The Reproductive System
in the pelvis, ascend along the sides of the uterus,
and send branches into the uterine wall (Figures 27.14 and
27.15b). Tese branches break up into several
ku-āt) within the myometrium. Te arcuate arteries send
into the endometrium, where they in turn give
to the stratum basalis and
to the stratum functionalis. Te spiral arteries repeat-
edly degenerate and regenerate, and it is their spasms that actu-
ally cause the functionalis layer to be shed during menstruation.
Veins in the endometrium are thin walled and form an exten-
sive network with occasional sinusoidal enlargements.
(“sheath”) is a thin-walled tube, 8–10 cm (3–4
inches) long. It lies between the bladder and the rectum and
extends from the cervix to the body exterior (see Figure 27.12).
Te urethra parallels its course anteriorly. O±en called the
, the mucosal lining of the uterine cavity
. It is a simple columnar epithelium under-
lain by a thick lamina propria. If fertilization occurs, the
young embryo burrows into the endometrium (implants)
and resides there for the rest of its development.
Te endometrium has two chief
cyclic changes in response to blood levels of ovarian hormones
and is shed during menstruation (approximately every 28 days).
Te thinner, deeper
forms a new functionalis a±er menstruation ends. It is unre-
sponsive to ovarian hormones. Te endometrium has numerous
that change in length as endometrial thickness
changes during the menstrual cycle (see Figure 27.22).
Te vascular supply of the uterus is key to understanding
the cyclic changes of the uterine endometrium, which we will
discuss later in the chapter. Te
arise from the
Lumen of uterus
Lamina propria of
The endometrium and its blood supply. (a)
Photomicrograph of the
endometrium, longitudinal section, showing its functionalis and basalis regions (28
Diagrammatic view of the endometrium, showing the straight arteries that serve the
stratum basalis and the spiral arteries that serve the stratum functionalis. The thin-walled
veins and venous sinusoids are also illustrated.