The uterus is pear shaped and consists of two major but unequal parts. The upper, larger portion is the body or corpus, whereas the lower smaller cervix projects into the vagina. The isthmus is the union site of these two. It is of special obstetrical significance because it forms the lower uterine segment during pregnancy. At each superolateral margin of the body is a uterine cornu, from which a fallopian tube emerges. This area also contains the origins of the round and ovarian ligaments. Between the points of fallopian tube insertion is the convex upper uterine segment termed the fundus.
The bulk of the uterine body, but not the cervix, is muscle.
The inner surfaces of the anterior and posterior walls lie almost in contact, and the cavity between these walls forms a mere slit. The nulligravid uterus measures 6 to 8 cm in length compared with 9 to 10 cm in multiparas. The uterus averages 60 g and typically weighs more in parous women (Langlois, 1970; Sheikhazadi,i2010).
Pregnancy stimulates remarkable uterine growth due to muscle iber hypertrophy. The uterine fundus, a previously flattened convexity between tubal insertions, now becomes dome shaped. Moreover, the round ligaments appear to insert at the junction of the middle and upper thirds of the organ. The fallopian tubes elongate, but the ovaries grossly appear unchanged.
This portion of the uterus is cylindrical and has small apertures at each end-the internal and external cervical ora. The endocervical canal runs through the cervix and connects these ora. The cervix is divided into upper and lower portions by the vagina's attachment to its outer surface. he upper portionthe portio supravaginalis-begins at the internal os, which corresponds to the level at which the peritoneum is reflected up onto the bladder (Fig. 2-10). The lower cervical portion protrudes into the vagina as the portio vaginalis.
Before childbirth, the external cervical os is a small, regular, oval opening. After labor, especially vaginal childbirth, the orifice
FIGURE 2-9 Anterior (A), right lateral (8), and posterior (C)views of the uterus of an adult woman. a = oviduct; b = round ligament; = ovarian ligament; Ur ureter.
Tubal & ovarian branches of uterine & ovarian aa.
External iliac a.
Uterine a.
Internal iliac a.
Inferior epigastric a. & n.
vaginalis of cervix
FIGURE 2-10 Uterus, adnexa, and associated anatomy. (Reproduced with permission from Corton MM: Anatomy. In Hoffman BL, Schorge JO, Bradshaw KD, et al (eds): Williams Gynecology, 3rd ed. New York, McGraw-Hili Education, 2016.) is converted into a transverse slit that is divided such that there are the so-called anterior and posterior cervical lips. If torn deeply during labor or delivery, the cervix may heal in such a manner that it appears irregular, nodular, or stellate (Fig. 36-1, p. 653).
The cervical surface that radially surrounds the external os is called the ectocervix and is lined predominantly by nonkeratinized stratified squamous epithelium. In contrast, the endocervical canal is covered by a single layer of mucin-secreting columnar epithelium, which creates deep cleftlike infoldings or "glands." Commonly during pregnancy, the endocervical epithelium moves out and onto the ectocervix in a physiological process termed eversion (Chap. 4, p. 51).