Cardiovascular System Quiz - Anatomy and Physiology

Heart Anatomy

• The heart is located in the mediastinum, between the lungs.
• It's positioned behind the sternum and above the diaphragm.
• The apex of the heart points towards the left hip.
• The heart is enclosed in a double-walled sac called the pericardium.
• The inner layer, the epicardium, is a part of this sac.
• The outer layer, the parietal pericardium, forms the outer protective barrier.
• Fluid within the pericardial cavity minimizes friction during heart movements.

Structure of the Heart Wall

• The wall of the heart comprises three layers:
• The epicardium (visceral pericardium). The outermost layer.
• The myocardium. The middle layer forming most of the heart, containing cardiac muscle tissue.
• The endocardium. The thin lining of the inner myocardial surface, continuous with the cardiovascular system's endothelium.
• The fibrous skeleton of the heart is a fibrous connective tissue layer encircling the cardiac muscle.

Heart Chambers

• The heart has four chambers: two atria and two ventricles.
• The atria receive blood returning to the heart.
• The ventricles pump blood out of the heart.
• Pectinate muscles are ridges within the right atrium.

Heart Valves

• Heart valves ensure unidirectional blood flow.
• The atrioventricular valves (AV valves) are between the atria and ventricles.
• The right AV valve is tricuspid, with three flaps.
• The left AV valve is bicuspid (mitral) with two flaps.
• Chordae tendineae connect the AV valve cusps to the papillary muscles.
• Semilunar valves (SL valves) are between the ventricles and arteries leaving the heart.
• The pulmonary semilunar valve is between the right ventricle and the pulmonary artery.
• The aortic semilunar valve is between the left ventricle and the aorta.

Blood Pathway Through the Heart and Lungs

• Deoxygenated blood arrives at the right atrium via superior and inferior vena cava.
• It then flows through the tricuspid valve to the right ventricle.
• The right ventricle pumps blood through the pulmonary semilunar valve to the pulmonary artery towards the lungs.
• In the lungs, blood is oxygenated.
• Oxygenated blood returns to the left atrium through pulmonary veins.
• It passes through the bicuspid valve to the left ventricle.
• The left ventricle pumps blood through the aortic semilunar valve to the aorta and onward to systemic circulation.

Heart Valves Function

• AV valves open when atrial pressure exceeds ventricular pressure, allowing blood flow into the ventricles.
• AV valves close when ventricular pressure exceeds atrial pressure to prevent backflow.
• SL valves open when ventricular pressure exceeds arterial pressure, allowing blood ejection into the arteries.
• SL valves close when ventricular pressure falls below arterial pressure to prevent backflow into the ventricles.

Coronary Circulation

• This is the functional blood supply to the heart muscle itself.
• Coronary arteries branch from the aorta and supply oxygenated blood to the myocardium.
• Coronary veins collect deoxygenated blood and return it to the coronary sinus, which empties into the right atrium.

Cardiac Muscle

• Cardiac muscle is striated, branched, and interconnected.
• Cardiac muscle cells are uni- or binucleate.
• Intercalated discs join cardiac cells and transmit impulses between cells, allowing for synchronized contraction.
• Cardiac muscle contracts as a functional syncytium.
• Cardiac muscle tissue is self-excitable (autorhythmic).

Cardiac Muscle Contraction

• Depolarization leads to Ca2+ influx, a prolonged process generating a plateau phase.
• Repolarization results from inactivation of Ca2+ channels and opening of voltage-gated K+ channels.
• Cardiac muscle action potentials last much longer than skeletal muscle potentials.

Heart Physiology: Intrinsic Conduction System

• The intrinsic conduction system is the specialized network that coordinates the heartbeat.
• Autorhythmic cells have unstable resting potentials called pacemaker potentials.
• The SA node (sinoatrial node), the heart's pacemaker, initiates action potentials.

Heart Physiology: Sequence of Excitation

• The SA node generates electrical impulses, initiating atrial depolarization approximately 75 times per minute.
• The AV node delays the impulse approximately 0.1 second.
• The impulse then travels to the AV bundle, which branches into the bundle branches and Purkinje fibers in the interventricular septum and walls.

Electrocardiography (ECG)

• ECG records the electrical activity of the heart.
• The P wave represents atrial depolarization, QRS represents ventricular depolarization, and the T wave represents ventricular repolarization.
• Atrial repolarization is obscured by the QRS complex.

Cardiac Cycle

• The cardiac cycle includes all events associated with blood flow through the heart. It contains electrical, mechanical events and phases such as systole and diastole.
• Phases of the cardiac cycle include: ventricular filling, atrial systole, ventricular systole, and isovolumetric relaxation.

Cardiac Output (CO)

• Cardiac output (CO) is the amount of blood pumped out by each ventricle in one minute.
• CO is directly correlated to the product of heart rate (HR) and stroke volume (SV).

Stroke Volume (SV)

• SV is the volume of blood pumped out of one ventricle per contraction.
• SV is determined by the difference between end-diastolic volume (EDV) and end-systolic volume (ESV).

Factors Affecting Stroke Volume

• Preload is the amount of stretching of the cardiac muscle cells before contraction (related to EDV).
• Contractility is the force of contraction independent of stretch.
• Afterload is the resistance against which the ventricles pump blood during systole.
• Increased sympathetic stimulation and certain hormones increase contractility, whereas acidosis and increased extracellular K+ decrease it.

Regulation of Heart Rate-Autonomic Nervous System

• The autonomic nervous system (ANS) governs heart rate.
• The sympathetic nervous system increases heart rate (accelerates).
• The parasympathetic nervous system decreases heart rate (inhibits), mediated by acetylcholine.

Extrinsic Factors Affecting Cardiac Output

• Various factors, like exercise, body temperature, age, and gender affect the heart rate.

Homeostatic Imbalance

• Tachycardia is an abnormally fast heart rate.
• Bradycardia is an abnormally slow heart rate.

Congestive Heart Failure (CHF)

• Congestive heart failure (CHF) is a condition in which the pumping efficiency of the heart is impaired.
• CHF can be brought on from several factors, including coronary atherosclerosis, persistent high blood pressure and others.

Cardiac Conditioning

• Exercise increases cardiac muscle mass.
• Cardiac muscle mass increase contributes to increased strength of contraction
• Increased conditioning results in less frequent heartbeat and a greater resting period.

Special Cardiovascular Reflexes

• Atrial (Bainbridge) reflex is a sympathetic reflex initiated by increased blood volume within the atria.
• Carotid sinus reflex and aortic sinus reflex control blood flow to the brain and systemic circulation using baroreceptors.

Chemical Regulation of the Heart

• Hormones like epinephrine and thyroxine can directly influence heart rate among other factors.