1. The Human Body in Health and Illness, 4th edition
Barbara Herlihy
Chapter 27:
Human Development
and Heredity

2. Lesson 27-1 Objectives
Describe the process of fertilizationwhen, where, and how it occurs.
Describe the process of developmentcleavage, growth, morphogenesis, and differentiation.
Explain the three periods of prenatal developmentearly embryonic, embryonic, and fetal periods.
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3. Lesson 27-1 Objectives (cont’d.)
State two functions of the placenta.
Explain hormonal changes during pregnancy.
Describe the hormonal changes and stages of labor.
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4. Fertilization: Sperm and Egg Unite
When:
Near midcycle, ovulation
Where:
First third of the fallopian tube
How:
At intercourse, sperm swim to fallopian tube
At fertilization, nuclei of sperm and egg unite
Result: The zygote
Has 46 chromosomes, 23 each from male and female
Fertilization is conception, resulting in a single-celled zygote.
The sperm and the egg each donate 23 chromosomes, restoring the human chromosomal number of 46.
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5. Prenatal Development Three periods Pregnancy: Conception to birth
Early embryonic, first 2 weeks
Embryonic, weeks 3 to 8
Fetal, week 9 to birth
Pregnancy: Conception to birth
38 weeks (~9 months)
Divided into trimesters
The early embryonic period is the first 2 weeks of pregnancy, moving from zygote to the late blastocyst stage and implantation.
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6. Prenatal development includes…
Cleavage: Cell division by mitosis
Growth: Size of the cells increase
Morphogenesis: Shaping of the cell cluster
Differentiation: Cellular specialization
The terms on the slide are used to describe development from zygote to fetus.
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7. Early Embryonic Period
Zygote
Fertilized ovum
Blastomeres
Mitosis
Morula
Raspberry (16 cells)
Blastocysts
Early and late
Trophoblastic cells
Implantation
Zygote
Fertilized ovum
Blastomeres
Mitosis
Morula
Raspberry (16 cells)
Blastocysts
Early and late
Trophoblastic cells
Implantation
During passage through the fallopian tube and through mitotic divisions, a zygote becomes a series of blastomeres.
Entering the uterus, the cluster of developing cells is called a morula. The transformation from zygote to morula takes about 3 days.
The morula is a 16-cell cluster that resembles a raspberry; it floats in the uterus for 3 to 4 more days, becoming a blastocyst.
The trophoblastic cells secrete hCG, maintaining the ovarian corpus luteum and assisting with implantation into the uterus.
Within the blastocyst is a cluster of cells called the inner cell mass, which will eventually become the baby.
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8. Twinning Monozygotic (identical) Dizygotic (fraternal)
Develop from the same zygote
Have identical genetic information
One egg, one sperm
Dizygotic (fraternal)
Develop from two different zygotes
Do not have the same genetic information
Like having two separate pregnancies
Two eggs, two sperm
Each cell within the morula or blastocyst can become a complete individual. Sometimes, one of these cells splits, becoming identical twins. Originating from one zygote, such a pair of twins is known as monozygotic.
Sometimes a woman ovulates two eggs. If they are fertilized by two sperm, fraternal twins develop. Because there are two zygotes, they are called dizygotic twins.
The same mechanisms can produce identical or fraternal triplets or quadruplets.
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9. Embryonic Period: Extraembryonic Membranes
Amnion amniotic sac, fluid
Chorion chorionic villi, placenta
Yolk sac RBCs, immature sex cells
Allantois urinary bladder, umbilical cord
The developing baby floats in amniotic fluid formed by the amnion. The baby’s urine also helps create much of the amniotic fluid. At term, there is about 1 liter of amniotic fluid.
The amniotic fluid protects the embryo, which also drinks and digests the fluid.
The embryo secretes waste and cells into the amniotic fluid. This is the basis for the diagnostic test called amniocentesis.
Rupture of the bag of waters often signals the onset of labor.
At birth, the membranes are expelled with the placenta as the afterbirth.
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10. Amnion It forms the amniotic sac around the embryo.
It is filled with amniotic fluid.
