Chapter 29
Lecture Outline
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1
29.0 Development, Pregnancy, and Heredity
• Development
– Series of progressive changes
– Leads to formation and organization of cell types
– Study of development prior to birth, embryology
• Pregnancy
– Comes with multiple anatomic and physiological changes
– Postpartum changes as well
• Heredity
– Transmission of genetic traits from parent to newborn
2
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29.1 Overview of the
Prenatal Period
1.
Learning
Objectives:
Define the prenatal period,
and identify the three shorter
periods that occur during the
prenatal period.
3
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29.1 Overview of the Prenatal Period
• Prenatal period
– Begins with fertilization
o Secondary oocyte and sperm unite
– Ends 38 weeks later with birth
– 3 sub-periods
o Pre-embryonic period
o Embryonic period
o Fetal period
4
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29.1 Overview of the Prenatal Period
• Prenatal period (continued)
– Pre-embryonic period
o First 2 weeks after fertilization
o Zygote, cell produced by fertilization, becomes spherical
multicellular structure blastocyst
o Ends when blastocyst implants in uterine lining
5
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29.1 Overview of the Prenatal Period
• Prenatal period (continued)
– Embryonic period
o 3rd through 8th weeks of development
o Rudimentary versions of major organs appear
o Now called an embryo
– Fetal period
o Remaining 30 weeks prior to birth
o Organism is now called a fetus
o Continues to grow and increase in complexity
• Embryogenesis, developmental period of preembryonic and embryonic periods
6
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Developmental
History of a
Human
Figure 29.1
7
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What did you
learn?
•
In which prenatal period do
the rudimentary organs form?
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8
29.2 Pre-Embryonic
Period
Learning
Objectives:
1.
2.
3.
4.
5.
Describe the events of
fertilization.
Explain capacitation of sperm
and its relationship to
fertilization.
Define cleavage, and explain
when it occurs.
Compare and contrast the
structures of the zygote,
morula, and blastocyst.
Define implantation, and
explain when it occurs.
9
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29.2 Pre-Embryonic
Period
(continued)
Learning
Objectives:
6.
7.
8.
9.
10.
Explain the physiologic
significance of the syncytiotrophoblast’s production of hCG.
Describe the development of the
bilaminar germinal disc.
Name the three extraembryonic
membranes and summarize their
functions.
Compare the maternal and fetal
portions of the placenta.
Describe the main functions of
the placenta, and name the
hormones that promote its
development.
10
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29.2a Fertilization
• Fertilization
– Two gametes fuse to form new diploid cell
o Contains genetic material derived from both parents
–
–
–
–
–
–
Restores diploid number of chromosomes
Determines the sex of the organism
Initiates cleavage
Occurs in widest part of uterine tube, ampulla
Oocyte viable for 24 hours following ovulation
Sperm remain viable for 3 to 4 days
11
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29.2a Fertilization
• Capacitation
– Physiological conditioning undergone by sperm to become
capable of fertilizing the secondary oocyte
– Occurs in female reproductive tract
– Glycoprotein coat and some proteins
o Removed from sperm plasma membrane
– Lasts several hours
12
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29.2a Fertilization
• Sperm
– Millions deposited in vagina during intercourse
o Few hundred with a chance at fertilization
– Attracted to oocyte by chemicals it releases
– Bound by progesterone released by cumulus cells around
oocyte
o Causes influx of Ca2+
o Necessary for capacitation, acrosome reaction, fertilization
– Attempt fertilization when reaching secondary oocyte
o Only one sperm able to fertilize
13
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29.2a Fertilization
• Corona radiata penetration
– First phase of fertilization
– Sperm reaching secondary oocyte
o Initially prevented entry by corona radiata and zona pellucida
– Can push through cell layers of corona radiata
14
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29.2a Fertilization
• Zona pellucida penetration
– Acrosome reaction
o Release of digestive enzymes from acrosomes
o Allows sperm to penetrate zona pellucida
– After penetration of secondary oocyte
o Immediate hardening of zona pellucida
o Prevents other sperm from entering this layer
o Ensures only one sperm fertilizes the oocyte
o Polyspermy, if two sperm enter simultaneously
˗ Immediately fatal with 23 triplets of chromosomes
15
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29.2a Fertilization
• Fusion of sperm and oocyte plasma and nuclei
– Contact of sperm and oocyte plasma membranes
o Immediately fuse
o Only sperm nucleus enters oocyte
– Secondary oocyte completing second meiotic division
o Forms an ovum
– Nucleus of sperm and ovum, pronuclei
o Each with haploid number of chromosomes
o Fuse to become diploid nucleus
– Zygote, the single diploid cell formed
16
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Fertilization of a Secondary Oocyte in Humans
Figure 29.2b
17
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29.2b Cleavage
• Cleavage
– Series of mitotic divisions of zygote
– Increases cell number but not overall size of structure
o Size only increases after implantation in uterine wall
– Before 8-cell stage
o Cells not tightly bound together
o Become tightly compacted after third cleavage divisions
o Compaction, process by which contact between cells is increased to
the max
18
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29.2b Cleavage
• Stages of development
– Morula, 16-cell stage
o Cells of morula continue to divide
o Develops fluid-filled cavity, blastocyst cavity
– At this stage, pre-embryo is a blastocyst
o Trophoblast, outer ring of cells surrounding cavity
˗ Will form the chorion
o Embryoblast, packed cells within one side of blastocyst
˗ Will form embryo proper
˗ Cells pluripotent, able to develop into any tissue
