Week 7- Microcirculation Flashcards
How does blood enter tissues?
Through arterioles
How is blood drained from capillaries to veins?
Via venules
What is the keyrole of the cardiovascular system?
Ensuring adequate blood flow through the capillaries
What is the equation for flow rate?
Pressure gradient / resistance
Define blood flow rate
Volume of blood passing through a vessel per unit time
What does increasing pressure gradient do to flow rate?
Increase it
What is resistance in terms of blood flow?
Hindrance to blood flow due to friction between moving fluid and stationary vessel walls
What is the main factor that affects resistance and actually changes?
Vessel radius
What is the major determinant to resistance?
Arterioles
Why is blood flow to different tissues different if the pressure difference is the same?
Due to differing resistance
What is vascular tone?
Arteriolar smooth muscle displaying a state of partial restriction
What is the point of vascular tone?
To allow arteries to either contract more or dilate so adjustments both ways are possible
Why are radii of arterioles adjusted?
- Match blood flow to metabolic needs of specific tissues
2. Help regulate systemic arterial blood pessure
What is active hyperaemia?
When chemicals act on chemoreceptors on arterioles to increase vasodilation to allow higher blood flow to the area (driven by increased metabolites and increased oxygen usage)
What is myogenic autorégulation?
When chemicals act on chemoreceptors on arterioles to cause vasoconstriction, may be physically driven via a drop in blood temperature and increased stretch due to increased BP
How does blood flow increase only to tissues that need extra blood?
At tissues that dont need extra blood, they respond to extra stretch and constrict to stop reception of extra blood
What arteriolar response will be seen in skeletal muscle arterioles in response to exercise?
Active hyperaemia
What arteriolar response will be seen in small intestine arterioles in response to exercise?
Myogenic vasoconstriction
What is the equation for cardiac output?
Blood pressure/ total peripheral resistance
What is the equation for blood pressure?
Cardiac output x total peripheral résistance
Where is the cardiovascular control center?
In the medulla
What hormones cause vasoconstriction?
Vasopressin/ADH
Angiotensin II
Adrenaline/noradrenaline
What is the purpose of capillary exchange?
The delivery of metabolic substrates to the cells of the organism
What is a typical capillary lumen diameter?
7 micrometers
What is a typical capillary cell width?
1 micrometer
Why is capillary density important?
It depends on how metabolically active the tissue is, more activity requires a higher density
What tissue has the highest capillary density and what is it?
Lungs- 3500cm^2/g
Describe the structure of capillary
Single line of endothelial cells with small water filled gap junctions in between cells
What is the size of acapillary fenestration?
80 nM
What tissues may have a discontinuous capillary wall structure?
Bone marrow (to allow white cells to move into blood)
Liver (to allow large compounds to get into the liver)
What are the 3 type of capillary wall structures?
Continuous
Fenestrated
Discontinuous
What capillary wall structure is found at the blood brain barrier? Describe it
Continuous- there are no gap junctions so only lipid soluble substances can get through freely, otherwise the brain controls what comes in
What is bulk flow?
A volume of protein free plasma that filters out of the capillary and mixes with surrounding interstitial fluid and is reabsorbed
What does oncotic mean?
To do with proteins
What is oncotic force?
Conc of proteins in vessels reduces water potential pulling water into the vessels
What is the opposing pressure to oncotic pressure?
Hydrostatic pressure
How do arterioles match blood flow to the metabolic needs of specific tissues?
Regulation via intrinsic controls (independant of nervous or endocrine stimulation)
How do arterioles help regulate systemic arterial blood pressure?
Regulation via extrinsic controls (travel via nerves or blood)
Which is more effective out of ultrafiltration and reabsorption?
Ultrafiltration
