a brief discussion on basic anatomy & embryology of urinary bladder

1. Anatomy and Embryology of
Bladder
Dr. Deepesh Kalra
Institute of urology
Madras medical college, chennai

2. Anatomy
• It is a hollow musculomembranous sac which acts as a reservoir of urine.
• Most anterior element of pelvic viscera.
• It is a subperitoneal organ with peritoneum covering only superior surface.
• It is separated from the pubic symphysis by an anterior prevesical space known as
the space of Retzius or retropubic space.
• When "Empty" , the adult urinary bladder is located in the "Lesser pelvis" lying
partially superior to and partially postetior to the pubic Bones.

3. Surfaces -
• Superior surface.
• Right inferolateral surface.
• Left inferolateral surface.
• Posterior surface.

4. • Bladder can be divided into-
 Body - lying above the ureteral orifices
and
 Base- consisting of the trigone and
bladder neck
 Apex - attched to median umblical
ligament
 Neck- lowermost part
 Extending from the dome of the
bladder to the umbilicus is a fibrous
cord, the median umbilical ligament,
which represents the obliterated
urachus.

5. Body
It holds the urine.
Capacity – 400-1000 m.l
The body of the bladder
receives inferior support from
the pelvic diaphragm in
females or prostate in
males and lateral support
from the obturator internus
and levator ani muscles

6. Fundus
It is base of the bladder.
▸ It has the shape of inverted
triangle.
▸ It faces postero-inferiorly
and , is formed by the
posterior wall of bladder.
▸ Trigone of the urinary
bladder is found on the
fundus

7. Trigone
 Ureters enter the bladder
posteroinferiorly ( 5c.m. apart )
 The orifices,situated at interureteric ridge
( MERCIER`S BAR ) that forms the proximal
border of the trigone, are about 2.5 cm
apart.
 The intramural ureters are each about 1.5
cm in length.
 The trigone is the triangular area between
the ridge and the bladder neck.

8. Detrusor
Muscularis Propria
 It is smooth muscle , found around the wall
of bladder.
 It is comprised of inner and outer
longitudinal, and middle circular layer.
 The bladder base has a laminar architecture
with a superficial longitudinal layer lying
beneath the trigone
 A circular muscle layer deep to the superficial
layer is continuous with the detrusor

9. Neck and internal sphincter-
 lowest portion of bladder.
 At the bladder neck, the
muscular bladder wall is more organized
and 3 relatively distinct layers become
apparent.
 The inner longitudinal muscle layer fuses with
the inner longitudinal layer of the urethra.
 The middle circumferential muscle layer is
most prominent in the proximity of the
bladder neck, and it fuses with the deep
trigonal muscle layer.
 The outer longitudinal muscle layer
contributes some anterior fibers to what
become the pubovesical muscles

10. • In addition to these muscle layers, the pubourethral ligament serves to support
the bladder neck and urethra.
• The bladder neck is fixed to neighboring structures by reflections of the pelvic
fascia and by true ligaments of the pelvis.
• It is densely innervated by Sympathetic supply
• It prevents the urine leakage, Retrograde ejaculation.

11. Relations

12. • Anterior to the bladder is the space of Retzius or retropubic space.
• The dome and posterior surface of the bladder are covered by parietal
peritoneum, which reflects superiorly to the seminal vesicles and is continuous
with the anterior rectal peritoneum.
• In females, the posterior peritoneal reflection is continuous with the uterus and
vagina and is referred to as the anterior cul-de-sac or vesicouterine pouch.

13. Bladder Compartments
Urothelium -
A multilayered epithelium with a basal, intermediate, and apical layer of cells.
The apical cells (umbrella cells) comprise the layer that is in contact with urine.
The urothelium is about seven layers thick.
Apical cells are also unique in their expression of an assembly of a specialized
class of proteins called uroplakins.

14. Lamina Propria-
• “Functional center” for localized control of the bladder, coordinating the activities
of the urothelium and detrusor smooth muscle.
• Contains – nerve fibre, myofibroblasts & microvasculature.
Stroma -
The main constituents of bladder wall stroma are collagen and elastin in a matrix
composed of proteoglycans.
The main cells are fibroblasts.

15. Bladder Wall Collagen -
Most of the bladder wall collagen is found in the connective tissue outside the muscle
bundles.
types I, III, and IV are the most common.
Bladder Wall Elastin and Matrix -
Elastic fibers are amorphous structures composed of elastin and a microfibrillar
component located mainly around the periphery of the amorphous component.
Elastin fibers are sparse in the bladder compared with collagen but are found in all layers
of the bladder wall.

16. Smooth Muscle -
Histologic examination of the bladder body reveals that myofibrils are arranged
into fascicles (bundles) in random directions.
The motor innervation of the bladder smooth muscle is from the postganglionic
parasympathetic nerve fibers

17. Arterial supply -
Branches of internal iliac arteries.
 Superior vesical arteries supply anterosuperior parts of the bladder.
 In males, inferior vesical arteries supply the fundus and neck of the bladder.
 In females, vaginal arteries replace the inferior vesical arteries and send small
branches to posteroinferior parts of the bladder.
 Obturator and inferior gluteal arteries also supply small branches to the bladder.

