Chpt9_ANS3319CFetalplacentaLab_10 - ANS 3319C Reproductive...

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ANS 3319C Reproductive Physiology & Endocrinology Lab Early Embryonic, Placental, and Fetal Development Objectives 1) To develop an understanding of fertilization and early embryonic development in mammals. 2) To introduce the anatomy of the early developing embryo and fetal/placental unit by dissecting pregnant reproductive tracts. 3) To discuss the developmental and functional significance of the fetal /placental unit of the pregnancy in farm animals. Early Embryonic Development 1. Cleavage - Mitotic cell division of zygote without an increase in cell mass. Initial nutrients come from the cytoplasm with continued development being aided by oviductal and uterine secretions known as uterine milk. After the first cleavage, the cells are referred to as blastomeres. The blastomeres of the early developing zygote are totipotent, meaning that they are capable of giving rise to an intact embryo. Once the zygotes reach the eight to sixteen cell stage, they are called morulas. Table 13-1 Timing of pre-attachment embryogenesis relative to ovulation within females of various species. Non- bolded values are in the oviduct. Bold values in the shaded area are in the uterus; (-) = no data Species 2-cell 4-cell 8-cell Morula Blastocyst Hatching Gestation Length (mo) Bitch 3-7 d - - - - 13-15 d 2 Cow 24 h 1.5 d 3 d 4-7 d 4-10 d 9-11 d 9 Ewe 24 h 1.3 d 2.5 d 3-4 d 4-10 d 7-8 d 5 Mare 24 h 1.5 d 3 d 4-5 d 6-8 d 7-8 d 11 Queen - - - 5 d 8 d 10-12 d 2 Sow 14-16 h 1.0 d 2 d 3.5 d 4-5 d 6 d 3.8 Woman 24 h 2 d 3 d 4 d 5 d 5-6 d 9 2. Blastocyst Formation Embryo starts to develop into two distinct cell populations: Inner cell mass gives rise to the embryo proper. Trophoblast forms the chorion of the placenta. Blastocyst expansion is a result of cellular hyperplasia and fluid accumulation. Results in the formation of the blastocoele (fluid-filled cavity). Zona hatching - release of blastocyst from the zona pellucida. Day 8 to11 of gestation. 3. Blastocyst Elongation Rapid growth of the conceptus occurs during the second week of gestation. Elongation is logarithmic and filamentous. By day 18 of gestation, the blastocyst has extended into the contralateral uterine horn. Cattle and sheep - elongation is slow and takes days to finish. Pig - elongation is very rapid and occurs within a couple of hours. o Pig embryos can become as long a meter in length. Horse - does not elongate but increases in diameter 2 to 3 mm per day. o Embryo become large and spherical like a baseball
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ANS 3319C Reproductive Physiology and Endocrinology – Early Embryonic, Fetal, and Placental Development 2 4. Differentiation - The period of development where the embryo forms specific tissue layers that
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Chpt9_ANS3319CFetalplacentaLab_10 - ANS 3319C Reproductive...

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