Session 5: The Female Reproductive System Flashcards
Describe the ovaries and their capsule
[*] The paired human ovaries are slightly flattened, almond-shaped and sized organs attached to the posterior surface of the broad ligament of the uterus by the mesovarium.
- The mesovarium is a short peritoneal fold or mesentery.
- Medially within the mesovarium, a short ovarian ligament tethers the ovary to the uterus.
- The ovarian ligament is a remnant of the superior part of the ovarian gubernaculum.
[*] The connective tissue capsule of the ovary, the Tunica Albuginea of the Ovary, is covered with a smooth layer of ovarian mesothelium that has a dull grayish appearance. This epithelium becomes progressively scarred and distorted because of the repeated rupture of ovarian follicles and discharge of oocytes during ovulation.
What do the ovaries contain?
[*] The outer cortex contains many follicles, each containing an oocyte (the female gamete) surrounded by stromal cells called the follicular cells.
- The oocytes originate outside the ovary from the primordial germ cells that colonize the ovary during early embryonic development.
[*] The gonads develop within the mesonephric ridge and descend through the abdomen before stopping in the pelvis. They become stuck because the newly forming uterus is a mechanical barrier, stopping the ovary’s progress through inguinal canal. The inferior pole of the ovary is connected by gubernaculum to the labioscrotal folds and the mesonephric ducts fuse to form the uterus, which is responsible for stopping the ovaries descent.
[*] In the ovary, the oocytes divide by mitosis to form oogonia, which develop into oocytes by undergoing meiosis. Although meiosis commences during fetal life, it is not totally completed until fertilization.
[*] During development, the fetal ovary contains several millions of oogonia which commence meiosis but not all of which complete it to form primary oocytes. The cell division does not progress beyond the diplotene stage of the 1st meiotic prophase until just before ovulation. At ovulation, the 1st meiotic division occurs to produce a haploid secondary oocyte and the 1st polar body.
The oocytes are surrounded by a layer of flattened stromal cells – the follicular cells; this structure is called a primordial follicle. Many follicles undergo degeneration (atresia) in the fetal and postnatal ovary, however up to 400,000 persist at puberty.
[*] The bulk of the human ovary consists of primordial follicles, each consisting of a large round primary oocyte with an eccentrically placed pale-staining nucleus, surrounded by a single layer of follicular cells. About 400 of these will develop fully and shed their ova periodically until menopause.
What 2 types of follicle populations do the ovaries contain from puberty up until menopause?
[*] After puberty and up to menopause, the human ovary contains two populations of follicles.
- By far the larger of the two is a reserve pool of non-growing follicles and a smaller pool of growing follicles derived periodically from the former groups.
It is thus obvious that the reserve pool is constantly depleted and is normally exhausted about the age of 50-55.
The reserve pool contains mainly primordial follicles and follicles that have a layer of follicular cells (granulosa) which are becoming cuboidal.
- Folliculogenesis: entry of follicles into the growth phase and their subsequent development
- Of the growing follicles, only one is normally destined to mature fully during each menstrual cycle to release its gamete (ovum) at ovulation; others undergo degeneration
How are growing and mature follicles classified?
[*] Growing and mature follicles are classified as primary, secondary (or Graafian) or tertiary (or pre-ovulatory) the latter being the largest.
- A primordial follicle slowly transforms into a primary follicle by transformation of the single layer of flattened follicular cells into a layer of cuboidal granulosa cells.
- Glycoproteins that contribute to the formation of the zona pellucida surrounding the oocyte, appear at this time and form a thick amorphous layer as the follicle grows.
- Further follicular growth involves the granulosa cells forming a layer of multiple layers and transformation of the surrounding stromal cells into theca folliculi, which comprises of a cellular theca interna and a fibrous theca externa. These follicles are called secondary pre-antral follicles.
- Appearance of a fluid-filled cavity (antrum), signals the formation of a tertiary or antral follicle. These follicles enlarge by an increase in the fluid volume and proliferation of the granulosa and thecal cells; Graafian follicles are large antral follicles and only one of the most advanced of these will become the ovulatory follicle.
How does the Corpus Luteum form?
Corpus Luteum: when the follicle ruptures to release the ovum at ovulation, the granulosa and theca interna cells show structural (and functional) transformation.
