Repro 7: Embryo transport, implantation, and establishment of pregnancy

Zona pellucida

Where does the blastocyst hatch from?

Embryo

• Organism in early stages of development

  • Has not acquired an anatomical form that is readily recognizable in appearance as a member of a specific species

Fetus

Potential offspring that is still within the uterus but is generally recognizable as a member of a given species

Conceptus

• Product of conception

  • Includes the embryo during the early embryonic stage

  • Includes the embryo and extraembryotic membranes during the preimplantation stage

  • Includes the fetus and placenta during the post-attachment stage

Embryo

What does the conceptus include during the early embryonic stage?

Embryo, extraembryonic membranes

What does the conceptus include during the preimplantation stage?

Fetus, placenta

What does the conceptus include during the post-attachment stage?

Implantation

Synchronized development of preimplantation embryo and establishment of receptive uterus

Estrogen and progesterone

What hormones regulate implantation?

Epithelial cells, stromal cells

Uterine cell types

Epithelial cell proliferation

Role of estrogen in implantation

Decidualization (stromal cell differentiation)

Role of progesterone in implantation

Decidualization

Stromal cell differentiation

Apposition, adhesion, invasion

Stages of implantation

Ruminants, pigs, horses

Which species only go through the apposition and adhesion stages of implantation?

Primates, rodents, carnivores

Which species go through all three stages (apposition, adhesion, invasion) of implantation?

Before luteolysis

When must maternal recognition of pregnancy occur if the pregnancy is to be maintained?

PGF2alpha, oxytocin

Maternal recognition:

Episodes of ___ that cause luteolysis do not occur because endometrial ___ receptor synthesis is blocked.

Progesterone

Which hormone is required to maintain a pregnancy?

Corpus luteum

Which structure is the source of progesterone during the early stages of pregnancy?

Placenta

Which structure secretes progesterone during the later stages of pregnancy?

Production of anti-luteolysin, production of luteotropin

Two strategies to extend lifespan of CL (strategy is chosen based on species)

Ruminants, pigs

Which species produce anti-luteolysin to extend the life of the CL?

Humans, primates, rodents

Which species produce luteotropin to extend the life of the CL?

IFN-tau

Anti-luteolytic signal of ruminants

Blocks oxytocin receptor in uterus to maintain pregnancy

Estrogen

Anti-luteolytic signal of pigs

Non-pregnant cycling sow

Endocrine secretion of PGF2alpha

Pregnant sow

Exocrine secretion of PGF2alpha

True

True or false?:

We do not know what the signal of horses is that causes them to prevent luteolysis and maintain pregnancy.

Chorionic gonadotropin (CG)

Luteotropic signal of primates

Prolactin, placental lactogens

Luteotropic signal of rodents

None

Pregnancy recognition signal of dogs and cats

Successful implantation

Synchronization of embryonic development to blastocyst stage and receptive uterus

B

The cells lining the lumen of the uterus are:

A) Stromal cells

B) Epithelial cells

C) Decidual cells

D) Fibroblast cells

B

Which of the following structures of the oviduct captures the ovulated oocyte?

A) Isthmus

B) Infundibulum

C) Ampulla

D) Uterotubal junction

B

Which signaling molecule is crucial for maternal recognition of pregnancy in ruminants (e.g. cows, sheep)?
A) Estrogen

B) Interferon tau (IFN-tau)

C) Oxytocin

D) Relaxin

B

Which structure must the blastocyst break free from during hatching?

A) Cytoplasm

B) Zona pellucida

C) Trophoblast

D) Endometrium

A

If an antibody to hCG is given during the first month of pregnancy, the pregnancy will be aborted. What is the explanation for this reason?

A) hCG stimulates the function of the corpus luteum.

B) hCG binds to progesterone receptors in the uterus.

C) hCG stimulates the secretion of LH from the pituitary.

D) The excitability of the uterine smooth muscle is inhibited by hCG.

B

What is the primary mode of movement for the embryo through the oviduct?

A) Active swimming

B) Ciliary action and muscular contractions

C) Gravity

D) Blood circulation

B

What is the primary effect of interferon tau (IFN-tau) in ruminants?

A) It stimulates uterine contractions.

B) It prevents prostaglandin F2alpha (PGF2alpha) secretion.

C) It induces ovulation.

D) It promotes fetal bone development.

D

In which of the following is the embryo deeply embedded in the endometrium?

A) Horses

B) Cows

C) Dogs

D) Humans

B

Fertilization of the oocyte usually occurs in which region of the oviduct?

A) Infundibulum

B) Ampulla

C) Isthmus

D) Uterotubal junction

C

In horses, what is the unique feature of maternal recognition of pregnancy?

A) The blastocyst hatches twice before implantation.

B) The placenta produces oxytocin instead of the pituitary gland.

C) The embryo must migrate throughout the uterus to prevent luteolysis.

D) hCG is secreted by the corpus luteum instead of the placenta.

D

Which of the following is produced by the trophoblast cells during the first three weeks of pregnancy in primates?

A) Estrogen

B) Luteinizing hormone

C) Oxytocin

D) Human chorionic gonadotropin (hCG)

B

Uterine receptivity for implantation is regulated by:

A) Peptide hormones

B) Steroid hormones

C) Prostaglandins

D) All of the above

D

Differentiation of uterine stromal cells to decidual cells is dependent on:

A) LH receptor

B) FSH receptor

C) Estrogen receptor

D) Progesterone receptor

A

IFN-tau is synthesized in the ruminants by the:

A) Embryonic cells

B) Uterine epithelial cells

C) Uterine stromal cells

D) Uterine immune cells

B

In pigs, how does the embryo prevent luteolysis and support implantation?

A) Secretion of interferon tau (IFN-tau)

B) Production of maternal recognition signal via estrogen secretion

C) Deep invasion of the endometrium

D) Blocking oxytocin receptors

B

After fertilization of an ovum, the successful development of an embryo depends on:

A) Implantation of the fertilized ovum in the oviduct

B) The maintenance of the corpus luteum

C) The maintenance of elevated pituitary LH level

D) The maintenance of elevated FSH level

B

What structure of the embryo is primarily responsible for implantation?

A) Inner cell mass

B) Trophoblast

C) Zona pellucida

D) Amnion

D

How does estradiol in pigs contribute to maternal recognition of pregnancy?

A) It converts the corpus luteum into the placenta.

B) It signals the pituitary gland to maintain LH production.

C) It stimulates embryo implantation directly.

D) It redirects prostaglandin F2alpha (PGF2alpha) secretion into the uterine lumen, preventing luteolysis.