Controlling the heart rate- effects of hormones and nervous mechanisms.

HEART

pumps blood around the body and is part of the circulatory system, which has many important roles (e.g. supplying cells with nutrients such as glucose and oxygen, removal of waste products such as carbon dioxide that may be toxic if built up, transport of urea from the liver to kidney and thermoregulation).

Essential that circulatory system adapts to stimuli so that it can meet the needs of the tissues. Heat rate can be raised or lowered (number of beats per minute). The force of contractions of the ventricular walls can also vary and the stroke volume may be altered. 

CO=SV X HR

Cardiac muscle is myogenic which means that it can initiate its own beat/ contractions without receiving neural signals. Beats at regular intervals. 

However, atrial muscles and ventricular muscles have different myogenic rates of contraction thus making the coordination very important and essential.

SAN- pacemaker, initiates waves of excitation/ electrical impulses in the wall of the right atrium. SAN is a region of tissue that can initiate its own action potential, which travels over the atrial walls causing atrial systole (atrium contract at the same time). 

Band of non-conducting collagen tissue prevents the signal from passing directly to the ventricles. Instead, the wave travels through the AVN, which passes electrical signals to the bundle of His and down the Purkyne fibres in the ventricular walls.

There is a slight delay before this…