ANT222-Pelvis and Perineum PDF

## GROSS ANATOMY OF PELVIS AND PERINIUM The pelvis is the inferior most part of the trunk. Consisting of the pelvic girdle and perineum, it supports the urinary and reproductive organs. Humans use pelvic organs for both pleasure and reproduction. ### The pelvic girdle (hip girdle) - Is formed by...

## GROSS ANATOMY OF PELVIS AND PERINIUM The pelvis is the inferior most part of the trunk. Consisting of the pelvic girdle and perineum, it supports the urinary and reproductive organs. Humans use pelvic organs for both pleasure and reproduction. ### The pelvic girdle (hip girdle) - Is formed by a single bone, the hip bone or coxal bone: coxal means "hip" - Serves as an attachment point for each lower limb. - Each hip bone is firmly joined to the sacrum of the vertebral column through the sacroiliac joints. - The right and left hip bones also converge anteriorly to attach to each other through the pubic symphysis. - The bony pelvis is the entire structure formed by the two hip bones, the sacrum, and the coccyx: the coccyx is attached inferiorly to the sacrum. ### The pelvic girdle in comparison to pectoral girdle: - Unlike the bones of the pectoral girdle, which are highly mobile, the bones of the pelvis are strongly united to each other to form a largely immobile, weight-bearing structure. - This is important for stability because it enables the weight of the body to be easily transferred laterally from the vertebral column, through the pelvic girdle and hip joints, and into either lower limb. - The immobility of the pelvis provides a strong foundation for the upper body as it rests on top of the mobile lower limbs. ### HIP BONE - The hip bone, or coxal bone, forms the pelvic girdle portion of the pelvis. - They are the large, curved bones that form the lateral and anterior aspects of the pelvis. - Each adult hip bone is formed by three separate bones that fuse together during the late teenage years (ilium, ischium, and pubis). - These names are retained and used to define the three regions of the adult hip bone. ### The ilium - The fan-like, superior region that forms the largest part of the hip bone. - Is firmly united to the sacrum at the largely immobile sacroiliac joint. ### The ischium - Forms the posteroinferior region of each hip bone. - Supports the body when sitting. ### The pubis - Forms the anterior portion of the hip bone. - Curves medially, where it joins to the pubis of the opposite hip bone at a specialized joint called the pubic symphysis. ### ILIUM - When you place your hands on your waist, you can feel the arching, superior margin of the ilium along your waistline: this is the iliac crest. - The rounded, anterior termination of the iliac crest is the anterior superior iliac spine. This important bony landmark can be felt at your anterolateral hip. - Inferior to the anterior superior iliac spine is a rounded protuberance called the anterior inferior iliac spine. - Both of these iliac spines serve as attachment points for muscles of the thigh. - Posteriorly, the iliac crest curves downward to terminate as the posterior superior iliac spine. - Muscles and ligaments surround but do not cover this bony landmark, thus sometimes producing a depression seen as a "dimple" located on the lower back. - More inferiorly is the posterior inferior iliac spine: this is located at the inferior end of a large, roughened area called the auricular surface of the ilium. - The auricular surface articulates with the auricular surface of the sacrum to form the sacroiliac joint. - Both the posterior superior and posterior inferior iliac spines serve as attachment points for the muscles and very strong ligaments that support the sacroiliac joint. - The shallow depression located on the anteromedial (internal) surface of the upper ilium: the iliac fossa. - The inferior margin of this space is formed by the arcuate line of the ilium, the ridge formed by the pronounced change in curvature between the upper and lower portions of the ilium. - The large, inverted U-shaped indentation located on the posterior margin of the lower ilium is called the greater sciatic notch. ### ISCHIUM - The posterolateral portion of the hip bone. - The large, roughened area of the inferior ischium is the ischial tuberosity. - Serves as the attachment for the posterior thigh muscles and also carries the weight of the body when sitting. - Projecting superiorly and anteriorly in the ischial tuberosity