Histology of Blood Vessels

Question 1

What are the 3 blood circulatory systems?

Answer 1

1. Systemic
2. Pulmonary
3. Portal

Question 2

What are the 3 concentric layers of a blood vessel?

Answer 2

1. Tunica intima = lining of squamous cells supoorted by connective tissue and bounded by an internal elastic lamina
2. Tunica media = smooth muscle cells, some collagen and elastin
3. Tunica adventitia = supporting layer of dense, fibroelastic connective tissue

Question 3

Give some examples of elastic arteries

Answer 3

Aorta, common carotid, subclavian and pulmonary arteries

Question 4

Describe each of the tunica layer in elastic arteries

Answer 4

Intima = single layer of endothelial cells, rich in elastin, contains fibroblasts
Media = concentric fenestrated sheets of elastin, separated by collagen and smooth muscle cells
Adventita = collagenous connective tissue containing vasa vasorum

Question 5

Give some properties of muscular arteries

Answer 5

• thin tunica intima
• tunica media made of smooth muscle cells to withstand pressure
• internal and external elastin lamina
• contraction stimulated by sympathetic nerves

Question 6

What is the equation for viscous resistance to flow?

Answer 6

constant / radius ^ 4

Question 7

Explain the process of microcirculation

Answer 7

• part of the circulatory system concerned with exchange of gases, nutrients and waste products
• exchange occurs mainly in capillaries
• capillaries drain into venules
• blood flow into the capillary bed is controlled by arterioles and sphincters

Question 8

What are the 3 types of capillaries?

Answer 8

continuous, fenestrated, discontinuous

Question 9

Describe continuous capillaries

Answer 9

• tube of endothelial cells linked by a tight junction
• embraced by pericytes which are important for survival and stabilisation of endothelial cells
• some small molecules can diffuse through the endothelial cells
• permeability to large molecules depends on the tightness of the junction
• transport of large molecules involves transcytosis across endothelial cell

Question 10

Where does transcytosis occur? Explain the process that this occurs

Answer 10

Various macromolecules are transported across the interior of the cell.
Flask - like pits called caveolae bud of vesicles which cross the cell and fuse with caveolae on the opposite face of the endothelial cell.

Question 11

Explain the structure of a fenestrated capillary

Answer 11

Found at sites where there is rapid movement of macromolecules into or out the blood system.
Luminal and basal plasma membranes of endothelial cells come together to form fenestrae.
Fenestrations are usually closed by a diaphragm. Basal lamina is continuous across the fenestrations.

Question 12

Explain where discontinuous endothelium is found. What does it allow you to do?

Answer 12

Sinusoids of liver and spleen.
Large gaps between the endothelial cells.
Basal Lamina is discontinuous also.
Allows for free passage of large macromolecules or even red blood cells in the spleen.

Question 13

What is the main site for the entry and exit of white blood cells and why?

Answer 13

Post - capillary venule due to the presence of seals.
Postcapillary venules unite to form collecting venules.
Collecting venules drain into muscular venules.

Question 14

What are veins formed from?
Explain each of the 3 tunica layers in a vein.
How can you tell a vein from an artery?

Answer 14

Formed from the union of muscular venules.
Intima - few more layers than the endothelium
Media - 2 or more layers of smooth muscle cells
Adventitia - broadest layer

Can tell a vein from an artery as a vein has a wider lumen compared to smooth muscle.

Question 15

Low pressure collecting system for return of blood from —- to the heart. Blood flow is passive and assisted by — pressure within the chest during inspiration. Return of blood from the limbs aided by muscular —-.

Answer 15

Capillaries
Negative
Contraction

Question 16

Describe the structure of the valves in the veins

Answer 16

Two semi-lunar projections of fibroelastic tissue from the t.intima. They are found in veins of more than 2mm in diameter

Question 17

Name the 7 functions of endothelial cells in blood vessels

Answer 17

1. Permeability layer
2. Synthesise components of basal lamina (basement membrane)
3. Synthesise and secrete molecules that promote blood clotting
4. Synthesise and secrete inappropriate molecules which prevent inappropriate blood clotting
5. Secrete vasoactive factors that promote or inhibit vasodilation
6. Promote inflammatory mediators
7. Produce some growth factors

Question 18

Explain how the lymphatic system works

Lymphatic vessels are found in all tissues except where?

Answer 18

High hydrostatic pressure at the arterial end of capillaries leads to plasma leaking out. Some of this plasma is reabsorbed due to osmosis and the remaining fluid drains into the subclavian veins.

Not found in the CNS, cartilage, bone, bone marrow, cornea and teeth.

Question 19

What are the endothelial cells like on lymphathic vessels?

Answer 19

Flattened cells with a basal lamina and lacking pericytes (cells which wrap around endothelial cells)

Question 20

What occurs during the process of angiogenesis?

Answer 20

Formation of new blood vessels from pre-existing capillaries.
It occurs during the process of the menstrual cycle and placental growth.
Begins as a capillary sprout and involves the movement and rapid increase of endothelial cells, recruitment of smooth muscle cells and pericytes and fibroblasts.

Question 21

Describe the orientation of the smooth muscle cells in the tunica media. What is the function of the smooth muscle?

Answer 21

Circumferential.

Withstand pressure and to vary lumen diameter to regulate pressure

Question 22

How is an arteriole and a lymphatic vessel identified?

Answer 22

Arteriole - vessel in arterial system with lumen <0.1mm or less than 6 layers of smooth muscle cells in T.media.

Lymphatic vessel - channel lined by endothelial cells, irregular shape and no red blood cells in the lumen.

Question 23

Why is the placement of the vasa vasorum in the adventitia?

Answer 23

So it can feed the thick media with blood vessels.

Question 24

What is the orientation of the elastic fibres in the tunica adventita and the inner elastic lamina?

Answer 24

t. A = longitudinal

inner elastic lamina = circumferential (continuous)

Question 25

Where is the interal elastic lamina found?

Answer 25

Between the endothelial cells and the tunica intima.

Question 26

What is the name of the junctions found in skeletal muscle?

Answer 26

Intercellular junctions