The area enclosed by the rectangle in figure above is shown here at higher magnification. The specimen shows a longitudinal section through a lymphatic vessel (Lym). In other planes of section, the lymphatic vessels are difficult to identify. The for tuitously sectioned lymphatic vessel is seen in the core of the mucosal fold, along with a highly cellular connective tissue (CT) and the blood vessels (BV) within the connective tissue. The epithelium lining the mucosa is shown in the inset. The ciliated cells are readily identified by the presence of well-formed cilia (C). Nonciliated cells, also called peg cells (PC), are readily identified by the absence of cilia; moreover, they have elongate nuclei and sometimes appear to be squeezed between the ciliated cells. The connective tissue (CT) contains cells whose nuclei are arranged typically in a random manner. They vary in shape, being elongated, oval, or round. Their cytoplasm cannot be distinguished from the intercellular material (inset). The character of the connective tissue is essentially the same from the epithelium to the muscularis, and for this reason, no submucosa is described.
PLATE 95 BV, blood vessels C, cilia CT, connective tissue Ep, epithelium L, lumen Lym, lymphatic vessel Muc, mucosa Mus, muscularis PC, peg cells KEY 880 The uterus is a hollow, pear-shaped organ with a thick wall and, in the nonpregnant state, a narrow cavity. The uterine wall is composed of a mucosa, referred to as the endometrium; a muscularis, referred to as a myometrium; and, externally, a serosal cover, the perimetrium. The myometrium consists of smooth muscle and connective tissue and contains the large blood vessels that give rise to the vessels that supply the endometrium. The uterus undergoes cyclical changes that are largely manifested by changes that occur in the endometrium. If implantation of an ovum does not occur after preparation for this event, the state of readiness is not maintained, and much of the endometrium degenerates and is sloughed off, constituting the menstrual flow. The part of the endometrium that is lost is referred to as the stratum functionale; the part that is retained is called the stratum basale. The stratum basale is the deeper part of the endometrium and adjoins the myometrium. The myometrium also undergoes changes associated with implantation of a zygote. In the nonpregnant uterus, the smooth muscle cells are about 50 m in length; during pregnancy, they undergo enormous hypertrophy, often reaching more than 500 m in length. In addition, new muscle fibers develop after division of existing muscle cells and division and differentiation of undifferentiated mesenchymal cells. The connective tissue also increases to strengthen the uterine wall. Fibroblasts increase by division and secrete additional collagen and elastic fibers. After parturition, the uterus nearly returns to its normal size. Most muscle fibers return to their normal size, and some degenerate. Collagen secreted during pregnancy is digested by the very cells that secreted it, the fibroblasts. Similar, but less pronounced, proliferation and degeneration of fibroblasts and collagen occur in each menstrual cycle.
Uterus, human, H&E ×25; inset ×120.