18. Venous supply -
 The venous return of the bladder is a rich network of vessels that generally
parallels the arteries in both anatomic course and name.
 The vast majority of venous return from the bladder drains into the internal iliac
vein.
Lymphatic drainage -
 The lymphatic drainage of the bladder is into the obturator, external iliac, internal
iliac (hypogastric), and common iliac lymph nodes

19. INNERVATION
• Detrusor muscle - Parasympathetic causes contraction
Sympathetic causes relaxation
• Afferent Pelvic nerve is stimulated when the bladder is stretched.
• Bladder neck (internal sphincter) - rich in sympathetic supply

20. Embroylogy

21. • The bladder and uretero-vesical junction form primarily during the fourth to
eighth weeks of gestation, and arise from the primitive urogenital sinus following
subdivision of the cloaca.
• The bladder develops through mesenchymal-epithelial interactions between the
endoderm of the urogenital sinus and mesodermal mesenchyme.
• Key signalling factors in bladder development include shh, TGF-β, Bmp4, and
Fgfr2.
• A concentration gradient of shh is particularly important in development of
bladder musculature, which is vital to bladder function.
• Source-2018 International Society of Differentiation. Published by Elsevier
• https://www.sciencedirect.com/science/article/pii/S0301468118301038

22.  3rd week- the cloacal membrane remains a
bilaminar structure composed of endoderm
and ectoderm.
 4th week - the neural tube and the tail of the
embryo grow dorsally and caudally, projecting
over the cloacal membrane, and this
differential growth of the body results in
embryo folding.
• The cloacal membrane is now turned to the
ventral aspect of the embryo.
• The terminal portion of the endoderm-lined
yolk sac dilates and becomes the cloaca.
 During 5th-6th weeks The partition of the
cloaca into an anterior urogenital sinus and a
posterior anorectal canal occurs by the
midline fusion of two lateral ridges of the
cloacal wall and by a descending urorectal
septum.

23. • The nephric (wolffian) duct fuses
with the cloaca by the 24th day .
• The entrance of the nephric duct
into the primitive urogenital sinus
serves as a landmark distinguishing
the cephalad vesicourethral canal
from the caudal urogenital sinus.
• The vesicourethral canal gives rise
to the bladder and pelvic urethra,
whereas the caudal urogenital sinus
forms the phallic urethra for males
and distal vaginal vestibule for
females.

24. Development of the Bladder -
• By the 10th week of gestation the bladder is a cylindric tube lined by a single
layer of cuboidal cells.
• By the 12th week the urachus involutes to become a fibrous cord, which becomes
the median umbilical ligament.
• The bladder epithelium begins to acquire mature urothelial characteristics
between the 13th and 17th weeks. By the 21st week it becomes four to five cell
layers thick and demonstrates ultrastructural features similar to the fully
differentiated urothelium.

25. • Bladder compliance is very low during early gestation and increases gradually
thereafter.
• During gestation the bladder wall muscle thickness increases and the relative
collagen content decreases, the amount of elastic fibers increases.

26. Formation of Trigone
 By day 33 of gestation, the
common excretory ducts (the
portion of nephric ducts distal
to the origin of ureteric buds)
dilate and connect to the
urogenital sinus.
 Right and left common
excretory ducts fuse in the
midline as a triangular area,
forming the primitive trigone,
structurally different from
bladder.
 Other theory - It was
previously thought that the
trigonal musculature
developed primarily from the
Wolffian duct, but it has been
shown to develop primarily
from bladder mesenchyme.

27. • The deep periureteral sheath arising from the intravesical ureteral wall
forms the deep trigonal muscles.
• The muscles of the intravesical ureter were differentiated longitudinally
and formed the superficial trigonal muscles.
• With time, the mesodermal lining of the trigone is replaced by endodermal
epithelium, so that finally, the inside of the bladder is completely lined with
endodermal epithelium.
• Development of the ureterovesical junction in human fetus. Available from: https://www.researchgate.net/publication/22551577_Development_of_the_ureterovesical_junction_in_human_fetus
[accessed Sep 06 2018].

28. UV junction development
• The uretero-vesical junction forms from the interaction between the
Wolffian duct and the bladder.
• The ending of the ureter fuses with the urogenital sinus by day 37,
the subsequent caudal growth remains vague, mainly the distention and
intravesical submucosal enlargement occurs which is considered most
responsible for the anti-reflux mechanism.
• Following emergence of the ureters from the Wolffian ducts, extensive
epithelial remodelling brings the ureters to their final trigonal positions via
vitamin A-induced apoptosis

29. • The length of the intravesical ureter in gestational weeks 20-30 as described by
Cussen is mean 3 mm
• During gestational weeks 30-40, the intravesical ureter has a mean length of 4
mm.
• The tunnel length relative to its diameter is thought to be important in the
prevention of reflux by closing the junction’s valvular mechanism.
• The ratio of tunnel length to ureteral diameter at the ureterovesical junction was
found to average 5 : 1 in Paquin’s study

30. Development of bladder neck and continence mechanism
• No functional study has been done to assess fetal continence mechanisms.
• A mesenchymal condensation forms around the caudal end of the urogenital
sinus after the division of the cloaca and the rupture of the cloacal membrane.
Muscle fibers can be seen clearly by the 15th week.
• At this time the smooth muscle layer becomes thicker at the level of bladder
neck.

31. Bladder Defects
Urachal defects -
• Urachal fistula - When the lumen of the intraembryonic portion of the
allantois persists.
• Urachal cyst - If only a local area of the allantois persists, secretory
activity of its lining results in a cystic dilation.
• Urachal sinus - When the lumen in the upper part persists.

32. Exstrophy of the bladder -
• A ventral body wall defect in which the bladder mucosa is exposed. Epispadias is a
constant feature.
• Exstrophy of the bladder is probably due to failure of the lateral body wall folds to close
in the midline in the pelvic region.
Exstrophy of the cloaca -
• A more severe ventral body wall defect in which progression and closure of the lateral
body wall folds are disrupted to a greater degree than is observed in bladder exstrophy.
• In addition to the closure defect, normal development of the urorectal septum is altered,
such that anal canal mal- formations and imperforate anus occur.
• Furthermore, because the body folds do not fuse, the genital sweilings are widely spaced
resulting in defects in the external genitalia.