Functions
Protective cushion
Fluid nourishes embryo (drinks and digests it)
At full term – 1 L of amniotic fluid
2/08 Placenta and Fetal Membranes total.pdf
amniocentesis
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11. Chorionic Villi and Placenta
Placenta formed when chronic villi penetrate endometrium
Site for fetal eating, breathing, excreting
Secretes hormones
Chronic villi – hCG
Placenta – progestins & estrogen
Umbilical cord joins fetus, placenta
The finger-like chorionic villi penetrate the endometrium; they sit in the blood-filled spaces called lacunae. The placental membrane ensures that the maternal and embryonic blood supplies are separate.
The umbilical cord connects the embryo to the placenta.
The cord’s blood vessels carry unoxygenated blood from the embryo to the placenta, where it is oxygenated and returned to the embryo.
Premature separation of the placenta causes the death of the developing baby. In placenta previa, the placenta prematurely separates from the uterine wall. In abruptio placenta, the separation occurs abruptly.
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12. Yolk sac Functions Produces red blood cells
Produces immature sex cells
Ceases to function after the sixth week
By the seventh month the bone marrow produces the red blood cells
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13. Allantois
Functions
Contributes to the formation of the urinary bladder
The blood vessels of the allantois help form the umbilical blood vessels
The allantois deteriorates after the second month
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14. Diagnostic Tests for Birth Defects
Amniocentesis
Chorionic villi sampling
Diagnostic tests for genetic defects can be done by sampling the amniotic fluid or the blood in the chorionic villi.
In both tests, embryonic cells can be examined.
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15. Placenta
Read page 500
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16. Umbilical Cord Connects embryo and mother at the placenta
Contains two arteries and one vein
Upon delivery, the umbilical cord is cut. The stump shrivels up and drops off
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17. Organogenesis The formation of body organs and organ systems
Embryonic disc which is formed from the inner cell mass
Embryonic disc gives rise to three primary germ layers: ectoderm, mesoderm, and endoderm
Ectoderm – rise to nervous system, special senses, & skin
Mesoderm – rise to muscle, bone, blood, & some structures of the cardiovascular system
Endoderm – rise to epithelial lining of digestive tract, respiratory tract, and parts of the urinary tract
Main organs by the end of week 8
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18. Embryonic Period Organogenesis: Formation of organs
Embryonic disc: Formed by blastocyst’s inner cell mass
Inner cell mass forms three primary germ layers
Ectoderm
Mesoderm
Endoderm
The word that characterizes the embryonic period is organogenesis. By week 8, the main internal organs have been established.
All the organs and tissues of the body develop from the three germ layers. The ectoderm gives rise to the nervous system, portions of the special senses, and the skin. The mesoderm gives rise to muscle, bone, blood, and many cardiovascular structures. The endoderm gives rise to the lining of the digestive tract, respiratory tract and parts of the urinary tract.
The embryo weighs 1 g and is 1 inch long.
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19. Embryonic Period: Teratogens
Particularly harmful in embryonic period
Cause severe birth defects
The term teratogen derives from a term meaning monster-producing.
There are many teratogens. In addition to those shown on the slide, aspirin can be a teratogen.
Because it is the period of organogenesis when all the organs are forming, defects caused during the embryonic period are usually more severe than those caused later in pregnancy. The embryo can be exposed to teratogens before the mother even knows that she is pregnant.
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20. Fetal Period: Shaping Up
Body proportions change.
Fetus is viable at 20 weeks.
Preterm: Birth before 38 weeks
Ask students to examine the figure on the slide and discuss the visible changes in the developing fetus.
Students may point out the development of limbs from buds, the very early appearance of the large head and eye, the appearance of external structures such as the ear, increased fetal length and size, and the appearance of gradually more human proportions.
Ask students to compare their observations about fetal development to Table 27-2 in the text.
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21. Fetal Period: Terms Quickening: Movement of fetus felt by mother
Lanugo: Fine hair covering the fetus
Vernix caseosa: White, cheese-like substance protecting fetal skin from amniotic fluid
Abortion: Loss of fetus at any time
Spontaneous (miscarriage)
Induced
Therapeutic
If anyone has been pregnant, can you describe how the first fetal movements or quickening felt?
Typically, quickening is described as a fluttery movement like a butterfly.
The baby is born with a covering of vernix. Once the baby warms up, the vernix will melt, giving the skin a soft and smooth feeling.
Not all abortion is intentionally induced. Most miscarriages, technically termed sponataneous abortions, result from problems with the embryo or fetus.