is a narrow segment of bone called the ischial ramus. - The slightly curved posterior margin of the ischium above the ischial tuberosity is the lesser sciatic notch. - The bony projection separating the lesser sciatic notch and greater sciatic notch is the ischial spine. ### PUBIS - The anterior portion of the hip bone. - The enlarged medial portion of the pubis is the pubic body. - Located superiorly on the pubic body is a small bump called the pubic tubercle. - The superior pubic ramus is the segment of bone that passes laterally from the pubic body to join the ilium. - The narrow ridge running along the superior margin of the superior pubic ramus is the pectineal line of the pubis. - The pubic body is joined to the pubic body of the opposite hip bone by the pubic symphysis. - Extending downward and laterally from the body is the inferior pubic ramus. - The pubic arch is the bony structure formed by the pubic symphysis, and the bodies and inferior pubic rami of the adjacent pubic bones. - The inferior pubic ramus extends downward to join the ischial ramus: these form the single ischiopubic ramus, which extends from the pubic body to the ischial tuberosity. - The inverted V-shape formed as the ischiopubic rami from both sides come together at the pubic symphysis: the subpubic angle. ### PELVIS - Consists of four bones: the right and left hip bones, the sacrum, and the coccyx. - The primary role is to support the weight of the upper body when sitting and to transfer this weight to the lower limbs when standing. - Serves as an attachment point for trunk and lower limb muscles, and also protects the internal pelvic organs. - When standing in the anatomical position, the pelvis is tilted anteriorly. - The anterior superior iliac spines and the pubic tubercles lie in the same vertical plane, and the anterior (internal) surface of the sacrum faces forward and downward. - The three parts of each hip bone, the ilium, pubis, and ischium, converge centrally to form a deep, cup-shaped cavity called the acetabulum: which fuses about 11 to 15yrs in males and 14 to 17yrs in females. - Located on the lateral side of the hip bone and is part of the hip joint. - The large opening in the anteroinferior hip bone between the ischium and pubis: the obturator foramen. - Largely filled in by a layer of connective tissue and serves for the attachment of muscles on both its internal and external surfaces. ### Several ligaments unite the bones of the pelvis: - The largely immobile sacroiliac joint is supported by a pair of strong ligaments that are attached between the sacrum and ilium portions of the hip bone. - These are the anterior sacroiliac ligament on the anterior side of the joint and the posterior sacroiliac ligament on the posterior side. - Also spanning the sacrum and hip bone are two additional ligaments. - These include the sacrospinous ligament: runs from the sacrum to the ischial spine. - This also includes the sacrotuberous ligament: runs from the sacrum to the ischial tuberosity. - These ligaments help to support and immobilize the sacrum as it carries the weight of the body. ### The sacrospinous and sacrotuberous ligaments also help to define two openings on the posterolateral sides of the pelvis through which muscles, nerves, and blood vessels for the lower limb exit. - The superior opening is the greater sciatic foramen. - It is formed by the greater sciatic notch of the hip bone, the sacrum, and the sacrospinous and sacrotuberous ligaments. - The smaller, more inferior sciatic foramen is formed by the lesser sciatic notch of the hip bone, together with the sacrospinous and sacrotuberous ligaments. ### The space enclosed by the bony pelvis is divided into two regions: - The broad, superior region, defined laterally by the large, fan-like portion of the upper hip bone, is called the greater pelvis (greater pelvic cavity; false pelvis). - This broad area is occupied by portions of the small and large intestines, and because it is more closely associated with the abdominal cavity: it is sometimes referred to as the false pelvis. - More inferiorly, the narrow, rounded space is the lesser pelvis (lesser pelvic cavity; true pelvis): contains the bladder and other pelvic organs, and thus is also known as the true pelvis. - The pelvic brim (also known as the pelvic inlet) forms the superior margin of the lesser pelvis: separating it from the greater pelvis. - The pelvic brim is defined by a line