Blood Vessels Flashcards
What is the increase in number of vessels and cross-sectional diameter going from the aorta to the capilaries
2-3 bilion-fold increase in number of vessels
500-fold increase in overall cross-sectional diameter
Where is blood flow slowest?
capillaries and venules
What are the layers, from innermost to outermost, in blood vessels?
tunica intima -> tunica media -> tunica adventitia
What is the tunica intima?
Innermost layer of blood vessels, comprised of a layer of endothelial cells in intimate contact with blood.
What is the tunica media?
A layer in the middle of a blood vessel, may be comprised of multiple layers of elastic laminae, smooth muscle cells, or collagen.
What is the tunica adventitia?
The supporting outer layer of a blood vessel, comprised of collagenous tissue.
What does the tunica adventitia of larger vessels contain?
vasa vasorum (“vessels of vessels”), blood vessels that actually supply oxygen and nutrients to the adventitia and outer part of the media (diffusion insufficient)
Compare wall thickness of arteries and veins
Arteries are quite thick-walled compared to veins, and have approximately the same wall thickness as the lumen of the vessel itself.
What does smooth muscle in arterioles allow for?
Permits control of blood flow to capillary beds.
What are the elastic arteries?
The aorta and large arteries branching from it.
What do myointimal cells do?
Similar structural features to smooth muscle cells
Describe arteriole structure
Arterioles contain an inner lining of endothelial cells on a thin basement membrane, surrounded by 1-2 layers of smooth muscle cells and outer collagenous tissue which blends in with surrounding connective tissue.
Describe arteriole function
Gatekeepers to local capillary beds, can greatly restrict flow of blood through them.
What do a metarterioles and arteriole-venule shunts accomplish?
Can connect larger arterioles and venules, can direct flow through or permit bypass of capillary beds
What is the diameter of capillaries?
5-15 um
What surrounds capillaries?
No muscular layer, but often surrounded by cells called pericytes
What are pericytes?
Relatively unspecialized cells that can give rise to smooth muscle cells during vessel growth and wound healing, can be contractile in nature.
Describe capillary structure
1-2 endothelial cells surrounding the lumen, no smooth muscle, possibly pericytes
What two main types of capillaries are recognized?
Continuous and fenestrated
Describe continuous capillaries
Endothelial cells form an uninterrupted lining, although transfer across the lining can occur via pinocytotic vesicles
Describe fenestrated capillaries
Fenestrated capillaries have pores (fenestrations, windows) in the endothelial cells, sometimes covered by a thin diaphragm
Where might you find fenestrated capillaries?
Glomerulus of the kidney In the sinusoidal capillaries of liver and spleen larger fenestrations called pores let red blood cells through
What do fenestrated capillaries permit?
Bulk flow of plasma past the endothelial boundary
Describe post-capillary venules
Initially similar to pre-capillary arterioles, but slightly larger diameter. Surrounded by pericytes. Leukocytes primarily diapedese through vessel walls. Endothelium responsive to vasoregulatory substances such as serotonin and histamine (controlled permeability). Larger venules get 1-2 layers of smooth muscle with thin layers of connective adventitia (muscular venules).