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22. Maternal Changes in Pregnancy
Rate of metabolism increases.
Blood volume expands 40%-50%.
Respiratory activity increases.
Kidneys produce more urine.
Nutritional needs increase.
Increased hormonal secretions: hCG, estrogen, progesterone, prolactin, oxytocin, prostaglandins, thyroid hormones, aldosterone
Most maternal changes are compensatory responses to the demands that the pregnancy places on the mother’s body.
Maternal intake of calcium, iron, and protein must increase.
Prenatal vitamins are often prescribed.
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23. Maternal Changes http://www.youtube.com/watch?v=VqtQQJKe21E
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24. Labor: The Mama Drama
Forceful contractions expel fetus from the uterus
Hormones involved
Progesterone: Quiets uterine contractions before labor
Estrogen: Sensitizes uterus to oxytocin
Prostaglandins: Initiate uterine contractions
Oxytocin: Stimulates uterine contractions
Braxton Hicks contractions normally occur during late pregnancy because of fluctuating levels of various hormones. The mother often mistakes these for the onset of labor.
The hormones involved in labor are progesterone, estrogen, prostaglandins, and oxytocin.
In patients prone to miscarriage, a weekly injection of progesterone often quiets uterine contractions, delaying the onset of labor.
An IV administration of pitocin (oxytocin) is used to induce labor. Such drugs are called oxytocic agents.
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25. Birth of Baby: Stages of Labor
Dilation stage (B)
Expulsion stage (C)
Placental stage (D)
Panel A shows the position of the baby before labor starts; the other panels illustrate the stages of labor
Any delivery but a head-first approach is considered a breech birth.
In a normal presentation, the baby’s head is face-down.
In Figures B and C, there is no cord compression.
Figure D shows the delivery of the afterbirth. The placenta and membranes should follow delivery of the baby.
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26. Lesson 27-2 Objectives
Describe the structure of the breast and lactation.
Describe the relationships among deoxyribonucleic acid (DNA), chromosomes, and genes.
Define karyotype.
Explain how the gender of the child is determined.
State the difference between congenital and hereditary diseases.
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27. Breast: Structure Mammary glands Alveolar glands Nipple and areola
15-20 lobes
Alveolar glands
Located in lobes
Each have many alveolar glands and a lactiferous duct
Secrete colostrum and milk into lactiferous ducts
Nipple and areola
Suspensory ligaments
Breasts secrete colostrom before milk. It is a yellowish, watery fluid rich in protein and antibodies. In 3 days, it is replaced by milk.
With aging, the suspensory ligaments weaken and the breasts sag; named the ligaments involved, this condition is called Cooper’s droop.
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28. Breast: Hormones of Lactation
Estrogen and progesterone
Prepare breasts for lactation
Prolactin
Suppressed during pregnancy by estrogen and progesterone
Stimulates milk production after birth
Oxytocin
Causes uterus to contract minimizing blood loss
Stimulates release of milk from breast
Milk let-down reflex
Stimulated by suckling of the breasts
A number of hormones are involved in lactation.
Prolactin makes milk, whereas oxytocin releases milk from the breast.
Why doesn’t a woman lactate during pregnancy?
Placental estrogen and progesterone suppress the production of prolactin. After delivery of the baby and placenta, levels of estrogen and progesterone decline, so that prolactin is secreted and lactation begins.
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29. Lactation: Milk Let-Down Reflex
Sensory stimulus, suckling
Posterior pituitary releases oxytocin
Oxytocin stimulates breasts’ smooth muscle to contract, releasing milk.
The milk let-down reflex is a reflex arc. The suckling baby stimulates the sensory arm and the posterior pituitary is the motor arm (releasing oxytocin). Oxytocin stimulates the effector organ, the smooth muscles of the breast, to release milk.
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30. Postnatal Adjustments in Baby
Breathing is established.
Blood flow through lungs begins.
Mechanisms for temperature regulation adjust.
Functioning digestive system produces meconium.
Baby’s first stool
Tarry and dark green
Most organs begin to function more efficiently.
Apgar scale
After birth, the baby must adjust from an aquatic environment to an air-breathing one.
The two most critical adjustments are air-breathing and temperature regulation.
