The urinary system includes the kidneys and the ducts that carry away their product, urine. The genital system includes the gonads and their ducts that carry away the products they form, sperm or eggs. Embryologically, urinary and reproductive organs arise from the same or adjacent tissues and maintain close anatomical association throughout the organism’s life.

1. Succession of Kidneys
and
Evolution of Urino-
Genital Ducts
Dr. Manju Bhaskar
Assistant Professor
Department of Zoology
D. B. S. College Govind
Nagar
Kanpur Uttar Pradesh
India

2. Kidneys are built in accordance with a
basic pattern consist of
Glomeruli
RenalTubule
A Pair Longitudinal Duct

4. • Larval fishes
• Earliest vertebrate kidneys probably extended the
entire length of the body cavity and had external
glomeruli that drained the coelomic fluid.

5. Basic Components of
Craniate Kidney
• External Glomeruli : most primitive glomeruli are
suspended in the coelom surrounded by coelomic fluid,
which swept into peritoneal funnel, nephrostome.
eg embryos and larvae.
• Internal Glomeruli : glomeruli in adults are embedded in
the dorsal body wall and ensheathed by Bowman’s
capsule, the capsular cavity collects the glomerular
filtrate which passes into renal tubule.

7. Renal tubule originates from embryonic
nephrogenic mesoderm, lies lateral to
mesodermal somites and extends the length of
embryonic trunk from behind the head to cloaca

9. Pronephros
The earliest embryonic tubules arise from the cephalic end of
nephrogenic mesoderm.
Tubules are segmental, one pair at each segment.
In anamniotes they have association with external
glomerulus.
No of pronephric tubules : 3 in larval frog, 7 in human
embryos, 12 in chicks.
The distal end of first several pronephric tubule unite end to
end and establishes an opening into cloaca. This is pronephric
duct.

10.  Pronephric tubules are temporary, they loose
their connection with dorsal aorta and regress.
Pronephric duct does not regress.
Although pronephric tubules develop in all
craniates, they function only in embryonic ray
finned fishes and in larval agnathans, dipnoans
and amphibians.
In amniote embryos they are vestigial or lost.

13. Mesonephros
Pronephric duct act as inductor, additional tubules
develop in nephrogenic mesoderm behind the pronephric
region and establish an entrance into the existing
pronephric duct.
Fishes, amphibian and nonavian reptiles have open
nephrostome that usually close later in development.
Mesonephros become functional throughout life in fishes
and amphibians.
Functional embryonic kidney of amniotes.

14. Some of the anterior mesonephros tubules in male fishes
and amphibians become utilized to transport sperm from
the testis to mesonephric duct via substance of kidney.
Mesonephric tubules are vasa efferentia.
The region of adult male kidney is preempted for sperm
transport and known as sexual kidney, coiled part of
mesonephric duct is known as epididymis.
Accessory urinary duct supplement or even replace
mesonephric duct as carrier of urine.

15. During mesonephros establishment, when last
mesonephric tubules formed, earliest tubules already
regressed. 15.12
During the time of mesonephros functioning, a new
kidney metanephros is organizing, when metanephros is
able to function, mesonephros regresses.

19. Metanephros
Metanephros organizes from the caudal end of nephrogenic
mesoderm which becomes displaced cephalad and laterad during
development.
Differentiation of metanephric kidney commences when a hollow
metanephric bud sprouts from the caudal end of the mesonephric
duct.
The hollow stalk connecting the metanephros with embryonic
mesonephric duct becomes ureter.
Urinary channels form within the kidney and open into common
collecting tubules.
Meanwhile ‘S’ shaped renal tubules grows and encapsulates
glomerulus to form renal corpuscle and other end form collecting
tubule.
 Renal pelvis collects urine from common collecting tubules.

25. Mesonephric duct
Female : Gartner’s duct
Male :Vas deferens
Muellerian duct
Female : Reproductive tract
Male : Portions are retained

26. Reproductive Organs
The reproductive system includes the gonads, their
products, hormones and gametes, and the ducts that
transport gametes.
Gonads have two major functions :
Produce gametes
Synthesize steroidal hormones
Hormones requires for differentiation, growth and
maintenance of accessory sex organs (reproductive
ducts and their glands), secondary sex
characteristics.

27. Gonads arise as genital ridge
Thickening in the splanchnic mesoderm
Indifferent gonad
Gonads of both sex contain germ cells (sperm or ova)
In females germ cells resides in cortex
In males germ cells resides in medulla

28. Testes and Male Genital Ducts
Germinal epithelium lines the seminiferous tubules
where sperms are formed.
Vasa efferentia are mesonephric tubules which conduct
sperm to spermatic duct.
In most craniates with mesonephric ducts carry both
sperm and urine.
Hagfishes, lampreys, some jawed fishes and urodeles
lack seminiferous tubules.
Germinal epithelium may be on the surface of the testis or
deep within and primordial germ cells migrate into cyst
like seminiferous ampullae.
After breeding season cyst collapse.

29. In some fishes, a new sperm duct replace the
mesonephric duct as a carrier of sperm, marginal
canal.
Other fishes, amphibians, reptiles to humans, the
embryonic mesonephric duct remains in adult males
to carry sperm known as vas deferens.

32. Female
Genital Tract

33. Female genital tract consist of paired muscular and
glandular oviducts that commence at an ostium, open to
coelom, leads to neck to oviducal funnel.
Oviducts end in cloaca or a subdivision of it.
Any differences along the length of the tract are in the
degree of regional specializations that support species
specific functions such as collecting egg from coelom,
coating them with protective or nutrient substances,
temporarily housing eggs, embryos or larvae and
maintaining them until the eggs are shed or young are
delivered.
In craniates other than ray finned fishes, the female duct
system differentiates from a pair of embryonic Muellerian
duct.

