PowerLecture: Chapter 17

PowerLecture:PowerLecture:Chapter 17Chapter 17

Development and AgingDevelopment and Aging

Learning ObjectivesLearning Objectives

Describe early embryonic development and Describe early embryonic development and distinguish each of the following: oogenesis, distinguish each of the following: oogenesis, fertilization, cleavage, gastrulation, and fertilization, cleavage, gastrulation, and organ formation.organ formation.

Correlate the three germ layers—ectoderm, Correlate the three germ layers—ectoderm, mesoderm, and endoderm—with the mesoderm, and endoderm—with the tissues that eventually form from each.tissues that eventually form from each.

Outline the principal events of prenatal Outline the principal events of prenatal development.development.

Learning Objectives (cont’d)Learning Objectives (cont’d)

Describe some of the risks to the early Describe some of the risks to the early development of the fetus.development of the fetus.

Describe the events of aging. Describe the events of aging.

Impacts/IssuesImpacts/Issues

Fertility Factors and Fertility Factors and Mind-Boggling BirthsMind-Boggling Births

Fertility Factors and Mind-Boggling Births Fertility Factors and Mind-Boggling Births

Multiple births are becoming more common; Multiple births are becoming more common; twins, triplets, quads, and so on are usually twins, triplets, quads, and so on are usually the result of the administration of fertility the result of the administration of fertility drugs to the prospective mother.drugs to the prospective mother.

Fertility Factors and Mind-Boggling Births Fertility Factors and Mind-Boggling Births

The rise in higher order The rise in higher order multiple births worries some multiple births worries some doctors.doctors.

The risk of miscarriage, The risk of miscarriage, premature delivery, and delivery premature delivery, and delivery complications is increased.complications is increased.

Multiples’ birth weights are lower Multiples’ birth weights are lower and mortality rates higher.and mortality rates higher.

Parents face more physical, Parents face more physical, emotional, and financial emotional, and financial burdens.burdens.

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Should we restrict the use of fertility drugs to Should we restrict the use of fertility drugs to conditions that could limit the number of conditions that could limit the number of embryos that form?embryos that form? a. Yes, multiple pregnancies are too risky and a. Yes, multiple pregnancies are too risky and

can lead to serious disabilities or death for can lead to serious disabilities or death for infants. infants.

b. No, reproductive decisions belong to b. No, reproductive decisions belong to individuals. There are other ways to reduce individuals. There are other ways to reduce multiple births. multiple births.

Section 1Section 1

The Six Stages of Early The Six Stages of Early Development: An OverviewDevelopment: An Overview

The Six Stages of Early DevelopmentThe Six Stages of Early Development

In the first three stages, gametes form, an In the first three stages, gametes form, an egg is fertilized, and cleavage occurs.egg is fertilized, and cleavage occurs.

DevelopmentDevelopment begins when begins when gametesgametes (sperm (sperm and eggs) form and mature in the prospective and eggs) form and mature in the prospective child’s parents.child’s parents.

FertilizationFertilization occurs when a sperm penetrates occurs when a sperm penetrates an egg; after a series of steps, fertilization an egg; after a series of steps, fertilization produces a produces a zygotezygote..

CleavageCleavage converts the zygote into a ball of cells converts the zygote into a ball of cells called a called a morulamorula..

Fig. 17.1, p. 314

zygote afterfirst cleavage

beginning ofthe ball of cells called a morula


• The number of cells increases but not individual cell The number of cells increases but not individual cell size.size.

• Each new cell (Each new cell (blastomereblastomere) contains a particular ) contains a particular portion of the egg’s cytoplasm, which will determine portion of the egg’s cytoplasm, which will determine its developmental fate.its developmental fate.

In stage four, three primary tissues form.In stage four, three primary tissues form. GastrulationGastrulation lays out the organizational lays out the organizational

framework for the body as the cells are framework for the body as the cells are arranged into three primary arranged into three primary germ layersgerm layers..


• EctodermEctoderm is the outer layer; it gives rise to the is the outer layer; it gives rise to the nervous system and the outer layers of the nervous system and the outer layers of the integument.integument.

• MesodermMesoderm is the middle layer; muscles as well as is the middle layer; muscles as well as organs of circulation, reproduction, excretion, and organs of circulation, reproduction, excretion, and the skeleton are derived from it.the skeleton are derived from it.

• EndodermEndoderm is the inner layer; it gives rise to the lining is the inner layer; it gives rise to the lining of the digestive tube and organs derived from it.of the digestive tube and organs derived from it.

Each layer will split into subgroups to give rise Each layer will split into subgroups to give rise to the body’s various tissues and organs. to the body’s various tissues and organs.


In stages five and six, organs begin to form, In stages five and six, organs begin to form, then grow and become specialized.then grow and become specialized.

OrganogenesisOrganogenesis begins as germ layers begins as germ layers subdivide into populations of cells destined to subdivide into populations of cells destined to become organs and tissues that are unique in become organs and tissues that are unique in structure and function.structure and function.

Growth and tissue specializationGrowth and tissue specialization allow allow organs to grow and acquire functional organs to grow and acquire functional capabilities.capabilities.


