Lecture 19: Vascular Histology Flashcards
What are the three layers of blood vessels?
Tunica Intima (innermost) Tunica Media (middle) Tunica Adventitia (outermost)
What is the tunica intima composed of?
1) Endothelium: reduces friction
2) Basal lamina
3) Subendothelial Layer
The endothelium of the tunica intima is composed of what type of cells?
Squamous epithelial cells (single layer)
The tunica media in the arteries is relatively ____.
The tunica media in the veins is relatively ____.
Arteries: thick
Veins: thin
Why does the tunica media have small openings?
Openings are for nutrients to diffuse
How is the tunica media arranged?
Circular pattern of arranged smooth muscle layers
What separates the tunica media from the tunica adventitia?
Layer of elastin
How is the tunica adventitia arranged?
Longitudinally (up/down) arranged
The tunica adventitia in the arteries is relatively ____.
The tunica adventitia in the veins is relatively ____.
Arteries: thin
Veins: thick
What is the vasa vasorum?
Vessels of tunica adventitia that supply blood to the tunics of the vessels (allows diffusion of nutrients)
What is the nervi vasorum?
Nerves of vessels that allow ANS input that can control the contraction
Describe the hallmarks of the large (elastic) arteries.
- Elastin found in concentric sheets b/t tunica layers
- No fibroblasts
- Very thick tunica media
Describe the hallmarks of the medium (muscular) arteries.
- Less elastin
- Internal and external elastic membranes are more prominent
- Smooth muscle in spiral fashion
- Tunica media and tunica adventitia about same thickness
Describe the hallmarks of the small arteries.
- Internal elastic membrane present
- Up to 8 layers of tunica media
Describe the hallmarks of the arterioles.
- Internal elastic membrane may/may not be present
- Up to 1-2 layers of tunica media
In arterioles, what will sympathetic innervation to the tunica media cause?
Vasoconstriction
In arterioles, what will parasympathetic innervation to the tunica media cause?
Vasodilation
What are pericytes?
Contractile cells that wrap around the endothelial cells that line the capillaries and venules throughout the body
What are the function of pericytes?
Promote stability of capillaries and postcapillary venules
What controls pericytes?
Nitric Oxide
What connects endothelial cells found in the innermost layer of tunica intima?
Cell-cell junction
What is the function of endothelial cells?
- Supports basement membrane
- Produces collagen
- Metabolically involved in blood coagulation and thrombosis, and local vasodilation/constriction
Describe continuous capillaries.
- Most common
- Tight junctions don’t allow many molecules to enter
- Pericytes present
- Continuous basement membrane
Describe fenestrated capillaries.
- Located in organs where blood exchange is most important
- Larger items can go through
- small windows in capillaries
- Continuous basement membrane
Describe sinusoidal capillaries.
- Open exchange for large molecules and cells
- Discontinuous basement membrane
What are metarterioles?
First branch off of arteriole supplying tissues
What are precapillary sphincters?
Regulate blood flow to capillaries
-can open/close
What are true capillaries?
Between arterioles and venules
-where proper gas exchange occurs
What is a thoroughfare channel?
Distal end of metarteriole
What does a thoroughfare channel connect to?
Postcapillary venule
Describe the hallmarks of veins.
- Tunica not well defined
- Thinner walls
- Larger lumen (often collapsed)
What does the tunica intima contain that arteries don’t have?
Have valves
In what direction do lymph in lymphatic vessels flow?
Unidirectional
In lymphatic capillaries, what are the openings between the endothelial cells called?
Anchoring filaments
Describe the flow of lymph.
- Lymphatic capillaries –> vessels –> trunks
- Either right lymphatic duct or thoracic duct
- Brachiocephalic vein
