THE HEART

•           The heart is positioned in an anatomical area called the middle mediastinum We can feel for the apex beat of the heart in the 5^thintercostal space (between ribs 5 and 6) in line with the middle of the clavicle (collar bone).

•           THE HEART IS MADE OF MUSCLE CALLED THE CARDIAC MUSCLE. This muscle is myogenic (meaning the contraction of the hart is not initiated by the nervous system)

•           IT IS KEPT SAFE WITHIN A FIBROUS SAC / MENBRANE KNOWN AS THE PERICARDIUM

•           The heart is divided in to 2 parts, the left and the right, by the septum. The septum also divides oxygenated and deoxygenated blood

•           The heart has a thin-walled collection chamber called the atria and a thick-walled pumping chamber called the ventricle.

•           The left ventricle is the thicker of the 2 ventricles because it pumps oxygenated blood around the body

•           The walls of the left ventricle is thicker than the walls of the right ventricle because:

•            it has more muscles  

•            it pumps blood  around the whole body

•           The walls must resist high blood pressure

•           Internal structure of the heart and the roles of the valves

•           Valves allow the one way flow of blood

•           Tricuspid valve divides the right atrium and the right ventricle

•           Bicuspid/ mitral valve divides the left atrium and ventricle  

•             Both the tricuspid and mitral valves prevent the backflow of blood

•           Role of the valves 

•           Tendinous chords attached to papillary muscles prevent the valves from turning inside out

•           Semilunar/ pulmonary valves prevent the backflow of bloodin the pulmonary artery and the dorsal aorta

•           Sounds of the heart

•           The ‘lub’ sound is heard when the cuspid valves shut 

•           And the ‘dub’ sound is heard when the pulmonary valves shut

       

Path taken by the blood into the heart

•           Deoxygenated blood enters the heart through the vena cava to the right atrium then it goes through the tricuspid valve the to the right ventricle then through the pulmonary valves into the pulmonary artery

•           The pulmonary artery takes the deoxygenated blood to the lungs and oxygenates it

•           Oxygenated blood enters the heart through the pulmonary vein then into the left atrium then moves through the bicuspid valve to the left ventricle through the aortic valve to the aorta and then the rest of the body 

 

The cardiac cycle 

•           His is the sequence of events which make up the heart beat or a complete cycle of blood

•           The cardiac cycle is made up of:

•           Atrial systole 

•           Ventricular systole

•           Ventricular diastole

•           Atrial systole

•           The muscles in the walls of the atria contract

•           Pushing more blood into the ventricles through the opened cuspid calves

•           Backflow of blood into the vein is prevented by the closure of valves in the vein

•           Ventricular systole

•           Both ventricles contract at the same time 

•           The atrioventricular valves shut to prevent backflow 

•           The valves are pushed by the pressurized blood in the ventricles

•           The aortic valves ( semilunar valves in the aorta ) are pushed open 

•           Ventricular diastole 

•           The hear muscles relax ( atria and ventricles relax )

•           Semilunar valves close to prevent backflow of blood from pulmonary artery and aorta

•           Blood enters the atria from the veins ( pulmonary veins bring oxygenated blood, vena cava brings deoxygenated blood )

•           The cycle is then ready to begin again