Cardiovascular physiology and mechanisms controlling cardiac output Flashcards
what is the role of the cardiovascular system?
- supplies blood to tissues and organs
- helps with homeostasis
- helps transport hormones/signaling molecules
what are the circulations in the heart?
the systemic and the pulmonary (right side takes blood to lungs, left part takes blood to rest of body)
what is the role of veins?
carry blood at low pressure from tissue/organs back to heart.
what is the role of arteries?
carries blood at high pressure to tissues/organs from the heart.
explain the transport of blood from lungs to tissues and back to lungs!
lungs to pulmonary veins, to left atrium, to left ventricles, to aorta to arteries, to arterioles, to capillaries, to venules, to veins, to vena cava to right atrium, to right ventriculces, to pulmonary artery, to lungs.
what valve separates the left atrium from the left ventricles?
mitral valves
what is it called when the heart is resting?
diastole
what is it called when the heart contracts?
systole
what valve separates the aorta from the left ventricles?
aortic semilunar valve
what happens to the rate of blood flow is the pressure gradient between the aorta and vena cava increased?
blood flow would increase
why does pressure drop in the circulation?
due to resistance between the blood and the vessel wall
what is stroke volume?
the volume of blood pumped by one ventricle
-this is approx 75ml
what is cardiac output?
the volume of blood pumped by one ventricle in one minute
what is venous return?
the volume of blood returned to the heart
what is cardiac output equal to?
the venous return
what is the Ca2+ sensor in cardiac cells?
troponin
explain how an action potential triggers atrial and ventricular contractions?
- action potential enters adjacent cell
- voltage gated Ca2+ channels open so Ca2+ enters
- this causes Ca2+ release from Ca2+ sarcoplasmic reticulum
- Ca2+ binds to troponin to intiate contraction
- Ca2+ unbinds from troponin causing relaxation
- Ca2+ is pumped back into the sarcoplasmic reticulum
- other Ca2+ leaves the cell in exchange with Na+
- Na+ gradient is maintained by Na+/K+ ATPase
How does action potential spread through the heart?
- electrical activity comes from the sinoatrial node
- this sends waves of electricity, via gap junctions in the inercalated disk, through the heart
- this leads to mechanical activity (contraction)
what is the role of gap junctions?
allow adjacent cardiac myocytes to communicate chemically and electrically
what is the annulus fibrosis and what does it do?
- it is the non-conducting layer between the atria and ventricles
- it electrically insulates the chambers from each other
what does the P wave show?
atrial depolarisation
what does the PQR interval show?
the interval between excitability of the atria and ventrincles
what is the QRS complex show?
ventricular depolarisation.
atrial repolarisation is also occurring but isn’t as dominant
what does the Q-T interval show?
when contraction is occurring and ventricular repolarisation
what does the S-T segment show?
all ventricular tissue depolarised and contraction is occuring
what does the T wave show?
ventricular repolarisation
how do you calculate cardiac output?
Heart rate X stroke volume
what determines heart rate?
the rate of depolarisation in the autorhythmic cels
what slows down your heart rate?
parasympathetic inenervation
what increases your heart rate?
sympathetic innervation (influenced by epinephrine)
what determines your stroke volume?
the force of contraction in ventricles
what is the transmitter in the sympathetic nervous system?
(nor)adrenaline
what is the transmitter in the parasympathetic nervous system?
acetylcholine
what do the transmitters do at cardiac cell membranes?
they bind to the receptors on the cell membrane and cause opening/closing of ion channels
how does the sympathetic nervous system affect the heart rate?
- sympathetic nerves are activated hence releasing nordrenaline
- this binds to beta-1 adrenoreceptors on the cardiac pacemakers and myocyte cell membranes
- this increases opening of HCN channels in pacemakers so Na+ moves in
- Ca2+ channels are opened so Ca2+ moves in
- this increases heart rate
how does the parasympathetic nervous system affect the heart rate?
- activation of the parasympathetic nerves causes the release of acetylcholine which binds to muscarinic cholinergic receptors
- this decreases the opening of HCN channels and slows the opening of Ca2+ channels. Therefore less Ca2+ and Na+ move in
- However, more ligand gated K+ channels are opened so K+ moves out
- this causes hyperpolarisation of the membrane and a decrease in heart rate
what is the sequence of mechanical events in the cardiac cycle?
- ventricular filling
- atrial contraction
- isovolumetric ventricular contraction
- ventricular ejection
- isovolumetric ventricular relaxation
what is preload?
the degree of stretch in the ventricles due to the end diastolic pressure and is dependent on the end diastolic volume (EDV)
what is starling’s law of the heart?
- force of contraction is proportional to the initial fibre length in diastole. As blood returns to the heart, there’s an increase in end diastolic volume. This stretches the cardiac muscle and produces a more forceful contraction.
- if there’s a low preload, there’s less contraction as less actin-myosin overlap
- if there’s a high preload, there’s more contraction due to cross bridges between actin and myosin and increased affinity of troponin to Ca2+
what two mechanisms regulate the force of contraction and the workload of the heart?
-heterometric (intrinsic) and homeometric (extrinsic)
is staling’s law homeometric or heterometric?
heterometric
what is the effect of the sympathetic nerve stimulation on cardiac workload?
it increases stroke volume without initially changing fibre length. It increases contractility hence increased stroke volume. i.e. produces more forceful but shorter contraction
how do you work out mean arterial blood pressure?
cardiac output X total peripheral resistance
