20 - napa valley college

Copyright © 2010 Pearson Education, Inc.

C h a p t e r

20

Development

and Inheritance

PowerPoint® Lecture Slides

prepared by Jason LaPres

Lone Star College - North Harris



20-1 Development is a continuous process that occurs from fertilization

to maturity


Development

• Gradual modification of anatomical

structures and physiological

characteristics from fertilization to

maturity


Development

• Differentiation

– Creation of different types of cells required in

development

– Occurs through selective changes in genetic activity:

• As development proceeds, some genes are turned off, others

are turned on

• Fertilization

– Also called conception

– When development begins


Development

• Embryological Development

– Occurs during first 2 months after fertilization

– Study of these events is called embryology

• Fetal Development

– Begins at start of ninth week

– Continues until birth


Development

• Prenatal Development

– Embryological and fetal development stages

• Postnatal Development

– Commences at birth

– Continues to maturity when aging process

begins


Development

• Inheritance

– Transfer of genetically determined characteristics

from generation to generation

• Genetics

– Study of mechanisms responsible for inheritance


20-2 Fertilization — the fusion of a secondary oocyte and a

spermatozoon — forms a zygote


Fertilization

• Fertilization

– Fusion of two haploid gametes, each

containing 23 chromosomes

– Produces zygote containing 46 chromosomes

Fertilization and the Preparation for Cleavage

20Fertilizat_NA_SWF.html


Fertilization

• Spermatozoon

– Delivers paternal chromosomes to

fertilization site

– Travels relatively large distance

– Is small, efficient, and highly streamlined


Fertilization

• Gamete

– Provides:

• Cellular organelles

• Inclusions

• Nourishment

• Genetic programming necessary to support

development of embryo for a week


Fertilization

• Fertilization

– Occurs in uterine tube within a day after

ovulation:

• Secondary oocyte travels a few centimeters

• Spermatozoa must cover distance between

vagina and ampulla


Fertilization

• Capacitation

– Must occur before spermatozoa can fertilize

secondary oocyte:

• Contact with secretions of seminal glands

• Exposure to conditions in female reproductive tract


Fertilization

• Hyaluronidase

– Enzyme breaks down bonds between adjacent

follicle cells

– Allows spermatozoon to reach oocyte

• Acrosin

– Is a proteolytic enzyme

– Is required to reach oocyte


Fertilization

• Acrosomal Caps

– Release hyaluronidase and acrosin

– Penetrate corona radiata, zona pellucida, toward

oocyte surface

• Oocyte Activation

– Contact and fusion of cell membranes of sperm and

oocyte

– Follows fertilization

– Oocyte completes meiosis II, becomes mature ovum


Fertilization

• Female Pronucleus

– Nuclear material remaining in ovum after oocyte

activation

• Male Pronucleus

– Swollen nucleus of spermatozoon

– Migrates to center of cell


Fertilization

• Amphimixis

– Fusion of female pronucleus and male

pronucleus

– Moment of conception

– Cell becomes a zygote with 46 chromosomes

– Fertilization is complete


Fertilization

Figure 20-1


20-3 Gestation consists of three stages of prenatal development: the first,

second, and third trimesters


Gestation

• First Trimester

– Period of embryological and early fetal development

– Rudiments of all major organ systems appear

• Second Trimester

– Development of organs and organ systems

– Body shape and proportions change:

• By end, fetus looks distinctively human

• Third Trimester

– Rapid fetal growth and deposition of adipose tissue

– Most major organ systems are fully functional


20-4 Cleavage, implantation, placentation, and

embryogenesis are critical events of the first

trimester


The First Trimester

• Cleavage

– Sequence of cell divisions begins immediately

after fertilization

– Zygote becomes a pre-embryo, which

develops into multicellular blastocyst

– Ends when blastocyst contacts uterine wall


The First Trimester

• Implantation

– Begins with attachment of blastocyst to

endometrium of uterus

– Sets stage for formation of vital embryonic

structures

• Placentation

– Occurs as blood vessels form around periphery of

blastocyst and placenta develops


The First Trimester

• Placenta

– Complex organ permits exchange between maternal and

embryonic circulatory systems

– Supports fetus in second and third trimesters

– Stops functioning and is ejected from uterus after birth

• Embryogenesis

– Formation of viable embryo

– Establishes foundations for all major organ systems


The First Trimester

• Most dangerous period in prenatal life

• 40% of conceptions produce embryos that

survive past first trimester


Cleavage and Blastocyst Formation

• Blastomeres

– Identical cells produced by cleavage divisions

• Morula

– Stage after 3 days of cleavage

– Pre-embryo is solid ball of cells resembling

mulberry

– Reaches uterus on day 4



• Blastocyst

– Formed by blastomeres

– Hollow ball with an inner cavity:

• Known as blastocoele



• Trophoblast

– Outer layer of cells separate outside world

from blastocoele

– Cells responsible for providing nutrients to

developing embryo



• Inner Cell Mass

– Clustered at end of blastocyst

– Exposed to blastocoele

– Insulated from contact with outside

environment by trophoblast

– Will later form embryo



Figure 20-2


Implantation

• Implantation

– Occurs 7 days after fertilization

– Blastocyst adheres to uterine lining

– Trophoblast cells divide rapidly, creating

several layers

Stage of Implantation

20StagImplant_NA_SWF.html


Implantation

• Cellular Trophoblast

– Cells closest to interior of blastocyst

• Syncytial Trophoblast

– Outer layer

– Erodes path through uterine epithelium by

secreting hyaluronidase


Implantation

Figure 20-3


Implantation

• Ectopic Pregnancy

– Implantation occurs outside of uterus

– Does not produce viable embryo

– Can be life threatening

• Lacunae

– Trophoblastic channels carrying maternal blood


Implantation

• Villi

– Extend away from trophoblast into endometrium

– Increase in size and complexity until day 21

• Amniotic Cavity

– A fluid-filled chamber

– Inner cell mass is organized into an oval sheet that is

two layers thick:

• Superficial layer faces amniotic cavity

• Deeper layer is exposed to fluid contents of blastocoele


Implantation

• Gastrulation

– Formation of third layer of cells

– Cells in specific areas of surface move

toward central line:

• Known as primitive streak


Implantation

• Primitive Streak

– Migrating cells leave surface and move between

two layers

– Creates three distinct embryonic layers, or germ

layers:

• Ectoderm: consists of the superficial cells that did not

migrate into the interior of the inner cell mass

• Endoderm: consists of cells that face blastocoele

• Mesoderm: consists of poorly organized layer of

migrating cells between ectoderm and endoderm


Implantation

• Embryonic Disc

– Oval, three-layered sheet

– Produced by gastrulation

– Will form body of embryo:

• Rest of blastocyst will be involved in forming

extraembryonic membranes


The Inner Cell Mass and Gastrulation

Figure 20-4


Implantation

• Formation of the Extraembryonic

Membranes

– Support embryological and fetal development:

