Overview
This lecture covers the anatomy, chambers, valves, blood flow, conduction system, and nerve supply of the heart, emphasizing structure-function relationships and clinical relevance.
Anatomical Position and External Features
- The heart is a muscular organ located in the mediastinum between the lungs.
- It is covered by the pericardium, which separates it from other mediastinal structures.
- The heart has four sides, a base (posterior), and an apex (anterior/left).
- Borders: superior (atria), inferior (right and part of left ventricle), right (right atrium), left (left ventricle and left auricle).
- Heart silhouette can be seen on a chest X-ray; right border (right atrium), left border (left ventricle/auricle).
Chambers of the Heart
- The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle.
- Right atrium receives deoxygenated blood from the superior/inferior vena cava and coronary sinus.
- Left atrium receives oxygenated blood from the four pulmonary veins.
- Right and left ventricles are separated by the interventricular septum.
Valves and Blood Flow
- Blood flows from right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve → pulmonary trunk → lungs.
- Oxygenated blood returns via pulmonary veins → left atrium → mitral (bicuspid) valve → left ventricle → aortic semilunar valve → aorta → body.
- Tricuspid valve (three cusps), mitral valve (two cusps), both anchored by chordae tendineae to papillary muscles.
- Semilunar valves (pulmonary, aortic) have three cusps, no chordae tendineae; prevent backflow during relaxation.
Internal Structure Details
- Right atrium: smooth posterior (sinus venarum), rough anterior (pectinate muscles), separated by crista terminalis.
- Right ventricle: trabeculae carneae, papillary muscles, moderator band; outflow part is the conus arteriosus.
- Interventricular septum: muscular and thin membranous parts.
- Left atrium: mostly smooth, pectinate muscles in auricle, no valves in pulmonary veins.
- Left ventricle: thickest wall, fine trabeculae carneae, aortic vestibule, mitral and aortic valves.
Conducting System and Nerve Supply
- SA node (pacemaker) sets heart rhythm, located at junction of superior vena cava and right atrium.
- AV node receives impulse, passes to AV bundle, then right/left bundle branches and Purkinje fibers for coordinated ventricular contraction.
- Cardiac plexus provides sympathetic (increases rate/force) and parasympathetic (decreases rate) innervation.
Key Terms & Definitions
- Pericardium — Membrane covering the heart.
- Auricle — Pouch-like extension of atrium increasing chamber capacity.
- Sinus venarum — Smooth area of right atrium's posterior wall.
- Crista terminalis — Ridge separating smooth and rough parts of right atrium.
- Trabeculae carneae — Muscular ridges in the ventricles.
- Papillary muscles — Muscles anchoring the valve cusps via chordae tendineae.
- Moderator band — Muscular band in right ventricle aiding contraction timing.
- SA node — Sinoatrial node; initiates heartbeat.
- AV node — Atrioventricular node; relays impulse to ventricles.
- Cardiac plexus — Network of nerves supplying the heart.
Action Items / Next Steps
- Review heart anatomy diagrams for chamber, valve, and vessel identification.
- Practice tracing the flow of blood through the heart and associated vessels.
- Read about the fetal circulation and developmental remnants (foramen ovale, ligamentum arteriosum).