The pelvic cavity is a basin-shaped region below and behind the pelvic inlet (Fig. 5.1). It is surrounded by the bones of the pelvic girdle supplemented by muscles, ligaments and fascia. The anterior wall, near the pubic symphysis, is shallow while the posterior wall, the sacrum, is deep and concave. Each lateral wall is lined by the obturator internus, a broad muscle covered on its medial surface by fascia. Above this muscle are two apertures providing access for nerves and vessels entering the lower limb. The greater sciatic foramen leads into the gluteal region, the obturator canal into the thigh.
Monday, October 19, 2020
Each ureter enters the pelvis by crossing in front of the common iliac vessels or the commencement of the external iliac vessels (Fig. 5.14). The ureter passes downwards and backwards before curving forwards to reach the posterior surface of the bladder. The ureter crosses the medial aspect of the obturator nerve and vessels and the superior vesical vessels before running forwards along the levatorani muscle. The pelvic peritoneum covers the medial aspect of the ureter and separates it from the rectum, sigmoid colon or coils of ileum.
Pelvic Cavity Anatomy and Physiology
Although the pelvic cavity is in direct continuity with the abdominal cavity, the two regions are delineated by the pelvic inlet (pelvic brim). This lies at approximately 45° to the horizontal and comprises the sacral promontory posteriorly, the arcuate and pectineal lines laterally and the pubic crests and upper border of pubic symphysis anteriorly (Figs 5.1 & 5.26).
Gender is determined by the presence of X and Y chromosomes in the genome. Two X chromosomes provide the female genotype, whereas X and Y chromosomes together give a genetic male. Undifferentiated gonads are apparent after about 4–6 weeks of gestation, and both Müllerian ducts, which eventually form the uterus and Fallopian tubes, and Wolffian ducts, which form the vas deferens, epididymis and seminal vesicles, are present. The early gonads secrete steroids just as they do in the adult, and these hormones determine the sexual phenotype. In the absence of the Sry gene on the Y chromosome and thus testosterone, the Müllerian ducts continue to differentiate whilst the Wolffian ducts regress. The development of reproductive organs and brain connectivity therefore defaults to a female pattern which is dependent on the secretion of oestrogens.
Monday, May 4, 2020
Female External Genitalia Anatomy
The perineal membrane is thinner in the female than in the male and is pierced by both the vagina and the urethra. Attached to the inferior surface of the membrane is erectile tissue similar to that in the male, namely the crura of the clitoris and the bulbs of the vestibule covered by the thin ischiocavernosus and bulbospongiosus muscles, respectively (Figs 5.40 & 5.41). The right and left crura attach to the medial margins of the ischial and pubic rami. Passing forwards and medially they merge beneath the pubic symphysis to form the shaft of the clitoris. This turns downwards and backwards towards the urethral opening, and its tip is capped by the glans of the clitoris.
Male External Genitalia Anatomy
The male external genitalia comprise the scrotum and the penis. An account of the scrotum and its contents is given on pp 149–151. The penis consists of a shaft, which is free, and a root, which lies in the superficial perineal pouch, attached to the inferior surface of the perineal membrane.
Below the pelvic floor lies the perineum, a superficial region traversed by the anal canal and the lower parts of the genital and urinary tracts. The perineum is diamond-shaped, extending anteriorly to the pubic symphysis, posteriorly to the coccyx and laterally to the ischial tuberosities (Figs 5.34 & 5.3). On each side, the region is bounded by the conjoined rami of the ischium and pubis and by the sacrotuberous ligament, which is overlapped by the inferior border of gluteus maximus. Inferiorly, the perineum is bounded by skin. By convention, the perineum is divided into two triangular areas by a line joining the ischial tuberosities. Posteriorly is the anal triangle, containing the anal canal and the ischioanal (ischiorectal) fossae, and anteriorly lies the urogenital triangle, containing the external genitalia.
Pelvic Blood Vessels and Lymphatics Anatomy
The pelvic walls and floor and the pelvic organs receive most of their arterial supply from branches of the internal iliac artery, which also provides branches to the perineum and lower limb. The rectum, however, receives its principal supply from the superior rectal artery (pp 182, 218 & 238), while the posterior wall of the pelvis is supplied by the median sacral artery (Fig. 5.31). The ovaries are supplied by the ovarian branches of the abdominal aorta (p. 190).
Pelvic Nerves Anatomy
The pelvic organs receive their autonomic innervation via the right and left pelvic plexuses, which lie adjacent to the internal iliac arteries and their branches (Fig. 5.30). Nerves pass from the plexuses to the bladder, reproductive organs and the rectum by accompanying the arteries to these organs. The plexuses and their branches contain efferent fibres from both the parasympathetic and sympathetic systems, which reach the pelvis from different parts of the spinal cord.
