the heart Flashcards
describe how a heartbeat is initiated and coordinated (5 MARKS)
- SAN sends wave of electrical activity across atria causing atrial contraction
- non-conducting tissue prevents immediate contraction of ventricles
- AVN delays impulse whilst blood leaves atria
- AVN sends wave of electrical impulse down Bundle of His
- causing ventricles to contract from base up
closed valves
higher pressure in front of a valve forces it closed
open valves
higher pressure behind a valve forces it open
heart dissection precautions
- carry sharp objects pointing away from body
- disinfect instruments
- disinfect hands
- put organ/glove in a separate bin
which blood vessel carries blood at the lowest pressure
vena cava
LEFT VENTRICLE
- THICKER muscular wall than the right ventricle
- needs to contract powerfully to pump blood all around the body
RIGHT VENTRICLE
- THINNER muscular wall than the left ventricle
- only needs to pump blood to the lungs which are near
VENTRICLES VS ATRIA
ventricles have thicker walls than the atria as they have to push blood out the heart whereas the atria just need to push blood to the ventricles
ATRIOVENTRICULAR (AV) VALVES
- link the atria to the ventricles
- stop blood flowing back into the atria when the ventricles contract
SEMI LUNAR (SL) VALVES
- link the ventricles to the pulmonary artery and aorta
- stop blood flowing back into the heart after the ventricles contract
CORDS/VALVE TENDONS
attach the atrioventricular valves to the ventricles to stop them being forced up into the atria when the ventricles contract
1. VENTRICLES RELAX, ATRIA CONTRACT
- ventricles relax
- ATRIOVENTRICULAR VALVES are OPEN
- SEMI LUNAR VALVES are CLOSED
- atria contract DECREASING the VOLUME of the atria and INCREASING the PRESSURE in the atria
- this pushes blood into the ventricles
- slight increase in VENTRICULAR PRESSURE and CHAMBER VOLUME as the ventricles receive the blood from the contracting atria
2. VENTRICLES CONTRACT, ATRIA RELAX
- atria relax
- ventricles contract
- DECREASES ventricular volume, INCREASES pressure
- pressure in the ventricles is HIGHER than the atria
- forces AV valves CLOSED to prevent black flow
- pressure in ventricles is higher than in the aorta and pulmonary artery
- forces SL valves OPEN
- blood forced out arteries
3. VENTRICLES RELAX, ATRIA RELAX
- ventricles and atria relax
- HIGHER pressure in pulmonary artery and aorta forces the SL valves closed to prevent back flow
- blood returns to the heart and the atria fill again due to the HIGHER pressure in the pulmonary vein and vena cava
- INCREASES atria pressure
- as the ventricles relax, pressure of ventricles falls below the pressure of the atria so the AV valves open
- blood flows passively into ventricles
