1. Structure of the Heart

6. List of important named veins Jugular veins Pulmonary veins Portal vein Azygos vein Superior vena cava Inferior vena cava Iliac vein Femoral vein Popliteal vein Great saphenous vein Small saphenous vein

9. Respiratory Diffusion

11. Where Is Your Heart? The heart lies behind the body of the sternum, extending from the 2 nd rib to the fifth intercostal muscle. About two thirds of the heart lies to the left of the mid line with the remaining third to the right.

12. An average adult heart is about the shape and size of a closed fist. Like a valentine heart, yours is slightly pointed at the lower end. The pointed end is called the apex

13. Although your heart is hollow, it isn't empty. In an average adult, about 5 quarts (4.7 litres) of blood flow through the heart each minute. Your heart's walls are made mostly of strong muscle, called the myocardium. The myocardium is the strongest, hardest-working muscle in your body. It continuously pumps your blood through 60,000 miles (96,560 kilometres) of blood vessels for a lifetime, without rest!

14. Heart Chambers The hollow centre of your heart is divided into four sections, called chambers. Each chamber is like a separate room, with doors that let blood in and out.

15. Where Blood Flows In — The Atria The two upper chambers in your heart are called the atria . The atria are the receiving chambers of your heart. When blood flows into your heart from the body or lungs, it always flows into either the right or left atrium—never anywhere else. (One upper chamber is called an atrium. Both upper chambers together are called the atria.)

16. Where Blood Is Pumped Out — The Ventricles The two lower chambers in your heart are called ventricles. The ventricles are the pumping chambers of your heart. When blood leaves your heart, it is always pumped out from the ventricles—never from anywhere else. The ventricles are very strong because they have to pump hard enough to push blood through your lungs and entire body.

17. Your Heart's Right and Left Sides Sometimes the right and left sides of your heart are called your right heart and left heart. The right atrium and right ventricle are, of course, on the right side of your heart (the same side as your right arm), and the left atrium and left ventricle are on the left side of your heart. However, when you look at a picture of the heart, the right heart is on your left A wall, called the septum, separates the left and right sides of your heart. Blood that hasn't yet been to the lungs (blood with no oxygen) stays on the right side of the septum. Blood returning from the lungs (blood with oxygen) stays on the left side of the septum. right left

18. right

29. left

36. The aorta is the largest artery in the human body, originating from the left ventricle of the heart and bringing oxygenated blood to all parts of the body in the systemic circulation. The aorta is an elastic artery, and as such is quite distensible. When the left ventricle contracts to force blood into the aorta, the aorta expands. This stretching gives the potential energy that will help maintain blood pressure during diastole, as during this time the aorta contracts passively.

38. What Do Your Valves Do? Your heart valves keep blood flowing in one direction through your heart, just like the one-way valves in your home's plumbing. They open to let blood flow through, and then close to prevent blood from flowing back the way it came. When a valve closes, flaps of tissue on the valve close tightly together to create a seal. These flaps of tissue are called leaflets. Where Are Your Heart Valves? Your heart has four valves. Blood flows through each valve one time on its way through your heart. The four valves can be grouped by their job.

40. Heart Valves What Makes the Sound of Your Heartbeat? When you listen to your heartbeat through a stethoscope ("lubb-dubb lubb-dubb"), you hear the sound of your heart valves closing. Although your heart has four valves, the valves open and close two at a time. That's why you hear only two thumps (one "lubb-dubb") per heartbeat, rather than four.