1. Development
    • : process by which multicellular organisms grow and increase in organization and complexity
    • Development is usually considered to begin with a fertilized egg and ends with a sexually mature adult
  2. embryotic development
    • fertilization- zygote
    • cleavage- blastulla
    • Gastrulation- Gastrula
    • Organo- Genesis- Tail bud embro

  3. Three principle mechanisms:
    • individual cells multiply
    • 2)some of their daughter cells differentiate

    3) as they differentiate, cells move about and become organized into multicellular structures

  4. How do cells differentiate into different structures with distinct functions?
    • different genes in
    • different places at
    • different times
  5. types of development
    • direct development- babies, mammals and reptiles (birds)
    • Indirect development- majority of animal species, newborn has a very different body structure than the adult

  6. Direct development
    • Juveniles are typically much larger than larvae
    • need much more nourishment before emerging into the world
    • Birds, most other reptiles, and many fish produce eggs that contain relatively large amounts of yolk
    • Mammals, some snakes, and a few fish have relatively little yolk in their eggs, and the embryos are nourished within the mothers body
  7. cleavage
    • Cleavage of the zygote begins development
    • The formation of an embryo begins with cleavage, a series of mitotic cell divisions of the fertilized egg or zygote
  8. blastula
    • As cleavage continues, a cavity opens within the morula, and the cells become the outer covering of a hollow structure called the blastula
  9. ectoderm
    • outer layer of the embryo
    • epidermis of skin and its derivatives- sweat glands
    • Nervous and sensory systems
    • Pituitary gland, adrenal medulla
    • Jaws and teeth
    • Germ cells
  10. Mesoderm
    • Middle layer of the embryo
    • skeletal and muscular systems
    • Circulatory and lymphatic systems
    • Execretory and reproductive systems
    • Dermis
    • Adrenal cortex
  11. Endoderm
    • inner ayer of the embryo
    • Epithelian lining of digestive tract and associated organs- liver pancreas

    • Epithelian lining of respiratory, execretory and reroductive tractts
    • Thymus, thyrooid and parathyroid glands
  12. Organogenesis
    • Organogenesis: the development of adults structures from the three embryonic tissue layers,
    • a series of master switch genes turn on and off, each controlling the transcription and translation of the many genes involved in producing, say, an arm or a backbone
    • Second, organogenesis prunes away superfluous cells just like Michelangelo chiseled away extra marble leaving behind his statue of David

  13. The amniotic egg -four extraembryonic membranes:
    • chorion
    • amnion
    • allantois
    • yolk sac

  14. How is Development Controlled?
    • A zygote contains all of the genes needed to produce an entire animal
    • Nearly every cell of the body also contains all of these genes
    • In any given cell, however, some genes are used, or expressed, while others are not

  15. What causes different cells to transcribe different genes?
    • Maternal molecules in the egg may direct early embryonic differentiation
    • Essentially all of the cytoplasm in a zygote was already in the egg before fertilization
    • Specific mRNA and protein molecules become concentrated in different places in the eggs cytoplasm during oogenesis
    • Some of these proteins are transcription factors that regulate which genes are turned on and off
  16. Homeobox
    • Homeobox genes regulate development of entire segments of the body

    code for transcription factors that regulate the transcription of many other genes

    Each homeobox gene has major responsibility for the development of a particular region in the body

    In all animals studied to date, the homeobox genes are arranged on the chromosomes in a head-to-tail order

  17. placenta
    • The complex intermingling of the chorion and the endometrium forms the placenta
  18. chorlon and endometrium
    • The complex intermingling of the chorion and the endometrium forms the placenta

    The chorion secretes chorionic gonadotropin (CG), which prevents the death of the corpus luteum

    • The corpus luteum sustains the pregnancy by secreting progesterone and estrogen for the first couple of months, until the placenta takes over the secretion of these hormones
  19. inner cell mass
    • All of the cells of the inner cell mass have the potential to develop into any type of tissue

    the inner cell mass: able to produce both the entire embryo and the remaining extraembryonic membranes