19
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Transit of the
Pre-Embryo
Through the
Uterine Tube:
Fertilization
Through
Implantation
Figure 29.4
20
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29.2c Implantation
• Implantation steps
–
–
–
–
Blastocyst enters lumen of uterus by end of first week
Zona pellucida around blastocyst breaks down
Blastocyst burrows into the endometrium, implantation
Begins by about day 7
o Trophoblast subdividing into 2 layers
˗ Cytotrophoblast, inner layer
˗ Syncytiotrophoblast, outer layer
– By day 9, blastocyst completely burrowed into uterine wall
o Contacts nutrients in uterine glands
21
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29.2c Implantation
• Human chorionic gonadotropin (hCG)
– Produced by syncytiotrophoblast
– Signals reproductive system that implantation occurred
– Promotes maintenance of corpus luteum
o Produces estrogen and progesterone to build uterine lining
– Detected in urine by end of 2nd week
o Basis of most pregnancy tests
– Levels high for first 3 months of pregnancy
o Then decline, causing corpus luteum degeneration
o By then placenta producing own estrogen to maintain pregnancy
22
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Hormone
Levels During
Pregnancy
Figure 29.6
23
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Clinical View: Chromosomal Abnormalities and Spontaneous Abortion
• Occur regularly during gametogenesis, fertilization, or
cleavage
• If severe, result in spontaneous abortion (miscarriage)
• Many within 2 to 3 weeks after fertilization, before
pregnancy known
• Perhaps 50% of pregnancies terminated from
spontaneous abortion
– Half from chromosomal abnormalities
24
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29.2d Formation of the Bilaminar Germinal Disc
and Extraembryonic Membranes
• Changes to embryoblast
– By day 8
o Cells of embryoblast starting to form two layers
o Hypoblast layer adjacent to blastocyst cavity
o Epiblast layer adjacent to amniotic cavity
o Together form flat disc, bilaminar germinal disc
25
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29.2d Formation of the Bilaminar Germinal
Disc and Extraembryonic Membranes
• Extraembryonic membranes
– Formed by bilaminar germinal disc and trophoblast
o Mediate between them and environment
– Protects embryo
– Assist in nutrition, gas exchange, and removal of waste
– Yolk sac
o 1st extraembryonic membrane to develop
o Continuous with hypoblast layer
o Does not store yolk (as it does in birds and reptiles)
o Important site for early blood cell and blood vessel formation
26
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29.2d Formation of the Bilaminar Germinal
Disc and Extraembryonic Membranes
• Extraembryonic membranes (continued)
– Amnion
o Membrane continuous with epiblast layer
o Eventually encloses entire embryo in fluid-filled sac, amniotic
cavity
o Protects membrane from drying out
o Specialized to secrete amniotic fluid bathing embryo
27
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29.2d Formation of the Bilaminar Germinal
Disc and Extraembryonic Membranes
• Extraembryonic membranes (continued)
– Chorion
o Outermost extraembryonic membrane
o Formed from cytotrophoblast cells and syncytiotrophoblast
o Cells blend with functional layer of endometrium
o Eventually form placenta
– Site of nutrient exchange between embryo and mother
28
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Implantation
of the
Blastocyst
Figure 29.5
29
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29.2e Development of the Placenta
• Placenta
–
–
–
–
–
Highly vascular structure
Site of exchange between maternal and fetal blood
Exchange of nutrients, waste products, and respiratory gases
Transmits maternal antibodies to developing embryo/fetus
Produces estrogen and progesterone
o Maintains and builds the uterine lining
– Begins to form during 2nd week
30
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29.2e Development of the Placenta
• Placental components
– Fetal portion developing from chorion
– Maternal portion from functional layer of uterus
– Connecting stalk
o Connects early embryo to placenta
o Eventually contains umbilical arteries and veins
o Precursor to future umbilical cord
31
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292e Development of the Placenta
• Placental components (continued)
– Chorionic villi
o Fingerlike structures formed from chorion
o Contain branches of umbilical vessels
– Gas and nutrient exchange
o Functional layer of endometrium with maternal blood vessels
o Maternal blood does not mix with fetal blood
o Bloodstreams so close that nutrients and gases mix
o O2 diffusing from maternal blood to fetal blood
o CO2 diffusing from fetal to maternal blood
32
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29.2e Development of the Placenta
• Placental characteristics
– Most growth during fetal period
– Adheres firmly to wall of uterus
– Expelled from uterus after the baby is born
o Afterbirth
– Selectively permeable structure
o E.g., respiratory gases passing freely
o Microorganisms and certain maternal hormones prevented
33
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29.2e Development of the Placenta
• Placental characteristics (continued)
– Some harmful substances able to cross
o E.g., viruses, bacteria, drugs, alcohol, toxins
o May cause birth defects or death
o Dose and timing affecting fetus susceptibility
o Pregnant women urged to quit smoking, refrain from taking drugs
and drinking alcohol
34
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Formation of
Extraembryonic
Membranes
Figure 29.7a
35
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Formation of Extraembryonic Membranes
Figure 29.7b
36
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Formation of Extraembryonic Membranes
Figure 29.7c
37
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•
What is the term for the release of
enzymes from the sperm that allows
penetration of the zona pellucida?
•
What is the outer ring of cells
surrounding the blastocyst cavity?
•
What is the functional role of hCG?
•
What are the two cell layers of the
bilaminar germinal disc?
•
What are the main functions of the
placenta?
What did you
learn?