formed by the upper margin of the pubic symphysis anteriorly, and the pectineal line of the pubis, the arcuate line of the ilium, and the sacral promontory (the anterior margin of the superior sacrum) posteriorly. - The inferior limit of the lesser pelvic cavity is called the pelvic outlet. - This large opening is defined by the inferior margin of the pubic symphysis anteriorly, and the ischiopubic ramus, the ischial tuberosity, the sacrotuberous ligament, and the inferior tip of the coccyx posteriorly. - The lesser pelvis is also angled, giving it an anterosuperior (pelvic inlet) to posteroinferior (pelvic outlet) orientation. ### Overview of Differences between the Female and Male Pelvis (Table 1) | Feature | Female pelvis | Male pelvis | |---|---|---| | Pelvic weight | Bones of the pelvis are lighter and thinner | Bones of the pelvis are thicker and heavier | | Pelvic inlet | Pelvic inlet has a round or oval shape | Pelvic inlet is heart-shaped | | Lesser pelvic cavity shape | Lesser pelvic cavity is shorter and wider | Lesser pelvic cavity is longer and narrower | | Subpubic angle | Subpubic angle is greater than 80 degrees | Subpubic angle is less than 70 degrees | | Pelvic outlet shape | Pelvic outlet is rounded and larger | Pelvic outlet is smaller | ### We shall be discussing the topic under the following subtopics 1. Pelvic floor 2. Perineum 3. Female pelvis 1. Female perineum 4. Male pelvis 1. Male perineum 5. Blood vessels 6. Innervation 7. Lumbar and sacral plexus ### The pelvic floor - Is formed by the funnel-shaped pelvic diaphragm. - The pelvic diaphragm comprises of the two paired muscles and their fasciae; levator ani muscle and the coccygeus muscle. - The function of the pelvic diaphragm is to support the pelvic organs and prevent them from prolapse. - Levator ani muscle is the main muscle here. - It consists of three parts; puborectalis, pubococcygeus, and the iliococcygeus. - The puborectalis part makes a U-turn around the anorectal junction (puborectal sling): forming the urogenital hiatus. - Besides the rectum and urethra in both sexes, in females, this hiatus also transmits the vagina. ### The four different pelvis shapes are: - Gynecoid: This is the most common type of pelvis in females and is generally considered to be the typical female pelvis. Its overall shape is round, shallow, and open. It is most favorable for vaginal birth. - Android: This type of pelvis bears more resemblance to the male pelvis. It's narrower than the gynecoid pelvis and is shaped more like a heart or a wedge. The narrower shape of the android pelvis can make labor difficult because the baby might move more slowly through the birth canal. C-section may be required. - Anthropoid: An anthropoid pelvis is narrow and deep. Its shape is similar to an upright egg or oval. The elongated shape of the anthropoid pelvis makes it roomier from front to back than the android pelvis. But it's still narrower than the gynecoid pelvis. Some pregnant women with this pelvis type may be able to have a vaginal birth, but their labor might last longer. - Platypelloid: The platypelloid pelvis is also called a flat pelvis. This is the least common type. It's wide but shallow, and it resembles an egg or oval lying on its side. The shape of the platypelloid pelvis can make a vaginal birth difficult because the baby may have trouble passing through the pelvic inlet. Many pregnant women with a platypelloid pelvis need to have a C-section. ### PELVIC FLOOR DISORDERS - Pelvic floor dysfunction: This is when the muscles of the pelvic floor have problem with coordination. It can lead to incontinence and pain in your pelvis or lower back. Pregnancy is a common cause. - Pelvic organ prolapse: Prolapse can happen when the muscles of the pelvic floor weakens. As a result, pelvic organs like the vagina, uterus can prolapse. Common causes are childbirth, menopause, and aging. - Sacroiliitis: Sacroiliitis is when the joint that connects the pelvis to the lower part of the spine (sacrum) becomes inflamed and painful. It can happen during pregnancy or due to an injury or arthritis. - Osteitis pubis: Osteitis pubis happens when the joint in the front part of the pelvis (pubic symphysis)becomes inflamed and painful. It's often caused by repeated stress to the area through activities like playing sports. - Pelvic fractures: This is when there's a break in one of the bones of the pelvis. Pelvic fractures are often caused by injuries or