    • The inner cell mass is also the source of human embryonic stem cells, which researchers hope may one day be used to replace damaged adult tissues
  20. Body structures formations
    • Body structures begin to form during weeks three to eight
    • 3rd week: embryo begins to form the spinal cord and brain
    • 4th week: heart expands and becomes muscular, starting to beat
    • the embryo bulges into the uterine cavity, bathed in fluid contained within the amnion
  21. the umbilical cord
    • The umbilical cord forms from the fusion of the yolk sac to the embryonic digestive tract
    • The body stalk contains the allantois, which contributes the blood vessels that will become the umbilical arteries and vein
    • The umbilical cord now connects the embryo to the placenta, which has formed from the merger of the chorion of the embryo and the lining of the uterus
  22. fetus by the end of the second month
    • Many structures, such as the arms and legs, are recognizably human in form
    • The gonads appear and develop into testes or ovaries
    • Sex hormones are secreted—either testosterone from the testes or estrogen from the ovaries

    • The first two months of pregnancy are a time of extremely rapid differentiation and growth for the embryo, and a time of considerable danger

  23. The placenta exchanges materials between mother and embryo
    • First few days after implantation, the embryo obtains nutrients directly from the endometrium
    • During the following week or so, the placenta begins to develop from the interlocking structures produced by the embryo and the endometrium
    • The outer layer of the blastocyst forms the chorion, which grows fingerlike chorionic villi that extend into the endometrium
    • The embryos blood and the mothers blood remain separated by the walls of the villi and their capillaries, so the two blood supplies do not actually mix to any great extent

  24. The placenta secretes hormones essential to pregnancy
    • By the end of the first trimester, the placenta secretes enough estrogen and progesterone, enough to sustain its own growth and development

    About this time, the corpus luteum degenerates

    • These hormones stimulate development of the mammary glands
    • Progesterone also inhibits premature contractions of the uterine muscles and lactation
  25. Labor
    • Whatever the initial stimulus, the placenta releases prostaglandins, which make the uterine muscles more likely to contract
    • As the uterus contracts, it pushes the fetus head against the cervix, stretching it
    • This has two effects:
    • First, the cervix expands so that the fetus head can fit through
    • Second, stretching the cervix sends nervous signals to the mothers brain, causing the release of the hormone oxytocin
  26. positive feedback of labor
    • Oxytocin stimulates contractions of the uterine muscles, pushing the baby harder against the cervix, which stretches further, causing still more oxytocin to be released
    • This positive feedback cycle continues until the baby emerges from the vagina
    • After a brief rest following childbirth, the uterus resumes its contractions and shrinks remarkably
    • During these contractions, the placenta is sheared from the uterine wall and expelled through the vagina
  27. prostaglandins
    • The umbilical cord now released prostaglandins that cause the muscles surrounding fetal blood vessels in the umbilical cord to contract and shut off blood flow
  28. estrogen and progesterone in pregnancy
    • Estrogen and progesterone, acting together with several other hormones, stimulate the milk-producing mammary glands in the breasts to grow, branch, and develop the capacity to secrete milk
  29. Prolactin
    • secreted by the anterior pituitary gland), promotes both mammary gland development and the actual secretion of milk, a process called lactation
    • Prolactin is stimulated by the high levels of estrogen produced by the placenta
  30. lactation
    • initiatied by prolactin, inhibited by progesterone
    • During childbirth, the placenta is ejected from the uterus
    • Progesterone level plummet, allowing prolactin to cause lactation
  31. Oxytocin
    • Oxytocin causes muscles surrounding the mammary glands to contract, ejecting the milk into the ducts that lead to the nipples

  32. aging is manifested in many ways:
    • Muscle and bone mass are lost
    • Skin elasticity decreases
    • Reaction time slows
    • Senses, such as vision and hearing, become less acute
    • A less-robust immune response renders the aging individual more vulnerable to disease
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