Overview
This lecture covers the structure and function of the heart, the circulatory system in humans, the pathway of blood through the heart, and how to calculate cardiac output.
The Heart: Structure & Function
- The heart is a double pump with left and right sides separated by the septum.
- The left side receives oxygenated blood from the lungs and pumps it to the body (systemic circuit).
- The right side receives deoxygenated blood from the body and pumps it to the lungs (pulmonary circuit).
- The left ventricle has a thicker muscular wall than the right to pump blood at high pressure around the body.
- Valves in the heart prevent the backflow of blood.
- Coronary arteries supply the heart's muscle tissue with oxygenated blood for constant aerobic respiration.
Pathway of Blood Through the Heart
- Deoxygenated blood enters the right atrium via the vena cava.
- Right atrium contracts, pushing blood through the tricuspid valve into the right ventricle.
- Right ventricle contracts, sending blood through the semilunar valve into the pulmonary artery and to the lungs.
- Gas exchange occurs in lung capillaries; oxygenated blood returns via the pulmonary vein to the left atrium.
- Left atrium contracts, blood passes through the bicuspid valve to the left ventricle.
- Left ventricle contracts, pushing blood through the semilunar valve and out the aorta to the body.
- Both atria and both ventricles contract simultaneously in each cycle.
The Circulatory System Overview
- The circulatory system consists of a closed network of blood vessels (arteries, veins, capillaries) connected to the heart.
- Arteries carry oxygenated blood away from the heart; veins return deoxygenated blood to the heart.
- Blood passes from arteries to arterioles to capillaries in organs, then to venules and veins.
- Lymphatic vessels collect excess tissue fluid from capillaries and return it to circulation.
Cardiac Output
- Cardiac output (CO) is the volume of blood pumped by the heart per minute.
- Average resting CO for adults is 4.7 liters per minute; higher in fitter individuals.
- CO increases with exercise to supply more oxygen and glucose for respiration.
- CO is calculated as: Cardiac output = heart rate (bpm) × stroke volume (cm³).
- Heart rate is beats per minute; stroke volume is blood pumped from the left ventricle per beat.
Key Terms & Definitions
- Double pump — heart structure that separately pumps blood to lungs and body.
- Septum — muscular wall dividing left and right sides of the heart.
- Systemic circuit — pathway carrying blood from the heart to the body and back.
- Pulmonary circuit — pathway carrying blood from the heart to the lungs and back.
- Coronary arteries — vessels supplying the heart muscle with oxygenated blood.
- Cardiac output — volume of blood pumped by the heart per minute.
- Stroke volume — volume of blood pumped out of the left ventricle per beat.
- Lymphatic vessels — vessels that collect tissue fluid and return it to the bloodstream.
Action Items / Next Steps
- Practice drawing and labeling the heart and main blood vessels.
- Memorize the pathway of blood through the heart and major vessels.
- Use the cardiac output formula to solve related exam questions.