What is the Pelvis?
The pelvis or pelvic girdle is a basin-shaped complex bone placed right between the abdomen and pelvic region that's thighs. The pair of hip bones (coxal bone) join the lower limbs and the spine. They are connected to the sacrum rearwards, attached anteriorly, and associated with the two femurs at the hip bones. The passage surrounded by the bony pelvis, termed the pelvic cavity, is a particular body division below the abdomen and essentially contains and supports the urinary bladder, intestines, and other internal reproductive organs.
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The bony pelvis has a rift in the centre in mammals which is significantly larger in females compared to males helping them with reproduction.
Pelvis Anatomy
The pelvic region of the torso is the lower part, between the things and the abdomen. The area comprises multiple structures: the pelvic cavity, the perineum, the bony pelvis, and the pelvic floor. The bony pelvis is the portion of the skeleton buried in the pelvic region of the body. It is divided into two sections, the pelvic spine and the pelvic girdle.
The pelvic bone consists of the coccyx and sacrum. The pelvic girdle, composed of ring-oriented appendicular hip bones (ilium, pubis, and ischium), attaches the pelvic area of the spine to the lower limbs.
The pelvic cavity is a little part of the space encircled by the bony pelvis. The pelvic area is delineated by the pelvic brim, at the above and the pelvic floor at the below. The cavity is also defined as a place completely enclosed by the pelvic skeleton, which is parted into:
the false (or greater) pelvis, over the pelvic brim
the true (or lessen) pelvis, under the pelvic brim
The pelvic floor is also known as the pelvic diaphragm (placed right below the pelvic cavity)
The perineum (placed below the pelvic floor)
Pelvic Bone
The pelvic skeleton is created in the back pelvic area by the coccyx and the sacrum, anteriorly and either side by a pair of hip bones.
Singly coxal bone consists of three segments, pubis, ilium, and ischium. During adolescence, these segments are separate bones linked by the triradiate cartilage. And throughout puberty, they blend to form an individual bone.
Pelvic Cavity
The pelvis bones surround the pelvic cavity and essentially hold reproductive organs and the rectum. A disparity is created between the true pelvis inferior to the terminal line and the false pelvis above it.
The superior pelvic aperture or the pelvic inlet that leads into the true pelvis is joined by the cape, the iliopubic eminence, the top portion of the pubic symphysis, the pecten of the pubis, and the arcuate line of the ilium. The pelvic socket is the section within the pubic arch, the coccyx, and the ischial tuberosities.
Pelvic Floor
The muscle of the pelvic floor has two essentially contradictory purposes. The first is to seal the abdominal and pelvic cavities and endure the weight of the visceral organs. The second is to regulate the openings of the rectum and urogenital organs that penetrate the pelvic floor and make it more vulnerable. The pelvic floor consists of several connective tissues and overlapping muscles to manage both tasks.
The pelvic diaphragm is constituted of the coccygeus muscle of the pelvic floor and the levator ani, which appears between the coccyx and the ischial spine and the symphysis and the anococcygeal ligament. It spreads between the anal hiatus and the tip of the coccyx, which leaves a gap for the urogenital openings and the anal. Hence a second closing means is needed because of the expanse of the genital gap, which is broader in females.
The urogenital diaphragm constitutes a profound intersecting perineal, which originates from the lower ischial and pubic rami and stretches to the urogenital break. The urogenital diaphragm is strengthened posteriorly by the shallow intersecting perineal.
The anus and urethra are closed by the urethral sphincters and the external anal. In contrast, the urethra is encircled by the bulbospongiosus that envelops the corpus spongiosum in males and shrinks the vaginal introitus in females. And, the ischiocavernosus muscle, present right below the surface of the perineum, compresses blood into the clitoris and the corpus cavernosum penis.
Variation
Modernised humans are, to a great extent, identified by bipedal movement and healthy brains. Since the pelvis is essential to both childbirth and locomotion, two opposing demands have defied natural assortment: a broad birth canal and movement efficiency, an "obstetrical dilemma." The gynaecoid pelvis, better known as the female pelvis, has emerged to its greatest width for reproduction. In contrast, the male pelvis isn’t necessitated by the obligation to give birth and consequently are absolute for bipedal movement.
Differences Between Male and Female Pelvis
Did You Know?
