Anatomy of the Male Pelvis and Perineum Pt. 2

Question 1

Describe the relations of the bladder

Label these

Answer 1

• Rectum: posterior to bladder
• Retro-pubic space (filled with fat) (of retzius): Anterior to bladder
• Recto-vesical pouch: Between bladder + rectum
• Seminal vesical: Posteroinferior to bladder
• Prostate: Directly inferior to bladder

Question 2

What holds and supports the bladder neck?

Answer 2

• Held in place by fibromuscular bands
• Sits above pelvic floor
• Supported by ligaments, endo-pelvic fascia and levator ani muscle

Question 3

What is the Puboprostatic ligament?

Answer 3

• Wraps around prostate
• Attached to pubic symphysis
Neck surrounded by internal urethral sphincter (smooth muscle)

Question 4

Label the internal features of the bladder

Answer 4

On image

Question 5

Describe the nervous innervation to the bladder

Answer 5

Nervous Supply

Neurological control is complex, with the bladder receiving input from both the autonomic (sympathetic and parasympathetic) and somatic arms of the nervous system:
• Sympathetic – hypogastric nerve (T12 – L2). It causes relaxation of the detrusor muscle, promoting urine retention.
• Parasympathetic – pelvic nerve (S2-S4). Increased signals from this nerve causes contraction of the detrusor muscle, stimulating micturition.
• Somatic – pudendal nerve (S2-4). It innervates the external urethral sphincter, providing voluntary control over micturition.

In addition to the efferent nerves supplying the bladder, there are sensory (afferent) nerves that report to the brain. They are found in the bladder wall and signal the need to urinate when the bladder becomes full.

Question 6

What is the The Bladder Stretch Reflex?

Answer 6

The bladder stretch reflex is a primitive spinal reflex, in which micturition is stimulated in response to stretch of the bladder wall. It is analogous to a muscle spinal reflex, such as the patella reflex.

During toilet training in infants, this spinal reflex is overridden by the higher centres of the brain, to give voluntary control over micturition.

Question 7

Describe the bladder stretch reflex arc

Answer 7

The reflex arc:
• Bladder fills with urine, and the bladder walls stretch. Sensory nerves detect stretch and transmit this information to the spinal cord.
• Interneurons within the spinal cord relay the signal to the parasympathetic efferents (the pelvic nerve).
• The pelvic nerve acts to contract the detrusor muscle, and stimulate micturition.
Although it is non-functional post childhood, the bladder stretch reflex needs to be considered in spinal injuries (where the descending inhibition cannot reach the bladder), and in neurodegenerative diseases (where the brain is unable to generate inhibition).

Question 8

What is the venous drainage of the bladder?

Answer 8

Bladder drained by:
• Vesical venous plexus Drains into internal iliac vein
Vesical venous plexus communicates inferiorly with:
 Inferior prostatic plexus (Utero-vaginal plexus, females)

Question 9

What are the 4 parts of the urethra and how long are they?

Answer 9

• Urethra approximately 20 cm

* 4 parts: Preprostatic/Prostatic/Membranous/Spongy

Question 10

Label and name the 4 parts of the urethra

Answer 10

• The periprostatic part – after the neck of the bladder, here is the internal urethral sphincter muscle, under voluntary control via the autonomic nervous system. This sphincter is required for to prevent the backflow of seminal fluid into the bladder during ejaculation
• Prostatic part of urethra – runs through prostate, prostatic ducts open into here and ejaculatory ducts open
• Membranous part of urethra – passes through urogenital diaphragm, through the deep perineal pouch. Within this part are the external urethral sphincter (voluntary control by pudendal nerve) and bulbourethral (pre-ejaculate fluid but fluid enters the spongy urethra)
• Spongy part of urethra – runs through the corpus spongiosum 2 bends

Question 11

What is the perineum and where is it located?

Answer 11

The perineum is an anatomical region in the pelvis. It is located between the thighs, and represents the most inferior part of the pelvic outlet. The perineum is separated from the pelvic cavity superiorly by the pelvic floor.

Question 12

What are the anatomical borders of the perineum?

Answer 12

The anatomical borders of the perineum are:

Anterior – pubic symphysis.
Posterior – tip of the coccyx.
Laterally – inferior pubic rami and inferior ischial rami, and the sacrotuberous ligament.
Roof – pelvic floor.
Base – skin and fascia.

