Pre-Implanatation and Implantation

What is implantation?

• The process by which the blastocyst embeds itself to uterine lining (endometrium)

• To establish a connection for nutrient and waste exchange

• Between developing embryo and mother

What occurs if the embryo doesn’t implant properly?

Results in growth defects and death of embryo

What are the 4 stages of the pre-implantation period (0-12 days)

• Uterus structural and functional remodeling #4fdff6

• Migration of embryo #2a8fee

• Spacing of embryo (in multiparous species) #2b5ced

• Maternal recognition of pregnancy

Pre-Implantation Period: Utero Structural and Functional Remodeling (uterine receptivity) #4fdff6

• What are the 2 hormones that causes structural changes

  • In which phase released

  • What does it cause

Estrogen: Prepares uterus for pregnancy

• Released in: Follicular phase

• Builds and maintain endometrium

• Increase

  • Endometrium size

  • Cell number

  • Blood flow

  • Protein and enzyme content

Progesterone:

• Released in: Luteal phase

• Maintains and controls endometrium

• Allow embryo to stick/implant

• Stimulates growth of blood vessels that supply endometrium

• Stimulates glands in endometrium to secrete nutrients

Pre-Implantation Period: Migration of the Embryo #2a8fee

• Embryo migrates through and into

  • By

• Importance

Embryo migrates: Through oviduct and into uterine cavity

• By: Peristalsis

Importance: Allows embryo to reach site in uterus that is ready for implantation

Pre-Implantation Period: Spacing of Embryos #2b5ced

• Only occurs in

• To ensure

• Reduces

• Develop

Only occurs in: Multiparous species (species that give birth to more than 1 offspring; pigs, cats, dogs)

To ensure: Proper development and growth as all embryos have room and access to nutrients

Reduces: Risk of overcrowding

Develop: Embryos also develop individual placentas to allow efficient nutrient and gas exchange

Pre-Implantation Period: Maternal Recognition of Pregnancy

• What occurs

  • By

• To prevent

What occurs: Embryo signals presence to maternal system

• By: Producing specific chemical signals (IFNT) that are recognised by maternal body

Prevents: Regression of corpus luteum (uterine lining)

Implantation (Day 12-21) #b600ff

• What occurs

• What serves as attachment site for fetal membranes

• Typical site of implantation

• Different is horse, so where does implantation occur

• Types of implantation

What occurs: Hatched blastocyte moves through uterus and attaches to uterine wall

What serves as attachment site for fetal membranes: Caruncles that become large and vascularised only during pregnancy

Typical site of implantation: Uterine horns

Different is horse, so where does implantation occur: Uterine horns and body

Types of implantation:

• Invasive

• Non-invasive

Invasive Implantation

• Occurs in which species

• What occurs

• Pattern of implantation

• Phases

Occurs in: Rodents and primates

What occurs: Trophectoderm of blastocyst invade through uterine stroma

Pattern of implantation: Eccentric and interstital

Phases:

• Apposition

• Adhesion

• Invasion

Invasive Implantation

• What occurs in these phases of implantation:

  • Apposition

  • Adhesion

  • Invasion

Apposition:

• Blastocyst reach uterus

• Loosely aligns with endometrial epithelium (uterine lining)

  • But doesn’t attach firmly

Adhesion:

• Trophectoderm firmly attached to endometrial epithelium

Invasion:

• Trophectoderm cross luminal epithelium (LE)

• Invade stroma

• This establishes contact between maternal blood and embryo for nutrient and gas exchange

Non-Invasive Implantation

• Occurs in which species

• What occurs

• Pattern of implantation

• Phases

#1bd700

Occurs in: Domestic animals (cats, dogs, cow, sheep, goat, pig)

What occurs: Trophectoderm of blastocyst attaches to uterine epithelium without deeply invading the uterine stroma

Pattern of implantation: Centric

Phases:

• Apposition

• Adhesion (interdigitated microvilli)

Non-Invasive Implantation

• What occurs in these phases

  • Apposition

  • Adhesion

Apposition:

• Trophectoderm loosely aligns with endometrial epithelium

  • But doesn’t attach firmly

Adhesion:

• Interdigitated microvilli formed at interface between trophectoderm and uterine epithelial cells

• Microvilli from trophectoderm and uterine epithelial cells interlock with each other

• This facilitates nutrient and gas exchange while maintaining superficial attachment

Pattern of Implantation

• What

• Categorised based on

• Types

#9000ff

What: How the embryo attaches to and interacts with endometrium during pregnancy establishment

Categorised based on: Position and degree of invasion

Types:

• Centric #00c0ff

• Eccentric

• Interstitial

Centric Pattern of Implantation

• What occurs

• In what type of implantation

#00c0ff

What occurs: Blastocyst remains within central lumen of uterus and attaches to endometrium superficially

Type of implantation: Non-invasive (domesticated animals)

Eccentric Pattern of Implantation

• What occurs

• In what type of implantation

What occurs: Blastocyst becomes lodged in uterine cleft (crypts) with proliferation of surrounding uterine mucosa

Type of implantation: Invasive (rodents and primates)

Interstitial Pattern of Implantation

• What occurs

• In what type of implantation

What occurs: Blastocyst burrows through the uterine epithelium to the uterine stroma where the embryo develops

Type of implantation: Invasive (rodents and primates)

Establishing Maternal-Fetal Connection

• Embryo initially nourished by

• What is histotroph

  • Contains

  • What occurs as the embryo continue to grow

• Therefore to meet nutritional needs, what occurs

  • Allows

  • Occurs due to

Embryo initially nourished by: Histotroph (uterine milk)

Histotroph: Fluid secreted by uterine lining

• Contains: Nutrients and growth factors that support early embryo development

• As embryo continue to grow: Histotroph no longer sufficient to meet embryo’s needs for nutrients, oxygen and waste removal

Therefore: A close relationship between extraembryonic tissues (tissues outside embryo) and maternal circulatory system needs to be established

• Allows: Embryo to import maternal nutrients, oxygen and export waste products

• Occurs due to: Formation of the placenta