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Urogenital System
General organization
Parts of the urinary and reproductive (genital) systems are closely related developmentally, so the two systems are often discussed together. The urinary system consists of the kidneys, ureters, bladder, and urethra. In women, major parts of the reproductive (genital) system are the ovaries, uterus, vagina, external genitalia, and breasts. In men, the reproductive system consists of the testes, epididymides, vas deferens, seminal vesicles, prostate, and external genitalia. In men, the reproductive ducts join the urethra in the pelvis so that the urethra transports both urine and semen.
Non-Binary Terminology
Trans/Non-Binary Anatomical Terminology
While anatomy is typically discussed in the gender-binary classification of female and male, many individuals do not fit into these models. These individuals include intersex, non-binary and transgender people. In some areas of this text, relevant anatomical/clinical distinctions are made between “ciswomen and cismen” and “transwomen and transmen.” “Cis” refers to individuals whose gender identity aligns with their assigned sex at birth, while “trans” refers to individuals whose gender identity does not align with their assigned sex at birth. “Non-binary” refers to an individual whose gender identity does not fit the binary model. Many trans or non-binary individuals receive a spectrum of gender-affirming care including hormones and surgery to meet their goals for gender transition that will alter their anatomy. The anatomical terminology in this chapter will reflect this (e.g., “In transwomen post-vaginoplasty). These differences are clinically relevant and vary from cisgender individuals.
Clinically, the anatomical terminology preferred by the patient should be used, which may include non-binary terms for classically gendered anatomy. In general, it is appropriate to use gender-inclusive anatomical language when engaging with nonbinary/transgender patients. Some common examples are as follows:
| Preferred Term | Instead of |
|---|---|
| Upper body | Chest/Breast |
| Erectile tissue | Penis/Clitoris |
| Gonads | Testes/Ovaries |
Clinicians should not assume based on an individual’s gender presentation which anatomical features are present. Acquiring a history of the patient’s relevant anatomy (organ inventory) should be considered, including the patient’s preferred terminology, to guide appropriate and sensitive care. Clinicians should base their clinical care on the present anatomy to diagnose, screen, and treat appropriately.
Throughout this chapter, many anatomical features are described using a gender-binary model (women and men). Anatomy has classically been taught in this way, which for the time being, has some advantages in its use. First, it is important to understand that these gendered terms are conceptual models that help us approximate the real world in order to more easily understand it, but they do not adequately describe all forms of variation. This includes biological variation in the anatomy that can be seen in intersex individuals or variations seen in persons receiving various degrees of gender-affirming care. Second, these terms continue to be used heavily in the literature, and so their use here helps maintain a degree of congruence with the preexisting information. The use of these terms is not intended to exclude individuals who do not fit gender-binary models. As we continue to develop our anatomical models, these terms may diminish in their use and be replaced by non-binary terminology such as “individuals with a prostate” or “individuals with a uterus.” Whenever possible, it is best practice both scientifically and clinically to discuss the anatomy present without assumptions based on gender presentation.
Intersex Individuals
Natural diversity in chromosomal arrangement, the presence or absence of specific genes, or other chance developmental events can lead to normal variations from the female-male sex binary. These individuals are called “intersex.” This most often means that one or more of a person’s chromosomal, genetic, hormonal, gonadal, or external genitalia do not fit into a binary model of female-male. At the level of the gonads, this could mean, for example, an individual having testes accompanied with moderate variations to the anatomy of the external genitalia (e.g., location of the urethral opening) or even more pronounced variations such as the presence of testes and a penis accompanied by a uterus and fallopian tubes. In some cases, an individual may have the presence of both a testis and ovary, or have one or more gonads that exists on a spectrum between these two organs (i.e., ovotestes).
The urinary system
Kidneys
The bean-shaped kidneys are retroperitoneal in the posterior abdominal region ( Fig. 4.1 ). They lie in the extraperitoneal connective tissue immediately lateral to the vertebral column. In the supine position, the kidneys extend from approximately vertebra TXII superiorly to vertebra LIII inferiorly, with the right kidney somewhat lower than the left because of its relationship with the liver. Although they are similar in size and shape, the left kidney is a longer and more slender organ than the right kidney, and nearer to the midline.
