Urinary Tract: Anatomy

Embryology

Kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy and ureters

Kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy go through 3 embryologic stages:

• Pronephros Pronephros The primordial kidney that develops from the intermediate mesoderm in the embryos of vertebrates, and is succeeded by the mesonephros. In higher vertebrates and humans, the pronephros is a vestigial and transient structure. Development of the Urogenital System:
  • A functionless, segmented structure made out of a duct from which a series of tubules branch off toward the midline (1 on each side)
  • Regresses and disappears on or right after the 4th week
• Mesonephros Mesonephros One of a pair of excretory organs (mesonephroi) which grows caudally to the first pair (pronephroi) during development. Mesonephroi are the permanent kidneys in adult amphibians and fish. In higher vertebrates, proneprhoi and most of mesonephroi degenerate with the appearance of metanephroi. The remaining ducts become wolffian ducts. Development of the Urogenital System:
  • Mesonephric tissue forms by the 4th week and is connected to the pronephric duct through the mesonephric duct Mesonephric duct A pair of excretory ducts of the middle kidneys of an embryo, also called mesonephric ducts. In higher vertebrates, wolffian ducts persist in the male forming vas deferens, but atrophy into vestigial structures in the female. Kidneys: Anatomy.
  • The mesonephric (wolffian) duct connects to the cloaca Cloaca A dilated cavity extended caudally from the hindgut. In adult birds, reptiles, amphibians, and many fishes but few mammals, cloaca is a common chamber into which the digestive, urinary and reproductive tracts discharge their contents. In most mammals, cloaca gives rise to large intestine; urinary bladder; and genitalia. Development of the Abdominal Organs, and the ureteric bud grows from the duct.
• Metanephros Metanephros Development of the Urogenital System:
  • The ureteric bud meets the metanephric blastema Metanephric blastema Wilms Tumor, forming the metanephros Metanephros Development of the Urogenital System.
  • Development from the ureteric bud: ureter, renal pelvis Renal pelvis Kidneys: Anatomy, 5 major calyces Major calyces Recesses of the kidney pelvis which divides into two wide, cup-shaped major renal calices, with each major calyx subdivided into 7 to 14 minor calices. Urine empties into a minor calyx from collecting tubules, then passes through the major calyx, renal pelvis, and ureter to enter the urinary bladder. Kidneys: Anatomy, minor calyces Minor calyces Recesses of the kidney pelvis which divides into two wide, cup-shaped major renal calices, with each major calyx subdivided into 7 to 14 minor calices. Urine empties into a minor calyx from collecting tubules, then passes through the major calyx, renal pelvis, and ureter to enter the urinary bladder. Kidneys: Anatomy, collecting ducts
  • Development from the metanephric blastema Metanephric blastema Wilms Tumor: Bowman capsule Bowman Capsule A double-walled epithelial capsule that is the bulbous closed proximal end of the kidney tubular system. It surrounds the cluster of convoluted capillaries of kidney glomerulus and is continuous with the convoluted proximal kidney tubule. Kidneys: Anatomy, proximal and distal tubules, loop of Henle Loop of Henle The U-shaped portion of the renal tubule in the kidney medulla, consisting of a descending limb and an ascending limb. It is situated between the proximal kidney tubule and the distal kidney tubule. Tubular System
  • The kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy ascend, accompanied by the elongation Elongation Polymerase Chain Reaction (PCR) of the ureters.

Bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess and urethra

• When the mesonephric duct Mesonephric duct A pair of excretory ducts of the middle kidneys of an embryo, also called mesonephric ducts. In higher vertebrates, wolffian ducts persist in the male forming vas deferens, but atrophy into vestigial structures in the female. Kidneys: Anatomy fuses with the cloaca Cloaca A dilated cavity extended caudally from the hindgut. In adult birds, reptiles, amphibians, and many fishes but few mammals, cloaca is a common chamber into which the digestive, urinary and reproductive tracts discharge their contents. In most mammals, cloaca gives rise to large intestine; urinary bladder; and genitalia. Development of the Abdominal Organs, a portion of the duct becomes a part of the posterior bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess.
• During gestational week 7, the cloaca Cloaca A dilated cavity extended caudally from the hindgut. In adult birds, reptiles, amphibians, and many fishes but few mammals, cloaca is a common chamber into which the digestive, urinary and reproductive tracts discharge their contents. In most mammals, cloaca gives rise to large intestine; urinary bladder; and genitalia. Development of the Abdominal Organs is divided by the urogenital membrane/septum into ventral ( urogenital sinus Urogenital Sinus Congenital Malformations of the Female Reproductive System) and dorsal ( rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy) components.
• The urogenital sinus Urogenital Sinus Congenital Malformations of the Female Reproductive System gives rise to the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess (cranially) and the urethra (caudally).

