Development and Aging

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 1 Day 2 Day 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 Uterine cavity blastocoel inner cell mass trophoblast

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

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 pharyngeal arches somites

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