Topic 6C: Control of Heart Rate Flashcards
The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN).
Describe how. [5]
- SAN sends wave of electrical activity (across atria) causing atrial contraction;
- Non-conducting tissue prevents immediate contraction of ventricles;
- AVN delays (impulse) whilst ventricles fill;
- (AVN) sends wave of electrical activity down Bundle of His and Purkyne fibres;
- Causing ventricles to contract from base up
Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in this process. [4]
- Chemoreceptors (in aorta/carotid artery) detects fall in pH;
- (chemoreceptors) send more impulses to medulla;
- (medulla then sends) more impulses to SAN;
- By sympathetic nerves/neurones
After exercise, heart rate decreases.
Describe the role of receptors and of the nervous system in this process. [4]
- (at rest) chemoreceptors (in aorta/carotid artery) detect increase in (blood) pH;
- Less impulses sent to medulla;
- (medulla then sends) more impulses to SAN;
- By parasympathetic nerves/neurones
Explain how a rise in blood pressure results in a decrease in the rate of heartbeat. [4]
- Pressure receptors (in aorta/carotid artery) detect rise in blood pressure;
- (pressure receptors) send more impulses to medulla;
- (medulla then sends) more impulses to SAN;
- By parasympathetic nerves/neurones
Explain how a fall in blood pressure results in an increased heart rate. [4]
- Pressure receptors (in aorta/carotid artery) detect fall in blood pressure;
- Send less impulses to medulla;
- (Which then sends) more impulses to SAN;
- By sympathetic nerves/neurones
Some drugs inhibit the transmission of nerve impulses to the heart. Explain how these drugs reduce high blood pressure. [2]
- Inhibits impulses along sympathetic nerves/neurones;
- (therefore) SAN not stimulated (so much) so heart rate lowers
Explain how the atrioventricular valve maintains a unidirectional flow of blood. [2]
- Pressure in atrium is higher than in ventricle causing valve to open;
- Pressure in ventricle is higher than in atrium causing valve to close
When a wave of electrical activity reached the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay. [2]
- Allows ventricles to fill;
- Before ventricles contract
When the heart beats, both ventricles contraction at the same time.
Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN.
- Electrical activity only through Bundle of His;
- Wave of electrical activity passes through both ventricles at the same time
Give two ways in which people with type 1 diabetes control their blood glucose concentration. [2]
- Treat with insulin (injection);
- Diet
Explain why increased cardiac output is an advantage during exercise. [3]
- More respiration;
- Increases O2 supply (to muscles);
- Increases glucose supply (to muscles);
- Increases CO2 removal (from muscles);
- Lactate removal;
- Increases heat removal (from muscles)
Mark point 1 + 2 others
Explain why increased cardiac output is an advantage during exercise. [3]
- More respiration;
- Increases O2 supply (to muscles);
- Increases glucose supply (to muscles);
- Increases CO2 removal (from muscles);
- Lactate removal;
- Increases heat removal (Frim muscles
Mark point 1 + 2 others
Describe the route taken when electrical impulses are transmitted from the sinoatrial node to the muscles of the ventricles. [2]
- Through cardiac muscle;
- To atrioventricular node;
- Along Bundle of His
The pulse felt in the artery in the wrist can be recorded and used to measure heart rate.
Suggest why the pulse felt can be used to measure heart rate. [2]
- Caused by pressure;
- From (one) contraction of (left) ventricle
