Flashcards in CONTROL OF CIRCULATION Deck (23)
what is resistance like in arteries?
low resistance - media contains elastic and smooth muscles which cushions systole
what is resistance like in arterioles?
total arteriolar resistance = total peripheral resistance
which circulating humoral factors are vasoconstrictors?
epinephrine - acts on alpha receptors
which circulating humoral factors are vaosdilators?
epinephrine - acts on beta receptors
atrial natriuretic peptide
which local humoral factors are vasoconstrictors?
endothelin-1 produced by endothelium
internal blood pressure - autoregulation
which local humoral factors are vasodilators?
NO- from endothelium
tissue breakdown products
how is NO produced?
ACh and insulin stimulate calcium release which leads to L arginine being converted to NO aided by NO synthase
NO results in target vessels dilating
how is endothelin - 1 produced?
angiotensin II, vasopressin, cytokines, thrombin, oxidative reactive species, shearing forces all stimulate production of endothelin-1
big endothelin 1 (ET1) converted to endothelin 1 by endothelin converting enzyme
endothelin 1 acts on G coupled proteins which stimulate IP3 calcium release - results in smooth muscle contraction
what systems control blood volume?
adrenal and kidneys
how is circulation controlled?
autoregulation (smooth muscles)
baroreceptors (pressure sensing)
central (neural control loops)
what are peripheral chemoreceptors sensitive to?
very sensitive to pO2
will also detect pCO2 and pH decrease
what happens when chemoreceptors detect a decrease in pO2?
increased sympathetic and decreased parasympathetic output
this increases heart rate
this increases cardiac output
increases breathing rate as well
what do central chemoreceptors detect?
most sensitive to PCO2 and pH
less sensitive to pO2
what does increased firing of central chemoreceptors result in?
increased sympathetic output
this causes arterial vasoconstriction in skeletal muscle, renal and splanchnic system
this increases TPR
where are baroreceptors found?
primarily in carotid sinus and aortic arch
secondary in vein, myocardium and pulmonary vessels
what are the afferent nerves from baroreceptors?
glossopharyngeal nerve to medulla
what are the efferent nerves from baroreceptors?
sympathetic and vagus
what happens when baroreceptors detect and increased blood pressure?
baroreceptors send impulses via glossopharyngeal nerve to medulla where there is increased firing
this results in parasympathetic stimulation of vagus nerve and a decrease in sympathetic stimulation
this results in decreased CO and TPR
what is the role of arterial baroreceptors?
- they are involved in short term regulation of BP
- new baseline is formed if arterial pressure has deviated for more than a few days - can lead to hypertension
what is the role of cardiopulmonary baroreceptors?
found in atria, ventricles and pulmonary artery
- when baroreceptors are stimulated, it decreases vasoconstrictors and decreases BP
- the decreased release of angiotensin, aldosterone and vasopressin leads to fluid loss
what is the effect of high PaCO2 being detected by central chemoreceptors?
this leads to high peripheral resistance and high blood pressure
what is the effect of low PaCO2 being detected by central chemoreceptors?
low medullary activity
this decreases blood pressure