Microcirculation Flashcards
How is blood flow to the capillaries calculated
Pressure gradient is pressure in arteriole - pressure at gas exchange surface (capillary)
Flow = deltaPressure/Resistance
What is the equation that determines the blood flow to an organ and what does it reveal about the role of arterioles
F= deltaP (MAP)/ R
As arterioles are the major resistance vessels and deltaP is usually constant, arteriolar vasoconstriction is the main factor affecting flow to an organ
How would you describe the tone of arterioles
Arterial smooth muscle has a state of partial constriction (basal tone)
What are the two functions of the changing of radii of arterioles and where does this control come from
Match blood flow to metabolic needs of specific tissues, regulated by local controls and independent of nervous or endocrine stimulation
Help regulate systemic arterial blood pressure, regulated by extrinsic control, vis nerves or blood, usually centrally coordinated
What drugs can reduce BP
Beta blockers (affect cardiac output, reduce adrenorelated vasoconstriction) ACE inhibitors (reduce angiotensin II) Angiotensin receptor blockers (blocks Angiotensin II from binding to smooth muscle receptors)
What is an active hyperaemia and how is it brought about
Increased blood flow in response to local need, eg muscles
Driven by increased metabolites and O2 used
What is myogenic auto regulation and how is it brought about
Vasoconstriction of arterioles locally in response to reduced blood temp and increased stretch (distension) due to increased blood pressure
What type of junction exists between two vascular endothelial cells
H2O filled gap junction
What is the difference between continuous, fenestrated and discontinuous capillary walls
continuous only have H2O filled gap junctions between cells
Fenestrated have ~80nM gaps in endothelium, but basement membrane is continuous
Discontinuous is the most leaky, fenestrae in endothelium and breaks basement membrane
What type of blood brain barrier would be present in premature babies or neonates
More fenestrated BBB, more susceptible to CNS infections
What two forces determine fluid accumulation in tissues and how do they change from arteriolar and venular end
What is bulk flow
Hydrostatic pushing force and on optic pulling force
Hydrostatic reduces, oncotic increases
Movement of fluids down pressure gradient between gaps in capillary wall
What occurs if the pressure inside the capillary > in the IF and vice versa
Ultrafiltration
Reabsorption
If a patient has had their auxiliary lymph nodes removed, where would you do their blood pressure reading and why
On forearm to avoid compression of upper arm lymph nodes
How is flow induced in lymph nodes? Is spthere a pump?
No pump, works down pressure gradient, collects excess ( high pressure in IF, lower pressure in lymph vessels)
Where is lymph drained
Right lymphatic duct and thoracic duct (left)
Returns to circulation in the right and left subclavian veins
Central to return back into circulation
