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Fetal Development Fertilization This occurs when a sperm has penetrated the egg’s outer membrane This typically occurs in the Fallopian Tube of the female reproductive system Fertilization Once the egg and the sperm join, the cell that is produced (zygote) now contains 46 chromosomes The cell division that begins in the early stages is called cleavage and forms a blastocyst Fertilization When the zygote reaches the uterus, it implants in the endometrium and that is where it begins the rest of fetal development Development Four days after fertilization, the zygote becomes an embryo For pregnancy to continue, the menstrual cycle cannot happen - this is aided through the secretion of hormones Hormones! hCG (human chorionic gonadotropic hormone) maintains the corpus luteum for the first three months of pregnancy This is what pregnancy tests are looking for BACKTRACK The corpus luteum is found in the ovary and is secreting progesterone to help maintain the endometrium, prevent contractions, and firm the cervix... Back to Hormones! Progesterone and estrogen levels remain high and fluctuate throughout the pregnancy to ensure the endometrium is maintained If LH, estrogen, or progesterone levels fall, menstruation could be stimulated leading to a miscarriage What happens to the Reproductive System? Changes to the Reproductive System The blastocyst gives rise to the chorion and amnion The chorion produces hCG and will eventually contribute to the placenta The amnion becomes the amniotic cavity which is a fluid filled sac that insulates the embryo and protects it Changes to the Reproductive System The yolk sac forms beneath the embryo and is where early blood cell formation occurs and later becomes part of the digestive tract The placenta is formed from cells of the embryo and endometrium - this is the place where many wastes and nutrients are exchanged between the mother and the fetus Changes to the Reproductive System The placenta begins producing estrogen and progesterone around the second trimester (4 months) The placenta is richly supplied with blood vessels and the allantois provides umbilical blood vessels connecting the embryo to the placenta Embryonic Development Morphogenesis is the development of an organism (or part of it) During the first trimester, there are many changes to the embryo The blastocyst has flattened into a two layer disk by the second week Embryonic Development This two layered structure forms a three layered gastrula during gastrulation These three layers are very important and will each play a unique role later in development Embryonic Development Embryonic Development Ectoderm - outer layer Mesoderm - middle layer Endoderm - inner layer Embryonic Development By the end of the first month: ➔ ➔ ➔ ➔ four chambered heart has formed brain is visible buds for limbs have formed tiny fingers and toes have developed Embryonic Development By the second trimester, all the organs have formed (not fully developed) Organs begin developing in this trimester and a skeleton begins to form There is a small chance for a baby born at the end of the second trimester to survive Embryonic Development During the third trimester, the embryo is known as a fetus and is growing rapidly Abortions An abortion is the early termination of a pregnancy In Alberta, this can occur as late as 24 weeks (the end of the second trimester) 2 forms Medical Abortion - use of medication Surgical Abortion - use of a vacuum or medication Sex Determination Females have XX sex chromosomes while males have XY sex chromosomes The SRY (sex-determining region of the y chromosome) is responsible for determining male phenotype Sex Determination Hormone balance is essential during development Too much estrogen in the blood can lead to a male embryo with female characteristics while too much testosterone can lead to a female embryo with male characteristics Birth The process of labour is called parturition (the parting of the fetus from the mother) Relaxin is released from the placenta causing the cervix to soften and pelvic muscles to relax allowing the body to have a baby pass through it Oxytocin is released from the pituitary and stimulates uterine contractions Lactation During pregnancy, the breasts are preparing for the birth of the baby through milk production Prolactin is a hormone produced by the pituitary that stimulates the production of milk The milk is not released from the breast automatically - the suckling of the baby stimulates receptors allowing for release Oxytocin is also used here to stimulate muscle contractions of the milk ducts allowing for the release of the milk Lactation Breast feeding is a very important role of the mother if she can do it She passes on many antibodies and immunities to her child through her breast milk Mother’s need to be careful though because they pass on any toxins or medications in their bodies through breast milk as well