Autumn assessment 1 - cardiovascular system, respiratory system, cardio-respiratory system 3.1.1.1, 3.1.1.2, 3.1.1.3

conduction system

a group of specialised cells located in the walls of the heart which sends electrical impulses to the cardiac muscle, causing it to contract (heartbeat)

how the heart beats - autonomous

electrical impulse is sent to the sinoatrial node (stage 1) which is a small mass of cardiac muscle that generates the heart beat - causes contraction

then send to the atrioventricular node (stage 2) this node relays the impulse between the upper and lower sections of the heart.

this node relays the impulse between the upper and lower sections of the heart which is then sent to bundle branches (bundle of his) (stage 3)

this impulse is then sent to purkinje fibres which are fibres that conduct impulses in the walls of the ventricles (stage 4)

the cardiac cycle

two active stages of conduction imbetween each impulse, each diastole - lubdub

atrial diastole - blood passively fills both atria

ventricular diastole - rising blood pressure against AV valves forces blood through in the ventricles

—> 0.5 secs

atrial systole - (contract and blood at high velocity) - the sinoatrial node contracting causing the left and right atria to force the remaining blood into ventricles

ventricular systole? - impulse travels - AV node - bundle of his - purkinjie fibres causing both ventricles to contract ejecting out the blood.

neural control mechanism

Involves the parasympathetic system and the sympathetic nervous system

nervous system is made up of two parts - Central nervous system (CNS) which consists of the brain of the brain and the spinal cord, and the peripheral nervous system which consists of nerve cells that transmit information to and from the CNS

These two systems are…

coordinated by the cardiac control centre located in the medulla oblongata of the brain

sympathetic nerve impulses are sent to the sinoatrial node and there is a decrease in parasympathetic nerve impulses so that heart rate increases

cardiac control centre is stimulated by chemoreceptors, baroreceptors and proprioceptors

Chemoreceptors

located = carotid arteries, aortic arch

detects= increase in blood acidity (pH) when exercising due to co2 and lactic acid

(chemical)

• chemoreceptors detect increase in co2 and the role of co2 is very important in controlling heart rate. an increased concentration of co2 in blood stimulates the sympathetic system so that the heart will beat faster

sympathetic nervous system

stimulates heart to beat faster

parasympathetic system

returns heart back to resting level

baroreceptors

located = aortic arch, carotid sinus, heart and blood vessels

detects = changes in blood pressure (above or below ‘set point’)

decrease in blood pressure results in increased breathing rate (neural)

• contain nerve endings that respond to the stretching of the arterial wall which are caused by changes in blood pressure - they establish a ‘set point’ and above or below this messages are sent to the medulla in the brain

• increase in arterial pressure causes increase in stretch of baroreceptor sensor which results in decrease of heart rate

• this then works conversely

• at the start of exercise, baroreceptor set point increases which is important as the body does not want heart rate to slow down as this would negatively affect performance

proprioceptors

located = muscles, tendons and joints

detects= increase in muscle movement when exercising

(neural)

when increase in muscle movement detected, these sensory nerve endings send impulse to the medulla which then sends impulse through sympathetic system to the SA node to increase heart rate romalh

hormonal control mechanism

release of adrenaline during exercise is known as hormonal control

• adrenaline is a stress hormone released by sympathetic nerves and cardiac nerve during exercise

• it stimulates the SA node (pacemaker) which results in both speed and force of contraction to increase - thereby increasing cardiac output - more blood to working muscles - more oxygen

Arteriovenous difference (AVO2

difference between the oxygen content in the arterial blood and venous blood

• at rest the A-VO2 difference is small

• during exercise the A-VO2 is big as the muscles use a greater percentage of the oxygen available

• training increases A-Vo2 difference as elite athletes can extract more oxygen from the blood

starlings law

greater diastolic filling → causes greater cardiac muscle stretch → causes more force of contraction → increased ejection fraction → increased SV

venous return=stroke volume

venous return

rate at which blood returns back to the heart

venous return

cardiac output

heart rate X stroke volume