Vascular Histology

Question 1

What 3 tunics are arteries and veins composed of?

From inner to outer

Answer 1

1. Tunica intima
2. Tunica media
3. Tunica adventitia

Question 2

What are the sub layers of the Tunica intima?

Answer 2

1. Endothelium
2. Basal lamina of endothelial cells
3. Subendothelium layer w/ internal elastic membrane

Question 3

How is the endothelium of the Tunica intima?

Answer 3

Single layer of squamous epithelial cells

Question 4

What is contained in the Basal lamina of the Tunica Intima ?

Answer 4

Thin EC layer w/ collagen, proteoglycans, glycoproteins

Question 5

What is the subendothelial layer of the Tunica Intima made up of?

It’s internal elastic membrane?

Answer 5

Loose CT

IEM: sheet like layer of fenestrated elastic material 2/ artieres and Arterioles

Question 6

What is seen in the TUnica media?

Difference in veins?

Answer 6

‣ Circumferentially arranged layers of SM. M.
‣ Relatively thick in arteries

-has external elastic membrane

Question 7

What is the external elastic membrane of the Tunica Media?

Answer 7

Layer of elastin that separates the tunica media and adventitia

Question 8

How is the Tunica adventitia composed?

How is it different in As. vs. Veins?

Answer 8

‣ Longitudinally arranged collagenous tissue w/ few elastic fibers

‣ Will merge w/ loos CT surrounding vessels

‣ Ranges from relatively thin (arterial system) to quite thick (venules/veins)

Question 9

What two things can we see in the tunic adventitia?

Answer 9

1. Vaso vasorum

2. Nervi vasorum

Question 10

What is the vaso vasorum?

Answer 10

• Vessels of the tunica adventitia that supply blood to the vascular tunics themselves
◦ Found in large arteries and veins

Question 11

What is the Nervi vasorum?

Answer 11

ANS input that controls contraction of vasc. Sm.

Question 12

What are the characteristics of LARGE (elastic) As.?

Answer 12

◦ Largest vessles of the arterial system
◦ Elastin forms concentric sheets/lamellar b/w muscle cell layers

◦ NO fibroblasts!

Question 13

What are the characteristics of MEDIUM (muscular) arteries?

Answer 13

◦ More SM - less elastin
◦ Prominent internal elastic membrane - big black ring around center

◦ Recognizable external elastic membrane
◦ Thick tunica adventitia - ~same thickness as tunica media

Question 14

What are the characteristics of Small arteries and Arterioles?

Answer 14

Different # of Sm. M. Layers in tunica media

	◦ Small arteries 
		‣ 8 layers of Sm M. 
		‣ Will also have internal elastic membrane
	◦ arterioles
		‣ 1-2 layers of Sm. M.

Question 15

What 2 cells are present in capillaries?

Answer 15

1. Pericytes

2. Endothelial cells

Question 16

What are pericytes?

What are they controlled by?

What do they promote?

Answer 16

perivascular contractile cells w/ branching cytoplasmic processes

• Enclosed w/ basal lamina continuous w/ that of the endothelium
• Controlled by NO (endothelial cells)
• Promote stability of capillaries and postcapillary venules

Question 17

How are endothelial cells connected in capillaries?

Function?

Answer 17

Via cell-cell junction (# of junctions will alter permeability)

Support the Bm and produce collagen
Involved in blood coagulation & thrombosis, local vasodilation/constriction

Question 18

What are the 2 subclassifications of venules?

Answer 18

1. Postcapillary

2. Muscular

Question 19

Histologically, what are the characteristics of venules?

Answer 19

1. Postcapillary - no true tunica media

2. Muscular- 1-2 layers of Sm. M. In tunica media w/ thin tunica adventitia

Question 20

What venule are small veins continuous w/?

Answer 20

Muscular venueles

Question 21

What are most of the named veins?

Answer 21

Medium veins

Question 22

How is the tunica media and adventitia of the medium veins different from small?

Answer 22

Thicker

Question 23

What will medium veins contain that is not seen in small?

Answer 23

VALVES

Question 24

What veins are classified as large veins?

Answer 24

Superior and inferior vena cava, hepatic portal vein

Question 25

How are the tunics of Large veins

Answer 25

1. Tunica adventitia - thickest layer w/ collagen and elastic fibers and fibroblasts 2. Tunica media = thin 3. Tunica intima = thin

Question 26

How are the valves in veins, histologically?

Answer 26

Intima will have valves - semilunar flaps consisting of a thing ct core covered by endothelial cells

Question 27

Is the lumen of veins or arteries larger?

Answer 27

Veins

Question 28

What are the 3 types of capillaries?

Answer 28

1. Continuous 2. Fenestrated 3. Discontinuous

Question 29

What is the most common type of capillary?

Answer 29

Continuous

Question 30

What are the characteristics of Continuous capillaries?

Answer 30

- tight occluding junctions that seal off intercellular clefts - continuous basement membrane - cells meet end to end

Question 31

How does molecular exchange occur w/ continuous capillaries?

Answer 31

Via diffusion or trans cytosine

Question 32

Where are continuous capillaries located?

Answer 32

Thru-out body (muscle, brain, peripheral nerves, exocrine glands)

Question 33

What are the characteristics of fenestrated capillaries?

Answer 33

Have tight junctions w/ fenestrations among endothelial cells -continuous basement membrane

Question 34

Where are fenestrated capillaries found?

Answer 34

in organs where molecular exchange w/ blood is important • Endocrine glands & sites of fluid/metabolite absorption (gallbladder, kidney)

Question 35

What do the fenestrations of Fenestrated Capillaries allow for?

Answer 35

Allows greater exchange across the endothelium, but limited to size of macromolecules

Question 36

What are the characteristics of Discontinuous Capillaries?

Answer 36

Large fenestrations among endothelial cells - discontinuous basal lamina - sinusoidal = discontinuous

Question 37

Where are discontinuous capillaries located?

Answer 37

‣ Located where exchange of macromolecules & cells (b/w tissue and blood) must openly occur • Bone marrow, liver, spleen

Question 38

What are the characteristics of true capillaries? Where do they come from?

Answer 38

Lack sm. M. -where gas exchange takes place -come from meta-arterioles

Question 39

What is a Thoroughfare channel?

Answer 39

Distal end of metarterioles (lacks sm. M. ) Will connect to a postcapillary venule

Question 40

What are the lymphatic capillaries?

Answer 40

CLOSE ENDED tubes found among cap beds

Question 41

How are lympahtic capillaries histologically composed?

Answer 41

Composed of overlapping endothelial cells, forming 1 way valves for collecting lymph -has incomplete basal lamina (increases permeability)

Question 42

How are the openings b/w endothelial cells held in place in Lymphatic caps?

Answer 42

Held in place via anchoring filaments

Question 43

What will lymphatic capillaries join up to form?

Answer 43

Lympahtic vessels

Question 44

What is the function of lymphatic vessels?

Answer 44

◦ Circulate lymph thru most parts of the body ◦ Serve as adjuncts to the blood vessels ◦ Collect lymph & retuns it to venous supply

Question 45

What junctions are present in lymphatic vessels?

Answer 45

Continuous tight junctions - to prevent leakage

Question 46

What should lymphatic vessels never have in it?

Answer 46

Blood

Question 47

What is the flow of lymph?

Answer 47

◦ Lympahtic caps —> vessels —> nodes —> trunks —> R. Lympahtic duct —> thoracic duct —> drain into brachiocephalic VV. —> superior vena cava