advanced reproduction physiology (part 4) isfahan university of technology college of agriculture,...
TRANSCRIPT
Advanced Reproduction Physiology
(Part 4)
Isfahan University of Technology
College of Agriculture, Department of Animal Science
Prepared by: A. Riasihttp://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
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
Ruminant have cotyledonary placenta.
Placentome consists of:
Fetal cotyledon contributed by the chorion
Maternal cotyledon, originating from caruncular
regions of uterus
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 formation
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
The placenta secretes progesterone and estrogen
Progesterone provides the stimulus for elevated
secretion by the endometrial glands
Progesterone inhibits myometrial contraction
(progesterone block)
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
Relaxin is also a product of placenta.
This 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
Placenta functions
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
Fetus ACTH
Placental estrogen Uterus PGF2α
Progesterone
Limited space for fetus Fetus hypothalamus
Fetus cortisol
Induction of parturition
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-pituitary-
adrenal 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
Physiology of parturition
Three stages of parturition are:
Initiation of myometrial contractions
Expulsion of the fetus
Expulsion of the fetal membranes
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
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
Physiology of parturition
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.