Overview
This lecture covers the structure of the circulatory system, comparing open and closed systems, detailing the human heart's anatomy, and describing different blood vessels.
Types of Circulatory Systems
- Open circulatory systems have blood vessels open at the ends, allowing blood to flow freely among tissues (e.g., insects).
- Closed circulatory systems keep blood contained within vessels at all times (e.g., humans, earthworms).
- Closed systems support larger body size and more specialized blood function.
Human Circulatory System Structure
- Humans have a closed, double circulatory system (blood passes through the heart twice per cycle).
- Systemic circulation moves oxygen-rich blood from the heart to the body; returns deoxygenated blood.
- Pulmonary circulation moves deoxygenated blood from the heart to the lungs for oxygenation, then returns it to the heart.
Structure of the Heart (External and Internal)
- The heart has four chambers: right/left atria (upper), right/left ventricles (lower).
- Superior vena cava and inferior vena cava bring deoxygenated blood to the right atrium.
- Right ventricle pumps blood to the lungs via the pulmonary artery.
- Left atrium receives oxygenated blood from pulmonary veins.
- Left ventricle pumps blood to the body via the aorta; it’s the thickest and most muscular chamber.
- Coronary arteries supply heart muscle with its own blood supply.
- Pericardium is the protective sac around the heart.
Heart Valves and Supporting Structures
- Tricuspid valve separates right atrium and right ventricle; mitral valve separates left atrium and left ventricle.
- Valves prevent backflow of blood.
- Papillary muscles and connective fibers control valve opening/closing.
- Septum separates left and right sides of the heart, preventing mixing of oxygenated and deoxygenated blood.
Layers of the Heart Wall
- Pericardium: outer protective layer.
- Epicardium: just inside the pericardium.
- Myocardium: thick muscular layer responsible for contraction.
- Endocardium: innermost layer.
Types of Blood Vessels
- Arteries have thick muscular and elastic walls, narrow lumens, and carry blood at high pressure away from the heart.
- Veins have thinner muscles, wider lumens, and valves to prevent backflow; they return blood to the heart at lower pressure.
- Capillaries are one cell thick, connect arteries to veins, and allow exchange of substances with tissues.
Blood Vessel Structure (Comparative)
- Arteries: thick wall, small lumen, high pressure.
- Veins: thin wall, large lumen, low pressure, irregular shape due to flexibility.
- Capillaries: only endothelium, very narrow.
Key Terms & Definitions
- Open circulatory system — blood leaves vessels and mixes with tissue fluids.
- Closed circulatory system — blood always remains inside vessels.
- Systemic circulation — blood flow from heart to body and back.
- Pulmonary circulation — blood flow from heart to lungs and back.
- Atria — upper heart chambers receiving blood.
- Ventricles — lower heart chambers pumping blood out.
- Pericardium — outer protective sac of the heart.
- Epicardium — outer layer just beneath pericardium.
- Myocardium — middle thick muscle layer of the heart.
- Endocardium — innermost heart layer.
- Tricuspid valve — valve between right atrium and ventricle.
- Mitral valve — valve between left atrium and ventricle.
- Septum — wall separating left and right heart sides.
- Artery — thick-walled vessel carrying blood away from heart.
- Vein — thin-walled vessel returning blood to heart, often with valves.
- Capillary — smallest vessel for exchange with tissues.
- Lumen — inner open space of a blood vessel.
Action Items / Next Steps
- Review diagrams of the heart and label major external and internal structures.
- Compare structure and function of arteries, veins, and capillaries.
- Study the difference between open and closed circulatory systems.