Relationships to other structures
The anterior surface of the right kidney is related to numerous structures, some of which are separated from the kidney by a layer of peritoneum and some of which are directly against the kidney ( Fig. 4.2 ):
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A small part of the superior pole is covered by the right suprarenal gland.
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Moving inferiorly, a large part of the rest of the upper part of the anterior surface is against the liver and is separated from it by a layer of peritoneum.
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Medially, the descending part of the duodenum is retroperitoneal and contacts the kidney.
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The inferior pole of the kidney, on its lateral side, is directly associated with the right colic flexure and, on its medial side, is covered by a segment of the intraperitoneal small intestine.
The anterior surface of the left kidney is also related to numerous structures, some with an intervening layer of peritoneum and some directly against the kidney ( Fig. 4.2 ):
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A small part of the superior pole, on its medial side, is covered by the left suprarenal gland.
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The rest of the superior pole is covered by the intraperitoneal stomach and spleen.
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Moving inferiorly, the retroperitoneal pancreas covers the middle part of the kidney.
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On its lateral side, the lower half of the kidney is covered by the left colic flexure and the beginning of the descending colon, and, on its medial side, by the parts of the intraperitoneal jejunum.
Posteriorly, the right and left kidneys are related to similar structures ( Fig. 4.3 ). Superiorly is the diaphragm and inferior to this, moving in a medial to lateral direction, are the psoas major, quadratus lumborum, and transversus abdominis muscles.
The superior pole of the right kidney is anterior to rib XII, while the same region of the left kidney is anterior to ribs XI and XII. The pleural sacs and specifically, the costodiaphragmatic recesses therefore extend posterior to the kidneys.
Also passing posterior to the kidneys are the subcostal vessels and nerves and the iliohypogastric and ilio-inguinal nerves.
Renal fat and fascia
The kidneys are enclosed in and associated with a unique arrangement of fascia and fat. Immediately outside the renal capsule, there is an accumulation of extraperitoneal fat—the perinephric fat (perirenal fat), which completely surrounds the kidney ( Fig. 4.4 ). Enclosing the perinephric fat is a membranous condensation of the extraperitoneal fascia (the renal fascia). The suprarenal glands are also enclosed in this fascial compartment, usually separated from the kidneys by a thin septum. The renal fascia must be incised in any surgical approach to this organ.
At the lateral margins of each kidney, the anterior and posterior layers of the renal fascia fuse ( Fig. 4.4 ). This fused layer may connect with the transversalis fascia on the lateral abdominal wall.
Above each suprarenal gland, the anterior and posterior layers of the renal fascia fuse and blend with the fascia that covers the diaphragm.
Medially, the anterior layer of the renal fascia continues over the vessels in the hilum and fuses with the connective tissue associated with the abdominal aorta and the inferior vena cava ( Fig. 4.4 ). In some cases, the anterior layer may . cross the midline to the opposite side and blend with its companion layer.
The posterior layer of the renal fascia passes medially between the kidney and the fascia covering the quadratus lumborum muscle to fuse with the fascia covering the psoas major muscle.
Inferiorly, the anterior and posterior layers of the renal fascia enclose the ureters.
In addition to perinephric fat and the renal fascia, a final layer of paranephric fat (pararenal fat) completes the fat and fascias associated with the kidney ( Fig. 4.4 ). This fat accumulates posterior and posterolateral to each kidney.
Kidney structure
Each kidney has a smooth anterior and posterior surface covered by a fibrous capsule, which is easily removable except during disease.
On the medial margin of each kidney is the hilum of the kidney, which is a deep vertical slit through which renal vessels, lymphatics, and nerves enter and leave the substance of the kidney ( Fig. 4.5 ). Internally, the hilum is continuous with the renal sinus. Perinephric fat continues into the hilum and sinus and surrounds all structures.
Each kidney consists of an outer renal cortex and an inner renal medulla. The renal cortex is a continuous band of pale tissue that completely surrounds the renal medulla. Extensions of the renal cortex (the renal columns) project into the inner aspect of the kidney, dividing the renal medulla into discontinuous aggregations of triangular-shaped tissue (the renal pyramids).
