Download The Heart

The Heart
General Information
The heart is situated between the lungs and
behind the sternum. About 2/3 of it lies to the left
of the body’s midline.
The heart is the size of a clenched fist.
Structure of the Heart
Pericardium = Outer double layered membrane of the heart
– it reduces friction to maintain the hearts shape.
Myocardium = Specialised cardiac muscle tissue. Cardiac muscles are
involuntary. It is responsible for the contraction of the heart.
Endocardium = Smooth inner membrane which lines the cavities of the
heart- it prevents friction between the heart and the blood.
The left hand side is bigger than the right – it has further to pump the blood.
Cardiac Cycle
1. The Pulmonary Vein carries oxygenated blood from the lungs to the
heart.
2. The Aorta carries oxygenated blood from the Heart to the body.
3. The Inferior and Superior Vena Cava carry deoxygenated blood from
the body to the heart.
4. The Pulmonary Artery carries deoxygenated blood from the heart to the
lungs.
PV
LA
Aortic Valve
Inferior Vena Cava
Bicuspid Valve
Aorta
LV
Body
Semilunar
Superior &
RA
Tricuspid Valve
Semilunar Pulmonary Valve
Pulmonary Artery
RV
Lungs
1. Pulmonary Circulation
Lungs
Pulmonary Vein
Heart
blood)
Pulmonary Artery
Heart (oxygenated blood)
Lungs (deoxygenated
2. Systematic Circulation
Heart
Body
Aorta
Vena Cava
Body (oxygenated blood)
Heart (deoxygenated blood)
Circulatory Systems
There are 2 circulatory systems. 1 molecule of blood travels through the
heart 2 times in a full cycle.
Both parts of the heart work simultaneously (double pump)
1 beat takes approximately 0.8 seconds
Lub noise = closing of the Bicuspid and Tricuspid valves.
Dub noise = closing of the Semilunar valves
Heart Diagram – Complete Labelling
1. Aorta
2. Superior Vena Cava
3. Pulmonary Artery
4. Right Atrium
5. Pulmonary Semilunar Valve
6. Tricuspid Valve
7. Inferior Vena Cava
8. Right Ventricle
9. Pulmonary Vein
10. Bicuspid Valve
11. Aortic Semilunar Valve
12. Left Ventricle
Cardiac Cycle
At rest, one complete cycle lasts 0.8 seconds and is repeated approximately 72 times a
minute. The cardiac Cycle consists of two phases that represent the contraction and
relaxation of the heart muscle.
1. Diastole – Relaxation phase (0.5 seconds)
2. Systole – Contraction phase (0.3 seconds)
DIASTOLE
*Both Atria fill with blood. Atrioventricular(AV) valves (bicuspid and tricuspid) are
closed.
*Atrial blood pressure rises above ventricular pressure.
*Rising blood pressure forces the AV valves to open and blood passively passes into
both ventricles.
* Back-flow of blood into the ventricles from major blood vessels is prevented by the
closed semilunar valves in the aorta and pulmonary artery.
SYSTOLE
 After diastole the systole begins
 There are two phases of systole:
– Atrial systole
– Ventricular systole
ATRIAL SYSTOLE
*Muscle of both atria contract forcing the remaining atrial blood to move through the
open AV valves into the ventricles.
*The semi-lunar valves remain closed during this period
VENTRICULAR SYSTOLE
*Muscle tissue of both ventricles contract.
*Aortic and pulmonary semilunar valves are forces open and the AV valves are shut to
prevent back-flow of blood into atria.
*Ventricle contraction forces open the SL valves
*Blood is forced into:
1. Aorta to the body tissues/muscles.
2. Pulmonary Artery to the lungs.
The heart then enters a period of diastole and the cycle is repeated.
Conduction System
The electrical impulse responsible for stimulating the heart to contract is
called the cardiac impulse.
Heart is myogenic – it generates its own electrical impulse.
1. The cardiac impulse is initiated from the sino-atrial (SA) node (often
known as the pacemaker).
2. The impulse travels through the atria walls causing both atria to contract.
The ventricles are insulated from the atria and cannot be stimulated at this
point.
3. The cardiac impulse reaches and activates the Atrioventricular (AV)
Node in the right atrium which passes the impulse down into the bundle of
His located within the septum of heart.
The AV node helps delay the impulse allowing the contraction of the atria
to finish before the ventricles begin to contract.
4. The bundle of His splits into left and right branches and spreads the
impulse down to the bottom of the heart and around the walls of the
ventricles via a network of Purkinje fibres, causing both ventricles to
contract.
The ventricles then relax and the cycle is repeated with the next cardiac
impulse.
SA Node – Atria – AV Node – Bundles of His – Purkinje Fibres.
Process can be known as “a wave of excitation”