Physiology Lec-1 PDF

Debarment of Anesthesia Tech - Physiology Lecture No.1 Electrical Components and Activity of The Heart : The heart is a pump made up of muscle tissue. The heart's pumping action is controlled by an electrical conduction system that coordinates the contraction of the heart chambers How does the hea...

Debarment of Anesthesia Tech - Physiology Lecture No.1 Electrical Components and Activity of The Heart : The heart is a pump made up of muscle tissue. The heart's pumping action is controlled by an electrical conduction system that coordinates the contraction of the heart chambers How does the heart beat? An electrical stimulus is generated in a special part of the heart muscle called the sinus node. It's also called the sinoatrial node (SA node). The sinus node is a small mass of special tissue in the right atrium of the heart. In an adult, the sinus node sends out a regular electrical pulse 60 to 100 times per minute. The right and left atria are stimulated first. They contract to push blood from the atria into the ventricles. The ventricles then contract to push blood out into the blood vessels of the body. Dr. Mohanad Alqattan Refractory Period of Cardiac Muscle. Cardiac muscle, like all excitable tissue, is refractory to restimulation during the action potential. Therefore, the refractory period of the heart is the interval of time during which a normal cardiac impulse cannot re-excite an already excited area of cardiac muscle. The normal refractory period of the ventricle is 0.25 to 0.30 second, which is about the duration of the prolonged plateau action potential. There is an additional relative refractory period of about 0.05 second during which the muscle is more difficult than normal to excite but nevertheless can be excited by a very strong excitatory signal. The term "excitation-contraction coupling" refers to the mechanism by which the action potential causes the myofibrils of muscle to contract. The Cardiac Cycle: The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the cardiac cycle. Each cycle is initiated by spontaneous generation of an action potential in the sinus node. This node is located in the right atrium near the opening of the superior vena cava, and the action potential travels from here rapidly through both atria and then through the A-V bundle into the ventricles. Diastole and Systole: The cardiac cycle consists of a, e period of relaxation called diastole during which the heart fills with blood, followed by a period of contraction called systole. Because of this special arrangement of the conducting system from the atria into the ventricles, there is a delay of more than 0.1 second during the passage of the cardiac impulse from the atria into the ventricles. This allows the atria to contract ahead of ventricular contraction, thereby pumping blood into the ventricles before the strong ventricular contraction begins. Dr. Mohanad Alqattan