The document outlines the development of the renal system in humans, detailing the progression through three stages: pronephros, mesonephros, and metanephros, with each phase having distinct anatomical characteristics and functional roles. It discusses the structural evolution of kidneys, including the formation of renal corpuscles and nephron units, as well as the anatomical transitions from embryo to functional kidneys. Additionally, it addresses congenital anomalies associated with renal development and variations in urinary structures.

1. DEVELOPMENT OF RENAL SYSTEM
By:
Phanindra Prasad Poudel
Assistant Professor
Department of Anatomy
MCOMS, Pokhara

2. DEVELOPMENT OF KIDNEY
3 systems develop
cranio-caudally:
1. Pronephros
2. Mesonephros
3. Metanephros
Source:
Intermediate
mesoderm

3. PRONEPHROS
 4th
week
 Cervical and upper thoracic regions
 7-10 segmentation- solid cell groups- vestigial excretory
units- Nephrotome/ Pronephric tubule
 By the end of 4th
week- pronephric system disappears

4. MESONEPHROS
 Lower thoracic and
upper lumbar region
(L3)
 After disappearance of
pronephros
 70-80 segmentation
appear- each segment-
nephrotome/
mesonephric tubule

5. Mesonephric tubule:
S- shaped loop
 Medial end
 forms glomerulus
enclosed by bowman’s
capsule- together k/a-
renal corpuscle
 Lateral end
 terminates in the
longitudinal collecting
duct k/a mesonephric
duct/ wolffian duct
 Opens distally in cloaca
(urogenital sinus)

6.  5th
week- proximal
mesonephric tubules
disappear
 By the end of 1st
trimester
 26 mesonephric tubules
& mesonephric duct
persist
In female- disappears
In male- persist- efferent
ductules of epididymis,
vasa deferens

7. METANEPHROS
 3rd
urinary organ
 Appears lastly in
lumbosacral segments
 Starts to function by 5th
weeks
 Develops from
metanephric mesoderm
 Persists as permanent
kidney
 Contains 2 parts:
i. Collecting part
ii. Excreting part

8. Collecting system:
 In 5th
week
 Ureteric bud appears
 Outgrowth from the
dorsomedial side of caudal
part of mesonephric duct just
before its entrance into cloaca
 Penetrates the metanephric
tissue
 Covered by cap like investment
k/a metanephric blastema
 Distal end dilates- primordial
renal pelvis
 Splits into cranial & caudal
portions- major calyces

9.  Ureteric bud further undergoes 12 or
more generations of division until the
end of 5th
month
 Terminal branches form ampullated
dilated extremities
 Branches of 2nd
, 3rd
and 4th
orders–
absorbed– to form minor calyces
 All other branches from 5th
&
subsequent orders– persist as– 1-3
millions collecting tubules, renal pyramid

10. Excretory system
 Developed from
metanephric blastema
(metanephros)
 Induction by cells of
collecting tubules to
the metanephric
blastema form small
vesicles- renal
vesicles/metanephric
tubules

11. Renal vesicle
 S-shaped tubule
 Proximal end– bowman’s
capsule
 Capillaries/glomeruli grow into
the bowman’s capsule– renal
corpuscle
 Distal end– connects with
collecting tubule
 Distal end of S-shaped tubule-
lengthens- forms- proximal
convoluted tubule, loop of
henle, distal convoluted tubule
 Tubules + capillaries form
nephron/ excretory unit
 Capillaries and mesangial cells
derived from mesenchyme

12. Fetal kidney
• Subdivided into lobes
• Lobulation disappears during infancy:
 due to growth and increase in size of
nephrons
• Glomerular filtration begins at 9/10th
week
• Urine production begins at 10th
week
After birth
• Kidney increases in size
 elongation of the PCT
 increase of interstitial tissue
• Uriniferous tubule consists of two
embryologically different parts:
 nephron is derived from metanephric
blastema
 collecting tubule is derived from ureteric
bud

13. ASCENDS OF KIDNEY
• Initial- metanephric kidneys- closer to
pelvis, ventral to the sacrum
• Later- in abdomen- 9th
week
 Due to more growth of embryo
caudal to the kidneys
 Too small pelvic cavity
 Search of better nutrition
 Continuous lengthening of ureteric
bud
Rotation of kidneys:
 Initially hilum of kidney- ventrally
 As kidney ascends, it rotates
medially almost 900
 At 9th
week- hilum directs- antero-
medially

14. DEVELOPMENT OF URETER
• Ureteric bud-
origins from
mesonephric duct
• Elongates
• Forms the ureter
• Mucosa + muscular
layer + adventitia-
mesoderm from
mesonephric ducts

15. II CLASS

16. CLOACA
• Expanded terminal part of
hind gut lined by endoderm
• Divided into dorsal and
ventral parts by urorectal
septum
• Ventral part- urogenital sinus-
part of urinary and
reproductive system
• Dorsal part- rectum and anal
canal