During the first several weeks of development During the first several weeks of development three key processes are at work:three key processes are at work:

• During During cell determinationcell determination, the eventual , the eventual developmental path is established.developmental path is established.

• In In cell differentiationcell differentiation, cells come to have specific , cells come to have specific structures, products, and functions associated with a structures, products, and functions associated with a specific purpose in the body.specific purpose in the body.

• MorphogenesisMorphogenesis is the organization of differentiated is the organization of differentiated cells into tissues and organs by means of localized cells into tissues and organs by means of localized cell division, movements of tissues, folding, and the cell division, movements of tissues, folding, and the like.like.

Fig. 17.2, p. 315

top view

Gamete Formation

Fertilization Cleavage GastrulationOrgan

FormationGrowth, TissueSpecialization

a Eggs form and mature in female reproductive organs. Sperm form and mature in male reproductive organs.

c Cell divisions carve up different regions of egg cytoplasm for daughter cells.

d Cell divisions, migrations, and rearrangements produce two or three primary tissues, the start of specialized tissues and organs.

e Subpopulations of cells are sculpted into specialized organs and tissues in spatial patterns at prescribed times.

f Organs increase in size and gradually assume their specialized functions.

b A sperm and an egg fuse at their plasma membrane. Then the nucleus of one fuses with the nucleus of the other to form the zygote

Fig. 17.2, p. 315

top view

Gamete Formation

Fertilization Cleavage GastrulationOrgan

FormationGrowth, TissueSpecialization

a Eggs form and mature in female reproductive organs. Sperm form and mature in male reproductive organs.

c Cell divisions carve up different regions of egg cytoplasm for daughter cells.

d Cell divisions, migrations, and rearrangements produce two or three primary tissues, the start of specialized tissues and organs.

e Subpopulations of cells are sculpted into specialized organs and tissues in spatial patterns at prescribed times.

f Organs increase in size and gradually assume their specialized functions.

b A sperm and an egg fuse at their plasma membrane. Then the nucleus of one fuses with the nucleus of the other to form the zygote

Stepped Art

Section 2Section 2

The Beginnings of You—The Beginnings of You—Fertilization to ImplantationFertilization to Implantation

Fertilization unites sperm and oocyte.Fertilization unites sperm and oocyte. Of the millions of sperm deposited in the vagina Of the millions of sperm deposited in the vagina

during coitus, only a few hundred ever reach during coitus, only a few hundred ever reach the upper region of the oviduct where the upper region of the oviduct where fertilization occurs.fertilization occurs.

• The acrosome of the sperm becomes structurally The acrosome of the sperm becomes structurally unstable in a process called unstable in a process called capacitationcapacitation..

• Many sperm will bind to the zona pellucida of the Many sperm will bind to the zona pellucida of the egg.egg.

The Beginnings of You – The Beginnings of You – Fertilization to ImplantationFertilization to Implantation

Only one sperm will successfully enter the Only one sperm will successfully enter the cytoplasm of the secondary oocyte because of cytoplasm of the secondary oocyte because of changes to the egg’s membrane that prevent changes to the egg’s membrane that prevent entry by additional sperm.entry by additional sperm.

• The arrival of that sperm inside stimulates the The arrival of that sperm inside stimulates the completion of meiosis II in the secondary oocyte, completion of meiosis II in the secondary oocyte, which yields a mature which yields a mature ovumovum and a second polar and a second polar body.body.

• The sperm nucleus fuses with the egg nucleus to The sperm nucleus fuses with the egg nucleus to restore the human diploid chromosome number of restore the human diploid chromosome number of 46.46.


zona pellucida

follicle cell

fusion of sperm nucleus with egg nucleus

FERTILIZATION

OVULATION

oviduct

ovary

uterus

opening of cervix

vagina

sperm enter

vagina

Fig. 17.3a-d, p. 316

nucleifuse

egg nucleus

a

b

d

c

Cleavage produces a multicellular embryo.Cleavage produces a multicellular embryo. Repeated divisions of the zygote produce the morula; Repeated divisions of the zygote produce the morula;

the cells are not necessarily larger but differ in size, the cells are not necessarily larger but differ in size, shape, and activity.shape, and activity.

When the morula reaches the uterus, it transforms into When the morula reaches the uterus, it transforms into a a blastocystblastocyst, consisting of a surface layer of cells—the , consisting of a surface layer of cells—the trophoblasttrophoblast—and an —and an inner cell massinner cell mass, from which the , from which the embryoembryo develops. develops.

Identical twinsIdentical twins are the result of a separation of the two are the result of a separation of the two cells produced by the first cleavage; cells produced by the first cleavage; fraternal twinsfraternal twins are are not identical because they are the result of two separate not identical because they are the result of two separate fertilizations.fertilizations.


Implantation gives a foothold in the uterus.Implantation gives a foothold in the uterus. ImplantationImplantation into the wall of the uterus takes into the wall of the uterus takes

place about a week after fertilization.place about a week after fertilization.• The blastocyst contacts and invades the The blastocyst contacts and invades the

endometrium; eventually the endometrium will endometrium; eventually the endometrium will

close over it.close over it.• Sometimes an Sometimes an ectopicectopic ((tubaltubal) )

pregnancypregnancy occurs; this is where the occurs; this is where the

fertilized egg implants outside of the fertilized egg implants outside of the

uterus, often in the oviduct, and must uterus, often in the oviduct, and must

be surgically removed.be surgically removed.


