1. Heart pt 1: Structure

2. Transportation of Blood In humans, blood is always contained within blood vessels – If a blood vessel leaks blood into the tissues the result is a bruise These blood vessels plus the heart make up the circulatory system −The heart squeezes regularly in order to keep blood moving throughout the body

3. Location of Heart in Chest

4. Layers of Heart Pericardium (includes connective and epithelial layers) – Innermost epithelial layer of pericardium is the epicardium Myocardium (heart muscle tissue) Endocardium (epithelial tissue for low friction)

5. Myocardium The myocardium is the cardiac muscle tissue that produces contractile force Muscle fibers are attached to each other with intercalated discs that contain gap junctions – These electrically couple the cells so they all contract more or less in unison Cardiac muscle fibers also take much longer to be ready to fire again than skeletal muscle and neurons – This prevents the heart from beating too fast

6. Heart Chambers The heart is divided into four chambers, two on the left and two on the right – Entry chamber: atrium (like the entry room to a building) – Main force propeller: ventricle – Division between right and left heart: septum The heart is two pumps in one, but both contract at the same time

7. Blood Circuits Blood from the right ventricle goes into the lungs and back to the heart (pulmonary circuit) Blood from the left ventricle goes to the entire body and back to the heart (systemic circuit) – Systemic circuit is under much higher pressure

8. Pulmonary Circuit Blood enters the right atrium, then squeezed into the right ventricle The right ventricle pumps blood out into the pulmonary trunk which branches into the pulmonary arteries that lead to the lungs Blood is oxygenated at the lungs and returns via the pulmonary veins

9. Systemic Circuit Blood enters the left atrium, is squeezed to the left ventricle, and is then pumped to the largest artery in the body, the aorta The aorta branches into the many arteries in the body, branch out into capillaries, then combine back to make the veins The largest veins are the superior vena cava and the inferior vena cava, which both return blood to the right atrium

10. “Lub Dub” Sound The two sounds of the heart beat are valves closing in the heart to prevent backflow – Heart murmurs are caused by leaky valves The atria (plural of atrium) contract first to fill the ventricles The ventricles then start contracting (“lub”) and squeeze blood to the lungs and body, then stop so the atria can refill (“dub”)

11. Heart Valves The valves that block backflow into the atria when the ventricles are squeezing are called atrioventricular valves or AV valves – Right atrium: tricuspid valve – Left atrium: bicuspid (mitral) valve The valves that block backflow into the ventricles when the atria are refilling are called semilunar valves – Pulmonary valve – Aortic valve

12. Valve Structure The AV valves are anchored in place by the chordae tendineae – Bands of fibrous connective tissue similar to tendons – Also known as “heart strings” The semilunar valves do not have chordae tendineae, since the force on them is not as great as on the AV valves

13. Heart Blood Supply The heart receives its own blood supply through the coronary arteries – Corona = crown Arteries can be blocked by excess blood cholesterol Coronary artery blockage can cut off blood to the heart, causing a myocardial infarction (heart attack)