36. The anatomy, histology and development of the ureter, urinary vesicle and urethra.

Anatomy of the ureter, urinary vesicle and urethra.

Ureter

*retroperitoneal
General Info:
musc tube that transmit urine via peristaltic waves, leads from kidney
is the most posterior structure that emerges from hilus of kidney
25-30 cm long
enter bladder @ anteromedially, superior to levator ani

Topography:

• crosses bifurcation of common iliac a @ pelvic brim
• desc retroperitoneally on lat pelvic wall –> med to umbilical a & obturator a/v
• post to ovary @ post surface of ovarian fossa
• 1-2 cm lat to uterus, runs w/ uterine a, which runs above and ant to base of broad lig
• passes post/inf to ductus deferens & lies in front of seminal vesicle before entering post/lat bladder (male)

2 parts – abdominal/pelvis

Abdominal
crossed by 3 structures: Topography
1. Gonadal a/v – in front
2. Psoas major – behind
3. Bifurcation of common iliac a w/ ureter in front of int iliac a

Male – ductus deferens crosses ureter in front

Female

• uterine a crosses in front
• @ bifurcation of common iliac, forms post border of ovarian fossa
• contacts lat fornix of vagina b4 entering bladder

Blood Supply:

• rec blood from aorta, renal, gonadal, common & int iliac, umbilical, sup/inf vesicle a, middle rectal a
• Vesicle venous plexus –> int iliac v (sometimes, prostatic vesicle plexus)

Lymph Drainage: lumbar, common iliac, ext iliac, int iliac l.n

Urinary Bladder

*Infraperitoneal – lower in female
located in pelvis minor when empty
located full, can enter major pelvis –> even up to umbilicus

General Info:

• THICK muscular wall = detrusor m
• holds urine, until ready to release it
• mucus membrane attaches, except @ trigone
  • mucus membrane attaches to CT underlying, no mucosal folds
  • originates from mesonephric duct
  • marked by entrances of ureter & ejaculatory duct
  • has 2 ureteric openings and urethral openings (int urethral sphincter)
• anchored by CT ligaments = paracysticum
• held @ neck  to pubic bone, via puboprostatic (male), or pubovesical (female) ligaments

Structure of Bladder (Detail):

The bladder itself consists of 4 layers:-

(1) Serous – this outer layer being a partial layer derived from the peritoneum,
(2) Muscular – the detrusor muscle of the urinary bladder wall, which consists of 3 layers incl. both longitudinal and circularly arranged muscle fibres,
(3) Sub-mucous – a thin layer of areolar tissue loosely connecting the muscular layer with the mucous layer
(4) Mucous – the innermost layer of the wall of the urinary bladder loosely attached to the (strong and substantial) muscular layer. The mucosa falls into many folds known as rugae when the bladder is empty or near empty.

• The features observable on the inside of the bladder are the ureter orifices, the trigone, and the internal orifice of the urethra.
• The trigone is a smooth triangular region between the openings of the two ureters and the urethra and never presents any rugae even when the bladder is empty – because this area is more tightly bound to its outer layer of bladder tissue.

Peritoneal relations of bladder:

Outer surfaces of the Bladder: The upper and side surfaces of the bladder are covered by peritoneum (also called “serosa”). This serous membrane of the abdominal cavity consists of mesthelium and elastic fibrous connective tissue. “Visceral peritoneum” covers the bladder and other abdominal organs, while “parietal peritoneum” lines the abdomen walls.

Topography of Bladder: Bladder Bed

• ant = pubic bone, separated from ant ab wall & pelvis by rectopubic space
• inf/lat = obturator int m, levator ani m
• inf/post = rectum

B/w bladder & rectum:
Male – seminal vesicles & ejaculatory duct, ductus deferens
Female – uterus & upper vagina

Vesicouterine Pouch:
ant = bladder
post = uterus
lat = vesicouterine ligaments (folds)

Normally, pouch so small, there is nothing in it
If Rectoversion occurs, may contain SI loops
bladder connected to CT except @ neck where puboprostatic lig anchors it (male)

Rectovesicle Pouch:
ant = bladder, seminal vesicle, DD
post = rectum
lat = rectovesicular fold

In male, pertioneum covers fundus, reflecting from upper post wall, and covers tip of seminal vesicle

