5.5.9: Controlling heart rate Flashcards
What is the role of blood circulation?
- Transport of oxygen and nutrients,such as glucose, fatty acids and amino acids to the tissues.
- Removal of waste products, such as carbon dioxide from the tissues to prevent accumulation that may become toxic.
- Transport of urea from the liver to the kidneys.
- Distribute heat around the body or deliver it to the skin to be radiated away.
How do the requirements of the cells and tissues vary according to their level of activity?
-When you are being physically active, your muscle cells need more oxygen and glucose so that they can respire more, releasing more energy for contraction.
How does the function of the heart muscles affect its requirements?
- Your heart muscle cells also need more oxygen and fatty acids.
- All the muscles will also need to remove more carbon dioxide and heat.
How can heart function be modified?
- By raising or lowering the heart rate (beats per min.)
- Altering the force of the contractions of the ventricular walls.
- Altering the stroke volume (volume of blood pumped per beat).
What is the hearts pacemaker?
- The sinoatrial node (SAN)
- The SAN initiates waves of excitation that usually override the myogenic action of the cardiac muscle.
Describe the action of the SAN.
- A region of tissue that can initiate an action potential…
- which travels as a wave of excitation over the atrial walls, through the AVN…
- and down the Purkyne fibres to the walls of the ventricles…
- causing them to contract.
Which hormone does the heart respond directly to?
- The hormone adrenaline in the blood.
- This increases heart rate.
At rest, what is heart rate controlled by and what is the typical frequency of excitation?
- The SAN.
- This has a set frequency, varying from person to person, at which it initiates waves of excitation.
- The frequency of excitation is typically 60-80 per minute.
What is the frequency of the excitation waves create by the SAN altered by and how?
- Output from the cardiovascular centre in the medulla oblongata.
- Nerves from here supply the SAN,
- These nerves are a part of the autonomic nervous system.
- These nerves don’t initiate a contraction but they can affect the frequency.
How can output from the cardiovascular centre in the medulla oblongata increase the frequency of contractions in the heart?
-Action potentials sent down a sympathetic nerve (the accelerans nerve) cause the release of noradrenaline at the SAN. This increases heart rate.
How can output from the cardiovascular centre in the medulla oblongata decrease the frequency of contractions in the heart?
-Action potentials sent down the vagus nerve release acetylcholine, which reduces heart rate.
How can environmental factors affect heart rate?
- Input from sensory receptors is fed into the cardiovascular centre in the medulla oblongata.
- Some inputs increase heart rate, others decrease it.
How can stretch receptors in the muscles lead to an increase in heart rate?
- Stretch receptors in the muscles detect movement of the limbs.
- These send impulses to the cardiovascular centre, informing it that extra oxygen may soon be needed.
- This leads to an increase in heart rate.
Why do athletes stretch to ‘warm up’?
-This boosts heart activity in preparation for the race, ensuring that the muscles will have a good supply of oxygen.
How does sensory output from chemoreceptors lead to an increase in heart rate?
- Chemoreceptors in the carotid arteries, aorta and brain monitor the pH of blood.
- During exercise, muscles produce more carbon dioxide.
- Some CO2 reacts with water in the blood plasma forming carbonic acid.
- This reduces the pH of blood.
- Change in pH is detected by chemoreceptors.
- This sends action potentials to the cardiovascular centre.
- Heart rate increases.
