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Focus: Like all animals, humans begin life as a single cell from which tissues and organs soon begin to develop.

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Presentation on theme: "Focus: Like all animals, humans begin life as a single cell from which tissues and organs soon begin to develop."— Presentation transcript:

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2 Focus: Like all animals, humans begin life as a single cell from which tissues and organs soon begin to develop.

3 Cleavage: zygote undergoing cell divisions  Morula: cluster of sixteen cells › Each cell called a blastomere  Gets a different portion of the cytoplasm  Helps determine the fate of the cells to come later

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5  Gastrulation › Rearranges the morula’s cells to form…  Germ layers ; three primary tissues 1. Ectoderm 2. Mesoderm 3. Endoderm

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7  Cell differentiation › Process of cell specialization › Begins in the germ layers › Different genetic instructions (genes) operate in different cells  Adults have ~200 differentiated cell types

8  Morphogenesis: › Tissues and organs formation › Cell division in certain areas of gastrula › Movement of cells and tissues within gastrula › Folding of tissues into organs › Death of certain cells

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11 Focus: A newly formed embryo cannot survive unless it implants in the mother’s uterus.

12  Fluid-filled cavity forms in the morula → blastocyst › Two tissues  Trophoblast  Inner cell mass: forms the embryo  Identical twins › Split usually during first cleavage or the inner cell mass  Fraternal twins

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14  Implantation › Begins ~one week after fertilization; completed two weeks after ovulation › Blastocyst breaks out of zona pellucida › Epithelial cells invade endometrium → cross into connective tissue of uterus › Endometrium covers blastocyst › Blastocyst secretes HCG  human chorionic gonadotropin

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17 Focus: The embryonic period lasts for eight weeks. During that time, the basic body plan of the embryo takes shape.

18  Embryonic disk › Primitive streak along axis and thickening of cells marks gastrulation  Ectoderm thickens and forms a neural tube › Forerunner of brain and spinal cord › Notochord; vertebral column forms around it  Mesoderm gives rise to somites › Gives rise to most bones and muscles › Coelom forms from spaces (body cavities)

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21  Neurulation: › Development of the nervous system from ectoderm  Cells move from place to place with chemical cues  Adhesive cues stop their movement  Apoptosis: programmed cell death

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26 Focus: During implantation and over the next few weeks, four specialized membranes form outside the embryo. These membranes include the all- important placenta.

27  Certain cells of the embryonic disk give rise to the extra-embryonic membranes 1. Yolk sac 2. Amnion 3. Allantois  gives rise to blood vessels that invade the umbilical cord 4. Chorion

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31  Placenta › Organ formed from chorion and upper cells of the endometrium › Chorionic villi contain small blood vessels › Site of exchange of nutrients and wastes  What other maternal substances can cross the placenta? › Alcohol, caffeine, drugs, pesticide residues, toxins in cigarette smoke, and HIV

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34 Focus: By the end of four weeks, the embryo has grown to 500 times its original size. Over the next several weeks it will develop recognizable human features.

35  Rapid growth and cell specialization  Umbilical cord forms; head region grows faster; gonads develop  After eight weeks, embryo → fetus › Heart beating; genitals well-formed  Miscarriage › Spontaneous expulsion of embryo or fetus

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39 Focus: In the second and third trimesters, organs and organ systems gradually mature in preparation for birth.

40  Fetus at three months › 4.5 inches long › Reddish skin  Fetus at four to six months › Facial muscles produce frowning, squinting, and sucking movements › Movement of fetus felt by mother › Eyelids and eyelashes form

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42  Fetus from seven months to birth › 11 inches at seven months › Organ systems maturing › Fetuses born between 23–25 weeks will need intensive care  Respiratory distress syndrome › Premature infants at risk › Lungs lack surfactant; can’t expand adequately

43  Umbilical cord vessels › Two arteries transport deoxygenated blood and waste to placenta › One vein brings oxygenated blood and nutrients to fetus  Fetal lungs bypassed with blood moving through the foramen ovale and the arterial duct  Fetal liver bypassed using the venous duct  Modifications occur at birth

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45 Focus: Birth, or parturition, takes place about 39 weeks after fertilization—about 280 days from the start of the women’s last menstrual period.

