functionalis

Functionalis, also known as the stratum functionalis, is the inner, glandular layer of the endometrium, the mucous membrane lining the uterus. It lies above the deeper stratum basale and undergoes cyclic remodeling in response to ovarian hormones. The functionalis is the portion of the endometrium that is shed during menstruation and is renewed each cycle.

Histologically, the functionalis consists of simple columnar epithelium covering uterine glands embedded in a stromal matrix. It contains spiral arteries and a variable amount of edema and secretory activity that change with the menstrual cycle. The basalis, which remains during menstruation, serves as the source for regenerating the functionalis after each cycle.

Hormonal regulation drives its changes. During the proliferative phase, estrogen stimulates growth and thickening of the functionalis with increased glandular activity. In the secretory phase, progesterone from the corpus luteum causes the glands to become more coiled and secrete products, and the stroma becomes edematous, preparing the lining for possible implantation. If implantation does not occur, the functionalis is shed during menses; the basalis persists to reconstitute a new functionalis in the next cycle. If pregnancy occurs, the functionalis undergoes decidualization under progesterone support to form decidual tissue that supports early gestation.

Clinically, the state of the functionalis is assessed in endometrial dating, ultrasounds measuring endometrial thickness, and endometrial biopsies. Pathologies may involve abnormal shedding, thickness, or glandular activity within the functionalis.