5. The Heart and Heart Disease Flashcards
What is the heart?
A muscular organ that lies in the thoracic cavity behind the sternum
Two separate pumps, lying side by side
Each pump has two chambers
What is the atrium?
Thin-walled and elastic and stretched as it collects blood
Only has to pump blood to the ventricles a short distance away so has a thin muscular wall
What is the ventricle?
Thicker muscles wall because it pumps blood either to the lungs or to the rest of the body
The right ventricles pumps blood to the lungs, whilst the left pumps it to the rest of the body, so it has a thicker muscular wall
After birth, there is no mixing of blood in either pump due to the septum
The atria and ventricles do, however, always contract together
Which valves are present in the heart?
There are valves between the ventricles and atria to prevent backflow of blood: the left atrioventricular (bicuspid) valves, which are two cup-shaped flaps on the left of the heart, and the right atrioventricular (tricuspid) valves, which are three cup-shaped flaps on the right of the heart
What do each of the vessels associated with the heart do?
Aorta – carries oxygenated blood to all parts of the body except the lungs
Vena cava – brings deoxygenated blood back from the tissues of the body
Pulmonary artery – carries deoxygenated blood to the lungs, where oxygenated blood is replenished and carbon dioxide is removed. Unusually for an artery, it carries deoxygenated blood
Pulmonary vein – carries oxygenated blood back from the lungs. Usually for a vein, it carries oxygenated blood
How is the heart muscle supplied with oxygen?
The coronary arteries branch off the aorta shortly after it leaves the heart
Blockage of these arteries e.g. by clotting leads to myocardial infarction, or a heart attack, because the heart muscle is deprived of oxygen so it dies
Describe diastole.
Blood flows back from the vena cava and pulmonary vein. As the volume of blood in the atria increases, the pressure inside both chambers increases. The walls of both the atria and ventricles are relaxed at this point. The increasing pressure inside of the atria forces the atrioventricular valves open, which allows blood to flow into the ventricles. Because the ventricular walls are still relaxed, the pressure within the ventricles decreases so the pressure inside the aorta and pulmonary artery is greater, forcing the semi-lunar valves closed (‘dub’).
Describe atrial systole.
Atria contract, forcing the remaining 30% of blood into the ventricles
Describe ventricular systole.
After a short delay to allow the ventricles to fill with blood, they contract at the same time. This increases the pressure within them, so the atrioventricular valves are forced shut (‘lub’). This further increases the pressure in the ventricles, which forces the semi-lunar valves open, so blood flows into the aorta and pulmonary artery because the pressure in the ventricles is higher than that in the vessels.
Read the paragraph on p91 all about valves.
Done!
What is cardiac output and how is it measured?
Volume of blood pumped by one ventricle of the heart in one minute
Cardiac output (dm^3min^-1) = heart rate (bpm) x stroke volume (cm^3)
Stroke volume is the volume of blood pumped out at each beat
The heart muscle is myogenic. What does this mean?
Its contraction is initiated from within the muscle, rather than by nervous impulses
How is the cardiac cycle controlled?
Wave of electrical activity spreads from the SAN across both atria - they contract
Wave passed through AVN after a short delay
AVN conveys a wave of electrical activity along the bundle of His, a series of specialised muscle fibres
BoH conducts the wave through the AV septum to the base of the ventricles, where it is then passed up the purkinje fibres and released at the end
The ventricles contract quickly at the same time, from the apex of the heart upwards
Read over pressure changes in the heart and heart disease.
Done!
