Where Is the Pelvis? Anatomy, Functions, and Key Facts

Where is the pelvis? What is the anatomy of the pelvis?

To start off, we can answer the initial question, ”Where is the pelvis and what does its anatomy look like?” The pelvis is formed by a set of intrinsically connected bones, joints, and muscles located in the lower part of the trunk, between the abdomen and the lower extremities. The bones that compose them are (1):

1. Hip bones

The human pelvis consists of two hip bones connected to the spine at the sacrum and joined at the pubic symphysis, forming the pelvic girdle (2):

The “hip bones,” located on either side of the pelvis, are composed of three separate bones: the ilium, ischium, and pubis bone. 

• Ilium: It is the largest and uppermost pelvis bone that is fan-shaped. You can feel the iliac crest by placing your hands on your hips.
• Ischium: It is located in the lower and back part of the pelvis.
• Pubis: It is the front part of the pelvis bone, where each hip bone connects to the other at the joint called the symphysis pubis.

These hip bones join the spine posteriorly by attaching to the sacrum, the lower part of the spine. Together with the coccyx bone, which is the lowest part of the spine, these elements form the pelvic girdle. 

When joined together, the ilium, ischium, and pubis form the acetabulum on its external face. This acetabulum is the socket in the pelvis where it articulates with the head of the femur, the thigh bone. 

Together, these three bones form the fundamental structure for the hip joint, allowing a wide range of motion and providing stability to the body during locomotion and other activities (3).

2. Sacrum

The sacrum is a large triangular-shaped bone at the base of the spine. It continues upward to the lumbar vertebrae and downward to the coccyx. This bone joins the iliac bones to form the sacroiliac joint.

3. Coccyx

The coccyx, also called the tailbone, is a set of 3 to 5 small fused vertebrae located in the lower part of the spine, below the sacrum.

Ligaments tightly bind these and provide attachment points for many muscles that contribute to stability and movement.

Function of the pelvis

The pelvis is shaped like a funnel and usually supports the body’s weight, facilitating movement. Its functions are (4):

• Spinal support: The pelvis is the base of the spine, which helps distribute the body’s weight evenly and maintain balance.
• Organ protection: It houses and protects vital organs, including the bladder, reproductive organs, and parts of the digestive system.
• Facilitating movement: The pelvis is an anchor point for muscles and ligaments involved in walking, running, and other activities.
• Childbirth: In women, the pelvis changes during pregnancy to accommodate the growing fetus and facilitate delivery (4).

The pelvis is composed of multiple bones connected by ligaments and muscles, which allows it to perform support, protection, and ease of movement functions.

What is the difference between the terms pelvic and pelvis?

It is common to confuse “pelvic” and “pelvis.” The term “pelvis” refers to the entire bony structure at the base of the spine, connecting the body’s trunk to the lower limbs. It consists of bones like the ilium, ischium, pubis, sacrum, and coccyx. The pelvis forms a sturdy framework supporting the body’s weight and protecting internal organs.

On the other hand, “pelvic” typically refers to the region within the pelvis, encompassing not only bones but also structures within the pelvic cavity, such as organs, blood vessels, nerves, and muscles. This includes the pelvic inlet, outlet, and all contents within this space.

What is the pelvic cavity?

The pelvic cavity is divided into two regions:

1. The greater pelvis: The upper region, which is part of the abdomen, is known as the “false pelvis” and includes the contents above the pelvic brim or pelvic inlet region. 
2. The lesser pelvis: Since it includes all the structures held within the pelvic structure, it is referred to as the “true pelvis.” This area includes the lower parts of the sacrum, coccyx, and pelvic floor. It has an inlet and an outlet (superior and inferior openings) and contains the bladder, pelvic colon, rectum, and some of the reproductive organs (1).

The perineum constitutes the lower part of the pelvic cavity floor, and its boundaries form the lower opening. It contains the external genitalia and the openings to the exterior of the genitourinary and digestive tracts (5).

Female organs in the pelvic region

In the pelvic region, we find most organs in the pelvic cavity. They are divided into organs of the urinary, genital, and digestive systems. 

Women have different genital organs in the pelvis than men, and their anatomical relationships are also distinct (6). Below, we discuss the urinary and digestive systems, common in both sexes and the female genital system.

Pelvic organs of the urinary system 

The urinary system is a set of organs responsible for producing, storing, and expelling urine. It includes the ureters, urinary bladder, and urethra (7).

Ureters

The ureters are urinary ducts composed of smooth muscle fibers that carry urine from the kidneys to the urinary bladder. Two ureters in the human body, right and left, are connected to each kidney. 

They are 25 to 30 centimeters long and extend from the kidneys through the abdominal cavity into the pelvic cavity to empty into the back wall of the bladder (8).

Bladder

The bladder is the organ responsible for storing urine. It is located just behind the pubic bone and in front of the rectum in men, while in women, it is positioned in front of the vagina (9). 

It usually holds about 500 to 600 milliliters of urine and is connected to the urethra through the internal sphincter, formed by smooth muscle. 