38
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29.3 Embryonic
Period
1.
Learning
Objectives:
3.
2.
4.
5.
Describe the process of
gastrulation.
List the three primary germ
layers that compose the
embryo.
Explain the process and the
purpose of the folding of the
embryonic disc.
Describe how the three
primary germ layers
differentiate.
Define organogenesis and
explain the risk of teratogens
during this period.
39
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29.3a Gastrulation and Formation of the Primary Germ Layers
• Gastrulation
– Occurs during third week of development
– Critical period
– Epiblast forms three primary germ layers
o Cells from which all body tissues develop
o Ectoderm, mesoderm, endoderm
– Three-layered structure called an embryo
40
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29.3a Gastrulation and Formation of the Primary Germ Layers
• Gastrulation (continued)
– Begins with formation of primitive streak
o Thin depression on surface of epiblast
– Primitive node
o Cephalic end of streak
o Consists of elevated area surrounding small primitive pit
– Invagination
o Cells detaching from epiblast layer
o Migrate through primitive streak between epiblast and hypoblast layer
41
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29.3a Gastrulation and Formation of the Primary Germ Layers
• Gastrulation (continued)
– Endoderm
o Cells that displace hypoblast
– Mesoderm
o New primary germ layer of cells formed by epiblast cells
– Ectoderm
o Cells remaining in epiblast
– Epiblast, source of 3 primary germ layers
o All body tissues and organs derived from these layers
42
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The Role of the Primitive Streak
Figure 29.8a
43
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The Role of the Primitive Streak
Figure 29.8b
44
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The Role of the Primitive Streak
Figure 29.8c
45
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29.3b Folding of the Embryonic Disc
• Embryonic disc
– Flattened, discshaped 3-week
embryo
– Starts to fold on
itself during late
3rd and 4th week
– Two types of
folding
o Cephalocaudal
o Transverse
Figure 29.9
46
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29.3b Folding of the Embryonic Disc
• Embryonic disc (continued)
– Cephalocaudal folding
o Occurs in cephalic and caudal regions of embryo
o Rapid growth of embryonic disc and amnion
o No growth of yolk sac
o Causes head and tail to fold on themselves
o Creates future head and buttocks
47
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Folding of the
Embryonic
Disc
Figure 29.10a
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48
29.3b Folding of the Embryonic Disc
• Embryonic disc (continued)
– Transverse folding
o Left and right sides of embryo curving toward midline
o Start to pinch off the yolk sac
o Fusing of sides of embryonic disc in midline
o Creates cylindrical embryo
o Ectoderm solely along exterior of embryo
o Endoderm confined to internal region of embryo
o Yolk sac pinching off from most of endoderm
˗ Except vitelline duct
o Creates torso region
49
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Folding of the
Embryonic
Disc
Figure 29.10b
50
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29.3b Folding of the Embryonic Disc
Differentiation of ectoderm
– On external surface of cylindrical embryo
– Responsible for forming nervous system tissue
• Neurulation
– Forms
o Epidermis, sense organs, pituitary gland, adrenal medulla, enamel of
teeth, lens of eye
51
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29.3b Folding of the Embryonic Disc
• Differentiation of mesoderm
• Five categories of mesoderm
– Notochord
o Formed by tightly packed midline group of mesodermal cells
o Basis for central body axis and axial skeleton
o Induces formation of neural tube
– Paraxial mesoderm
• Found on both sides of neural tube
• Forms somites, blocklike masses
– Forms axial skeleton, muscle, and cartilage, dermis, and
connective tissues
52
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29.3b Folding of the Embryonic Disc
Differentiation of mesoderm (continued)
– Intermediate mesoderm
• Lateral to paraxial mesoderm
• Forms most of kidneys, ureters, and reproductive system
– Lateral plate mesoderm
• Most lateral layers of mesoderm
• Forms spleen, adrenal cortex, and cardiovascular system
• Serous membranes and connective tissue of limbs
– Head mesenchyme
• Forms connective tissues and musculature of face
53
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Differentiation of Mesoderm
Figure 29.12
54
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29.3b Folding of the Embryonic Disc
• Differentiation of endoderm
– Becomes innermost tissue after transverse folding
– Forms
o Linings of GI, respiratory, urinary, and reproductive tracts
o Tympanic cavity, auditory tube
o Liver, gallbladder, pancreas, palatine tonsils, thyroid and
parathyroid glands, thymus
55
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The Three
Primary
Germ Layers
and Their
Derivatives
Figure 29.11
56
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29.3c Organogenesis
• Organogenesis
– Organ development
– Begins once layers have formed and folding complete
– By week 8
o Upper/lower limbs have adult shape
o Most organ systems have rudimentary form
– By end of embryonic period
o Embryo only 2.5 cm but appears human
– Particularly sensitive to teratogens during this time
o Substances causing birth defects or death
o Include: alcohol, tobacco, drugs, and some viruses
57
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29.3c Organogenesis
• Organogenesis (continued)
– “Peak development” periods at different times
o E.g., limbs, weeks 4–8
o External genitalia, late embryonic through early fetal period
– Teratogens most dangerous during peak development of
particular system
58
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What did you
learn?
•
Which germ layer forms between
the epiblast and hypoblast? Which
one forms from cells displacing the
hypoblast? Which forms from cells
remaining in the epiblast?
•
From which primary germ layers
do the following structures derive:
(a) epidermis of skin, (b) muscle
tissue, (c) pancreas?
•
By what week of development have
most rudimentary organs formed?
