroke Volume: Preload (stretch of cardiac muscle fibers) influences stroke volume through the Frank-Starling law. Contractility (strength of contraction) increases stroke volume. Afterload (pressure ventricles overcome to eject blood) decreases stroke volume.

• Electrocardiogram (ECG) Waves: ECG's P wave represents atrial depolarization; QRS complex, ventricular depolarization; and T wave, ventricular repolarization.

• Frank-Starling Law: The Frank-Starling law describes how increased filling of the heart (preload) leads to a stronger contraction, thus greater stroke volume.

Additional Concepts

• Coronary Circulation: Coronary arteries supply oxygen-rich blood to the heart muscle (myocardium); deoxygenated blood is collected by cardiac veins, draining into coronary sinus.

• Cardiac Muscle Refractory Period: Cardiac muscle has a longer refractory period than skeletal muscle, preventing tetanus and ensuring rhythmic pumping.

• Autonomic Nervous System & Heart Rate: The sympathetic nervous system increases heart rate and contractility via norepinephrine. The parasympathetic nervous system decreases heart rate via acetylcholine.

• Heart Conduction System: The SA node initiates the action potential, which spreads through the atria, AV node, bundle of His, bundle branches, and Purkinje fibers, leading to coordinated ventricular contraction.

• Calcium Influx in Cardiac Contraction: Calcium influx from both extracellular space and sarcoplasmic reticulum triggers actin-myosin sliding, causing contraction. Calcium-induced calcium release amplifies this process, enhancing contraction strength.

• Congestive Heart Failure (CHF): Causes include coronary artery disease, high blood pressure, multiple myocardial infarctions, and cardiomyopathy. This condition causes fluid accumulation in lungs or body tissues due to impaired heart's ability to pump blood efficiently.

Action Potential Phases

• Ventricular Contractile Cell Phases: Action potentials in ventricular cells have phases: rapid depolarization (Na+ influx), partial repolarization(Na+ channel inactivation), plateau phase (Ca2+ influx counteracting K+ efflux), rapid repolarization (K+ efflux), and resting potential.

Cardiac Output and Stroke Volume

• Stroke Volume (SV): The volume of blood pumped by one ventricle per beat, calculated as the difference between end-diastolic volume (EDV) and end-systolic volume (ESV). Increased EDV and decreased ESV increase SV.

Congestive Heart Failure (CHF) Consequences

• Pulmonary Congestion: Left side heart failure causes blood to back up in the lungs, leading to fluid leakage (pulmonary edema).

• Peripheral Congestion: Right side heart failure results in blood pooling in systemic circulation, causing edema in extremities and organs.

This quiz covers the essential components of the cardiovascular system, including the heart's enclosing structures, the pulmonary and systemic circuits, and the function of various heart valves. Test your understanding of these foundational concepts critical to human physiology.