The vascular brain L12 Flashcards
Blood Volume Distribution
What and where is blood pressure?
Pressure in the large arteries, the aorta, the arterioles is quite high (120/80), then drops in the capillaries
Capillary Exchange
The movement of substances between blood and interstitial fluid, across the capillary wall
Diffusion
Solute exchange - down concentration gradients
Transcytosis
Transport of vesicles of large, lipid-insoluble molecules (eg. insulin)
Bulk flow/Filtration
Passive movement of fluid + substances, faster than diffusion alone
Diagram of capillary exchange
Bulk flow/filtration
Net flow is driven by a difference between the balance of pressure and osmotic gradients
What are the two lines in bulk flow/filtration?
There is an osmotic gradient due to intrinsic osmolarity in your blood.
1) Pressure or hydrostatic gradient going from an artery to vein (red)
2) A blood colloid osmotic pressure (large proteins in your blood) (blue)
Changes in bulk flow/filtration
As pressure gradient is higher than the osmotic pressure gradient, there is a net drive to push fluid out of the capillary. But when the pressure inside the venous end of the capillary is much lower, the driving gradient for the movement of fluid is reabsorption.
Interstitial fluid hydrostatic pressure
~0mmHg
Net filtration pressure = (BHP + IFOP) [favour filtration] - (BCOP + IFHP) [favour absorption]
Interstitial fluid osmotic pressure
~1mmHg
Key for the bulk flow/filtration
What is filtration imbalance - oedema?
Fluid build-up which is noticeable as a swelling of your legs and ankles due to systemic imbalance in your filtration.
What happens during heart failure?
There is a ventricle that is struggling to eject blood (filtration>ejection), boost up your blood volume and therefore increasing the venous return to the heart which helps cardiac output. The consequence for heart failure is that more blood volume will increase your venous hydrostatic pressure as there is more blood happening in the veins. Due to more volume accommodated in the veins, you can stretch and extend the veins as they are such thin and pliable vessels, which increases the capillary permeability and that itself can increase the interstitial fluid osmotic pressure.
Series version of the circulatory structure
Parallel version of the circulatory structure
For capillary exchange to work,
Every cell in your body needs to be within two cells
What is velocity proportional to?
1/cross-sectional area
How do we match blood flow supply and demand?
What are Precapillary sphincters?
Precapillary sphincters are small rings of smooth muscle located at the entrance to capillary beds where arterioles (or metarterioles) transition into capillaries.
What happens when precapillary sphincters are relaxed?
Blood flows through capillaries: When the precapillary sphincters are relaxed (open), blood is allowed to flow from the metarterioles into the capillary bed. This allows for the exchange of oxygen, nutrients, and waste products between the blood and surrounding tissues.
Maximizing nutrient and gas exchange: This happens when tissues have high metabolic demands, such as during exercise or increased activity, where more oxygen and nutrients are needed.
What happens when precapillary sphincters are contracted?
Blood flows through the thoroughfare channel: When the precapillary sphincters are contracted (closed), blood is directed away from the capillary bed and flows through the thoroughfare channel, a more direct pathway from the arteriole to the venue.
Reduced exchange: This happens when the metabolic needs of the tissue are low, such as during rest, or when the body is conserving blood flow for vital organs during shock or other stress conditions. In this case, the thoroughfare channel allows for faster, more efficient blood flow without engaging the full capillary network.
