Chapter 16- The Microcirculation and The Lymphatic System

Question 1

What is the key function of the microcirculation?

Answer 1

Transport of nutrients into the tissue and removal of cell excreta

Question 2

The peripheral circulation of the entire body has approximately how many capillaries ?

Answer 2

10 billion

Question 3

What are metarterioles ?

Answer 3

These are terminal arterioles that supply blood to the capillary bed. They have intermittent smooth muscle coats. As opposed to completely muscular arterioles

Question 4

From where the capillaries Arises?

Answer 4

The true capillaries arise from the metarterioles.

Question 5

What is the precapillary sphincter?

Answer 5

The precapillary sphincter is the muscular rim located at the origin of the true capillary from the metarteriole.

Question 6

The significance of metarteriole- precapillary sphincter location on the microcirculation?

Answer 6

The local tissue homeostasis can directly alter the function of the metarterioles and precapillary sphincter to control local blood flow

Question 7

What is the function of the intercellular clefts between the endothelial cells?

Answer 7

It is the principle route taken by the water soluble substances to exocytose from the capillary to the interstitial space.

Question 8

What is the function of capillary caveolae ?

Answer 8

It transports macromolecules across the cell membrane.

Question 9

How does endothelial vesicular channels form

Answer 9

The caveolae coalesce to form the endothelial vesicular channels which facilitate transcytosis of macromolecules.

Question 10

The most important factor that affects the degree of opening and closing of the metarterioles and precapillary sphincter is ?

Answer 10

Tissue PaO2.

Question 11

What is called capillary vasomotion ?

Answer 11

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.

Question 12

How does lipid soluble substances like oxygen and carbon dioxide cross the capillary wall?

Answer 12

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

Question 13

What is the rate of water exchange between the plasma and interstitium as compared to the flow of plasma within the capillary lumen?

Answer 13

It is 80 times greater than the rate at which plasma itself flows linearly through the capillary

Question 14

What is the definition of interstitial space?

Answer 14

It is the space between the cells which harbors 1/6 th of the total body fluid called interstitial fluid.

Question 15

What is the composition of proteoglycans ?

Answer 15

98% hyaluronic acid and 2% protein

Question 16

What is tissue gel ?

Answer 16

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.

Question 17

What happens to the free fluid in the interstitium?

Answer 17

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

Question 18

How to calculate the transcapillary net filtration pressure?

Answer 18

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.

Question 19

What is the average capillary hydrostatic pressure of the skeletal muscle and the gut as determined by the direct micropipette cannulation of the capillaries?

Answer 19

25 mmHg

Question 20

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?

Answer 20

17 mmHg

Question 21

What is the interstitial fluid hydrostatic pressure of the subcutaneous tissue?

Answer 21

It is a few mmHg less than the atmospheric pressure

Question 22

What is the interstitial fluid hydrostatic pressure of the capsulated organs ?

Answer 22

It is a few mmHg Greater than the atmospheric pressure

Question 23

What is the normal cerebrospinal fluid pressure in a lateral decubitus animal?

Answer 23

+10 mmHg

Question 24

What is the intrapleural space hydrostatic pressure?

Answer 24

It is negative (-8 mmHg)

Question 25

What is the hydrostatic pressure of the synovial joint space?

Answer 25

Negative ( -4 to- 6 mmHg)

Question 26

What is the epidural space hydrostatic pressure?

Answer 26

-4 to -6 mmHg

Question 27

What is the basic cause of negative interstitial fluid pressure?

Answer 27

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

Question 28

What is the average colloid osmotic pressure of human plasma?

Answer 28

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.

Question 29

What determines osmotic pressure?

Answer 29

Osmotic pressure is determined by the number of molecules dissolved in a fluid rather than by mass of the molecules.

Question 30

What is the molecular weight of albumin?

Answer 30

69000

Question 31

What is the molecular weight of globulin?

Answer 31

140,000

Question 32

What is the molecular weight of fibrinogen?

Answer 32

400,000

Question 33

What is the contribution of albumin to total plasma oncotic pressure?

Answer 33

21.8 mmHg

Question 34

What is the contribution of globulin to total plasma oncotic pressure?

Answer 34

6.0 mmHg

Question 35

What is the contribution of fibrinogen to plasma oncotic pressure?

Answer 35

0.2 mmHg

Question 36

What is Gibbs -Donnan effect?

Answer 36

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.

Question 37

What is Donnan potential?

Answer 37

It is the difference in transmembrane Galvani potential caused by the Gibb's - Donnan equilibrium.

Question 38

What is the total outward force exerted by the forces tending to move fluid out from the capillaries?

Answer 38

Capillary hydrostatic pressure ( 30 mmHg)+ negative interstitial fluid hydrostatic pressure (3 mmHg)+ interstitial fluid colloid osmotic pressure (8 mmHg) = total outward force ( 41 mmHg)

Question 39

What is the total inward force tending to move fluid inward at the arterial end ?

Answer 39

Plasma colloid osmotic pressure= 28 mmHg

Question 40

What is the net outward force at the arterial end ?

Answer 40

Total outward force (41 mmHg)- Total inward force( 28 mmHg)= 13 mmHg

Question 41

What is the he mathematics of starling equilibrium for capillary exchange?

Answer 41

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)

Question 42

What is the normal net capillary filtrate rate / min of the entire body?

Answer 42

2ml/ min.

Question 43

What is the physics of edema?

Answer 43

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.

Question 44

What is the mechanism of lymph pumping?

Answer 44

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.

Question 45

The formula of estimating the rate of lymph flow

Answer 45

Rate of lymph flow= the intestinal fluid pressure X the activity of the lymphatic pump

Question 46

What are the key Roles of the lymphatic system?

Answer 46

1) To regulate the concentration of proteins in the intestitial fluid. 2) To regulate interstitial fluid volume. 3) To regulate interstitial fluid pressure.

Question 47

What is the significance of negative interstitial pressure for holding body tissue together?

Answer 47

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.