Urogenital System
Updated 4 November 2004
Urogenital
A. Urogenital (Excretory + Reproductive) develops embryonically
from same or adjacent tissues; maintain close morphological association
throughout ontogeny; slide 1
(urogenital ridge)
B. Kidney develops
first (functional; reproductive later)
C. Reproductive
system takes over parts of excretory system
A. Functions: excrete
nitrogenous metabolites, osmoregulation (water
balance)
B. Functional unit -
uriniferous tubule; slide 2
1. Structure
a. glomerulus (arteriole, capillary bed); high pressure filter
b. nephron (renal capsule, proximal, intermediate & distal
convoluted tublules); selective reabsorption
c. collecting
tubule; common collection and transport
2. Development -
gross morphology of kidney conservative (reflects phylogeny)
a. nephrotome (=intermediate mesoderm - segmental); slide 3
b. anterior®posterior
development; complexity (# tubules/segment) increases
A. Kidney types
(tripartite model); slide 4
1. Pronephros (functional in larval fishes & amphibians, adult
hagfish, and a few adult teleosts)
a. few
tubules/segment
b. short-lived (head
kidney)
c. connected to coelom (nephrostome =peritoneal funnel)
d. initiates duct
formation (archinephric =pronephric
duct); slide 5
e. tubules
degenerate (duct remains)
2. Mesonephros (embryonic only)
a. elongate
(functional in most)
b. not connected to coelom
c. modified in most
adult nonamniotes (opistonephros;
“extended” mesonephros)
d. trends:
concentrate function in more posterior portions (anterior portions incorporated
into reproductive system), increased # tubules/segment
e. degenerates in amniotes
f. tubules tap on to
existing archinephric duct (=mesonephric
duct); slide 5
g. mesonephric duct transports sperm in males (=vas deferens), degenerates
in females
3. Metanephros (amniotes)
a. concentrated at
extreme posterior (bird - last segment); at level of pelvis - move anterior
later (cf position in cat)
b. complex
(thousands of tubules/segment)
c. not connected to coelom
d. ureter (metanephric duct); slide 5
D. Structure and function (microstructure of uriniferous tubules reflects physiological function; readily adaptive – cf gross morphology)
1. Freshwater
fish/amphibians (physiological problem: hyposmotic -
too much water)
a. little drink,
water and salt in (gills, mucous membranes)
b. excrete
continuously
2. Marine teleosts (problem: hyperosmotic -
too little water)
a. drink, salt
intake
b. excrete
occasionally; also urea excreted by gills
c. salt glands
3. Marine hagfish, elasmobranchs, coelacanths (isosmotic
- osmocomformer)
a. little drink
b. gills impervious
to urea (water in)
c. salt glands
4. Terrestrial
vertebrates (problem - limited water)
a. loose water
through lungs, skin, excretory wastes; gain water primarily through drinking
b. conservation of
water primarily through kidneys
c. excretory
products (breakdown of proteins and nucleic acids)
1) ammonia (highly
toxic, highly soluble); excreted by kidneys, gills, and most mucous membranes
in many aquatic forms where water is not limiting
a) e.g., fishes,
amphibians, turtles, crocodilians
2) urea (relatively
non-toxic, highly soluble; converted from ammonia)
a) e.g., amphibians,
some turtles, mammals
b) some birds and
all mammals able to concentrate urine (cf blood; long
nephrons with specialized intermediate portion
(looped) – man reclaims 169 of 170 l/d (~45 gal)
c) birds w/o loops?
(kidneys are like those of reptiles)
d) concentration
varies (e.g., vampire bat vs. K-rat [25X cf blood])
3) uric acid (non-toxic,
insoluble [does not exert osmotic pressure – sequester]; costly to convert)
a) e.g., many
reptiles, birds; marine species (limited water)
b) often with
associated salt glands (nasal, crocodile tears)
5. Summary (phylogenetic, adaptive, acclimation effects) – slide 6
A. Life cycles
(vertebrates - diplontic)
B. Sexual
reproduction (recombination alternating with meiosis)
1. Parthenogenetic (some fish, salamanders, lizards)
2. Gonochoristic (separate sexes)
3. Hermaphroditic
(hagfish, some teleosts)
a. simultaneous:
common in deep-sea fishes
b. sequential: protogyny (F®M; 14 families)
c. protandry (M®F; 8 families)
d. some normally M
or F vertebrates have potential for developing opposite sex
4. Embryology:
undifferentiated®differentiated
(all vertebrates have potential for developing into either sex [early in
mammals])
a. examples: toads
(Bidder’s organ [undifferentiated gonad®ovary])
b. chicken (1 ovary
+ 1 undifferentiated gonad)
1. Gonads (produce
gametes – eggs/sperm)
2. Ducts (transport
gametes within body)
3. Copulatory organs (transfer sperm to female)
a. claspers, gonopodium (fin ray)
b. hemipenes, penis (erectile tissue, bone)
4. Secondary sexual
characters (vertebrates often sexually dimorphic; often important in sexual
behavior, e.g., courtship)
1. Female ovary
a. discrete or
diffuse, subject to seasonal change in size
b. cyclic oogenesis slide 7
c. modifications for
elongate bodies (fusion, deletion, ant-post positioning)
3. Ducts
a. agnathans - no ducts (abdominal pores); also some teleosts
b. most other males
- closed system derived from embryonic excretory system; testis (seminiferous tubules)®efferent ducts®epididymis®vas deferens
c. most other
females - open system derived from embryonic excretory system and mullerian duct; ovary®coelom®oviduct
1. Ovisac (dilation, egg storage) – fishes
2. Jelly gland
(albumin) - amphibians
3. Shell gland
(albumin, shell) – amniotes
4. Uterus -
muscular, glandular (cyclic growth) slide 13
5. Vagina -
reception of penis (mammals)
D. Termination of
ducts (both sexes); cloaca
1. Embryonic cloaca (proctodeum, urodeum [=U-G sinus], coprodeum, urorectal septum); DRAW
2. Adult structure –
highly variable
3. Cloacal differentiation in embryonic mammals slide 14
A. Fertilization
(transfer of sperm)
1. External
(behavioral rituals; amplexus [frogs], cloacal apposition [birds])
2. Internal (behaviorial [salamanders - spermatophore],
or structural [copulatory organ])
3. Amniote [shelled egg] - must be fertilized early
Chondrichthyes |
10 |
Reptilia |
>100 |
Osteichthyes |
12 |
Aves |
0 |
|
Amphibia |
4 |
Mammalia |
1 |