Chapter 16- The Microcirculation and The Lymphatic System Flashcards
What is the key function of the microcirculation?
Transport of nutrients into the tissue and removal of cell excreta
The peripheral circulation of the entire body has approximately how many capillaries ?
10 billion
What are metarterioles ?
These are terminal arterioles that supply blood to the capillary bed. They have intermittent smooth muscle coats. As opposed to completely muscular arterioles
From where the capillaries Arises?
The true capillaries arise from the metarterioles.
What is the precapillary sphincter?
The precapillary sphincter is the muscular rim located at the origin of the true capillary from the metarteriole.
The significance of metarteriole- precapillary sphincter location on the microcirculation?
The local tissue homeostasis can directly alter the function of the metarterioles and precapillary sphincter to control local blood flow
What is the function of the intercellular clefts between the endothelial cells?
It is the principle route taken by the water soluble substances to exocytose from the capillary to the interstitial space.
What is the function of capillary caveolae ?
It transports macromolecules across the cell membrane.
How does endothelial vesicular channels form
The caveolae coalesce to form the endothelial vesicular channels which facilitate transcytosis of macromolecules.
The most important factor that affects the degree of opening and closing of the metarterioles and precapillary sphincter is ?
Tissue PaO2.
What is called capillary vasomotion ?
It is the intermittent flow of blood through the capillaries instead of continuous flow every few seconds due to intermittent contraction of the metarterioles and precapillary sphincter.
How does lipid soluble substances like oxygen and carbon dioxide cross the capillary wall?
They can just easily diffuse through the lipophilic membrane without having to go through the pores taken by water soluble substances. Therefore, the rate of transcapillary exchange of oxygen and carbon dioxide are much faster than the water soluble substances
What is the rate of water exchange between the plasma and interstitium as compared to the flow of plasma within the capillary lumen?
It is 80 times greater than the rate at which plasma itself flows linearly through the capillary
What is the definition of interstitial space?
It is the space between the cells which harbors 1/6 th of the total body fluid called interstitial fluid.
What is the composition of proteoglycans ?
98% hyaluronic acid and 2% protein
What is tissue gel ?
It is the capillary filtrate fluid that is entrapped between the miniscule spaces of the proteoglycan filaments of the interstitial space as it has the appearance of gel.
What happens to the free fluid in the interstitium?
It usually gets in small rivulets and vesicles. It is under physiological conditions is less than 1% only. However, when edema occurs free fluid expand tremendously until greater than one half of the free fluid becomes edema fluid
How to calculate the transcapillary net filtration pressure?
NFP= Pc- Pi - Pip + Pi If
If the NFP is positive the fluid moves from the blood to the interstitium. If the NFP is negative, the converse happens.
What is the average capillary hydrostatic pressure of the skeletal muscle and the gut as determined by the direct micropipette cannulation of the capillaries?
25 mmHg
What is the average capillary hydrostatic pressure of the skeletal muscle and the gut as determined by the indirect functional measure of the capillary pressure?
17 mmHg
What is the interstitial fluid hydrostatic pressure of the subcutaneous tissue?
It is a few mmHg less than the atmospheric pressure
What is the interstitial fluid hydrostatic pressure of the capsulated organs ?
It is a few mmHg Greater than the atmospheric pressure
What is the normal cerebrospinal fluid pressure in a lateral decubitus animal?
+10 mmHg
What is the intrapleural space hydrostatic pressure?
It is negative (-8 mmHg)
What is the hydrostatic pressure of the synovial joint space?
Negative ( -4 to- 6 mmHg)
What is the epidural space hydrostatic pressure?
-4 to -6 mmHg
What is the basic cause of negative interstitial fluid pressure?
It is caused by the pumping action of the lymphatic vessels. When the interstitial fluid reaches the terminal end of the lymphatic capillaries they contract for a few seconds and relax to pump it into the blood. This pumping action causes negative interstitial fluid pressure
What is the average colloid osmotic pressure of human plasma?
28 mmHg of which 19 mmHg is caused by the dissolved plasma proteins and 9 mmHg by the Donnan effect which is osmotic pressure exerted by the sodium, potassium and other cations bound to the plasma proteins.
What determines osmotic pressure?
Osmotic pressure is determined by the number of molecules dissolved in a fluid rather than by mass of the molecules.
What is the molecular weight of albumin?
69000
What is the molecular weight of globulin?
140,000
What is the molecular weight of fibrinogen?
400,000
What is the contribution of albumin to total plasma oncotic pressure?
21.8 mmHg
What is the contribution of globulin to total plasma oncotic pressure?
6.0 mmHg
What is the contribution of fibrinogen to plasma oncotic pressure?
0.2 mmHg
What is Gibbs -Donnan effect?
It is the phenomenon that causes an unequal distribution of ionic species on either side of a semi-permeable membrane. In blood it occurs due to the presence of large anionic plasma proteins to which small cations are attracted, while the small anions are repelled an driven out to the extracellular space from the large plasma proteins, which create an uneven distribution of small ionic species across the plasma membrane.
What is Donnan potential?
It is the difference in transmembrane Galvani potential caused by the Gibb’s - Donnan equilibrium.
What is the total outward force exerted by the forces tending to move fluid out from the capillaries?
Capillary hydrostatic pressure ( 30 mmHg)+ negative interstitial fluid hydrostatic pressure (3 mmHg)+ interstitial fluid colloid osmotic pressure (8 mmHg) = total outward force ( 41 mmHg)
What is the total inward force tending to move fluid inward at the arterial end ?
Plasma colloid osmotic pressure= 28 mmHg
What is the net outward force at the arterial end ?
Total outward force (41 mmHg)- Total inward force( 28 mmHg)= 13 mmHg
What is the he mathematics of starling equilibrium for capillary exchange?
Starling equilibrium is a near equilibrium state which is created by the difference between the total outward force and total inward forces.
Total outward force 28.3 mmHg= mean capillary pressure( 17.3) + negative interstitial fluid hydrostatic pressure( 3.0) + interstitial fluid colloid osmotic pressure ( 8.0)
Total inward force 28 mmHg= plasma colloid osmotic pressure (28 )
Outward 28.3 - inward 28.0 = 0.3 ( which is the filtration pressure at starling equilibrium)
What is the normal net capillary filtrate rate / min of the entire body?
2ml/ min.
What is the physics of edema?
If the mean capillary pressure raises significantly it will cause concomitant increase in net filtration pressure which will cause a 0.3 + N mmHg increase in net filtration rate. This will result in too much fluid flowing into the interstitial space that can’t be drained by the lymphatic vessels leading to edema.
What is the mechanism of lymph pumping?
The lymph pumping is mediated by both the contraction of muscular lymphatic vessels and by the contraction of the endothelial cells that have actomyosin filaments in it.
The formula of estimating the rate of lymph flow
Rate of lymph flow= the intestinal fluid pressure X the activity of the lymphatic pump
What are the key Roles of the lymphatic system?
1) To regulate the concentration of proteins in the intestitial fluid.
2) To regulate interstitial fluid volume.
3) To regulate interstitial fluid pressure.
What is the significance of negative interstitial pressure for holding body tissue together?
The negative interstitial fluid pressure is responsible for holding the tissues together along with connective tissues. The negative interstitial pressure acts as a vacuum in places like face palm etc. The lose of negative interstitial pressure will cause fluid accumulation and edema.
