control of heartrate Flashcards
how is cardiac output measured
cardiac output = heart rate (bpm) x stroke volume (cm3min-1 or dm3min-1)
define myogenic
contraction is initiated from WITHIN the muscle itself (without receiving external nerve impulses)
give the steps of how to control heart rate
- sinoatrial node is in wall of right atrium (commonly known as pacemaker)
- wave of electrical excitation spreads out from SAN across both atria causing them to contract
- atrioventricular septum prevents wave crossing to ventricles
- wave of excitation enters the atrioventricular node (AVN)
- AVN after a short delay conveys a wave of electrical excitation between ventricles along the purkyne tissue which collectively makes up the bundle of his
- bundle of his conducts the electrical wave through the atrioventricular septum to base of ventricle where bundle of his branches into smaller purkyne tissue
- wave of excitation is released from purkyne tissue, causing ventricles to contract quickly at the same time from the bottom of the heart upwards
Describe the autonomic nervous system
The autonomic nervous system controls the involuntary activities of internal muscles and glands. It has two branches sympathetic (stimulates effectors and speeds up responses) and parasympathetic (inhibits effectors and slows responses)
Explain the role of chemical receptors in the control of heart rate
Chemoreceptors in wall of carotid arteries and aorta are sensitive to changes in pH of blood that occur as a result of changes in carbon dioxide concentration (carbon dioxide lowers pH)
Chemoreceptors detect lowered pH and increase frequency of impulses to centre in medulla oblongata that increases heart rate
Centre increases frequency of impulses via sympathetic nervous system to SAN which increases rate of nerve impulses and therefore heart rate
Increased blood flow increases carbon dioxide removed by lungs and therefore carbon dioxide concentration and pH of blood is reduced
The change is detected by the chemoreceptors and impulses via the sympathetic nervous system decrease, decreasing heart rate
Explain the role of pressure receptors in the control of heart rate
Pressure receptors in the walls of the carotid artery and aorta detect high blood pressure and transmit more impulses to the centre in the medulla oblongata that decreases heart rate
Centre sends impulses via the parasympathetic nervous system to the SAN which decreases heart rate
Pressure receptors in the walls of the carotid artery and aorta detect low blood pressure and transmit more impulses to the centre in the medulla oblongata that increases heart rate
Centre sends impulses via the sympathetic nervous system to the SAN which increases heart rate
why is the delay between the AVN sending a wave of electrical excitation between the ventricles important?
the delay is important as it allows the flow of blood from atrium to ventricles
this ensures atria are fully empty before ventricles contract
why is it important that the wave of excitation causes ventricles to contract at the same time from the bottom of the heart upwards
helps with flow of blood as heart contracts as it pushes blood upwards out of the heart
where are the chemoreceptors in the heart
in the aorta, carotid arteries, medulla
what do chemoreceptors in the heart respond to
changes in blood glucose concentration and pH
where are the baroreceptors located in the heart
in aorta and carotid arteries
what do the baroreceptors in the heart respond to
high or low blood pressure
