Microcirculation & Edema Flashcards by Karen Fouad

Functions of microcirculation

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

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Compare not-true capillaries & true capillaries

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.
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.

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

> 75

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

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

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Mention site & functions of sinusoidal capillaries

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

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Compare types of continuous capillaries (site/function)

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

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GR: Blood velocity in capilkaries is extremely slow

Mention the speed

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

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Mention how RBCs pass through capillaries

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

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GR: Capillaries withstand pressure

Due to their small radius accirding to Laplace law

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…. Capillaries rupture easily

Dilated

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… test measures capillary permeability

Hess

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Define vasomotion, & its rate

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

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Mention mechanisms of vasomotion

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

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Describe metabolic & myogenic factors

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

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

Adrenimed

Substance P, bradykinin, histamine

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Mention effect of nervous & temp factors

Nervous, no effect

Temp, rise of temp inc blood flow to active areas

GR: Capillary pressure is affected more by venous than ABP

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.

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

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

Mention factors affecting mean capillary pressure

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

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

5 mmHg

0 mmHg

Mention factors affecting capillary permeability

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

Mention factors affecting diffusion

Capillary permeability

Concentration gradient, lipid solubility, molecular size of substance

Mention the starling forces

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

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

20
18
Lymphatic system

Lymph obstruction causes.....

Non-pitting edema

Compare flow limited and diffusion limited exchange

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.

GR: Albumin is consideref an imp component of lymph

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.

Describe composition of lymph

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

Mention factors affecting lymph flow

Lymphatic pumps Lymphagogue Interstitial tissue pressure Activity of tissue

Mention the role of lymphatic pumps

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

Compare primary and secondary class agents of lymphagogues

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

Causes of oedema

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

Compare localized and generalized edema

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

Compare pitting and non pitting edema

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)

Mention the edema safety factors

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.

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

17 mmHg | 27 mmHg