Unit 18 Week 2 > Pelvic Floor and childbirth > Flashcards
Pelvic Floor and childbirth Flashcards
Label the diagram
What is the perineum?
The Perineum is a shallow compartment inferior to the pelvic floor muscles
Muscles of the pelvic floor and walls
What are the attachments of the levator ani muscle?
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Explain the passage of a baby’s head through
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Explain cardinal movements
F. Anterior shoulder
G. Posterior shoulder
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What is in the true pelvis/pelvic cavity?
The pelvic viscera (bladder, rectum, pelvic genital organs and terminal part of the urethra)
Explain the pelvic floor structures
The pelvic floor is a funnel-shaped structure. It attaches to the walls of the lesser pelvis, separating the pelvic cavity from the perineum inferiorly (region which includes the genitalia and anus).
In order to allow for urination and defecation, there are a few gaps in the pelvic floor. There are two ‘holes’ that have significance:
- Urogenital hiatus – an anteriorly situated gap, which allows passage of the urethra (and the vagina in females).
- Rectal hiatus – a centrally positioned gap, which allows passage of the anal canal.
Between the urogenital hiatus and the anal canal lies a fibrous node known as the perineal body, which joins the pelvic floor to the perineum
What is the function of the pelvic floor?
As the floor of the pelvic cavity, these muscles have important roles to play in the correct functioning of the pelvic and abdominal viscera.
The roles of the pelvic floor muscles are:
- Support of abdominopelvic viscera (bladder, intestines, uterus etc.) through their tonic contraction.
- Resistance to increases in intra-pelvic/abdominal pressure during activities such as coughing or lifting heavy objects.
- Urinary and faecal continence.The muscle fibres have a sphincter action on the rectum and urethra. They relax to allow urination and defecation.
What are the muscles in the pelvic floor?
When learning about the muscles of the pelvic floor, it is important to keep in mind its funnel-shaped structure. There are three main components of the pelvic floor:
- Levator ani muscles (largest component).
- Coccygeus muscle.
- Fascia coverings of the muscles.
We shall now consider each of these components in more detail.
Levator Ani Muscles
Innervated by the anterior ramus of S4 and branches of the pudendal nerve (roots S2, S3 and S4).
The levator ani is a broad sheet of muscle. It is composed of three separate paired muscles; pubococcygeus, puborectalis and iliococcygeus.
These muscles have attachments to the pelvis as follows:
- Anterior – pubic bodies of the pelvic bones.
- Laterally – thickened fascia of the obturator internus muscle, known as the tendinous arch.
- Posteriorly – ischial spines of the pevlic bones.
Puborectalis
The puborectalis muscle is a U-shaped sling, extending from the bodies of the pubic bones, past the urogenital hiatus, around the anal canal. Its tonic contraction bends the canal anteriorly, creating the anorectal angle (90 degrees) at the anorectal junction (where the rectum meets the anus).
The main function of this thick muscle is to maintain faecal continence – during defecation this muscle relaxes.
Some fibers of the puborectalis muscle (pre-rectal fibers) form another U-shaped sling that flank the urethra in the male and the urethra and vagina in the female (in some textbooks they appear as pubovaginalis or sphincter urethrae / vaginae). These fibers are very important in preserving urinary continence, especially during abrupt increase of the intra-abdominal pressure i.e. during sneezing.
Pubococcygeus
The muscle fibres of the pubococcygeus are the main constituent of the levator ani. They arise from the body of the pubic bone and the anterior aspect of the tendinous arch. The fibres travel around the margin of the urogenital hiatus and run posteromedially, attaching at the coccyx and anococcygeal ligament.
Iliococcygeus
The iliococcygeus has thin muscle fibres, which start anteriorly at the ischial spines and posterior aspect of the tendinous arch. They attach posteriorly to the coccyx and the anococcygeal ligament.
This part of the levator ani is the actual “levator” of the three: its action elevates the pelvic floor and the anorectal canal.
Coccygeus
Innervated by the anterior rami of S4 and S5.
The coccygeus (or ischiococcygeus) is the smaller, and most posterior pelvic floor component – as the levator ani muscles are situated anteriorly.
It originates from the ischial spines and travels to the lateral aspect of the sacrum and coccyx, along the sacrospinous ligament.
What is the perineum?
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.
In clinical practice, the term “perineum” is frequently used to describe the area between the external genitalia and the anus. However, in anatomical terms, the perineum is a diamond-shaped structure.
The anatomical borders of the perineum?
- 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.
The surface borders of the perineum?
- Anterior – mons pubis in females, base of the penis in males.
- Laterally – medial surfaces of the thighs.
- Posterior – superior end of the intergluteal cleft.
Neurovascular Supply of perineum
The major neurovascular supply to the perineum is from the pudendal nerve (S2 to S4) and the internal pudendal artery.
Explain the anal triangle
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.
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.
Explain the urogenital triangle
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.
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.
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.
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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.
Explain the perineal body
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.
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.
In women, it acts as a tear resistant body between the vagina and the external anal sphincter, supporting the posterior part of the vaginal wall against prolapse. In the male, it lies between the bulb of penis and the anus.
