2.2 Blood circulation and control Flashcards
What are the principle vessels of resistance?
Arterioles
What do arterioles respond to?
Blood pressure changes. Local, neural and hormonal factors.
Name 2 local factors that result in vasoconstriction.
Endothelin, internal BP.
Name 7 local factors that result in vasodilation.
Hypoxia, NO, K+, CO2, H+, adenosine, bradykinin, tissue breakdown products.
What neural factors result in vasoconstriction?
Sympathetic nerves that release noradrenaline.
What neural factors result in vasodilation?
Parasympathetic innervation.
Name hormonal factors that result in vasoconstriction.
Epinephrine (adrenaline)
Angiotensin 2
Vasopressin
Name 2 hormonal factors that result in vasodilation.
Atrial natriuretic peptide
Acetylcholine
What is myogenic auto-regulation of blood flow?
An intrinsic mechanism in smooth muscle blood vessels. If BP increases the vessel constricts. This is important in regulating blood flow.
Describe capillaries
40 000km
large surface area = slow flow
What determines the interstitial fluid flow?
The distribution of extra cellular fluid between compartments
What is capillary flow determined by?
Arteriolar resistance
Number of open pre-capillary sphincters
What is the uni-directional flow of lymphatics aided by?
Smooth muscle in lymphatic vessels
Skeletal muscle pump
Respiratory pump
Name 3 effectors in circulation control.
- Blood vessels - vasoconstrict/dilate and effect TPR.
- The heart - can affect rate or contractility.
- Kidneys - regulates blood volume and fluid balance.
Where are baroreceptors located?
Aortic arch and carotid sinus.
What activates baroreceptors?
They contain stretch receptors which respond to pressure.
Are atrial baroreceptors involved in short-term or long-term regulation of BP?
Short-term. (Cardiopulmonary = long-term).
Where central chemoreceptors located?
In the medulla oblangata.
What do central chemoreceptors respond to?
Changes in pH/(H+).
Increased PaCO2
increases H+ and so decreases pH.
What does increased PaCO2 result in?
Vasodilation
Short term and long term pathway of BP control:
Short term: Baroreceptors
Long term: Volume of blood
Describe the arterial baroreceptor reflex in response to an increase in blood pressure.
High bp,
Increased parasympathetic outflow,
Decreased contractility,
Decreased CO,
Increased vasodilation,
Lowers bp.
Describe the arterial baroreceptor reflex in response to a decrease in blood pressure.
Low bp,
Increased sympathetic outflow,
Increased contractility,
Increased CO,
Increased vasoconstriction,
Increases bp.
How do central chemoreceptors respond to an increase in PaCO2?
Vasoconstriction to increase blood pressure.
Why do central chemoreceptors stimulate vasoconstriction in response to an increase in PaCO2?
They act to counter the affect of CO2 as a vasodilator and so maintain blood flow to tissues.