Ureters

Anatomy

Description: 

• Collapsible, muscular S-shaped tubes
• Approximately 25 cm in length
• Start: ureteropelvic junction
  • At the level of the second lumbar vertebra on the left
  • Right slightly lower
• End: ureterovesicular junction

Function: 

The function of the ureters is to transport urine from the renal pelvis Renal pelvis Kidneys: Anatomy to the urinary bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess.

Route of ureters:

• Leave the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy posterior to the renal artery Renal artery A branch of the abdominal aorta which supplies the kidneys, adrenal glands and ureters. Glomerular Filtration and vein
• Descend anterior to the psoas major Psoas major Posterior Abdominal Wall: Anatomy muscle, where gonadal vessels cross anteriorly. 
• The right ureter travels behind the duodenum Duodenum The shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. It is named for having the length equal to about the width of 12 fingers. Small Intestine: Anatomy.
• The left ureter travels lateral to the inferior mesenteric vessels.
• Ureters then enter the pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy, crossing the iliac vessels (usually at the common iliac artery bifurcation into the internal and external iliac arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology).
• Ureters go into the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess on the posterior aspect in the trigone.

3 sites of narrowing:

• Ureteropelvic junction 
• Crossover of the common iliac arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
• Ureterovesicular junction

Vasculature and lymphatic drainage:

• Upper or abdominal ureter arterial blood supply:
  • Renal artery Renal artery A branch of the abdominal aorta which supplies the kidneys, adrenal glands and ureters. Glomerular Filtration
  • Gonadal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
  • Ureteric branch of abdominal aorta Abdominal Aorta The aorta from the diaphragm to the bifurcation into the right and left common iliac arteries. Posterior Abdominal Wall: Anatomy
  • Common iliac arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
• Distal ureter: common iliac branches and internal iliac branches (uterine and vesical arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology) 
• Venous drainage follows arterial supply.
• Lymphatic drainage:
  • Internal, external, and common iliac nodes
  • Left ureter mainly to the left paraaortic nodes
  • Right ureter mainly to the right paracaval and interaortocaval nodes

Innervation:

• Intrinsic pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias: peristalsis Peristalsis A movement, caused by sequential muscle contraction, that pushes the contents of the intestines or other tubular organs in one direction. Gastrointestinal Motility is generated by pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias cells in the renal pelvis Renal pelvis Kidneys: Anatomy to facilitate movement of urine. 
• Sympathetic:
  • Preganglionic: T10–L1
  • Postganglionic: fibers from the aorticorenal, superior, and inferior hypogastric autonomic plexuses 
• Parasympathetic: S2 S2 Heart Sounds– S4 S4 Heart Sounds

Histology

Ureteral wall structure from the lumen toward the outside:

• Tunica mucosa: consists of a layer of transitional epithelium Transitional epithelium Surface Epithelium: Histology (urothelium)
• Lamina propria Lamina propria Whipple’s Disease: loose connective tissue Loose connective tissue Connective Tissue: Histology
• Tunica muscularis: thickest layer, with spirally organized muscular tissues that are responsible for peristalsis Peristalsis A movement, caused by sequential muscle contraction, that pushes the contents of the intestines or other tubular organs in one direction. Gastrointestinal Motility.
  • Longitudinal layer (stratum longitudinale)
  • Circular layer (stratum circulare) 
• Tunica adventitia Tunica adventitia The outermost covering of organs, blood vessels, and other such structures in the body. Arteries: Histology:
  • Connective-tissue layer 
  • Site of blood and nerve vessels