• Yolk sac

• Amnion

• Allantois

• Chorion


Implantation

• Yolk Sac

– Begins as layer of cells spread out around outer edges

of blastocoele to form complete pouch

– Important site of blood cell formation

• Amnion

– Combination of mesoderm and ectoderm

– Ectodermal layer enlarges and cells spread over inner

surface of amniotic cavity

– Mesodermal cells create outer layer

– Continues to enlarge through development


Implantation

• Amniotic Fluid

– Contained in amniotic cavity

– Surrounds and cushions developing embryo or

fetus

• Allantois

– Sac of endoderm and mesoderm

– Base later gives rise to urinary bladder


Implantation

• Chorion

– Combination of mesoderm and trophoblast

– Blood vessels develop within mesoderm

– Rapid-transit system for nutrients that links

embryo with trophoblast

– First step in creation of functional placenta


Placentation

• Chorionic Villi

– In contact with maternal tissues

– Create intricate network within endometrium carrying

maternal blood

• Body Stalk

– Connection between embryo and chorion

– Contains distal portions of allantois and blood vessels

that carry blood to and from placenta


Placentation

• Yolk Stalk

– Narrow connection between endoderm of embryo

and yolk sac


Placentation

Figure 20-5


Placentation

• Umbilical Cord

– Connects fetus and placenta

– Contains allantois, placental blood vessels, and

yolk stalk

• Blood Flow to Placenta

– Through paired umbilical arteries

– Returns in single umbilical vein


Placentation

Figure 20-6


Placentation

• The Endocrine Placenta

– Synthesized by syncytial trophoblast, released into

maternal bloodstream:

• Human chorionic gonadotropin (hCG)

• Human placental lactogen (hPL)

• Placental prolactin

• Relaxin

• Progesterone

• Estrogens


Placentation

• Human Chorionic Gonadotropin (hCG)

– Appears in maternal bloodstream soon after

implantation

– Provides reliable indication of pregnancy

– Pregnancy ends if absent

– Helps prepare mammary glands for milk

production

– Stimulatory effect on other tissues

comparable to growth hormone (GH)


Placentation

• Placental Prolactin

– Helps convert mammary glands to active status

• Relaxin

– A peptide hormone secreted by placenta and corpus

luteum during pregnancy

– Increases flexibility of pubic symphysis, permitting

pelvis to expand during delivery

– Causes dilation of cervix

– Suppresses release of oxytocin by hypothalamus and

delays labor contractions


The First Trimester

• Embryogenesis

– Body of embryo begins to separate from embryonic

disc

– Body of embryo and internal organs start to form

– Folding, differential growth of embryonic disc produces

bulge that projects into amniotic cavity:

• Projections are head fold and tail fold

• Organogenesis

– Process of organ formation


The First Trimester

Figure 20-7a


The First Trimester

Figure 20-7b


The First Trimester

Figure 20-7c


The First Trimester

Figure 20-7d


20-5 During the second and third trimesters, maternal

organ systems support the developing fetus, and the

uterus undergoes structural and functional changes


The Second and Third Trimesters

• Second Trimester

– Fetus grows faster than surrounding placenta

• Third Trimester

– Most of the organ systems become ready

– Growth rate starts to slow

– Largest weight gain

– Fetus and enlarged uterus displace many of mother’s

abdominal organs



Figure 20-8a



Figure 20-8b


Changes in Body Form and Proportion During Development

Figure 20-9


Effects of Pregnancy on Mother

• Pregnancy and Maternal Systems

– Developing fetus is totally dependent on maternal

organ systems for nourishment, respiration, and waste

removal

• Maternal adaptations include increases in

– Respiratory rate and tidal volume

– Blood volume

– Nutrient and vitamin intake

– Glomerular filtration rate

• Uterus and mammary glands increase in size


Effects of Pregnancy on Mother

• Progesterone

– Released by placenta

– Has inhibitory effect on uterine smooth muscle

– Prevents extensive, powerful contractions

• Opposition to Progesterone

– Three major factors:

• Rising estrogen levels

• Rising oxytocin levels

• Prostaglandin production



• Parturition is forcible expulsion of fetus

• Contractions

– Begin near top of uterus, sweep in wave toward

cervix

– Strong, occur at regular intervals, increase in force

and frequency

– Change position of fetus, move it toward cervical

canal


Factors Involved in the Initiation of Labor and Delivery

Figure 20-10


20-6 Labor consists of the dilation, expulsion, and

placental stages


Labor

• Dilation Stage

– Begins with onset of true labor

– Cervix dilates

– Fetus begins to shift toward cervical canal

– Highly variable in length, but typically lasts over 8 hours

– Frequency of contractions steadily increases

– Amniochorionic membrane ruptures (water breaks)