Parts of Bladder:

1. Apex (ant end)
   • retro to symphysis
   • origin of median umbilical ligament – remnant of embryonic urachus (connection b/w urinary bladder and embryonic allantois)
2. Fundus (post/inf)
   • contact w/ rectum in male, separated by rectovesicular septum
   • contacts w/ ant surface of vagina in female
3. Neck (lat/post — converges here)
   • urethra originates from bladder here
   • just above = uvula – small eminence projects into urethra

Blood Supply:

• Sup vesicle a (int iliac a)
• Fundus of bladder
  • inf vesicle a (Male)
  • vaginal a (uterine a – Female)
• veins = vesicle venous plexus –> int iliac v (prostatic venous plexus)

Lymph Drainage:

• body = ext iliac lymph nodes
• fundus = int iliac l.n
  
• neck = sacral & common iliac l.n.

Innervation:

• PNS from pelvic splanchnic n (S2-4)
  • VM for detrusor m
  • (-) for int urethral sphincter
• SNS (T12-L2)
  • VM for int urethral sphincter
  • (-) detrusor m

Urethra
From bladder –> opens @ perineum, urine emptied thru it

Male Urethra

Parts to it:
1. Prostatic urethra
3 cm long, and w/in prostate
widest part of urethra
covered w/ urothelium = transitional epithelium

The prostatic urethra begins at the neck of the bladder and includes all of the section that passes through the prostrate gland. It is the widest and most dilatable part of the male urethral canal.

Structures opening here:
1. Prostatic glands
2. Ejaculatory ducts
3. Prostatic utricle

long ridge = urethral crest

• runs through out w/ 2 grooves beside it = prostatic sinuses
• opening of submucosal ducts & prostatic glands
• @ upper crest = seminal collicus

Seminal colliculus

• small hill like structures protruding into urethra
• lat to colliculus are prostatic sinuses, where prostate glands open
• 3 small openings:
  • @ midline = utricle of prostate (remnant of paramesonephric duct – regresses in male)
  • inf to that = 2 ejaculatory ducts

secretions of prostate, seminal vesicle, and bulbourethral glands mixes w/ spermatozoa from testis = semen

2. Membranous urethra
1 cm long
passes thru UG diaphragm – here ext urethral sphincter seen

The membranous urethra is the shortest and narrowest part of the male urethra. This section measures approx. 0.5 – 0.75 inches (12 – 19 mm) in length and is the section of the urethra that passes through the male urogenital diaphragm.
The external urethral sphincter (muscle) is located in the urogenital diaphragm (as for the female urethra).
The passage of urine along the urethra through the urogenital diaphragm is controlled by the external urethral sphincter, which is a circular muscle under voluntary control (that is, it is innervated by the somatic nervous system, SNS).

3. Penile urethra
enters bulbous part of  penis
Pathway: turns up @ sharp angle (1st turn)  –> runs along bulb of penis –> to pubic symphysis –> bends down (2nd turn) –> corpus spongiosum –> runs down to tip of penis & opens @ navicular fossa

The spongy (penile) urethra is the longest of the three sections. It is approx. 6 inches (150 mm) in length and is contained in the corpus spongiosum that extends from the end of the membranous portion, passes through the penis, and terminates at the external orifice of the urethra – which is the point at which the urine leaves the body.

@ navicular fossa: str columnar –> str sq non keratinazing epith

CLINICAL NOTE: B/c of 2 sharp bends – makes it difficult to insert catheter

Blood supply: prostatic br of inf vesicle a & middle rectal a, v follow a

Lymph Drainage: int/ext iliac l.n

Nerve supply: pudendal n, prostatic plexus (inf hypogastric plexus)

Female urethra

At only about 1.5 inches (35 mm) long, the female adult urethra is shorter than the adult male urethra (approx. or 8 inches, or 200mm). The female urethra is located immediately behind (posterior to) the pubic symphysis and is embedded into the front wall of the vagina.

The urethra itself is a narrow membranous canal that consists of three layers:

1. Muscular layer – continuous with the muscular layer of the bladder, this extends the full length of the urethra.
2. Thin layer of spongy erectile tissue – including plexus of veins and bundles of smooth muscle fibres. Located immediately below the mucous layer.
3. Mucous layer – internally continuous with the bladder and lined with laminated epithelium that is transitional near to the bladder.

