The pelvic cavity is a body cavity that houses several essential organs and structures within the lower part of the torso. It is enclosed by the pelvic bones and serves as a crucial compartment for the reproductive organs, urinary bladder, pelvic colon, and rectum. This cavity is anatomically divided into two regions: the false pelvis (greater pelvis), which is the upper part and part of the abdominal cavity, and the true pelvis (lesser pelvis), which is the lower part and more confined. The true pelvis is of particular importance as it contains the pelvic inlet and outlet, which are critical in childbirth.
Location
The pelvic cavity is located within the bony pelvis, beneath the abdominal cavity, and above the pelvic floor. It is situated between the hip bones, providing a base for the attachment of various muscles and ligaments. The cavity extends from the pelvic brim at the top to the pelvic floor muscles at the bottom.
Anatomy
Boundaries
Superior Boundary
The superior boundary, or the pelvic inlet, is formed by the pelvic brim. This brim includes the promontory and alae of the sacrum, the arcuate line of the ilium, the pectineal line of the pubis, and the pubic crest.
Inferior Boundary
The inferior boundary, or the pelvic outlet, is defined by the tip of the coccyx posteriorly, the ischial tuberosities laterally, and the pubic arch anteriorly.
Anterior Boundary
The anterior boundary consists of the pubic symphysis, the body of the pubis, and the pubic rami.
Posterior Boundary
The posterior boundary is composed of the sacrum and coccyx.
Lateral Boundary
The lateral boundary includes the ilium and ischium bones, and the obturator internus muscle and its fascia.
Divisions
False Pelvis (Greater Pelvis)
Located above the pelvic brim, the false pelvis is part of the abdominal cavity. It provides support to the intestines and transmits part of their weight to the anterior wall of the abdomen.
True Pelvis (Lesser Pelvis)
The true pelvis lies below the pelvic brim and is more confined. It is significant for housing the pelvic organs and forming the birth canal in females. The true pelvis is further divided into the pelvic inlet, midpelvis, and pelvic outlet.
Contents
Reproductive Organs
In females, this includes the ovaries, fallopian tubes, uterus, and part of the vagina. In males, it includes the prostate, seminal vesicles, and part of the vas deferens.
Urinary Organs
The urinary bladder and parts of the ureters are located within the pelvic cavity. The bladder rests on the pelvic floor and is supported by the pubic bones anteriorly.
Digestive Organs
The pelvic colon (sigmoid colon) and rectum are part of the digestive organs housed within the pelvic cavity.
Musculature
Pelvic Floor Muscles
The pelvic floor is made up of a group of muscles, including the levator ani (which consists of the puborectalis, pubococcygeus, and iliococcygeus muscles) and the coccygeus muscle. These muscles support the pelvic organs and maintain continence.
Obturator Internus Muscle
This muscle lines the lateral wall of the true pelvis and helps form the obturator foramen, through which nerves and blood vessels pass.
Piriformis Muscle
Located at the posterior wall of the pelvis, the piriformis muscle extends from the sacrum to the greater trochanter of the femur, assisting in the lateral rotation of the hip.
Ligaments
Sacrotuberous Ligament
Extends from the sacrum to the ischial tuberosity, forming part of the border of the lesser sciatic foramen.
Sacrospinous Ligament
Stretches from the sacrum and coccyx to the ischial spine, dividing the greater and lesser sciatic foramina.
Obturator Membrane
A fibrous sheet covering the obturator foramen, leaving a small opening for the passage of the obturator nerve and vessels.
Nerves
Sacral Plexus
A network of nerves located on the posterior pelvic wall, providing innervation to the lower limb and pelvic organs. Major branches include the sciatic nerve, pudendal nerve, and superior and inferior gluteal nerves.
Pudendal Nerve
Arises from the sacral plexus and provides sensory and motor innervation to the perineum.
Blood Vessels
Internal Iliac Artery
Supplies blood to the pelvic organs, gluteal region, and medial thigh. It branches into several arteries, including the superior and inferior gluteal arteries, internal pudendal artery, and obturator artery.
Internal Iliac Vein
Drains blood from the pelvic organs and gluteal region, eventually joining the common iliac vein.
Function
Support of Pelvic Organs
Reproductive System Support
In females, the pelvic cavity houses the uterus, ovaries, fallopian tubes, and part of the vagina. It provides a secure environment for these reproductive organs, facilitating their roles in menstruation, conception, and childbirth. In males, the pelvic cavity supports the prostate, seminal vesicles, and part of the vas deferens, essential for semen production and ejaculation.
Urinary System Support
The pelvic cavity holds the urinary bladder and parts of the ureters. It ensures the proper functioning and positioning of these organs, enabling the collection and expulsion of urine.
Digestive System Support
The pelvic cavity supports the sigmoid colon and rectum, aiding in the storage and elimination of feces. The cavity’s structure ensures the proper alignment and functioning of these digestive organs.
