Uterus

Uterus resembles an upside-down pear located between the bladder and rectum. It consists of the fundus at the top, the body, and the cervix, which opens into the vagina. The uterine wall has three layers: the perimetrium (outer covering), myometrium (smooth muscle), and endometrium (inner lining that thickens each cycle).

During the menstrual cycle, estrogen from the ovaries rebuilds the endometrium after menstruation. Progesterone later makes it spongy and nutrient-rich to welcome a fertilized egg. If implantation occurs, the placenta forms and the uterus expands dramatically to house the growing fetus. If not, hormone levels fall and the endometrium sheds as menstrual flow.

The myometrium's strong muscle fibers are arranged in spirals and longitudinal bundles. They remain relatively quiet most of pregnancy but respond to hormonal cues and stretching near birth, creating coordinated contractions that dilate the cervix and push the baby through the birth canal. After delivery, contractions help reduce bleeding and return the uterus to its pre-pregnancy size.

The cervix acts as a gateway, producing mucus that changes texture across the cycle—thin and stretchy near ovulation to allow sperm entry, thicker at other times to block pathogens. Regular Pap tests and HPV vaccines help protect the cervix from cancer by detecting abnormal cells early.

Uterine health includes managing conditions such as fibroids, endometriosis, adenomyosis, and infections, which can cause pain, heavy bleeding, or fertility issues. Treatments range from medication and lifestyle changes to surgery, including minimally invasive techniques. Advances in prenatal care, maternal health, and reproductive technology underscore the uterus's central role in human development.