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29.4 Fetal Period
Learning
Objectives:
1.
59
Describe the major events that
occur during the fetal stage of
development.
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60
29.4 Fetal Period
• Fetal period
From beginning of 3rd month to birth
Maturation of tissues and organs
Rapid growth of body
Length of fetus measured as crown-rump length or crownheel length
– 2.5 cm embryo grows to average 53cm at birth
– Weight increase most striking during last two months
–
–
–
–
61
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Fetal Stage of
Development (Table 29.3)
62
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Clinical View: Infertility and Infertility Treatments
• Inability to conceive and maintain a pregnancy
• Multiple causes
̶ Blocked uterine tubes
o Caused by pelvic inflammatory disease or endometriosis
̶ Ovulation disorders
̶ Anti-sperm antibodies or low sperm count
̶ Abnormal sperm, impaired sperm delivery
• Multiple possible treatments
̶ Intrauterine insemination
̶ Oral medications (Clomid)
̶ In vitro fertilization (IVF)
̶ Donor oocytes
63
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29.5 Effects of
Pregnancy on the
Mother
Learning
Objectives:
1.
2.
3.
4.
5.
Compare and contrast the first,
second, and third trimesters of
pregnancy.
Discuss the critical effects of
estrogen and progesterone
during pregnancy.
Identify other hormones whose
levels are altered during
pregnancy.
Explain the changes to the uterus
in a pregnant woman.
Describe the hormones that
affect mammary gland
development during pregnancy.
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64
29.5 Effects of
Pregnancy on the
Mother (continued)
Learning
Objectives:
6.
7.
8.
9.
10.
Describe the effects of HPL and
other hormones on the pregnant
woman’s ability to utilize
glucose.
List some common GI
complaints and conditions that
occur during pregnancy and their
causes.
List the cardiovascular changes a
woman typically exhibits during
pregnancy.
Explain the changes to the
respiratory system during
pregnancy.
Describe the effects of
pregnancy on the mother’s
urinary system.
65
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29.5a The Course of Pregnancy
• Pregnancy divided into trimesters
– First trimester
o First 3 months of pregnancy
o Zygote becoming embryo and then early fetus
– Second trimester
o Months 4 to 6 of pregnancy
o Growth of fetus and expansion of maternal tissues
– Third trimester
o Months 7 to 9 of pregnancy
o Fetus growing most rapidly
o Mother’s body preparing for labor and delivery
66
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29.5a The Course of Pregnancy
• Experience of pregnancy
– Varies between women
o E.g., “morning sickness,” weight gain, and pregnancy length
– Varies between same women during different pregnancies
o E.g., one labor easy, another long and difficult
67
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29.5b Hormonal Changes
• Estrogen and progesterone
– Produced by corpus luteum during first trimester
– Mostly produced by placenta in 2nd and 3rd trimesters
– High levels suppressing FSH and LH secretion
o Ovarian cycle and follicular development arrested
– Facilitate
o Uterine enlargement, mammary gland enlargement, and fetal growth
o Faster-growing nails, fuller hair
o Relaxation of ligamentous joints
o Functional layer growth due to progesterone
68
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29.5b Hormonal Changes
• Relaxin
– Secreted by corpus luteum and placenta
– Promotes blood vessel growth in uterus
• Corticotropin-releasing hormone (CRH)
– Secreted from placenta in large amounts
– Role in length of pregnancy and timing of childbirth
– Responsible for aldosterone rise in mother
o Promotes fluid retention and edema
69
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29.5b Hormonal Changes
• Human chorionic thyrotropin (HCT)
– Secreted by placenta
– Stimulates the thyroid gland
o Increases woman’s metabolic rate
• Human placental lactogen (HPL)
– Secreted from placenta
– Affects how pregnant woman metabolizes certain nutrients
o Mother metabolizing more fatty acids instead of glucose
o Inhibits effects of insulin
o More glucose available for fetus
70
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29.5b Hormonal Changes
• Prolactin
– Increased levels (10×) produced by anterior pituitary
– Ensures lactation occurs after giving birth
• Oxytocin
–
–
–
–
Increased levels produced by hypothalamus
Involved in uterine contractions
Involved in milk expulsion from mammary glands
Increase in second and third trimesters
o In response to rising estrogen levels
71
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29.5c Uterine and Mammary Gland Changes
• Uterine expansion
– Begins to enlarge once implantation occurs
– By 12 weeks
o Uterus just superior to pubic symphysis
– Impinges on space of urinary bladder
o Causes more frequent urination
o Especially during first and third trimesters
– Most of enlargement due to
o Muscle hypertrophy, hyperplasia, placental growth, and amniotic
fluid
72
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29.5c Uterine and Mammary Gland Changes
• Uterine expansion (continued)
– By 16 weeks
o Fundus at midpoint between pubic symphysis and umbilicus
–
–
–
–
–
–
Reaches level of umbilicus by week 22
Temporarily decreases pressure on urinary bladder
By ninth month fundus at xiphoid process of sternum
Compresses many abdominopelvic organs
Once again impinges on bladder
May cause GI ailments
73