accidents. Some may require surgery to repair. ### Perineum - The part of the pelvis which contains the external genitalia and anus. - It is inferior to the pelvic diaphragm. - Regarding the surface anatomy, the perineal area is the region between the thighs, extending from the pubic symphysis anteriorly to the coccyx posteriorly. - It is the erogenous zone in both males and females: it correspond to the outlet of the pelvis. ### The perineum is diamond shaped, and the borders of that diamond are the: - Pubic symphysis anteriorly - Sacrum and coccyx posteriorly - Ischial tuberosities on each lateral side - The pelvic diaphragm is the roof, while the perineal skin forms the floor. - An imaginary line connecting the ischial tuberosities divides the perineum into the urogenital triangle (UGT) anteriorly, and the anal triangle posteriorly. ### The anal triangle includes the rectum and the two ischioanal fossae: - These fossae are filled with fat tissue which supports the movements of the pelvic diaphragm. - They communicate with the UGT through their anterior recesses. ### The urogenital triangle contains the perineal membrane and superficial fascia of Colles. - It bounds two anatomical spaces within the UGT: superficial perineal pouch and deep perineal pouch. - In both sexes, there are anatomical differences only within the contents of the urogenital triangle as it contains the external genitals (the penis and the vaginal). - A mass of connective, skeletal and smooth muscle tissues called the perineal body is found between the triangles. - It is the central mass of the perineum which anchors most of the perineal muscles. - In females the perineum may be torn or incised (with scissors- episiotomy) during child birth: especially for first timer: to create more expansion of the vaginal for the fetus. ### Female pelvis - Broader and larger than the male pelvis to provide a comfortable environment for fetal development. - The greater pelvis as mentioned earlier contains terminal ileum, cecum and sigmoid colon in both sexes. ### The lesser pelvis in females contains: - Distal parts of the urinary and digestive systems: ureter, urinary bladder, urethra and rectum. - Internal genitalia: ovaries, uterine tubes, uterus and vagina. - External genitalia, contained by the perineum. ### Let's look at the anatomical relationships for the female pelvic viscera: - In the medial view, from anterior to posterior we see the rectum just anterior to the coccyx, urinary bladder posterior to the pubic symphysis, and the uterus sandwiched between the two of them. ### Peritoneum overlays the superior surfaces of these organs, creating two peritoneal pouches: - The rectouterine pouch of Douglas between the rectum and the uterus (fluid collection in this pouch is a sign of some disease conditions), and the vesicouterine pouch between the uterus and the bladder. - These three organs communicate with the outside of the body by extending through the perineum: - The urethra extends from the inferior surface of the bladder and opens at the external urethral orifice. It is shorter in females than males (about 4cm). - The vagina extends from the cervix of the uterus and opens at the ostium of the vagina. - The rectum continues as the anal canal which opens at the anus. - Now, where are the uterine tubes and the ovaries? In the peritoneal cavity suspended within their respective peritoneal folds, mesovarium and mesosalpinx. - The uterine tubes extend from each lateral side of the body of the uterus and open near the ovaries. ### Female perineum - The urogenital triangle in females includes the internal genitalia and perineal muscles. - Compared to males, it has two more muscles in the deep perineal pouch. ### Deep perineal pouch: - Proximal urethra - Deep transverse perineal muscle - Inferior part of external urethral sphincter - Urethrovaginal sphincter and compressor urethrae muscle - Dorsal nerves and vessels of the clitoris - Roots of the erectile tissues (corpora cavernosa, bulbs of the vestibule) - Bulbospongiosus, Ischiocavernosus, bulbs of the vestibulesch - Muscles mnemonic: Bulb Is Super ### Superficial perineal pouch: - Root of the penis (corpora cavernosa, corpus spongiosum) - Bulbospongiosus, Ischiocavernosus, Superficial transverse perineal muscle - Muscles mnemonic: Bulb Is Super ### Surface anatomy: - Mons pubis - Labia majora - Labia minora - Glans of clitoris - Vaginal orifice ### Male pelvis - In comparison