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1 Embryo Exam 1 Study Guide Quiz 1 Primary oocytes o Oogonia entering the first meiotic division late in the fetal period o Enter the diplotene stage of prophase I in the early months after birth Oogonia o Primordial germ cells during the second through fifth month of pregnancy undergo intense meiosis in the embryonic ovary o After meiosis they undergo atresia (degeneration) Primordial germ cells o Arise in the extraembryonic mesoderm near the base of the allantois o Become recognizable in the lining of the yolk sac o Migrate to the wall of the gut and the dorsal mesentery as they make their way to the gonads Occurs during 4th -5th weeks Multiply my mitosis during migration o Differentiate into oogonia or spermatogonia Spermatogonia o In males o Just before puberty primordial germ cells differentiate into these! Spermatocytes o Graffian follicles o tertiary (Graafian) follicle protrudes at the surface of the ovary (stigma) and sharp spike in LH from the pituitary leads to completion of meiosis I and ovulation. The completion of meiosis I now forms a secondary oocyte [1n, 2c], that is, half the number of chromosomes but they are double the DNA, still connected by a centromere. A polar body is produced and lies between the zona pellucida and egg. Meiosis II begins and arrested in metaphase II. About three hours will pass before ovulation. After ovulation, the Graafian follicle becomes a corpus luteum. Unless fertilization occurs 24 hours after ovulation, the egg will die. The layer granulosa cells still adherent to the zona pellucida is called the corona radiata. Puberty o For males, primordial germ cells continue to divide by mitosis throughout life or differentiate into spermatogonia just before puberty. 2 o Spermatogenesis begins in the seminiferous tubules of the male after the onset of puberty. Up to that time, spermatogonia maintain their population through mitosis of type A spermatogonia. After puberty, some type A give rise to type B spermatogonia that differentiate into primary spermatocytes and enter prophase I of meiosis but are not held at the diplotene stage, as are the oocytes. o Shortly before puberty the sex cords acquire lumens, becoming seminiferous tubules and at puberty primordial germ cells are transformed into type A spermatogonia [2n, 2c]. o At puberty and just before ovulation (egg breaks free from ovary), the process continues through diakenesis, metaphase I, anaphase I, and telophase I. o Early development of the follicle occurs without the significant influence of hormones, but as puberty approaches, continued follicular maturation requires the action of the pituitary gonadotrophic hormone folliclestimulating hormone (FSH) on the granulosa cells, which by this time developed FSH receptors on their surfaces. Late in the fetal period o oogonia enter the first meiotic division late in the fetal period, they are called primary oocytes At the time of ovulation o In the primary oocyte, the first three stages of prophase occur promptly, but shortly after birth the process is held in the diplotene stage until ovulation. The diplotene stage is where the homologous pairs exchange genetic material by crossing over at areas called, chiasma. At puberty and just before ovulation (egg breaks free from ovary), the process continues through diakenesis, metaphase I, anaphase I, and telophase I. After fertilization o At fertilization, for each of the 23 chromosomes (1n, 1c) donated from the egg there is a homologous (related and hopefully normal) chromosome donated from a sperm, and vice versa. When chromosomes condense during mitosis, each half of the pair is called a chromatid. So, after duplication of DNA, and just when anaphase begins, there are 92 (2n, 4c) chromatids in the dividing cell. This is still diploid, but with twice the DNA. After anaphase, each daughter cell is back to the 46 chromosomes (2n, 2c). Diplotene