The Cardiac Control Centre and factors affecting it

Neural factors affecting the CCC

Baroreceptors, chemoreceptors and proprioceptors

Where the CCC is found

The medulla oblongata

Baroreceptors

found in the arteries, detect changes in blood pressure

Proprioceptors

Found in muscles, tendons and joints, detect body and limb movement

Chemoreceptors

found in the blood vessels, detect changes in CO2 and pH levels in the blood

Hormonal factors affecting the CCC

Adrenaline, noradrenaline

Adrenaline

increases HR by stimulating the adrenergic receptors and SA node

Noradrenaline

released during stressful situations

Intrinsic factors affecting the CCC

when core temp is too high, HR increases to decrease blood flow to the skin

Venous return

Volume of blood returning to the heart

Cardiovascular drift

an increase in HR despite working at the same intensity. It occurs after 20 minutes of exercise.

Reasons for cardiovascular drift (3)

Sweating - leads to a loss of fluid, and therefore dehydration

Plasma loss - makes blood more viscous which therefore decreases stroke volume and venous return

Hot conditions - exaggerates the effects of cardiovascular drift

Starling's law of the heart

Stroke volume increases due to increased volume of blood filling ventricles before contracting, which increases muscle fibres. The more the cardiac muscle is stretched, the stronger the contraction.

5 ways to support venous return

• Skeletal muscle pump

• Respiratory pump

• Valves

• Smooth muscle

• Gravity

Skeletal muscle pump

Blood vessels squeeze as muscles around them contract, which forces blood against gravity

Respiratory pump

Pressure gradient between thoracic cavity and abdominal cavity forces blood through veins

Valves

prevent back flow of blood

Smooth muscle

constricts in order to increase venous return

Gravity

Aids the VR of blood flow from areas ABOVE the heart

Vascular shunt mechanism

the redistribution of blood flow from non-essential organs to the working muscles during exercise. It is controlled by the vasometer centre in the medulla oblongata.

precapillary sphincters

Smooth muscle surrounding the intersection between arterioles and capillaries that regulate vasoconstriction/dilation

Affinity

how easily haemoglobin binds to oxygen

Oxyhaemoglobin disassociation curve explained (3)

• The affinity of haemoglobin for O2 reduced as partial pressure of O2 decreases

• This means O2 is closely bound to haemoglobin near the alveoli and less closely bound near the muscles

• This allows O2 to be taken into the blood near the lungs and redistributed from the blood to the muscles

Oxyhaemoglobin disassociation curve graph (axes and relationship)

y-axis: % saturation of haemoglobin with oxygen
x-axis: Partial pressure of oxygen
relation is a steep upwards curve that plateaus halfway

Bohr shift

Drop in pH lowers the affinity of haemoglobin for O2