The Heart:
32 000 000 beats per year!
Muscular organ located between lungs
structure
Composed of myocardium (cardiac muscle tissue)
Inside the heart is lined with endocardium (squamous epithelial)
Outside of heart is lined with pericardium which forms pericardial sac (for heart lubrication)
The heart is divided into two halves by the septum
Two halves of the heart are divided into 4 chambers
Blood flow through the heart is controlled by valves
The atrio-ventricular valves are held in place by chordae tendinae
The semi lunar valves direct flow out of the heart (resemble a half moon)
Function
The heart acts as a double pump The right side of the heart pumps blood to
the lungs (called the pulmonary circuit) The left side pumps blood to the rest of the
body (called systemic circuit) This is why the left side of the heart is
larger (has to pump blood farther)
Pathway of blood
Venae cavae (inferior and superior) to the right atrium
Right atrium to right ventricle Right ventricle to pulmonary artery (to
lungs/pulmonary veins and back to heart) Left atrium to left ventricle Left ventricle to aorta to the body
Systole – contraction: first atria contract, then ventricles
Diastole – relaxation Sound: lub-dupp Lub: atrioventricular valves close Dupp: closing of semi-lunar valves Heart murmur often due to ineffective
valves (hear a “slush” sound instead of “lub”) this can cause back-flow in the heart
Blood pressure
Average = 120/80 mm Hg
systole of left ventricle
diastole of left ventricle The ratio of the contraction and relaxations
Heart beat control
The heart beat is intrinsic, meaning it can beat independently of the central nervous system
The heart has its own pacemaker: the sino-atrial node
This is located in the upper dorsal wall of the right atrium
The SA node initiates the heart beat by causing the atria to contract
The electrical impulse then reaches the atrio-ventricular node located at the base of the right atrium
The signal is then transmitted through the ventricles by purkinje fibres
This then causes the ventricles to contract
The heart is controlled by the nervous system at the medulla oblongota (brain stem)
Heart beat is sped up or slowed down depending on what your body requires
Electrocardiogram (ECG) shows voltage changes across the heart during contraction