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
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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
• Mothers 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

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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

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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