|1 cell||8 Cell||Blastocyst||Enter Uterus||Length of|
|Ectoderm||1. Central nervous system
2. Sense organs
3. Mammary glands
|4. Sweat glands
|Mesoderm||1. Circulatory system
2. Skeletal system
|4. Reproductive systems
(male and female)
6. Urinary ducts
|Endoderm||1. Digestive system
5. Thyroid gland
6. Most other glands
7. Primordial germ cells
Function of Fetal Membranes and Fluids
|Yolk sac:||Early nutrient supply for early embryo.|
|Amnion:||Protects fetus from injury, provides lubrication for parturition, reservoir for urine and wastes.|
|Allantois:||Fuses with chorion (chorio-allantoic placenta), carries blood vessels of placenta, reservoir for nutrients and wastes. Umbilical cord attaches fetus to allantois.|
|Chorion:||Attaches to uterus, absorbs nutrients from uterus, allows maternal/fetal gas exchange, Produces hormones.|
Attachment of the placenta to the uterus. (Implantation)
Maternal Recognition of Pregnancy
|Establishment of Pregnancy||Sow||Mare||Cow||Ewe|
|Days of Estrous Cycle|
Placental lactogens (Protein Hormones)
High levels in the last 1/3 of gestation.
High levels facilitate higher milk production.
Placenta highly permeable to water and electrolytes i.e., stored in and exchange between allantoic and amniotic fluids.
Placenta converts glucose to fructose.
Fetal fat formed from fatty acids transferred across the placenta.
Fetus makes proteins from transferred amino acids.
Water soluble vitamins cross the placenta easier than fat soluble.
Minerals are transferred across the placenta.
Antibodies to fight disease do not cross the placenta - the newborn will get these antibodies from the first milk - Colostrum.
|Sheep||CL to day 50 then placenta||148 days|
|Cow||CL throughout gestation. However, after ~ day 215 placenta
and adrenal are producing enough progesterone to maintain pregnancy.
|Sow||All from CL||114 days|
|Mare||1st CL produces progesterone up to ~ 180 days, FSH stimulates follicle
growth and eCG causes CL's to form from follicles. They secrete
progesterone and are active from day 40-180. Progesterone is low until 270 days- rises in last 5 months due probably to placental progesterone production.
Mare Hormone Levels During Pregnancy