Vertebrate Development Chapter 60

Transcription

2 Stages of Development Fertilization requires that sperm and egg interact to form a zygote(fertilized Cell)--(2N: diploid= 46 chromosomes in humans). a. Sperm has three parts. 1) Head haploid(1 N=23 chromosomes in humans) contains nucleus covered by a cap-like acrosome containing enzymes allowing sperm to penetrate egg. 2) Middle piece contains ATP-producing mitochondria. 3) Tail is flagellum that allows sperm to swim. Activation Events initiated by sperm penetration. - Sharp increase in metabolic activity. Nuclei Fusion - Third stage of fertilization is fusion of the entering sperm nucleus with the haploid egg nucleus to form the diploid nucleus. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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4 Embryonic Development Development includes all changes that occur during life cycle of an organism. 2. An organism is an embryo during first stages of development. 3. Most go through same embryonic stages: zygote, morula, blastula, early and late gastrula. 4. Yolk is dense nutrient material. 5. After fertilization, a zygote undergoes cleavage, cell division without growth. 6. DNA replication and mitosis occur repeatedly; cells get smaller each division. 7. Because the lancelet has little yolk, the cell divisions are equal in the resulting morula. (size: ~ 32 cells large) 8. A cavity called blastocoel develops forming hollow ball called blastula. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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7 Embryonic Development 9. Gastrulation is invagination of some cells into blastocoel to form three primary germ layers. a. Middle mesoderm begins as outpocketing of the primitive gut. 1. The outpocketings grow and fuse, forming two layered mesoderm. 2. Space between them is the coelom that contains the body organs. 3. Mesoderm gives rise to skeleton, dermis of skin, skeletal system, muscular system, excretory system, reproductive system (including most epithelial linings), and outer layers of respiratory and digestive systems. b. Outer layer of cells becomes ectoderm; it gives rise to epidermis of skin, epithelial lining of mouth and rectum, and nervous system. c. Inner layer of cells becomes endoderm that gives rise to epithelial lining of digestive tract and respiratory tract, associated glands of digestive system and respiratory system, and lining of urinary bladder. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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10 How Cells Communicate During Development Nature of Development Decisions Some cells become determined as to what type they will be early in development. At some stage, every cell s fate becomes fixed (commitment). - Not irreversible, but rarely reverses under normal conditions. Those cells that are not committed yet (stem cells) Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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12 Development Process Development requires growth, differentiation, and morphogenesis 1. Cellular differentiation occurs when cells become specialized in structure and function. (Differ into types of 220 cells) 2. Morphogenesis produces a change in shape and form of a body part; includes cell movement and pattern formation. 3. Each body cell contains full set of chromosomes; so differentiation is not due to parceled out genes. 4. Cells in adult body are totipotent: cells capable of expressing their entire genome (could form any type of cell). 5. Only red blood cells produce hemoglobin, etc.; therefore there is differential gene expression in each cell Multipotent: can give rise to several versions of a certain cell type Ex: multipotent blood cell can give rise to several types of blood cells but not brain cells. Pluripotent: can give rise to serval types of cells but not all Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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14 Human Embryonic Devlopment First Trimester: 4 th Week - Organ Development (Organogenesis). Human gestation period is 9 months, calculated by adding 280 days to start of last menstruation. Only about 5% of babies arrive on forecasted date due to many variables. Most women not yet aware of pregnancy. (fetal alcohol) Most fetal damage is from environment not genetics!!! Second Month - Morphogenesis Limbs take adult shape; Major organs become evident. Embryo is about one inch in length. Third Month - Completion of Development Now referred to as fetus. - Nervous system and sense organs develop. - All major organs established. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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21 Second and Third Trimesters Second Trimester - Growth Bone formation occurs. Covered with fine hair (lanugo). By the end of the sixth month, baby is one foot in length. Third Trimester - Pace of Growth Accelerates Weight of fetus more than doubles. Most major nerve tracts formed within brain. By end, fetus is able to survive on own. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