Protection of Organs
Bony Protection
The pelvic bones form a rigid structure that protects the delicate organs within the cavity from external trauma. This bony protection is crucial for the reproductive, urinary, and digestive systems.
Muscular Protection
The pelvic floor muscles and surrounding musculature provide additional protection and support, maintaining the integrity and positioning of pelvic organs.
Facilitation of Childbirth
Birth Canal Formation
The true pelvis forms the birth canal, crucial for the delivery of a baby. The pelvic inlet, midpelvis, and pelvic outlet provide the necessary passages through which the baby descends during labor.
Pelvic Floor Muscles
These muscles play a vital role during childbirth by stretching to allow the passage of the baby and then contracting to help return the pelvic organs to their original positions post-delivery.
Urinary and Fecal Continence
Pelvic Floor Muscles
The pelvic floor muscles, including the levator ani and coccygeus, support the bladder and rectum, maintaining continence. They contract to close the urethra and anus, preventing involuntary leakage of urine and feces.
Sphincter Mechanism
The pelvic cavity contains sphincters (such as the external urethral and anal sphincters) that regulate the release of urine and feces. These sphincters ensure controlled expulsion when appropriate and maintain continence when not.
Sexual Function
Support for Sexual Organs
The pelvic cavity supports the internal reproductive organs, which are essential for sexual function and reproduction. In females, this includes the uterus, ovaries, and part of the vagina. In males, this includes the prostate and seminal vesicles.
Pelvic Floor Muscles
These muscles contribute to sexual function by supporting the genital organs and contributing to the sensations experienced during sexual activity.
Facilitation of Movement and Stability
Pelvic Girdle
The pelvic bones form the pelvic girdle, which provides a stable base for the attachment of the spinal column and lower limbs. This stability is crucial for maintaining an upright posture and enabling various movements.
Muscular Attachments
The muscles attached to the pelvic bones (such as the iliacus, obturator internus, and piriformis) aid in movements of the hip and thigh, contributing to locomotion and balance.
Circulation and Innervation
Blood Supply
The pelvic cavity contains major blood vessels, including branches of the internal iliac artery and vein, which supply blood to the pelvic organs and lower limbs. This vascular network ensures adequate oxygen and nutrient delivery and waste removal.
Nerve Supply
The sacral plexus and its branches provide innervation to the pelvic organs and lower limbs. This nerve supply is essential for the sensory and motor functions of the pelvic region, including reflexes and voluntary control.
Clinical significance
The pelvic cavity holds critical clinical significance due to its involvement in various physiological functions and its susceptibility to numerous medical conditions. Understanding the anatomy and functions of the pelvic cavity is essential for diagnosing and treating disorders related to the reproductive, urinary, and digestive systems.
Reproductive Health
- Gynecological Conditions: Disorders such as endometriosis, pelvic inflammatory disease (PID), and uterine fibroids can affect the organs within the female pelvic cavity, causing pain, infertility, and other complications.
- Obstetrics: The pelvic cavity’s structure is crucial during childbirth. Conditions like cephalopelvic disproportion, where the baby’s head is too large to pass through the birth canal, require careful medical management or surgical intervention, such as a cesarean section.
Urinary Disorders
- Urinary Incontinence: Weakness or damage to the pelvic floor muscles can lead to urinary incontinence, particularly in women post-childbirth or post-menopause. Treatments include pelvic floor exercises, medications, and sometimes surgery.
- Bladder Prolapse (Cystocele): When the bladder descends into the vaginal canal due to weakened pelvic muscles, it can cause urinary problems and discomfort. Surgical repair or pessary insertion is often required.
Digestive Issues
- Rectal Prolapse: This occurs when the rectum protrudes through the anus, often due to weakened pelvic floor muscles. Treatment options range from lifestyle changes to surgical correction.
- Constipation and Obstructed Defecation: Conditions like pelvic floor dyssynergia, where the pelvic muscles fail to coordinate properly during bowel movements, require specialized therapies and sometimes surgical intervention.
Chronic Pelvic Pain
Pelvic Pain Syndrome: Chronic pelvic pain can be caused by a variety of conditions, including interstitial cystitis, endometriosis, and pelvic inflammatory disease. Multidisciplinary approaches are often needed for management.
Oncological Concerns
Pelvic Cancers: Cancers such as cervical, ovarian, prostate, and colorectal cancer originate in or spread to the pelvic cavity. Early detection and treatment are crucial for improving outcomes.
Surgical Interventions
Pelvic Surgery: Various surgical procedures, including hysterectomies, prostatectomies, and colorectal surgeries, involve the pelvic cavity. Understanding the intricate anatomy is essential for successful surgical outcomes and minimizing complications.
Pelvic Trauma
Injuries: Trauma to the pelvic region, such as fractures from accidents, can have serious consequences, including internal bleeding and damage to pelvic organs. Immediate medical attention and often surgical repair are necessary.