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29.5c Uterine and Mammary Gland Changes
• Mammary glands
– Tender during first trimester
o Due to increasing levels of estrogen and progesterone
– Melanocyte-stimulating hormone
o Secreted by placenta
o Darkening of areola and nipples
o Darkens linea alba, now linea nigra
– Growth of mammary glandular tissue
o Development of additional acini
74
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Uterine and Mammary Gland Changes
During Pregnancy
Figure 29.13
75
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29.5d Digestive System, Nutrient, and Metabolic Changes
• Increased insulin resistance in pregnancy
– Due to increased levels of corticosteroids, estrogen,
progesterone, and HPL
– Can lead to gestational diabetes in mother
• Morning sickness
–
–
–
–
Experienced by many pregnant women in 1st trimester
Does not occur just in morning
Some with a little nausea, others with severe symptoms
Cause unknown, possibly due to high hormones
76
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29.5d Digestive System, Nutrient, and Metabolic Changes
• Abdominal complaints during pregnancy
–
–
–
–
Slowed intestinal motility
Higher progesterone resulting in relaxed smooth muscle
Materials remaining in GI tract for longer periods
Abdominal organ compression
o Resulting in heartburn and indigestion
– Constipation common
o Can lead to hemorrhoids
77
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29.5d Digestive System, Nutrient, and Metabolic Changes
• Nutrition
– Weight gain due to
o Fetus
o Placenta, breast, and uterine enlargement
o Fluid retention
o Adipose tissue
– About 300 extra calories/day needed
– Require adequate folic acid, calcium, protein, and iron
78
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Clinical View: Gestational Diabetes
•
•
•
•
•
Diabetes that first develops during pregnancy
Increased insulin resistance and high blood glucose
Symptoms appearing in 2nd trimester
May develop high blood pressure and complications
Risk of large baby
̶ Increased risk of cesarean section and birth complications,
hypoglycemia
• Special diet to regulate blood glucose levels
• At increased risk for type 2 diabetes later in life
79
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Clinical View: Hyperemesis Gravidarum
• Severe nausea and vomiting during pregnancy
• Results in dehydration, electrolyte imbalance, and
weight loss
• May require hospitalization and IV fluids
• Relatively rare
80
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29.5e Cardiovascular and Respiratory
System Changes
• Cardiovascular system
– Undergoes dramatic changes during pregnancy
– More blood needed
o To distribute respiratory gases and nutrients, to mother and fetus
o Plasma volume up by 50%
o Cardiac output increasing 30–50%
o Heart rate and stroke volume increased
81
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29.5e Cardiovascular and Respiratory System
Changes
• Cardiovascular system (continued)
– Changes in blood pressure
o May initially increase during first trimester
o Later drops due to decreased peripheral resistance
– Compression of abdominal blood vessels by fetus
o May impair venous return from lower body
o May cause varicose veins, hemorrhoids, and edema in lower limbs
82
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29.5e Cardiovascular and Respiratory
System Changes
• Respiratory system
– Expanding uterus prevents diaphragm from fully
descending and lungs from fully expanding
– May cause dyspnea, uncomfortable awareness of breathing
– May have epistaxis (nosebleeds)
o Due to increased circulation
83
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29.5e Cardiovascular and Respiratory
System Changes
• Respiratory system (continued)
– Progesterone
o Increases brainstem sensitivity to CO2
o Lowers blood CO2 levels
o Facilitates diffusion of gases across the placenta
– Providing oxygen to mother and fetus
o Increased tidal volume, pulmonary ventilation, respiratory rate, and
oxygen consumption
84
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29.5f Urinary System Changes
• Urinary system
–
–
–
–
Eliminates waste from mother and fetus
Must filter 50% more plasma volume
GFR increased 30–50%
Dilation of ureters and renal pelvis
o May result in urine stasis
– Ureters sometimes compressed by uterus
o Urinary tract infections more common
85
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Clinical View: Preeclampsia
• High blood pressure occurring by second half of pregnancy
• Risk factors of obesity, diabetes, older age, and previous
preeclampsia
• Cause unknown
• General risks of hypertension for mother
• Placenta with poor perfusion
• Only cure, giving birth
̶ May be prescribed bedrest, medications, or labor induction
• Eclampsia
̶ High blood pressure causing seizures
̶ Medical emergency
86
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What did you
learn?
•
What are the actions of human
chorionic thyrotropin? Oxytocin?
•
What hormone is responsible for
the darkening of the areolae?
•
What happens to the tidal volume
and pulmonary ventilation during
pregnancy?
Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education
29.6 Labor
(Parturition) and
Delivery
1.
2.
Learning
Objectives:
3.
4.
5.
87
Explain the physiologic
processes that initiate labor.
List the signs and
characteristics of false labor.
Explain the signs and
characteristics of true labor.
Describe the positive feedback
mechanisms of true labor.
List the three stages of true
labor and events of each stage.
