The pelvic area is a basin-shaped anatomical region located at the base of the spine, linking the torso and the lower limbs. This complex structure facilitates balance and movement while providing a protective enclosure for numerous internal organs. Its architecture manages the mechanical demands of upright posture and locomotion, transferring body weight from the upper body down to the legs.
The Skeletal Framework
The physical boundaries of the pelvic area are defined by a robust ring of bones known as the pelvic girdle. This girdle consists of four main bones: the sacrum and the coccyx at the back, and the two large, paired hip bones at the sides and front. Each hip bone, or innominate bone, is formed from the fusion of three separate bones—the ilium, the ischium, and the pubis—which fully join together during puberty.
The pelvic girdle connects the vertebral column to the femurs, providing attachment points for the powerful muscles that move the legs. The sacrum is a triangular bone formed by five fused vertebrae that articulates with the fifth lumbar vertebra and the two hip bones at the sacroiliac joints. The coccyx is a small, curved bone attached to the inferior end of the sacrum.
This bony ring is anatomically divided into two regions by a continuous line called the pelvic brim or inlet. The section above this line is the greater pelvis, sometimes referred to as the false pelvis, which is functionally considered part of the abdominal cavity. This upper region primarily supports and protects the lower portions of the abdominal organs.
The region situated below the pelvic brim is the lesser pelvis, which forms the pelvic cavity. The true pelvis is structurally narrower and deeper, housing the reproductive and urinary organs within this protected space. The female true pelvis is typically broader and shallower than the male pelvis, featuring a larger, more oval-shaped inlet adapted to facilitate childbirth.
Organs Housed Within the Pelvic Cavity
The true pelvic cavity contains a collection of organs involved in reproduction, urination, and digestion. In women, this cavity is dominated by the reproductive organs, including the uterus, ovaries, fallopian tubes, and vagina. These organs occupy the central portion of the space, nestled between the urinary system anteriorly and the digestive system posteriorly.
The uterus is a thick-walled, pear-shaped muscular organ that is the site of fetal development during pregnancy. It is typically positioned in an anteverted and anteflexed orientation, meaning it is slightly tilted forward and bent over the superior surface of the urinary bladder. The bladder, which temporarily stores urine, is the most anterior organ in the pelvic cavity, situated just behind the pubic bone.
Posterior to the uterus and vagina is the rectum, which is the final section of the large intestine, ending at the anal canal. The vagina is a muscular canal that extends from the cervix, the lower part of the uterus, to the external opening. The ovaries, which produce eggs and hormones, are situated laterally, on either side of the uterus, near the lateral walls of the pelvis.
The fallopian tubes extend from the sides of the uterus and terminate close to the ovaries, providing a passageway for the egg to travel. Numerous ligaments, which are dense bands of connective tissue, offer additional support by anchoring these organs to the pelvic walls and floor.
The Supportive Musculature
Beneath the pelvic organs lies a muscular structure that forms the functional base, known as the pelvic floor. This group of muscles and connective tissues stretches across the bottom of the bony pelvis, acting like a dynamic sling. The primary components include the levator ani and coccygeus muscles, which collectively form the pelvic diaphragm.
These muscles have the demanding job of providing continuous support to the weight of the abdominal and pelvic organs against the force of gravity. They also assist in stabilizing the spine and pelvis during movement and changes in posture. The pelvic floor is penetrated by three passages in women: the urethra, the vagina, and the rectum.
The muscular sling plays an active role in controlling the functions of these passages. By contracting, the muscles constrict the openings of the urethra and anus, which is important for maintaining continence and preventing the involuntary leakage of urine or feces. The ability of these muscles to contract and relax is also integral to normal sexual function and supports the baby during pregnancy and labor.