[*] The entire mass of the tissue becomes highly vascularised via the growth and infiltration of blood vessels from the surrounding tissue.
[*] Granulosa cells of the follicle have undergone hypertrophy and form a thick and folded layer of granulosa lutein cells which have a spherical nucleus and pale-stained vacuolated cytoplasm containing numerous lipid droplets.
[*] The theca interna cells have become transformed into theca lutein cells and occupy the depressions formed by the granulosa lutein cells, accompanied by blood vessels.
[*] The central cavity of the corpus luteum contains mainly undifferentiated connective tissue.
Describe the arterial supply, venous drainage and lymphatic drainage of the ovaries
Arterial Supply of the Ovaries
[*] The ovarian arteries come directly off the abdominal aorta, just below the renal arteries. They travel through retroperitoneum.
Venous Drainage of the Ovaries
[*] Venous drainage of the ovaries is asymmetrical, by the left and right ovarian veins
- Right ovarian vein => inferior vena cava
- Left ovarian vein => left renal vein => inferior vena cava
Lymphatic Drainage of the ovaries: lymphatic drainage of the ovaries is to the Para-aortic nodes.
What ligaments are associated with ovaries?
[*] The ovarian ligament (ligament of ovary) is attached to the ovary inferiorly and connects the ovary to the side of the uterus.
- Structurally, it is a fibrous band of tissue that lies within the broad ligament.
- It joins the uterus just below the origin of the fallopian tubes.
[*] The suspensory ligament of ovary extends outwards from the ovary to the lateral abdominal wall. It consists of a fold of peritoneum, thus some sources consider it to be part of the broad ligament. The function of this ligament is to contain the ovarian vessels and nerves (ovarian artery, ovarian vein, ovarian nerve plexus and lymphatic vessels)
Describe the common pathology relevant to the ovaries
[*] The ovary may develop ovarian cysts, which are usually derived from follicles. Polycystic ovaries (with >10 cysts) are usually associated with infertility.
[*] The tumours of the ovary arise most commonly from epithelial components or from germ cells
What are the parts and function of the uterine tubes?
The Uterine Tubes (Fallopian tubes, oviducts)
[*] The uterine tube is a muscular tube that is narrow medially and has a funnel-shaped abdominal opening (near the ovary), the ostium. The margins of the ostium are drawn into finger-like projections called the fimbria, an extension of the infundibulum.
[*] The infundibulum, continues medially into an expanded intermediate segment, the ampulla.
[*] The tube continues into the narrow isthmus and opens into the uterine cavity. The function of the tube is to assist in the transfer and transport the ovum from the ovary to the uterine tube and then to the uterus.
How does the uterine job perform its function?
[*] Histologically, at low magnification the wall of the tube is seen to consist of a mucous membrane, a muscular layer and a serous coat
- The mucous membrane is thrown into complex folds and thus the lumen, in cross-section, appears as a labyrinthine system of narrow spaces.
- The epithelium lining the mucous membrane is of a simple columnar type and consists of ciliated and non-ciliated (secretory ) cells. The secretory cells provide the nutrients to the early conceptus following fertilization. As it is not the same as the endometrium of the uterus, there are consequences in ectopic pregnancies.
[*] The movement of the fimbria over the surface of the ovary and the ciliated cells (lining the tube) are thought to assist in the transfer of the ovum from the surface of the ovary into the uterine tube. Normally the site of fertilisation is in the ampulla.
[*] The contractions of the smooth muscle layer assists in the **transport of sperm to the site of fertilization and the transport of the conceptus to the uterus. **
What is salpingitis and describe its possible consequences
Clinical Correlation: inflammation of the uterine tube, caused by microorganisms, is called salpingitis.
[*] It causes fusions or adhesions of the mucosa, and thus can partially or completely block its lumen leading to infertility.
[*] Blocked or dysfunctional tubes may result in ectopic pregnancy (tubal) or implantation outside the uterus.
Describe the parts of the uterus, locaiton and its relationships (anatomical)
[*] The uterus consists of the fundus, body, uterine tubes and cervix.
