VASCULAR: CAPILLARIES, LYMPH, AND VEINS Flashcards
Function of capillaries
Exchange site for gases, nutrients, water, and waste
Where is capillary density greatest and lowest?
In tissues with high O2 consumption such as cardiac muscle, skeletal, glands, brain
Low density: cartilage and subcutaneous
At rest, how many capillaries are open?
20%
What regulates capillary opening?
Capillary opening is regulated by small arteries, arterioles, metarterioles
Describe this type of capillary: continuous capillary
- Most common
- Junctions 10-15 nm wide
- Blood brain barrier has tight junctions
Describe this type of capillary: fenestrated capillary
- Fenestrations: membrane lined holes through cell
- 20-100 nm wide
- Can be closed by diaphragm
- Exist in the intestine, glomerulus, and exocrine glands
Describe this type of capillary: sinusoidal (discontinuous) capillary
- Large gaps between cells
- 100-1000 um
- Facilitate exchange
- Exist in the liver, bone marrow, and spleen
_________ form at the ends of endothelial cells which prevents the leakage of _________ from capillary. This makes it appear as if their membranes are _____
- Tight junctions
- macromolecules
- fused
List the mechanisms of transcapillary exchange?
- Diffusion (gases, small solutes)
- Filtration
- Bi-directional vesicular transport
a. transcytosis of macromolecules
b. transendothelial channels (stack of fused endocytotic vesicles across cell)
State diffusion equation
J = ([solute]out - [solute]in)PA
J: flux : quantity moved per unit time
P: permeability coefficient
A: capillary surface area
What can diffuse during capillary exchange?
- Gases - direct diffusion across endothelial membrane
- Small solutes - diffusion through small pores and clefts
- Polar molecules have decreased permeability due to poor lipid solubility
- Large molecules have no diffusion above 60 kDa (ex: albumin can’t diffuse)
What are the two forces that govern filtration at the capillary?
- Hydrostatic pressure - blood pressure
- Oncotic or plasmoid osmotic pressure - blood proteins
What is the net filtration pressure?
The net filtration pressure is 0.3 mmHg or 2-3 litres a day
Name where capillaries mainly filter and mainly absorb
renal glomerulus
intestinal mucosa
precapillary sphincters
regulate flow of blood to capillaries depending on demand.
Describe how injury to the capillaries, severe burns, or inflammation will disturb the net filtration balance
If you injure capillaries, severe burns, or inflammation, this will all result in damage or increased leakiness of the capillaries → we lose plasma protein concentration in the blood → oncotic pressure decreases → increased filtration → increased interstitial fluid → edema