to the female pelvis, the male pelvis is narrower. - The lesser pelvis in males contains: - Distal parts of the urinary and digestive systems: ureter, urinary bladder, urethra and rectum. - Internal genitalia: testes, epididymis, ductus deferens, seminal glands, ejaculatory ducts, prostate, and bulbourethral glands. - External genitalia within the perineum. - The rectum is found anterior to the coccyx. - Anteriorly is the urinary bladder. - Between the rectum and bladder are the seminal glands superiorly and the prostate inferiorly. - The rectum continues as the anal canal and then opens through the anus. - The male urethra extends from the inferior wall of the bladder, penetrates the prostate and then enters the perineum. - It passes through the penis and opens at the external urethral orifice. - Each seminal gland also has its own canal called the ejaculatory duct. - These ducts also penetrate the prostate where they open into the urethra: so this is where the male reproductive and urinary systems meet. - Testes and epididymides are found in the scrotum. - They are considered to be internal genitalia because of their development in the abdominopelvic cavity. - Ductus deferens is the continuation of the epididymis which joins the ducts of the seminal gland in forming the ejaculatory duct. - Finally, bulbourethral glands are small glands just inferiorly to the prostate, which opens into the penile urethra. ### Male perineum - The urogenital triangle in males contains the perineal muscles and external genitalia. - The contents are presented in the table below. ### Deep perineal pouch: - Perineal part of the urethra - Deep transverse perineal muscle - Inferior part of eternal urethral sphincter - Bulbourethral glands - Dorsal nerves and vessels of the penis ### Superficial perineal pouch: - Root of the penis (corpora cavernosa, corpus spongiosum) - Bulbospongiosus, Ischiocavernosus, Superficial transverse perineal muscl - Muscles mnemonic: Bulb Is Super ### Surface anatomy: - Penis (body and glans) and scrotum ### Blood vessels - There are four main arteries of the pelvis: - Paired internal iliac arteries, which supply the pelvic viscera. - Paired gonadal arteries (testicular and ovarian), which supply the internal genitalia outside of the pelvic cavity (testis, epididymis; ovaries, uterine tubes). - A single median sacral artery that supplies sacrum and coccyx. - A single superior rectal artery that supplies the rectum. - Most significant is the internal iliac artery. - Its branches are grouped into the anterior and posterior divisions. - The true pelvic viscera are supplied by the many branches of the anterior division. - The internal pudendal branch is the main artery of the perineum. - The remainder include the umbilical, obturator, inferior vesical (males), uterine (females), middle rectal and inferior gluteal arteries. - The posterior division of the internal iliac artery supplies the pelvic and gluteal muscles. - Venous blood from the pelvis is drained by the venous plexuses that surround the pelvic organs. - These include the rectal, vesical, prostatic, uterine and vaginal venous plexuses. - Most of them empty into the internal iliac vein, which is a tributary to the inferior vena cava. - Other than the vena cava, some portion of the venous blood flows into the inferior mesenteric vein and then into the hepatic portal system. ### Innervation - There are four major nervous structures found in the pelvis: - Lumbosacral trunk - Sacral plexus - Coccygeal plexus - Autonomic pelvic nerves: these nerves supply the pelvic viscera, muscles of the pelvic floor and perineum, gluteal region and the lower limb. - The lumbosacral trunk is a nerve bundle formed by the anterior rami of L4-L5 lumbar nerves. - It is a root which contributes to the sacral plexus. - The lumbosacral trunk and anterior rami of S1-S4 interconnect to form the sacral plexus. - Whilst the anterior rami of S4, S5 and Co (coccygeal nerve) unite to form the coccygeal plexus. - Concerning the autonomic pelvic nerves, there are sympathetic and parasympathetic inputs. - They are given by the lumbar, sacral and pelvic splanchnic nerves. - Lumbar and sacral splanchnic nerves provide the pelvis with sympathetic innervation, whereas the parasympathetic supply is given by the pelvic splanchnic nerves. - Splanchnic nerves contribute to forming additional pelvic plexuses, such as the inferior hypogastric plexus. - This plexus is the source