Figure 17.25Figure 17.25

The implanted embryo releases The implanted embryo releases HCGHCG (human (human chorionic gonadotropin), which stimulates the chorionic gonadotropin), which stimulates the corpus luteum to continue secreting estrogen corpus luteum to continue secreting estrogen and progesterone to maintain the uterine lining; and progesterone to maintain the uterine lining; the presence of HCG in the mother’s urine is the presence of HCG in the mother’s urine is the basis for home pregnancy tests. the basis for home pregnancy tests.


Days 1-2 Day 3 Day 4

inner cell mass

Day 5

endometriumimplantation

fertilization

Fig. 17.4, p. 317

a b c d Days 6-7e

endometrium

blastocoel

trophoblast (surfacelayer of cells of theblastocyst)

uterinecavity

inner cell mass

fluid

The first cleavagefurrow extendsbetween the twopolar bodies.

After the thirdcleavage, cells form a compact ball

By 96 hoursthere is a ball of 16to 32 cells. This is themorula. Cells of the surface layer will function in implantation and will give rise to amembrane, the chorion.

A fluid-filledcavity forms in the morula.By the 32-cell stage,differentiation is occurringin an inner cell mass thatwill give rise to the embryo.This embryonic stage is the blastocyst.

Some ofthe blastocyst’s surface cells attach themselves to the endometrium andstart to burrow into it. Implantation has started.

Days 1-2 Day 3 Day 4

inner cell mass

Day 5

endometriumimplantation

fertilization

Fig. 17.4, p. 317

a b c d Days 6-7e

endometrium

blastocoel

trophoblast (surfacelayer of cells of theblastocyst)

uterinecavity

inner cell mass

fluid

Stepped Art

Section 3Section 3

How the Early Embryo How the Early Embryo Takes ShapeTakes Shape

How the Early Embryo Takes Shape How the Early Embryo Takes Shape

First, the basic body plan is established.First, the basic body plan is established. By the time of implantation, the inner cell mass By the time of implantation, the inner cell mass

has transformed into a pancake-shaped has transformed into a pancake-shaped embryonic diskembryonic disk..

Gastrulation rearranges the cells into the three Gastrulation rearranges the cells into the three germ layers and the germ layers and the primitive streakprimitive streak; ectoderm ; ectoderm thickens around the streak to establish the thickens around the streak to establish the neural tubeneural tube and and notochordnotochord, which eventually , which eventually forms the brain, spinal cord, and vertebral forms the brain, spinal cord, and vertebral column.column.

epidermis

lined body cavity (coelom); lining also holds internal organs in place

peritoneum

gut cavity

Fig. 17.5a, p. 318


By week three, blocks of mesoderm called By week three, blocks of mesoderm called somites form and will give rise to connective somites form and will give rise to connective tissues, bones, and muscles; pharyngeal tissues, bones, and muscles; pharyngeal arches (face, neck, and associated parts) and arches (face, neck, and associated parts) and the coelom (body cavity) also begin to form.the coelom (body cavity) also begin to form.

primitive streak

yolk sac

embryonic disk amniotic

cavity

chorionic cavity

a DAY 15. A primitive streak appears along the axis of the embryonic disk. This thickened band of cells marks the onset of gastrulation.

Fig. 17.5b, p. 318

future brain

somites

b DAYS 19-23. Cell migrations, tissue folding, and other morphogenic events lead to the formation of a hollow neural tube and to somites (bumps of mesoderm). The neural tube gives rise to the brain and spinal cord. Somites give rise to most of the axial skeleton, skeletal muscles, and much of the dermis.

pharyngeal arches

c DAYS 24-25. By now, some cells have given rise to pharyngeal arches, which contribute to the face, neck, mouth, nasal cavities, larynx, and pharynx.

neuraltube


Next, organs develop and take on the Next, organs develop and take on the proper shape and proportions.proper shape and proportions.

NeurulationNeurulation is the first stage in the is the first stage in the development of the nervous system.development of the nervous system.

• Ectodermal cells at the midline of the embryo Ectodermal cells at the midline of the embryo elongate to form a neural plate.elongate to form a neural plate.

• Cells of the neural plate fold over and meet at the Cells of the neural plate fold over and meet at the midline to form a neural tube that will eventually form midline to form a neural tube that will eventually form the spinal cord and brain.the spinal cord and brain.


The folding of sheets of cells is an The folding of sheets of cells is an important part of morphogenesis.important part of morphogenesis.

• Cells migrate from one place to another Cells migrate from one place to another by sending out pseudopods that guide by sending out pseudopods that guide them along prescribed routes using them along prescribed routes using adhesive and chemical cues.adhesive and chemical cues.

• Body parts are sculpted by Body parts are sculpted by apoptosisapoptosis, , a mechanism of genetically a mechanism of genetically programmed cell death.programmed cell death.

