Histo 2 Flashcards
What are “tunics”?
3 layers of the walls of arteries and veins
What’s to know about veins and arteries?
Arteries branch extensively to decrease in diameter
Veins merge repeatedly to increase in diameter
What is the Tunica Intima?
What are the 3 layers?
what is only really in large arteries?
most closely associated to the lumen of the vessel.
- It’s lined with a single layer of simple squamous endothelium
- deep to that you have basal lamina of the endothelial cells. Located here is a thin EC layer (collagen, proteoglycans, glycoproteins)
- Subendothelial layer –> has loose Areolar CT. link the endothelial Layer to the next layer as we move to the outside of the external vessel.
Internal elastic membrane –> sheet like layer of fenestrated elastic material w/in arteries and arterioles (this allows for rubber band functions as blood moves through)
What is the Tunica Media?
In the middle
It’s going to be much thicker in arteries than in veins
this is where you have smooth muscle layers that are arranged in a circular pattern that allows the vessels to constrict down or dilate
Within the tunica media what two membranes do you have?
Internal and External Elastic Membranes
The external elastic membrane has a layer of elastin that separates the tunica media from the adventitia
What is the Tunica Adventitia?
What is this thinner in? veins or arteries
what is it composed of and why is it important?
Outermost layer of the vessel.
This is a thinner layer in arteries than in veins
in veins this is where they get their structural support.
This is loose CT that allows it to adhere to other structures in close proximity –> vessels like to travel with nerves (neuromuscular bundle). that gluing of those structures together is because of the tunica adventitia likes to glue it to it.
what gives veins and arteries their structural support?
Veins = tunica adventitia
Arteria = Tunica media
Especially in veins, because the blood is deoxygenated, the nutrients available from the blood to diffuse out to the walls is what?
lacking compared to the arteries
blood from the aorta to systemic it has tons of oxygen and the nutrients can diffuse across the arterial walls.
in veins it’s opposite so you’re not going to have much going across the vessel wall and it needs nutrients though.
Vasa Vasorum?
Vasa Vasorum
additional blood vessels located in the tunica adventitia especially in large veins.
you’ll see it in larger arteries.
some of the nutrients diffuse into the lumen and we need nutrients to go to the vascular walls themselves.
this literally means “vessels of vessels”
it’s how larger vessels receive their nutrients.
What is nervi Vasorum
ANS input that controls contraction of vascular contraction
Why are large arteries also called elastic arteries?
where are these elastic fibers located.. what are they arranged in?
what do they not have? How do we make all the fibers then?
because of the large amount of elastin
in the super thick tunica media. arranged in lamellae
NO fibroblasts! smooth muscle makes all ECM components
What is the purpose of fenestrations in the tunica media of the large arteries?
allows nutrients to pass through
What happens with regards to lamellae as you age?
the amount of lamellae increases, so this makes blood pressure feedback a bit tougher.
What do think of when you see muscular arteries?
things that aren’t the great vessels but also have names… i.e. brachial, axillary, femoral
What are the muscular arteries composed of?
what is a hallmark of this?
what’s to note about the tunica adventitia?
more smooth muscle but less elastin. we don’t have as much blood pressure here!
Prominent Internal Elastic Membrane
also have a recognizable External Elastic Membrane
it’s thicker than usual, about the same size as the tunica media
How do you tell the difference between a large elastic artery and a medium muscular artery?
Elastic has the wavy lines in the tunica media, muscular does not
Remember, the internal elastic membrane is part o what structure?
Tunica Intima
How many layers of smooth muscle are in small arteries? arterioles?
what’s in small arteries but may not be in arterioles?
8
1-2
internal elastic membrane
What do small arteries drain into?
What is the key role of arterioles?
What does sympathetic innervation and parasympathetic innervation do to the tunica media of arterioles?
Arterioles
regulate flow into the capillary beds, vasoconstriction + vasodilation
Vasoconstriction
Vasodilation
Capillaries do what?
what is the diameter associated with?
what are these beds surrounded by? what do they do?
Site of metabolic gas exchange and they form true capillary beds.
RBC
Pericytes –> contractile cells that surround the capillary vessels. they enclose the basal lamina. they can contract down on the capillary bed
Why are pericytes important for capillary beds?
they don’t have a tunica media or adventitia, so the pericyte is in its place. you need the pericyte to contract down.
What are pericytes sensitive to?
what are they helpful for?
Nitric Oxide
structural stability and constriction if needed.
Endothelial Cells are found where?
cells that are found lining capillary beds.
in most typical capillaries they are connected by tight junctions.
What are the 3 types of capillaries?
continuous
Fenestrated
Discontinuous
What are continuous capillaries?
most common
widespread layer of endothelial cells lining the lumen of the capillary, surrounded by a uniform and complete basal lamina
this allows for things to not get into or out of the capillary bed unless they’re super small molecules.
What are Fenestrated Capillaries?
“finistra” means window. these are open pores that allow for things of larger size to move through
The basal lamina surrounding it is also complete and continuous.
What are Discontinuous Capillaries?
There is no regulation at all. the openings are large enough for cells to fit through and the basal lamina is incomplete / discontinuous.
proteins, cells, other things can move into these types.
Where might you find discontinuous capillaries
Bone Marrow
Liver
Spleen
When an artery shoves it’s blood into a capillary bed, what’s the first thing it goes through?
what is the process from here?
metaarteriole –> feeds into a true capillary bed which has a thoroughfare channel that has other branches that feed into this channel
leave through post capillary venules
What allow constriction in the capillary beds?
Precapillary sphincters.
they can clamp down if you don’t want to do gas exchange
when it shunts the blood it just moves it to a different spot. moves quickly into the postcapillary venule.
If we are in the GI and during Sympathetic stage, are the sphincters going to be open or closed in the capillary beds
closed
What do venules do?
smallest veins.
they join back together to form muscular venules.
continue to combine to small veins, then medium veins, and then large veins.
What are the features of the veins?
what about the tunics?
there are valves that are in the tunica intima.
the tunica are not as well distinct but the large and medium have all 3 layers
If you see a vein and an artery in the same histo slide, how do you know it’s a vein?
veins have a collapsed lumen and the walls are thinner (except in large veins)
What do medium veins travel with?
what do medium veins have that helps distinguish them from smaller arteries?
muscular arteries
thicker tunica media and adventitia.
it has valves!
the wall is often folded around large lumen
What’s the difference between large veins and large arteries histologically?
in veins you have bundles that are there. the smooth muscle is in the adventitia rather than in the media because the media isn’t that thick.
the tunica media is what all of the elastin.
What is the lymphatic system?
lymphatic capillaries?
blood leaks out of the capillary bed and it’s collected as lymph.
closed-ended tubes found among capillary beds.
they have overlapping endothelial capillaries that form 1-way valves for collecting lymph
what do lymphatic capillaries become?
how do you know it’s a lymphatic capillary?
lymphatic vessels
it’s super thin in the wall, almost 1 layer thick. it looks super pale staining and a gritty looking substance.
there’s no blood in it.
