Overview
This lecture introduces the anatomy and function of the heart as part of the circulatory (cardiovascular) system, detailing heart structure, blood flow, muscle characteristics, and conduction mechanisms.
The Circulatory System and Heart Function
- The circulatory system (cardiovascular system) includes the heart, arteries, veins, and capillaries.
- The heart acts as a pump located in the mediastinum, moving blood through the body.
- The heart participates in two circuits: pulmonary (to lungs) and systemic (to body tissues).
Heart Anatomy
- The heart has four chambers: right atrium, left atrium, right ventricle, and left ventricle.
- Right atrium receives oxygen-poor blood from the body via the superior vena cava, inferior vena cava, and coronary sinus.
- Left atrium receives oxygen-rich blood from lungs through four pulmonary veins.
- Right ventricle pumps blood to the lungs via the pulmonary trunk.
- Left ventricle pumps blood into the aorta, the body's largest artery.
Heart Wall and Coverings
- The heart is covered by the pericardium (fibrous and serous layers).
- The serous pericardium consists of parietal and visceral (epicardium) layers.
- Heart wall layers: epicardium (outer), myocardium (cardiac muscle), endocardium (inner lining).
Heart Valves
- Atrioventricular (AV) valves: tricuspid (right), mitral or bicuspid (left), separate atria from ventricles.
- Semilunar valves: aortic and pulmonary, prevent backflow from arteries into ventricles.
- Valves ensure unidirectional blood flow by responding to pressure changes during contraction.
Cardiac Muscle Features
- Cardiac muscle fibers are short, branched, striated, and have one or two nuclei.
- Intercalated discs contain desmosomes (structure) and gap junctions (ion passage).
- Cardiac muscle displays automaticity, allowing some cells to self-excite.
Cardiac Conduction System
- Pacemaker cells generate and distribute electrical impulses to coordinate heart contraction.
- Gap junctions allow rapid spread of depolarization, ensuring the heart contracts as a unit.
- The refractory period in cardiac muscle is longer, preventing premature contractions.
- Conduction issues lead to arrhythmias or fibrillation (irregular or rapid heart rhythms).
Key Terms & Definitions
- Circulatory system — network transporting blood throughout the body.
- Atrium/Ventricle — upper (receiving) and lower (pumping) chambers of the heart.
- Pericardium — protective membrane surrounding the heart.
- AV (Atrioventricular) valves — valves between atria and ventricles.
- Semilunar valves — valves between ventricles and arteries.
- Intercalated discs — junctions between cardiac muscle cells.
- Automaticity — ability of cardiac cells to self-excite.
- Pacemaker cells — specialized cells initiating electrical impulses.
Action Items / Next Steps
- Review heart structure and trace the pathway of blood through its chambers.
- Prepare for a detailed study of blood vessels in the next lecture.