Overview
This lecture introduces the anatomy and function of the heart as the central organ of the circulatory (cardiovascular) system, focusing on heart structure, circulation pathways, tissue composition, and intrinsic electrical activity.
The Circulatory System
- The circulatory system (cardiovascular system) includes the heart, arteries, veins, and capillaries transporting blood throughout the body.
- Its main function is to circulate blood, delivering oxygen and nutrients and removing waste.
Heart Anatomy and Circuits
- The heart is located in the mediastinum within the thorax.
- The heart serves as a pump, not a center of thought or emotion.
- It operates in two circuits: pulmonary (right heart to lungs, returns oxygenated blood to left heart) and systemic (left heart to body, returns deoxygenated blood to right heart).
- Four heart chambers: right atrium and left atrium (receiving); right ventricle and left ventricle (pumping).
- Atria separated by interatrial septum; ventricles by interventricular septum.
Pericardium and Heart Wall Layers
- The heart is enclosed by the pericardium (fibrous and serous layers).
- The serous pericardium includes parietal and visceral (epicardium) layers.
- Heart wall layers: epicardium (outer), myocardium (cardiac muscle), endocardium (endothelial inner lining).
Blood Flow and Heart Chambers
- Right atrium receives blood from: superior vena cava, inferior vena cava, and coronary sinus.
- Left atrium receives oxygenated blood from lungs via four pulmonary veins.
- Right ventricle pumps blood into pulmonary trunk (to lungs); left ventricle pumps blood into aorta (to body).
Heart Valves
- AV valves: tricuspid (right), mitral/bicuspid (left), prevent backflow from ventricles into atria.
- Semilunar valves: aortic (left ventricle to aorta), pulmonary (right ventricle to pulmonary trunk), prevent backflow into ventricles.
Cardiac Muscle Structure and Function
- Cardiac muscle is striated, with short, branched cells joined by intercalated discs.
- Intercalated discs contain desmosomes (structural support) and gap junctions (ion flow).
- Cardiac fibers are not multinucleate, differ in sarcomere structure from skeletal muscle.
Electrical Activity and Pacemaker Cells
- Some cardiac muscle cells have automaticity and generate their own action potentials.
- Gap junctions allow the heart to contract as a coordinated unit.
- The refractory period in cardiac muscle is longer, preventing premature contractions.
- Pacemaker cells (intrinsic conduction system) initiate and coordinate heartbeats.
- Arrhythmias and fibrillation are caused by malfunctions in this conduction system.
Key Terms & Definitions
- Circulatory system — system responsible for circulating blood throughout the body.
- Mediastinum — central thoracic cavity where the heart is located.
- Pulmonary circuit — heart-to-lungs-to-heart blood flow for oxygenation.
- Systemic circuit — heart-to-body-to-heart blood flow for nutrient delivery and waste removal.
- Pericardium — double-walled sac enclosing the heart.
- Atria — upper heart chambers receiving blood.
- Ventricles — lower heart chambers that pump blood out.
- AV (atrioventricular) valves — valves between atria and ventricles.
- Semilunar valves — valves between ventricles and major arteries.
- Cardiac muscle — specialized muscle tissue of the heart.
- Intercalated discs — junctions between cardiac cells enabling coordination.
- Automaticity — ability of cardiac cells to self-excite.
- Pacemaker cells — heart cells that set the pace for heartbeat.
Action Items / Next Steps
- Review the anatomy and flow of blood through heart chambers and valves.
- Prepare to study arteries, veins, capillaries, and details of the coronary circulation in the next lesson.