Homeostasis

Question 1

Describe the pathway of the wave of electrical excitation through the heart.

Answer 1

the sinoatrial node (SAN) initiates the heartbeat by stimulating the atria to contract
a layer of collagen fibres prevents direct electrical flow from atria to ventricles
the atrioventricular node (AVN) picks up the electrical activity from the SAN
it causes a slight delay
the bundle of His receives electrical activity from the AVN and conducts the wave of excitation to the apex/base of the heart
the Purkyne fibres branch off the bundle of His, causing the right and left ventricles to contract from the bottom upwards

Question 2

How does increased blood pressure impact on heart rate

Answer 2

• This increase in blood pressure is detected by pressure receptors (baroreceptors) in the wall of the aorta and the carotid artery (carotid sinus).
• If the blood pressure increases too far above normal, these pressure receptors send more impulses to the medulla stimulating the cardioinhibitory centre and inhibiting the cardioaccelerator centre.
• More impulses are sent from the cardiac centre along parasympathetic neurones to the SAN causing a decrease in heart rate preventing the heart from overworking.

Question 3

How can exercise impact heart rate

Answer 3

• Increasing rates of respiration increase carbon dioxide concentration
• Dissolves in the blood producing carbonic acid - lowering blood pH by increasing hydrogen ions
• Chemoreceptors in aortic and carotid bodies are simulated
• They transmit more impulses to the cardiac centre which transmitting more impulses to the SAN via the sympathetic neurones - increase heart rate
• Provides more oxygen required for respiration and removes excess carbon dioxide
• When the pH of the blood lowers after exercise fewer impulses are transmitted from the chemoreceptors to the medulla reducing heart rate