46  Fetal organs (hypothalamus, pituitary, and adrenal glands) produce hormones › Indirectly cause mother’s uterus to contract  Hormones cause placenta to produce more estrogen › Triggers oxytocin and prostaglandins to be produced › Stronger uterine contractions  Labor length varies

47  First stage › Contractions push fetus against cervix, which dilates to 10 cm; usually amniotic sac ruptures  Second stage › Very strong contractions; baby delivers head first › “Bottom-first” or breech delivery; complications  Third Stage › Placenta forced out of the mother › Baby’s first breath

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50  Estrogen and progesterone during pregnancy › Growth of mammary glands and ducts › Colostrum produced initially  Prolactin › Stimulates milk production › lactation  Oxytocin › Regulates flow of milk › Reflex; positive feedback control

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54 Focus: From fertilization until birth, a woman’s future child is at the mercy of her diet and lifestyle.

55  Pregnant women should: › Follow a healthy diet › Take supplemental vitamins and minerals  Folic acid important for neural tube development:  spina bifida exposure of spinal cord in utero › Gain between 20–35 pounds

56  Pregnant woman’s IgG antibodies cross the placenta › Protects fetus against many infections  Teratogens › Agents that cause serious birth defects  Example: Rubella (German measles) › Serious birth defects during first trimester › Mother should be vaccinated to avoid this threat

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59  Fetus most susceptible during the first trimester  Tranquilizers › Thalidomide: 1960s; caused missing or deformed limbs  Some sedatives and barbiturates › Similar but less severe damage  Anti-acne drugs › Increased risk of facial and cranial deformities

60  Antibiotics › Streptomycin  Hearing problems; may affect the nervous system › Tetracycline  Child may develop yellowed teeth  Alcohol › Fetal alcohol syndrome  Many defects: smaller brain and head, facial deformities, poor motor coordination, heart defects

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62  Cocaine, especially crack › Improper nervous system development  Tobacco smoke › Great risk of miscarriage, stillbirth, and premature delivery › Underweight › Less vitamin C in blood › Effect of secondhand smoke still unknown

63 1. Chorionic villus sampling (CVS) › Removes sample of chorionic cells by suction 2. Amniocentesis › Samples fluid from the amnion 3. Preimplantation diagnosis › Uses recombinant DNA technology 4. Fetoscopy › Uses sound waves

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67 Focus: After a child enters the world, a gene-dictated course of further growth and development leads to adulthood.

68 1. Newborn and infancy 2. Childhood and adolescence › Puberty: arrival of sexual maturity › Growth stops by early twenties 3. Adult and old age

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72  Senescence › Body parts and functioning begin to deteriorate after age 40  Average life expectancy in the United States › Males: 74 › Females: 79

73 Focus: Time takes a toll on body tissues and organs. To some extent, our genes determine how long each of us will live.

74  Consistency of lifespan within a species  Most human cells divide between 80–90 times: › Chromosomes capped with segments of DNA called telomeres  These shorten with each cell division  Cancer cells and cells in gonads that give rise to sperm and oocytes: › Produce an enzyme that lengthens the telomere › These cells can divide over and over

75  Aging probably involves many factors including: › Genes › Free radical damage › Decline in DNA repair mechanisms

76  Aging: gradual loss of vitality › Cells, tissues, and organs function less and less efficiently  Skin: thinner, collagen more rigid, less elasticity, drier, less hair, graying of hair  Muscles: loss mass and strength; lost muscle replaced with fat  Bones: osteoporosis and osteoarthritis

77  Lungs › Walls of alveoli break down; less surface area for gas exchange  Heart › Slightly enlarged; less-efficient pump  Blood transport › Vessels become stiffer › Cholesterol plaques narrow the vessels

78  Immune system › T cell numbers fall; B cells become less active › Autoimmune response increase  Digestive tract › Mucus glands in the lining break down › Pancreas secretes fewer digestive enzymes › Basal metabolic rate decreases  Hormones: most keep steady levels; sex hormones are the exception

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80  Brain neurons die throughout life  brain shrinks  Aged brain › Neurofibrillary tangles: may disrupt normal cell operations › Beta amyloid forms: clotlike plaques between neurons  Sensory organs and taste buds › Less efficient over time

81  Alzheimer’s disease › Physiology  Masses of neurofibrillary tangles riddled with beta amyloid plaques › Symptoms  Progressive memory loss  Disruptive changes to personality › Causes  Some are genetic › Treatments  Limited; may slow progression

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