Urinary Bladder

Anatomy

Description: 

• Hollow, muscular organ that sits on the pelvic floor Pelvic floor Soft tissue formed mainly by the pelvic diaphragm, which is composed of the two levator ani and two coccygeus muscles. The pelvic diaphragm lies just below the pelvic aperture (outlet) and separates the pelvic cavity from the perineum. It extends between the pubic bone anteriorly and the coccyx posteriorly. Vagina, Vulva, and Pelvic Floor: Anatomy and accepts urine via the ureters.
• Musculature connects with that of the urethra, functioning as an internal urethral sphincter.
• Connected:
  • To the umbilicus via the median umbilical ligament 
  • To the pelvic walls by thickened areas of the pelvic fascia Fascia Layers of connective tissue of variable thickness. The superficial fascia is found immediately below the skin; the deep fascia invests muscles, nerves, and other organs. Cellulitis
• The average bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess capacity is 400 mL.

Parts:

• Apex: located anterosuperiorly, toward the pubic symphysis Pubic Symphysis A slightly movable cartilaginous joint which occurs between the pubic bones. Vagina, Vulva, and Pelvic Floor: Anatomy
• Body: main part of the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess
• Fundus Fundus The superior portion of the body of the stomach above the level of the cardiac notch. Stomach: Anatomy: base of the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess, located posteriorly
• Trigone: triangular area within the fundus Fundus The superior portion of the body of the stomach above the level of the cardiac notch. Stomach: Anatomy, defined by the 2 ureteral orifices 
• Bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess:
  • Formed by the convergence Convergence Pupil: Physiology and Abnormalities of the fundus Fundus The superior portion of the body of the stomach above the level of the cardiac notch. Stomach: Anatomy and the 2 inferolateral surfaces of the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess
  • Continuous with the urethra

Spatial relations:

• In females, the urinary bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess is anterior to the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy and anterior vaginal wall. 
• In males, the urinary bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess is anterior to the rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal: Anatomy.

Vasculature and lymphatic drainage:

• Arterial supply:
  • Superior and inferior vesical arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology (indirect branches of the internal iliac arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology)
  • Also from the obturator artery and the inferior gluteal artery Inferior gluteal artery Gluteal Region: Anatomy
• Venous drainage: most drain into the internal iliac vein
• Lymphatic drainage: most via external iliac nodes

Innervation:

• Sympathetic innervation:
  • The lower thoracic and upper lumbar spinal levels (T10–L2) in the hypogastric plexuses and nerves
  • Produces detrusor relaxation → urine retention
• Parasympathetic innervation:
  • The sacral spinal nerves Spinal nerves The 31 paired peripheral nerves formed by the union of the dorsal and ventral spinal roots from each spinal cord segment. The spinal nerve plexuses and the spinal roots are also included. Spinal Cord: Anatomy ( S2 S2 Heart Sounds– S4 S4 Heart Sounds) form the pelvic splanchnic nerves.
  • Produces detrusor contraction → urination
• Somatic innervation:
  • The pudendal nerve Pudendal nerve A nerve which originates in the sacral spinal cord (s2 to s4) and innervates the perineum, the external genitalia, the external anal sphincter and the external urethral sphincter. It has three major branches: the perineal nerve, inferior anal nerves, and the dorsal nerve of penis or clitoris. Gluteal Region: Anatomy ( S2 S2 Heart Sounds– S4 S4 Heart Sounds), a branch of the sacral plexus Sacral plexus Pelvis: Anatomy
  • Voluntary control to the external urethral sphincter
• Mechanoreceptors ( bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess wall):
  • Sense bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess fullness or distention 
  • Signals are transmitted to CNS via the general visceral afferent Afferent Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology fibers of the hypogastric and pelvic splanchnic nerves.