Figures 17.6b and 17.7Figures 17.6b and 17.7

neural tube

Fig. 17.6, p. 319

ectoderm at gastrula stage

neural plate formation

a

b

“climbing”nerve cell

Section 4Section 4

Vital Membranes Vital Membranes Outside the EmbryoOutside the Embryo

Four extraembryonic membranes form.Four extraembryonic membranes form. The inner cell mass becomes the embryonic The inner cell mass becomes the embryonic

disk; some cells will give rise to the embryo, disk; some cells will give rise to the embryo, others to the others to the extraembryonic membranesextraembryonic membranes..

• The The yolk sacyolk sac gives rise to the digestive tube and is a gives rise to the digestive tube and is a source of early blood cells.source of early blood cells.

• The The amnionamnion is a fluid-filled sac that keeps the is a fluid-filled sac that keeps the embryo from drying out and acts as a shock embryo from drying out and acts as a shock absorber; the fluid is absorber; the fluid is amniotic fluidamniotic fluid..

Vital Membranes Outside the Embryo Vital Membranes Outside the Embryo

• The The allantoisallantois gives rise to the blood vessels that will gives rise to the blood vessels that will become enclosed in the become enclosed in the umbilical cordumbilical cord, linking the , linking the embryo to the placenta.embryo to the placenta.

• The The chorionchorion, a protective membrane around the , a protective membrane around the embryo, secretes HCG to maintain the uterine lining embryo, secretes HCG to maintain the uterine lining after implantation.after implantation.


start of amniotic cavity

start of embryonic disk

start of yolk sac

a DAYS 10-11. The yolk sac, embryonic disk, and amniotic cavity have started to form from parts of the blastocyst.

Fig. 17.8, p. 320

b DAY. 12 Blood filled spaces form in maternal tissue. The chorionic cavity starts to form.

c Day 14 A connecting stalk has formed between the embryonic disk and chorion. Chorionic villi which will be features of a placenta start to form.

blood-filled spaces

start of chorionic cavity

yolk sac

chorionic cavity

chorionic villi

chorion

amniotic cavity

connecting stalk

The placenta is a pipeline for oxygen, The placenta is a pipeline for oxygen, nutrients, and other substances.nutrients, and other substances.

The The placentaplacenta is a combination of endometrial is a combination of endometrial tissue and embryonic chorion.tissue and embryonic chorion.

• The maternal tissue consists of tissues rich in The maternal tissue consists of tissues rich in arterioles and venules.arterioles and venules.

• The embryo’s chorion extends into the maternal The embryo’s chorion extends into the maternal tissue as tiny tissue as tiny chorionic villichorionic villi..


Materials are exchanged between the blood Materials are exchanged between the blood capillaries of mother and fetus where these capillaries of mother and fetus where these vessels associate in the blood-filled spaces of vessels associate in the blood-filled spaces of the endometrium; exchange is by diffusion.the endometrium; exchange is by diffusion.

• Maternal and fetal bloods do not mix.Maternal and fetal bloods do not mix.• Harmful substances, such as alcohol, caffeine, Harmful substances, such as alcohol, caffeine,

drugs, and even infectious agents such as HIV drugs, and even infectious agents such as HIV

can also cross the placenta.can also cross the placenta.


4 weeks

8 weeks

12 weeks

appearance of the placenta at full term

Fig. 17.9 (1), p. 321

MATERNAL CIRCULATION

mother’sblood vessels

tissuesof uterus

FETAL CIRCULATION

embryonic blood vessels

umbilical cordspace between chorionic villi

chorionic villus

fused amniotic and chorionic membranes

AMNIOTIC FLUID

blood passes to and from mother’s vessels

Section 5Section 5

The First Eight Weeks—The First Eight Weeks—Human Features Human Features

EmergeEmerge

The embryonic stage ends as the eighth The embryonic stage ends as the eighth week draws to a close; by this time week draws to a close; by this time morphogenesis has begun to form the morphogenesis has begun to form the features that show us to be human.features that show us to be human.


The First Eight Weeks – The First Eight Weeks – Human Features EmergeHuman Features Emerge

Fig. 17.10a, p. 322

WEEK 4

taillower limb bud neural tube

forming

somitesupper limb bud

developing heart

pharyngealarches

future lens

forebrain

embryo

connecting stalk

yolk sac

a

Fig. 17.10b, p. 322

head growth exceedsgrowth of other regions

umbilical cord formsbetween weeks 4 and 8(amnion expands, formstube that encloses theconnecting stalk and aduct for blood vessels)

upper limb differentiation(hand plates develop, then digital rays of future fingers;wrist, elbow start forming)

foot plate

future external earretinal pigment

WEEKS 5–6

b

Fig. 17.10c, p. 322

WEEK 8

final week of embryonic period; embryo looks distinctly human compared to other vertebrate embryos

upper and lower limbs well formed; fingers and then toes have separated

early tissues of all internal, external structures now developed

tail has become stubby

Gonad development begins by the second Gonad development begins by the second half of the first trimester.half of the first trimester.

