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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