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Can change diameter
don't have muscular coat
smooth muscle fibers that encircle the vessel at various points.
2. Precapillary sphincter
Where exchange takes place
Capillary originates from metarteriole smooth muscle that encircles the capillary
2. Precapillary sphincter- can open or close the capillary
Larger than arterioles
Weaker muscular coat
Can contract (low pressure inside)
Function of pores in Capillary membrane
small pathways that connect the interior of the capillary with the exterior.
Intracellular cleft of capillary membrane
Thin slit curving channel that lies at the bottom of the figure between endothelial cells.
Interrupted by protein attachments
Uniform spacing smaller than the diameter of albumin
Water molecules can diffuse with ease
Pores of capillaries in Blood Brain Barrier
Tight junctions that only allow extremely small molecules through
Pores of capillaries in Liver
Clefts between capillary endothelial cells are wide so that almost all dissolved substances of plasma including plasma proteins can come through.
Blood flow through the capillaries
Does not flow continuously,
Intermittently on and off every few seconds or minutes
Intermittent contraction of metarterioles and precapillary sphincters. (This causes blood to flow. )
The most important factor leading to degree of opening and closing of metarterioles and precapillary sphincters in vasomotion is?
Oxygen in the tissues
Regulation of Vasomotion
- 1. Concentration of O2 in tissues
- 2. When tissue use of oxygen is high the intermittent flow in the capillaries occurs more frequently, for a longer duration.
- 3. Leads to increased oxygen and nutrients to the tissues.
Most important means of transportation through the plasma and interstitial fluid?
Or capillary membrane?
- Results from thermal motion of water molecules and dissolved substances in the fluid.
What substances can diffuse directly through the cell membranes of the capillary endothelium
Lipid soluble substances
- Can diffuse directly through cell membrane
Amount of free fluid in interstitium
Less than 1%
Unless edema is present, number is much higher
Hydrostatic Pressure in capillaries does what?
forces fluid and dissolved substances through capillary pores into the interstitial fluid.
Osmotic pressure in the capillaries is caused by what?
Plasma protein exert osmotic pressure and this tends to cause fluid movement by osmosis from the interstitial fluid into the blood.
Osmotic pressure that is exerted normally prevents loss of fluid volume from the blood into the interstitial spaces
Four primary forces that determine whether the fluid will move in or out of the blood.
capillary hydrostatic pressure= Pc
interstitial hydrostatic pressure= Pi
plasma colloid osmotic pressure=TTp
interstitial fluid osmotic pressure=TTif
1. Capillary pressure- force fluid outward
2. Interstitial pressure- force fluid inward through capillary membrane, inward if positive, outward if negative.
3. Plasma colloid osmotic pressure- cause osmosis of fluid inward
4. Interstitial fluid colloid osmotic pressure- causes osmosis of fluid outward.
- Jv= free movement
- Pc=capillary hydrostatic pressure
- Pi= interstitial hydrostatic pressure
- TTp= plasma osmotic pressure
- TTi= interstitial osmotic pressure
Under normal conditions what is net filtration pressure?
Interstitial pressure in loose subcutaneous tissue is generally________?
generally slightly less than sub atmospheric pressure
Plasma Oncotic Pressure (called this to differentiate from osmosis that occurs in the cell)
aka Plasma colloid osmotic pressure
What causes it?
- Proteins molecules in plasma and interstitial fluid that do not readily pass through semipermeable membrane and capillary pores are responsible for causing oncotic pressure.
- Causes pressure on both sides of capillary membrane.
- This causes osmosis to occur through capillary membrane
- 28 mmHg for normal human plasma
- 19 from dissolved protein
- 9 from Donnan effect
- 80% albumin, 20% globulin, 0.2% fibrinogen
Value of plasma oncotic pressure aka plasma colloid osmotic pressure in normal human plasma
How much is dissolved protein?
Broken down into percentage
- 19 mm from dissolved protein
- 8 from Donnan effect.
- 80% albumin fraction
- 20% globulins
- 0.2% fibrinogen
Interstitial osmotic pressure
aka interstitial fluid colloid osmotic pressure
Average protein concentration ____?
Small amount of protein leaks through pores into interstitial spaces. ( some pores allow this)
Average protein concentration is only 40% of plasma
Pressure =8 mmhg
Exchange of fluid through capillary membrane.
Average capillary pressure at the arterial ends of capillaries is __________ than at venous ends.
Average capillary pressure at the arterial ends of capillaries is 15-25 mmHg greater than at venous ends.
Difference causes fluid to filter out of the capillaries at their arterial ends but at their venous ends fluid is reabsorbed.
Total outward force at arterial end
Arterial end of capillary moves fluid ______?
Venous end of capillary moves fluid _______?
Total inward force at venous end?
Essential to life
Accessory route which fluid can flow from interstitial spaces into the blood
- Essential function is to return protein to blood, without this we would die within 24 hours.
Lymph vessels from lower body empty into___?
The thoracic duct- which empties into the blood venous system at the juncture of the left internal jugular vein and left subclavian vein.
Lymph from left side of head, arm, and chest enter _______ prior to emptying into veins?
Lymph from right neck and head and arm and part of thorax enter_______ and empties into _____ and _____ and ________?
right lymph duct and empties into the blood venous system and the right subclavian and internal jugular veins.
1/10th of fluid enters the lymphatic capillaries instead of traveling to veins.
Total quantity of lymph ______?
Protein can enter the lymph ______?
2-3 liters per day
Proteins can enter lymph system unimpeded.
Protein concentration of the interstitial fluid is about ______, and protein concentration of lymph is _______?
about the same
Just know they are the same