Lecture 9: Blood vessels 2

Question 1

Describe the structure of the microcirculation:

Answer 1

• Arterioles (Distribution of blood)
• Terminal arterioles (SM layer)
• Metarterioles (Incomplete SM layer)
• Precapillary sphincter

Question 2

What does the precap sphincter shut blood off to?

Answer 2

Prevents blood going to meta-arterioles or capillaries

= Travels throughfare channel to venule [Known as aterovenous anastomosis]

Question 3

Describe the structure of capillary walls:

Answer 3

• Endothelium with basement membrane

- NO connective tissue or muscle

Question 4

What are the different types of capillaries?

Answer 4

• Continuous (Endothelial cells form continuous sheet)
• > Closed intracellular clefts
• > Open intracellular clefts
• Fenestrated (Endothelial, perforated with small holes)
• > Closed perforations
• > Open perforations
• Sinusoids

Question 5

Where are continuous endothelial cells with closed intracellular clefts found?

Answer 5

• CNS

- Forms impermeable BBB

Question 6

Where are continuous endothelial cells with open intracellular clefts found? what can passage?

Answer 6

• Muscle, CT, lung etc
• Water, ions, small molecules
• NOT plasma proteins

Question 7

Where are fenestrated endothelial cells with closed perforations found?

Answer 7

• Intestine

- Fenestrae have very thin membranous diaphragm

Question 8

Where are fenestrated endothelial cells with open perforations found?

Answer 8

• Endocrine glands, kidney glomeruli, where water exchange is important

Question 9

Whats the function of sinusoids?

Answer 9

• Wide bore caps

- Passage of large molecules and whole cells

Question 10

Where do sinusoids occur?

Answer 10

• Bone marrow and spleen (RBC)

- Liver

Question 11

How do sinusoids maximise exchange?

Answer 11

• The intracellular clefts

- Slow flow due to large lumen

Question 12

Describe the structure of post cap venules?

Answer 12

• No smooth muscle
• Pericytes
• Accompany arteriole often.
• Drains cap bed

Question 13

Whats the function of venules?

Answer 13

• During inflammation/allergic reaction histamine and serotonin increase leakage of blood plasma into tissue fluid (oedema)
• Also neutrophils into CT, and monocytes and lymphocytes.

Question 14

Describe muscular venules?

Answer 14

• Up to 2 layers SM
• Thin walled in relation to lumen
• ENDOTHELIAL NUCLEI BULGE INTO LUMEN

Question 15

Write some notes on veins:

Answer 15

• Same basic 3 layer structure
• Never well developed internal elastic lamina
• Thin walled

Question 16

What are vein valves?

Answer 16

• Bicuspid
• Prevent backflow
• Made from folds of tunica intima

Question 17

Why do legs veins have more SM?

Answer 17

When standing the pressure in legs can be huge thus more muscular

Question 18

Why does venous thrombosis occur?

Answer 18

• Slow blood flow
• Increased coagulability
• Damage to epithelium

i.e surgery, childbirth, trauma, OC pill

Question 19

Signs and symptoms of venous thrombosis?

Answer 19

• Swollen
• Red
• Painful

History

Question 20

Whats the compression test for venous thrombosis?

Answer 20

Compress vein and then observe no flow

Question 21

What is varicose veins?

Answer 21

• Superficial veins valves become incompetant

- Veins can become dilated, swollen and tortuous

Question 22

What are the smallest lymphatic vessels?

Answer 22

• Lymphatic capillaries

= Blind ended endothelial tubes

Question 23

Describe the structure of lymphatic caps?

Answer 23

• Endothelial cells

- Anchoring filaments (strands) help open clefts

Question 24

How do lymphatic caps function?

Answer 24

• Endo tubes are tethered to surrounding CT by delicate anchoring filaments
• CT swells with fluid, anchoring filaments pull tubes open
• NO BASEMENT MEMBRANE (increases perm)
• LARGE GAPS b/w endo cells allows protein and cells to enter vessels

Question 25

Describe large lymphatic vessels:

Answer 25

• Like veins but walls are thinner and more valves

- Lymph propelled by SM (stretch activated) and vasomotion

Question 26

Are lymphatics everywhere?

Answer 26

No, i.e none in brain

Question 27

Whats lymphoedema?

Answer 27

Lymphatic obstruction resulting in oedema