for all subsequent plexuses that innervate the pelvic viscera: prostatic plexus (males), uterovaginal plexus (females) and middle rectal plexus. ### Lumbar and sacral plexus - Lumbar plexus (Plexus lumbalis): formed by the anterior rami L1-L4 and a contribution from the anterior ramus of T12. - The plexus spreads over the anterior surface of the psoas major muscle. - Forming 6 main branches, it provides innervation for the muscles of the posterior abdominal wall and thigh, as well as for the skin of the scrotum, labiae, inguinum, and thigh. - Sacral plexus is formed by the lumbosacral trunk (L4, L5), anterior rami of S1-S4 and a part of the anterior ramus of S5. - The plexus is found inferiorly to the lumbar plexus, lying on the anterior surface of the piriformis muscle. - Most of its branches supply the gluteal and lower limb muscles. - The perineum is supplied by the pudendal nerve. ### Branches of the lumbosacral plexus are; - iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, obturator, short muscular branches and accessory obturator nerves. - Nerve to quadratus femoris and gemellus inferior, nerve to obturator internus and gemellus superior, nerve to piriformis, superior gluteal, inferior gluteal, posterior femoral cutaneous, sciatic, perforating cutaneous, pudendal, nerves to levator ani and external anal sphincter ### External Female Genitalia - The vulva, also known as the pudendum: a term used to describe those external organs that may be visible in the perineal area. - The vulva consists of the following organs: mons pubis, labia minora and majora, hymen, clitoris, vestibule, urethra, Skene glands, greater vestibular (Bartholin) glands, and vestibular bulbs. - The boundaries include the mons pubis anteriorly, the rectum posteriorly, and the genitocrural folds (thigh folds) laterally. ### Mons pubis - The rounded portion of the vulva where sexual hair development occurs at the time of puberty. - This area may be described as directly anterosuperior to the pubic symphysis. ### Labia - The labia majora are 2 large, longitudinal folds of adipose and fibrous tissue. - They vary in size and distribution from female to female: the size is dependent upon adipose content. - They extend from the mons anteriorly to the perineal body posteriorly. - The labia majora have hair follicles. - The labia minora, also known as nymphae, are 2 small cutaneous folds that are found between the labia majora and the introitus or vaginal vestibule. - Anteriorly, the labia minora join to form the frenulum of the clitoris. ### Hymen - A thin membrane found at the entrance to the vaginal orifice. - Often, this membrane is perforated before the onset of menstruation, allowing flow of menses. - The hymen varies greatly in shape. ### Clitoris - An erectile structure found beneath the anterior joining of the labia minora. - Its width in an adult female is approximately 1 cm, with an average length of 1.5-2.0 cm. - The clitoris is made up of 2 crura, which attach to the periosteum of the ischiopubic rami. - It is a very sensitive structure, analogous to the male penis: it is innervated by the dorsal nerve of the clitoris, a terminal branch of the pudendal nerve. ### Vestibule and urethra - Between the clitoris and the vaginal introitus (opening) is a triangular area known as the vestibule, which extends to the posterior fourchette. - The vestibule is where the urethral (urinary) meatus is found, approximately 1 cm anterior to the vaginal orifice, and it also gives rise to the opening of the Skene glands bilaterally. - The urethra is composed of membranous connective tissue and links the urinary bladder to the vestibule externally. - A female urethra ranges in length from 3.5 to 5.0 cm. ### Skene and Bartholin glands - The Skene glands secrete lubrication at the opening of the urethra. - The greater Vestibular (Bartholin) glands are also responsible for secreting lubrication to the vagina, with openings just outside the hymen, bilaterally, at the posterior aspect of the vagina. - Each gland is small: similar in shape to a kidney bean. ### Vestibular bulbs - 2 masses of erectile tissue that lie deep to the bulbocavernosus muscles bilaterally. ### Internal Genitalia - Vagina - Extends from the vulva externally to the uterine cervix internally. - Located within the pelvis, anterior to the rectum and posterior to the urinary bladder. - The vagina lies at a 90° angle in relation to the uterus. - The vagina is held