Vascular Histology Flashcards
What are the three layers of blood vessels walls from outside to inside?
tunica adventitia
tunica media
tunica intima
What part(s) of the blood vessel walls give recoil ability?
- internal elastic membrane in the subendothelial layer of the tunica intima
- external elastic membrane in the tunica media
What structures are present on the tunica intima of veins, but not arteries?
valves
What are the three layers of the tunica intima?
- endothelium (single layer of squamous epithelium)
- basal lamina (collagen, proteoglycans, glycoproteins)
- subendothelial layer (loose connective tissue)
What is the composition of the tunica media?
-circumferentially arranged layers of smooth muscles
What is the purpose of the tunica media?
-ctx to briefly close off lumen and continually pump blood through the vasculature
Is the tunica media thick or thin in the arteries?
thick
Is the tunica media thick or thin in the veins?
thin
What is the composition of the tunica adventitia (externa)?
longitudinally-arranged collagenous tissue
True or False: the tunica adventitia merges with the surrounding connective tissue of a neurovascular bundle
True
Is the tunica adventitia thick or thin in the arteries?
thin
Is the tunica adventitia thick or thin in the veins?
thick
What is the purpose of the tunica adventitia?
prevents overexpansion of the vessels
How do the tissues of the blood vessels themselves get nutrients?
vasa vasorum located in the tunica adventitia
In which vessels are the vasa vasorum most numerous and why?
large veins d/t lack of diffusion properties
In which vessels do vasa vasorum not exist and why?
arterioles and capillaries because they can get their nutrients by diffusion
What provides innervation to the vasculature and in what layer of the vessel wall is it located?
nervi vasorum in the tunica adventitia = ANS input that controls ctx of vascular smooth muscle
What are two main histological characteristics of large (elastic) arteries?
- elastin forms concentric lamellae b/w muscle layers
- majority of the vessel wall is tunica media
What are three main histological characteristics of medium (muscular) arteries?
- more smooth muscle, less elastin
- prominent internal elastic membrane
- tunica media equal in size to tunica adventitia
How many layers of smooth muscle do small arteries have and how does that differ from arterioles?
small arteries have up to 8, while arterioles have only 1-2
-arterioles also may not have an internal elastic membrane present
In which type of vessel does the ANS do most of its regulation (constriction and dilation)?
-arterioles
Which vessels is the site of metabolic exchange?
capillaries
What is the diameter of the capillaries?
big enough for one RBC to flow through
What types of cells are present in the endothelial layer of capillaries?
pericytes
What is the function of pericytes?
contractile cells controlled by nitric oxide that surround capillaries and promote stability
What are the three types of capillaries?
continuous (most common)
fenestrated
discontinuous
What are characteristics of continuous capillaries?
- restrict passage of molecules
- locations: muscle, brain, peripheral nerves
What are characteristics of fenestrated capillaries?
- allow things to seep through
- locations: kidneys, gallbladder
What are characteristics of discontinuous capillaries?
- massively leaky, not selective
- discontinuous basal lamina
- locations: bone marrow, liver, spleen
How is blood flow regulated through capillary beds?
pre-capillary sphincters
What connects arterioles to capillaries?
metarterioles
What connects metarterioles to poscapillary venules to bypass the capillary bed if necessary?
thoroughfare channels
- contain no smooth muscle
- still have a small amt of metabolic exchange
What are the two types of venules and what distinguishes them from each other?
postcapillary venules
–have no tunica media
muscular venules
Most named veins are in which category?
medium veins
What are the histological characteristics of medium veins?
thicker tunics
obvious valves
What is a histological characteristics of large veins?
tunica adventitia is the thickest layer
What are histological characteristics of veins overall?
- tunics not as distinct
- thinner walls
- larger lumen
What is the purpose of the lymphatic vessels?
-return fluid to the venous system
Where does the lymphatic system originate?
-within the capillary beds as closed-ended tubes
What keeps lymph flowing unidirectionally?
overlapping endothelial cells acting as valves
What gives lymph vessels their high permeability?
incomplete basal lamina
Are lymph vessels moveable or stationary and why?
stationary d/t anchoring filaments
Delineate the progession of lymph vessels?
lymphatic capillaries collecting lymphatic vessels lymphatic trunks lymphatic ducts brachiocephalic vv.
What prevents fluid from leaking back out of the lymphatic vessels?
tight junctions
What is a major histological characteristic of lymphatic vessels?
NO RBC
