Transcript Reproduction - Animal Sciences Home Page

Reproduction
Female
http://trc.ucdavis.edu/mjguinan/apc100/modules/Reproductive/mammal/female.html
• The reproductive system of female
mammals consists of the:
– ovaries,
– oviducts,
– uterus,
– vagina, and
– external genitalia (vulva, etc).
Overview
• The compact ovary contains thousands
of ovarian follicles, of which a few at a
time rapidly go through several stages
of maturation before ovulation.
• The ova is transported to the uterus via
the oviduct where, if fertilized, it
implants, forms a placenta, develops,
and is delivered via the vagina.
Overview-continued
• The entire duct system is lined by
epithelia with regional specializations.
• There are a variety of species
differences in the shape of the uterus,
and the type of placentation that
supports the embryo.
• In contrast to the male, the urinary tract
uses separate ducts until reaching the
vestibule of the vagina.
Mammal, female
The mammalian female reproductive tract consists of paired ovaries
and a multi-part duct system.
Vestibule
The vestibule is the terminal part of the duct system. It is shared
with the urinary system
Vagina
The vagina is a thick-walled fibromuscular tube that extends from
the cervix to the vulva. The walls consist of a mucosa, muscularis,
and adventitia.
The urethra from the urinary bladder joins with the reproductive
duct in female mammals.
Cervix
The cervix is a muscular valve which separates the vagina from
the uterus. It may produce a mucus plug during infertile periods.
Uterus - body
The body of the uterus is the site of implantation and development
in primates.
Uterine horns
Uterine horns provide additional space for the young to implant
and develop. The length of the uterine horns varies between
species, and may be nearly absent in primates.
Oviduct (fallopian tube)
The uterine (fallopian) tube carries the ova to the uterus.
Infundibulum
The infundibulum is the initial part of the duct system
Ovaries
The ovaries are the female gonads. They produce the ova.
Ovaries
• Produce 1 ova per cycle in cow
• Produces 12-20 ova per cycle in sow
• Produces 1-3 ova per cycle in ewe
• The bovine uterus has
two horns.
• Both ovaries are shown
and the one on your left
has a corpus luteum
present.
• Developing follicles may
be seen as little bumps
on the surface of the
ovary on the right.
Uterus
The uterus, with layers called endometrium,
myometrium and perimetrium, respectively.
Cervix
CERVIX. The cervix acts as the valve of the reproductive tract.
It separates the vagina from the uterus and is usually closed
except during estrus and parturition.
Ovaries
• OVARY/FOLLICLE. The two ovaries in
mammals are the site of oogenesis,
production of the female gametes.
• In most mammals the OOGONIA have
formed primordial follicles at the time of birth.
These primordial follicles will go through
several developmental stages until a mature
follicle ruptures, expelling the ovum.
• The ovaries also produce hormones
important to reproductive cyclesand
pregnancy.
Ovary (canine)
Primordial follicles
Primary follicles
• The PRIMARY FOLLICLE develops from the
primordial follicle and is characterized by
several layers of follicular cells surrounding
the oocyte. The follicular cells become more
cuboidal and secretory in appearance and
are referred to as granulosa cells. At this time,
a clear layer of extracellular material, called
the zona pellucida, can be seen around the
oocyte.
• PRIMORDIAL FOLLICLE. In most mammals the
OOGONIA have formed primordial follicles at the time
of birth. It is generally believed that all of the
primordial follicles that are going to develop are
present at the birth of the animal. The primordial
follicle is a single egg or oocyte surrounded by a
single layer of flattened cells called the follicular cells.
Many of the follicles will not develop and will undergo
a gradual breakdown or atrophy: this process is
called atresia and the follicles are said to be atretic.
Secondary follicles
• SECONDARY FOLLICLES develop from
primary follicles and are characterized by the
formation of an antrum.
– The antrum is a fluid-filled space which begins as
a number of small spaces between the granulosa
cells.
– As the several spaces unite into a single fluid-filled
chamber, the oocyte remains on a mound of
granulosa cells, the cumulus oophorus, to one
side of the follicle.
– A layer of granulosa cells remains surrounding the
oocyte.
– The cells secrete the female sex steroids.