An embryo with a Y chromosome will have a An embryo with a Y chromosome will have a sex-determining region on the chromosome that sex-determining region on the chromosome that triggers the development of testes; testes will triggers the development of testes; testes will produce male hormones that will influence produce male hormones that will influence further sex differentiation.further sex differentiation.

An XX embryo will become a female because of An XX embryo will become a female because of the absence of testosterone; no other the absence of testosterone; no other hormones are necessary at this point.hormones are necessary at this point.


10 weeks

Y chromosome present

Y chromosome absent

7 weeks

birth approaching

penis

vaginal opening

Fig. 17.11, p. 323

birth approaching

10 weeks

Y chromosome present

Y chromosome absent

7 weeks

birth approachingFig. 17.11, p. 323

vaginal opening

birth approaching

penis

Stepped Art

At the end of eight weeks of development, At the end of eight weeks of development, the embryo is designated a the embryo is designated a fetusfetus; a heart ; a heart monitor at this point can detect the fetal monitor at this point can detect the fetal heartbeat. heartbeat.

MiscarriageMiscarriage is the spontaneous expulsion is the spontaneous expulsion of an embryo or fetus.of an embryo or fetus.

This occurs in about 20% of all conceptions, This occurs in about 20% of all conceptions, usually during the first trimester.usually during the first trimester.

More than half of all spontaneous abortions More than half of all spontaneous abortions occur because of genetic disorders in the occur because of genetic disorders in the embryo/fetus.embryo/fetus.


Section 6Section 6

Development Development of the Fetusof the Fetus

Development of the Fetus Development of the Fetus

In the second trimester movements begin.In the second trimester movements begin. The second trimester encompasses the fourth The second trimester encompasses the fourth

through sixth months.through sixth months. Fuzzy hair (Fuzzy hair (lanugolanugo) and a cheesy coating ) and a cheesy coating

((vernix caseosavernix caseosa) cover the body.) cover the body. The sucking reflex is evident, as is movement The sucking reflex is evident, as is movement

of the arms and legs; the fetus is about 4-5 of the arms and legs; the fetus is about 4-5 inches long at this point.inches long at this point.


Organ systems mature during the third Organ systems mature during the third trimester.trimester.

The third trimester extends from month seven The third trimester extends from month seven until birth; the earliest delivery in which survival until birth; the earliest delivery in which survival on its own is possible is the middle of this on its own is possible is the middle of this trimester.trimester.

Babies born before seven months’ gestation Babies born before seven months’ gestation often suffer from often suffer from respiratory distress respiratory distress syndromesyndrome..


Fig. 17.12(1), p. 324

placenta

WEEK 16

Length: 16 cm(6.4 inches)

Weight: 200 gm(7 ounces)

WEEK 38 (full term)

Length:

Weight:

50 centimeters (20 inches)

3,400 grams (7.5 pounds)

WEEK 29

Length: 27.5 centimeters (11 inches)

Weight: 1,300 grams (46 ounces)

placenta


The blood and circulatory system of a fetus The blood and circulatory system of a fetus have special features.have special features.

Deoxygenated blood is carried from the fetus to Deoxygenated blood is carried from the fetus to the placenta in two umbilical arteries; the placenta in two umbilical arteries; oxygenated blood is returned to the fetus via oxygenated blood is returned to the fetus via the umbilical vein.the umbilical vein.

The lungs are bypassed due to the The lungs are bypassed due to the foramen foramen ovale ovale and the and the ductus arteriosusductus arteriosus..

The The ductus venosusductus venosus allows blood to proceed allows blood to proceed directly from the placenta to the heart, directly from the placenta to the heart, bypassing the liver.bypassing the liver.

aorta

superior vena cava

foramen ovale

liver

umbilical veinumbilical cord

placenta

arterial duct (ductus arteriosus) pulmonary vessels

heart

venous duct (ductus venous)

inferior vena cava

allantois

umbilical arteries

urinary bladder

Fig. 17.13a, p. 325

closed foramen ovale(fossa ovalis)

hepatic vein

umbilicus (navel)ligament

umbilical ligaments

ligament pulmonary artery

pulmonary veins

hepatic portal vein serving the liver

degenerated allantois

(urinary bladder)

Fig. 17.13b, p. 325

Section 7Section 7

Birth and BeyondBirth and Beyond

Birth and Beyond Birth and Beyond

Hormones trigger birth. Hormones trigger birth. Birth (Birth (parturitionparturition) usually takes place about 39 ) usually takes place about 39

weeks after fertilization.weeks after fertilization. The process of “labor” begins when the smooth The process of “labor” begins when the smooth

muscles of the uterus begin to contract, muscles of the uterus begin to contract, stimulated by the hormones oxytocin and stimulated by the hormones oxytocin and prostaglandin.prostaglandin.

Labor has three stages.Labor has three stages.


In the first stage, contractions of the uterine In the first stage, contractions of the uterine muscles push the fetus against the cervix; the muscles push the fetus against the cervix; the cervical canal dilates to about 10 centimeters, cervical canal dilates to about 10 centimeters, and the amniotic sac ruptures.and the amniotic sac ruptures.

