The Histology Guide

A comparison of all the structures

Heart:

Tunica Adventitia (epicardium) contains fibroelastic connective tissue, blood vessels, lymphatics and adipose tissue.

Tunica media (myocardium) is the largest of the three layers, and contains cardiac muscle fibres, and loose endomysial connective tissue that contains lots of capillaries.

Tunica Intima (endocardium) of the heart - stratified squamous epithelium.


photo of elastic artery

Elastic Artery

Tunica adventitia - has small 'vasa vasorum' - - as the large arteries need their own blood supply.

Tunica media - broad, elastic - concentric fenestrated sheets of elastin, and collagen, few muscle fibres.

Tunica intima - single layer of flattened epithelial cells, supporting layer of elastin rich collagen. Has 'myointimal cells' that accumulate lipid with ageing - first sign of atherosclerosis.


photo of muscular artery

Muscular Artery

Tunica intima - flattened endothelial cells

Tunica media: - muscle layer, (with some elastin and collagen), sandwiched by an Internal Elastic Layer (IEL), and an External Elastic Layer (EEL).
Notice how the tunica media layer is relatively smaller than that for the elastic artery.

Tunica Adventitia - very broad, mostly collagen and elastin.


photo of arteriole

Arteriole

Tunica intima - single layer of squamous epithelium.

Tunica media - few or single layer of smooth muscle cells

Tunica adventitia - much reduced, merges in with surrounding tissue.


photo of vasa vasorum

Capillary/Venules

This shows a vasa vasorum. The large lumen suggests that it is a venule. It consists of a single layer of flattened endothelial cells. There is no tunica media or tunica adventitia layer.

 


photo of a vein

Vein.

Tunica adventitia layer is the most prominent layer, and has collagen fibres.


photo of muscular vein

Muscular Vein

Tunica Media is the most prominent layer.
There is no inner or outer elastic layer, as in a Muscular Artery.


Some questions for you to think about:

questionHow do the structures of muscular arteries and veins differ?

questionMuscular arteries and veins both regulate their diameters by contraction of the muscle layers in the tunica media, yet this layer appears very different in the two types of vessel.How do you explain this?

questionHow does the structure of the tunica adventitia differ from that of the muscular artery?

questionThe lumen of the artery on this slide is very regular but that of the vein is very irregular. How is this difference related to the structure of their walls?