Urethra

The urethra is the final conduit of the urinary system. It also participates in the reproductive system in men as a passageway for semen during ejaculation.

The internal sphincter surrounds the connection between the bladder and the urethra, while the external sphincter is located outside the bladder and around the urethra. 

The external sphincter is formed by striated muscle and is under voluntary control, which means a person can contract this muscle to control urination. 

In men, the urethra passes through the penis and opens at the tip of the glans penis. On the other hand, the urethra is shorter and lies between the clitoris and the vaginal opening in women (10).

Pelvic organs of the genital system

The reproductive system is the set of organs whose function is related to sexual reproduction, sexuality, and the synthesis of sex hormones. It differs between men and women.

Female internal genital organs

The female reproductive system comprises internal and external genital organs. The internal genital organs include the ovaries, fallopian tubes, uterus, and vagina. In contrast, the external genital organs consist of the vulva, clitoris, labia majora, labia minora, and the entrance to the vaginal orifice (11).

The internal genital organs are mainly related to reproduction, as they are responsible for egg production, fertilization, and embryo development. On the other hand, the external genital organs are visible to the naked eye and are associated with sexual pleasure and erotic stimulation (11).

Below, we discuss the female internal genital organs located inside the pelvic cavity: the ovaries, uterine tubes, uterus, and vagina.

Ovary

The ovary is the female reproductive organ that produces eggs and sex hormones. One is located on each side of the uterus, in the upper part of the pelvic cavity. They are connected to the uterus by the fallopian tubes and ligaments.

Each ovary consists of two main regions (12):

1. Cortex: This ovarian outer layer is responsible for producing sex hormones and the ovarian follicles that are released during each menstrual cycle.
2. Medulla: This internal region of the ovaries contains blood vessels and nerves.

The ovaries produce estrogens and progesterone, which are sex hormones that regulate the menstrual cycle, sexual development, and reproductive function.

Fallopian tubes

The fallopian tubes are anatomical structures that connect the ovaries to the uterus in the female reproductive system. They consist of several parts: the infundibulum, ampulla, isthmus, and interstitium. 

Their main function is to capture and transport the egg released by the ovary to the uterus, providing a site for fertilization by the sperm and transporting the embryo to the uterus for implantation and development (13).

Uterus

The uterus is a thick-walled, pear-shaped organ located behind the bladder and in front of the rectum. Pelvic ligaments and muscles support it and it consists of three layers: endometrium, myometrium, and perimetrium.

The uterus has three main parts:

1. Corpus: This is the largest and most central part of the uterus, where the embryo implants and grows during pregnancy.
2. Cervix: This is the lower, narrow part of the uterus that projects into the upper part of the vagina. The cervical canal runs through the cervix and connects the uterine cavity to the vagina.
3. Fundus: This area surrounds the uterus’s body and connects to the fallopian tubes.

This organ performs the following functions (14):

• Accommodate and maintain the development of the fetus during pregnancy.
• Provide a site for embryo implantation after fertilization.
• Participate in menstruation, in which the endometrium sheds monthly if the pregnancy doesn’t occur.

In summary, the uterus is an essential organ in the female reproductive system, where key processes such as embryo implantation, fetal development during pregnancy, and menstruation occur.

Vagina

The vagina is a tubular, muscular organ that connects the cervix to the vulva. It is composed of a vaginal vestibule, a vaginal canal, and an external vaginal orifice. Its wall contains mucosa, muscle, and connective tissue, while its functions include a channel for menstruation, childbirth, and sexual intercourse.

Pelvic organs of the digestive system

The digestive system converts food into nutrients that the body can absorb. Its function ranges from transporting food to eliminating waste through defecation.

Rectum, located in the pelvic cavity, ends in the anus, through which non-digestible waste is expelled. 

Although the sigmoid colon and part of the small intestine are also in the pelvic cavity but are considered abdominal organs due to their location.

Rectum

The rectum is the final portion of the digestive tract, located just after the sigmoid colon. It is one of the organs of the pelvic cavity and extends from the sigmoid colon to the anal canal. This structure collects the waste from the digestive process, which forms the feces (15).

The anatomy of the pelvis is quite complex, as it houses several important organs. It is important for a complete understanding of the human body’s structure and function.

Conditions related to the pelvic organs

Multiple diseases can affect the pelvic organs. The list is extensive because multiple pathologies can affect each structure. The most frequent conditions that affect the pelvic organs vary with age and gender, but the most common ones include:

Urogenital conditions in women (16):

• Urinary tract infections
• Pregnancy pain
• Ovarian cysts
• Endometriosis

Urogenital conditions in men (17):

• Benign prostatic hyperplasia
• Prostatitis

Common urogenital conditions: 

• Urinary tract infections (18)
• Urethral stones (19)

Trauma:

• Hip trauma
• Hip osteoarthritis
• Groin strain
• Pubalgia (sports hernia)

These conditions are common in the general population. However, the symptoms and treatments are different from person to person. If you have pelvic pain, consult your doctor.