In the second stage, birth occurs and the fetus In the second stage, birth occurs and the fetus is forcefully expelled from the uterus because of is forcefully expelled from the uterus because of contractions and the mother’s urge to push; the contractions and the mother’s urge to push; the baby usually comes out head first (bottom first baby usually comes out head first (bottom first is called is called breechbreech position). position).

The third stage occurs after birth; continued The third stage occurs after birth; continued contractions force fluid, blood, and the placenta contractions force fluid, blood, and the placenta ((afterbirthafterbirth) from the mother’s body and the ) from the mother’s body and the umbilical cord is severed.umbilical cord is severed.

detaching placenta

umbilical cord

Fig. 17.14, p. 326

placenta uterus

umbilical cord

dilatingcervix

a b c


Hormones also control milk production in a Hormones also control milk production in a mother’s mammary glands.mother’s mammary glands.

The mammary glands produce a special fluid The mammary glands produce a special fluid ((colostrumcolostrum) for the newborn for the first few ) for the newborn for the first few days; then, under the influence of prolactin, milk days; then, under the influence of prolactin, milk production (production (lactationlactation) occurs.) occurs.

Suckling by the baby stimulates the pituitary to Suckling by the baby stimulates the pituitary to release oxytocin, which in turn forces milk into release oxytocin, which in turn forces milk into the ducts of the breast tissue in a positive the ducts of the breast tissue in a positive feedback circuit.feedback circuit.

adipose tissue

nipple

(a) Breast anatomy.

milk-producing mammary gland

milk duct

(b) Breast of lactating female.Fig. 17.15, p. 327

Section 8Section 8

Potential Disorders of Potential Disorders of Early DevelopmentEarly Development

Good maternal nutrition is vital.Good maternal nutrition is vital. Maternal diet, especially vitamins and minerals, Maternal diet, especially vitamins and minerals,

is important throughout pregnancy for the is important throughout pregnancy for the proper development of the fetal tissues.proper development of the fetal tissues.

Folic acid (folate) is vital for preventing Folic acid (folate) is vital for preventing spina spina bifidabifida, a condition where the neural tube does , a condition where the neural tube does not form properly and the baby is born with an not form properly and the baby is born with an exposed spine.exposed spine.

Severe restriction of the maternal diet can Severe restriction of the maternal diet can result in underweight babies; a pregnant result in underweight babies; a pregnant woman should expect to gain between 20 and woman should expect to gain between 20 and 35 pounds, on average, during pregnancy.35 pounds, on average, during pregnancy.

Potential Disorders of Early DevelopmentPotential Disorders of Early Development

Infections present risks.Infections present risks. Risk of infection in the fetus is Risk of infection in the fetus is

minimized by maternal antibodies minimized by maternal antibodies that cross over into the fetal blood.that cross over into the fetal blood.

However, viral diseases in the However, viral diseases in the mother (such as mother (such as rubellarubella, or , or German measles) can cause fetal German measles) can cause fetal malformations; such agents act as malformations; such agents act as teratogensteratogens..


Prescription drugs can harm.Prescription drugs can harm. Thalidomide can cause limb deformities; Thalidomide can cause limb deformities;

retinoic acid, such as is found in anti-acne retinoic acid, such as is found in anti-acne creams, increases the risk of facial and cranial creams, increases the risk of facial and cranial deformities.deformities.

Antibiotics can be a problem also: tetracycline Antibiotics can be a problem also: tetracycline causes yellowed teeth, and streptomycin causes yellowed teeth, and streptomycin causes hearing problems.causes hearing problems.


Alcohol and other drugs can also harm.Alcohol and other drugs can also harm. Alcohol can cross the Alcohol can cross the

placenta and cause placenta and cause many effects collectively many effects collectively known as known as fetal alcohol fetal alcohol syndromesyndrome (FAS), which (FAS), which is one of the most common is one of the most common causes of mental retardation causes of mental retardation in the U.S.; children with in the U.S.; children with FAS never catch up, FAS never catch up, physically or mentally.physically or mentally.



Cocaine, especially crack cocaine, prevents a Cocaine, especially crack cocaine, prevents a child’s nervous system from developing child’s nervous system from developing normally; affected children are chronically normally; affected children are chronically irritable and small for their chronological age.irritable and small for their chronological age.

Cigarette smoking can cause miscarriage, Cigarette smoking can cause miscarriage, stillbirth, and premature delivery; long term stillbirth, and premature delivery; long term studies show that toxic substances build up in studies show that toxic substances build up in the fetuses of nonsmokers who are exposed to the fetuses of nonsmokers who are exposed to second-hand smoke.second-hand smoke.


Sensitivity to TeratogensSensitivity to Teratogens


Section 9Section 9

Prenatal Diagnosis: Prenatal Diagnosis: Detecting Birth DefectsDetecting Birth Defects

Medical technology now allows us to detect Medical technology now allows us to detect more than 100 genetic disorders before more than 100 genetic disorders before birth.birth.

AmniocentesisAmniocentesis samples the fluid within the samples the fluid within the amnion surrounding the fetus to retrieve amnion surrounding the fetus to retrieve sloughed off cells, which can be analyzed for sloughed off cells, which can be analyzed for genetic abnormalities.genetic abnormalities.