Question 13

What triangles form the perineum?

Answer 13

The perineum can be subdivided by a theoretical line drawn transversely between the ischial tuberosities. This split forms the anterior urogenital triangle and the posterior anal triangle. These triangles are associated with different components of the perineum.

Question 14

What are the surface borders of the perineum?

Answer 14

The surface boundaries are best shown when the lower limbs are abducted, and a diamond shape is depicted:

Anterior – mons pubis in females, base of the penis in males.
Laterally – medial surfaces of the thighs.
Posterior – superior end of the intergluteal cleft.

Question 15

What is the anal triangle, what is it bounded by?

Answer 15

The anal triangle is the posterior half of the perineum. It is bounded by the coccyx, sacrotuberous ligaments, and a theoretical line between the ischial tuberosities.

Question 16

What are the components of the anal triangle?

Answer 16

The main contents of the anal triangle are:

Anal aperture – the opening of the anus.
External anal sphincter muscle – voluntary muscle responsible for opening and closing the anus.
Ischioanal fossae (x2) – spaces located laterally to the anus.

The anal aperture is located centrally in the triangle with the ischioanal fossae either side. These fossae contain fat and connective tissue, which allow for expansion of the anal canal during defecation. They extend from the skin of the anal region (inferiorly) to the pelvic diaphragm (superiorly).

Another important anatomical structure within the anal triangle is the pudendal nerve, which supplies the whole perineum with somatic fibers.

Question 17

What is the urogenital triangle bounded by?

Answer 17

The urogenital triangle is the anterior half of the perineum. It is bounded by the pubic symphysis, ischiopubic rami, and a theorectical line between the two ischial tuberosities. The triangle is associated with the structures of the urogenital system – the external genitalia and urethra.

Question 18

How is the anterior urogenital triangle different to the posterior anal triangle?

Answer 18

Structurally, the urogenital triangle is complex, with a number of fascial layers and pouches. Unlike the anal triangle, the urogenital triangle has an additional layer of strong deep fascia; the perineal membrane. This membrane has pouches on its superior and inferior surfaces.

Question 19

What are the layers of the urogenital triangle?

Answer 19

The layers of the urogenital triangle (deep to superficial):

Deep perineal pouch – a potential space between the deep fascia of the pelvic floor (superiorly) and the perineal membrane (inferiorly). It contains part of the urethra, external urethral sphincter, and the vagina in the female. In males, it also contains the bulbourethral glands and the deep transverse perineal muscles.

Perineal membrane – a layer of tough fascia, which is perforated by the urethra (and the vagina in the female). The role of the membrane is to provide attachment for the muscles of the external genitalia.

Superficial perineal pouch – a potential space between the perineal membrane (superiorly) and the superficial perineal fascia (inferiorly). It contains the erectile tissues that form the penis and clitoris, and three muscles – the ischiocavernosus, bulbospongiosus and superficial transverse perineal muscles. The greater vestibular glands (Bartholin’s glands) are also located in the superficial perineal pouch. The pouch is bounded posteriorly to the perineal body.

Perineal fascia – a continuity of the abdominal fascia that has two components:
Deep fascia: covers the superficial perineal muscles and protruding structures (e.g. penis & clitoris).
Superficial fascia is composed of a further two layers of fascia:

Superficial layer – continuous with Camper’s fascia of the anterior abdominal wall
Deep layer (Colles’ fascia) – continuous with Scarpa’s fascia of the anterior abdominal wall

Skin – The urethral and vaginal orifices open out onto the skin.

Question 20

What is the perineal body?

Where it found?

Answer 20

The perineal body is an irregular fibromuscular mass. It is located at the junction of the urogenital and anal triangles – the central point of the perineum. This structure contains skeletal muscle, smooth muscle and collagenous and elastic fibres.

Question 21

Where does the perineal body lie and attach?

Answer 21

Anatomically, the perineal body lies just deep to the skin. It acts as a point of attachment for muscle fibres from the pelvic floor and the perineum itself:

Levator ani (part of the pelvic floor).
Bulbospongiosus muscle.
Superficial and deep transverse perineal muscles.
External anal sphincter muscle.
External urethral sphincter muscle fibres.