The Microcirculation

Question 1

What is vasomotion?

Answer 1

Continuous, cyclical dilation and constriction of arteriole

Cycles are short (~ 1 second)

Produces intermittent flow of blood through capillaries

Question 2

Describe the density of capillaries in a tissue

Answer 2

Dependent on the metabolic demand of the tissue

i.e. cardiac muscle => increased density of capillaries

Question 3

How do post-capillary venules change to cause inflammation?

Answer 3

Become increasingly permeable and leaky, leading to plasma leaking into interstitium

Question 4

What is the most important mechanism for net movement of water out of capillary?

Answer 4

Convection

Not diffusion

Question 5

Where in the circulation is diffusional permeability greatest?

Answer 5

Venous end of capillary => increased reabsorption

Question 6

Which molecules are capillary walls more permeable to, and why?

Answer 6

Lipid-soluble molecules
- since can cross through cell membranes % th. can diffuse through intracellular pathway

(note: hydrophilic molecules must diffuse through pores)

Question 7

Describe the speed of diffusion based on the size or pores and solutes

Answer 7

Small pores allow quick diffusion of small solutes and water into interstitium

Large pores (small amount) allow very slow diffusion of large solutes into interstitium

Question 8

Name the three types of capillaries

Answer 8

Continuous capillaries

Fenestrated capillaries

Sinusoids

Question 9

Where do continuous capillaries occur?

Answer 9

Skin, lungs, connective tissue, muscle,, CNS etc.

Question 10

Where do fenestrated capillaries occur?

Answer 10

In areas of increased fluid filtration out of capillaries

- e.g. kidneys, exo/endocrine glands, choiroid plexus, ciliary bodies, intestinal mucosa

Question 11

Where do sinusoids occur?

Answer 11

In areas of cellular exchange, e.g.

- liver, spleen, bone marrow

Question 12

How does the circulation prevent fluid accumulation in the interstitium?

Answer 12

Vasomotion

Lymphatic drainage of tissue

Question 13

What physiological inequality occurs for oedema to occur?

Answer 13

Capillary filtration rate > lymphatic drainage rate

Th. either Increased CFR or decreased LDR

Question 14

Name three mechanisms for increased capillary filtration rate?

Answer 14

Increased hydrostatic pressure in capillaries

Decreased oncotic pressure

Increased permeability of post-capillary venules

Question 15

What can cause decreased lymphatic drainage?

Answer 15

In west, most commonly:
- Cancerous /surgical damage to lymph nodes

Worldwide
- filiariasis

Question 16

Why does oedema become not pitting in chronic lympathic oedema?

Answer 16

Since chronic oedema leads to stimulation of fibrous tissue production

Question 17

What is the cause for venous ulcers?

Answer 17

Chronic venous hypertension in legs, via:

• hypoxia
• chronic inflammation resulting in tissue breakdown

Question 18

Which other features commonly accompany venous ulcers?

Answer 18

Varicose veins
Eczema
Brown pigmentation
Leg oedema

Question 19

What effect does venous HTN have on blood vessels?

Answer 19

Produces:

• dilated, coiled veins and capillaries
• blocked and fragmented lymphatics