Regressing CL’s
• The corpus luteum
forms from the cells
of the theca interna
and the granulosa
cells under the
influence of the
pituitary luteinizing
hormone.
• Blood vessels and connective tissue
grow into the luteal cells to form an
endocrine gland which secretes
progestins.
• Hormones from the corpus luteum will
support fetal development during
pregnancy.
• Afterwards it will become a scar (corpus
albicans).
Bovine ovary, with CL
Bovine ovary medium & high magnification
Estrous Cycle
• Begins with puberty
• Prepares the female for pregnancy
• 4 periods to cycle
– Proestrus
– Estrus
– Metestrus
– Diestrus
• Proestrus
– follicular development from FSH
– Estrogen increasing
Estrus
• Female sexually receptive (standing
heat)
• estrogen levels high
• length ~ 12 hrs to several days
• surge of LH & FSH
• Ovulation late or following estrus
Metestrus
• CL (corpus luteum) forms
• Produces progesterone
Diestrus
• If pregnanacy occurs, CL remains
– progesterone high
• if no pregnancy, prostaglandin from
uterus causes CL regression
Species cycle heat
time of
time to
d
hr
ovulation
mate
------------------------------------------------------------------------Cow
21 12-18 12-15 hr post-E 4-8 after E END
Sow
20-21 48-72 18-40 h after
1st d & again 2nd
start of estrus
Ewe 16-17 24-36 18-26 h after start 12-18 after start
Goat 19-20 34-39 9-19 h after start alternate days
Mare 19-23 90-170 1d before to 1 d alternate days
after estrus
Estrous Cycle Review
• Development of
Follicle from FSH
• Ovulation, from LH
surge
• CL Develops
– progesterone
– keeps animal preg.
• CL regresses
– to corpus albicans
– cycle begins again
• ANESTRUS
– period of no cycling
• Polyestrous vs
seasonally
polyestrous
– cow vs sheep
HORMONES - review
– GnRH
• hypothalamus
• controls LH & FSH
– FSH
• stimulates follicle
– LH
• triggers ovulation &
CL
– Estrogen
• from follicle, prepares
for preg.
• Progesterone
– from CL
– prevents further cycling
– maintains pregnancy
• Prostaglandin (Pf2)
– regresses CL
PREGNANCY
• Length of Pregnancy, days
– cow 282,
– sow 114,
– ewe 150,
– mare 336,
9 mo, 12 days
3 mo, 3 wk, 3 days
5 mo
11 mo +
• Sperm combines with ovum
• ONLY 1 sperm can enter ovum
• Cell divisions start
– sometimes split, forming identical twins
• Fertilization takes place in oviduct
• Fertilized ovum moves down to uterine
horn (or uterus) for implantation
Placentation
• After implantation into the uterine
endometrium, the developing embryo
becomes surrounded by the chorionic,
amniotic, and allantoic membranes.
• In fish and birds these same
membranes allow diffusive exchange of
of CO2 and O2 with the environment,
while nutrients are provided by the yolk
sac.
• In mammals, nutrients and wastes are
exchanged with the maternal circulation
across a specialized region of these
these membranes called the placenta.
• The placenta provides a large surface
area of close association between the
two independant circulations for
diffusive and carrier mediated
exchange.
• In addition the placenta produces
hormones to support the pregnancy.
• The gross arrangement of the placenta
may be diffuse, zonary discoid, or
cotyledonary, depending on the species.
Bovine placenta
Allantoic
sac
Amniotic
sac
Bovine placenta
Fetal cotyledons are seen on the surface of the chorioallantoic membrane
which attach to the maternal caruncles (maternal cotyledons) to provide
for gas and nutrient exchange. The fetal cotyledon is shown here with
villi, which develop off the surface of the chorio-allantoic membrane
and grow into sulci of the maternal caruncle.This interdigitation is the
site of blood gas and nutrient exchange. (There is no mixing of blood
between the fetus and the mother.)
