HISTOLOGY REVIEW Vasculature Dr. Tim Ballard Department of Biology and Marine Biology

Overview of vessel histology Tunica intima endothelium basement membrane internal elastic lamina Tunica media circular smooth muscle external elastic lamina Tunica adventitia endothelium basement membrane ARTERYVEIN CAPILLARY

Large or elastic arteries A = tunica intima (interna) B = tunica media C = tunica adventitia (externa) Aorta–section – H&E – 4x objective

Large or elastic arteries arrowheads = elastic fibers arrows = nuclei of smooth muscle Aorta–section – H&E– high magnification With H&E, elastin fibers and smooth muscle cells are hard to discern. Under high power, focus up and down with the fine focus knob, and look for fibers that are birefringent (they look like they glow). These are elastin fibers.

Large or elastic arteries Verhoeff’s stain is used to visualize elastin fibers because it stains them purple-black. How many layers of elastin fibers can you count in the tunica media? Large vessels are so thick that they must have their own blood supply. This is the vasa vasorum. Aorta–section – Verhoeff’s stain for elastin fibers– 4x objective A = tunica intima (interna) B = tunica media C = tunica adventitia (externa) arrowheads = vasa vasorum

Large or elastic arteries The purple-black fibers are elastin fibers. The pink fibers are smooth muscle cells. Aorta–section – Verhoeff’s stain for elastin fibers– 40x objective

Medium (muscular or distributing) arteries A = tunica adventitia B = tunica media arrow = tunica intima of vein Companion vessels – H&E– 10x objective artery vein Muscular arteries are smaller than elastic arteries and have more smooth muscle than elastin fibers the tunica media. In addition, there are two specialized structures, the internal elastic lamina and the external elastic lamina, which are easily seen with the Verhoeff stain. As a general rule, medium arteries have at least one companion vein alongside. Be sure to compare the differences in relative thicknesses of the wall components.

Medium (muscular or distributing) arteries arrowhead = internal elastic lamina double arrowheads = external elastic lamina Companion vessels – Verhoeff – 40x objective artery vein tunica media tunica adventitia

Arterioles ARTERIOLE VENULEtunica intima tunica adventitia tunica media Arterioles and venules are microscopic, compared to small arteries, which can be seen with the naked eye. Typically, there are 1 – 5 layers of smooth mucsle in the tunica media of the arterioles. Again, compare the relative sizes of the walls. Companion vessels – H&E– 40x objective

Arterioles A = arteriole B = venule arrowhead = very small arteriole (it has a single smooth muscle cell layer) Again note the companion venule with the arteriole. Also, note that the thinner-walled venule tends to be collapsed while the arteriole tends to be more rounded and open.

Capillaries Arrowheads = capillaries Striated muscle – cross section – H&E – 40x objective Capillaries have very small diameters and walls that consist of only a single layer of endothelium.

Capillaries Arrowhead = capillaries Capillaries have very small diameters and walls that consist of only a single layer of endothelium. Adipose tissue – cross section – H&E – 40x objective end