05 Microcirculation

Question 1

Describe the basic structure of microcirculation

Answer 1

Primary order arteriole
Terminal arteriole
Capillary
Pericytic venule (post capillary venules)
Venules

Question 2

What is the determinant to ensure blood flows into the capillary bed

Answer 2

Pressure difference

eg Pressure at primary order arteriole (93 mmHg = MAP) and terminal arteriole 37 mmHg

Question 3

What are the two functions of the arteriole resistance and what are they regulated by

Answer 3

To match the metabolic demand of the tissues - intrinsic mechanism independent of nervous system and hormones
To maintain BP - extrinsic control

Question 4

Describe some examples of intrinsic control and how do they achieve their goal

Answer 4

Active hyperemia: response to the metabolites and oxygen usage to cause vasodilation to increase flow to the tissues

Myogenic vasoconstriction: response to increase in pressure and result in vasoconstriction to maintain flow

Response to icepack to vasoconstrict

Question 5

What are the extrinsic regulation of arterial BP

Answer 5

Neural: heart (beta receptor) and vascularture (alpha receptor)
Hormonal: Ang II, ADH and adrenaline

Question 6

What are the thickness of capillary endothelial cells and the diameter of capillaries. What are they trying to achieve

Answer 6

1 um
7 um
Fick’s law: trying to maximse the rate of diffusion by reducing diameter, thickness and maximise surface area by branching

Question 7

Although metabolically active tissues have dense capillary supply, why does skeletal muscle usually have relatively low supply

Answer 7

At rest, skeletal muscle capillary supply is restricted by the contraction of precapillary sphincters

Question 8

What are the different types of capillaries and give examples of each

Answer 8

Continuous: with H2O filled gap junction
Fenestrated - kidneys
Discontinuous - bone marrow to allow cells to pass through

Question 9

Define bulk flow

Answer 9

A volume of protein free plasma filters out of the capillary, mixes with the surrounding interstitial fluid (IF) and is reabsorbed

Question 10

Where do the lymphatics end at and what is the typical flow

Answer 10

Right lymphatics, thoracic duct and right & left subclavian veins
3 L/day due to the discrepancy between ultrafiltration and reabsorption

Question 11

Give a pathology associated with oedema

Answer 11

Elephantiasis