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88
29.6 Labor (Parturition) and Delivery
• Labor
– Physical expulsion of fetus and placenta from uterus
– Typically at 38 weeks for full-term pregnancy
– Not all uterine contractions lead to true labor
• Increased levels of estrogen
– Increase uterine myometrium sensitivity
– Stimulate production of oxytocin receptors on uterine
myometrium
o More receptors available for binding this hormone
89
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29.6a Factors That Lead to Labor
• Contractions weak and irregular at first
– Can be noticed as soon as second trimester
– Become more intense and frequent with increasing estrogen and
oxytocin
• Premature labor
– Labor prior to 38 weeks
– Undesirable because infant’s body system not fully developed
o Especially lungs
o If very premature, at greater risk for morbidity and mortality
90
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29.6b False Labor
• Uterine contractions not resulting in 3 stages of labor
– Braxton-Hicks contractions
o Irregularly spaced and do not become more frequent
o Relatively weak and do not increase in intensity
o Pain limited to lower abdomen and pelvic region
o Pain sometimes stops with movement
o Do not lead to cervical changes
91
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29.6c Initiation of True Labor
• Uterine contractions that increase in intensity and
regularity, result in changes to the cervix
– Mother’s hypothalamus secrets increasing levels of oxytocin
– Fetus’s hypothalamus also secreting oxytocin
– Both sources stimulate placenta to secrete prostaglandins
o Fatty acids and hormonelike substances
o Stimulate uterine muscle contraction
o Soften and dilate the cervix
– Combined maternal and fetal oxytocin initiates true labor
92
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29.6c Initiation of True Labor
• Characteristics of true labor
–
–
–
–
–
Increase in frequency over time
Increase in intensity as labor progresses
Pain radiating from upper abdomen to lower back
Pain not going away in response to movement
Contractions facilitate cervical dilation and expulsion of
fetus/placenta
93
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29.6c Initiation of True Labor
• Positive feedback mechanism of labor
– Intense contractions pushing fetus’s head against cervix
o Stimulates stretching and dilation of cervix
o Signals hypothalamus to secrete more oxytocin
o Stimulate placenta to secrete more prostaglandins
– More intense uterine contractions
– Continues to intensify until fetus expelled
o With expulsion, major source of prostaglandins removed
o Uterus and cervix no longer fully stretched
o Drop of oxytocin levels
o Labor ceases
94
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Positive Feedback
Mechanism of True
Labor
Figure 29.14
95
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Clinical View: Inducing Labor
• Recommended if 2 weeks past due date
• Hospitalized night before
• Prostaglandin gel administered
̶ Assists with cervical dilation
• IV synthetic oxytocin (Pitocin) given to initiate true
labor
96
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Clinical View: Anesthetic Procedures
to Facilitate True Labor
• Pudendal nerve block
̶
Numbs pudendal nerve, main sensory nerve of perineum
Numbs lower vagina and perineum
Can feel contractions and vaginal stretching
May be given during 2nd stage of labor
̶
̶
̶
• Epidural nerve block
̶
Placed in epidural space
Numbs uterus, vagina, perineum, and lower limbs to some extent
Relieves pain associated with contractions
Usually does not interfere with contractions themselves
̶
̶
̶
• Spinal nerve block
̶
̶
̶
Reserved for cesarean sections
Anterior abdominal wall numbed prior to incisions
Limbs and pelvis completely numbed
97
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29.6d Stages of True Labor
• Dilation stage
–
–
–
–
–
1st stage of labor
Begins with onset of regular uterine contractions
Ends when cervix is effaced (thinned) and dilated to 10 cm
Longest of 3 stages
Greatest variability
o Nulliparous women (who have not given birth) experience longer
dilation stage, 8 to 24 hours
o Parous women (who have given birth) may be in this stage for 4 to
12 hours
98
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29.6d Stages of True Labor
• Dilation stage (continued)
– Starts with regularly spaced uterine contractions
o Increases in intensity and frequency
o Baby’s head against cervix causes effacing and dilation
– Rupture of amniotic sac and release of amniotic fluid
o “Water breaking”
o Manually ruptured if necessary
99
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Stages of True Labor and Childbirth
Figure 29.15a,b
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100
29.6d Stages of True Labor
• Expulsion stage
–
–
–
–
–
Begins with complete dilation of cervix
Ends with expulsion of fetus
Usually 30 min to several hours
Nulliparous women with longer stage
Uterine contractions help push fetus through vagina
o Facilitated if woman “bears down”
o Uses Valsalva maneuver to increase abdominal pressure
101
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29.6d Stages of True Labor
• Expulsion stage (continued)
– Crowning
o When first part of baby’s calvarium distends vagina
– Head followed by rest of the body
– Episiotomy sometimes necessary
o Perineal muscles surgically incised
o Creates wider opening for body
– Umbilical cord clamped and tied off
102
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Stages of True Labor and Childbirth
Figure 29.15c
103
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29.6d Stages of True Labor
• Placental stage
– Occurs after baby is expelled
– Uterus continuing to contract
o Compresses uterine blood vessels
o Displaces placenta from uterine wall
– Afterbirth
o Placenta and remaining fetal membranes
o Expulsion completed within 30 minutes
o Carefully examined to make sure all expelled
o If fragments left, can have extensive bleeding, other complications
104
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Stages of True Labor and Childbirth
Figure 29.15d
105
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Clinical View: Fetal Positioning and the Dilation Stage
• Normally fetus in vertex position
̶ Head down; face toward sacrum
̶ Ideal position for dilating cervix and pushing fetus through vagina
• Breech position
̶ Buttocks first
̶ May delay cervical dilation
• Variant positions extraction
̶ Forceps, vacuum may be needed
̶ Cesarean section
o Fetus delivered through abdominal incision
106
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What did you
learn?
•
What are the five signs of true
labor?
•
What are the three stages of labor?
Which usually lasts the longest?
Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education
29.7 Postnatal
Changes for the
Newborn
Learning
Objectives:
1.
2.
107
Describe the respiratory
events that occur as the
newborn adjusts to life outside
of the uterus.
Compare and contrast the fetal
circulatory pattern with the
newborn circulatory pattern.
