The Heart Flashcards
Name some common features of a
mammalian circulatory system.
- Suitable medium for transport, water-based to
allow substances to dissolve. - Means of moving the medium and maintaining
pressure throughout the body, such as the heart. - Means of controlling flow so it remains
unidirectional, such as valves.
Describe the properties of the heart?
The heart is surrounded by a protective sac called the pericardium. This allows the heart to beat smoothly as it reduces friction.
Relate the structure of the vessels to their function.
● Arteries have thick walls to handle high pressure
without tearing, and are muscular and elastic to
control blood flow.
● Veins have thin walls due to lower pressure,
therefore requiring valves to ensure blood doesn’t
flow backwards. Have less muscular and elastic
tissue as they don’t have to control blood flow.
Relate the structure of the chambers to
their function.
● Atria: thin-walled and elastic, so they can
stretch when filled with blood
● Ventricles: thick muscular walls pump blood
under high pressure. The left ventricle is
thicker than the right because it has to pump
blood all the way around the body.
Why are two pumps (left and right) needed instead of one?
To maintain blood pressure around the whole body.
When blood passes through the narrow capillaries of
the lungs, the pressure drops sharply and therefore
would not be flowing strongly enough to continue
around the whole body. Therefore it is returned to the
heart to increase the pressure.
Describe what happens during cardiac
diastole.
The heart is relaxed. Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves. This allows blood to flow into the ventricles. Pressure in the heart is lower than in the arteries, so semilunar valves remain closed.
Describe what happens during atrial
systole.
The atria contract, pushing any remaining blood into the ventricles.
Describe what happens during ventricular systole.
The ventricles contract. The pressure increases, closing the atrioventricular valves to prevent backflow and opening the semilunar valves. Blood flows into
the arteries.
Name the nodes involved in heart contraction and where they are situated.
● Sinoatrial node (SAN)= wall of the right atrium.
● Atrioventricular node (AVN)= in between the two atria.
What does myogenic mean?
The heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses.
Explain how the heart contracts.
● SAN initiates and spreads impulse across the
atria, so they contract.
● AVN receives, delays, and then conveys the
impulse down the bundle of His.
● Impulse travels into the Purkinje fibres which
branch across the ventricles, so they contract
from the bottom up.
Why does the impulse need to be
delayed?
If the impulse spread straight from the atria into the ventricles, there would not be enough time for all the blood to pass through and for the valves to close.
What does diastole mean?
When the heart relaxes.
What does systole mean?
When the heart contracts.
What happens when there is high pressure in the valve?
The valve opens (prevents backflow)
What happens when there is low pressure in the valves?
The valve shuts. (Prevents backflow)
Why do we need a transport system?
Low SA: V ratio so materials needed from the environment can’t be received by body surface alone
- High respiratory rate (very active)
What is the vein that pumps deoxygenated blood in the right atrium?
The vena cava
What is the first chamber that deoxygenated blood travels through?
The right atrium
What is the role of atrioventricular valves?
They prevent blood from flowing back into the atria from the ventricles.
What is the role of the semi-lunar valves?
- They prevent blood from flowing back into the right ventricle from the pulmonary artery.
- They also prevent blood from flowing back into the left ventricle from the aorta.
What direction of blood flow is halted by the semi-lunar valves?
Back into the ventricles.
Simply state the steps in the cardiac cycle
- Atrial contraction
- Ventricular contraction
- Relaxation of both atria and ventricles.
What happens to the pressure in the atria when it contracts?
The pressure increases
What happens when the atria relax and ventricles contract
The pressures in the atria decreases.
What happens when both the atria and ventricles relax?
When the atria relax and the ventricles contract, the pressure in the atria decreases.
What happens when the ventricles contracts?
Pressures increase dramatically. The pressure increases considerably more than when the atria contract.
What happens when the atria contract?
The pressure increases considerably more than when the atria contract.
What happens when both the atria and the ventricle relax
When both the atria and the ventricles relax, there is a slight increase as the ventricles fill with blood again.
What happens to the volume when the atria contracts
The volume in the atria decreases
What happens to the volume when the atria and then ventricles contract?
The volume in the atria increases again.
What happens to the volume when the atria and the ventricles relax?
There is a slight decrease when blood flows into the ventricles from the atria.
What happens to the volume when the atria contract
The volume in the ventricles increases slightly as they fill with blood.
What happens to the volume when the ventricles contract
the volume decreases dramatically. The volume decreases considerably more than when the atria contract.
What happens to the volume when both the atria and the ventricles relax?
The volume increases as the ventricles expand again.
What causes a significant decrease in volume in the ventricles?
Ventricular contraction
What is the Aorta?
The major artery takes blood to the body.
Four ways the structure of the aorta is related to its function?
- Elastic tissue to allow stretching/recoil / smoothes outflow of blood / maintains pressure;
- (Elastic tissue) stretches when the ventricles contract
Recoils when the ventricle relaxes; - Muscle for contraction / vasoconstriction;
- Thick wall withstands pressure OR stop bursting;
- Smooth endothelium reduces friction;
- Aortic valve / semilunar valve prevents backflow.
What is the renal artery?
The main artery carries oxygenated blood to the kidneys from the heart.
What is the renal vein?
The main vein carries deoxygenated blood away from the kidneys back to the heart.
What causes the significant decrease in volume in the ventricles?
Ventricular contraction
Simple stages of the cardiac cycle
- Contraction of the aorta
- Blood is forced into the ventricles
- Contraction of the ventricles
- The atrioventricular valves shut
- Blood is forced out of the heart
- The semi-lunar valves shut
- Relaxation of the ventricles and the aorta