Histology

Microscopic description of the wall structure (from the lumen toward the outside):

• Transitional epithelium Transitional epithelium Surface Epithelium: Histology (urothelium):
  • The urothelium forms a series of rugae, thick mucosal folds that flatten out when the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess becomes full.
  • The area that is smooth (or without rugae) is the trigone.
  • The trigone consists of:
    • Apical (umbrella cell) layer: innermost layer acting as a barrier for the lumen
    • Intermediate layer: 2–3 layers of polygonal cells
    • Basal layer: 2–3 layers of cuboidal cells
• Lamina propria Lamina propria Whipple’s Disease: loose connective tissue Loose connective tissue Connective Tissue: Histology supporting separation of the urothelium from the muscularis propria
• Muscularis propria ( detrusor muscle Detrusor muscle Urinary Incontinence of the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess wall):
  • Consists of:
    • Inner longitudinal layer
    • Intermediate circular layer
    • Outer longitudinal layer
  • The internal urethral orifice is surrounded by the internal urethral sphincter, which is under sympathetic autonomic control.
  • Parasympathetic signals cause contractions of the detrusor muscle Detrusor muscle Urinary Incontinence, leading to urination.
• Serosa: thin layer of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology that continues with the peritoneal layer
• Adventitia: layer connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology where serosa is not present

Urethra: Male and Female

Male urethra

Description:

• Extends from the internal urethral orifice in the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess to the external urethral orifice of the glans penis Glans Penis Penis: Anatomy
• Much longer than the female urethra (up to 25 cm long)
• Responsible for passage of both urine (from the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess) and semen (from the ejaculatory ducts Ejaculatory Ducts Paired ducts in the human male through which semen is ejaculated into the urethra. )

Structure segments:

• Preprostatic urethra:
  • Intramural
  • Extends from bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess to the prostate Prostate The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid.
• Prostatic (within the prostate Prostate The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. ) urethra:
  •  3–4 cm long
  • Receives the prostatic ducts Prostatic ducts and ejaculatory ducts Ejaculatory Ducts Paired ducts in the human male through which semen is ejaculated into the urethra. (from the testes Testes Gonadal Hormones and the seminal vesicles Vesicles Female Genitourinary Examination)
• Membranous urethra:
  • 2 cm long
  • Runs through urogenital diaphragm Urogenital diaphragm Vagina, Vulva, and Pelvic Floor: Anatomy
  • Surrounded by the external urethral sphincter, which voluntarily controls micturition
• Penile (spongy) urethra:
  • Passes through the corpus spongiosum Corpus spongiosum Penis: Anatomy of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy 
  • Ends at the external urethral orifice (meatus)
  • Receives the ducts of the bulbourethral (Cowper) glands

Neurovasculature and lymphatic drainage:

• Arterial blood supply:
  • Prostatic urethra Prostatic urethra : inferior vesical artery (branch of the internal iliac artery)
  • Membranous urethra: bulbourethral artery (branch of the internal pudendal artery)
  • Penile urethra: branches of the internal pudendal artery
• Venous drainage: follows the arterial supply
• Lymphatic drainage:
  • Internal iliac nodes
  • Deep and superficial inguinal nodes
• Innervation: prostatic plexus (sympathetic, parasympathetic and visceral afferent Afferent Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology fibers)

Histology:

• Urothelium:
  • Urothelium from the preprostatic urethra to proximal prostatic urethra Prostatic urethra  
  • Pseudostratified or stratified columnar epithelium Stratified columnar epithelium Surface Epithelium: Histology form the membranous urethra to the penile urethra.
  • Stratified squamous epithelium Stratified squamous epithelium Surface Epithelium: Histology distally (glans)
• Lamina propria Lamina propria Whipple’s Disease: connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology with venous plexus 
• Muscularis: longitudinal and circular layers

Female urethra

Description:

