Gestation and Parturition

Gestation

Placenta

Placenta endocrine function

Parturition

Final preparation steps of reproduction

aquistion of endocrine function of the placenta

initiation of parturition

formation of a placenta

Placentas are classified according to the distribution of chorionic villi. These classifications are:

Zonary Screen Shot 2022-12-04 at 4.07.50 PM

discoid

Diffuse Screen Shot 2022-12-04 at 4.07.26 PM

cotyledonary Screen Shot 2022-12-04 at 4.08.03 PM

Diffuse placentas have uniform distribution of chorionic villi that cover the surface of the chorion. Example = pig

have a band like zone of chorionic villi. Example = dogs and cats

form a regionalized disc Example = rodents and primates

have numerous, discrete button- like structures called condyles Example = ruminants

Prefix = maternal side "epithelio" , Suffix = fetal side "Chorial", epitheliochorial

epitheliochorial= 6 layers, sow and mare Screen Shot 2022-12-04 at 4.10.57 PM

Endothelialchorial = 5 layers, dogs and cats Screen Shot 2022-12-04 at 4.11.04 PM

hemochorial = 3 layers, primates and rodents Screen Shot 2022-12-04 at 4.11.11 PM

The placenta secretes hormones that can:

influence fetal growth

stimulate mammary function

maintain pregnancy

assist in parturition

stimulate ovarian function

eCG in the mare Screen Shot 2022-12-04 at 4.15.00 PM

The placenta secretes progesterone and estrogens

placental lactogen (also called somatomammotropin)

three stages of parturition

Stage 2: expultion of the fetus

Stage 3: expulsion of fetal membranes

Stage 1: initiation of myometrial contractions (removal of progesterone block)

The fetus initiates stage 1 of parturition

Expulsion of the fetus requires strong myometrial and abdominal muscle contractions Screen Shot 2022-12-04 at 4.21.24 PM

expulsion of fetal membranes requires myometrial contractions