Anatomy guide

On this page, we will explore the anatomy of the pelvis and bowel – what they do, how they work, and how cancer can sometimes change this. It is important to note that cancer and the treatments available, like surgery, radiotherapy, or chemotherapy, can sometimes change how bones, muscles, and organs sit and function within the pelvis. These changes can be temporary or long-term, and they vary from person to person.

The Pelvis

The pelvis is in the lower part of the tummy, just below the belly button. It is a sturdy bowl-like shape made of bones, holding and protecting some of our internal organs.

Inside the pelvis, you’ll find:

• The bladder, which stores urine (wee)
• The bowel, which digests food and carries stool (poo) out of the body
• In females; the uterus (womb), ovaries, cervix, and vagina
• In males; the prostate, testis, seminal vesicles, and penis
• Blood vessels, muscles, and nerves also run through the pelvis, helping everything to work together

The Bowel

The bowel is another name for the intestines. It’s made up of two main parts:

• The small bowel, which absorbs nutrients from the food we eat
• The large bowel, also called the colon, which absorbs water and forms stool

At the end of the large bowel is the rectum, where poo is stored before leaving the body through the anus.

The Bladder

The bladder is a stretchy, muscular bag. It stretches to fill with urine from the kidneys and contracts to empty urine when we go to the toilet. The urethra is the tube that urine passes through to exit the body.

The Uterus (or Womb)

This is a hollow, muscular organ which sits between the bladder and the lower bowel (rectum). It is made up of three layers; the endometrium (inner lining), the myometrium (muscular middle layer), and serosa (outer covering). The uterus provides a supportive environment for a fertilised egg to develop into a foetus during pregnancy. If a pregnancy does not occur, the uterine lining sheds during menstruation. The uterus also has a role in hormonal production, produces prostaglandins which help to regulate blood flow, inflammation, and uterine muscle contraction.

The Ovaries

These are oval shaped organs which sit on the upper right and upper left side of the uterus. They produce, store, and release eggs (ova) for potential fertilization. The ovaries also produce and secrete hormones, such as oestrogen and progesterone, which play a big role in regulating the menstrual cycle, and facilitate puberty, pregnancy, and the development of the female body.

The Fallopian Tubes

These tubes connect the right and left upper corners of the uterus to the two separate ovaries. They provide a passage for eggs (ova) to travel into the uterus.

The Vulva

The vulva refers to the external female genitalia. This includes multiple structures that protect the internal organs as well as play important roles in urination, sexual function, and childbirth. Key structures of the vulva include:

• Mons pubis – a fatty, rounded area over the pubic bone
• Labia majora – the outer folds of skin that provide protection for the more delicate inner structures
• Labia minora – thinner inner folds that surround the vaginal opening and the urethral opening
• Clitoris – a highly sensitive organ of erectile tissue, important for sexual arousal
• Vestibule – the area between the labia minora, containing the openings of the urethra and the vagina
• Bartholin’s glands – small glands near the vaginal opening that secrete fluid for lubrication

The vulva also contains lots of sensory nerve endings, making it sensitive to touch and temperature.

The Vagina

This is a muscular, tubular structure that plays an important role in reproduction, sexual function, and childbirth. It extends from the external vaginal opening, located between the urethra and the anus, to the cervix (the lower part if the uterus). The vagina has three main layers:

• Mucosa – the inner lining that is moist, elastic, and rich in folds called rugae which allow for expansion (particularly during arousal or childbirth)
• Muscular layer – smooth muscle that provides strength and flexibility
• Adventitia – the outer connective tissue that anchors the vagina to surrounding organs

The Penis

The penis has three main parts:

• The root – the base that anchors it to the pelvic structures
• The shaft – the elongated portion containing erectile tissue
• Glans – the sensitive, enlarged tip

The urethra runs through the middle of these structures serving as a passage for both urine and semen.

The Testis

These are small oval shaped glands within the scrotum which produce sperm (stored in the epididymis – a small tube at the back of each testis) and testosterone. The spermatic cord suspends the testis and provides them with necessary nerves, blood vessels and lymphatic vessels. When the penis is erect, sperm moves from the epididymis through a small tube called the vas deferens and to the urethra. The seminal vesicles make a fluid which mixes with the sperm in the urethra.

The Prostate Gland

This is a walnut-sized organ located just below the bladder, surrounding the urethra. It produces slightly alkaline fluid that nourishes and protects the sperm. This fluid mixes with sperm and seminal vesicle fluid in the urethra to form semen. During ejaculation, the prostate contracts, helping to propel the semen through the urethra. The penis and prostate play key roles in urinary, sexual, and reproductive function.

Take a look at this Cancer UK Male Anatomy video for further explanation.

The Pelvic Floor Muscles

This is a group of muscles found at the base of the pelvis which form a bowl like shape and support the internal pelvic organs. These muscles span from the pubic bone at the front of the pelvis, to the tailbone (coccyx) at the back, and attach to the sitting bones on each side. These muscles are made up of two key layers:

• Superficial layer – this includes muscles around the openings of the urethra, vagina (in females), and anus
• Deep layer – these muscles form the sling of the pelvic floor and have an important role with supporting the bladder, bowel, uterus (in females), and prostate (in males)

The pelvic floor has three key functions:

• Support – they hold up the pelvic organs (e.g. the bladder, bowel, uterus or prostate, and rectum)
• Control – they help to regulate the passing of urine through the urethra, and stool (poo) or gas through the anus
• Sexual function – they also contribute to arousal, orgasm, and vaginal or penile function during intimacy and intercourse

If you want to know more about improving the function of these muscles, take a look at our informative videos:

Male –

Female –

AMAB –

AFAM –

The Diaphragm

This is a large, dome-shaped muscle that separates the chest cavity from the abdominal cavity. Is it the primary muscle of respiration. It has three main parts:

• Sternal portion – attached to the back of the sternum (chest bone)
• Costal portion – attached to the inner surfaces of the lower ribs
• Lumbar portion – anchored to the upper lumbar vertebrae (lower back)

When the diaphragm contracts, it flattens downward, allowing air to be drawn into the lungs. When the diaphragm relaxes, it rises back into its dome shape, pushing air out of the lungs.

The diaphragm and the pelvic floor muscles work in coordination as a pair:

• During inhalation, the diaphragm contracts and moves downward and at the same time the pelvic floor gently lengthens and descends to allow for increased pressure in the abdominal cavity caused by the descending diaphragm
• During exhalation, the diaphragm relaxes upward, while the pelvic floor recoils and lifts, helping to restore abdominal pressure and supporting the internal organs

This synchronized movement helps to create a dynamic pressure system within the abdomen that supports the body with breathing, posture, spinal stability, and functions like coughing, sneezing, and even childbirth. This is sometimes referred to as the ‘Core Canister’, with the diaphragm being at the top of the canister, the pelvic floor as the base of the canister and the abdominal walls and back muscles acting as the cylindrical walls.