Physiology Flashcards
What is the electrical conduction system?
Specialised cardiac cells generate their own action potential/electical currents that stimulate the heart to contract and relax
They are electrically unstable - discharge impulses rapidly and regularly
What is the pathway for the electrical conduction system?
SA node
AV node
Bundle of his
Two bundle branches
Purkinje fibres
What happens when the SA node transmit a signal?
Atria contract
Transmitted to AV node
Why does the AV node delay electrical transmission?
To ensure atria have completely contracted
What is stroke volume?
The amount of blood the heart pumps out each ventricle each heartbeat
What is cardiac output?
The amount of blood the heart pumps out in one minute
What is the equation for cardiac output?
Stroke volume x heart rate
What are the three factors that regulate stroke volume?
- Preload
- Force of contraction
- Afterload
What is preload?
The amount of stretch in the cardiac muscle relates to the force they contract during systole
The stretch relates to how much blood is in the ventricle before the next contraction and this is dependent on venous return
The more the ventricles fill, the more the muscle will stretch resulting in stronger force of contraction which increases stroke volume and cardiac output
What is force of contraction?
Strong contractions increase stroke volume
Can be affected by hormones
Sympathetic nervous system increases force
What is afterload?
Refers to the pressure in the arteries that the ventricles must overcome in order to eject blood
An increase in arterial pressure increases afterload, making it more difficult for ventricles to pump blood
What sets the heart rate?
SA node
What can change heart rate?
NS activated -
Sympathetic nerves release noradrenaline which leads to excitation of SA
Parasympathetic releases acetylcholine and reduces impulses in the SA
What is BP?
Force or pressure which blood exerts of the wall of the blood vessels when the ventricles contract
What is a healthy BP?
120/80
What is the equation for BP?
Cardiac output x peripheral resistance
What is a baroreceptor?
Specalised receptors in carotid sinus and aortic arch
Sensitive to changes in BP
Sense impulses to the medulla oblongata
Provides a quick response
Short term BP regulation
What are chemoreceptors?
Nerve endings in the aortic arch and carotid arteries
Sensitive to change in oxygen, Co2 and pH
Receptors send impulses to medulla oblongata
Increases sympathetic activity
Increases cardiac output and BP
What are the 5 phases of the cardiac cycle? What happens at each?
- Artial diastol
- Artia and ventricles are relaxed
- Blood fills the atria
- Mitral and tricuspid valves are open due to low pressure in atria and ventricles
- Blood flows through to ventricle - Artrial systole
- SA node sends impulse
- Atria contract forcing blood into ventricles - Isovolumetric ventricular contraction
- Mitral and tricuspid valves close due to higher pressure in the ventricles
- Ventricles begin to stretch and contract
- Lub sound - Ventricular systole
- AV node sends impulse down bundle of his
- Ventricles contract
- Rise of pressure in ventricles
- Pulmonary and aortic valves open
- Ejection of blood - Ventricular disastole
- Ventricles relax and pressure falls
- Pressure is higher in arteries so aortic and pulmonary valves close
- Dub sound - Complete cardiac diastole
What is the normal heart rate?
60-100 bpm
What is the P wave?
SA node impulses travel to the atria
Atria contracts
What is the QRS wave?
Electrical impulses reach the ventricles
Both ventricles contract
What is the T wave?
Relaxation of ventricles
What is sytole?
Contraction
What is diastole?
Relaxation
What does the top and bottom number mean in BP?
Systole
_______
Diastole
What is depolarisation?
Contraction
What is repolarisation?
Relaxation
