The heart Flashcards
What are the properties of the heart?
Hollow, muscular organ
300 grams (size of a fist)
4 chambers
found in chest between lungs
surrounded by membrane called Pericardium
Pericardial space is fluid-filled to nourish and
protect the heart.
The heart pumps about 100,000 times and moves
7200 liters (1900 gallons) of blood every day.
What three layers make up the wall of the heart?
Outer epicardium – a layer of flattened epithelial cells and supporting connective
tissue
Very thick, muscular myocardium made up of cardiac muscle
Inner endocardium – layer of flattened epithelial cells supported by a fine layer of connective tissue
What is the name for sequential contraction of the heart?
Systole
What is the name for sequential relaxation of the heart?
Diastole
What are the steps of contraction for the cardiac cycle?
- Atrial (top) and Ventricular (bottom) diastole (relaxation) for around 0.4 seconds, AV valves open (atrium to ventricle) and semilunar valves closed (ventricle to body/lungs)
- Atrial systole and Ventricular diastole for around 0.1 seconds
- Ventricular systole and atrial diastole, for around 0.3 seconds, AV valves close and semilunar valved open.
Repeat
Steps in the cardiac cycle for deox/ox blood
Deoxygenated blood returns to the heart via the superior and inferior vena cava, enters the right atrium, passes into the right ventricle, and from here it is ejected to the pulmonary artery.
Oxygenated blood returning from the lungs enters the left
atrium via the pulmonary
veins, passes into the left
ventricle, and is then ejected to the aorta.
CARDIAC CYCLE IN DETAIL
We shall start when the atria and ventricles are in
diastole.
Blood at a low pressure in the veins flows into the
atria.
This increases the pressure inside the empty atria
as they fill.
The two atrioventricular valves, the tricuspid and
mitral valves, are both open, Some of the blood
trickles through the open atrioventricular valves
into the relaxed ventricles below.
2.
When the atria are full, they go into atrial systole,
their walls contract and blood is pushed through
the valves into the ventricles.
The pressure in the atria is increased due to the
contractions and the pressure is increasing in the
ventricles as they fill with blood.
When the atria contract, blood cannot flow back
into the veins because the pressure of the blood
pushes on the valves in the veins to shut them.
3.
After a short delay the ventricles contract from the apex
(base) upwards.
The pressure inside the ventricles increases due to the
ventricular systole.
As the pressure increases to a higher level than the
pressure in the atria, blood pushes against the
atrioventricular valves, shutting them (the first heart
sound) and preventing backflow.
The semilunar valves open under the pressure and blood
leaves the heart.
The ventricles relax - ventricular diastole - and the
semilunar valves snap shut behind the blood (the second
heart sound).
The two semilunar valves, the pulmonary and aortic
valves, are closed, preventing backflow of blood into the
right and left ventricles
What are the steps in the cardias conduction cycle?
The sinoatrial (SA)
node and the remainder of the conduction system are at rest.
The sinoatrial (SA) node and the remainder of the
conduction system are
at rest.
After reaching the atrioventricular node, there is a delay of approximately 100 ms that allows the atria to complete pumping blood before the impulse is transmitted to the atrioventricular bundle.
Following the delay, the impulse travels through the atrioventricular bundle and bundle branches to the Purkinje fibres, and also reaches the right papillary muscle via the moderator band.
The impulse spreads to
the contractile fibres of
the ventricle.
Ventricular contraction
begins
Blood Pressure and
Flow Velocity in the heart
As arteries branch, the
cross-sectional area increases
causing blood pressure and
flow velocity to fall.
In mammals there is a an
800-fold increase in
cross-sectional area from the
aorta to the capillaries.
Capillary - Tissue Fluid Exchange
Fluid exchange between blood and interstitial fluid is determined by the balance between the positive blood
pressure (hydrostatic pressure) and the net negative osmotic potential in the blood plasma.
Proteins in the blood plasma that cannot easily leave the capillary are the source of this difference in osmotic potential. Otherwise, the interstitial fluid and blood plasma have similar concentrations of ions and other small molecules
What is the lymphatic system?
A separate system of
vessels, the lymphatic
system, returns excess
tissue fluid to the blood.
Lymphatic ducts drain
into the venous system
near the heart.