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108
29.7 Postnatal Changes for the Newborn
• Respiratory changes in neonate
– Fetus after being expelled from uterus
– Fetal lungs not fully inflated prior to birth
o Takes breath within 10 seconds of birth
o Caused by central nervous system reactions to change in environment
o Lungs inflated with first breath
o Surfactant keeping alveoli open
o If born earlier than 28 weeks, surfactant insufficient
– May need ventilator until lungs mature
109
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29.7 Postnatal Changes for the Newborn
• Circulatory changes in neonate
– Prior to birth
o Blood shunted away from nonfunctional lungs
o E.g., ductus arteriosus, foramen ovale
– With first breath
o Drop of pulmonary resistance
o Dilation of pulmonary arteries
o Decreases pressure on right side of heart
o Pressure then greater on left side of heart
110
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29.8 Changes in the
Mother after
Delivery
Learning
Objectives:
1.
2.
3.
4.
Compare and contrast the
hormonal levels of a woman
prior to birth and after birth.
List the various ways that the
mother loses the excess fluids
gained during pregnancy.
Describe the process by which
lactation occurs.
Explain the mechanisms by
which the uterus returns close
to its pre-pregnancy size.
111
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29.8 Changes in the Mother after Delivery
• Postpartum
– Time period after giving birth
– Woman’s body undergoing further changes
o Feed neonate
o Return to pre-pregnancy form and function
112
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29.8a Hormonal Changes
• Estrogen and progesterone
– Levels plummeting within a few days of birth
o Uterine lining no longer needed
o Feelings of sadness and depression
o Hair reverts back to normal hair loss cycle
˗ Peak in loss about 3–4 months after delivery
o Chemoreceptors less sensitive to CO2 due to low progesterone
˗ Respiratory rate, tidal volume, and pulmonary ventilation return to
normal
113
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29.8a Hormonal Changes
• Corticotropin-releasing hormone (CRH)
– Levels drop dramatically
o Placenta stops producing CRH
o High levels during pregnancy associated with postpartum
depression
– Severe depression needing immediate treatment
114
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29.8b Blood Volume and Fluid Changes
• Fluid reduction
– Additional fluid was retained during pregnancy
o Requires quick and efficient expulsion
– Amniotic fluid expelled during labor
– Lochia
o Portion of blood volume, mucus endometrial tissue
o Expelled via the vagina
o Heaviest first five days, continues for several weeks
115
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29.8b Blood Volume and Fluid Changes
• Fluid reduction (continued)
– Excess fluid expelled via urination
o Decline in aldosterone via decline in CRH
o Precipitates overall drop in blood volume
o Increased urination in first 24 hours after birth
– Profuse sweating also common, which reduces fluid
116
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29.8c Lactation
• Lactation
̶ Production and release of breast milk from mammary glands
• Prolactin
̶ Produced by anterior pituitary
̶ Responsible for milk production
̶ Secretion inhibited by dopamine in nonpregnant women and
in men
̶ Increased by high levels of estrogen
• Both cause acini proliferation/branching of lactiferous ducts
• Responsible for preventing breast milk secretion until after
birth
117
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29.8c Lactation
• Colostrum
– Produced by mammary glands
o During late pregnancy and first few days after birth
– Watery, milklike substance
– Lower concentration of fat than true breast milk
– Rich in immunoglobulins, especially IgA
o Infant acquiring passive immunity from the mother
– Laxative effect, facilitating infant’s first bowel movement
118
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29.8c Lactation
• Breast milk
– Starts to be produced few days postpartum
– Higher fat content than colostrum
– Has essential fatty acids, enzymes for digestion, and
immunoglobulins
– More easily digestible than breast milk substitutes
– Optimal source of nutrition for an infant
119
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29.8c Lactation
• Milk letdown
– Release of breast milk
– Involves positive feedback mechanism
o With suckling, mechanoreceptors in breast stimulated
o Send signals to hypothalamus
o Hypothalamus is stimulated to produce oxytocin, released into blood by
pituitary
o Targets myoepithelial cells in mammary acini
– Cells contract, releasing breast milk from acini
o As milk released, infant continuing to nurse
– Facilitates further milk release
120
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29.8c Lactation
• Milk letdown (continued)
–
–
–
–
Prolactin spikes occur in prolactin production each time baby breastfeeds
Promotes new breast milk production
As infant feeds, dopamine release inhibited by hypothalamus
Inhibition stimulates large amounts of prolactin secretion
Figure 29.16b
121
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Lactation
Figure 29.16a
122
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29.8c Lactation
• Inhibition of ovulation
–
–
–
–
–
Often occurs with regular breastfeeding
GnRH release inhibited from the hypothalamus
Without GnRH, FSH and LH not released
Prevents ovulation
Not a reliable form a birth control
123
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29.8d Uterine Changes
• Afterpains
–
–
–
–
–
Contractions of uterus after giving birth
Stimulate shrinkage of uterus to close to pre-pregnancy size
Stimulated by oxytocin
Less severe after first week
Facilitated by breastfeeding
See Figure 29.17b: Anatomic and Physiologic Changes That Occur in the
Mother: Postpartum
124
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What did you
learn?
What effect does suckling
have on the hypothalamus?
•
125
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29.9 Heredity
Learning
Objectives:
1.
2.
3.
4.
Become familiar with
common genetic terminology.
Compare and contrast the
types of inheritance patterns.
Describe the sex-linked
inheritance and give a clinical
example of this type of
inheritance.
Explain how the environment
may influence genetic
expression.