Prenatal Diagnosis: Prenatal Diagnosis: Detecting Birth Defects Detecting Birth Defects

Fig. 17.19a, p. 330

Centrifugation

Growth for weeks in culture medium

Fetal cells

A few biochemical analyses with some of the amniotic fluid

Quick determination of fetal sex and analysis of purified DNA

Biochemical analyses for the presence of genes that cause many different metabolic disorders

Removal of about 20ml of amnioticfluid containing suspended cellsthat were sloughed off from the fetus

Additional analysisFig. 17.19b, p. 330

Chorionic villus samplingChorionic villus sampling (CVS) carefully (CVS) carefully harvests tissue from the placenta for cell harvests tissue from the placenta for cell analysis.analysis.

In In preimplantation diagnosispreimplantation diagnosis, an embryo , an embryo conceived by IVF is analyzed for genetic conceived by IVF is analyzed for genetic defects before it is implanted into the uterus to defects before it is implanted into the uterus to begin gestation.begin gestation.


FetoscopyFetoscopy allows allows

direct visualization direct visualization

of the developing of the developing

fetus using a fetus using a

fiber-optic device.fiber-optic device. All of these All of these

procedures carry procedures carry

risks to the unborn risks to the unborn

fetus.fetus.



Video: Pre-implantation GeneticsVideo: Pre-implantation Genetics

This video clip is available in CNN Today This video clip is available in CNN Today Videos for Genetics, 2005, Volume VII. Videos for Genetics, 2005, Volume VII. Instructors, contact your local sales Instructors, contact your local sales representative to order this volume, while representative to order this volume, while supplies last.supplies last.

Section 10Section 10

From Birth to AdulthoodFrom Birth to Adulthood

From Birth to Adulthood From Birth to Adulthood

There are many transitions from birth to There are many transitions from birth to adulthood.adulthood.

PrenatalPrenatal development occurs before birth; a development occurs before birth; a newborn is referred to as a newborn is referred to as a neonateneonate..

The stages of The stages of postnatalpostnatal development are: development are: neonate (first two weeks) >>> infant (two weeks neonate (first two weeks) >>> infant (two weeks to 15 months) >>> child (to 12 years) >>> to 15 months) >>> child (to 12 years) >>> pubescent (individual at pubescent (individual at pubertypuberty) >>> ) >>> adolescent (from puberty to 3–4 years later) adolescent (from puberty to 3–4 years later) >>> adult >>> old age.>>> adult >>> old age.


Certain of these stages are characterized by Certain of these stages are characterized by more noticeable changes such as the growth more noticeable changes such as the growth spurt and the reproductive changes of puberty. spurt and the reproductive changes of puberty.



Adulthood is also a time of bodily change.Adulthood is also a time of bodily change. Aging (Aging (senescencesenescence) is the progressive cellular ) is the progressive cellular

and bodily deterioration built into the life cycle and bodily deterioration built into the life cycle of all organisms.of all organisms.

• Beginning around age 40 there is a gradual decline Beginning around age 40 there is a gradual decline in bone and muscle mass, increased skin wrinkling, in bone and muscle mass, increased skin wrinkling, and more fat deposition.and more fat deposition.

• Metabolic rates decline, reflexes become slower, and Metabolic rates decline, reflexes become slower, and reduced collagen contents make tissues all over the reduced collagen contents make tissues all over the body less elastic.body less elastic.

The definitive causes of aging are not known.The definitive causes of aging are not known.

Stages of Human Stages of Human DevelopmentDevelopment


Time’s Toll: Time’s Toll: Everybody AgesEverybody Ages

AgingAging is the gradual loss of vitality as body is the gradual loss of vitality as body functions become less and less efficient.functions become less and less efficient.

Skin begins to noticeably wrinkle and sag; body Skin begins to noticeably wrinkle and sag; body fat accumulates; injuries fat accumulates; injuries

are more frequent and are more frequent and

harder to heal.harder to heal. In the connective tissues, In the connective tissues,

more crosslinks form in more crosslinks form in

the collagen, making it less pliable.the collagen, making it less pliable.

Time’s Toll: Everybody Ages Time’s Toll: Everybody Ages


Genes may determine the maximum human Genes may determine the maximum human life span.life span.

Cells may have some internal, biological clock Cells may have some internal, biological clock with a predetermined life span.with a predetermined life span.

Support for this idea comes from our knowledge Support for this idea comes from our knowledge of of telomerestelomeres, which cap the ends of , which cap the ends of chromosomes; at each cell division a small bit chromosomes; at each cell division a small bit of telomere is lost until none is left and cell of telomere is lost until none is left and cell division is no longer possible.division is no longer possible.


Cumulative damage to DNA may also play Cumulative damage to DNA may also play a role in aging.a role in aging.

A “cumulative assaults” hypothesis suggests A “cumulative assaults” hypothesis suggests that aging results from mounting damage to that aging results from mounting damage to DNA combined with a lack of DNA repair.DNA combined with a lack of DNA repair.

• Free radicals of oxygen could cause damage to Free radicals of oxygen could cause damage to proteins and mitochondrial DNA.proteins and mitochondrial DNA.

• There may be a decline in the ability of cells to repair There may be a decline in the ability of cells to repair DNA.DNA.

