Lecture 4: Endothelial Function

Question 1

What are the functions of endothelium?

Answer 1

• Non-thrombogenic surface
• Control vascular smooth muscle via NO and endothelin
• Permeability barrier
• Metabolism of blood-borne substances (Angiotensin 1 converting enzyme ACE, Lipoprotein Lipase (LPL))
• Adhesion and extravasation of leukocytes
• Angiogenesis

Question 2

What are pericytes?

Answer 2

Small mesenchymal-like cells that support the small blood vessels and capillaries

Question 3

Pericytes are relatively _____________ but can differentiate into __________, _________ or _____________.

Answer 3

Undifferentiated
Macrophages
Fibroblast
Smooth muscle cells

Question 4

Pericytes are important in ____________ and the stability of the _____________.

Answer 4

Angiogenesis

Blood-brain barrier

Question 5

What is the microcirculation?

Answer 5

The system of small vessels that control blood flow through tissues

Question 6

How is blood flow controlled in the capillaries?

Answer 6

Precapillary sphincters, dense areas of smooth muscle, that are sensitive to metabolites can open and shut different pathways

Question 7

Endothelial cells are very _______ and have a diameter of ____, this is to decrease the _____________.

Answer 7

Thin (1 μm)
7 μm
Diffusion distance

Question 8

Extensive branching of the vascular tree ensures that every cell is within approximately _____ from a capillary

Answer 8

0.01cm

Question 9

How is the surface area maximised for exchange?

Answer 9

~10-40 billion capillaries

Total surface area for exchange ~600m^2

Question 10

How is time for exchange maximised?

Answer 10

• blood flow velocity is inversely proportional to the sum of the cross-sectional area
• Large area of the capillaries means that the flow in them is slow

Question 11

What are the 3 types of capillaries?

Answer 11

Continuous
Fenestrated
Discontinuous

Question 12

Describe continuous capillaries:

Answer 12

• found in muscle, skin, lungs and brain

- have small ~4nm water filled pores between endothelial cells

Question 13

Describe fenestrated capillaries:

Answer 13

• found in the kidney, glands and intestines

- have pores (20-100nm) or fenestrations that allow rapid movement across the capillaries

Question 14

Describe discontinuous capillaries:

Answer 14

• found in the liver and spleen

- large leaky pores (10-1000nm) that allow passage of plasma protein

Question 15

What is oncotic pressure?

Answer 15

The osmotic pressure that is generated by the presence of large plasma proteins and is approximately constant along the capillary

Question 16

What pressures affect fluid in the vessels and in the interstitial fluids?

Answer 16

Both are affected by the hydrostatic pressure and osmotic/oncotic pressure

Question 17

Net filtration exceeds net absorption and so the excess is drained by the ____________

Answer 17

Lymphatics

Question 18

What is lymph?

Answer 18

Blood without cells, it’s an ultrafiltrate of the plasma