[*] The fundus lies superior to the pubic ramus and is not normally palpable but becomes palpable when uterus enlarges, entering the abdominal cavity – upper part is examined during pregnancy
[*] Relationships of the Uterus. The uterus is enveloped by the broad ligament (specialised peritoneum)
- Uterovesical pouch anteriorly (between uterus and urinary bladder)
- Rectouterine pouch (pouch of Douglas) posteriorly (inferior most recess of the peritoneal cavity).
The Pouch of Douglas is accessible through the posterior fornix of the vagina
Describe the development of the uterus and the creation of the broad ligament
- Paramesonephric ducts (a pair of ducts that are open cranially and connect to the urogenital sinus caudally) persist in the absence of (testis-derived) MIH.
- Fusion of the ducts in the midline creates a broad transverse fold draped by peritoneum => broad ligament which contains the uterus, uterine tubes and ovaries etc (intraperitoneal structures)
Describe the uterus including the myometrium and the endometrium
[*] The uterus is a thick-walled muscular organ covered for the most part by serous membrane, the peritoneum.
[*] The greater part of the uterine wall is a mass of smooth muscle, the myometrium. The cells of the myometrium undergo considerable hypertrophy and hyperplasia during pregnancy in preparation for the requirements to expel the foetus at birth.
[*] Internally the uterine cavity is lined by mucous membrane, the endometrium
- The endometrium consists of tubular glands that extend from the surface into the connective tissue (stroma).
- Most of the superficial part of the endometrium (called the stratum functionalis = functional layer) is subject to cyclical growth, degeneration and shedding of the dead tissues.
- The deeper part of the endometrium (stratum basalis = basal layer) in the vicinity of the myometrium does not exhibit the cyclical changes and is responsible for the regeneration of the upper endometrium.
Describe how the cyclical changes of the endometrium are regulated
The hormones secreted by the ovary regulate the cyclical changes in the structure of the endometrium.
- Oestrogen secreted during the folliculogenesis stimulates growth and proliferation of the endometrium; this is the proliferative phase of the endometrium.
- After ovulation, the newly formed corpus luteum secretes progesterone, which stimulates the endometrial glands to secrete glycogen, and causes their extensive coiling and enriches the vascular supply to the mucous membrane. This is the secretory phase of the endometrium.
- These changes in the endometrium are in preparation for the receipt and embedding (implantation) of the conceptus following fertilization.
If the conceptus fails to implant, the endometrium enters the menstrual phase, which is brought about by the withdrawal of hormonal support (degeneration or luteolysis of the corpus luteum) and changes in the vascular supply of the endometrium. This results in the breakdown and degeneration of the bulk of the upper endometrium (statum functionalis), bleeding and the shedding of the dead tissues; these constitute the production of menses.
Describe the uterus in the proliferative phase
- The bulk of the organ is composed of bundles of smooth muscle fibres.
- The endometrium is covered by an epithelium overlying the stroma containing uterine glands forming the functional layer
- The uterine glands are long, narrow and straight and often slightly dilated.
- In the deepest part of the endometrium (basal layer), the glands show some bifurcation in the zone adjacent to the myometrium and occasionally they penetrate a short distance among the muscle bundles.
- The epithelium lining the uterine cavity and the glands is simple columnar and is composed of a mixture of ciliated and secretory cells.
- Numerous mitoses are evident in the epithelium (particularly in the epithelium lining the glands) and in the endometrial stroma
- The stroma consists of stellate cells surrounded by a fine reticular network
- The arteries (called spiral or coiled arteries) are mostly located in the lower part of the endometrium and appear transversely sectioned.
Describe the uterus in the secretory phase
- The endometrial glands have enlarged to become more tortuous and have developed marked sacculation, resulting in a relatively wide lumen of irregular outline containing secretion.
- The endometrial stroma appears oedematous and some of the stromal cells have undergone hypertrophy.
- The blood supply to the endometrium has become more extensive and the arteries are now present in the superficial regions too.
- The histology of the basal layer of the endometrium remains essentially unaltered
Describe the endometrium in the menstrual phase
The upper endometrium has undergone extensive necrosis and shows ruptured blood vessels.
Describe the position of the uterus
Anteflexed in relation to the cervix (angle of inclination)
Anteverted in relation to the vagina
What ligaments support the uterus?
