Development and Aging

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Chapter 17

• Development and Aging

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Outline

• Fertilization
• Pre-Embryonic and Embryonic Development
• Fetal Development
• Pregnancy and Birth
• Development after Birth (including Aging)

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Fertilization

• Steps of fertilization (Conception).
• Several sperm penetrate corona radiata.
• Several sperm attempt to penetrate zona
  pellucida.
• One sperm enters egg and nuclei fuse, producing a
  zygote.
• Eggs plasma membrane and zona pellucida change
  to prevent polyspermy.

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Fertilization
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Occurrence of Pregnancy

• When a zygote begins dividing, it is termed an
  embryo (pre-embryo).
• Developing embryo travels down oviduct and
  eventually implants in endometrium.
  (Implantation / pregnancy)
• Presence of human gonadotropic hormone (HCG) in
  the blood confirms pregnancy.
• If implantation does not occur, a woman never
  knows fertilization took place.

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Human Development before Implantation
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• Following implantation, the placenta
• originates from maternal and fetal
• tissues.
• Placenta then produces human chorionic
• gonadotropin (HCG) which maintains the
• corpus luteum in the ovary until the
• placenta begins its own production of
• progesterone and estrogen.
• Physical signs of pregnancy include no
• menstruation, increased urination,
• morning sickness, increased size of
• breasts, and darkening of areolae.

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Pre-Embryonic and Embryonic Development

• Processes of development.
• Cleavage - Cell division without growth.
• Growth - Increase in size of cells.
• Morphogenesis - Shaping of embryo.
• Differentiation - Cells take on specific
  structure and function.

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Extraembryonic Membranes

• Membranes that extend out beyond the embryo.
• Amnion - Provides fluid environment for
  developing embryo and fetus.
• Yolk sac - First site of red blood cell
  formation.
• Allantois - Contributes to cardiovascular system.
• Chorion outermost membrane, develops from the
  trophoblast, contributes to the placenta.

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Extraembryonic Membranes
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Pre-Embryonic and Embryonic Development

• Stages of development.
• Morula - Solid mass of cells resulting from
  cleavage.
• Blastocyst (Blastula) - Ball of cells formed from
  morula.
• Embryonic disk - Inner mass of cells of
  blastocyst.
• Gastrula - Embryo composed of three tissues.
• Ectoderm, mesoderm, endoderm.
• These are the foundation of the body systems
  (Germ Layer Theory).

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Early Developmental Stages
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Pre-Embryonic and Embryonic Development

• Stages of development.
• Neurula - Nervous system develops from ectoderm
  located just above the notochord.
• Involves induction as one tissue influences the
  development of another tissue.

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Primitive Streak and Neurula
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Germ Layer Theory of Organ System Development
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Embryonic Development

• Embryonic development occurs from the second week
  to the eighth week.
• Fetal development occurs from the third month
  through the ninth month.
• See Table 17.1 Human Development (in text) for
  a summary of key events during the 9 months of
  pregnancy.

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Embryonic Development

• Immediately after fertilization, the embryo
  divides and develops into a blastocyst
  (Blastula).
• Bounded by a layer of cells (trophoblast) that
  becomes the chorion.
• Implantation completed by the end of the second
  week.
• Embryo is a gastrula by the end of the third
  week.
• Placenta is forming by end of fourth week.

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Embryonic Development
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Embryonic Development

• By the end of the second month, all organs have
  appeared and the placenta is fully functioning.
• Embryonic development complete.

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Five-Week-Old Embryo
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Fetal Circulation

• The umbilical cord stretches between the placenta
  and the fetus and contains the umbilical arteries
  and veins.
• Placenta functions
• Exchange of gases and nutrients between maternal
  and fetal blood takes place in the umbilical
  arteries.
• Umbilical vein carries blood and oxygen away from
  the placenta to the fetus.
• Produce hormones to maintain pregnancy (estrogen,
  progesterone, HCG)

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Fetal Circulation and the Placenta
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Science Focus

• Cloning Humans Can It Be Done?

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Fetal Development

• At the beginning of the third month, head growth
  begins to slow and the body increases in length.
• Ossification centers appear in bones.
• Sex can be determined sometime in the third month.