Pelvic Wall and Floor Anatomy
The pelvic wall is formed by the bones of the pelvic girdle and their associated ligaments, muscles and fascia. The bony component comprises the right and left hip bones anterolaterally and the sacrum and coccyx posteriorly. The pelvic cavity is usually wider and shallower in females because of the differences in the shapes of the surrounding bones.
Male Internal Organs of Reproduction Anatomy
The organs of reproduction in the male comprise the paired testes, epididymides, ductus (vasa) deferentia, seminal vesicles, ejaculatory ducts and bulbourethral glands, as well as the prostate and penis. The superficial organs (the external genitalia) include the penis (p. 245) and the testes and epididymides within the scrotum (pp 149–151).
Saturday, May 2, 2020
Male Urethra Anatomy
The male urethra is a fibromuscular tube approximately 20 cm long. Beginning at the internal urethral meatus of the bladder, it descends through the prostate and the pelvic floor and enters the bulb of the penis (Fig. 5.19). It then traverses the corpus spongiosum and glans of the penis and terminates at the external urethral meatus. In the male the urethra not only drains urine from the bladder but also receives secretions from the prostatic ducts, the ejaculatory ducts and the ducts of the bulbourethral glands.
Female Urethra Anatomy
The female urethra is a fibromuscular tube 3–4 cm long and begins at the internal urethral meatus of the bladder. Embedded in the anterior wall of the vagina, it inclines downwards and forwards through the pelvic floor (Fig. 5.18) and terminates in the vestibule at the external meatus between the clitoris and the vaginal opening.
The urinary bladder lies in the anterior part of the pelvic cavity. When distended, the organ has an approximately spherical shape, but when empty, it assumes the form of a tetrahedron with four angles and four surfaces. The two posterolateral angles receive the ureters while the inferior angle, the bladder neck, is continuous with the urethra. The anterior angle gives attachment to a fibrous cord, the median umbilical ligament (Fig. 5.17). This remnant of the fetalallantois ascends in the extraperitoneal tissues of the anterior abdominal wall to the umbilicus. If it remains patent, urine may leak from the umbilicus.
Thursday, February 13, 2020
Pelvic Ureters Anatomy
Each ureter enters the pelvis by crossing in front of the common iliac vessels or the commencement of the external iliac vessels (Fig. 5.14). The ureter passes downwards and backwards before curving forwards to reach the posterior surface of the bladder. The ureter crosses the medial aspect of the obturator nerve and vessels and the superior vesical vessels before running forwards along the levator ani muscle. The pelvic peritoneum covers the medial aspect of the ureter and separates it from the rectum, sigmoid colon or coils of ileum.
Thursday, November 21, 2019
The rectum is the distal portion of the large intestine and lies in the posterior part of the pelvic cavity. It is continuous with the sigmoid colon at the rectosigmoid junction in front of the third piece of the sacrum (Fig. 5.7), where there is often an acute angulation. The rectum curves downwards and forwards, lying first on the anterior surface of the sacrum and then on the upper surface of the pelvic floor. It deviates to either side of the midline and these lateral flexures become pronounced when the organ is distended. The lowest part of the rectum, the ampulla, is its most dilatable portion. Turning abruptly downwards and backwards, the rectum pierces the pelvic floor and terminates at the anorectal junction, where it is continuous with the anal canal (Fig. 5.5). The sharp angulations at the anorectal and rectosigmoid junctions must be navigated with care during endoscopy.
Sunday, November 17, 2019
Female Pelvis: Cross Section of Vagina and Urethra Anatomy
Urethra, Vagina, Rectum, Vaginal venous plexus, Lymph node, Greater saphenous and femoral veins, Femoral artery, Femoral nerve, Deep femoral artery, Gluteus medius muscle, Sciatic nerve, Ischium, Internal pudendal vessels and pudendal nerve,
Wednesday, November 13, 2019
Nerves of Pelvic Viscera: Male Anatomy
Anterior vagal trunk, Posterior vagal trunk and, Celiac branch, Inferior phrenic arteries and plexuses, Left gastric artery and gastric plexus, Celiac ganglia, plexus, and trunk, Left aorticorenal ganglion, Superior mesenteric ganglion, Superior mesenteric artery and plexus, Intermesenteric (abdominal aortic) plexus, Inferior mesenteric ganglion, artery, and plexus, Ureter and ureteric plexus, Superior hypogastric plexus, Superior rectal artery and plexus,