Lecture 6 -- Reproduction, Embryogenesis, MRP & Placentation

These flashcards cover the key concepts of reproduction, embryogenesis, maternal recognition of pregnancy, and placentation as discussed in the lecture.

What is the embryonic period in gestation?

Up to 20/30% of gestation.

What is the foetal period in gestation?

From 20/30% of gestation to parturition.

What is maternal recognition of pregnancy (MRP)?

A process by which an early conceptus signals its presence to the maternal system and prevents the lysis of the corpus luteum.

What is the mechanism of maternal recognition of pregnancy in ruminants (cattle & sheep)?

The blastocyst produces interferon → Blocks the synthesis of oxytocin receptors in endometrium → Prevent oxytocin induced PGF release from the endometrium to corpus luteum → No luteolysis

What is the mechanism of maternal recognition of pregnancy in pigs?

Embryo produce oestradiol → Re-route PGF into the uterine lumen = Prevent it from reaching the CL in ovaries → No PGF = No luteolysis

What is the maternal recognition of pregnancy signal in humans?

Developing blastocyst produces hCG → hCG has a similar structure to LH → Act on LH receptors in CL to prolong its life → Maintain progesterone levels

What is unique about maternal recognition of pregnancy in horses?

The blastocyst remains globular and migrates over the endometrial surface instead of elongating

What structures develop from the endoderm?

• Endocrine system

• Digestive system

• Lungs

What structures develop from the mesoderm?

• Muscle

• Skeleton

• Reproductive system

• Cardiovascular system

What structures develop from the ectoderm?

• Skin

• Hair

• Nervous system

Describe the formation of the yolk sac, amnion, chorion, and allantois during early embryonic development.

Hatched blastocyst: Inner cell mass, trophoblast & blastocoel

Step 1:

• Inner cell mass develops into embryo

• Primitive endoderm grows downward forming a lining on the inner surface of trophoblast → Yolk sac forms

Step 2:

• Trophoblast becomes trophectoderm

• Mesoderm beings to develop between primitive endoderm and the embryo

  • Continues to grow upward → Amnionic fold

  • Continues to grow downward, wrapping around the yolk sac

Step 3:

• Mesoderm push against the trophectoderm and fuse together → Form chorion

• Amnionic folds grow up around embryo

• Diverticulum from the primitive gut → Form allantois

Step 4:

• Yolk sac regress + Allantois continues to expand

• Allantois + chorion fuse = Chorioallantois/ Allantochorion

• Trophectoderm + mesoderm = Amnion + amniotic cavity

What is the allantoic cavity connected to?

Continuous with the bladder of the developing foetus

What is the functional part of the foetal placenta and its role?

Chorionic villus

• Finger-like projections that increase surface area for maternal–foetal exchange

What are the three types of placenta based on microscopic anatomy?

1. Epitheliochorial

2. Endotheliochorial

3. Haemochorial

What is an epitheliochorial placenta and in which species is it found?

• Layers: 6 layers (3 foetal + 3 maternal)

• Maternal layers: Endometrial epithelium, interstitium, capillaries

• Foetal layers: Chorionic epithelium, interstitium, capillaries

• Species: Horses, pigs, ruminants

What is an endotheliochorial placenta and in which species is it found?

• Layers: 5 layers (all foetal layers + 2 maternal layers)

• Maternal layers: Endometrial interstitium, capillaries

• Foetal layers: Chorionic epithelium, interstitium, capillaries

• Species: Carnivores (dogs, cats)

What is a hemochorial placenta and in which species is it found?

• Layers: 3 layers

• ONLY foetal layers; maternal tissue completely eroded

• Species: Humans and other primates

What are the types of placental distribution based on chorionic villi?

1. Zonary placenta

   • Band-like zone of chorionic villi

2. Cotyledonary placenta

   • Button-like chorionic villi

   • Commonly seen in cows and sheep

     • Cows: Convex chorionic villi

     • Sheep: Concave chorionic villi

3. Diffuse placenta

   • Uniformed distribution of chorionic villi

   • Commonly seen in horses and sows

Which factor regulates sexual differentiation in the embryo?

The SRY protein directed by a gene on the Y chromosome.

Describe the process of sexual differentiation regulated by SRY protein.

What outcome occurs if there is no SRY protein in the embryo?

The embryo will develop into a female with no AMH to degenerate the paramesonephric ducts.

What happens if a male is twinned with a female (freemartin phenomenon)?

Testis develop before the female ovaries → AMH and testosterone produced by sertoli cells of testis → As they are fat-soluble steriod hormone, they can cross the shared placenta, exposing the female twin to male hormones → Reproductive tract does not develop properly (Canalisation is not complete + Ovaries do not continue to grow)