After passing through the urogenital diaphragm (as shown in the diagram), the female urethra ends at the external orifice of urethra – which is the point at which the urine leaves the body. This is located between the clitoris and the vaginal opening.

The passage of urine along the urethra through the urogenital diaphragm is controlled by the external urethral sphincter, which is a circular muscle under voluntary control (that is, it is innervated by the somatic nervous system, SNS).

The female urethra is a much simpler structure than the male urethra because it carries only urine (whereas the male urethra also serves as a duct for the ejaculation of semen – as part of its reproductive function
upper 1/2 = prostatic urethra
lower 1/2 = “membranous”

@ upper part = Paraurethral glands –> ducts @ ext urethral orifice

@ lower part
goes through UG diaphragm
transverse perineal m wraps around to form = urethro vaginal sphincter
closely associated w/ ant wall of vagina

• attached via strong CT sheath = urethrovaginal septum
• b/w them = urethrovaginal space

Blood supply: int pudendal a, vaginal a, veins follow a

Lymph Drainage: sacral/int iliac l.n

Nerve supply: pudendal n

Process of Urination:
Initiated by (+) of stretch receptors in detrusor m in bladder in wall by inc volume of uring
innervated by S2-4 via pelvic splanchnic n
can be assisted by contraction of abdominal m = inc intra abdominal & pelvic pressures

Process:
1. SNS = (+) relaxation of bladder wall
contract inner sphincter –> (-) emptying
may stimulate detrusor m to prevent reflux of semen into bladder during ejaculation

2. PNS = preggl fibers in pelvis splanchnic n
synapse in pelvic (inf hypogastric plexus)
post ggl to bladder musc induc reflex = contraction of detrusor m
and relaxation of int sphincter
inc urge to urinate

3. SM fibers in pudendal n cause voluntary relaxation of ext urethral sphincter
bladder begins to release

4. @ end of urination
the ext urethral sphincter ( & bulbospongiosus m in male) contracts
expel the last few drops of urine from urethra

Histology  of the ureter, urinary vesicle and urethra.

Slide #63 Ureter * H&E

Structures to Identify:

• 3 layers = mucosa, muscularis, adventia
• transitional epith
• umbrella cells
• a/v
• CT
• piriform cells
• basal cells

General Info

• paired tubular structures that convey urine from kidney –> bladder
• lined w/ transitional epith to adapt to changing environment (fluid v no fluid)

Mucosa

• Epith = urothelium
  • thick, with cells that change shape
• star shaped irregular lumen, made by mucosal folds, due to musc. contractions
• Note that lumen is long , narrow and star shaped, not circular *like DD
• 3 main cell types of Epith
  • umbrella cells – come in contact with urine, and adjust accordingly, can be bi-nucleated, shape change due to actin filaments
  • piriform cells – underneath umbrella cells and above basal cells, can also adjust morphologically
  • basal cells – located at lowest layer of stratified epith
• LP = fibroelastic CT, denser near epith –> looser towards muscularis ext, with diffuse lymph tissue = MALT
• No real muscularis mucosae

transitional epithelium or urothelium and cells of it

Muscularis Ext

• 3 layers:
  • inner longitudinal layer
  • middle circular layer
  • outer longitudinal – but only in last 1/3 of ureter
• smooth m responsible for creating peristaltic contractions to convey urine through ureter (30cm)

Adventia

• 3rd main layer
• ureter = retroperitoneal, so covered w/ adventia
• CT + a/v/n
• adipose

Slide #64 Urinary Bladder * H&E

Contracted Bladder - Our slide doesnt look like this, but this shows layers well

Structures to Identify:

• urothelium
• muscularis
• a/v
• CT
• mesothelium
• PNS ggl

General Info

• Receives urine from 2 ureters and under appropriate stimulation, will secrete it through urethra
• lined by urothelium, which allows bladder to adjust to amount of urine

