Vascular Histology Flashcards
Lymph flow throughout the body
lymphatic capillaries
to
lymphatic vessels
to
lymphatic trunks
to
right lymphatic duct
to
thoracic duct
to
brachiocephalic v.
Lymphatic capillaries/vessels all have what features?
vascular tunics and posses valves
walls increase in thickness as vessels increase in size
tight junctions prevent leaks
there are afferents and efferents
What are close ended tubes found among capillary beds?
- overlapping endothelial cells form 1-way valves for collecting lymph
- incomplete basal lamina increases permeability
- endothelial cells held in place by anchoring filaments
- form lymphatic vessels
What is the function of lymphatic vessels?
- circulate lymph through most of the body
- unidirectional, convey fluid only from tissues
- collect lymph and return it to the venous supply
Large Veins: Tunica Adventitia
thickest layer of the vessel wall
contains collagen and elastic fibers and fibroblasts
contains longitudinal smooth muscle cells
Large Veins: Tunica media
thin, circumferentially arranged smooth muscle cells, collagen and fibroblasts
Large Veins: Tunica Intima
thin and blends with tunica media
Medium Veins
travel with muscular arteries
thicker tunica media and adventitia
wall is often folded around large lumen
contains valves
Postcapillary venules
muscular venules
small veins
drain capillaries, no true tunica media
1-2 layers of smooth muscle in tunica media, thin tunica adventitia
3 tunics, 2-3 layers in tunica media, tunica adventitia thicker
Venules
receive blood from capillaries and have a diameter as small as 0.1mm
subclassified as postcapillary and muscular venules
Small Veins
Less than 1mm in diameter, are continuous with muscular venules
Medium veins
a diameter of as much as 10mm, represent most of the named veins
Large Veins
usually have a diameter >10 mm
superior and inferior vena cava, hepatic portal vein
Tunics are not as distinct or well defined in veins, but large and medium veins have ____
Tunica intima may contain ____
all three tunics
valve (thin CT core covered in endothelial cells)
Veins have thinner walls than ____
____ have larger lumens than ____
lumen in ____ often collapse
arteries!
Veins; arteries!
Veins!
How does blood bypass a capillary bed?
Contracted precapillary sphincters will “shunt” blood flow
this prevents exchange within true capillaries and forces blood to enter venous return more quickly
differentially occurs based on metabolic demand
Describe blood flow through the well-perfused capillary bed
Metarterioles first branch off of the arteriole supplying tissues
precapillary sphincters regulate blood through the capillaries
then true capillaries branch from the metarteriole, lacking SM and may have pericytes
the thoroughfare channel is the distal end of the metarteriole and connects to a postcapillary venule
Compare and contrast continuous, fenestrated and discontinous capillaries
Continuous: only certain, small (size, charge, etc) things can get through
Fenestrated: “holey”, larger things can get through, important for filtering urine
Discontinuous: very leaky, discontinuous basal lamina
What forms the innermost layer of the tunica intima?
What is the function of this layer?
single layer of endothelial cells connected via cell-cell junctions
support the basement membrane and produce collagen
involved in blood coagulation and vasodilation/constriction
What is the function of the pericytes?
perivascular contractile cells with branching cytoplasmic processes
they are enclosed within the basal lamina, continuous with that of the endothelium
controlled by NO
promote stability of capillaries and venules
What is special about small arteries?
up to 8 layers and will have an internal elastic membrane
What is special about arterioles?
1-2 layers, internal elastic membrane may/may not be present
FLOW REGULATORS of capillary beds
SNS: tunica media causes vasoconstriction
PNS: tunica media causes vasodilation
Where does a prominent internal elastic membrane become apparant as well as a recognizeable external elastic membrane?
Medium (Muscular) arteries
(thicker tinuca adventitia, about the same as the tunica media)
What are the hallmark features of the large (elastic) arteries?
elastin forms sheets between muscle cell layers
NO fibroblasts
lumen size reduces pressure and allows strong blood flow to continue during diastole
The tunica adventitia contains the vasa vasorum and nervi vasorum which are what?
VV: vessels of the tunica adventitia that supply blood to the vascular tunics themselves (found in large arteries and veins)
NV: ANS input that controls contraction of vascular smooth muscle
what are the hallmark features of the tunica adventitia/externa
long. arranged collagen tissue with some elastic fibers
merges with loose CT around vessels
thin in arteries, thick in veins
What are some hallmark features of the tunica media?
layers of smooth muscle
thick in arteries
spans from the internal elastic membrane to the external elastic membrane
What are the hallmark features of the tunica intima?
endothelium
basal lamina (thin EC layer with collagen, PTG, GP)
subendothelial layer (loose CT, internal elastic membrane)
Everything we need to know about continuous vessels
- most common
- tight, occluding junctions that seal off intercellular clefts
- molecular exchange happens via diffusion or transcytosis
- continuous basement membrane
- muscle, brain, peripheral nerves, exocrine glands
- cells meet end-to-end
Everything we need to know about Fenestrated vessels
- located in organs where molecular exchange with blood is important
- tight junctions with fenestrations
- greater exchange across the endothelium, limited to size of macromolecule
- continuous basement membrane
- endocrine, fluid/metabolite absorption, gallbladder, kidney
Everything we need to know about discontinuous/sinusoidal vessels
- located where exchange of macromoleucles and cells must openly occur
- large fenestrations (the largest)
- open exchange occurs, large cell movements allowed
- partial discontinuous basement membrane
- bone marrow, liver, spleen
Everything we need to know about large arteries (elastic)
>10mm
tunica intima: endothelium, CT, Sm. M
tunic MEDIA: Sm. M., elastic lamellae
tunica adventitia: thinner, CT, elastic fibers
Everything we need to know about medium arteries (muscular)
2-10mm
tunica intima: endothelium, CT, Sm. M, BIG internal elastic membrane
tunica media: Sm.M, collagen fibers, relatively little elastic tissues
tunica adventitia: thinner than tunica media, CT, some elastic
Everything we need to know about small arteries
0.1-2mm
tunica intima: endothelium, CT, Sm. M, internal elastic membrane
tunica media: Sm. M (8-10layers), collagen
tunica advenitia: thinner, CT, some elastic
Everything we need to know about arterioles
10-100um
tunica intima: endothelium, CT, Sm.M
tunica media: Sm. M (1-2 cell layers)
tunica adventitia: thin, CT (poorly defined)
Everything we need to know about capillaries
4-10um
tunica intima: endothelium
tunica media and adventitia: NONE
Everything we need to know about postcapillary venules
10-50um
tunica intima: endothelium and pericytes
tunica media and adventitia: NONE
Everything we need to know about muscular venules
50-100 um
tunica intima: endothelium
tunica media: Sm. M (1-2 cell layers)
tunica adventitia: thicker than tunica media, CT, some elastic
Everything we need to know about small veins:
0.1-1mm
tunica intima: endothelium, CT, Sm. M (2-3 layers)
tunica media: Sm. M (2-3 layers with tunica intima)
tunica adventitia: thicker, CT, some elastic
Everything we need to know about medium veins
1-10mm
tunica intima: endothelium, CT, Sm. M, internal elastic membrane sometimes
tunica media: Sm. M, collagen
tunica adventitia: thicker, CT, some elastic
Everything we need to know about large veins
>10mm
tunica intima: endothelium, Ct, Sm. M
tunica media: Sm. M, collagen fibers
tunica adventitia: Much thicker, Ct, some elastic, long. Sm. M, cardiac muscle extensions into great veins near heart (myocardial sleeves)
