Vascular System and Peripheral Circulation Flashcards
How is blood flow and capillary cross-sectional area related?
Speed is inversely related to cross-sectional area.
SLowest where cross-sectional area is the greatest (thus slowest in capillaries, where heaps of tiny capillaries add up to give greatest cross sectional area)
What are the 3 types of capillaries?
Continuous - endothelial cells form continuous tube
Fenestrated - have pores
Sinusoids - wider, more windy with large fenestrations.
What is net filtration dependent upon?
- Pressure that promotes filtration
- Capillary hydrostatic pressure (CHP) (from CO)
- Interstitial fluid osmotic pressure (IFOP) - Pressure that promotes reabsorption
- Interstitial fluid hydrostatic pressure (IFHP)
- Plasma colloid osmotic pressure (PCOP)
At the arteriolar end of a capillary, BP > PCOP
- Plasma leaks out into interstitial fluid
At the venous end, BP < PCOP
- Plasma is drawn in, out of interstitial fluid
Where does the remaining bit that capillaries don’t reabsorb go?
Into the lymph.
What causes oedema?
Increased capillary hydrostatic pressure
Decreased plasma colloid osmotic pressure (decreased plasma proteins)
Increased interstitial fluid osmotic pressure
Decreased interstitial fluid hydrostatic pressure
What is capacitance, and how do arteries and veins differ?
Capacitance = ability to deal with volume increses without affecting pressure.
Increase in arterial circulation have large increase in pressure (arteries are stiff), increase in venous circulation won’t change pressure much.
Why does the venous system need valves, but the arterial system doesn’t?
Venous system needs valves to prevent backflow. Arterial system doesn’t as blood is only getting pushed away.
How does vaso and veno constriction affect peripheral resistance and capacitance?
Venoconstrction doesn’t change peripheral resistance much, but reduces capacitance.
Vasoconstriction doesn’t change capacitance much, bt increases peripheral resistance.
What are the systemic controls for vasoconstriction?
Noradrenaline
Vasopressin (ADH)
Angiotensin II
What are the systemic controls for vasodilation?
Adrenaline
ACh
Atrial natriureitc peptide
List the local substances which alter smooth muscle activity (vasoconstrictors and vasodilators)
Vasoconstrictors:
- Serotonin
- Endothelin
Vasodilators
- Nitric oxide
- Bradykinin
- Histamine
- Adenosine (e.g. build up of ADP during hypoxia)
- Metabolite accumulation
When do coronary arteries perfuse?
During diastole.
DUring systole, cardiac artieres are under so much pressure that flow is almost 0.
How is coronary flow regulated?
Mostly autoregulation - local response to O2 levels
Adenosine is the major metabolite responsible for dilating coronary vessels to increase flow.