Pelvis bone provides support to the spinal cord.
High-speed accidents or falls from great heights are the most common cause of pelvis fracture.
There are differences between the male and female pelvis. That female pelvis is bigger and broader than that of the male pelvis.
The principal difference between male and female pelvis is the pelvis ligament, which is present in the female body and help in an easier birth process.
Severe injuries to the pelvic bone can be life-threatening.
During pregnancy, the body secretes hormones that soften pelvis ligaments for an easier birth.
There are four muscles of the pelvic floor, namely, pubococcygeus, coccygeus, iliococcygeus, and puborectalis muscles.
FAQs on Pelvic Bone
1. What is the pelvic bone, and what are its main components?
The pelvic bone, more accurately called the pelvic girdle, is a complex, basin-shaped structure at the base of the spine. It is not a single bone but is formed by the fusion of several bones. The main components are:
- Two Hip Bones (Coxal Bones): Each hip bone is formed by the fusion of three individual bones: the ilium (the large, flaring upper part), the ischium (the lower, posterior part you sit on), and the pubis (the anterior part).
- Sacrum: A triangular bone formed by the fusion of five vertebrae, connecting the hip bones at the back.
- Coccyx: The tailbone, located at the very bottom of the spine.
2. What are the primary functions of the human pelvis?
The pelvis serves several critical functions in the human body. Its primary roles include:
- Support and Weight Transfer: It supports the weight of the upper body and transfers it from the axial skeleton (spine) to the appendicular skeleton (legs) for standing and walking.
- Protection: It forms a protective ring around delicate abdominopelvic organs, such as the urinary bladder, rectum, and internal reproductive organs.
- Muscle Attachment: It provides a large surface area for the attachment of powerful muscles of the lower back, abdomen, and thighs, which are essential for locomotion and maintaining posture.
- Childbirth: In females, the pelvis is adapted to allow for the passage of a baby during childbirth.
3. How does the female pelvic bone structurally differ from the male pelvic bone, and why are these differences important?
The structural differences between the male and female pelvis are primarily adaptations for childbirth in females. These differences are crucial for this biological function. The key distinctions are:
- Overall Structure: The female pelvis is generally wider, shallower, and lighter than the male pelvis, which is narrower, deeper, and more robust.
- Pelvic Inlet: The female pelvic inlet (the upper opening) is typically oval or rounded and larger, whereas the male inlet is heart-shaped and smaller.
- Subpubic Angle: The angle beneath the pubic bones is wider in females (usually > 90 degrees) compared to males (usually < 70 degrees).
These adaptations create a wider, more spacious birth canal in females, making childbirth possible, while the male pelvis is optimized for supporting a heavier build and stronger muscle attachments.
4. How do the three bones—ilium, ischium, and pubis—form the hip bone?
The hip bone, or coxal bone, starts as three separate bones in a child: the ilium, ischium, and pubis. These bones are connected by cartilage. During adolescence, typically between the ages of 15 and 17, they begin to fuse together. The point where all three bones meet and fuse forms a deep, cup-shaped socket called the acetabulum. This fusion creates a single, solid hip bone in adults. The acetabulum is a critical structure as it serves as the socket for the head of the femur (thigh bone), forming the hip joint.
5. What is the pubic symphysis and what is its role in the pelvic girdle?
The pubic symphysis is a cartilaginous joint located at the front of the pelvis, connecting the left and right pubic bones. It is not a rigid, fused joint but a secondary cartilaginous joint that allows for very slight movement. Its primary role is to provide stability to the pelvic ring while absorbing shock during activities like walking and running. During pregnancy, hormonal changes cause this joint to become more flexible, allowing the pelvis to widen slightly to facilitate childbirth.
6. How does the structure of the pelvic girdle contribute to human bipedal locomotion?
The pelvic girdle's unique structure is a key adaptation for efficient upright, two-legged (bipedal) walking. It contributes in several ways:
- The broad, basin-like shape provides robust support for the upper body, centering the weight directly over the legs.
- The wide, flaring ilia provide large attachment points for the powerful gluteal muscles, which are crucial for stabilising the trunk and propelling the body forward during walking.
- The rigid, ring-like structure of the pelvis, along with the sacroiliac joints, effectively transmits forces from the legs up through the spine, creating a stable base for movement.
