Cardiovascular System - Fluid Exchange in Capillaries

Question 1

What are the 3 types of capillaries?

Answer 1

Continuous - continuous endothelial lining without fenestrations and are bound together by tight junctions, relatively impermeable to large molecules
Discontinuous - discontinuous endothelial lining with large gaps, highly permeable, found in liver, spleen, bone marrow
Fenestrated - have pores within their endothelial lining, allowing for increased permeability to small molecules and fluids, Fenestrations are covered by a thin diaphragm, which regulates the movement of substances across the capillary wall.

Question 2

Describe the structure and function of capillaries.

Answer 2

Structure;
no smooth muscle
highly permeable
endothelium and basement membrane
large surface area and very thin
Function - exchange of nutrients and gasses between blood and interstitial fluid

Question 3

Describe the structure and function of microcirculation.

Answer 3

Capillary bed - network of capillaries within a tissue

Question 4

Describe the causes of oedema.

Answer 4

Oedema is the abnormal accumulation of fluid in the interstitial spaces of tissues, leading to swelling and tissue enlargement.
Causes;
Increased capillary hydrostatic pressure
Increased capillary permeability
Decreased Plasma Oncotic Pressure

Question 5

Describe the consequences of oedema.

Answer 5

Swelling and discomfort
Impaired tissue function - disrupts cellular interactions
Compromised blood flow - can compress blood vessels and impede blood flow
Skin changes

Question 6

What are the Starling forces acting across the capillary wall?

Answer 6

Starling forces = the balance of hydrostatic and oncotic pressures across the capillary wall that govern the movement of fluid between the bloodstream and the interstitial space.

Question 7

What are the 4 different Starling forces?

Answer 7

• Capillary hydrostatic pressure - pressure exerted by the blood within the capillary, higher at the arterial (afferent) end of the capillary bed, where blood enters the capillary network.
• Interstitial Fluid Hydrostatic Pressure - opposes the movement of fluid out of the capillary and into the interstitial space, low compared to CHP
• Capillary Oncotic Pressure - refers to the osmotic pressure exerted by proteins (albumin) present in the blood plasma within the capillary, draws fluid back into the capillary from the interstitial space
• Interstitial Fluid Oncotic Pressure - opposes the movement of fluid into the capillary from the interstitial space, low compared to COP as proteins less concentrated in interstitial fluid

Question 8

Describe diffusion across capillary.

Answer 8

Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, driven by the concentration gradient.
Oxygen (O2) and carbon dioxide (CO2) diffuse across the capillary walls according to their concentration gradients, allowing for the exchange of respiratory gases between the blood and tissues

Question 9

Describe bulk flow across the capillary.

Answer 9

Bulk flow refers to the overall movement of fluid along with dissolved solutes across the capillary wall due to pressure differentials.
It is driven by the combined effects of hydrostatic and oncotic pressures and is responsible for the continuous exchange of fluid and solutes between the bloodstream and tissues.

Question 10

Describe vesicular transport across the capillary.

Answer 10

Facilitated transport involves the movement of specific molecules across the capillary wall with the assistance of carrier proteins or channels