The ligaments of the uterus:
- The superior aspect is supported by the broad ligament and the round ligaments.
- The middle aspect is supported by the cardinal, pubocervical and uterosacral ligaments.
- The inferior aspect of uterus is supported by the structures in the pelvic floor: the levator ani, perineal membrane and perineal body.
Describe the broad ligament including its parts
[*] Broad ligament: double layer of peritoneum (mesentery) [peritoneal fold] that extends from the sides of the uterus to the lateral walls and floor of the pelvis. It folds over the internal female genitalia, covering their surface anteriorly and posteriorly. It is comprised of the mesentery of the uterus, uterine tube and ovary. The broad ligament assists in keeping the uterus in position. It may be divided into 3 subcomponents
- Mesometrium – the mesentery of the uterus; the largest portion of the broad ligament. It runs laterally to cover the external iliac vessels, forming a distinct fold over them. It also encloses the proximal part of the round ligament of the uterus.
- Mesosalpinx – the mesentery of the Fallopian tube. It originates superiorly to the mesovarium, enclosing the fallopian tubes.
- Mesovarium – the mesentery of the ovaries. It projects from the posterior surface of the broad ligament and attaches to the hilum of the ovary, enclosing its neurovascular supply. It does not, however, cover the surface of the ovary itself.
What are the contents of the broad ligament?
[*] Contents of the broad ligament: uterine tubes, ovary (some sources consider the ovary to be on the broad ligament but not in it), ovarian artery (in the suspensory ligament), uterine artery, ovarian ligament, round ligament of uterus and suspensory ligament of the ovary.
Describe the Round Ligament
The round ligament is the second embryological remnant of the (inferior part) gubernaculum. The round ligament originates at the uterine horns – the point at which the fallopian tubes enter the uterus) and the labium majus as well as travelling through the inguinal canal.
- This gives consequences to the lymphatic drainage of the uterus – the fundus drains to the aortic nodes (where it is embryologically derived from)
- The round ligament can be a source of pain during pregnancy due to increased force placed on the ligament by the expanding uterus.
What is Endometriosis?
[*] Endometriosis is a condition in which ectopic endometrial tissue is dispersed to various sites along the peritoneal cavity and beyond (e.g. near to the umbilicus). It may be associated with the ovaries or the attachments of the uterus and is often associated with severe period pain (dysmenorrhoea), infertility or both.
Describe the Cervix
[*] The cervix of the uterus is a fibromuscular neck, which protrudes into the upper vagina and contains the endocervical canal which links the uterine cavity with the vagina. Internal os and external os at either end. The external os is seen on speculum
[*] The function of the cervix is to allow the sperms, deposited in the vagina at coitus, to enter the uterine cavity to proceed to the site of fertilization and, at other times, to protect the uterus and upper genital tract from bacterial invasion.
[*] It is composed of two regions, the endocervix and the exocervix.
Describe the endocervix and the exocervix
[*] The endocervix is lined by tall columnar epithelium with basally placed nuceli and the greater part of the cytoplasm filled with mucus.
[*] The mucosa contains numerous large glands that are also lined with tall, mucus-secreting columnar cells.
[*] The exocervix is covered with a stratified squamous non-keratinized epithelium (as of the vagina).
[*] The change from the columnar to the stratified squamous epithelium, at the transformation zone, is abrupt and can occur anywhere along the cervix.
[*] The remainder of the cervix is composed of circularly arranged smooth muscle fibres, lying in abundant dense connective tissue.
Describe relevant pathology of the cervix
The junction between the columnar cells of the endocervix and the squamous cells of the exocervix is the site where the majority of neoplasms form.
Endometrial carcinoma is a malignancy of the endometrium usually occurring in postmenopausal women. The major symptom is abnormal uterine bleeding.
Major symptom is abnormal uterine bleeding
Describe the Arterial Supply and Venous Drainage of the Uterus
Arterial Supply of the Uterus
[*] The Uterine Artery arises from the Anterior Division of the Internal Iliac Artery.