Labor

Figure 20-11


Labor

• Expulsion Stage

– Begins as cervix completes dilation

– Contractions reach maximum intensity

– Continues until fetus has emerged from vagina:

• Typically less than 2 hours

• Delivery

– Arrival of newborn infant into outside world


Labor

Figure 20-11


Labor

• Placental Stage

– Muscle tension builds in walls of partially empty uterus

– Tears connections between endometrium and placenta

– Ends within an hour of delivery with ejection of placenta, or

afterbirth

– Accompanied by a loss of blood


Labor

Figure 20-11


Labor

• Episiotomy

– Incision through perineal musculature

– Needed if vaginal canal is too small to pass

fetus

– Repaired with sutures after delivery


Labor

• Cesarean Section (C-section)

– Removal of infant by incision made through

abdominal wall

– Opens uterus just enough to pass infant’s

head

– Needed if complications arise during dilation

or expulsion stages


Labor

• Premature Labor

– Occurs when true labor begins before fetus

has completed normal development

– Newborn’s chances of surviving are directly

related to body weight at delivery


Labor

• Immature Delivery

– Refers to fetuses born at 25 to 27 weeks of gestation

– Most die despite intensive neonatal care

– Survivors have high risk of developmental

abnormalities

• Premature Delivery

– Refers to birth at 28 to 36 weeks

– Newborns have a good chance of surviving and

developing normally


Multiple Births

• Dizygotic Twins

– Also called fraternal twins

– Develop when two separate oocytes were

ovulated and subsequently fertilized

– Genetic makeup not identical

– 70% of twins


Multiple Births

• Monozygotic Twins

– Identical twins

– Result either from:

• Separation of blastomeres early in cleavage

• Splitting of inner cell mass before gastrulation

– Genetic makeup is identical because both

formed from same pair of gametes


Multiple Births

• Conjoined Twins

– Siamese twins

– Genetically identical twins

– Occurs when splitting of blastomeres or of

embryonic disc is not completed


Multiple Births

• Rates of Multiple Births

– Twins in 1 of every 89 births

– Triplets in 1 of every 892 (7921) births

– Quadruplets in 1 of every 893 (704,969) births


20-7 Postnatal stages are the neonatal period, infancy, childhood, adolescence,

maturity, and senescence


Postnatal Life

• Five Life Stages

– Neonatal period

– Infancy

– Childhood

– Adolescence

– Maturity


Postnatal Life

• Neonatal Period: extends from birth to 1 month

• Infancy: 1 month to 2 years of age

• Childhood: 2 years until adolescence

• Adolescence: period of sexual and physical

maturation

• Senescence: process of aging that begins at end

of development (maturity)


Postnatal Life

• Developmental Stages

– Neonatal period, infancy, childhood, and

adolescence

– Two major events occur:

• Organ systems become fully operational

• Individual grows rapidly and body proportions

change significantly


Postnatal Life

• Pediatrics

– Medical specialty focusing on postnatal

development from infancy to adolescence

• Neonate

– Newborn


Postnatal Life

• Neonatal Period

– Transition from fetus to neonate

– Systems begin functioning independently:

• Respiratory

• Circulatory

• Digestive

• Urinary


Postnatal Life

• Colostrum

– Secretion from mammary glands

– Ingested by infant during first 2 to 3 days

– Contains more proteins and less fat than breast milk:

• Many proteins are antibodies that help ward off infections

until immune system is functional

– Mucins present inhibit replication of rotaviruses

– As production drops, mammary glands convert to milk

production


Postnatal Life

• Breast Milk

– Consists of water, proteins, amino acids,

lipids, sugars, and salts

– Also contains large quantities of lysozymes —

enzymes with antibiotic properties


Postnatal Life

• Milk Let-Down Reflex

– Mammary gland secretion triggered when

infant sucks on nipple

– Continues to function until weaning, typically 1

to 2 years


Figure 20-12


Postnatal Life

• Infancy and Childhood

– Growth occurs under direction of circulating

hormones:

• Growth hormone

• Suprarenal steroids

• Thyroid hormones

– Growth does not occur uniformly

– Body proportions gradually change


Postnatal Life

• Puberty is a period of sexual maturation and marks the

beginning of adolescence

– Generally starts at age 12 in boys, age 11 in girls

• Three major hormonal events interact

– Hypothalamus increases production of GnRH

– Circulating levels of FSH and LH rise rapidly

– Ovarian or testicular cells become more sensitive to FSH and LH

• Hormonal changes produce sex-specific differences in

structure and function of many systems


Postnatal Life

• Adolescence

– Begins at puberty

– Continues until growth is completed

• Maturity (Senescence )

– Aging

– Reduces functional capabilities of individual

– Affects homeostatic mechanisms

– Sex hormone levels decline at menopause or male

climacteric


Postnatal Life

• Geriatrics

– Medical specialty dealing with problems

associated with aging

– Trained physicians, or geriatricians


Postnatal Life

Figure 20-9


20-8 Genes and chromosomes

determine patterns of inheritance


Patterns of Inheritance

• Nucleated Somatic Cells

– Carry copies of original 46 chromosomes present in

zygote

• Genotype

– Chromosomes and their component genes

– Contain unique instructions that determine anatomical

and physiological characteristics

– Derived from genotypes of parents

• Phenotype

– Physical expression of genotype

– Anatomical and physiological characteristics



• Homologous Chromosomes

– Members of each pair of chromosomes

– 23 pairs carried in every somatic cell:

• At amphimixis, one member of each pair is

contributed by spermatozoon, other by ovum



• Autosomal Chromosomes

– 22 pairs of homologous chromosomes

– Most affect somatic characteristics

– Each chromosome in pair has same structure

and carries genes that affect same traits



• Sex Chromosomes

– Last pair of chromosomes

– Determine whether individual is genetically male or

female

• Karyotype

– Entire set of chromosomes


Chromosomes of a Normal Male

Figure 20-13



• Alleles are various forms of a given gene

– Alternate forms determine precise effect of gene on

phenotype

• Homozygous

– Both homologous chromosomes carry same allele of a

particular gene

• Simple Inheritance

– Phenotype determined by interactions between single

pair of alleles



• Heterozygous

– Homologous chromosomes carry different allele of a

particular gene

– Resulting phenotype depends on nature of interaction

between alleles

• Strict Dominance

– Dominant allele expressed in phenotype, regardless

of conflicting instructions carried by other allele



• Recessive Allele

– Expressed in phenotype only if same allele is present on both

chromosomes of homologous pair

• Codominance

– Exhibits both dominant and recessive phenotypes for traits

• Punnett Square

– Simple box diagram used to predict characteristics of offspring


Predicting Genotypes and Phenotypes

Figure 20-14 a,b



• Polygenic Inheritance

– Involves interactions among alleles on several genes

– Cannot predict phenotypic characteristics using

Punnett square

– Linked to risks of developing several important adult

disorders

• Suppression

– One gene suppresses other

– Second gene has no effect on phenotype



• Carriers

– Individuals who are heterozygous for

abnormal allele but do not show effects of

mutation



• Sex Chromosomes

– X Chromosome:

• Considerably larger

• Has more genes than does Y chromosome

• Carried by all oocytes

– Y Chromosome:

• Includes dominant alleles specifying that the individual will be

male

• Not present in females



• Sperm

– Carry either X or Y chromosome

– Because males have one of each, can pass

along either



• X-Linked

– Genes that affect somatic structures

– Carried by X chromosome:

• Inheritance does not follow pattern of alleles on

autosomal chromosomes


The Human Genome Project and Beyond

• Human Genome Project

– Goal was to transcribe entire human genome

– Has mapped thousands of human genes

• Genome

– Full complement of genetic material


The Human Genome Project and Beyond

• Karyotyping

– Determination of individual’s complete

chromosomal complement


Figure 20-15

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