Arteries and Arterioles Flashcards
what are arteries also known as?
conductance vessels
briefly describe the structure of arteries
thick
highly elastic walls with large radius, providing little resistance to blood flow
what is the function of arteries?
serve as a passageway from hearts to organs and as a pressure reservoir (forces blood movement when heart relaxes)
storage of potential energy
what are 4 components of arterial wall? state their function
1) smooth muscle cells - regulate vessel diameter
2) endothelial cells - regulate smooth muscle function and vessel permeability
3) collagen fibers - impart rigidity to arterial wall
4) elastic laminae - impart elasticity to arterial wall
is there significant loss of energy down arterial tree? why or why not?
nope
pressure is essentially the same throughout the system
what is blood pressure?
force exerted by blood on arterial wall (fcn of the volume of blood in the vessel and the compliance of the vessel)
what is the aorta?
highly distensible artery that receives a lot of blood per contraction
What is Vin and Vout?
Vin - volume blood entering vessels
Vout - volume blood leaving vessels
whats larger during systole? Vin or Vout? what does this do to pressure?
Vin
increases pressure and vessel wall expands
whats larger during diastole? Vin or Vout? what does this do to pressure?
Vout
decreases pressure and vessel wall contracts
What is the blood pressure during cardiac arrest?
~0mmHg
what property of arteries allow them to expand? why is this significant? what protein is behind this?
elastic properties - store potential energy as blood volume increases with contraction
elastin = protein
does capillary bloodflow show the same contraction/relaxation cycle of the heart?
nope
what makes elastin different from other proteins, giving it its elasticity?
entropy of beta-coils in the AA sequence is maximal in non-stretch molecules
elastin don’t got that
what are arterioles also known as?
resistance vessels
briefly describe the structure of arterioles
highly muscular (thick muscle, little connective tissue) well innervated walls with a small radius
why is arteriole resistance important?
creates the pressure differential which encourages blood to flow from the heart to various downstream organs
converts non-pulsatile pressure swings to nonfluctuating pressure in capillaries
what determines and measures distribution of blood throughout the circulatory system?
measured as % of cardiac output
depends on metabolic needs of the organs: kidneys/digestive system receive the most, bone and liver receive the least
which structures in the body are sensitive to blood flow changes? why is this important?
brain and heart
can easily be damaged by changes in blood flow
what is another equation to calculate MAP?
MAP = CO x TPR CO = cardiac output TPR = total peripheral resistance
what happens in terms of resistance and blood flow when arteriolar smooth muscle contracts?
vessel radius decreases, leading to a higher resistance and decreased blood flow
what 3 things regulate arteriolar radius?
vasoconstriction
vasodilation
vascular tone
what is vasoconstriction?
smooth muscle contraction decreases vessel circumference
what is vasodilation?
smooth muscle relaxation increases vessel circumference
what is vascular tone? what is its importance?
partial constriction of arteriole that is always present
allows for fine control of resistance
what two things control vascular tone?
myogenic activity
continual release of NE
how does myogenic activity affect vascular tone? what happens if there is incr/decr myogenic activity?
smooth muscle cell resting potential can fluctuate, leading to self-induced contractile activity to ocur
incr myo - vasoconstriction
decr myo - vasodilation
how does NE release affect vascular tone?
release of NE from sym fibers innervating the VSMCs can contribute to enhanced vascular tone
what other factors can affect vasoconstriction or vasodilation?
const - incr. O2, sym stimulation or decr. CO2
dil - decr. O2, sym stimulation, or incr. CO2
what sympathetic stimulation factors can affect vasoconstriction?
vasopressin
angiotensin 2
cold
what sym. stimulation factors can affect vasodilation?
histamine
heat
What 2 main factors does perfusion depend on? which has more control?
intrinsic (local) factor - override extrinsic
extrinsic (systemic) factor
how do intrinsic and extrinsic factors affect perfusion?
1) determine vasodilation/constriction
2) regulate systemic BP and maintain within a physiologic range
how do intrinsic factors regulate extrinsic factors?
either reinforce the systemic signals or oppose them
how do sym nerves affect the heart and blood vessels? what happens if you increase sym activity?
sym nerve fibers supply all the smooth muscle and maintain vascular tone (vasoconstriction)
incr. sym = increase contractility, vasoconstriction, HR, and BP (due to incr. CO and TPR)
what three extrinsic central regulators regulate heart activity?
1) central command (brain)
2) arterial baroreflex
3) skeletal muscle afferents (mechano/metaboreceptors)
what is central command central regulation? how does it work?
a feed forward system where volitional activity can influence CV responses
activity of motor cortex can influence PNS/SNS regulation, ultimately affecting CV regulation
what is arterial baroreflex?
pressure-sensitive receptors in carotid sinus/aortic arch that respond to high or low blood pressure and regulate it by influencing the SNS and PNS
how do mechanoreceptors and metaboreceptors have an effect on heart activity?
sense mechanical and metabolic signals associated with muscle contraction and act on the SNS to incr. BP and HR
contribute to central control of blood flow
what autonomic reflexes exist to maintain blood pressure?
baroreceptors
chemoreceptors
low pressure receptors
what hormone is responsible for vasodilation? how does it affect vasodilation?
bradykinin
lasts only a few minutes but causes powerful dilation and increased capillary permeability
what 4 hormones are responsible for vasoconstriction? which is most potent?
NE and E
ang 2
vasopressin - potent
how does NE and E affect vasoconstriction?
released from adrenal medullae into blood and promote systemic vasodilation and incr. BP.
mediated by alpha adrenoreceptors
what other effect can E have on blood flow?
can bind to beta2 adrenoreceptor and cause vasodilation in tissues with an abundance of beta2 receptors
how does ang 2 affect vasoconstriction?
acts to incr. TPR and BP
where is vasopressin produced? how does it affect BP?
formed in nerve cells in hypothalamus and stored in post pit gland.
it can regulate BP during severe haemorrhage.
how does intrinsic regulation generally affect blood flow?
matches blood flow to a specific tissues metabolic needs
how does extrinsic regulation generally affect blood flow?
overall regulation of arterial blood pressure
what chemical intrinsic regulators affect blood flow? what affect do they have?
high O2 tension - vasoconstriction
high CO2 tension - vasodilation
why is oxygen important in blood flow? what happens when O2 levels are low?
O2 required for ATP production leading to smooth muscle contraction (maintain vascular tone)
metabolic demands increase mean depleted O2 meaning muscle tension cannot be maintained and the vessel dilates leading to increased flow
what is active hyperemia?
increase in blood flow in order to meet increased metabolic demand