stage of prophase I o oocytes enter the diplotene stage of prophase I in the early months after birth Metaphase of meiosis I o ??? Diplotene stage of meiosis II o ??? Prophase of meiosis II o ??? Spermatid 3 o Primary spermatocytes give rise to secondary spermatocytes that will go through meiosis II to make spermatids, and finally, spermatozoa o Secondary spermatocytes complete meiosis II, becoming spermatids [1n, 1c], which shed excess cytoplasm, the residual body, and differentiate into spermatozoa. Spermatogenesis is divided into two parts. (1) spermatocytogenesis – spermatogonia up to spermatids, and (2) spermiogenesis – spermatids to mature sperm. Secondary spermatocyte o Primary spermatocytes pass through the blood-testes barrier (made by Sertoli cells) and complete meiosis I to become secondary spermatocytes [1n, 2c]. Secondary spermatocytes complete meiosis II, becoming spermatids [1n, 1c], which shed excess cytoplasm, the residual body, and differentiate into spermatozoa. o Metamorphosis of spermatids to spermatozoa includes: formation of and acrosome (an enzyme-filled structure important for fertilization) and a flagellum with mitochondria around its proximal part. The sperm cell has a (1) head with the acrosome and nucleus, (2) midpiece with the centrioles and proximal flagellum with the mitochondria, and (3) the tail. Mesoderm of the gonad Surface epithelial cells of the ovary Yolk sac endoderm Stroma of the ovary Theca interna Leydig Theca externa Sertoli Corona radiate Cumulus oophorus Stigma Residual body o Not part of a spermatozoon Head of spermatozoon Mouthpiece of spermatozoon Midpiece of spermatozoon Flagellum of spermatozoon Leydig cells Androgen-binding protein LH receptors Sertoli cells Testosterone Quiz 2 4 Gonadotropin-releasing hormone FSH Progesterone Androgens 10 days 19 days 28 days 36 days Zona pellucida Cumulus oophorus Theca interna Yolk sac Polar body Antrum Theca externa Granulosa cells Estrogens Testosterone Granulose lutein cells Corona radiata Trophoblast After egg is fertilized Several hours before fertilization In the late fetal period In the yolk sac Fimbria Infundibulum Ampulla Isthmus HCG LH Capacitation Spermiogenesis An acrosomal reaction Meiosis II Ovulation Fertilization Zona reaction 5 Morula Zygote Gamete Blastocyst Inner cell mass Outer cell mass Mittelschmerz Quiz 3 Trophoblast Morula Epiblast Embryoblast Hypoblast Cytotrophoblast Synctiotrophoblast Epiblast Chorionic cavity Amniotic cavity Exocoelomic cavity Lacunae Somatopleuric mesoderm Cytotrophoblastic Splanchnopleuric mesoderm Chorionic plate Endometrium/synctiotrophoblast Cytotrophoblast/synctiotrophoblast Synctiotrophoblast/endometrium Extraembryonic mesoderm/umbilical cord High levels of HCG Spotting 13th day of pregnancy Pain during ovulation Severe abdominal pain at about 6-7 weeks of gestation Quiz 4 Prechordal plate Notochord Yolk sac Cloacal membrane Chorionic cavity 6 Lacunae Exocoelomic cyst Buccopharyngeal membrane Allantois Blood flow Lefty-1 Dynein Fate map Cytotrophoblastic Synctiotrophoblastic Endometrial Mesodermal Primary villi Anchoring villi Tertiary villi Free villi Holoprosencephaly Sirenomelia Sacrococcygeal teratoma Immotile cilia Primitive node Primitive streak Quiz 5 The hypoblast Epiblast Cytotrophoblast Yolk sac Neural tube Posterior neuropore Neural crest cells Neural folds Anterior neuropore Gut tube Neural crest cells Enamel of teeth Dorsal root ganglia (sensory) Melanocytes Autonomic postganglionic nerve cells 7 Persistent truncus arteriosus Sacrococcygeal teratoma Sirenomelia Situs inversus Somatic mesoderm Extraembryonic mesoderm Visceral mesoderm Amniotic mesoderm Neuromeres Paraxial Lateral plate Somitomeres Dermomyotome Sclerotome Myotome Dermatome Splanchnic mesoderm Endoderm Somatic mesoderm Ectoderm Allantois Vitelline duct Oropharyngeal membrane Cloacal plate Notochord Mesoderm Embryonic period Fetal period Bilaminar period Trilaminar period