cardiovascular system Flashcards
what and where is the heart?
- large organ in the centre of thoracic cavity
what kind of structure does the heart have?
- upside down structure as the base is at the top and the apex is at the bottom
what is the heart surrounded by? why is this important?
- fibrous sac called pericardium which has fluid that provides lubrication
- also anchors heart against diaphragm and spine
what are the atriums?
- top receiving chambers
what are the ventricles?
- bottom part that contracts with force to pump blood around
what is the biggest vein in the body?
- vena cava
what happens when blood arrives via vena cava?
- reaches right atrium which contracts slightly to push blood
- via tricuspid valve to right ventricle
what does the right ventricle do after it receives blood?
- pushes blood through pulmonary valve into pulmonary arteries
what happens after the blood has exited via pulmonary arteries and gone round the lungs?
- comes back via pulmonary veins into left atrium which contracts to push blood through mitral valve to left ventricle
what does the left ventricle do with the blood?
- pushes the blood through aortic valve into aorta
what are the atrioventricular valves?
- separate atrium and ventricle; mitral and tricuspid valves are thick to allow blood to passively pass through
what are the semi- lunar valves?
- pulmonary and aortic valve
- control release of blood as open to allow blood through and close to ensure no backflow
what is cardiac muscle?
- similar to skeletal muscle in terms of its structure but it operates similarly to smooth muscle as act involuntary
what are cardiac muscles controlled by?
- autonomic nervous system
what are the properties of cardiac muscle?
- contains striated muscle fibres
- less and smaller sarcoplasmic reticulum
- highly oxidative
what is the gap junction?
- electrical and chemical connection between fibres; allows an electrical signal to originate from specialised part of the heart and propagate from fibre in organised pattern
what does contraction depend on?
- depolarisation
- extracellular calcium ions to activate the receptors to allow more calcium ions in
can tetanic contraction occur in cardiac muscles?
- no because action potentials is almost as long as contraction period
- muscle fibres in refractory period
- always relaxes before another action potential
what is the sinoatrial node?
- can initiate cardiac contraction in absence of any external control as it is myogenic
why do SA node cells initiate the action potential?
- due to unstable membrane potential that is continuously drifting towards threshold
what does sympathetic stimulation to SA node cause?
- increase in slope of drift due to increase of permeability of Na+ current
what does parasympathetic stimulation to SA node cause?
- decrease in slope of drift due to overall decrease of inward current
- and hyperpolarisation of membrane due to increased K+ permeability
what does firing rate depend on?
- initial value of membrane potential
- on the slope of drift towards threshold
how does stimulation spread in atria?
- from fibre to fibre via gap junctions
what network allows ventricular stimulation to spread?
- network of conduits
- begins at atrioventricular node and terminates at cardiac muscle fibres via purknje fibres
what is the first step of propagation of electrical signal?
- stimulus spreads through muscle fibres and stimulate both atria almost simultaneously
what happens after atria contract?
- AV node delays the electrical signal to allow atria to empty before contraction
where does signal travel down?
- interventricular septum via two bundle branches
what happens after the impulse travels down septum?
- ventricles begin to contract as stimulus spreads upwards
- depolarising muscle fibres via purknje fibres
what is the tricuspid valve?
- separates right atrium and right ventricle
when does tricuspid valve open?
- opens when right atrial pressure is higher than ventricular pressure
when does tricuspid valve close?
- when right ventricular pressure is higher than right atrial pressure
what is the mitral valve?
- separates the left atrium and left ventricle
when does mitral valve open?
- when left atrial pressure is higher than left ventricular pressure
when does mitral valve close?
- when left ventricular pressure is greater than left atrial
what is the pulmonary valve?
- separates right ventricle and pulmonary artery
when does pulmonary valve open?
- when right ventricular pressure is greater than pulmonary artery pressure
when does pulmonary valve close?
- when pulmonary artery pressure is greater than right ventricular pressure
what is the aortic valve?
- separates left ventricle and aorta
when does aortic valve open?
- when left ventricular pressure is greater than aortic pressure
when does aortic valve close?
- when aortic pressure is larger than left ventricular pressure
what happens to the valves during systole?
- aortic and pulmonary valves open meanwhile AV valves stay closed
what is the electrocardiogram?
- graphical representation of the electrical activity across heart
what do waves and troughs represent?
- waves= depolarization
- troughs= repolarization
is there a lag in the cardiac cycle?
- lag between depolarization of myocardiocytes and actual contraction of muscles
what does P wave represent?
- atria depolarization
what is the QRS complex?
- represents ventricular depolarization which causes ventricles to contract
what does T wave represent?
- time of ventricular repolarization and subsequent relaxation
what is the Frank- starling mechanism?
- heart will pump all the blood that returns to it by way of the veins