• Much shorter than the male urethra (approximately 5 cm long)
• Extends from the internal urethral orifice in the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess to an area between the labia minora Labia minora Vagina, Vulva, and Pelvic Floor: Anatomy; embedded in the anterior wall of the vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor: Anatomy
• Runs behind the pubic symphysis Pubic Symphysis A slightly movable cartilaginous joint which occurs between the pubic bones. Vagina, Vulva, and Pelvic Floor: Anatomy and pierces through the perineal membrane and pelvic floor Pelvic floor Soft tissue formed mainly by the pelvic diaphragm, which is composed of the two levator ani and two coccygeus muscles. The pelvic diaphragm lies just below the pelvic aperture (outlet) and separates the pelvic cavity from the perineum. It extends between the pubic bone anteriorly and the coccyx posteriorly. Vagina, Vulva, and Pelvic Floor: Anatomy 

Parts:

• Proximal area (about ⅔) is surrounded by the external urethral sphincter muscle (circular fibers)
• Distal end is encircled by the compressor urethrae muscle.
• The external urethral orifice is located:
  • Anteriorly to the vaginal opening 
  • 2–3 cm posteriorly to the clitoris Clitoris An erectile structure homologous with the penis, situated beneath the anterior labial commissure, partially hidden between the anterior ends of the labia minora. Vagina, Vulva, and Pelvic Floor: Anatomy
• 2 mucous glands ( Skene glands Skene glands Vagina, Vulva, and Pelvic Floor: Anatomy) lie on either side of the orifice.

Neurovasculature and lymphatic drainage:

• Arterial blood supply: internal pudendal artery, vaginal artery Vaginal artery Vagina, Vulva, and Pelvic Floor: Anatomy
• Venous drainage: internal pudendal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology
• Lymphatic drainage:
  • Internal iliac nodes (proximal urethra) 
  • Superficial inguinal nodes (distal urethra)
• Innervation: pudendal nerve Pudendal nerve A nerve which originates in the sacral spinal cord (s2 to s4) and innervates the perineum, the external genitalia, the external anal sphincter and the external urethral sphincter. It has three major branches: the perineal nerve, inferior anal nerves, and the dorsal nerve of penis or clitoris. Gluteal Region: Anatomy, vesical plexus

Histology:

• Urothelium
  • Multilayered transitional epithelium Transitional epithelium Surface Epithelium: Histology
  • Has nonkeratinized squamous epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology distally
• Lamina propria Lamina propria Whipple’s Disease: connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology with venous complex
• Muscularis: consists of a longitudinal and a circular layer (stratum longitudinale and circulare)

Micturition

Regulation

• The bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess has 2 states of function:
  • Urine storage ( bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess filling) phase
  • Emptying phase
• Control mediated by the CNS and spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: Anatomy:
  • Pontine micturition center (PMC):
    • Controls bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess/detrusor contraction and sphincter relaxation Sphincter relaxation Gastrointestinal Motility
    • Allows micturition (emptying) when suppression Suppression Defense Mechanisms from higher brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification centers is withdrawn
  • Periaqueductal gray (PAG):
    • Receives signals of bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess distention (from sacral cord)
    • Sends information to higher brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification centers (e.g., prefrontal cortices) and PMC, thus serving as a relay station
  • Higher brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification centers:
    • Play a crucial role in inhibiting PMC if voiding is deemed inappropriate
    • Reduce urge to urinate and allows urine storage
    • Also, the motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology cortex controls the external urethral sphincter (voluntary muscle).

Urination

• The filling phase is characterized by:
  • Sympathetic contraction of the inner urethral sphincter
  • Distention of the detrusor without reflex contractions under sympathetic stimulation
  • Increased tone of the intrinsic urethral muscles 
• As the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess fills to capacity, the contractility of the detrusor increases, sending afferent Afferent Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology signals to the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification (PMC and higher brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification centers) via the PAG:
  • If micturition is not possible, the cortex overrides these signals and urination is delayed.
  • If micturition is possible, signals are sent from the pontine center to the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: Anatomy to initiate the micturition reflex.
  • Beyond maximal capacity filling of the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess, the micturition reflex overrides cortical control.
• The micturition phase is characterized by:
  • Relaxation of the external urethral sphincter (somatic innervation)
  • Relaxation of the internal urethral sphincter and opening of the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess (sympathetic innervation)
  • Detrusor muscle Detrusor muscle Urinary Incontinence contraction (parasympathetic innervation)
  • The abdominal wall Abdominal wall The outer margins of the abdomen, extending from the osteocartilaginous thoracic cage to the pelvis. Though its major part is muscular, the abdominal wall consists of at least seven layers: the skin, subcutaneous fat, deep fascia; abdominal muscles, transversalis fascia, extraperitoneal fat, and the parietal peritoneum. Surgical Anatomy of the Abdomen and pelvic floor Pelvic floor Soft tissue formed mainly by the pelvic diaphragm, which is composed of the two levator ani and two coccygeus muscles. The pelvic diaphragm lies just below the pelvic aperture (outlet) and separates the pelvic cavity from the perineum. It extends between the pubic bone anteriorly and the coccyx posteriorly. Vagina, Vulva, and Pelvic Floor: Anatomy muscles assist by increasing the force on the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess to help achieve complete emptying.