in place by endopelvic fascia and ligaments: the vagina is lined by rugae, which gives the fold-like appearance throughout the vagina. - These folds allow easy distention, especially during child bearing. - The structure of the vagina is a network of connective, membranous, and erectile tissues. - The pelvic diaphragm, the sphincter urethrae and transverse peroneus muscles, and the perineal membrane support the vagina. - The sphincter urethrae and the transverse peroneus are innervated by perineal branches of the pudendal nerve. - The vascular supply to the vagina is primarily from the vaginal artery: a branch of the anterior division of the internal iliac artery. - Several of these arteries may be found on either side of the pelvis to richly supply the vagina. - The nerve supply to the vagina is primarily from the autonomic nervous system. - Sensory fibers to the lower vagina arise from the pudendal nerve, and pain fibers are from sacral nerve roots. - Lymphatic drainage of the vagina is generally to the external iliac nodes (upper third of the vagina), the common and internal iliac nodes (middle third), and the superficial inguinal nodes (lower third). ### Uterus - The inverted pear-shaped female reproductive organ that lies in the midline of the body, within the pelvis between the bladder and the rectum. - It is thick-walled and muscular: with a lining (endometrium) that, during reproductive years, changes in response to ovarian hormone stimulation throughout a woman's monthly cycle. - The uterus can be divided into 2 parts: - The most inferior aspect is the cervix, and the bulk of the organ is called the body of the uterus (corpus uteri). - Between these 2 is the isthmus: a short area of constriction. - The body of the uterus is globe-shaped and is typically situated in an anteverted position, at a 90° angle to the vagina. - The upper aspect of the body is dome-shaped and is called the fundus: it is typically the most muscular part of the uterus. - The body of the uterus is responsible for holding a pregnancy: strong uterine wall contractions help to expel the fetus during labor and delivery. - The average weight of a nonpregnant, nulliparous uterus is approximately 40-50 g. - A multiparous uterus may weigh slightly more than this, with an upper limit of approximately 110 g: a menopausal uterus is small and atrophied and typically weighs much less. - The cavity of the uterus is flattened and triangular: the uterine tubes enter the uterine cavity bilaterally in the superolateral portion of the cavity at the cornua. ### The uterus consist of 3 different layers; - Endometrium: is the innermost lining. - Myometrium: the smooth muscle layer. - Perimentrium: the outer layer/covering made up of connective tissue. - The uterus is connected to its surrounding structures by a series of ligaments and connective tissue. - The pelvic peritoneum is attached to the body and the cervix as the broad ligament, reflecting onto the bladder. - The broad ligament attaches the uterus to the lateral pelvic side walls. - Within the broad base of the broad ligament, between its anterior and posterior laminae, connective tissue strands associated with the uterine and vaginal vessels help to support the uterus and vagina. - These strands are referred to as the cardinal ligament. - Rectouterine ligaments, lying within peritoneal folds, stretch posteriorly from the cervix to reach the sacrum. - The round ligaments of the uterus are much denser structures and connect the uterus to the anterolateral abdominal wall at the deep inguinal ring. - They lie within the anterior lamina of the broad ligament. - Within the round ligament is the artery of Sampson: a small artery that must be ligated during hysterectomy. ### The vasculature of the uterus is derived from the uterine arteries and veins. - The uterine vessels arise from the anterior division of the internal iliac, and branches of the uterine artery anastomose with the ovarian artery along the uterine tube. - The nerve supply and lymphatic drainage of the uterus are complex. - Lymphatic drainage is primarily to the lateral aortic, pelvic, and iliac nodes that surround the iliac vessels. - The nerve supply is by the sympathetic nervous system (via the hypogastric and ovarian plexuses) and the parasympathetic nervous system (via the pelvic splanchnic nerves from the second through fourth sacral nerves). ### Cervix - The inferior portion of the uterus: separating the