Higher Human Biology Unit 2 Physiology and Health 3. Cardiac conducting system and blood pressure

 What is the cardiac cycle?  What is the difference between systole and diastole?  What effect does a change in pressure have on the Atrioventricular valve?  What effect does a change in pressure have on the semi lunar valve? What do I remember?

 What is the name and location of the hearts ‘pacemaker’?  What is the function of the hearts ‘pacemaker’?  What is the location and purpose of the atrioventricular node (AVN)?  What is an electrocardiogram?  How is the heart controlled by the nervous system? What do I need to know?

 Name the part of the brain that is involved in controlling heart and breathing rate?  What are the two parts of the autonomic nervous system?  What effect does the sympathetic nervous system have on heart rate?  What effect does the parasympathetic nervous system have on heart rate? Revision!!

What is the hearts pacemaker?  The sino-atrial node (SAN)  Found on wall of right atrium  Area of auto rhythmic cells that exhibit spontaneous contraction

 The sino-atrial node (SAN) controls the rate of contraction of the cardiac muscle.  Initiates electrical impulses to contract at specific rate  A wave of excitation spreads from SAN through the atria causing simultaneous contraction  Works automatically  Can be externally controlled by other factors What is the function of the SAN?

 Located at base of atria  The atrio-ventricular node (AVN) picks up the electrical impulse sent from the SAN  A bundle of conducting fibres continue to transmit impulse from AVN to each ventricle  Contraction occurs from (apex) centre upwards  Squeezing blood out of each ventricle What is the location and purpose of the AVN?

 The SAN creates impulse causing atria to contract simultaneously  AVN picks up impulse and transmits to ventricles causing them to contract slightly later  The later contraction of ventricles allows the blood to flow from atria to ventricle before they are emptied  3D Heart animation 3D Heart animation Co-ordinating contraction

Two factors can affect heart rate:  Nervous control  Hormonal control How does the nervous system control the heart?

Role of the nervous system The medulla regulates the rate of the SAN via the sympathetic and parasympathetic branches of the autonomic nervous system  Sympathetic  Cardio-accelerator centre of medulla sends impulses via  Sympathetic nerve using  Norepinephrine  Heart rate increases  Parasympathetic  Cardio-inhibitor centre of medulla sends impulses via  Parasympathetic nerve using  Acetylcholine  Heart rate decreases System is antagonistic If number of sympathetic impulses reaching the SAN is greater than that of parasympathetic then heart rate increases and vice versa

Hormonal Control  Exercise or stress can have an influence on heart rate  Adrenaline temporarily over rides normal control of heart rate  As adrenaline concentration reaching SAN increases heart rate also increases  Rev: Preparation for “fight or flight”

 What is the name and location of the hearts ‘pacemaker’?  What is the function of the hearts ‘pacemaker’?  What is the location and purpose of the atrioventricular node (AVN)?  How is the heart controlled by the nervous system? What do I know?