34. Cyclostomes ovary lack oviducts, eggs are shed into
coelom
From coelom ova reach to cloaca (lamprey) or anus
(hagfish) through secondary pores
In elasmobranchs ovaries are initially paired, but in
some only one may develop

35. Muellerian duct develop in both, but do not perisist in males.
The Muellerian duct of Elasmobranchs and Amphibians arise
by longitudinal splitting of the pronephric duct and their ostia
develop from one or several pronephric nephrostomes.
In other craniates, each Muellerian duct arise as longitudinal
groove in the coelomic epithelium parallel to mesonephric
duct, which becomes tube like structure.

36. • The Mullerian duct or oviduct has 4 regions
Funnel : it collects eggs shed from the ovary, anterior end of
paired oviducts may fuse into single funnel
Shell gland : it stores sperm in most elasmobranchs,
secretes albumen and mucus.
• In oviparousspecies, the shell gland produces the egg case as well.
• In viviparous species, may be indistinguishable.
Isthmus : it connects shell gland to uterus.
Uterus : Nutritionallysupports embryos.
• Oviducts may join before they enter the cloaca, or they may enter
separately.
• The genital ducts of chimaeras are similar to those of sharks, except
the oviducts always share a common funnel and each oviduct opens
separately into the cloaca.

37. The Muellerian
duct of female
sharks’s give
rise to an
oviduct that
develops a
shell gland and
uterus

40. The lining of amphibian oviduct are richly supplied with glands
that secrete several layers of protective jelly envelops around
each egg as it moves down the tube.
Female tract of reptiles and monotremes mammals conform
closely to the basic pattern.
only one of the two embryonic Muellerian duct may
differentiate (crocodile and most birds).
Albumen gland line part of the oviduct and usually a shell gland
anterior to cloaca.
Albumen secreting area in fowl is known as magnum, shell
gland is a uterus and short glandular and muscular segment at
the base of entrance to the cloaca is vagina

41. Therian mammals
In other craniates, paired muellerian ducts in mammals
give rise to female genital tract commencing with the
ostium of the oviduct.
Muellerian duct of eutherian mammals unite at their
caudal ends to one degree or another.
The tract of eutherian mammals consist of two oviducts, a
uterus with or without horns (cornu) and a vagina.
Oviducts are short and small in diameter (microlecithal
egg), more or less convulated.
Oviducal funnel has a fringed border.

42. In some teleosts, such as salmonids, eggs released
from the ovaries fill the body cavity. Eventually they
reach short, funnel-like remnants of the oviducts
situated at the posterior part of the coelom. However,
in many teleosts, the oviducts regress entirely,
leaving egg transport to new ovarian ducts
Most teleost fishes lay eggs, but some bear live
young. Among these viviparous teleosts, maternal
tissues may nourish the embryo

43. Tetrapod
Amphibian ovaries are paired, hollow structures that
usually show a prominent cortex covered by germinal
epithelium. The genital ducts of female amphibians are
usually simple and consistent. The archinephric ducts
serve the Opisthonephric kidneys; the oviducts
(Müllerian ducts) serve the ovaries.

44. Amniotes
In amniotes, remnants of the mesonephros may persist in
larval stages, but adults have metanephric kidneys drained
exclusively by new paired ducts, the ureters (metanephric
ducts).
In females, the archinephric ducts are rudimentary. The
oviducts (Müllerian ducts) persist in their roles of transporting
ova from the ovaries and supporting the embryo while it is in
transit.
The tubular oviducts (Müllerian ducts) of amniotes often have
prominent sheets of smooth muscle within their walls and a
lumen lined by a secretory mucosa.
In oviparous amniotes, a shell gland may be prominent; in
viviparous amniotes the uterus may be distinct

45. Uterus
The uterus is the terminal portion of the oviduct.
Shelled eggs waiting to be laid or embryos completing their
development are held within the uterus.
In eutherian mammals and a few other vertebrates, the walls
of the uterus and extraembryonic membranes of the embryo
establish a close vascular association through a placenta.
Nutrients and oxygen are transported to the developing
embryo, and carbon dioxide is given up to the maternal
circulation via the placenta.

46. Uteri : Four types
Duplex : The muellerian duct of marsupials are paired all
the way to urino-genital sinus (subdivision of claoca).
Marsupials have two completely separate uteri and two
vagina. Eg. Kangaroos
Bipartite : a uterus with two horns may have totally
separate passageways within the body of the uterus, but
share a single cervix. Eg ruminants, cats horses.
Bicornuate : the uteri of eutherian mammals exhibit
varying degree of fusion distally (no partition in fused
portion, middle to post. part fused) eg. Dogs, pigs,
elephants, whale
Simplex : maximum fusion occurs in muellerian duct, in
which fusion commences at the ends of short oviduct and
there are no uterine horns eg primates (human )

47. Bicornuate : the uteri of eutherian mammals exhibit
varying degree of fusion distally (no partition in fused
portion, middle to post. part fused) eg. Dogs, pigs,
elephants, whale
Simplex : maximum fusion occurs in muellerian duct, in
which fusion commences at the ends of short oviduct
and there are no uterine horns eg primates (human )

50. References
KennethV. Kardong:Vertebrates : Comparative anatomy, Function,
EvolutionVth edition, McGraw-Hill Primis