22 Birth and Postnatal Development Uterus releases prostaglandins. Begin uterine contractions, but then sensory feedback from the uterus stimulates the release of oxytocin from the mother s pituitary gland. - Rate of contraction increases to one contraction every two or three minutes. Strong contractions, aided by the mother s pushing expels the fetus. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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24 Birth and Postnatal Development Nursing Milk production, lactation, occurs in the alveoli of mammary glands when they are stimulated by prolactin. Milk secreted in alveolar ducts, surrounded by smooth muscle, and lead to the nipple. - First milk produced after birth is colostrum. Rich in maternal antibodies. Milk synthesis begins about three days following birth. Nursing stimulates uterine contractions. Brings uterus back to normal size. Postnatal Development Babies typically double birth weight within a few months. Neuron production occurs for six months Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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27 Embryonic Development - Vertebrate Evolution Ontogeny Recapitulates Phylogeny Embryological development (ontogeny) involves the same progression of changes that have occurred during evolution (phylogeny). Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

28 Chicken vs Human Development Chick extraembryonic membranes develop from extensions of germ layers, which spread over yolk. a. Chorion lies next to shell and carries on gas exchange. b. Amnion contains protective amniotic fluid that bathes developing embryo. c. Allantois collects nitrogenous wastes. d. Yolk sac surrounds remaining yolk that provides nourishment. Humans have these membranes; their function is modified for internal development. a. Chorion develops into fetal half of placenta. b. Yolk sac is first site of blood cell formation. c. Allantoic blood vessels become umbilical blood vessels. d. Amnion surrounds embryo and cushions it with amniotic fluid. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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31 Stem Cells Stem cells are primal cells common to all multi-cellular organisms that retain the ability to renew themselves through cell division and can differentiate into a wide range of specialized cell types. (Wikipedia) 3 Main Types: 1. Embryonic Stem Cells: derived from blastocysts 2. Adult Stem Cells: found in adult tissues 3. Cord Blood Stem Cells: found in umbilical cord 4. ips: induced pluripotent stem cell (Feb 08) - Scientist in Wisconsin and Japan found 4 signals in cells cytoplasm - Each signal was a transcription factor which play a role in protein synthesis Ex: turning skin cells into stem cells Video Link: Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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37 Potential Uses for ips Correct Human sickle cell anemia in mouse (12/07) Fibroblast derived ips used for Parkinson s inrat (4/7/08) ips for: Huntington Dx, Muscular Dystrophy, Type 1 Diabetes, Lesch-Nyhan Carrier, Down syndrome(in vitro) Where should the government s money be focused? Would ips have been found if Pres. Bush never outlawed new lines of embryonic stem cells? What does the current law state? Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

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39 In August 2001, President George W. Bush approved the use of federal funding for ES cell research, BUT ONLY on cell lines already in existence, in order to avoid the destruction of additional human embryos. Critics say that existing ES cell lines have only a limited lifespan before their usefulness for research is lost, and that the number of available lines is insufficient. Do you agree or disagree with President Bush s decision? Should ES cell research prove fruitful, it raises the issue of a particular type of cloning known as therapeutic cloning. Therapeutic cloning would not result in the production of a new human being, but it would mean creating an embryo from which ES cells could be removed that would match the cells of a person s own body. This would prevent the rejection of transplanted cells by the immune system of the recipient. Would you support the use of therapeutic cloning in order to produce ES cells for treatment of disease or injury? Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

40 An alternative way of avoiding the transplant rejection problem mentioned would be to reprogram adult body cells and make them into stem cells. Research in this area is already underway. Do you think that research efforts currently focused on ES cells should be shifted to this venue, or that a variety of approaches should be pursued? Embryonic Stem Cell Video Adult skin cells reprogrammed into stem cells Cord blood Banking Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

41 Embryonic Stem Cells Do you think that a five-day-old embryo should be accorded the status of a human person? If not, why not? If so, do the potential benefits of ES cell research outweigh the ethical Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies objections? Explain.

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