Cardiovascular Physiology Flashcards
What is the role of the cardiovascular system?
Blow flow to tissues
Homeostasis
Transport of hormones
What are 2 circulations arranged in?
Systemic + pulmonary
What is systemic?
Left side of the heart pumping blood to the rest of the body
What is the pulmonary?
Deoxygenated to the lungs
Which part does blood pressure measure?
Systemic
Describe veins
Thin layers of muscle
=low pressure
Describe arteries
Thick, muscular walls
= high pressure
What is the biggest artery?
Aorta
Describe arterioles
Smaller arteries
Thick, muscular walls
= modest pressures
Describe capillaries
Thickness of single endothelial cell
= low pressure
Describe venules
NO thick muscular walls
= low pressure
Where is arteriole B.P generated?
In the left ventricle
Describe ventricular muscle relaxation
Diastole
Ventricular filling
Describe ventricular muscle contraction
Systole
Ejection of blood into arteries
Why is measuring ejection of blood important?
Measure of cardiac output
Called ejection factor
Describe the pressure gradient that is proportional to blood flow
Tube exerts resistance to flow
As it moves = friction = loses energy to surroundings (arteriole walls)
= pressure decreases = creation of pressure gradient
What is stroke volume?
Vol of blood pumped by one ventricle
What is cardiac output?
Vol pumped per ventricle per minute
What is venous return?
Vol of blood returning to the heart
What should VR be equal to?
CO
What is infarction?
Death of muscle
Describe cardiac muscle contraction
Similar to smooth muscle
BUT troponin
What are increases levels of troponin in the blood a sign of?
Cardiac infarction
Describe AP trigger ventricular contraction
AP enters cell
Ca2+ gates open
Entry of Ca2+
Triggers more Ca2+
Binds to troponin
Describe relaxation of ventricular contraction
Occurs when Ca2+ unbinds
Ca2+ pumped back into SR
Ca2+ exchanged with Na+
Na+ gradient maintained by NaK pump
What are the specialisations of cardiac muscle?
Intercalated discs
= packed full of proteins = gap junctions
= connect muscles together
Describe the cells of the SAN
Groups of cells that can spontaneously fire APs
= do NOT need external stimuli
What do gap junctions allow?
Adjacent cardiomyocytes to communicate chemically + electrically
Briefly describe the spread of electrical activity
Originates in SAN
Spreads via gap junctions
Waves of electrical activity lead to mechanical activity
What does an ECG do?
Record what happens in the whole of the heart electrically
What is the annulus fibrosis?
Fibrous tissue that sits between atrial + ventricular muscle
Non-conducting
What is the annulus fibrosis?
Fibrous tissue that sits between atrial + ventricular muscle
Non-conducting
What are the different parts of the ECG?
P wave
P-R interval
QRS complex
Q-T interval
S-T segment
T wave
What is a P wave?
Atrial depolarisation
What is a P-R interval?
Interval between beginning of excitability of atria + ventricles
What is the QRS complex?
Ventricular depolarisation
What is the Q-T interval?
Contraction
BUT also ventricular repolarisation
What S-T segment?
All ventricular tissue depolarised
What is T wave?
Ventricular repolarisation
= SWITCHING OFF
What determines the no. of times the heart will beat?
No. of times SAN fires
How can HR be modified?
Increase sympathetic, decrease parasympathetic
What happens if there is a more forceful contraction?
= more blood forced out
= influences SV
What is contractility?
Amount of Ca2+ in cystolic muscle
Describe Starling’s Law
Stretch LV = more forceful contraction = increased blood
How do you calculate CO?
HR X SV
What do transmitters do?
Bind to receptors on cardiac cell membrane which lead to opening/closing of channels
What is the sympathetic transmitter?
Noradrenaline (adrenaline)
What is the parasympathetic transmitter?
Acetylcholine
What does activation of sympathetic nerves do?
Cause release of noradrenaline
Increase opening of HCN channels
Open Ca2+ channels
HR increases
What does noradrenaline do?
Bind to beta1 adrenoreceptors on cardiac pacemaker + myocyte cells
What does sympathetic stimulation do to the SAN pacemaker activity?
Changes rate of firing
= fires more quickly + reaches threshold quicker
What does opening of Ca2+ channels do?
Depolarises quicker
What does activation of parasympathetic do?
Cause release of Ach
Decreases opening of HCN channels
Slows opening of Ca2+ channels
Opens K+ channels
HR decreases
What does parasympathetic stimulation do to SAN pacemaker activity?
Slows down = makes it harder to reach threshold
= fires less frequently
What does Ach bind to?
Muscarinic cholinergic receptors
Why is parasympathetic constantly on?
Normal intrinsic rate is too high
= on SAN to decrease HR
Decsribe the sequence of mechanical events
Ventricular filling
Atrial contraction
Isovolumetric ventricular contraction
Ventricular ejection
Isovolumetric ventricular relaxation
What is isovolumetric ventricular contraction?
NO difference in blood vol
= has to overcome aortic BP
= then ventricular ejection
ONLY BRIEF
What does the AVN delay allow?
Atrial systole to be complete
What is atrial systole?
Stretch ventricle
= doesn’t pump blood out
What is preload?
The amount of pressure/stress that is put on the heart (LV) when blood returns to the heart
What is End Diastolic Vol (EDV)?
Vol of blood in LV at end of diastole
What is the difference between LV EDV + LV ESV equal to?
SV
Describe heterometric (intrinsic) cardiac workload
Starling’s Law
= cardiac muscle stretched
= more forceful contraction
Describe heart failure
Actin + myosin are physically separated
= SV decreased
= blood going in BUT not enough being pumped out
= LV becomes overstretched
= less forceful contractions
What are the effects of sympathetic nerve stimulation on cardiac workload?
Increase in SV without change in initial fibre length
Increase in contractility
= positive inotropic effect
What is an example of a positive inotropic drug?
Norepinephrine
Describe homeometric (extrinsic) mechanisms
Effects of catecholamines
Produce more forceful BUT shorter contraction
Describe norepinephrine + epinephrine results
Bind to beta1 on myocardial cell
Activates cAMP 2nd messenger
= phosphorylation
= EITHER open Ca2+ channels or phospholamban
Which BOTH = more forceful contractions + shorter duration
What controls mean arterial BP (MAP)?
LV generates it
Arteries/arterioles cause resistance
What are the main factors that determine MAP?
CO
Total peripheral resistance
So how do you calculate MAP?
CO X TPR
What do carotid + aortic baroreceptors do?
Keep BP within limits
Change their rate of firing based on pressure changes
Blood vessels vasoconstrict/dilate