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Three-to-Four Month-Old Fetus
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Fifth through Seventh Months

• Mother begins to feel fetal movement.
• Wrinkled skin covered by fine hair, lanugo, is
  covered by a greasy substance vernix caseosa.
• Lungs lack surfactant so if baby is born
  prematurely it will have to be on a respirator
  (respiratory distress syndrome).

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Six-Month-Old-Fetus
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Eighth and Ninth Months

• Fetus usually rotates so head is pointed down
  toward cervix.
• Fetus is now about 530 mm in length and weighs
  about 3,400 g.
• Full-term babies have the best chance of
  survival.
• Breech birth (rump first) may require a
  cesarean section.

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Development of Male and Female Genitals

• Sex of an individual is determined at the moment
  of fertilization.
• Gonads arise from indifferent tissue that can
  develop into ovaries or testes, depending on the
  action of hormones.
• In the absence of a Y chromosome and in the
  presence of two X chromosomes, ovaries develop
  instead of testes.

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Development of Male and Female Genitals

• Abnormal Development of Genitals
• XY female syndrome / XX male syndrome
• Due to misplaced SRY gene (sex
  determining region of the Y).
• Ambiguous Sex Determination
• androgen insensitivity syndrome
• male pseudohermaphroditism.

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HEALTH FOCUS

• Preventing Birth Defects

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Pregnancy and Birth

• Major changes that take place in the mothers
  body during pregnancy are due to placental
  hormones
• 1. The uterus relaxes.
• 2. The pulmonary values increase.
• 3. Other effects incontinence, edema, varicose
  veins, pregnancy-induced diabetes, striae
  gravidarum (stretch marks), increase in
  melanocyte activity.

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Birth

• False-labor (Braxton Hicks contractions)
  preliminary contractions that occur periodically
  but lasting less than 30 seconds.
• True labor is marked by uterine contractions that
  occur regularly every 15-20 minutes and last for
  40 seconds or more.
• Positive feedback control.
• Parturition is the technical term for giving
  birth to an offspring.

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Birth

• Stage 1.
• Mucous plug may be expelled from cervical canal
  called bloody show before stage 1 technically
  begins.
• Cervical canal slowly disappears called
  effacement (taking up the cervix).
• Breaking of the water
• Cervix dilates completely.

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Birth

• Stage 2.
• Babys head descends into the vagina.
• Episiotomy?
• Baby is delivered.

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• Stage 3.
• Placenta delivered, usually within 15 minutes.
• Called the afterbirth.

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Stages of Parturition
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Female Breast and Lactation

• Female breast contains 15-20 lobules, each with a
  milk duct beginning at the nipple and ending in
  alveoli.
• In pregnancy, breasts enlarge as ducts and
  alveoli increase in number and size.
• Milk usually not produced during pregnancy.
• Prolactin (lactogenic hormone) suppressed due to
  increase in estrogen and progesterone.
• Suckling stimulates release of oxytocin.

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Female Breast Anatomy
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Development after Birth

• Development is a lifelong process into adulthood,
  after which aging occurs.
• Gerontology is the study of aging.
• Aging encompasses progressive changes that
  contribute to an increased risk of infirmity,
  disease, and death.
• Theories.
• Genetic in Origin.
• Whole-Body Process.
• Extrinsic Factors.

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Effect of Age on Body Systems

• Skin.
• Skin becomes less elastic due to changes in
  elastic fibers.
• Processing and transporting.
• Heart shrinks due to a reduction in cardiac
  muscle.
• Blood pressure gradually increases.
• Liver not as efficient in metabolizing drugs.
• Blood supply to kidneys reduced.

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Effect of Age on Body Systems

• Integration and coordination.
• Few neural cells of the cerebral cortex are lost
  during the aging process.
• Reaction time slows.
• Loss of skeletal muscle mass not uncommon.
• Reproductive system.
• Females undergo menopause (Ch. 16).
• Male androgen levels fall between ages 50-90, but
  sperm produced until death.

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BIOETHICAL FOCUS

• Maternal Health Habits

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Outline

• Fertilization
• Pre-Embryonic and Embryonic Development
• Fetal Development
• Pregnancy and Birth
• Development after Birth (including Aging)

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