Regulation of fluid balance in the microcirculation

Question 1

Definition of microcirculation

Answer 1

Part of vascular system comprising of terminal arterioles, capillaries, post capillary venules

Gases, water, nutrients, waste materials and other substances exchanged here between blood and tissues via tissue fluid

Question 2

Definition of terminal arterioles

Answer 2

Have sparse amount of smooth muscle

Vessels between the arterioles and capillaries

Question 3

Definition of glycocalyx

Answer 3

Glycoprotein layer covering the luminal surface of endothelium

Question 4

Definition of oedema

Answer 4

Fluid accumulates in interstitial as net filtration has increased/lymphatic system blocked

Question 5

Definition of reflection coefficient

Answer 5

The measure of how much osmotic pressure a solute applies

Increased RC = increased osmotic pressure

Question 6

Definition of hydrostatic pressure

Answer 6

Pressure exerted by a fluid at equilibrium at a given point within the fluid

Question 7

Definition of osmotic pressure

Answer 7

Pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis
Often used to express the concentration of solution

Question 8

Definition of lymphangion

Answer 8

1 way valve in the lymphatic capillary

Question 9

Definition of envenomation

Answer 9

Process by which pressure immobilization is to contain venom within a bitten limb and prevent it from moving through the lymphatic system to vital organs

Question 10

Describe the functions of the structures in the microcirculation

• terminal arterioles
• capillaries, post capillary venules
• lymphatic capillaries

Answer 10

Terminal arterioles
-Sparse SM = control cap flow, local control

Capillaries, post capillary venules

• No SM, monolayer of endothelium with fibrous support
• exchange vessels for tissues

Lymphatic capillaries

• transport fluid, fats, proteins => blood
• transport microbes => lymph glands

Question 11

Where are the 3 types of capillaries found
Describe their structures
-continuous
-fenestrated
-discontinuous

Answer 11

Continuous

• most tissues
• endothelium monolayer, tight junctions => least permeable

Fenestrated

• kidneys, joints, GI mucosa
• fenestrations => more permeable to small hydrophilic

Discontinuous

• liver, bone marrow, spleen
• spaces between endothelial cells => large molecules

Question 12

What molecules can be transported via these methods

• Intercellular gap (acute inflammation)
• transendothelial channel
• vesicular transport
• transcellular
• paracellular
• fenestrated

Answer 12

Intercellular gap
Transendothelial channel
Vesicular transport
-large lipophobic

Transcellular
-lipophilic

Paracellular (water)
Fenestrated
-small lipophobic

Question 13

Describe the 2 ways water can move across the capillary wall

• what is the net direction of fluid movement, how much
• describe the route of water from the plasma => blood
• what happens when this balance is altered?

Answer 13

Into tissue => filtration
Into capillaries => reabsorption

Net 4-8L filtered

Plasma => TF => Lymph => Subclavian => VC

If net filtration increases/lymphatics blocked => oedema

Question 14

What 2 forces regulate filtration

Answer 14

Hydrostatic pressure

• net mv => IS
• altered by gravity

Oncotic pressure

• net mv => capillaries
• water moves from low to high oncotic pressure

Question 15

What 2 factors affect filtration

• orthostatic reflex
• organs specialise to absorb water

Answer 15

Orthostatic reflex
-arteriole VC => lowers cap HSP => compensates for increased net filtration

Organs specialized to absorb water
-in nephrons, higher oncotic P in capillaries than tubules => net reabsorption into caps

Question 16

Describe the 4 causes of oedema

• Increased hydrostatic cap P
• increased venule/cap permeability
• decreased oncotic P in plasma
• lymphatic obstruction

Answer 16

Increased hydrostatic cap P
-increased venous pressure backs up into capillaries => NET FILTRATION

Increased venule/cap permeability
-inflammation => plasma proteins leak into the IS => increases oncotic pressure => NET FILTRATION

Decreased oncotic P in plasma
-due to malnutrition/burns => net filtration

Lymphatic obstruction

• due to removal/inflammation
• fluid cannot be removed

Question 17

Describe the structure of the lymphatic system

• how does fluid move
• where are they found

Answer 17

intracellular clefts => 1 way movement of fluid

afferent trunks run alongside major vessels

SM in lymphangion contracts rhythmically (pacemaker cells) => pumps fluid forward

lymph nodes receive lymphocytes from blood
-cells activated by antigens