[*] Abdominal aorta => Common iliac => Internal iliac => Anterior division of Internal iliac => Uterine
[*] The ureter passes inferiorly to the uterine artery (water under the bridge)
[*] Branches of the uterine artery and ovary artery anastomose
Venous Drainage of the Uterus
[*] Venous drainage of the uterus is via the uterine venous plexus, which merges to form the uterine veins, which are tributaries of the internal iliac vein
[*] Uterine venous plexus => Uterine vein => Internal iliac vein => Common iliac vein => Inferior vena cava
Describe the lymphatic drainage of the uterus and the cervix
[*] Fundus of the uterus => Aortic nodes (and inguinal nodes)
[*] Body of the uterus => External Iliac nodes
[*] Cervix => External and Internal Iliac Nodes and Sacral Nodes
[*] The uterus drains to paraaortic, external and internal iliac (develops as paramesonephric ducts fuse together), sacral nodes as well as inguinal nodes (due to round ligament, providing a route of drainage to superficial inguinal nodes)
[*] The ovary drains to paraaortic nodes
What are the Vaginal Fornices? Where does the vaginal orifice open into?
[*] The Vaginal Fornices are the recesses of vagina around the cervix
[*] Vaginal orifice opens into the vestibule along with the external urethral orifice and the ducts of the greater and lesser vestibular glands.
Describe the Arterial Supply and Venous Drainage to the vagina
[*] The arteries supplying the superior part of the vagina derive from the uterine arteries. The middle and inferior parts of the vagina are supplied by the vaginal and internal pudendal arteries, a branch off the anterior division of the internal iliac artery
- Abdominal aorta => Common iliac => Internal iliac => Anterior division of internal iliac => uterine => Vaginal
- Abdominal aorta => Common iliac => Internal iliac => Anterior division of internal iliac => uterine => internal pudendal
Venous Drainage of the Vagina
[*] The vaginal veins form the Vaginal Venous Plexuses along the sides of the vagina and within the vaginal mucosa. These veins merge to form the Vaginal Vein which drains into the internal iliac veins via the uterine vein.
[*] The vaginal venous plexus also communicates with the vesical and rectal venous plexuses
- Vaginal plexus => Vaginal => Uterine => Internal iliac => Common iliac => Inferior vena cava
Compare the peritoneal reflections in male and female
In the female the peritoneal cavity is open via the ostium of the uterine tube
Describe the Cardinal Ligament
Transverse cervical ligament (aka cardinal or Mackenrodt’s ligament)
- Thickening at base (inferior border) of broad ligament
- House the uterine artery and uterine veins
- The transverse cervical ligaments arise from the side of the cervix and the lateral fornix of the vagina. They provide an extensive attachment on the lateral pelvic wall at the level of the ischial spines. Some fibres of the cardinal ligaments interdigitate with fibres from the uterosacral ligaments.
- When a hysterectomy is being performed due to a malignancy, the cardinal ligaments are often removed as they are common reservoir of cancerous ligaments
- Lateral stability of the cervix + support of the middle aspect of the uterus - part of the support for pelvic viscera
Describe the uterosacral ligament
[*] Uterosacral ligament (from uterus to sacrum)
- Bilateral fibrous bands which attach the cervix to the sacrum.
- AKA recto-uterine ligaments or sacrocervical ligaments
- Opposes anterior pull of round ligament, assists in maintaining anteversion (normal anatomical position) – support and hold uterus in place
What are the pubosacral ligaments?
Bilateral structures which attach the cervix to the posterior surface of the pubic symphysis. They function to support the uterus within the pelvic cavity.
What is meant by Cervix and Bimanual examinations?
Cervical Examination: use of a speculum to isolate the external os of the cervix
Bimanual Examination:
[*] 2 fingers are inserted into the vagina until they isolate the cervix – test of the cervical motion tenderness (sign of PID – pelvic inflammatiory disease)
[*] Examiner palpates the uterus – the fundus part
Describe the innervation of the perineum
[*] Largely supplied by somatic pudendal nerve
[*] PLUS ilioinguinal nerve
[*] The pudendal nerve exits pelvis via greater sciatic foramen and enters perineum via lesser sciatic foramen. It travels through pudendal canal.
Describe the pelvic girdle
The bony pelvis is a funnel-shaped structure made up of the innominate (hip) bones, the sacrum and the coccyx. Dense ligaments bind the bones to each other
[*] 4 bones contribute to the pelvic girdle.
