Heart and Circulatory System Quiz

Heart Overview

• The heart is a four-chambered muscular organ, the size of a clenched fist.
• It beats approximately 100,000 times daily.
• Functions as two pumps: the right side for lung circulation, the left side for systemic circulation.

Heart Location and Shape

• Located in the thoracic cavity between the lungs in the mediastinum.
• Positioned behind the sternum, predominantly to the left of the midline with the apex directed downwards.
• The base is the broad superior end for major vessel attachment.

Heart Structure

• Enclosed by the parietal pericardium, which separates it from other thoracic organs; consists of an outer fibrous and inner serous layer.
• The heart wall consists of three layers:
  • Epicardium (outer)
  • Myocardium (thick middle layer of cardiac muscle)
  • Endocardium (smooth inner lining).

Cardiac Muscle Characteristics

• Unique to the heart, controlled by the autonomic nervous system.
• Features branched fibers in a striated arrangement.
• Cardiac muscle cells connected by intercalated discs, enabling smooth and repetitive contractions.

Heart Chambers

• Comprises four chambers: right and left atria (upper) and right and left ventricles (lower).
• Atria are receiving chambers, while ventricles are pumping chambers; separated by interatrial and interventricular septa.

Blood Flow through the Heart

• The right atrium receives deoxygenated blood from the superior and inferior vena cavae.
• Blood flows from the right atrium to right ventricle through the tricuspid valve during diastole.
• In systole, the right ventricle contracts, closing the tricuspid valve.
• Left atrium receives oxygenated blood from pulmonary veins post gas exchange.
• Blood moves from left atrium to left ventricle via the mitral valve; the left ventricle pumps blood through the aortic semilunar valve into the aorta.

Heart Sounds

• Heart sounds are resultant from turbulence created by valve closure, identifiable as S1 ('Lub') and S2 ('Dub').
• Variations in these sounds, known as heart murmurs, may indicate valve problems.

Heart Conduction System

• Comprises sinoatrial node (SA node), atrioventricular node (AV node), Bundle of His, and Purkinje fibers.
• SA node initiates heartbeat by generating spontaneous depolarization during diastole.
• Impulses spread through atria (atrial systole), converge at AV node, which delays signals for full atrial emptying.
• Bundle of His conducts signals to ventricles via Purkinje fibers, stimulating ventricular systole.

Electrocardiogram (ECG)

• Non-invasive test providing insights into heart rate and rhythm via P wave, QRS complex, and T wave.
• Useful for detecting arrhythmias, enlarged heart, and myocardial infarctions.

Circulatory System Functions

• Also called the cardiovascular system; circulates blood, transports nutrients, oxygen, hormones, and removes waste.
• Pulmonary circulation: right ventricle to lungs, left atrium to heart.
• Systemic circulation: involves all other body vessels.

Coronary Circulation

• Heart has its own blood supply through right and left coronary arteries for oxygenation.
• Blood from myocardium enters cardiac veins, draining into the right atrium.

Fetal Circulation

• In utero, oxygenation occurs via the placenta, making pulmonary circulation unnecessary.
• Blood is rerouted through foramen ovale to left atrium and ductus arteriosus to aorta.

Blood Vessel Types

• Arteries: Carry oxygenated blood (except in pulmonary system), feature thick muscular walls, and withstand high pressure.
• Veins: Return deoxygenated blood to the heart, contain valves to prevent backflow, and act as blood reservoirs.
• Capillaries: Smallest vessels, composed of a single endothelial layer, facilitate gas and nutrient exchange between blood and tissues.

Blood Pressure

• Defined as the force of circulating blood on arterial walls, measured in mmHg (e.g., 120/80 mmHg).
• Influenced by various physiological factors and can vary based on activity and health conditions.