The bases of the renal pyramids are directed outward, toward the renal cortex, while the apex of each renal pyramid projects inward, toward the renal sinus. The apical projection (renal papilla) is surrounded by a minor calyx.
The minor calices receive urine and represent the proximal parts of the tube that will eventually form the ureter ( Fig. 4.5 ). In the renal sinus, several minor calices unite to form a major calyx, and two or three major calices unite to form the renal pelvis, which is the funnel-shaped superior end of the ureters.
Renal vasculature and lymphatics
A single large renal artery, a lateral branch of the abdominal aorta, supplies each kidney. These vessels usually arise just inferior to the origin of the superior mesenteric artery between vertebrae LI and LII ( Fig. 4.6 ). The left renal artery usually arises a little higher than the right, and the right renal artery is longer and passes posterior to the inferior vena cava.
As each renal artery approaches the renal hilum, it divides into anterior and posterior branches, which supply the renal parenchyma. Accessory renal arteries are common. They originate from the lateral aspect of the abdominal aorta, either above or below the primary renal arteries, enter the hilum with the primary arteries or pass directly into the kidney at some other level, and are commonly called extrahilar arteries.
Multiple renal veins contribute to the formation of the left and right renal veins, both of which are anterior to the renal arteries ( Fig. 4.6 ). Importantly, the longer left renal vein crosses the midline anterior to the abdominal aorta and posterior to the superior mesenteric artery and can be compressed by an aneurysm in either of these two vessels.
The lymphatic drainage of each kidney is to the lateral aortic (lumbar) nodes around the origin of the renal artery.
Ureters
The ureters are muscular tubes that transport urine from the kidneys to the bladder. They are continuous superiorly with the renal pelvis, which is a funnel-shaped structure in the renal sinus. The renal pelvis is formed from a condensation of two or three major calices, which in turn are formed by the condensation of several minor calices (see Fig. 4.5 ). The minor calices surround a renal papilla.
The renal pelvis narrows as it passes inferiorly through the hilum of the kidney and becomes continuous with the ureter at the ureteropelvic junction ( Fig. 4.7 ). Inferior to this junction, the ureters descend retroperitoneally on the medial aspect of the psoas major muscle. At the pelvic brim, the ureters cross either the end of the common iliac artery or the beginning of the external iliac artery, enter the pelvic cavity, and continue their journey to the bladder.
At three points along their course the ureters are constricted ( Fig. 4.7 ):
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The first point is at the ureteropelvic junction.
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The second point is where the ureters cross the common iliac vessels at the pelvic brim.
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The third point is where the ureters enter the wall of the bladder.
Kidney stones can become lodged at these constrictions.
Ureteric vasculature and lymphatics
The ureters receive arterial branches from adjacent vessels as they pass toward the bladder ( Fig. 4.7 ):
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The renal arteries supply the upper end.
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The middle part may receive branches from the abdominal aorta, the testicular or ovarian arteries, and the common iliac arteries.
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In the pelvic cavity, the ureters are supplied by one or more arteries from branches of the internal iliac arteries.
In all cases, arteries reaching the ureters divide into ascending and descending branches, which form longitudinal anastomoses.
Lymphatic drainage of the ureters follows a pattern similar to that of the arterial supply. Lymph comes from:
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the upper part of each ureter drains to the lateral aortic (lumbar) nodes,
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the middle part of each ureter drains to lymph nodes associated with the common iliac vessels, and
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the inferior part of each ureter drains to lymph nodes associated with the external and internal iliac vessels.
Ureteric innervation
Ureteric innervation is from the renal, aortic, superior hypogastric, and inferior hypogastric plexuses through nerves that follow the blood vessels.
Visceral efferent fibers come from both sympathetic and parasympathetic sources, whereas visceral afferent fibers return to T11 to L2 spinal cord levels. Ureteric pain, which is usually related to distention of the ureter, is therefore referred to cutaneous areas supplied by T11 to L2 spinal cord levels. These areas would most likely include the posterior and lateral abdominal wall below the ribs and above the iliac crest, the pubic region, the scrotum in males, the labia majora in females, and the proximal anterior aspect of the thigh.
