Isfahan University of Technology
College of Agriculture, Department of Animal Science
Advanced Reproduction
Physiology
(Part 4)
Prepared by: A. Riasi
http://riasi.iut.ac.ir
Placentation, the Endocrinology of
Pregnancy and Parturition
Reference: Pathways to Pregnancy and Parturition (Second revised edition)
By: P. L. Senger, 2005
Placenta formation
 The
phenomenon of intrauterine development
ensures that the developing conceptus will
receive adequate nutrient and protection during
its development.
Placenta formation
 The
placenta is a transient organ of metabolic
interchange between the conceptus and dam.
 It
is also a transient endocrine organ.
 The
placenta in composed from two parts:

Fetal component derived from the chorion

Maternal component derived from modifications of
the uterine endometrium
Placenta formation
 The
functional unit of the fetal placenta is the
chorionic villus.
 Specific

of mare placenta:
It has many specialized microzones of chorionic villi
known as microcotyledons

It contains unique transitory structure known as
endometrial cups.
Placenta formation
Placenta formation
 Ruminant
have cotyledonary placenta.
 Placentome
consists of:

Fetal cotyledon contributed by the chorion

Maternal cotyledon, originating from caruncular
regions of uterus
Placenta formation
The migrating binucleate giant cells (BGC) in the ruminat placenta
Placenta formation
 The

characteristics and functions of BGC:
They are quite large and two nuclei originated from
trophoblast cells.

They are formed continuously throughout gestation.

The BGC migrate from the chorionic epithelium and
invade the endometrial epithelium.
Placenta formation
 The

characteristics and functions of BGC (continue):
They are believed to transfer complex molecules
from the fetal to maternal placenta.

These cells secrete pregnancy specific protein B
(PSPB) and placental lactogen.
Placenta functions
 The
placenta regulate the exchange between
fetus and dam.

Placental exchange ways:

Simple diffusion

Facilitated diffusion

Active diffusion
Placenta functions
 Placental
transportation:

Gases

Water

Minerals and vitamins

Glucose and Amino Acids

Proteins

Lipids
Placenta functions
 Placental

transportation (continue):
Large peptide hormones (TSH, ACTH, GH, insulin,
glucagon)

Smaller molecular weight hormones (steroids, T3 and
T4) and catcholamines

Toxic substances

Bacteria and viruses
Placenta functions
 In
addition to serving as a metabolic exchange
organ, the placenta serves as a transitory
endocrine organ.
 Hormones
from the placenta gain accesss to both
the fetal and the maternal circulation.
Placenta functions
 The
placenta produces hormones that can affect:

Stimulate ovarian function

Maintain pregnancy

Influence fetal growth

Stimulate mammary function

Assist in parturition
Placenta functions
Placenta functions
Placenta functions
Placenta functions
 The

placenta secretes progesterone and estrogen
Progesterone provides the stimulus for elevated
secretion by the endometrial glands

Progesterone
inhibits
(progesterone block)
myometrial
contraction
Placenta functions
Placenta functions
 In
addition to progesterone, estrogens are also an
important product of the placenta.

The placental estrogens are particularly important
during the last part of gestation and in most species
signals the early preparturient period.
Placenta functions
 The
placenta produce placental lactogen or
somatomammotropin.
 This
hormone have two major effect:

Promoting the growth of fetus

Stimulating the mammary gland of the dam
Placenta functions
Placenta functions
 Relaxin
 This
is also a product of placenta.
hormone is produce in some species:

Humans

Mares

Rabbits

Pigs and monkeys

Cats and dogs
Placenta functions
 Relaxin
cause:

Softening of the connective tissue in the cervix

Promotes elasticity of pelvic ligaments
Physiology of parturition
 The
fetal hypothalamo-pituitary-adrenal axis is
obligatory for initiation of parturition.
 During
the conclusion of gestation, fetal mass
approaches the inherent space limitations of the
uterus.
Physiology of parturition
Limited space for fetus
Fetus cortisol
Fetus hypothalamus
Fetus ACTH
Placental estrogen
Uterus PGF2α
Induction of parturition
Progesterone
Physiology of parturition
Plasma cortisol concentration changes during sheep gestation (Yuen et al. 2004)
Physiology of parturition
 Prepartum
increase in sheep circulating cortisol
is required for the differentiation and maturation
of key fetal organs:

Lung

Liver

Kidney

Brain
Physiology of parturition
A
positive relationship between the level of
activation of the fetal hypothalamus-pituitaryadrenal axis and leptin synthesis and/or secretion
in late gestation.
Physiology of parturition
 The
endocrine changes cause two major events
to occur:

Removal of the myometrial “progesterone block”
enabling myometrial contractions to begin

Increased reproductive tract secretions particularly by
the cervix
Physiology of parturition
 Three
stages of parturition are:

Initiation of myometrial contractions

Expulsion of the fetus

Expulsion of the fetal membranes
Physiology of parturition
 Effect
of fetal corticoids:

Converting progesterone to estradiol

Synthesizing PGF2α by placenta

As both estradiol and prostaglandin become elevated, the
myometrium becomes increasingly more active

The CL of pregnancy regress
Physiology of parturition
Physiology of parturition
Physiology of parturition
Relative hormone profiles in the cow during the periparturient period
Physiology of parturition
Physiology of parturition
Physiology of parturition
 Follistatin
and activin
may be also involved in
the
mechanism
of
natural parturition
(Xia et
al. 2009)
Physiology of parturition
 In
pre-parturition period birth canal is lubricated
by:

Mucus secretion in cervix and vagina

Fetal membrane rupture and loss of amniotic and
allantoic fluid
Physiology of parturition
 As
the fetus enters the birth canal, it becomes
hypoxic
 Hypoxia
promotes fetal movement that, in turn,
promotes further myometrial contraction
Physiology of parturition
 In
most
species,
expulsion
of
the
fetal
membranes quickly follows expulsion of the
fetus
 It
is believed that vasoconstriction of arteries in
villi reduces pressure and thus allows the villi to
be release from the crypts
Physiology of parturition
 Prolonged
parturition can result in serious
complications to both the fetus and dam.
 Different
causes for dystocia:

Excessive size of fetus

Failure of proper fetal ritation

Multiple births in monotocous species
Some research papers associated to this lecture
1. Leibovicha, H., et al. 2001. Effects of recombinant ovine placental lactogen and
recombinant ovine growth hormone on growth of lambs and milk production of ewes.
Livestock Production Science 68: 79–86.
2. Probo, M., et al. 2011. Peripartal Hormonal Changes in Alpine Goats: a Comparison
Between Physiological and Pathological Parturition. Reprod Dom Anim 46: 1004–
1010.
3. Leury, B. J., et al. 2003. Effect of insulin and growth hormone on plasma leptin in
periparturient dairy cows. Am. J. Physiol. Regul. Integr. Comp. Physiol. 285: 1107–
1115.
4. Murawski, M., et al. 2011. Cortisol, progesterone and estradiol secretion in vitro in
postpartum placental cotyledons of ewes that gave birth to single or twin lambs. Ann.
Anim. Sci., 11: 53–60.