Parturition (giving birth)
•
•
•
•
Placenta produces more estrogen
Causes prostaglandin from uterine wall
Regression of CL, reduced progesterone
RELAXIN causes pelvic muscles,
ligaments to ‘loosen’
• PROLACTIN stimulates milk synthesis
• Oxytocin stimulates & strenghtens uterine
contractions
Difficulties at Birth
• Orientation at birth
–
–
–
–
–
rear first
one leg back
head twisted
too large
inadequate
contraction strength
– too long a birth
process
• stillborn
• Membranes cover
nose, prevent
breathing
• Retained placenta
• Abnormal bleeding
• Premature births
Female Reproduction Review
• The ovaries contain a large number of
follicles, of which a few rapidly mature
during each cycle. The theca and
granulosa cells proliferate as each
follicle develops from a primordial, to
primary, to secondary, to mature follicle
(Graafian) which releases the oocyte
and then transforms into a corpus
luteum and later a corpus albicans.
• The ova move into the first part of the
uterine tube (oviduct, fallopian tube)
where fertilization may take place.
Implantation and embryo development
occurs in the uterus which has a
nourishing, glandular epithelia
(endometrium) surrounded by smooth
muscle (myometrium).
• The uterus of some species have
elongated horns or a dividing septum.
• The placenta developes from portions of
the fetal membranes (chorion, amnion
and allantois) that contact the
endometrium. The close association of
the independent maternal and fetal
blood supplies allows diffusive
exchange of nutrients and wastes.
• The muscular cervix separates the
uterus from the vagina, and produces a
thick mucus.
• If pregnancy results, the CL remains
and produces progesterone,
maintaining pregnancy. If not, the CL
regresses and the cycle begins anew.
Repro in BIRDS
• The form of the reproductive tract of
female birds is in some ways simlar to
that seen in mammals: ova produced in
the ovary are fertilized in the proximal
oviduct and progress though the uterus
and vagina.
• As in mammals the oviduct is lined by
an epithelia surrounded by smooth
muscle. However the function of various
portions of the tract are quite different
from mammals.
• Along the various parts of oviduct the
different componants of the eggshell are
formed. The process takes about 25
hours in a chicken.
• The completed egg with shell is passed
to the outside world via the cloaca, the
shared terminal portion of the
reproductive, urinary and
gastrointestinal tracts.
• Embryo development largely occurs
outside the mother. Gaseous exchange
occurs through the shell while nurients
are provided by the yolk.
1. Infundibulum
2. Ovary
3. Ovum
4. Magnum
5. Isthmus
6. Uterus
7. Vagina
8. Cloaca
• The egg is in the isthmus for about 1.5
hours where it receives the shell
membranes.
• The egg occupies the uterus for about
20 hours. During the first 8 hours most
of the activity is the addition of water,
leading to a doubling of the weight of
the albumen. During the last 12 hours,
the shell is calcified by the secretion of
calcium from the glands.
• It takes about 24 hours for an egg to
travel from the infundibulum to the
vagina.
• The vagina has a muscular wall. Their
purpose is to move the egg rapidly out
of the reproductive system .
Bird male
• The proximal portions of the male bird
reproductive system is quite similar to
mammals. It consists of testes
containing seminferous tubules which
produce sperm with the help of
interstitial and sertoli cells.
• The spermatozoa travel via efferent
ductules to the epididymis,and then on
to the ductus deferens.
• The bird is different from most
mammals in that the testes are located
in the abdominal cavity (and therefore
subject to the high body temperature of
birds).
• In addition, the bird lacks a penis; the
ductus deferens deliver sperm to the
cloaca, which are transfered to the
vagina during mating.
Bird Reproduction Review
• The female bird has a single functional
ovary which produces the ova.
• The oviduct consists of five parts. Fertilization
occurs in the infundibulum, where sperm are
stored. The protein coat of the egg is added
during the 3 hour passage through the
magnum. The shell membranes are added by
the keratin secreting glands of the isthmus.
Water is added and the shell is calcified during
the 20 hours spent in the uterus. The vagina
adds a waxy coating and serves as a sperm
storage site.
• The testes of the male are within the
abdominal cavity and operate at higher
temperatures than those of most
mammals.
• Each testes produces sperm in the
seminiferous tubules under the
influence of interstitial and sustentacular
cells.
• The sperm are transported via the
efferent ductules, epididymes, and
ductus deferens to the cloaca.
• The cloaca is a common terminal
passage for the reproductive, urinary,
and digestive tract in both male and
female birds.
• The reproductive tract enters the cloaca
at the urodeum.