3.6.2 Heart
- The heart is a muscular pump with four chambers that permits the efficient movement of blood throughout the body.
- The heart chambers are the two upper atria (singular: atrium), which have relatively thin walls and receive blood from veins, and the two lower ventricles, which have thicker walls and pump blood towards other organs.
- A cardiac cycle is one complete sequence of pumping, as the heart contracts, and filling, as it relaxes and its chambers fill with blood. - The contraction phase is called systole, and the relaxation phase is called diastole. - Blood pressure is the pressure of the blood against the walls of the arteries. - The higher (systolic) number represents the pressure while the heart contracts to pump blood to the body. - The lower (diastolic) number represents the pressure when the heart relaxes between beats. - The systolic pressure is always stated first. For example: 118/76 (118 over 76); systolic = 118, diastolic = 76.
