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Embryonic development and implantation

Embryonic development and implantation

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Embryonic development and implantation. Pregnancy. Preparation of uterus Steroid hormones Fertilization Coitus Gamete transfer Capacitation of sperms Fusion of gamates. Embryonic development Preimplantation Implantation Placentation Differentiation of cells Organogenesis. - PowerPoint PPT Presentation

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Page 1: Embryonic development and implantation

Embryonic development and implantation

Page 2: Embryonic development and implantation

Pregnancy

• Preparation of uterus– Steroid hormones

• Fertilization– Coitus– Gamete transfer– Capacitation of sperms– Fusion of gamates

Page 3: Embryonic development and implantation

• Embryonic development– Preimplantation– Implantation

• Placentation• Differentiation of cells• Organogenesis

Page 4: Embryonic development and implantation

• Must alter cyclic changes in the ovarian steroid hormones– Progesterone

• High • Must maintain the CL

– Most species– Some can maintain pregnancy without CL after

certain stage (placental progesterone)

Page 5: Embryonic development and implantation

Luteolysis• Destruction of the CL

– Reinitiation of reproductive cycle– Two types

• Active• Passive

• Active luteolysis– Production of luteolytic agent (PGF2)

• Uterus

• Passive luteolysis– Loss of luteotropic agents

Page 6: Embryonic development and implantation

• From ovary to uterus (and back to the ovary)– Positive feedback loop

• Uterine production of PGF2

• Production of oxytocin by the CL

– Ultimately leads to corpus luteum regression

• Reinitiation of reproductive cycle

PGF2

Progesterone

Oxytocin

PGF2

Page 7: Embryonic development and implantation

• Progesterone production by CL – Begins to decline. – Initiated by increased

production of PGF2

– Increased production of PGF2

• Ablated when pregnancy has been initiated, resulting in continued Progesterone production by the CL and pregnancy maintenance

PGF2

Progesterone

Pregnancy

Page 8: Embryonic development and implantation

Maternal recognition of pregnancy

• Two types– Anti-luteolytic

• Diversion of PGF2 secretion

• Inhibition of PGF2 secretion

– Luteotropic• Maintenance of the CL by providing necessary

hormone– Gonadotropin

Page 9: Embryonic development and implantation

Early embryonic development

• Zygote – Begins to divide as it moves through the oviduct towards the

uterus– Numbers of cells increase after each division

• The size of the embryo does not (cell size decreases by approximately 20 % after each division)

AmpullaIsthmus

Ampullary-isthmic Junction

Uterotubal Junction

Page 10: Embryonic development and implantation

Early embryonic development

• Cells of the embryo remain within the zona pellucida as they divide– The size of the nucleus increases– All chromosomes remain intact– In cows, the embryo divides three to four times (approximately one

division a day) while in the oviduct• Usually at the 16-cell or morula stage when it reaches the uterus

2-cell embryo 8-cell embryos

Page 11: Embryonic development and implantation

Early embryonic development

• Morula stage– All the cells of the embryo

are in a tightly packed clump – Cells on the inside of the

clump• Different from those on the

outside

• Cells inside begin to further pack themselves together and form a mass of cells called the inner cell mass (ICM), located at one end of the embryo

ICM

Blastcoele

Morula-stageembryo

Blastocyst-stageembryo

Page 12: Embryonic development and implantation

Early embryonic development

• The ICM – Develops into the fetus

• The outer layer of cells lining the zona pellucida– Trophoblast

• Placenta

– Formation of a fluid-filled cavity

• Blastcoele

• Blastocyst

ICM

Blastcoele

Morula-stageembryo

Blastocyst-stageembryo

Page 13: Embryonic development and implantation

Early embryonic development

• Cells in the ICM and trophoblast – Continue to divide– Blastacoele continues to

accumulate fluid

• Hatching– Floats freely until it

attaches itself within lumen of the uterus

Hatched blastocystZona

Page 14: Embryonic development and implantation

Attachment and establishment of pregnancy

• After hatching – Rapid growth and development phase.

• In cows, the blastocyst begins to rapidly elongate around 13 days after estrus, transforming from an ~3 mm spherical blastocyst into a long, thread-like form (around 25 cm in length) in 3 to 4 days

– The elongation of the bovine embryo• Due to rapid proliferation of trophoblast cells • Cells in the ICM divide slowly during elongation

ICM

ICM

Embryo

Placenta

Page 15: Embryonic development and implantation

Attachment and establishment of pregnancy

• Cattle and sheep– Attachment of trophoblast to the uterine wall

• Superficial with some fusion between uterus and trophoblast cells

Inner cell mass

Trophoblast layer

Uterine endometrium

Page 16: Embryonic development and implantation

Implantation and establishment of pregnancy

• Conceptus (embryo plus placental tissue)– Produces interferon-tau

(IFN-) as it elongates• Prevents production of

PGF2 by endometrium of the uterus

IFN-IFN-IFN-

IFN-

PGF PGFPGF PGF

PGF PGFPGF

PGF

Uterinevein

Non-Pregnant

PregnantConceptus

Endometrium

Uterine vein

Endometrium

Page 17: Embryonic development and implantation

• Diversion of PGF2 secretion

– Pigs• Non-pregnant

– Endocrine factor

• Conceptus– Divert secretion(exocrine)

– Estradiol• Increased production during 11-12 days post

coitus– Conceptus

Page 18: Embryonic development and implantation

• Diversion of PGF2 secretion– Local factor rather than systemic factor

• Conceptus must be present in both uterine horns

Page 19: Embryonic development and implantation

Secretion of luteotropic substances

• Species with passive luteolysis– Primates

• Secretion of glycoprotein hormone

– Syncytiotropoblast

• Human chorionic gonadotropin (hCG)

– Basis of pregnancy test

– Secretion begins around 10 days after ovulation

Page 20: Embryonic development and implantation

• hCG– Luteotropic hormone

• LH-like activity• Binds to LH receptors in the CL

– Maintenance of progesterone production– Increased lifespan during early stage of pregnancy

– Production• Peaks around 9 to 14 weeks of pregnancy

– CL loses its function during this time– Switch in steroidogenesis (placenta)

• Declines gradually thereafter

Page 21: Embryonic development and implantation

• Neuroendocrine system– Rodents and rabbits– Coitus as stimulus

• Physical contact• Physical stimulation of reproductive tract

(cervix)• Release of prolactin by the anterior pituitary

gland

Page 22: Embryonic development and implantation

• Neuroendocrine system– Prolactin

• Luteotropic hormone• Switch to placental hormones

– Placental lactogen

– CL• Eventually dies

– Steroid production by placenta

Page 23: Embryonic development and implantation

• Horses– Recognition of pregnancy

• Movement of embryo within the uterus– 12-14 times a day during day 12-14 of pregnancy– Eventual lock-down of the embryo

– Production of glycoprotein• eCG• Cause luteinization of the large follicle

– Formation of secondary CL

• FSH-like activity in other mammals

– Loss of both CLs• Placental progestigens

Page 24: Embryonic development and implantation

Placental steroidogenesis

• Cholesterol– Lipoproteins from circulation

• No De Novo synthesis

• Progesterone– Replace CL in some species

• Maintenance of pregnancy• Precursor for fetal adrenal steroids

Page 25: Embryonic development and implantation

• Estrogens– Limited production

• Limited 17-hydroxylase activity– Abundant in fetal adrenal gland

– Androgens from fetal adrenal gland• Converted to estrogens in the placenta

– Production of estriol rather than estradiol

– Secretion of estrone• Majority of placental estrogen in some species

Page 26: Embryonic development and implantation