Pregnancy and parturition · Pregnancy and parturition Vibuntita Chankitisakul Advanced Animal...
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Pregnancy and parturition
Vibuntita Chankitisakul Advanced Animal Physiology (137739)
4 steps must be achieved before embryo can attach to the uterus
1. Development of embryo within confinement of the ZP
2. Hatching of the embryonic cells (blastocyst) from the ZP
3. Formation of extra embryonic membranes (e.g placenta)
4. Maternal recognition of the pregnancy
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1. Development of embryo within confinement of the ZP
http://www.fao.org/docrep/004/t0117e/t0117e07.htm
2.Hatching of the embryonic cells (blastocyst) from the ZP
http://www.ajog.org/article/S0002-9378%2808%2900805-3/abstract
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http://www.sciencedirect.com/science/article/pii/S0968432812001539
3. Formation of extra embryonic membranes (e.g placenta)
http://www.medicine.mcgill.ca/physio/vlab/other_exps/endo/reprod_horm.htm
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Classification Based on Placental Shape and Contact Points
The number of layers of tissue between maternal and fetal vascular systems.
4. Maternal recognition of the pregnancy
• For pregnancy, luteolysis must be prevented (CL must be maintained)
• Two major events have to take place:
1) PGF2α synthesis and secretion must be stopped
2) Progesterone must be maintained
• The conceptus must provide a biochemical signal to dam (before luteolysis)
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In cows
Recognition of Pregnancy in Bovine and Ovine
Conceptus Secretions • Interferons
•oIFN-t •bIFN-t
Mechanism •Antiluteolytic
• Inhibit oxytocin receptor synthesis
• Inhibit PGF2a synthesis
Critical Days • Bovine - 16 to 17 • Ovine - 12 to 13
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In pigs
http://www.jasbsci.com/content/pdf/2049-1891-4-23.pdf
Recognition of Pregnancy in the Porcine
PGF2a
PGF2a
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PGF2a
PGF2a PGF2a
PGF2a
E2
E2
E2
E2
E2
E2
Recognition of Pregnancy in the Porcine
Conceptus Secretions
• Estrone sulfate
Critical Days
11 to 12
Mechanism
•Antiluteolytic
»Redirect PGF2a
»Requires 2 embryos per horn
PGF2a
PGF2a PGF2a
PGF2a
E2
E2
E2
E2
E2
E2
Recognition of Pregnancy in the Porcine
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http://www.webpages.uidaho.edu/avs-222/word/Embryo%20development.pdf
HORMONAL CHANGE DURING PREGNANCY
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Mean (± SEM) jugular plasma progesterone concentrations in pregnant, cyclic and inseminated non-pregnant heifers during an 18-day period
http://www.fao.org/wairdocs/ilri/x5442e/x5442e04.htm#2.2.3%20endocrinology%20of%20pregnancy
http://www.fao.org/wairdocs/ilri/x5442e/x5442e04.htm#2.2.3%20endocrinology%20of%20pregnancy
Mean (± SEM) jugular plasma progesterone concentration in zebu cattle during pregnancy
P4 from placenta & adrenals (D120-D250) P4 from CL
Not response to PGF2alpha
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Hormonal changes during pregnancy(human)
Chorionic gonadotropins • stimulating the gonads, similar to the pituitary gonadotropins.
• The only species known to produce a placental gonadotropin are primates and equids.
• In human: is called human chorionic gonadotropin or simply hCG.
– is produced by fetal trophoblast cells.
– binds to the luteinizing hormone receptor on cells of CL, which prevents luteal regression.
– Thus, hCG serves as the signal for maternal recognition of pregnancy.
• Equine chorionic gonadotropin is also produced by fetal trophoblast cells. It is actually the same molecule as equine luteinizing hormone.
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PARTURITION
Fetal control of parturition
• fetus controls time of parturition due to stress response : – lack of space
– lack of gas exchange
– lack of nutrients
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Hormonal pattern during parturition
Hormonal changes at the end of gestation
Fetal pituitary - hypothalamus axis essential • increased stress from fetal nutritional demands and placental insufficiency • Hypothalamus release CRH (Corticotropin releasing hormone) • Anterior pituitary in turn releases ACTH
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Fetal adrenal gland • in response to ACTH releases cortisol (corticosteroids) –effects of cortisol on fetus
»Lung produces surfactants »liver increases storage of glycogen »thyroid increases metabolism
–effects of cortisol on placentome »shift from progesterone to estradiol production »progesterone decreases »estrogen increases »PGF increases
Hormonal changes at the end of gestation
Placentome hormones
• estradiol –increase gap junctions in myometrium
»leads to better co-ordination and communication among muscle cells in the myometrium
»begin to get coordinated contractions toward the cervix
–increase in uterine oxytocin receptors
–primes cervix to response to relaxin
–stimulates ovary to secrete relaxin and oxytocin
–acts with PGF to trigger CL regression
Hormonal changes at the end of gestation
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Placentome hormones
• PGF –regression of CL –synthesis and release of oxytocin and relaxin from ovary (in some species relaxin from placenta) –stimulates most of the contractions in the uterus
Hormonal changes at the end of gestation
• progesterone
–shift from progesterone to estrogen production leads to its decrease from the placentome
–PGF stimulates luteolysis so progesterone from CL decreases
–release from "progesterone block“
• Oxytocin • stimulates final contractions of uterus but only once fetal head enters cervix
Hormonal changes at the end of gestation
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• Relaxin • comes from ovary or placenta
• synthesis stimulated by PGF
• stimulates softening of the cervical connective tissue to cause dilation
• promotes elasticity of the pelvic ligaments
Hormonal changes at the end of gestation
LACTATION
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Physiological effects of prolactin
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Regulation of prolactin secretion
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Milk Let-Down • Neuro-hormonal reflex • The suckling stimulus or massaging of the udder stimulates somatic nerves in
the teat, which send a signal to the posterior pituitary gland and causes the release of the hormone oxytocin.
• Oxytocin causes the myoepithelial (muscle) cells around the alveoli to contract. • For efficient milking, there are several important factors to remember.
– Stimulate 1 min before milk let-down – The maximal effect of oxytocin occurs during tfirst 2 to 3 minutes of milk let-down.
– Stress during cow preparation or during milking will inhibit oxytocin release. – Inhibition of oxytocin release