- 2 innominate bones (the hip bones – ilium, ischium and pubis)
- Iliac crest
- (Arcuate line + pectineal line + pubic crest) = linea termnalis (complete line around the pelvic girdle)
- Ischial spine: defines greater and lesser sciatic notches
- Ischial tuberosity
- Sacrum (formed by the fusion of five, originally separate sacral vertebrae)
- Sacral Promontory – anterior superior edge of 1st sacral vertebra (very prominent)
- Coccyx
[*] The hip bones articulate with the sacrum at the Sacroiliac joint and with each other at the pubic symphysis.
What is the Pelvic Inlet?
[*] The superior aperture (the pelvic inlet aka pelvic brim) leading into the pelvis is wider than the inferior aperture (the pelvic outlet)
The pelvic inlet is demarcated by the broad ‘wings’ of the iliac bones, the sacrum and the pubic symphysis.
- Promontory and ala of the sacrum posteriorly (superior surface of its lateral part, adjacent to the body of the sacrum)
- Right and left linea terminalis anteriorly (arcuate line on the inner surface of the ilium, pectineal line and pubic crest)
In the erect position, the pelvis is tilted so that the plane of its inlet is at an angle of 60 degrees to the horizontal.
What is the Pelvic Outlet?
[*] The pelvic outlet (inferior pelvic aperture) is demarcated by the paired inferior pubic rami (pubic arch anteriorly), the ischial tuberosities (laterally), the inferior margin of the sacrotuberous ligament (posterolaterally) and the tip of the coccyx (posteriorly).
The pelvic outlet is bony anteriorly, but is partially made up by the sacrotuberous ligament posteriorly. The ligament is potentially stretchy and indeed through pregnancy, progesterone works to soften the ligaments to increase the size of the pelvic outlet to aid childbirth.
The pelvis is made up of the greater and lesser pelvis. What does it mean?
A greater (“false”) pelvis which is the ‘space’ surrounded by the upper portions of the iliac bones and upper part of the sacrum posteriorly. It lies superior to the linea terminalis and has no obstetric relevance.
- Superior to the pelvic inlet
- Bounded by the iliac alae posterolaterally
- Bounded by the anterosuperior aspect of the S1 vertebra posteriorly
- Occupied by abdominal viscera (e.g. the ileum and sigmoid colon).
A lesser (“true”) pelvis which is placed more deeply and surrounded by the margins of the obturator foramen, the ischial spines and the lower portion of the sacrum – it is inferior to the linea terminalis. The bony canal between the pelvic inlet and outlet is solid and immobile.
- Bounded by the pelvic surfaces of the hip bones, sacrum and coccyx
- The lesser pelvis is of major obstetrical and gynaecological significance
The greater pelvis is in fact the lower portion of the abdominal cavity, while the lesser pelvis contains the true structures of the pelvis, including the internal genitalia and the bladder.
What are the sex differences of the pelvis?
associated mainly with 2 features
- The heavier build and stronger muscles in the male account for the stronger bone structure and better-defined muscle markings
- The comparatively wider and shallower pelvic cavity in the female is correlated with its specialisation to accommodate the passage of the infant’s head.
On plain x-rays, sex differences can be easily determined by the following features:
[*] The pelvic inlet is heart-shaped in the male and oval in the female
[*] The subpubic angle (angle between the inferior pubic rami) is narrow in the male and wide in the female
[*] The soft tissue shadow of the penis and scrotum can usually be seen when not shielded by a lead screen.
What makes a good pelvis for childbirth?
a gynecoid pelvis
[*] Round inlet
[*] Straight side walls – no funnelling
[*] Ischial spines not too prominent (cannot project too far into the birth canal)
[*] Well-rounded greater sciatic notch
[*] Well-curved sacrum (to allow a nice fit with the foetal head as it passes through the pelvis during delivery)
[*] Sub-pubic arch > 90 degrees
How are pelvic conjugates used to assess the plane of the pelvic inlet?
[*] Plane of the Pelvic Inlet/Pelvic brim is bounded posteriorly by the sacral promontory (can be palpated superiorly), laterally by the iliopectineal lines and anteriorly by the superior pubic rami and upper margin of the pubic symphysis.
