2. #11 The atria contract, forcing deoxygenated blood from the right atrium, through the atrio-ventricular valve into the right ventricle. #4 occurs simultaneously.

3. #1 The right ventricle contracts, slamming shut the atrio- ventricular valve, and forcing blood out of the heart to through the pulmonary artery. Occurs simultaneously with #5.

4. # 2 Blood flows through the pulmonary artery (arteries) to both the right and left lungs. As the ventricle relaxes, the semi- lunar valve slams shut, producing the second heart sound. Occurs simultaneously with #6.

5. #3 In the lungs, blood releases CO 2 and absorbs O 2 from the air. This occurs by simple diffusion (although there are some cool details we’ll talk about later). Blood returns to the heart through the pulmonary veins to the left atrium.

6. #4 Blood returns from the lungs to the left atrium. The left atrium contracts, which forces blood into the left ventricle (occurs simultaneously with #11).

7. #5 The left ventricle contracts, slamming shut the atrio- ventricular valve and forcing blood out of the heart through the aorta. Occurs simultaneously with #1.

8. #6 Blood moves out of the heart through the aorta. As the ventricle relaxes, high back- pressure in the aorta slams shut the semi- lunar valve, producing the second heart sound. Occurs simultaneously with #2.

9. #7 & 8 Blood is carried by arteries, and arterioles to the head, forelimbs, abdominal organs, and hind limbs. There arterioles split into much smaller vessels called capillaries, where cells can exchange nutrients and waste products.

10. #9 & 10 Capillaries reform into venules and then veins, and finally to either the inferior vena cava or the superior vena cava. This blood re-enters the heart at the right atrium, and the cycle repeats.

12. Arteries Arteries carry high pressure blood away from the heart. They have thick, strong layers of muscle and connective tissue surrounding them, which allows them to carry high pressures.

13. Capillaries Capillaries are specialized for material exchange. They are very tiny, and allow a single file line of blood cells to pass. They are “fenestrated” to allow fluids to leak out and bathe the surrounding tissue cells. Materials enter and leave blood by diffusion and osmosis.

14. Veins Veins carry low pressure blood back to the heart. Veins have thinner layers of muscle and connective tissue so they remain flexible. They also have one- way valves to prevent low pressure blood from flowing backwards due to gravity or inactivity.

15. Atherosclerosis Is the build up of fats and cholesterol along the inner wall of arteries. This narrows the lumen of the arteries and restricts blood flow.

16. Atherosclerosis occurs when there is damage to the inner wall of the arteries - caused by high blood pressure and/or chemicals in the blood. This results in the release of growth factors which cause the muscle layer around the wall to thicken, and the wall to be more permeable to fats and cholesterol.

17. LDL (Low density lipoproteins) deposit cholesterol along the walls of the arteries. These deposits eventually crystalize and harden (atherosclerosis is also called “hardening of the arteries”). The build-up reduces blood flow and causes turbulence which can lead to Thrombosis or the formation of blood clots. Together, atherosclerosis and thrombosis can cause CHD, or coronary heart disease.

18. Some of the first arteries to branch from the aorta are the coronary arteries. These arteries supply the heart muscle itself with the blood and oxygen needed to keep pumping. –See model

19. If atherosclerosis and thrombosis (CHD) lead to a blockage of the coronary arteries, the cells of the heart are starved of oxygen, and lose the ability to contract. This is a heart attack, or a myocardial infarction. If arteries in the brain become blocked, a stroke results.

20. Risk factors for CHD Genetics Age Gender Diet/obesity Activity level Lifestyle (smoking, etc.)