The ureters enter the pelvic cavity from the abdomen by passing through the pelvic inlet. On each side, the ureter crosses the pelvic inlet and enters the pelvic cavity in the area anterior to the bifurcation of the common iliac artery. From this point, it continues along the pelvic wall and floor to join the base of the bladder.
In the pelvis, the ureter is crossed by:
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the ductus deferens in men, and
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the uterine artery in women.
Bladder
The bladder is the most anterior element of the pelvic viscera. Although it is entirely situated in the pelvic cavity when empty, it expands superiorly into the abdominal cavity when full ( Fig. 4.8 ).
The empty bladder is shaped like a three-sided pyramid that has tipped over to lie on one of its margins ( Fig. 4.9A ). It has an apex, a base, a superior surface, and two inferolateral surfaces.
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The apex of the bladder is directed toward the top of the pubic symphysis; a structure known as the median umbilical ligament (a remnant of the embryological urachus that contributes to the formation of the bladder) continues from it superiorly up the anterior abdominal wall to the umbilicus.
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The base of the bladder is shaped like an inverted triangle and faces posteroinferiorly. The two ureters enter the bladder at each of the upper corners of the base, and the urethra drains inferiorly from the lower corner of the base. Inside, the mucosal lining on the base of the bladder is smooth and firmly attached to the underlying smooth muscle coat of the wall—unlike elsewhere in the bladder where the mucosa is folded and loosely attached to the wall. The smooth triangular area between the openings of the ureters and urethra on the inside of the bladder is known as the trigone ( Fig. 4.9B ).
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The inferolateral surfaces of the bladder are cradled between the levator ani muscles of the pelvic diaphragm and the adjacent obturator internus muscles above the attachment of the pelvic diaphragm. The superior surface is slightly domed when the bladder is empty; it balloons upward as the bladder fills.
Neck of bladder
The neck of the bladder surrounds the origin of the urethra at the point where the two inferolateral surfaces and the base intersect.
The neck is the most inferior part of the bladder and also the most “fixed” part. It is anchored into position by a pair of tough fibromuscular bands, which connect the neck and pelvic part of the urethra to the posteroinferior aspect of each pubic bone.
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In women, these fibromuscular bands are termed pubovesical ligaments ( Fig. 4.10A ). Together with the perineal membrane and associated muscles, the levator ani muscles, and the pubic bones, these ligaments help support the bladder.
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In men, the paired fibromuscular bands are known as puboprostatic ligaments because they blend with the fibrous capsule of the prostate, which surrounds the neck of the bladder and adjacent part of the urethra ( Fig. 4.10B ).
Although the bladder is considered to be pelvic in the adult, it has a higher position in children. At birth, the bladder is almost entirely abdominal; the urethra begins approximately at the upper margin of the pubic symphysis. With age, the bladder descends until after puberty when it assumes the adult position.
Urethra
The urethra begins at the base of the bladder and ends with an external opening in the perineum. The paths taken by the urethra differ significantly in women and men.
In women
In women, the urethra is short, being about 4 cm long. It travels a slightly curved course as it passes inferiorly through the pelvic floor into the perineum, where it passes through the deep perineal pouch and perineal membrane before opening in the vestibule that lies between the labia minora ( Fig. 4.11A ).
The urethral opening is anterior to the vaginal opening in the vestibule. The inferior aspect of the urethra is bound to the anterior surface of the vagina. Two small para-urethral mucous glands (Skene’s glands) are associated with the lower end of the urethra. Each drains via a duct that opens onto the lateral margin of the external urethral orifice.
In men
In men, the urethra is long, about 20 cm, and bends twice along its course ( Fig. 4.11B ). Beginning at the base of the bladder and passing inferiorly through the prostate, it passes through the deep perineal pouch and perineal membrane and immediately enters the root of the penis. As the urethra exits the deep perineal pouch, it bends forward to course anteriorly in the root of the penis. When the penis is flaccid, the urethra makes another bend, this time inferiorly, when passing from the root to the body of the penis. During erection, the bend between the root and body of the penis disappears.
The urethra in men is divided into preprostatic, prostatic, membranous, and spongy parts.
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