Microcirculation & Edema

Question 1

Functions of microcirculation

Answer 1

1. Connection between arterial & venous side for transport of blood (close the circuit)
2. Exchange of nutrients & metabolites, to maintain homeostasis
3. Distribution of fluid between extravascular & intravascular compartments

Question 2

Compare not-true capillaries & true capillaries

Answer 2

1. Not-true capillaries are not desgined for exchange conduct blood rapidly from arterial to venous side, they are large capacitance vessels, larger than terminal arterioles. They are metarterioles, AV shunts & thoroughfare vessels, they are rich in SM & nerves have temp regukatory function.
2. True capillaries are only desgined for exchange, arise from thoroughfare vessels & terminal arterioles, for every capillary arising from connecting vessel there is a precapillary sphincter, under local tissue control while muscle fibers before it are under neural control.

Question 3

At rest, …..% of capillaries are inactive & closed

Answer 3

> 75

Question 4

Fenestrated capillaries are found in ….., their fenestratioms are equal to …..

Answer 4

Endocrine glands, intestinal villi, glomerular membrane of kidney
20-100 nm in diameter

Question 5

Mention site & functions of sinusoidal capillaries

Answer 5

Liver (allow oassage of plasma protein)
Bone marrow (allow passage if RBCs)

Question 6

Compare types of continuous capillaries (site/function)

Answer 6

1. Skeletal, cardiac, smooth muscle veins, fenestrations are 10 nm in diameter, allow bulk flow of water & wtaer soluble ions.
2. In brain, the capillaries are non-fenestrated with continuous endothelium there are tight junctions allow passage of small molecules.

Question 7

GR: Blood velocity in capilkaries is extremely slow

Mention the speed

Answer 7

Due to large TCSA of capillary network, this slow flow is most appropriate for the essential function of capillaries which is exchange between capillary & tissue.
0.1-0.5 mm/sec

Question 8

Mention how RBCs pass through capillaries

Answer 8

Squeeze as a single file with the center ahead of the edges (parachute shape).

Question 9

GR: Capillaries withstand pressure

Answer 9

Due to their small radius accirding to Laplace law

Question 10

…. Capillaries rupture easily

Answer 10

Dilated

Question 11

… test measures capillary permeability

Answer 11

Hess

Question 12

Define vasomotion, & its rate

Answer 12

It is defined as alternating closure and opening of capillaries according to metabolic activity, thus blood flows in certain capillaries and they close & blood shifts to other capillaries.
6-12 cycles/min

Question 13

Mention mechanisms of vasomotion

Answer 13

Metabolic, myogenic, chemical & hormonal, nervous & temperature factors

Question 14

Describe metabolic & myogenic factors

Answer 14

O2 lack and CO2 excess increases the number & duration of open phase of vasomotion, injection of high O2 blood decreases the vasomotion cyvles per minute & vice versa.
Pacemaker may be present in in smooth muscles of arterioles

Question 15

…….cause VC, while ……cause VD of precapillar

Answer 15

Adrenimed

Substance P, bradykinin, histamine

Question 16

Mention effect of nervous & temp factors

Answer 16

Nervous, no effect

Temp, rise of temp inc blood flow to active areas

Question 17

GR: Capillary pressure is affected more by venous than ABP

Answer 17

Due to higher precapillary resistance compared to postcapilary resistance (tone if arteriole of precapilkary sphincter is 4-5 times stronger than postcapillary resistance i.e. tone of venules & veins.

Question 18

Compare effects of rise in arterial or venous BP on capillary pressure

Answer 18

Rise in arterial causes increase in capillary P by 1/4 the inc in ABP
Rise in venous pressure causes equal rise in capillary pressure

Question 19

Mention factors affecting mean capillary pressure

Answer 19

Diameter of preceding arteriole and tone of precapillary sphincter
Post capillary pressure i.e. venous pressure
Effect of gravity

Question 20

Capillary pulse pressure is ….. at arterial end & ….. at venous end.

Answer 20

5 mmHg

0 mmHg

Question 21

Mention factors affecting capillary permeability

Answer 21

1. Depends on organ, in liver, kidney & endocrine organs more than muscle but least in brain.
2. Venular end is more permeable than arteriolar end
3. Plasma proteins dec permeability as they close capillary pores, permeability is inc in liver & renal disease.
4. Inc in active tissues by dilator effect of metabolites.
5. Permeability increases in response inglammatory subtance as substance P, pyrogens & toxins.

Question 22

Mention factors affecting diffusion

Answer 22

Capillary permeability

Concentration gradient, lipid solubility, molecular size of substance

Question 23

Mention the starling forces

Answer 23

1. Filtration pressure, hydrostatic pressue in capillary and in interstitial tissue.
2. Reabsorption pressure, osmotic pressure due to albumin together with its Gibbs-Donan effect

Question 24

… L are filtered daily,…..are reabsorbed, the rest return to circulation by….

Answer 24

20
18
Lymphatic system

Question 25

Lymph obstruction causes.....

Answer 25

Non-pitting edema

Question 26

Compare flow limited and diffusion limited exchange

Answer 26

F, equilibrium is rapid and reached near the arterioles, it depends on amount of blood coming tgrough them e.g. O2. D, where equilibrium of the substance is slow and exchange accurs more along the capillary. It depends on diffusion itself.

Question 27

GR: Albumin is consideref an imp component of lymph

Answer 27

Because it can pass outside the capillaries due to its cigar shape, but it does not return through the same pores due to its low conc in tissue fluid than in plasma.

Question 28

Describe composition of lymph

Answer 28

It has the same composition of tissue fluid in that area, lower protein content than plasma (2 gm%) A/G ratio is higher than that of plasma Lymph in lymphatics of liver is nearer in composition to plasma because it is the site of PP synthesis

Question 29

Mention factors affecting lymph flow

Answer 29

Lymphatic pumps Lymphagogue Interstitial tissue pressure Activity of tissue

Question 30

Mention the role of lymphatic pumps

Answer 30

``` Rhytgmic contraction of the wall of large ducts Arterial pulsations Contraction of skeletal muscle Negative intrathoracic pressure Valves prevent backward flow ```

Question 31

Compare primary and secondary class agents of lymphagogues

Answer 31

1ry cause inc lymph flow by causing capillary dilation as bacterial toxins and peptones 2ry cause inc lymph flow after initial decrease, e.g. hypertonic solution

Question 32

Causes of oedema

Answer 32

Increased filtration pressure (arteriolar dilation, venular constriction, inc venous pressure) Increased capillary permeability Dec oncotic pressure (nutritional edema, liver cirrhosis and kidney duseases) Inadequate lymph flow

Question 33

Compare localized and generalized edema

Answer 33

L, as in triple response | G, cardiac, renal, hepatic, nutritional, toxic or allergic and in lymph obstruction.

Question 34

Compare pitting and non pitting edema

Answer 34

P, yields to pressure, albumin content of tissue fluid is not high (as in heart failure, renal, hepatic, nutritional) N, doesn't yield to pressure, there is high interstitial tissue fluid pressure and high albumin content (lymph obstruction)

Question 35

Mention the edema safety factors

Answer 35

1. -ve interstitial pressure, leads to low compliance. 2. Lymph flow can inc 10-50 folds 3. Dec protein content in interstitial fluid, bec the amount removed is usually greater than that filtered by the blood capillaries due to the much greater permeability of lymph capillaries, this leads to low tissue oncotic pressure.

Question 36

Oedema safety factor is .... systemicly and ....in pulmonary circulation.

Answer 36

17 mmHg | 27 mmHg