1.2 Cardiovascular System

Pathway of Blood:

1) The walls of the right atrium squeeze and push the blood downwards to the right ventricle

2) The ventricles contract and the pulmonary artery then transports deoxygenated blood to the lungs

3) Blood is oxygenated (due to gas exchange) at the lungs

4) The pulmonary vein transports oxygenated blood back to the left atrium

5) Blood is pushed downwards and collects in the left ventricle

6) Oxygenated blood is the ejected and transported to the body (muscles) through the aorta

7) The deoxygenated blood is returned to the heart through the vena cava

Neural Control

• Chemoreceptors

• Baroreceptors

• Proprioceptors

Neural Control - chemoreceptors

• in aorta and carotid arteries

• detects a decrease in blood pH due to an increase in lactic acid and CO2

Neural Control - baroreceptors

• in blood vessel walls

• informs CCC of increased blood pressure

Neural Control - proprioceptors

• in muscles, tendons, and joints

• informs the CCC that movement has increased

Intrinsic Control

• Temperature

• Venous Return

Intrinsic Control - temperature

affect blood viscosity and and the speed of nerve impulse transmission

Intrinsic Control - venous return

affects the stretch in ventricular walls, force of contraction, and so stoke volume

Hormonal Control

• Adrenaline - released from the adrenal glands and increase SV and HR

• Noradrenaline - released from the adrenal glands and increases SV and HR

Regulation of HR during exercise

• Controlled by the autonomic nervous system (ANS) and determines the frequency of firing of the SA node

• Located in the medulla oblongata - brain

• Responsible for regulating the heart via motor nerves

Sympathetic Nervous System

• accelerator nerve

• during exercise

• increases heart rate

Parasympathetic Nervous System

• vagus nerve

• during recovery

• decreases heart rate

Myogenic

Generates its own impulse

Conduction System

1. SA Node - generates an electrical impulse, causing atrial systole

   • SA Node is known as the pacemaker and causes the hearts walls to contract

2. AV Node - collects the impulse and delays it by 0.1 seconds to allow the atria to finish contracting

3. Bundle of His - located in the septum, and splits the impulse in 2, and is ready to be distributed to the ventricles

4. Bundle Branches - carries the impulses to the bases of each ventricles

5. Purkinje Fibres - distributes the impulse through the ventricle walls, causing them to contract

Atrial Systole

• Atria contract

• Forces blood into the ventricles

• AV valves remain open

• Semilunar valves are closed

Ventricular Systole

• Ventricles contract

• AV valves close

• Semilunar valves open

• Blood is forced out the ventricles and into the arteries leaving the heart

Diastole

• Relaxation of the atria and ventricles

• Blood passively flows through atria and into the ventricles

• AV valves are open - blood can move from atria to ventricles

• Semilunar valves are closed

Heart Rate

number of beats per minute

Heart rate - untrained at rest

70-72

Heart rate - trained at rest

50

Heart rate - untrained at sub-maximal

100-130

Heart rate - trained at sub-maximal

95-120

Heart rate - untrained at maximal

220-age

Heart rate - trained at maximal

220-age

Stroke Volume

volume of blood ejected from the left ventricle per beat

Stroke volume - untrained at rest

70

Stroke volume - trained at rest

100

Stroke volume - untrained at sub-maximal

100-120

Stroke volume - trained at sub-maximal

160-200

Stroke volume - untrained at maximal

100-120

Stroke volume - trained at maximal

160-200

Cardiac Output

total volume of blood ejected from the left ventricle per minute

Cardiac output - untrained at rest

5

Cardiac output - trained at rest

5

Cardiac output - untrained at sub-maximal

10-15

Cardiac output - trained at sub-maximal

15-20

Cardiac output - untrained at maximal

20-30

Cardiac output - trained at maximal

30-40

Heart rate response to sub-maximal exercise

Anticipatory rise, Rapid increase, Steady plateau, Rapid decrease

Heart rate response to maximal exercise

Anticipatory rise, Rapid increase, Slower increase, Rapid decrease, Slower decrease

Stroke volume response to exercise

Increases proportionately to exercise intensity until a plateau is reached at around 40-60% of working capacity

• increased venous return

• the Frank-Starling mechanism (increased venous return - increased SV - walls stretch more - more forceful contractions)

Frank-Starling Mechanism

• dependent on venous return

• more blood returns to the heart during exercise

• causes the atria to stretch more than at rest

• forces more blood into the ventricles - they stretch more

• recoil produces a larger contraction, forcing more blood out the heart per beat

• increases stroke volume

Why does stroke volume plateau during exercise

Plateaus because increased HR towards maximal intensity doesn't allow enough time for the ventricles to fully fill during diastole

Cardiac output response to exercise

increases in line with exercise intensity and will plateu during maximal exercise

Recovery

• SV is maintained during early stages of recovery as HR rapidly decreases

• Maintains blood flow and the removal of waste products

• Lowers stress and workload on cardiac muscle

• In recovery, there is a rapid decrease of CO followed by a slower decrease back to resting levels 

Arteries

• carry oxygenated blood from the heart to organs

• high blood pressure

• large layer of smooth muscle and elastic tissue

• vasoconstrict and vasodilate - control blood flow and pressure

Capillaries

• walls are one cell thick

• gas exchange takes place

• oxygen passes through the walls and into the tissues

• CO2 passes from the tissue into the capillary walls

Veins

• carry deoxygenated blood from muscles and organ to the heart

• thin walls

• smooth layer of muscle - vasoconstrict and vasodilate

• blood under low pressure

• one way pocket valves - prevent backflow of blood

Venous return mechanisms

• pocket valves - prevent backflow of blood - located in the veins

• smooth muscle - vasoconstricts and pushes blood back towards the heart - vein walls

• gravity - gravity aids blood in the upper body

• muscle pump - veins are located between skeletal muscle - surrounding muscles squeeze on veins and push blood back to the heart

• respiratory pump - returns blood in the thoracic cavity - changes the pressure between high and low during exercise - pushes blood back to the heart

Cardiovascular drift

• occurs during exercise in the heat

  • sweating

  • lose fluids

  • decreased blood plasma volume

  • blood becomes more viscous

  • SV decreases

  • HR increases to maintain CO

Blood pooling

• blood builds up in the pocket valves, and pools - often in lower body

• occurs after going from exercise to rest with no cooldown

• can be prevented by performing a cooldown after exercise