ECG's and blood pressure Flashcards
Explain what the components of an ECG rhythm strip are
P wave- depolarisation of atrial contractile fibres produces P wave
P-Q interval- atrial systole- total time taken for the impulse to start in the SA node and to travel to the AV node to begin the ventricular depolarisation and contraction
QRS complex- ventricular contraction- blood pressure in ventricles is high, then falls once blood has been ejected
Q-T interval- total time from the start of ventricular systole to when myocardium around ventricles are fully depolarised
T wave- ventricles are repolarised, and T wave represents relaxation of this phase (ventricular diastole)
How does the nervous system control the normal cardiac rhythm?
controlled by the pacemaker and the conduction of impulses through the conduction system
-abnormalities of either system can disrupt normal sinus rhythm causing arrhythmias or dysrhythmias
How does the autonomic nervous system support the heart?
- sympathetic nervous system= raises the heart rate by stimulating the B1 adrenergic receptors
- parasympathetic nervous system= via the vagus nerve, lowering the heart rate
what is the SA node?
-a cluster of cells that is triggered by the autonomic nervous system, its impulse leads the contracting of the heart
-it is located at the top of the right atrium near the superior vena cava entrance
Explain how the SA node stimulates the heart beat
-generates electrical impulse which spreads across the two atria, to the myocardial cells and atrial contraction occurs
-the SAN can independently initiate an electoral impulse to create a heart beat, = pacemaker
How is the AV node involved in contracting the heart beat?
-located at the intertribal septum near the tricuspid valve
-the impulse that goes to the atria doesn’t reach the AV node as there is fibrous connective tissue that doesn’t conduct impulses well
-the function of the AV node is to momentarily delay the impulse to the ventricles, ensuring that the ventricles are full of blood before contracting, maintaining peak cardiac output
What is the bundle of His involvement in contracting the heart beat?
-from the AV node the impulse travels down the Bundle of His separating into the 2 branches which head down towards respective ventricles
-impulses travel faster down the left bundle branch as left myocardium is thicker, allowing both ventricles to contract at the same time
What is the purkinje fibres involvement in contracting the heart beat?
-the bundle branches end in the purkinje fibres which stretch deep into the myocardial tissue, therefore conducting the impulse through the myocardium
-myocytes contract together creating the ventricular contraction
How is the myocardium structured to help with muscle contraction?
-muscle contains myofibrils in bundles composed of 2 types of filament: myosin (thick) and actin (thin, composed of troponin and tropomyosin)
-interconnecting cross bridges along the myosin filament help the muscles to contract, whereby myosin flies over actin filaments using ATPase
-each myofibril consists of a chain of sarcomeres which can contract, containing both dark and light bands
What is the actual process of muscle contraction?
-initaited by intracellular calcium concentration and release of calcium ions from sarcoplasmic reticulum
-proteins troponin and tropomyosin regulate contraction according to calcium levels
-immediate energy is supplied by hydrolysis of ATP by actin-myosin ATPase
-done on the cross-bridges formed between myosin and actin filaments
What is cardiac output?
-The amount of blood pushed out of the left ventricle over a minute
-so this is stroke volume (volume of blood in one beat) multiple by heart rate (beats per minute)
How is the heart beat controlled neuraly?
the centre that regulates blood pressure is located in the brain, in the reticular formation of the medulla and in the pons
-the pons contains both the vasomotor and cardiac control centres
How does the cardiovascular centre control the heart beat?
-initiates impulses via the parasympathetic nervous system, through the vagus nerve (slows HR) and sympathetic nervous system through the spinal cord and peripheral sympathetic nerves (increases HR and contractibility)
-these control the rate of the heart beat and the force of contraction
Explain how baroreceptors monitor blood pressure
-pressure sensitive and located in the blood vessel walls in the carotid and aortic arteries
-respond to changes in blood volume as they are stretched
-baroreceptors respond to change where blood circulating volume is triggered by the pons and medulla to increase heart rate and trigger sympathetic nervous system to constrict the blood vessels
Explain how chemoreceptors monitor chemical blood changes?
-monitor blood levels of oxygen, carbon dioxide and hydrogen ions in the carotid and aortic bodies
-their main function is to regulate respiration to maintain the body’s pH level and oxygenation, but these can trigger vasoconstriction increasing the peripheral vascular resistance
