The Heart 2 Flashcards
What does the heart posses?
What is the heart refers to as
It possess autorythymicity - which means it generate its own ELECTRICAL impulses and beats independently of nervous or hormonal control.
It’s supplied by sympathetic and parasympathetic nerve fibres which increase and decrease respectfully.
What hormone supplies the heart
In addition the heart responds to a number of circulating hormones including adrenaline and thyroxine
What generate the regular impulses of the heart
The sinoatrial node(SA) generate these regular impulse because they are electrical unstable
The instability leads them to discharge(depolarise) and this is followed by a recovery(reporilisatio)
This instability lead them to discharge again
The SA node are found near the opening of the superior vena cava
Which node discharge faster
What set the heart rate
The SA node discharged faster than any part of the heart
The SA node set the heart rate and it is known as pacemaker of the heart
What causes atrial to contract
Firing of SA node triggers the atrial contractions.
What does the Atrioventicular (AV) node does?
Where is SA node located
The AV node has a secondary pacemaker function and takes over this role if there is a problem with the SA node itself,
It’s intrinsic firing rate however is slower than that set by SA node (40-60 bpm)
It is located in the wall of the septum near the atrial ventricular valves
What does AV node do
The AV node forward electrical impulses to the ventricle
Electrical impulses spread from the SA node through the atrial to the AV node
The AV node forward electrical impulses to the ventricle
What is the AV bundle
The atriaventicular bundle is known as AV bundle or bundle of His
The AV bundle is from the AV node and is made up of special fibers.
It is divided into the left and right bundle and it is found in the ventricular myorcadium Which the bundle breaks up into fine fibres known as the perkinje fibers
Perkins j fibers transmit electrical impulses from the AV node to the apex of the the myorcadium where wave of ventricular contraction begins
Describe the nerve supply to the heart
The heart is influenced by autonomic sympathetic and parasympathetic nerves which originates from the Cuddy vascular Center in the medulla oblongata
The Vegas nerve which is known as the (parasympathetic)supplies mainly the SA and AV node and atrial muscles
Virgo stimulation reduces the rate of S a node firing decrease in the rate and force of heartbeat
Sympathetic nerves supply the SA and AV node and the myorcadium and simulation increases the rate of the force of the heartbeat
What is the heart influence by
The heart is influenced by sympathetic and parasympathetic nerves which originate from the cardiovascular centre in the medulla oblongata
What is the Vagus nerve
The Vegas nerve is known as the parasympathetic nerves. It’s supplies mainly the SA and AV node and atrial muscle. The vagal stimulation
Reduces the rate Of SA node firing, Decrease the rate and force of the heartbeat
Sympathetic nerves supply the SA and AV node and myocardium and simulation increases the rate and force of the heartbeat.
Stages of cardiac cycle
Atrial systole- contraction of the atrial
Ventricular systole contraction of the ventricles
Complete cardiac diastole - relaxation of the atria and ventricles
What are the main factors affecting heart rate
Autonomic activity Circulation hormones Activity and excercise Gender Age Temperature Baroreceptor reflex Emotional state
How many % if the ventricles filling before contraction
70% of the ventricles fill by the help of gravity without atria contraction
What is the role of SA and Av node in cardiac cycle
The SA node triggers a wave of contraction that spreads over the myocardium of both atria, emptying the atria and completing ventricular filling (atria systole 0.1 second )when the electrical impulses reach the AV node it’s a slowed down delaying atriaventicular a
transmission.
This allow atria to finish emptying into ventricles before the ventricles begin to contract
After this brief delay the AV node tragus trigger it’s on electrical impulse which quickly spreads to Ventricular muscle via the AV bundle the bundle branches and purkinje fibres. This results in the wave that sweeps upwards from the Apex of the heart and across the walls of the ventricles pumping the blood into the pulmonary artery and the iota ventricular ventricular( systole is 0.3seconds)
The high pressure generated during ventricular contraction forces the atriaventicular valves to close preventing back flow of blood into the atria.
What is followed by contraction of ventricles
Contraction of the ventricles is followed by complete cardiac diastole a period of 0.4 seconds when atria and ventricle relax
During this time the myorcadium recovers ready for the next heart beat and the atrial refuel ready for the next cycle .
How many heart sounds
There are 4 heart sound which corresponds to a particular event in the cardiac cycle.The First to a maze most easily distinguished through stethoscope sounds like lub dup.the first sound is the lub Is fairly loud due to the closure of atriaventicular (tricuspid snd mitral )valves. This corresponds with the start of ventricular systole the second sound dup is softer and it’s due to the closure of the aortic and pulmonary valves.This corresponds with ventricular diastole
Who conducts electricity in the body
The body tissues and fluids conduct electricity well say that so the electrical activity in the heart can be recorded on the skin surface using electrodes positioned on the limbs or the chest.
What does ECG recording shows
The recording call The electrocardio gram shows the spread of electrical signal generated by the SA node as it travels through the atria, the AV node and the ventricles.
What are the five waves of the Treyson of the heart
The normal ECG tracing shows five ways which by convention have been named P, Q, R and T
The P-wave represent the impulses from the SA node sleeping over at the atria(atrial depolarisatio)
The QRS complex represents the very rapid spread of the impulses from the AV node through the AV bundle in the purkinje fibre is and the electrical activity of the ventricle muscles ventricular depolarisation)
Note the delay between the completion of the P-wave and the onset of the QRS complex. This represent the conduction of the impulse through the AV node which is much slower than the conducion elsewhere in the heart
And allow atria contraction to finish completely before ventricular contraction starts.
The T wave represent the relaxation of the ventricular muscle(ventriclar repolarusatio)
Atria repolarisation occurs during ventricular contraction and so is not seen because of the larger QRS complex.
