IB biology: topic 6: blood and the heart

what is the SAN?

sinoatrial node

what is the broader term for the tricuspid and bicuspid valves?

atrioventricular valves

where is the sinoatrical node found?

in the right atrium (nearer the top)

where is the atrioventricular node found

in the right atrium (nearer the bottom)

what are the purkinje fibres?

nerve fibres that spread from the apex of the heart, upwards towards the top of the ventricles

what is the bundle of His?

a nerve bundle that runs down the septum of the heart, to the apex

what is the AVN?

atrioventricular node

what is a key feature of the electrical conductivity of the heart?

there is a delay between atrial and ventricular contractions - two heart sounds (beats)

what does the delay in heart beats/contractions allow for in the ventricles?

allows time for the ventricles to fill with blood after atrial contractions, maximising blood flow

describe the electrical conduction of the heart

the SAN sends out an electrical impulse that stimulates the contraction of the heart muscle tissue,

the impulse causes the atria to contract and stimulates the AVN to send signals to down the septum via the bundle of His,

the bundle of His passes this impulse to the Purkinje fibres, causing ventricular contraction

the contraction of the heart is myogenic - what does this mean?

the signal for cardiac compression arises within the cardiac tissue itself

what is the role of the sinoatrial node? (SAN)

primary pacemaker - controls the rate at which the heart breats

what is fibrillation?

interference of the natural pacemakers in the heart, causing irregular and uncoordinated contractions of the heart muscle

what is defibrillation?

a controlled electrical current is used to re-establish a normal sinus rhythm.

how does the sinoatrial node (SAN) initiate heart muscle contractions?

its cells membranes depolarise as the cell contracts, which causes depolarisation of adjacent cells and so further contraction.

what is myocardium?

the muscle that the SAN and other heart muscle in made of

what features allow the SAN to simultaneously contract and send out electrical singals?

interconnections between adjacent fibres,

branching of fibres

describe the process of blood flow through the heart, including the times of contractions and key events

blood is pumped from the atria to ventricles between 0 and 0.1s. ventricles start to contract at 0.1s.

AV valve closes at 0.1s as atrial pressure falls below ventricular pressure.

SL valve opens at 0.15s as ventricular pressure rises above arterial pressure.

SL valve closes at 0.4s as ventricular pressure falls below arterial pressure.

blood is pumped from the ventricle to artery from 0.15 to 0.4s

what two nerves run from the brain to the heart?

accelerator nerve and vagus nerve

what part of the brain controls the heart beat?

the brain stem

what is the role of the accelerator nerve?

releases epinephrine at SA node which increases heart rate

what is the role of the vagus nerve?

releases acetylcholine at SA node which decreases heart rate

in what environments does the accelerator nerve act?

low blood pressure, low oxygen levels, low pH

in what environments does the vagus nerve act?

high blood pressure, high oxygen levels, high pH

what response causes a change in heart rate?

fight or flight response to external stressor