This specimen includes the surrounding dense irregular connective tissue of the tendon, the epitendineum (Ept). The tendon fascicles (TF) that make up the tendon are surrounded by a less dense connective tissue than that associated with the epitendineum. In longitudinal sections such as this, the connective tissue that surrounds the individual fascicles, the endotendineum (Ent),
Dense regular connective tissue, tendon, longitudinal section, human, H&E ×400.
This higher magnification micrograph shows the ordered single-file array of the tendinocyte nuclei (TC) along with the intervening collagen. The latter has a homogeneous appearance.
seems to disappear at certain points, with the result that one fascicle appears to merge with a neighboring fascicle. This is due to an obliqueness in the plane of section rather than an actual merging of fascicles. The collagen that makes up the bulk of the tendon fascicle has a homogeneous appearance as a result of the orderly packing of the individual collagen fibrils. The nuclei of the tendinocytes appear as elongate profiles arranged in linear rows. The cytoplasm of these cells blends in with the collagen, leaving only the nuclei as the representative feature of the cell.
The cytoplasm of the cells is indistinguishable from the collagen, as is typical in H&E paraffin specimens. The variation in nuclear appearance is due to the plane of section and the position of the nuclei within the thickness of the section. A small blood vessel (BV) coursing within the endotendineum is also present in the specimen.
Dense regular connective tissue, tendon, cross section, human, H&E ×400.
This specimen is well preserved, and the densely packed collagenous fibers appear as a homogeneous field, even though the fibers are viewed on their cut ends. The nuclei appear irregularly scattered, as opposed to their more uniform pattern in the longitudinal plane. This is explained by examining the dashed line in lower left figure which is meant to represent an arbitrary cross-sectional cut of the tendon. Note the irregular spacing of the nuclei that are in the plane of the cut. Lastly, several small blood vessels (BV) are present within the endotendineum (Ent) within a fascicle.
KEY BV, blood vessel Ent, endotendineum Ept, epitendineum TC, tendinocytes nuclei TF, fascicle of tendon dashed line, arbitrary cross-sectional cut of tendon
PLATE 5 • DENSE REGULAR CONNECTIVE TISSUE, TENDONS, AND LIGAMENTS