1. Development and Aging Chapter 17

2. Stages of Development Gamete formation Fertilization Cleavage Gastrulation Organ formation Growth, tissue specialization

3. Cleavage Divides up cytoplasm Each blastomere ends up with a portion Creates variation among blastomeres

4. Three Primary Tissues Gastrulation rearranges blastomeres and creates: Endoderm Mesoderm Ectoderm

5. Organogenesis Process by which organs form Cell determination Cell differentiation Morphogenesis

6. Fertilization Sperm penetrates to egg cytoplasm Secondary oocyte undergoes meiosis II; forms mature egg Egg nucleus and sperm nucleus fuse to form diploid zygote

7. Pregnancy Averages 38 weeks from fertilization Takes 2 weeks for blastocyst to form Weeks 3 to 8 are embryonic period Weeks 9 to birth are fetal period

8. Early Divisions Cleavage begins within 24 hours of fertilization Day 1Day 2Day 3 Day 4 (morula)

9. Day 5 - Blastocyst Forms Cell secretions produce a fluid-filled cavity in center of ball of cells Layers of blastocyst –Inner cell mass –Trophoblast –Blastocoel inner cell mass

10. Implantation Begins Blastocyst attaches to endometrium; begins to burrow into maternal tissues blastocoel inner cell mass trophoblast Uterine cavity

11. Human Chorionic Gonadotropin (HCG) Hormone secreted by the blastocyst Stimulates corpus luteum to keep making progesterone and estrogens This maintains endometrium, prevents menstruation Can be detected by week 3 with a home pregnancy test

12. Extraembryonic Membranes DAY 14 yolk sac chorionic cavity chorionic villi chorion amniotic cavity connecting stalk The amniotic membrane will enclose embryo Yolk sac forms Chorion begins to form fingerlike villi

13. The Placenta Interlocking fetal and maternal tissues Performs digestive, respiratory, and urinary functions for the fetus Materials exchanged across membrane that separates bloodstreams

14. Gastrulation - Day 15 Primitive streak forms along one axis of the inner cell mass Cells migrate inward here to form endoderm and mesoderm

15. Vertebrate Body Plan Emerges paired neural folds somites pharyngeal arches

16. Morphogenesis Orderly changes result in specialized tissues and early organs Cells migrate Whole sheets of cells expand and fold Programmed cell death sculpts body parts Cell migration

17. Embryonic Period Weeks 3 to 8 By the close of embryo period –Appears human –Primordial tissues of all internal and external structures have formed Week 4 Week 8

18. Fetal Period Weeks 9 to birth Fetus is initially about 1 inch long Fetus born before 22 weeks cannot survive Survival is poor before 28 weeks because lungs are not fully formed By 36 weeks, survival is 95 percent

19. Fetal Circulation Fetal hemoglobin Temporary bypass vessels form and function until birth Umbilical arteries Foramen ovale and the arterial duct Venous duct

20. Birth (Labor) Cervical canal dilates Amniotic sac ruptures Uterine contractions drive fetus from uterus Placenta is expelled as afterbirth

21. Lactation During pregnancy, progesterone and estrogen stimulate gland development After birth, prolactin induces synthesis of enzymes for milk production Oxytocin triggers contractions

22. Cloning Embryos Biological carbon copy of an organism Use chemicals to spur unfertilized, donated eggs to divide OR Fuse enucleated egg with an adult cell

23. Fetal Nutrition All nutrients for fetal growth and development must be delivered via the placenta Mother’s diet affects fetal health Smoking may affect ability to absorb nutrients and to pass them to fetus

24. Teratogens Drugs and environmental factors that may induce deformities during development Effect depends upon time of exposure Most have no effect until after second week Thalidomide

25. Stages of Human Development - Prenatal Zygote - Single cell Morula - Solid ball of cells Blastocyst - Ball with fluid-filled cavity Embryo - 2 weeks to 8 weeks Fetus - 9 weeks to birth

26. Stages of Human Development - Postnatal Newborn - First 2 weeks after birth Infant - 2 weeks to 15 months Child – To 10-12 years Pubescent - At puberty Adolescent - Puberty to maturation Adult Old age

27. Aging Programmed life-span hypothesis Cumulative-assaults hypothesis

28. Aging Skin and Hair Number of fibroblasts in the dermis starts to decrease Elastin replaced by collagen Loss of sweat glands Hair follicles die or become less active Pigment-producing cells die

29. Aging Muscle and Bone Fibers in skeletal muscle atrophy Lost muscle tends to be replaced by fat and, with time, collagen Bones become weaker, more porous, and brittle Cartilage in joints deteriorate

30. Aging Cardiovascular and Respiratory Systems Walls of alveoli break down Heart muscle becomes slightly smaller Less blood and oxygen are delivered to muscles and other tissues Blood vessels become narrowed and less elastic

31. Aging Nervous System Brain neurons die steadily throughout life Neurofibrillary tangles Beta amyloid plaques Memory loss Slowed reflexes Farsightedness

32. Aging Reproductive Systems Reduced secretion of estrogens and progesterone triggers menopause Falling levels of testosterone reduce male fertility Vascular changes impair ability to achieve erection Prostate-gland enlargement

33. Aging Immunity, Nutrition, and Urinary System Number of T cells falls and B cells become less active Mucus-secreting glands of GI tract degenerate Basal metabolic rate declines Weakening of muscles causes urinary incontinence