Development in Utero - 1

What are the two stages of development from zygote?

1. embryonic period

2. fetal period

Embryonic Period

• 0-42d

• starts with formation of zygote after fertilization

• morulation → blastulation → gastrulation

• ends with formation of basic structure of organs

Fetal Period

• 43-278d

• growth, maturation, remodelling or organs

• ends with birth of offspring

Totipotent

• can differentiate into any type of embryonic or extra-embryonic cells

Blastulation

• totipotent blastomeres differentiate into ICM + trophoblast

Multipotent

• cells capable of differentiation into any type of cell within a certain lineage (placental OR fetal)

Pluripotent

• can differentiate into type of cell in the embryo

Trophoblast

• multipotent

• placental lineage

Inner Cell Mass (ICM)

• pluripotent

• differentiates into hypoblast + pluripotent epiblast

Gastrulation

• epiblast differentiates from 1 layer of cells → 3 somatic germ layers (mesoderm, ectoderm, endoderm)

• lengthening of conceptus occurs at this time

• bilaminar disk → trilaminar disk

Trilaminar Disk

• ectoderm + mesoderm + endoderm

What does the ECTODERM differentiate into?

• neural plate → develops into brain, spinal cord (nervous system)

• skin, hair, external part of repro tract

What does the ENDODERM differentiate into?

• GIT, lungs, endocrine system

What does the MESODERM differentiate into?

• muscle, skeleton, cardiovascular system, urogenital system

Oogenesis

• trophoblast + hypoblast + part of mesoderm → extra-embryonic membranes (placenta)

How is the spine created?

• neural groove (within neural plate) closes and forms neural tube

What regulates the growth in # of cells during gastrulation?

• under epigenetic control

What occurs after gastrulation?

• 3 layers → various cell types (outline of most organs)

• this is the end of the embryonic period

How does fetal growth occur?

• linearly

How does body mass growth occur?

• exponentially

Final Growth Stage

• occurs right before parturition

• partitioning of nutrients from mother and fetus

What factors effect variability in birth weight and postnatal performance?

• genetics of dam + embryo (breed)

• type of embryo

• health + nutrition

• maturity of dam

• infectious disease

• environmental stress + gestation length

• litter size

Fetal Programming

• differences in postnatal life as a consequence of events in utero

• can effect meat quality later in life