Clinical Relevance

• Bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess exstrophy: congenital anomaly involving protrusion of the urinary bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess through a defect in the abdominal wall Abdominal wall The outer margins of the abdomen, extending from the osteocartilaginous thoracic cage to the pelvis. Though its major part is muscular, the abdominal wall consists of at least seven layers: the skin, subcutaneous fat, deep fascia; abdominal muscles, transversalis fascia, extraperitoneal fat, and the parietal peritoneum. Surgical Anatomy of the Abdomen. The condition is occasionally associated with other anomalies of the genitalia, urinary tract, or pelvic wall. The diagnosis is obvious at birth. The treatment is surgical reconstruction of the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess and should be undertaken at experienced medical centers. 
• Disorders of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy and male urethra: congenital conditions, which include epispadias Epispadias A birth defect due to malformation of the urethra in which the urethral opening is above its normal location. In the male, the malformed urethra generally opens on the top or the side of the penis, but the urethra can also be open the entire length of the penis. In the female, the malformed urethral opening is often between the clitoris and the labia, or in the abdomen. Penile Anomalies and Conditions (urethra opens not at the tip of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy but on the dorsal penile surface) and hypospadias Hypospadias A birth defect due to malformation of the urethra in which the urethral opening is below its normal location. In the male, the malformed urethra generally opens on the ventral surface of the penis or on the perineum. In the female, the malformed urethral opening is in the vagina. Penile Anomalies and Conditions (urethra opens not at the tip of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy but on the ventral surface of the penis Penis The penis is the male organ of copulation and micturition. The organ is composed of a root, body, and glans. The root is attached to the pubic bone by the crura penis. The body consists of the 2 parallel corpora cavernosa and the corpus spongiosum. The glans is ensheathed by the prepuce or foreskin. Penis: Anatomy). 
• Urinary tract infection: inflammatory condition of infectious etiology that involves the urinary tract. Anatomically, these infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease can be divided into upper and lower urinary tract infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease.
• Nephrolithiasis Nephrolithiasis Nephrolithiasis is the formation of a stone, or calculus, anywhere along the urinary tract caused by precipitations of solutes in the urine. The most common type of kidney stone is the calcium oxalate stone, but other types include calcium phosphate, struvite (ammonium magnesium phosphate), uric acid, and cystine stones. Nephrolithiasis: clinical condition characterized by the presence of stones in the kidney or along the urinary tract. Nephrolithiasis Nephrolithiasis Nephrolithiasis is the formation of a stone, or calculus, anywhere along the urinary tract caused by precipitations of solutes in the urine. The most common type of kidney stone is the calcium oxalate stone, but other types include calcium phosphate, struvite (ammonium magnesium phosphate), uric acid, and cystine stones. Nephrolithiasis presents with acute flank pain Flank pain Pain emanating from below the ribs and above the ilium. Renal Cell Carcinoma, dysuria Dysuria Painful urination. It is often associated with infections of the lower urinary tract. Urinary Tract Infections (UTIs), and occasionally hematuria Hematuria Presence of blood in the urine. Renal Cell Carcinoma. Noncontrast CT is the diagnostic method of choice. Management depends on the size of the stone. Small stones that are likely to pass on their own are managed conservatively with hydration and analgesics. Large stones that are unlikely to pass spontaneously are managed with extracorporeal shock-wave lithotripsy, ureterorenoscopy, or percutaneous nephrolithotomy.