body of the uterus from the vagina. - Cylindrical in shape, with an endocervical canal located in the midline, allowing passage of semen into the uterus. - The external opening into the vagina is termed the external os, and the internal opening into the endometrial cavity is termed the internal os: the internal os is the portion of a female cervix that dilates to allow delivery of the fetus during labor. - The average length of the cervix is 3-5 cm. - The vasculature is supplied by descending branches of the uterine artery, which run bilaterally at the 3 o'clock and 9 o'clock position of the cervix. - The nerve supply to the cervix is via the parasympathetic nervous system through S2 -S4 sacral segments. - Many pain nerve fibers run alongside these parasympathetics. - Lymphatic drainage of the cervix is complex: the obturator, common iliac, internal iliac, external iliac, and visceral parametrial nodes are the main drainage points. ### Uterine tubes - Also referred to as oviducts or fallopian tubes: are uterine appendages located bilaterally at the superior portion of the cavity (cornua). - Their primary function is to transport sperm toward the egg, which is released by the ovary, and then to allow passage of the fertilized egg back to the uterus for implantation. - The uterine tubes exit the uterus through an area known as the cornua and form a connection between the endometrial and peritoneal cavities. - Each tube is approximately 10 cm in length and 1 cm in diameter and is situated within a portion of the broad ligament called the mesosalpinx: the distal portion of the uterine tube ends in an orientation encircling the ovary. ### The uterine tube consist of the following parts: - The first segment: closest to the uterus is the intramural part. - This enters the cornua of the uterus. - This is followed by the isthmus (constricted portion and is notorious for ectopic pregnancies). - This is followed by the ampulla, which becomes more dilated in diameter and is the typical place of fertilization. - The infundibulum (funnel shaped) extend from the ampulla. - From the infundibulum arise fingerlike projections called the fimbriae, which are responsible for catching the egg that is released by the ovary. ### The arterial supply to the uterine tubes is from branches of the uterine and ovarian arteries, small vessels that are located within the mesosalpinx: - The nerve supply to the uterine tubes is via both sympathetic and parasympathetic fibers. - Sensory fibers run from thoracic segments 11-12 and lumbar segment 1: lymphatic drainage of the uterine tubes is through the iliac and aortic nodes. ### Ovaries - Paired organs located on either side of the uterus within the mesovarium portion of the broad ligament below the uterine tubes. - The ovaries are responsible for housing and releasing the ova, or eggs, necessary for reproduction. - At birth, a female has approximately 1-2 million eggs, but only 300 of these eggs ever mature and are released for the purpose of fertilization. - The ovaries are small and oval-shaped: exhibit a grayish color, and have an uneven surface. - The actual size of an ovary depends on a woman's age and hormonal status: the ovaries are approximately 3-5 cm in length during childbearing years and become much smaller and atrophic once menopause occurs. - A cross-section of the ovary reveals many cystic structures that vary in size: these structures represent ovarian follicles at different stages of development and degeneration. ### Several ligaments support the ovary. - The ovarian ligament connects the uterus and ovary: the posterior portion of the broad ligament forms the mesovarium, which supports the ovary and houses the vascular supply. - The suspensory ligament of the ovary (infundibular pelvic ligament), a peritoneal fold overlying the ovarian vessels, attaches the ovary to the pelvic side wall. - Blood supply to the ovary is via the ovarian artery: both right and left ovarian arteries originate directly from the descending aorta at the level of the L2 vertebra. - The ovarian artery and vein enter and exit the ovary at the hilum. - The left ovarian vein drains into the left renal vein, and the right ovarian vein empties directly into the inferior vena cava. - Nerve supply to the ovaries run with the vasculature within the suspensory ligament of the ovary, entering the ovary at the hilum: supply is through the ovarian, hypogastric, and aortic plexuses. - Lymphatic