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Veins

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Largest vessels that drain

Tunica Externa

These vessels can be so large that the tunica media needs to be vascularized!  In this case, a structure called a vaso vasorum is implanted in the tunica externa. This structure provides the blood needed for the tunica media.  Vaso vasorum means vessels of the vessels.

Tunica Media

Unlike their companion elastic arteries, the tunica media of veins does not have the internal and external elastic lamina.

Tunica Interna (Intimia)

Simple squamous epithelium

Lumen

Much like venules, veins are unable to maintain a shape upon fixation to a slide.  They sometimes are so collapsed on themselves that they are only recognizable by locating their associated artery.

Microscopic view of a biological tissue sample, centrally featuring a vein horizontally oriented and distended with closely packed, globular red blood cells. The background contains irregularly shaped, clear adipocyte cells with pink nuclei pressed to the periphery. Elsewhere, the tissue sample is heavily striated with pink-stained connective fibers. The image exhibits high contrast with soft focus, typical of histological prepared slides. All tissue elements are stained in Hematoxylin and Eosin.
Figure 1: Vein in large intestine tissue sample, microscopic view, stained pink. Red blood cells visible.
Microscopic image of a vein wall, hematoxylin and eosin (H&E) stain. The layered structure includes the intima (thin, top layer), media (smooth muscle bundles), and adventitia (connective tissue matrix). Staining shows cell nuclei in a darker pink/red, while cytoplasm and extracellular components appear lighter pink. Focus is sharp, revealing cellular details and tissue architecture.
Figure 2: Microscopic view of a vein wall with smooth muscle layers and connective tissues stained in shades of pink.
Microscopic histological slide stained pink, showing cross-section of inferior vena cava wall. Vaso vasorum (blood vessels supporting vessel walls) appear as clusters of pink cells with dark purple nuclei. A lighter area with a layered appearance is visible along the top left margin, representing the outer layer of the vein. The image is composed of varying shades of pink and purple.
Figure 3: Microscopic view of the inferior vena cava wall showing vaso vasorum, the blood vessels within the vein wall.

Figure 1: Recto anal junction [rectum at far right], H&E, 20X Slide 177-3
Figure 2: Slide 95 Small arteries and veins, H&E, 20X.
Figure 3: Slide Drexel MCP35 Inferior Vena Cava
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.

Explore More on Blood Vessel Histology

Link to more on Blood Vessel Histology

Elastic Arteries
Muscular Arteries
Arterioles
Sinusoidal Capillaries
Fenestrated Capillaries
Continuous Capillaries
Venules
Veins

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