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28 Cards in this Set
- Front
- Back
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What is I on the embryonic development and birth diagram?
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placenta
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What is II on the embryonic development and birth diagram?
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umbilical cord
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What is III on the embryonic development and birth diagram?
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amniotic sac
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What is IV on the embryonic development and birth diagram?
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amniotic fluid
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What is V on the embryonic development and birth diagram?
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uterus/ uterine wall
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What is VI on the embryonic development and birth diagram?
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cervix
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What is VII on the embryonic development and birth diagram?
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placental villi
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What is VIII on the embryonic development and birth diagram?
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intervillus space
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What are the major steps in the provess of fertilization IN ORDER?
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1. sperm swin to egg 2. acrosome reaction 3. penetration of egg membrane by a sperm 4. cortical reaction
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Where does fertilization normally occur?
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oviduct
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Describe the acrosome reaction
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1. When a sperm and egg meet, the contact causes enzymes in the acrosome of the sperm are released by exocytosis. 2. These hydrolytic enzymes digest through the glycoproteins that make up the zona pellucida (jelly coat) 3. Actin in the sperm extends to make the acrosomal process 4. Proteins on the tip of the acrosomal process bind to sperm-binding receptor proteins on the surface of the egg’s plasma membrane. (Results of acrosomal reaction: The sperm plasma membrane fuses with the egg plasma membrane and the sperm nucleus enters the egg. Opening of ion channels to depolarize membrate: fast block to polyspermy.)
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Describe what happens immediately following the penetration of the egg membrane by the sperm
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The sperm plasma membrane fuses with the egg plasma membrane and the sperm nucleus enters the egg. (Remember, the egg had to finish meiosis at this point, then they two haploid nuclei can join) Fusion of the sperm and egg membranes also causes ion channels to open, depolarizing the cell. This depolarization prevents additional sperm from entering the egg…called the fast block to polyspermy. It starts 1-3 seconds after fertiliztion and lasts about 1 minute.
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Describe the cortical reaction
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1. Fusion of sperm and egg membrane causes Ca2+ ions to be released by the ER. 2. Ca2+ causes the cortical granules to fuse with the plasma membrane. 3. Cortical granules release enzymes and other molecules into the perivitelline space (between the plasma membrane and the vitelline layer) 4. The enzymes and other molecules cause the vitelline layer to harden and push away from the plasma membrane. Also, the sperm-binding receptors are clipped off, causing any other sperm that may be attached to be released. These actions create the long-term slow block to polyspermy.
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What is the role of HCG in early pregnancy? Where is HCG made?
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HCG causes the continued production of progesterone during pregnancy, which is critical because it maintains the endometrium. HCG is made by the embryo after conception (and is what you look for in a pregnancy test). In the first trimester, HCG from the embryo maintains the corpus luteum, which makes progesterone. Beginning in the second trimester, the placenta makes make its own progesterone (and some HCG), so embryonic HCG production declines and the corpus luteum disintegrates.
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Outline early embryo development
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There are several mitotic divisions (without growth). First you get a solid ball of cells called a morula. Then you get a hollow ball of cells called the blastocyst (blastula), which is particularly important because it implants in the uterus. The gastrula and neurula are the next two stages.
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When does the embryo implant in the uterus?
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24-48 hours after fertilization…when the embryo is at the blastocyst stage
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Describe the structure of the placenta.
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The placenta is composed of maternal and fetal tissues. Maternal and fetal blood come into close proximity to permit efficient transfer of oxygen nutrients, waste, etc. by diffusion but maternal and fetal blood never mix. Fetal capillaries are within the placental villi (which increase surface area and therefore efficiency of transport). Maternal blood leaves open-ended vessels and goes into the intervillus spaces which surround the placental villi.
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What are the functions of the placenta?
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Materials are exchanged between maternal and fetal blood in the placenta. Secretes estrogen to maintain uterine lining; Secretes progesterone to maintain uterine lining; Allows for gas and nutrient exchange for the fetus; Removes waste products; Antibodies can cross placenta – allows for acquired passive immunity; Secretes HCG (stimulates the secretion of progesterone)
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What is the function of the amniotic sac and amniotic fluid?
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Support and protect the fetus; cushion and absorb shocks.
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Where are materials exchanged between maternal and fetal blood?
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Placenta
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Describe the process of birth
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In the first stage of birth (labor) involves a series of involuntary contractions of the smooth muscles of the uterus; Dilation/opening of the cervix; Breaking of the amniotic sac containing amniotic fluid (breaking of water); Delivery occurs as the baby is released through the birth canal (Vagina); Doctor will cut the baby’s umbilical cord; The afterbirth (placenta) is released from the uterus
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Describe the hormonal control of birth
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Labour is marked by contractions of the uterus. Decreased levels of progesterone and estrogen levels in the mother’s blood cause the release of oxytocin by the pituitary gland (progesterone inhibits labor). Oxytocin stimulates contractions. Pressure of baby’s head on the cervix causes increased nerve impulses from the cervix to the brain. This stimulates the release of more oxytocin (positive feedback)
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Describe positive feedback as it relates to birth
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Oxytocin causes contractions. This pushes the baby's head towards the cervix, causing more nerve impulses to travel from the cervix to the brain, which causes the release of more oxytocin. More oxytocin will cause contractions to become stronger and closer together. This causes more nerve impulses and thus more oxytocin release. The cycle of positive feedback continues until the baby is born
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Outline the process of in vitro fertilization (IVF)
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1. Egg Aspiration (Ovaries are stimulated hormonally to produce multiple follicles
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Outline the process of amniocentesis
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The follicles are harvested by sucking them out with a syringe ) 2. Insemination (The harvested eggs are mixed with sperm from the prospective father. If the quality of the sperm is poor, a sperm cell may be injected directly into the egg) 3. Incubation (The fertilized eggs are cultivated to the blastocyst stage) 4. Embryo transfer (The blastocysts are placed into the uterus of the female who will carry the children. Usually no more than 4 embryos are placed into the uterus at the same time. If one or more of the embryos implant successfully, a pregnancy will result)
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What is chorionic villus sampling?
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Prenatal test to look for disease; can be done earlier in pregrancy than amniocentesis; uses tissue from the placenta
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What are some ethical arguments against IVF?
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Fertilized egg has the potential to become a person…IVF requires the production of multiple eggs. Fate of extra embryos is an ethical concern; Ethics of long term storage; Stem cell research is blurring the issue as other cells now have the possibility of becoming a person; Procedure may result in multi-embryo pregnancy which places stress on the family (unwanted children); Issues of equal access as the procedure is expensive; ownership/responsibility for stored embryos; Religious opposition – are we playing God?
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What are some ethical arguments in favor of IVF?
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Only way some couples can have children; Allows for genetic screening; Allows for surrogate mothers
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