17. • 7th
week- urorectal septum
fuses with cloacal membrane
& divides it into– ventral
urogenital membrane &
dorsal anal membrane
• Urogenital membrane-
ruptures- openings of urethra
(M&F) & vagina (F)
• Anal membrane- ruptures-
anus
• Area of fusion of urorectal
septum with cloacal
membrane- perineal body

18. UROGENITAL SINUS
Primitive urogenital
sinus- receives-
mesonephric ducts- 5th
week- divides it into
two parts:
a. Cephalic part- k/a
vesicourethral part
b. Caudal part- k/a
definitive urogenital
sinus

19. VESICOURETHRAL PART
Dilated upper part
Communicates
with allantois

20. DEFINITIVE UROGENITAL SINUS
Subdivided into:
a. Upper:
 Pelvic part
 Receives opening of
mesonephric ducts
b. Lower:
 Phallic part
 Closed below by cloacal
membrane
 Receives paramesonephric
ducts forming mullerian
tubercle

21. DEVELOPMENT OF URINARY BLADDER
 Vesicourethral part of urogenital
sinus except internal trigone
 Apex of bladder- proximal part of
allatois, distal part- obliterates-
urachus/ median umbilical
ligament
 Internal trigone- incorporation of
caudal part of mesonephric ducts,
later- overgrown by endoderm
from surrounding bladder wall
 Lamina propria, submucosa,
muscularis externa-
splanchnopleuric layer of lateral
plate mesoderm

22. DEVELOPMENT OF MALE URETHRA a. Prostatic part:
Above the ejaculatory ducts
 Dorsal wall-
mesonephric ducts
 Ventral wall-
vesicourethral part of
urogenital sinus
 Seminal colliculus-
mullerian eminence
 Prostratic utricle-
remnant of
paramesonephric/
mullerian ducts
Below the ejaculatory ducts:
 pelvic part of
urogenital sinus

23. b. Membranous
part: pelvic part
of urogenital sinus

24. c. Spongy part:
 Urethral groove
 At 4th
month- ectodermal
cells- tip of glans penis-
epithelial cord- later
acquire lumen- external
urethral meatus

25. DEVELOPMENT OF FEMALE URETHRA
Upper part-
vesicourethral
part of
urogenital sinus
Lower part- pelvic
and phallic parts
of urogenital
sinus

26. CONGENITAL ANOMALIES

27. Renal agenesis
• Ureteric bud fail to
develop
• Congenital absence of
kidney
• Two types:
a. Unilateral
b. Bilateral

28. Multiple kidneys
• More than one kidney
• Early splitting of ureteric bud
& metanephric blastema
Ectopic kidney/ Pelvic kidney
• Kidney fails to ascend
Fused kidney
• Sometimes kidney of one side
fuses with kidney of other
side
Lobulated kidney
• Persistent of fetal lobulations
Accessory renal arteries & veins
• Supernumerary renal arteries
above & below renal arteries

29. Horseshoe shaped kidney
• Lower poles of both kidneys are
connected by isthmus of kidney
• Ascent of kidneys are arrested
by inferior mesenteric artery
• At lower lumbar vertebra
Pancake kidney
• Also k/a disc kidney
• Complete fusion of both
kidneys across the midline
• Abnormal ascend of kidneys
with fusion
Floating kidney
• Suspended by a fold of
peritoneum from the posterior
abdominal wall

30. Mal-rotated kidney
• Failure of rotation or
abnormal rotation
• Hilum- faces- posterior,
anterior
Duplication of ureter
• Results from early
splitting of ureteric bud
• Splitting may be partial
or complete

31. Extrophy of bladder/
Ectopia vesicae
 Anterior wall of
bladder is deficient
 Interior of bladder is
exposed to the
infraumbilical part of
anterior abdominal
wall

32. URACHAL ANOMALIES
a. Urachal cyst:
 Obliteration of
allantois in proximal &
distal part leaving
central as a cyst
b. Urachal fistula:
 Persistent of allantois
 Urine appears through
umbilicus
c. Urachal sinus:
 Persitent of distal
part of allantois and
enlarge as a sinus

33. HYPOSPADIASIS
Opening of penile part of
urethra along the
undersurface of penis,
perineum
a. Balanic/ glandular
hypospadias:
 Urethra opens on the
undersurface of base of
glans penis
b. Penile type:
 Urethra opens on the
undersurface of body of
penis

34. c. Penoscrotal hypospadias:
 Urethra opens on the
undersurface of penis
and scrotum
d. Complete perineal
hypospadias:
 Complete failure of
fusion of genital folds
 Urethra opens on the
undersurface of whole
length of penis &
scrotum, perineum

35. EPISPADIAS
 Urethra opens on the
dorsal surface of
penis, close to the
anterior abdominal
wall

36. THANK YOU