normal structure and function Flashcards
name 5 blood pressure determinants in terms of the systems involved and state how they influence BP
heart (pumping i.e. CO, which = SV x HR)
blood vessels (tone: TPR. sympathetic nervous system and abnormal sensitivity to catecholamines)
vascular volume (capacitance of the vascular system)
arterial wall distensibility (baroreceptor control)
kidney (regulates blood volume)
fluid flows along vessels only when a ___ ___ exists between the 2 ends of the vessel. The pressure ____ supplies the driving for the flow of fluid.
pressure difference
head
what is resistance a measure of in terms of fluid moving through vessels?
how difficult it is for fluid to flow along a vessel
why does resistance occur for fluid moving along a vessel?
frictional forces between the stationary wall any the moving fluid resist fluid flow through the vessel. (in addition frictional forces also exist within the fluid itself, and are influence by the viscosity of the fluid)
fluid ordinarily flows in an organised streamlined pattern. What is this called?
laminar flow
blood flow (Q) within the cardiovascular system is determined by (2)
- a head of pressure developed by the heart
- the resistance to flow encountered within the vessels
write the basic flow equation that highlights the relationship between flow, pressure and resistance
flow = pressure difference/ resistance
using your knowledge of the basic flow equation (flow, pressure, resistance equation) write an equation to calculate total systemic resistance
total systemic resistance (PRU) = (aortic pressure - right atrial pressure)/ systemic blood flow
using your knowledge of the basic flow equation (flow, pressure, resistance equation) write an equation to calculate pulmonary vascular resistance
pulmonary vascular pressure = (pulmonary trunk pressure - atrial pressure)
resistance to flow through a vessel if influenced by which three main factors to do with the vessel?
length
inner radius
viscosity of the fluid flowing through the vessel
why is damage to the arterial tree by hypertension particularly worrying?
it damages not only the arterial tree itself, but causes also damage to major organs i.e. brain, eye, heart, blood vessels and kidneys
state the structural and functional changes that may result from prolonged hypertension
larger (elastic) arteries internal elastic lamina thickening, smooth muscle hypertrophy and fibrosis. these changes reduce the lumen, increase shear stress on the intima, increase turbulence, decrease endothelial function and reduce distensibility/ compliance
as a result of prolonged, uncontrolled hypertension the smaller arteries show ___ ___ which narrows the lumen. This can greatly reduce vessel diameter
hyaline sclerosis
what effect do the structural changes found in arteries following hypertension have on peripheral vascular disease?
PVR increases. this in turn results in a further increase in blood pressure.
the rapid development of _____ is an additional complication of hypertension. This is an additional cause of increased ____ ____ resistance.
atherosclerosis
peripheral vascular
does atherosclerosis develop at the same/ an accelerated pace in hypertension?
an accelerated pace (particularly in the aorta, cerebral, peripheral and coronary arteries.)
in hypertension, atherosclerosis develops at an accelerated pace - acceleration is more marked in those with associated high risk factors for atheroma, such as (4)
diabetes
hypercholesterolaemia
cigarette smoking
impaired glucose tolerance.
name the 2 types of hypertension and state which is the most common
essential and secondary (by far the most common is essential: 90-95% of cases)
what is the difference between essential and secondary hypertension?
essential is raised BP without obvious case (aka primary or idiopathic) whereas secondary is raised blood pressure when there is an identifiable cause
secondary hypertension often develops before the age of ___ years or after ___ years
35
55
hypertension results in damage to several organs in the body and to the aorta and its main branches. Name some of the adverse effects of hypertension
cerebrovascular disease: cerebral haemorrhage
hypertensive retinopathy
carotid artery disease
coronary artery disease: MI, renal artery disease, aortic disease, peripheral arterial occlusive disease
name 6 cardiac complications of hypertension
left ventricular hypertrophy, MI, myocardial ischaemia, atrial fibrillation, LV failure, congestive cardiac failure
what is ischaemia?
an inadequate blood supply to an organ or part of the body, especially the heart muscles
the myocardium (muscular tissue of the heart) is composed of ___ and non-___ cells
myocyte
myocyte
cardiac myocytes are enmeshed in a _____ network that acts a supporting framework for the heart.