[*] The true conjugate or anteroposterior diameter of the pelvic inlet is the distance between the midpoint of the sacral promontory and the superior border of the pubic symphysis anteriorly. The diameter measures ~11cm. Also known as the anatomic conjugate.
[*] The shortest distance and the one of greatest clinical significance is the obstetric conjugate diameter. This is the distance between the midpoint of the sacral promontory and the nearest point (~midpoint) on the posterior surface of the pubic symphysis. It is ~10cm. It is the minimum diameter as this is where the pubic bone is the thickest.
[*] It is not possible to measure either of these diameters by clinical examination; the only diameter at the pelvic inlet amenable to clinical assessment is the distance from the inferior margin of the pubic symphysis to the midpoint of the sacral promontory. This is known as the diagonal conjugate diameter and is approximately 1.5cm greater than the obstetric conjugate.
[*] In practical terms, it is not usually possible to reach the sacral promontory on clinical examination and the highest point that can be palpated is the second or third piece of the sacrum. If the sacral promontory is easily palpable, the pelvic inlet is contracted.
Describe the Sacrospinous and Sacrotuberous ligaments
[*] Sacrospinous ligament: attached to sacrum and ischial spine
[*] Sacrotuberous ligament: attached to sacrum and ischial tuberosity – demarcates the pelvic outlet posteriorly.
[*] Both contribute to the pelvic outlet
[*] Ligaments are potentially stretchy under influence of progesterone so pelvic outlet is less rigid
Describe the structure and function of the pelvic floor
The pelvic floor is formed from muscular layer(s) which support pelvic viscera. It exerts a sphincter action on rectum and vagina and can resist increases in intra-abdominal pressure associated with coughing, defecaion, heavy lifting etc
The pelvic floor is composed of:
- Pelvic diaphragm – consisting of levator ani and coccygeus, and related fascial coverings (fascia covering the superior and inferior aspects of these muscles). The pelvic diaphragm is bowl or funnel-shaped.
- Superficial muscles and structures
- Anterior (urogenital) perineum
- Posterior (anal) perineum
In other words: What is the pelvic floor?
[*] Muscular and fibrous tissue diaphragm
[*] Fills the lower part of the pelvic canal
[*] Closes the abdominal cavity
[*] Defines the upper border of the perineum
[*] Pierced by the urethra, vagina and rectum.
Role of the Pelvic Floor
[*] Supports the pelvic organs –retains uterus and bladder in correct position
[*] Contributes to continence – sphincter mechanism directly and indirectly
[*] Contributes to the process of childbirth – shape of levator ani muscles is very important for rotation of the head for successful delivery
[*] Contributes to “truncal stability”
What are the layers of the Urogenital Triangle?
[*] Layers are listed deep to superficial.
- Deep perineal pouch: a potential space between the pelvic floor superiorly and the perineal membrane inferiorly. It contains part of the urethra and the external urethral sphincter. 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 vagina. The role of the membrane is to provide attachment for the muscles of the superficial external genitalia, and to help support the pelvic viscera.
- Superficial perineal pouch: a potential space between the perineal membrane superiorly, and the 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 (in the male). The greater vestibular glands (Bartholin’s glands) are also located in the superficial perineal pouch. The superficial perineal pouch is the site of collection if the urethra is ruptured below the perineal membrane
- Deep perineal fascia: fascia covering the superficial perineal muscles.
- Superficial perineal fascia: it is continuous with the superficial fascia of the abdominal wall. The superficial fascia itself can be divided into superficial and deep layers. The superficial layer is fatty in structure, forming the labia majora and mons pubis in women.
- Skin: the urethral and vaginal orifices open out onto the skin.
[*] The urogenital diaphragm also contains the bulbourethral glands and is pierced by the urethra and vagina.
Describe the Posterior (Anal) triangle
[*] Triangle between ischial tuberosities on each side and the coccyx. It is also bounded by the sacrotuberous ligaments. It comprises of the anal aperture (the opening of the anus), external anal sphincter muscle (voluntary muscle responsible for opening closing the aus) and two ischiorectal fossae – 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 aid expansion of the anal canal during defecation. They extend from the skin of the anal region inferiorly to the pelvic diaphragm superiorly. The fossae may become infected.
