Week 5
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What is the role of Acetylcholine in Cardiac regulation ?
• Slows heart rate by delaying sinus discharge
Name the two ways in which parasympathetic stimulation slows heart rate
• Via Acetylcholine release - Vagus Nerve stimulation
Sympathetic nerve fibres innervate the ________ and the ________
SA node Ventricles
Sympathetic nervous system releases __________ and activates ___________ receptors in the heart
Noradrenaline Beta-Adrenergic
Where is the cardiac control centre ?
Medulla Oblongata
What are the two factors affecting blood flow
• Pressure gradient between the two ends of the vessel 2. Inversely to the resistance encountered to fluid flow
What are the three factors determining resistance to blood flow ?
• Blood thickness/viscosity • Length of the conducting tube • Vessel radius
Name local factors causing vasodilation
• decreases tissue O2 • local increase in blood flow • Body temp. • CO2 levels • acidity • NO Production
Name three factors that stimulate NO production as a result from increased blood flow
Signal chemicals Sheer stress Vessels stretch
What is considered a reflection of the functional capacity of the CV system ?
Cardiac Output
At rest, why does CO vary ?
Emotional conditions that alter cortical outflow to Cardioaccelorator nerves
Name two factors decreases HR in Endurance athletes
• Increased Vagal Tone 2. Decreased sympathetic drive
Name 3 factors contributing to increased stroke volume in endurance athletes
• Increased blood volume • Increased ventricular volume • Increased compliance of left ventricle
What 2 mechanisms aid in venous return
Skeletal muscle pump Respiratory (abdomino-thoracic) pump
Define Cardiovascular Drift
Gradual time-dependent downward drift in several CV responses
At rest, Roughly 80% of cardiac output is distributed to where?
Digestive tract, liver, spleen, brain, kidneys
What type of muscle with receive most of the blood distribution during exercise
Fibres with higher oxidative capacity/tendencies
What is blood O2 reserve and how much is there?
Extra O2 circulating above the requirement at rest Roughly 750 ml
A ____L increase in blood flow accompanies a ___L increase in O2 consumption
5-6 Litres 1Litre
Aterial-Venous O2 difference during exercise = ?
50ml of O2 per litre of blood perfusing tissue-capillary bed
Expanding a-VO2 functions to?
Increase O2 consumption for energy
How is a-vO2 expanded
Extracting more O2 from blood
How does arterial blood O2 concentration change during exercise
Varies little from the 200ml range
How does the mixed-venous O2 content change with exercise
Decreases progressively with increased intensity