Cardiovascular System Lesson (A Level PE) - Part 2

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The hormonal, neural and chemical regulation of responses during physical activity and sport.

Anticipatory rise
 Prior to exercise commencing, heart rate increases due to a release of adrenaline.
 This helps prepare the body for exercise as it causes an increase in oxygen supply to the muscles.
 It is also known as the fight or flight response.
 Adrenaline has the effect of increasing the speed and quality of the impulses sent via the nervous system that regulate cardiac contractions.

Redistribution of blood (vascular shunting, vasoconstriction, vasodilation)
 There is higher demand for blood during exercise therefore blood vessels supplying working muscles dilate (expand) to increase flow to their destinations.
 Vessels to lower priority tissue constrict, restricting flow to their destinations.
 Pre-capillary sphincters are rings of tissue at the entrance to a blood vessel. When contracted, they lock off the proceeding vessel and there is limited blood flow to the areas that vessel supplies.

Cardiac conduction system
 The heart is myogenic, generating its own electrical impulses to make it contract.
 The sinoatrial node is responsible for this. Impulses generated spread across both atria, causing contraction.
 The impulse reaches the atrioventricular node, which delays it slightly, before passing it down the Bundle of HIS and into the purkinje fibres.
 These spread the impulse in the myocardium surrounding the ventricles, causing contraction.

Sympathetic and parasympathetic
 The Cardiac Control Centre resides within the Medulla Oblongata.
 This uses the Sympathetic Nervous System and the Para-sympathetic Nervous System to regulate heart rate.
 When exercise commences the SNS passes neuron transmissions at a higher rate via the conduction system of the heart to increase the frequency and force of its contractions.
 The PNS is then used to bring heart rate back to resting levels by transmitting impulses of smaller velocity and magnitude.

Carbon dioxide
 Aerobic respiration produces CO2 as a by-product that when dissolved in blood and surrounding tissue forms carbonic acid. Acidity reduces a muscles ability to function, causing the performer to experience fatigue.
 When oxygen levels drop or carbon dioxide levels rise or blood acidity rises, chemoreceptors are there to detect it.
 They relay this information to the medulla oblongata which then uses appropriate motor neurons, be it the SNS or PNS, to regulate heart rate and contractile force.
 Chemoreceptors are located in the heart, coronary arteries and medulla oblongata.