126
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29.9a Overview of Human Genetics
• Genetics definitions
– Heredity
o Transmission of genetic characteristics from parent to child
– Genetics
o Field of biology studying heredity and transmission patterns
– Karyotype
o Display of chromosomes pairs, ordered and arranged by size and similar
features
– Homologous chromosomes
o Paired chromosomes with genes for equivalent biological characteristics
– Autosomes
o Twenty-two pairs of chromosomes without genes determining sex
127
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Karyotype
Figure 29.18
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128
29.9a Overview of Human Genetics
• Genetics definitions (continued)
– Sex chromosomes
o Last two chromosomes containing genes that specify sex
– Locus
• Specific space where each gene is located on a chromosome
– Alleles
• Variants of one gene found at some locus on homologous chromosomes
• E.g., alleles determining type A or type O blood
– Dominant allele
• Expresses, or physically shows, the trait
• Represented by capital letter
129
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29.9a Overview of Human Genetics
• Genetics definitions (continued)
– Recessive allele
• Trait is masked
• Expressed only if present on both homologous chromosomes
• Represented by lowercase letter
– Punnett square
• Box showing specific gene combinations resulting from two parents
• Gives probability that a particular gene combination can occur
– Homozygous
• If identical alleles present
130
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29.9a Overview of Human Genetics
• Genetics definitions (continued)
– Heterozygous
o Both dominant and recessive allele present
o But only dominant allele expressed
o Expression of the recessive allele may appear to skip generations
˗ Its phenotype is masked by the dominant allele
– Genotype
o Genetic makeup of an individual
– Phenotype
o Physical expression of genotype
131
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Dominant
Versus
Recessive
Alleles
Figure 29.19
132
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29.9b Patterns of Inheritance
• Strict dominant-recessive inheritance
–
–
–
–
–
Mendelian inheritance
Dominant allele always expressed in the phenotype
Relatively few traits follow this pattern
Most involving interaction of multiple genes
May be affected by environmental factors
See Table 29.4: Traits That Follow a Strict Dominant-Recessive Inheritance
133
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29.9b Patterns of Inheritance
• Incomplete dominance
– Two heterozygous alleles
o Phenotype is intermediate between homozygous dominant or recessive
– E.g., sickle cell trait
o Most individuals with two identical alleles, A
˗ Code for normal hemoglobin A in erythrocytes
o Sickling allele (s) produces abnormal hemoglobin (S)
˗ Erythrocytes brittle and sickle-shaped
o Sickle cell disease if two homozygous recessive alleles
o Heterozygous individuals carrying sickle cell trait
˗ Under low oxygen conditions some erythrocytes may develop sickle
shape
134
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29.9b Patterns of Inheritance
• Codominant inheritance
– Two alleles equally dominant
– Both alleles expressed in the phenotype
– E.g., ABO blood group
o Blood types A and B codominant
o A allele from one parent, B allele from other parent
– Leads to AB blood type
o Third allele, i, is recessive
o ii results in O blood type
135
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29.9b Patterns of Inheritance
• Polygenic inheritance
–
–
–
–
Multiple genes interacting to produce phenotypic trait
Genes on same or different chromosomes
Most human traits result from this
E.g., eye color, height, skin color, predispositions to many
diseases
136
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29.9c Sex-Linked Inheritance
• Sex-linked traits
– Traits expressed by genes on X or Y chromosomes
o 900–1400 genes on X chromosome
– Most not involved in sex determination
o 70–200 genes on Y chromosome
– Mostly for male development
o Sex-linked traits most often on X chromosome
137
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29.9c Sex-Linked Inheritance
• X-linked recessive traits
– Always expressed in a male
o Has only one X chromosome
– Expressed in a female only if she has two recessive alleles
o Low probability
– Carrier, woman with one X-linked recessive allele only
o Does not exhibit phenotypic effects
o May pass X-linked allele to children
o If passed to female, also a carrier
o If passed to a male, will express X-linked trait
138
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29.9c Sex-Linked Inheritance
• X-linked recessive traits (continued)
– E.g., color blindness
o Individual has trouble distinguishing red and green
o Women rarely color-blind
– Requires recessive allele from both mother and father
– More often carriers
o If man inherits allele
– Lacks normal allele to counteract color-blindness
– Will be color-blind
139
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29.9c Sex-Linked Inheritance
• X-linked recessive traits (continued)
– E.g., hemophilia A
o Disorder of blood clotting
o Individuals with disorder bleeding profusely after injury
o Females carriers; males affected
Figure 29.20a
140
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Hemophilia A
Figure 29.20b
141
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29.9c Sex-Linked Inheritance
• X-linked dominant traits (continued)
– Relatively rare
– Expressed in both males and females who carry it
– Men typically more severely affected
o Have no normal recessive allele to counteract effects of dominant
allele
o Many male zygotes with X-linked dominant disorder are
spontaneously aborted
142
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29.9d Penetrance and Environmental
Influences on Heredity
• Penetrance
– Percentage of population with genotype exhibiting expected
phenotype
– Influenced by a variety of factors
o E.g., hereditary pancreatitis with penetrance of 80%
o 20% of individuals with genotype without symptoms
143
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29.9d Penetrance and Environmental
Influences on Heredity
• Environmental effects on genetic traits
– Variable influence on many genetic traits
o Especially during embryonic and fetal development
– Teratogens can cause harm and interfere with phenotypic
development
o E.g., fetal alcohol syndrome
– Poor nutrition can have a negative effect on development
– Alleles with risk of cancer development
– Combination of genetics plus environment
144
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What did you
learn?
•
How does codominant inheritance
differ from incomplete dominance?
•
If a woman homozygous for color
blindness has children with a man
having normal vision, what would
be the phenotypes of her offspring?
145
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