Specimen:

Specimen Details:

Organ: Aortic wall
Origin: Monkey
Staining: RFAL

Method and Specimen Description:

Normal histological sections were prepared and stained with RFAL, a method that vividly demonstrates elastic fibers within the vessel wall. The tissue originates from a region close to the heart — an area involved in the Windkessel effect (pressure reservoir function of the aorta).

Objective of the Examination:

To study the elastic wall structure of an artery, to identify its individual layers, and to recognize other incidentally sectioned structures.

Special Features of the Specimen:

The aorta, like all arteries, possesses a three-layered wall structure clearly visible at low magnification:

1. Tunica intima
2. Tunica media
3. Tunica adventitia

In this section, minor folding artefacts may be observed, resulting from the cutting process.

Tunica intima:

• Lined by a delicate endothelium, not preserved in all regions.
• Beneath it lies the subendothelial layer (stratum subendotheliale), which may contain occasional longitudinally oriented smooth muscle cells.
• The internal elastic lamina demarcates the border between the intima and media and is distinctly visible as a strong elastic layer.

Tunica media:

• Composed of circularly arranged smooth muscle cells interspersed with elastic and collagen fibers arranged in concentric sheets.
• RFAL staining highlights the elastic fibers particularly well.
• An external elastic lamina is often indistinct or absent in the aorta.
• The transition to the tunica adventitia is clearly defined by the disappearance of smooth muscle cells and the appearance of larger elastic fibers.

Tunica adventitia:

• Contains numerous vasa vasorum, collagen fibers, and fat cells.
• Represents the outermost supportive layer of the vessel.
• May also include co-sectioned connective tissue, adipose tissue, and skeletal muscle fibres at the periphery of the specimen.

Tasks:

• Identify and delineate the individual layers of the aortic wall: tunica intima, tunica media, and tunica adventitia.
• Locate regions with intact endothelium and examine the structure of the subendothelial layer.
• Trace the internal elastic lamina over a longer distance and compare it with the elastic fibers within the tunica media.
• Assess the ratio of elastic fibers to smooth muscle cells in the aortic wall.
• Locate several vasa vasorum and fat cells within the tunica adventitia.
• Examine the peripheral regions of the specimen and identify any co-sectioned structures (e.g. fat tissue, vessels, skeletal muscle).

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