• Urinary incontinence Urinary incontinence Urinary incontinence (UI) is involuntary loss of bladder control or unintentional voiding, which represents a hygienic or social problem to the patient. Urinary incontinence is a symptom, a sign, and a disorder. The 5 types of UI include stress, urge, mixed, overflow, and functional. Urinary Incontinence: involuntary loss of bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess control or unintentional voiding. There are 5 types of urinary incontinence Urinary incontinence Urinary incontinence (UI) is involuntary loss of bladder control or unintentional voiding, which represents a hygienic or social problem to the patient. Urinary incontinence is a symptom, a sign, and a disorder. The 5 types of UI include stress, urge, mixed, overflow, and functional. Urinary Incontinence: stress, urge, mixed, overflow, and functional. The etiology of urinary incontinence Urinary incontinence Urinary incontinence (UI) is involuntary loss of bladder control or unintentional voiding, which represents a hygienic or social problem to the patient. Urinary incontinence is a symptom, a sign, and a disorder. The 5 types of UI include stress, urge, mixed, overflow, and functional. Urinary Incontinence is multifactorial. For women, risk factors include prior vaginal deliveries and menopause Menopause Menopause is a physiologic process in women characterized by the permanent cessation of menstruation that occurs after the loss of ovarian activity. Menopause can only be diagnosed retrospectively, after 12 months without menstrual bleeding. Menopause; for men, the main risk factor is prior prostate Prostate The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. surgery. Diagnosis is clinical. Management depends on the type(s) of incontinence and the etiology.
• Urinary tract obstruction Urinary tract obstruction Urinary tract obstruction (UTO) refers to the blockage of the urinary tract, which can occur anywhere in the urinary tract. Urinary tract obstruction can be acute or chronic, partial or complete, and unilateral or bilateral. Urinary tract obstruction can cause acute or chronic kidney disease. Urinary Tract Obstruction: manifests as an inability of urine to pass through the ureters, bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess, or urethra due to a partial or complete blockage. Benign Benign Fibroadenoma prostatic hyperplasia Hyperplasia An increase in the number of cells in a tissue or organ without tumor formation. It differs from hypertrophy, which is an increase in bulk without an increase in the number of cells. Cellular Adaptation, malignancies, and kidney stones Kidney stones Nephrolithiasis is the formation of a stone, or calculus, anywhere along the urinary tract caused by precipitations of solutes in the urine. The most common type of kidney stone is the calcium oxalate stone, but other types include calcium phosphate, struvite (ammonium magnesium phosphate), uric acid, and cystine stones. Nephrolithiasis are among the etiologies of obstruction. Presentation and management is dependent on the underlying condition.
• Vesicoureteral reflux Vesicoureteral Reflux Vesicoureteral reflux (VUR) is the retrograde flow of urine from the bladder into the upper urinary tract. Primary VUR often results from the incomplete closure of the ureterovesical junction, whereas secondary VUR is due to an anatomic or physiologic obstruction. Vesicoureteral Reflux: retrograde flow Retrograde flow Veins: Histology of urine from the urinary bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess to the ureter and the kidney. Vesicoureteral reflux Vesicoureteral Reflux Vesicoureteral reflux (VUR) is the retrograde flow of urine from the bladder into the upper urinary tract. Primary VUR often results from the incomplete closure of the ureterovesical junction, whereas secondary VUR is due to an anatomic or physiologic obstruction. Vesicoureteral Reflux can be asymptomatic and resolve spontaneously, or may need to be corrected surgically. The condition is associated with frequent urinary tract infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease, leading to pyelonephritis Pyelonephritis Pyelonephritis is infection affecting the renal pelvis and the renal parenchyma. This condition arises mostly as a complication of bladder infection that ascends to the upper urinary tract. Pyelonephritis can be acute or chronic (which results from persistent or chronic infections). Typical acute symptoms are flank pain, fever, and nausea with vomiting. T Pyelonephritis and Perinephric Abscess and nephropathy.