Vascular control of Circulation Flashcards
What is the difference between the elasticity of arteries and veins?
Arteries are elastic and bounce back
Veins are expandable
How do arterioles manage the pulsatile nature of heartbeat and systole?
They resist the pressure prior to entry into capillary beds creating a continuous flow. Entry into capillaries doesn’t need a huge amount of pressure due to drop in volume at capillaries creating adequate pressure difference.
How are capillaries different to the other blood vessels?
They are fenestrated, thin and have no smooth muscle. Continuous capillaries are surrounded by epithelial cells
What happens to flux if distance of diffusion is increased?
Increasing distance of diffusion will reduce flux
Do capillaries change diameter in response to exercise?
Nope
Do veins and venules have smooth muscle?
Yes but only a little bit due to low pressure. Venules very small amount
Do arterioles have smooth muscle?
Yes and they have a lot of it
What gives arteries their elasticity?
Internal elastic layer of tissue and surrounding adventitia (containing collagen and elastin)
What do veins have more of elastin or collagen?
Elastin to allow them to expand in response to greater volume
What is the difference between elastic arteries and muscular arteries?
The concentration of elastin and smooth muscle
Where does most resistance to blood flow take place?
Arterioles
What happens to velocity of blood flow?
It is inversely related to CSA and so at the capillaries it is very slow due to massive amount of CSA.
What are the 3 different types of capillaries?
Continuous with tight tight junctions and desmosomes between cells forcing nutrients to need to cross the endothelial plamsa membranes to get through making them more regulated and slower diffusion.
Fenestrated capillaries which have holes in them (eg glomerulus) diameter is small enough to only let small proteins and ions through. Nothing is regulated and is purely dependent on pressure and diffusability.
Sinusoids are extremely leaky and have holes that only keep RBCs in the blood and everything else leaves through them.
This is a spectrum rather than default 3 categories.
How is total capillary blood flow determined?
CO - Pressure and Resistance
How are things moved across the capillary walls?
Diffusion, filtration, and reabsorption
What does the blood brain barrier contain?
Continuous capillaries with lots of tight tight junctions.
What is Starling’s law?
Filtration pressure is a balance of 2 pressure.
Pressure that promotes filtration
Pressure that promotes reabsorption
What is the balance of filtration promoting pressure?
Between Capillary Hydrostatic Pressure (35 -> 16mmHg)
And
Interstitial fluid osmotic pressure (1 mmHg)
What is the balance of reabsorption promoting pressure?
Plasma colloid osmotic pressure (approx 36 mmHg)
Interstitial fluid hydrostatic pressure (close to 0 mmHg)
NFP = ?
NFP = (CHP + IFOP) - (PCOP + IFHP)
What happens to Hydrostatic pressure as you move along the capillary?
It drops significantly and proteins in blood draw blood back in towards the end of the capillaries
What is the purpose of the lymphatic system?
Excess fluid moves into the lymphatic fluid.
Where is lymphatic fluid returned into circulation?
Thoracic duct empties at the subclavian artery
What happens to the body in response to standing?
Reduces blood plasma volume for greater than 10%
What happens if fluid is not being absorbed?
Oedema
Where is most blood stored?
In venous system
What is capacitance?
How well is pressure dealt with. Stiff vessels have low capacitance and elastic vessels have high compliance
What is higher compleance veins or arteries?
Veins (more elastin less smooth muscle and less collagen)
What is the effect of venoconstriction?
Increase in CO but no direct effect on BP
Does arteriole constriction affect capacitance?
No because they have a small amount a volume
Why are valves necessary in veins?
They don’t get driven by high pressure
How is pulmonary blood flow different to systemic blood flow?
It is almost identical but there is lower pressure and so also lower resistance (resistance is 1/10th of Systemic Vascular Resistance)
Pulmonary vessels have less smooth muscle and low intravascular pressure
Pulmonary pressure is more well distributed.
Reasons for difference in pressure between pulmonary and systemic circulations:
Gravity and distance (distance above or below heart affects arterial and venous pressure)
Control of regional perfusion in systemic circulation (large pressure head allows alterations in local vascular resistance to redirect blood flow to areas of increased demand)
Consequence of pressure differences (Left ventricle work load is greater than right ventricle, difference in wall thickness indicates difference in work load)
What is the difference in perfusion demands between pulmonary and systemic circulation?
No need to open up capillary beds with pressure in pulmonary circulation whereas in systemic circulation the capillary beds are closed off.