Mucosa

• Epith = urothelium,  transitional epithelium
  • same cell types as ureter
  • up to 10 layers when bladder empty, # layers dec when bladder is full
• when bladder is full, cells flatten and appear squamous, & when bladder was empty, cells became dome shaped
• LP = CT tissue fibers, fibroblasts, a/v, many layers
  • Can either say LP has 2 layers = upper cell rich, and lower fibrous layer
  • Or can say there is a cell rich LP with a fibrous submucosa
  • fibrous layer not present in bladder trigone
• changes in appearence and cells shapes in transitional epithelium are from thickened regions called plaques
  • interconnected via interplaque regions
  • allow  cell membrane to fold – which disappear when urine flows into bladder

Muscularis Mucosae

• 3 muscular layers: – inner longitudinal, middle circular, outer longitudinal
• not as organized as ureter
• may be ggl cells wich are part of ANS
  • helps regulate urine secretion via relaxation & contraction of muscularis
  • controls detrusor m
• Internal urethral sphincter = fromed @ site of entry of bladder –> Urethra
• w/ CT in between, and a/v and capillaries, and occasional n. fibers

Adventia

• Infraperitoneal
• fundus covered by peritoneum
• serosa/ subserosa can be present where peritoneal pres – superiorly –> simple squamous = mesothelial cells
• SNS n fibers maybe

Beyond the serosa/adventitia covering of the bladder is perivesical fat.  This is a layer of fat surrounding bladder.

It's upside down - sorry

Slide #71 Penile Urethra * H&E

Structures to Identify:

• lumen
• corpus spongiosum
• smooth m
• str columnar/ psuedo str columnar
• tunica albuginea
• urethral glands of Littre
• paraurethral ducts
• endo-epith glands

Mucosa

• Epith = pseudostratified non keratinized epith
  • epith changes depend on part of urethra
  • Pars prostatica –  urothelium
  • Pars membranous – str columnar
  • Pars spongiosum –  str columnar – until navicular fossa – str squamous
• LP = thin layer, merges with surrounding corpus spongiosum, cell rich
• lumen is shaped like ureter, but does NOT have urothelium in our slide, so look for that, and the glands of Littre
• mucosal folds makes small dips in lumen, and forms lacunae
• lacunae attached to urethral ducts of urethral glands of Littre
  • mucus secretions
  • thin basophillic (blue) outer layer with pale interior (mucus)
  • duct is more basophillic, with small circular lumen

Corpus spongiosum

• network  of cavities lined by simple squamous epith
• a/v in b/w

Outer layer = Tunica albuginea

• thick eosinophillic layer, with smooth m and elastic fibers

Ducts of Littre

Development of the ureter, urinary vesicle and urethra.

Ureter:

• intermediate mesoderm forms longitudinal ridge on post body wall = urogenital ridge
• part of UG ridge becomes nephrogenic cord –> urinary system
• nephrogenic cord develops into 3 structures: pronephros, mesonephros, metanephros
• metanephros further develops from ureteric bud and from grouping of mesoderm w/in nephrogenic cord, metanephric mesoderm
• further development of ureteric bud –> becomes ureters
  

Urinary bladder:

• urinary bladder is formed from upper end of urogenital sinus, continuous w/ allantois
• allantois becomes fibrous cord = urachus * stays in adult as median umbilical lig
• lower end of mesonephric ducts –> post wall of bladder as trigone
• mesonephric ducts open into urogenital sinus below bladder
• transitional epith from endoderm
  

Urethra:

Female Urethra:

• female urethra is formed from lower end of urogenital sinus
• develops as endodermal outgrowths into surrounding mesoderm = urethral glands, paraurethral glands
• end @ vestibule of vagina, also forms from urogenital sinus
• vestibule of vagina – develop endoderm growths = greater vestibular glands
• endoderm = epith
  

Male Urethra:

• Prostatic urethra, membranous urethra, prox urethra
  • formed from lower end of urogenital sinus
  • endoderm = transitional epith, str columnar epith
  • prostatic urethra have endoderm outgrowth into mesoderm = prostate gland
  • membranous urethra have endoderm outgrowth into mesodem = bulbourethral glands
  • prox part of penile urethra have endoderm outgrowth into mesoderm = Littre’s glands
• distal part of penile urethra
  • formed from ingrowth of surface ectoderm = glandular plate
  • glandular plate joins penile urethra and becomes tube = navicular fossa
  • ectodermal septa lat to navicular fossa –> becomes foreskin
  • str sq epith lines part of urethra = ectoderm