collagen
cardiac myocytes are comprised of _____ and ____ myofilaments whose organisation gives rise to the classic ____ appearance of cardiac muscle
actin
myosin
striated
blood is supplied to individual cardiac myocytes through which vessels
capillaries which are in close proximity to them
there are 2 prominent organelles within cardiac myocytes - what are these?
mitochondria - produce energy
SR - regulates calcium handling in the cell
cardiac contraction is initiated when extracellular _____ moves into the cell across the which type of channels?
what does this calcium that enters the cell trigger?
what is this process called
calcium
voltage-dependant L-type calcium channels
calcium release from the ryanodine receptor
calcium induced calcium release - CICR
how does the calcium released from the SR by CICR induce contraction of the sarcomeres?
it binds to the actin thin filaments
what happens to the calcium at the end of the contraction sequence?
it comes off of the myofilament and is actively transported back into the SR by the calcium pump in its membrane
Calcium is also transported out of the cell to the extracellular space by a membrane bound pump sodium-calcium exchanger
cardiac contraction is brought about by interactions between the ____ thin filament and the ____ cross-bridges that project from the thick filament shown in red
actin
myosin
what prevents actin interacting with the myosin cross-bridges when the cardiac muscle is relaxed?
the conformation of troponin and tropomyosin
–> as a result actin is unable to interact with the myosin cross-bridges containing bound ATP
how can the actin interact with the myosin cross-bridges in activated cardiac muscle then?
calcium binds to the troponin which then shifts troponin complexes and tropomyosin to an active conformation and enables actin to interact with the myosin cross-bridges
what provides the requisite energy for the myosin cross-bridges to interact with the actin thin filament?
myosin ATPase on the myosin heads hydrolyses the bound ATP on myosin
what does the myosin heads do to the actin thin filaments when they do interact?
pulls them towards the centre of the sarcomere in a ratchet like fashion (the whole process is known as excitation-contraction coupling)
the process of excitation-contraction coupling becomes disregulated in cardiac ______ and cardiac ______
hypertrophy
failure
following sustained hypertension the heart develops concentric ______, which is characterised by thickening of the ___ ___ and the ____ ____ of the left ventricle
hypertrophy
IV septum
free wall
true or false: ventricular hypertrophy in response to sustained hypertension is immediately a problem for the heart as soon as it develops
false - it is initially adaptive, allowing the heart to maintain normal pump performance with the increased afterload (resistance against which heart has to pump) imposed by an elevated BP
name a maladaptive change that occurs in the extracellular matrix as a result of ventricular hypertrophy and state what effect this has on normal heart function
increase in the fibrillar collagen network that surrounds the individual cardiac myocytes (prevents heart from contracting and relaxing normally)
name a maladaptive change that occurs within the cardiac myocytes as a result of ventricular hypertrophy and state what effect this has on normal heart function
decrease in the amount of calcium that’s released from the SR - causing a decrease in the amount of sarcomere shortening causing myocyte dysfunction
one of the best recognised of sustained hypertension is the development of dilated ________. What is this characterised by?
cardiomyopathy
progressive dilation of the left ventricle and decreased systolic performance of the left ventricle
one of the hallmarks of dilated cardiomyopathy is the progressive thinning of the ____ ____ wall as well as an increase in overall ____ ____ cavity dimension
left ventricular
left ventricular
how does dilated cardiomyopathy affect the myofilaments? what is this accompanied by? what are both these abnormalities throught to contribute towards?
leads to progressive dissarray of the myofilaments accompanied by excessive myocardial fibrosis
to the depressed systolic performance of the left ventricle
what is myopathy
a disease of muscle tissue
how does dilated cardiomyopathy affect the contraction-excitation coupling in the failing myocyte?
calcium influx through the L-type calcium channel results in decreased release of calcium from the SR. The decrease in calcium available to activate the cross-bridges leads to decreased sarcomere shortening and to myocyte dysfunction. In addition there is also decreased function of the calcium pump of the SR that removes calcium from the cytosol back to the SR (contributing to the decrease in calcium that’s available to activate the cross-bridges as the myocyte contracts)
there are abnormalities of excitation-contraction coupling in the hypertrophied heart - what is the net result of these in terms of sarcomere shortening?
These abnormalities are thought to contribute to the development of ____ ____ systolic dysfunction in the failing heart
decreased speed and extent
left ventricular