Aging may ultimately be due to a wide range of Aging may ultimately be due to a wide range of controlling factors.controlling factors.



Aging Skin, Muscle, Aging Skin, Muscle, Bones, and Bones, and

Reproductive SystemsReproductive Systems

Changes in connective tissue affect skin, Changes in connective tissue affect skin, muscles, and bones.muscles, and bones.

Changes in the skin include: slower Changes in the skin include: slower replacement of epidermis; elastin fibers are replacement of epidermis; elastin fibers are replaced with more rigid collagen; fewer oil and replaced with more rigid collagen; fewer oil and sweat glands are present, resulting in drier skin; sweat glands are present, resulting in drier skin; and loss of hair pigment.and loss of hair pigment.

Changes in muscle include: loss of mass and Changes in muscle include: loss of mass and strength; muscle replacement by fat.strength; muscle replacement by fat.

Aging Skin, Muscle, Bones, and Aging Skin, Muscle, Bones, and Reproductive Systems Reproductive Systems

Changes in the skeleton are Changes in the skeleton are

also seen: bones become also seen: bones become

weaker, more porous, and weaker, more porous, and

brittle due to loss of calcium; brittle due to loss of calcium;

intervertebral disks deteriorate, intervertebral disks deteriorate,

leading to loss of height; joints leading to loss of height; joints

deteriorate from wear and tear.deteriorate from wear and tear. Reproductive systems and sexuality Reproductive systems and sexuality

change.change.



Falling secretions of estrogen and progesterone Falling secretions of estrogen and progesterone trigger menopause in women, whereas trigger menopause in women, whereas declining testosterone in men causes reduced declining testosterone in men causes reduced fertility.fertility.

Because the effects of declining hormones may Because the effects of declining hormones may be more troublesome in women, hormone be more troublesome in women, hormone replacement therapy (HRT) may be replacement therapy (HRT) may be recommended.recommended.

Despite declines in hormones and other Despite declines in hormones and other potential problems, men and women both retain potential problems, men and women both retain their capacity for sexual response well into old their capacity for sexual response well into old age.age.



Age-Related Changes in Age-Related Changes in Some Other Body Some Other Body

SystemsSystems

The nervous system and senses decline.The nervous system and senses decline. Neurons are generally not replaced when they Neurons are generally not replaced when they

die, regardless of age.die, regardless of age. Neurofibrillary tanglesNeurofibrillary tangles may may

form inside the neurons, and form inside the neurons, and

beta amyloidbeta amyloid plagues may plagues may

form between neurons; form between neurons;

both of these are present in both of these are present in

people with people with Alzheimer’s Alzheimer’s

diseasedisease (AD). (AD).

Age-Related Changes in Some Other Age-Related Changes in Some Other Body Systems Body Systems

Figure 17.24a-bFigure 17.24a-b

• AD manifests with progressive memory AD manifests with progressive memory loss and disruptive personality changes.loss and disruptive personality changes.

• Low levels of acetylcholine and chronic Low levels of acetylcholine and chronic inflammation of brain tissue may also be inflammation of brain tissue may also be part of the cause of AD.part of the cause of AD.

• No effective treatment for AD currently No effective treatment for AD currently exists.exists.

• Persons who inherit one version of a gene that codes Persons who inherit one version of a gene that codes for for apolipoprotein Eapolipoprotein E are at significantly higher risk are at significantly higher risk for Alzheimer’s disease.for Alzheimer’s disease.

All of us will experience some short-term All of us will experience some short-term memory loss as we age, as well as less efficient memory loss as we age, as well as less efficient responses to many stimuli.responses to many stimuli.


Figure 17.24cFigure 17.24c

The cardiovascular and respiratory systems The cardiovascular and respiratory systems deteriorate.deteriorate.

Changes to the respiratory system are mainly Changes to the respiratory system are mainly due to the breakdown of the alveoli, resulting in due to the breakdown of the alveoli, resulting in less respiratory surface.less respiratory surface.

Changes in the cardiovascular system include Changes in the cardiovascular system include reduction in heart pumping capacity, stiffening reduction in heart pumping capacity, stiffening of blood vessels, and deposition of plaque in of blood vessels, and deposition of plaque in the vessels.the vessels.

The combined effect of deterioration of these The combined effect of deterioration of these systems is less efficient blood transport.systems is less efficient blood transport.


The immune, digestive, and urinary The immune, digestive, and urinary systems become less efficient.systems become less efficient.

The numbers of T cells drops, B cells become The numbers of T cells drops, B cells become less active, and autoimmune diseases can less active, and autoimmune diseases can occur, possibly due to mutations in self-occur, possibly due to mutations in self-markers.markers.

Fewer digestive enzymes are produced in the Fewer digestive enzymes are produced in the intestines and basal metabolic rate falls, intestines and basal metabolic rate falls, resulting in weight gain if not compensated for resulting in weight gain if not compensated for by changes to diet and exercise.by changes to diet and exercise.

Urinary incontinenceUrinary incontinence may also occur, may also occur, particularly in women who have borne children.particularly in women who have borne children.


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PowerLecture: Chapter 17