Vascular Histology Flashcards
What 3 tunics are arteries and veins composed of?
From inner to outer
- Tunica intima
- Tunica media
- Tunica adventitia
What are the sub layers of the Tunica intima?
- Endothelium
- Basal lamina of endothelial cells
- Subendothelium layer w/ internal elastic membrane
How is the endothelium of the Tunica intima?
Single layer of squamous epithelial cells
What is contained in the Basal lamina of the Tunica Intima ?
Thin EC layer w/ collagen, proteoglycans, glycoproteins
What is the subendothelial layer of the Tunica Intima made up of?
It’s internal elastic membrane?
Loose CT
IEM: sheet like layer of fenestrated elastic material 2/ artieres and Arterioles
What is seen in the TUnica media?
Difference in veins?
‣ Circumferentially arranged layers of SM. M.
‣ Relatively thick in arteries
-has external elastic membrane
What is the external elastic membrane of the Tunica Media?
Layer of elastin that separates the tunica media and adventitia
How is the Tunica adventitia composed?
How is it different in As. vs. Veins?
‣ 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)
What two things can we see in the tunic adventitia?
- Vaso vasorum
2. Nervi vasorum
What is the vaso vasorum?
• Vessels of the tunica adventitia that supply blood to the vascular tunics themselves
◦ Found in large arteries and veins
What is the Nervi vasorum?
ANS input that controls contraction of vasc. Sm.
What are the characteristics of LARGE (elastic) As.?
◦ Largest vessles of the arterial system
◦ Elastin forms concentric sheets/lamellar b/w muscle cell layers
◦ NO fibroblasts!
What are the characteristics of MEDIUM (muscular) arteries?
◦ 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
What are the characteristics of Small arteries and Arterioles?
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.
What 2 cells are present in capillaries?
- Pericytes
2. Endothelial cells
What are pericytes?
What are they controlled by?
What do they promote?
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
How are endothelial cells connected in capillaries?
Function?
Via cell-cell junction (# of junctions will alter permeability)
Support the Bm and produce collagen
Involved in blood coagulation & thrombosis, local vasodilation/constriction
What are the 2 subclassifications of venules?
- Postcapillary
2. Muscular
Histologically, what are the characteristics of venules?
- Postcapillary - no true tunica media
2. Muscular- 1-2 layers of Sm. M. In tunica media w/ thin tunica adventitia
What venule are small veins continuous w/?
Muscular venueles
What are most of the named veins?
Medium veins
How is the tunica media and adventitia of the medium veins different from small?
Thicker
What will medium veins contain that is not seen in small?
VALVES
What veins are classified as large veins?
Superior and inferior vena cava, hepatic portal vein
How are the tunics of Large veins
- Tunica adventitia - thickest layer w/ collagen and elastic fibers and fibroblasts
- Tunica media = thin
- Tunica intima = thin
How are the valves in veins, histologically?
Intima will have valves - semilunar flaps consisting of a thing ct core covered by endothelial cells
Is the lumen of veins or arteries larger?
Veins
What are the 3 types of capillaries?
- Continuous
- Fenestrated
- Discontinuous
What is the most common type of capillary?
Continuous
What are the characteristics of Continuous capillaries?
- tight occluding junctions that seal off intercellular clefts
- continuous basement membrane
- cells meet end to end
How does molecular exchange occur w/ continuous capillaries?
Via diffusion or trans cytosine
Where are continuous capillaries located?
Thru-out body (muscle, brain, peripheral nerves, exocrine glands)
What are the characteristics of fenestrated capillaries?
Have tight junctions w/ fenestrations among endothelial cells
-continuous basement membrane
Where are fenestrated capillaries found?
in organs where molecular exchange w/ blood is important
• Endocrine glands & sites of fluid/metabolite absorption (gallbladder, kidney)
What do the fenestrations of Fenestrated Capillaries allow for?
Allows greater exchange across the endothelium, but limited to size of macromolecules
What are the characteristics of Discontinuous Capillaries?
Large fenestrations among endothelial cells
- discontinuous basal lamina
- sinusoidal = discontinuous
Where are discontinuous capillaries located?
‣ Located where exchange of macromolecules & cells (b/w tissue and blood) must openly occur
• Bone marrow, liver, spleen
What are the characteristics of true capillaries?
Where do they come from?
Lack sm. M.
-where gas exchange takes place
-come from meta-arterioles
What is a Thoroughfare channel?
Distal end of metarterioles (lacks sm. M. )
Will connect to a postcapillary venule
What are the lymphatic capillaries?
CLOSE ENDED tubes found among cap beds
How are lympahtic capillaries histologically composed?
Composed of overlapping endothelial cells, forming 1 way valves for collecting lymph
-has incomplete basal lamina (increases permeability)
How are the openings b/w endothelial cells held in place in Lymphatic caps?
Held in place via anchoring filaments
What will lymphatic capillaries join up to form?
Lympahtic vessels
What is the function of lymphatic vessels?
◦ Circulate lymph thru most parts of the body
◦ Serve as adjuncts to the blood vessels
◦ Collect lymph & retuns it to venous supply
What junctions are present in lymphatic vessels?
Continuous tight junctions - to prevent leakage
What should lymphatic vessels never have in it?
Blood
What is the flow of lymph?
◦ Lympahtic caps —> vessels —> nodes —> trunks —> R. Lympahtic duct —> thoracic duct —> drain into brachiocephalic VV. —> superior vena cava
