Vascular Histology

Question 1

What are the 3 layers found in arteries and veins?

Answer 1

Tunica intima (inner most)
Tunica media (middle)
Tunica adventitia (outer most)

Question 2

How are arteries and veins different?

Answer 2

arteries branch to decrease in diameter

veins merge to increase in diameter

Question 3

Describe the layers of tunica intima

Answer 3

endothelium (simple squamous epithelial cells)

basal lamina (collagen, proteoglycans, glycoproteins)

subendothelial layer (loose CT) w/ internal elastic membrane

Question 4

What is the internal elastic membrane?

Answer 4

found in the subendothelial layer of the tunica intima in ARTERIES & ARTERIOLES

fenestrated elastic material (many elastic fibers to add recoil properties to vessels)

Question 5

How is the tunica intima different in veins from arteries?

Answer 5

tunica intima in veins contains valves

Question 6

Describe the tunica media

Answer 6

part of layers that can contract to close off lumen

arranged layers of smooth muscle

extends from internal elastic membrane to external elastic membrane

Question 7

What separates the tunica media & tunica adventitia?

Answer 7

layer of elastin

Question 8

What is the tunica media composed of?

Answer 8

smooth m & varying amounts of elastin, reticular fibers & proteoglycans

Question 9

Describe the tunica adventitia

Answer 9

longitudinal collagenous tissue w/ few elastic fibers

merges w/ loose CT surrounding the vessels (assoc w/ neurovasc bundles)

Question 10

How is the tunica adventitia different in arteries & veins?

Answer 10

thin in arteries & thick in veins

Question 11

How do the tunics receive blood & nervous innervation?

Answer 11

vasa vasorum & Nervi vasorum

Question 12

What is the vasa vasorum?

Answer 12

vessels of the tunica adventitia that supply blood to vascular tunics (found in large arteries & veins)

Question 13

What is the nervi vasorum?

Answer 13

ANS input that controls contraction of vascular smooth m (control of vascular tone)

Question 14

Defining features of large arteries

Answer 14

lots of elastic fibers forming concentric sheets between muscle cell layers

NO fibroblasts (smooth m makes collagen, elastin & ECM)

Question 15

Why do large arteries have lots of elastin?

Answer 15

strong pressure of blood pulsating during systole will expand arterial wall

large lumen size reduces pressure & allows strong blood flow to continue during diastole

Question 16

What makes large arteries distinct on an image?

Answer 16

concentric sheets of elastin w/ in smooth m

tunica media makes up majority of wall

Question 17

Defining features of medium (muscular) arteries

Answer 17

prominent internal elastic membrane (that lines the lumen) & external elastic membrane

smooth m cells arranged in SPIRAL fashion

thicker tunica adventitia

Question 18

Defining features of small arteries

Answer 18

have up to 8 layers of smooth m & internal elastic membrane

Question 19

Defining features of arterioles

Answer 19

only 1-2 layers of smooth m & internal elastic membrane is more variable

Question 20

What is the role of arterioles?

Answer 20

flow regulators for capillary beds

where sympathetics act on tunica media to cause vasoconstriction & where parasympathetics act on tunica media to cause vasodilation

Question 21

Defining features of capillaries

Answer 21

smallest blood vessels that form capillary beds

vessels surrounded by Pericytes

single layer of endothelial cells

Question 22

What is the role of capillaries?

Answer 22

site of metabolic exchange

Question 23

What are Pericytes?

Answer 23

perivascular contractile cells w/ branching cytoplasmic processes surrounding capillaries

controlled by NO from endothelial cells & promote stability of capillaries & post-cap venules

Question 24

Where are endothelial cells found & what is their role?

Answer 24

single layer of cells forming innermost aspect of tunica intima

support basement membrane & produce collagen

involved in blood coagulation, thrombosis, local dilation & constriction

Question 25

How do endothelial cells communicate?

Answer 25

via cell-cell junctions (# of junctions alter permeability) connection between endothelial cells defines capillary bed function

Question 26

What are the 3 types of capillaries?

Answer 26

Continuous capillary Fenestrated capillary Discontinuous capillary

Question 27

Defining features of continuous capillaries

Answer 27

tight, occluding junctions to seal of intercellular clefts continuous basement membrane & cells meet end-to-end

Question 28

Where are continuous capillaries found? How does exchange occur in these capillaries?

Answer 28

throughout body in muscle, brain, peripheral nerves, exocrine glands all molecular exchange must occur via diffusion or transcytosis

Question 29

Where are fenestrated capillaries found? How does exchange occur?

Answer 29

organs where molecular exchange w/ blood is important (endocrine glands, kidney, gallbladder) tight junctions w/ openings that allows greater exchange across endothelium (limited by size of molecule)

Question 30

Where are discontinuous capillaries found? How does exchange occur?

Answer 30

where exchange of marcomolecules & cells must occur openly (bone marrow, liver, spleen) open exchange occurs b/c larger openings among endothelial cells (leaky & non-selective)

Question 31

Describe flow of blood into & out of capillary bed

Answer 31

metarterioles branch off supplying arteriole & send blood into true capillaries gas exchange occurs in true capillaries blood leaves thru thoroughfare channel (distal end of metarteriole lacking smooth m) blood continues to flow into postcapillary venule

Question 32

How do capillaries differ from metarterioles?

Answer 32

capillaries do NOT have smooth m

Question 33

How is blood flow thru capillary beds regulated?

Answer 33

via sphincters of smooth m @ arterial end (on metarterioles) occurs differentially based on metabolic demand (sphincters shunt blood flow to different areas)

Question 34

How do veins differ from arteries?

Answer 34

veins have thinner walls & lumen is larger which often collapses

Question 35

Defining features of venules

Answer 35

post-capillary venules do NOT have tunica media muscular venules have some smooth m in tunica media & thin tunic adventitia

Question 36

Defining features of small veins

Answer 36

have all 3 layers of tunics tunica media is 2-3 layers & thicker tunica adventitia (endothelium is continuous w/ 2-3 layers of smooth m)

Question 37

Defining features of medium veins

Answer 37

thicker tunica media & adventitia, some elastic fibers contain valves, travel w/ muscular arteries

Question 38

Defining features of large veins

Answer 38

tunica adventitia is thickest layer of vessel wall (blends w/ thin tunica media) has collagen, elastic fibers & fibroblasts longitudinal smooth m cells

Question 39

Role of lymphatic vessels

Answer 39

circulate lymph thru most parts of body in 1 direction & return it to venous supply collects fluid that leaks out @ capillary bed due to pressure gradient & returns to blood volume can clean fluid to prevent infection

Question 40

Defining features of lymphatic capillaries

Answer 40

close-ended tubes found among capillary beds w/ overlapping endothelial cells (1 way valves) incomplete basal lamina to increase permeability

Question 41

How are endothelial cells of lymphatic capillaries connected?

Answer 41

openings held in place by ANCHORING FILAMENTS (so can collect as much fluid as possible)

Question 42

Defining features of lymphatic vessels

Answer 42

have all vascular tunics & possess valves for 1 way flow walls increase in thickness & cells connected via tight junctions

Question 43

What are afferent & efferent lymphatic vessels?

Answer 43

afferent lead into lymph node & efferent exit lymph node

Question 44

Describe flow of lymph

Answer 44

``` lymphatic capillaries lymphatic vessels lymphatic trunks R lymphatic duct Thoracic duct Brachiocephalic v ```