The baby’s first stool has important clinical implications. A fetus in distress during labor may inhale the meconium-stained fluid and develop a life-threatening infection. A baby with an imperforate anus will not pass a stool.
Development of some organs, such as the nervous system, continues after birth.
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31. Developmental Stages: Life Span
Neonatal period: Birth to 4 weeks
Infancy: 2nd to 12th month
Childhood: 2nd year to puberty
Adolescence: Puberty to adulthood
Adulthood: Adolescence to old age
Senescence: Old age to death
Human development does not stop at birth.
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32. Heredity Transmission of traits from parent to child
Examples: Color of hair and eyes, dimples, Rh factor, ear lobes
DNA: Location of genetic information
Chromosomes: Threadlike structures of tightly wound DNA in nuclei of most cells
Genes: Segments of DNA carrying information for a specific trait
DNA, chromosomes, and genes transmit the hereditary information.
A gene is a piece of a chromosome that carries a specific trait, such as eye color or dimples.
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33. Chromosomes Exist in pairs Autosomes Sex chromosomes
23 pairs, one chromosome from male and female
Autosomes
22 pairs of non-sex chromosomes
Sex chromosomes
One pair , either X or Y
The 23 pairs of chromosomes (male and female) produce the human number of 46 chromosomes.
There are 22 pairs of autosomes, or non-sex chromosomes.
There is one pair of sex chromosomes. Each sex chromosome can carry either an X or a Y.
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34. Karyotype: Genetic Art
Displays the paired chromosomes
Used to diagnose genetic disorders
The construction of a karyotype involves matching the 23 pairs of chromosomes.
This chromosomal test is used to diagnose genetic disorders.
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35. Heredity: Dominance
Dominant gene expresses itself; overshadows a recessive gene
Recessive gene unexpressed if paired with
a dominant gene
Codominant genes express a trait equally
Blood types
Looking at Table 27-3 in the text, students can reflect on their personal traits and those of their parents.
For example, a student with parents whose ear lobes are attached might note that the trait is carried on a recessive gene, and he or she has similar lobes.
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36. Heredity: Dominance (cont’d.)
Eye color: Dominant and recessive genes
When a child gets both a brown eye gene and a blue eye gene, the brown eye color will be expressed.
Because the blue eye gene is recessive, both parents must contribute a blue eye gene for the child to have blue eyes
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37. Too Many or Too Few Chromosomes
Caused from nondisjunction, when chromosomes fail to separate during meiosis
Examples:
Down syndrome – Trisomy 21
Edwards syndrome- Trisomy 18
Patau syndrome – Trisomy 13
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38. Gender Determination: Xs and Ys
Girl’s sex chromosome is XX.
Boy’s sex chromosome is XY.
Male determines gender of offspring.
Sex-linked traits are carried on sex chromosomes.
Why does the father determine the gender of the child?
As Figure indicates, a female has XX pair of sex chromosomes, whereas a male has an XY pair of sex chromosomes. Each parent transmits only one sex chromosome. Because the mother can only contribute an X chromosome, the father determines the gender of the child. A male can contribute either an X or a Y sex chromosome.
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39. Not the Right number of Sex Chromosomes
XO Turner syndrome – do not develop secondary sex characteristics, shorter than average, webbed neck, normal intelligence
XXY Klinefelter syndrome
XYY
Triple X – XXX
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40. Sex-linked Trait
A sex-linked trait is a trait that is carried on a sex chromosome.
X chromosome is larger so carries more traits.
X-linked traits are traits carried on the X chromosome
Sex-linked diseases:
Hemophilia
Duchenne muscular dystrophy
Fragile X syndrome
Baldness
Red-green color blindness
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41. Heredity: Terms Genetic expression: Determines offspring’s appearance
Genetic mutation: Change in the genetic code
Congenital condition: Any disease or defect present at birth
Hereditary disease: Genetically transmitted
Gene therapy: Insertion of normal genes into cells with abnormal genes
Many genetic mutations occur. Most are insignificant, but some are incompatible with life.
It is important to differentiate between hereditary and congenital conditions.
Hereditary conditions are genetically determined. For example, sickle cell anemia has a genetic cause.
Congenital conditions appear at birth, but are not genetically programmed. For example, a prenatal measles infection might cause hydrocephalus and spina bifida, but there is no genetic component.
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