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Reproduction and Embryology Jess MckenzieLearning objectives:The Germ line ▶ Germ line = the population of cells that are responsible for passing on genetic material to the offspring (eg. sperm and egg cells) ▶ Primordial germ cell = cells that give rise to gametes ▶ In males: ▶ Present from birth, but only active after puberty ▶ Does not shut down with age ▶ In females: ▶ Exist only in foetal lifeWhich phase of meiosis are oocytes in when a female is born? A. prophase I B. metaphase II C. prophase II D. metaphase II E. anaphaseWhich phase of meiosis are oocytes in when a female is born? A. prophase I B. metaphase II C. prophase II D. metaphase II E. anaphaseSpermatogenesis ▶ = the production of spermatozoa in the seminiferous tubules of the testes Stage 1: Proliferation of germ line stem cells by mitosis Stage 2: Reduction to haploid state by meiosis Stage 3: Differentiation into mature spermatozoa (spermiogenesis)Question Which of the following describes the ploidy of primary spermatocytes? A. Haploid (N) B. Diploid (2N)Answer Which of the following describes the ploidy of primary spermatocytes? A. Haploid (N) B. Diploid (2N)Spermiogenesis Mature spermatozoa: ▶ nucleus becomes small and packed ▶ layers of the golgi apparatus fuse to produce the acrosome ▶ mitochondria rearrange around the developing flagellum ▶ any excess cytoplasm is phagocytosedSpermatogenesis: Hormonal control FSH -> Sertoli cells -> Spermatogenesis LH -> Leydig cells -> TestosteroneFolliculogenesis Pre-puberty Post pubertyWhich type of follicle is shown in the image? A. Primordial B. Primary C. Secondary D. AntralWhich type of follicle is shown in the image? A. Primordial B. Primary C. Secondary D. AntralOogenesis ▶ During the menstrual cycle, the pituitary gland releases a surge of LH ▶ This LH surge allows meiosis 1 to complete and meiosis 2 to begin, producing a mature oocyteFertilisation ▶ Oocyte enters fallopian tube ▶ Sperm enters female reproductive tract, allowing capacitation to occur Fertilisation 1. Acrosome reaction 2. Sperm burrows towards the egg, and reaches the egg membrane. 3. Waves of calcium.Artificial reproductive techniquesWhich artificial reproductive technique is shown by the image? A. ROSI B. Classic IVF C. ICSIWhich artificial reproductive technique is shown by the image? A. ROSI (Round sperm injection) B. Classic IVF C. ICSI (Intracytoplasmic sperm injection)Normal development - creation of the blastocystImplantationFormation of the placentaGastrulation Gastrulation = the process by which three germ layers are established Embryo is known as gastrula.The 3 germ layersDuring which weeks of development does gastrulation occur? A. Week 1 B. Week 3 C. Week 5 D. Week 7During which weeks of development does gastrulation occur? A. Week 1 B. Week 3 C. Week 5 D. Week 7Stem cells ▶ are undifferentiated cells capable of self-renewal and differentiation ▶ can be totipotent, pluripotent, or multipotentWhich of the following cells can be described as totipotent? A. Embryonic stem cells B. Zygotes C. Adult stem cellsWhich of the following cells can be described as totipotent? A. Embryonic stem cells B. Zygotes C. Adult stem cellsNeurulation ▶ Describes the formation of the neural tube during weeks 3-4, which goes on to form the CNS ▶ This arises from the neural plate, which is a thickening of the ectodermNeural tube defects occur when the neural tube does not fully close. Which of the following is not a neural tube defect? A. Spina bifida B. Anencephaly C. HydrocephalusNeural tube defects occur when the neural tube does not fully close. Which of the following is not a neural tube defect? A. Spina bifida B. Anencephaly C. HydrocephalusNeural tube defects ▶ Spina bifida = incomplete closure of the spinal cord ▶ Range of phenotypes ▶ Anencephaly = failure of closure in the brain ▶ Incompatible with post-natal lifeNeural tube defects A 25 year old woman comes in to the clinic as she has just had a positive home pregnancy test and is confirmed to be 5 weeks pregnant. She is given all the recommended advice but she says she does not want to take any supplements at this time. What is her baby currently most at risk for? A. Premature birth B. Cleft lip C. Cleft palate D. Spina bifidaNeural tube defects A 25 year old woman comes in to the clinic as she has just had a positive home pregnancy test and is confirmed to be 5 weeks pregnant. She is given all the recommended advice but she says she does not want to take any supplements at this time. What is her baby currently most at risk for? A. Premature birth B. Cleft lip C. Cleft palate D. Spina bifidaEmbryo vs Fetus Gestational age Conceptional age Embryonic period Weeks 5-10 Weeks 3-8 Fetal period Weeks 10 - 40 Weeks 8 - 38Sex differentiation Up to week 6/7 the embryos develop the same way (indifferent gonad).Development of females ▶ Described as the “default” pathway ▶ Requires the absence of testosterone and AMH ▶ Wolffian ducts regress and Mullerian remain ▶ MD go on to form the uterus, oviducts, cervix and upper vagina ▶ Oversimplification: requires other genes such as RSPO1, WNT4, DAX1, FOXL2 to maintain female pathway and silence male pathway Development of males ▶ Males are XY: Y chromosome contains the SRY gene ▶ SRY activates SOX9, which induces development of testes ▶ Leads to production of testosterone (Leydig cells) and AMH (Sertoli cells): ▶ Testosterone causes survival of wolffian ducts, which develop into vas deferens, epididymis, and the seminal vesicles ▶ AMH causes regression of Mullerian ductsDisorders of sex development (DSD) Genotype DSD Genotype Phenotype Turner’s syndrome XO ● Shorter stature ● Irregularity of periods or infertility ● Wide webbed neck Klinefelter's syndrome XXY ● May be asymptomatic ● Slight feminisation ● Infertility Complete androgen insensitiviXY ● Female phenotype ● No womb or ovaries, but fully or partially undescended testes ● InfertilityQuestion A 16-year old girl is brought to the clinic by her father because she has never had a menstrual period. Tanner stage 3. No axillary or pubic hair is seen. Pelvic examination shows a vagina that is about 2 cm in length. Pelvic ultrasound shows no uterus. What is the likely diagnosis? A. Turner’s syndrome B. Complete androgen insensitivity C. Partial androgen insensitivity Tanner scale (female)Question A 16-year old girl is brought to the clinic by her father because she has never had a menstrual period. Tanner stage 3. No axillary or pubic hair is seen. Pelvic examination shows a vagina that is about 2 cm in length. Pelvic ultrasound shows no uterus. What is the likely diagnosis? A. Turner’s syndrome B. Complete androgen insensitivity C. Partial androgen insensitivity Tanner scale (female)Congenital abnormalities ▶ Congenital disorders = structural or functional anomalies that occur during intrauterine lifeCongenital abnormalities Omphalocele (exomphalos) Cleft lip/palate Hypospadias Preterm births ▶ Any births that occur < 37 weeks of pregnancy ▶ mechanism ? ▶ Major global health issue ▶ Preterm birth complications are the leading cause of death among children under 5 years of age, responsible for approximately 900 000 deaths in 2019 ▶ Three-quarters of these deaths could be prevented with current, cost-effective interventions. 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