[*] The pudendal nerve passes along the lateral wall of the fossa.
Describe the levator ani? What 3 muscles constitute it?
Levator ani are paired muscles forming 3 slings of muscle extending from the posterior aspect of pubic bone, the fascia over obturator internus and the ischial spines. The muscle is innervated by branches of the pudendal nerve, roots S2, S3 and S4. The 3 slings are
[*] The puborectalis 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.
[*] 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. As the fibres run inferiorly and medially, some fibres divide and loop around the prostate in males (levator prostatae) and around the vagina in females (pubovaginalis). Some also terminate in the perineal body.
[*] The iliococcygeus has thin muscles, which start anteriorly at the ischial spines and posterior aspect of the tendinous arch. They attach posteriorly to the coccyx and the anococcygeal ligament.
[*] These muscles have attachments to the pelvis as follows:
- Anterior: the pubic bodies of the hip bone
- Laterally: thickened fascia of the obturator internus muscle, known as the tendinous arch - arcus tendineus fascia pelvis.
- Posteriorly: the ischial spines of the hip bone
Describe the Coccygeus
Posteriorly coccygeus lies over the sacrospinous ligament
[*] Innervated by the anterior rami of S4 and S5
[*] The coccygeus is the smaller, and most posterior, pelvic floor component. The levator ani muscles are situated anteriorly.
[*] The coccygeus originates from the ischial spines and travels to the lateral aspect of the sacrum and coccyx, along the sacrospinous ligament.
Describe the Perineum
The perineum is an anatomical region located in the pelvis. It is the most inferior part of the pelvic outlet, located between the thighs. It is separated from the pelvic cavity superiorly by the pelvic floor.
[*] Fibromuscular sheet
[*] Lower limit of perineal space
[*] Perineal space continuous with ischiorectal fossa
[*] Contains perineal muscles and the perineal body.
Contents: the perineum can be subdivided by a theoretical line drawn transversely between the ischial tuberosities. This split forms the anterior urogenital and posterior anal triangles.
Anatomical Borders:
- Anterior – Pubic symphysis.
- Posterior- The tip of the coccyx.
- Laterally – Inferior pubic rami and inferior ischial rami, and the sacrotuberous ligament.
- Roof – The pelvic floor.
- Base – Skin and fascia.
Surface Borders (Clinically relevant)
- Anteriorly: Mons pubis in females, base of the penis in males.
- Laterally: Medial surfaces of the thighs.
- Posteriorly: Superior end of the intergluteal cleft.
Describe the role of perineal body
This most important structure is a pyramidal fibromuscular node (connective tissue node) at the junction of the anterior and posterior perineum (between the urogenital and anal triangles) – in the centre of the perineum.
[*] In males it is found between the bulb of the penis and the anus.
[*] In females it is found between the vagina and anus (~1.25cm in front of the anus)
The perineal body is essential for the integrity of the pelvic floor, especially in females, anchoring the perineal muscles and rectum. It is the central fulcrum for pelvic support.
[*] It is the point of attachment of anal sphinters, bulbospongiosus, superficial transverse perineal muscles and fibres of levator ani.
Describe how the perineal body may be damaged, possible consequences and how it may be avoided in childbirth via episiotomy.
Damage to (rupture of) the perineal body in childbirth can cause weakness in the pelvic floor leading to prolapse of structures such as the vaginal and uterus. This may be avoided by episiotomy (a surgical cut in the perineum). This inevitably causes damage to the vaginal mucosa but prevents uncontrolled tearing of the perineal body. If the medial fibres of the puborectalis are torn within the perineal body, then rectal herniation can also occur.
Other causes of perineal body damage include inflammatory disease, infection or trauma.
NICE Guideline Intrapartum Care (CG55)
[*] Carry out episiotomy only when there is:
- Clinical need such as instrumental birth
- Suspected fetal compromise
[*] Do not routinely offer following previous third- or fourth degree trauma
[*] Use mediolateral technique (between 45 and 60 degrees to right side, originating at vaginal fourchette)
[*] Use tested effective analgesia
- Midline tear or episiotomy endangers anal sphincter (could => to faecal incontinence if not correctly repaired)
- Mediolateral tear or episiotomy protects anal sphincter (by relieving pressure)
