Transcript Chapter_033 - CESA 10 Moodle

Chapter 33
Growth and Development
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Slide 1
Introduction

Prenatal period—period beginning with
conception and ending at birth

Postnatal period—period beginning with birth
and continuing until death

Human developmental biology—study of
changes occurring during the cycles of life
from conception to death
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Slide 2
A New Human Life

Production of sex cells—spermatozoa are produced by
spermatogenesis; ova are produced by oogenesis

Meiosis (Figures 33-1 and 33-2)
• Special form of cell division that reduces the number of chromosomes
in each daughter cell to one half of those in the parent cell
• Mature ova and sperm contain only 23 chromosomes, half as many
as other human cells
• Meiotic division—two cell divisions that occur one after another in
succession


Meiotic division I and meiotic division II
Both divisions made up of an interphase, prophase, metaphase,
anaphase, and telophase
• During prophase I of meiosis, “cross over” occurs where genetic
material is “shuffled”
• Daughter cells formed by meiotic division I contain a haploid number
of chromosomes
• Meiotic division II—essentially the same as mitotic division;
reproduces each of the two cells formed by meiotic division I and
forms four cells, each with the haploid number of chromosomes
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Slide 3
A New Human Life

Production of sex cells (cont.)

Spermatogenesis (Figure 33-3)—process by
which primitive male sex cells become
transformed into mature sperm; begins
approximately at puberty and continues
throughout a man’s life
• Meiotic division I—one primary spermatocyte forms two
secondary spermatocytes, each with 23 chromosomes
• Meiotic division II—each of the two secondary
spermatocytes form a total of four spermatids
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Slide 4
A New Human Life

Production of sex cells (cont.)

Oogenesis (Figure 33-4)—process by which primitive
female sex cells become transformed into mature ova
• Mitosis—oogonia reproduce to form primary oocytes; most
primary oocytes begin meiosis and develop to prophase
I before birth; there they stay until puberty
• Once during each menstrual cycle, a few primary oocytes
resume meiosis and migrate toward the surface of the ovary;
usually only one oocyte matures enough for ovulation, and
meiosis again halts at metaphase II
• Meiosis resumes only if the head of a sperm cell enters
the ovum
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Slide 5
A New Human Life

Ovulation and insemination

Ovulation—expulsion of the mature ovum from the
mature ovarian follicle, into the abdominopelvic
cavity, and then the uterine (fallopian) tube

Insemination—expulsion of seminal fluid from
male into the female vagina; sperm travel through
cervix and uterus and into uterine (fallopian) tubes
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Slide 6
A New Human Life

Fertilization—also known as conception (Figure 33-5)

Most often occurs in the outer one third of oviduct

Ovum attracts and “traps” sperm with special receptor
molecules on its surface

When one spermatozoon enters ovum, ovum stops collecting
sperm on its surface

The sperm releases its nuclear chromosomes into the ovum;
proteins and RNA from the sperm enter the ovum to assist with
early development

23 chromosomes from the sperm head and 23 chromosomes in
the ovum comprise a total of 46 chromosomes

Zygote—fertilized ovum; genetically complete
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Slide 7
Prenatal Period


Begins with conception and continues until the birth of a child
Cleavage and implantation (Figure 33-6)—once zygote is formed, it
immediately begins to divide

Morula—solid mass of cells formed from zygote; takes approximately 3
days; continues to divide (Figure 33-7)
 Blastocyst—by the time developing embryo reaches uterus, it has
formed a hollow ball of cells, which implants into uterine lining (Figure
33-8)
 Approximately 10 days pass from fertilization until implantation in
uterine lining; ovum has a store of nutrients that support this embryonic
development until implantation has occurred
 Blastocyst has an outer layer of cells and an inner cell mass
• Trophoblast—outer wall of blastocyst
• Inner cell mass—as blastocyst develops, yolk sac and amniotic cavity are
formed (Figure 33-9)


In humans, yolk sac’s functions are largely nonnutritive
Amniotic cavity becomes a fluid-filled, shock-absorbing sac (bag of waters) in
which embryo floats during development (Figure 33-10)
• Chorion develops from trophoblast to become an important fetal membrane
in the placenta
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Slide 8
Prenatal Period

Cleavage and implantation (cont.)

Placenta (Figure 33-11)
• Anchors fetus to uterus and provides “bridge” for exchange
of nutrients and waste products between mother and baby
• Also serves as excretory, respiratory, and endocrine organ
• Placental tissue normally separates maternal and fetal
blood supplies
• Has important endocrine functions—secretes large
amounts of human chorionic gonadotropin (HCG), which
stimulates the corpus luteum to continue its secretion of
estrogen and progesterone (Figure 33-12)
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Slide 9
Prenatal Period

Periods of development
(Figures 33-13 through 33-15)

Gestation period—approximately 39 weeks;
divided into three 3-month segments called
trimesters

Embryonic phase extends from fertilization until
the end of week 8 of gestation

Fetal phase—weeks 8 to 39
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Slide 10
Prenatal Period

Formation of the primary germ layers

Three layers of specialized cells develop early in
first trimester of pregnancy

Cells of embryonic disk differentiate and form each
of the three primary germ layers

Each primary germ layer gives rise to specific
organs and systems of the body (Figure 33-16)

There are three primary germ layers:
• Endoderm—inside layer
• Ectoderm—outside layer
• Mesoderm—middle layer
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Slide 11
Prenatal Period

Histogenesis and organogenesis (Figure 33-19)



Histogenesis—process by which primary germ layers develop
into different kinds of tissues
Organogenesis—how tissues arrange themselves into organs
Differentiation and development of the reproductive systems
are an example
• Reproductive tract (Figure 33-17)

Gonads attach to mesonephric (Wolffian) ducts, which become the male
reproductive tract

Gonads (unattached) and paramesonephric (Müllerian) ducts develop
into the female reproductive tract
• External genitals (Figure 33-18)

In the male, the genital tubercle eventually becomes the glans of the
penis and the folds become the penis shaft and scrotum

In the female, the genital tubercle becomes the clitoris and the folds
become the labia
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Slide 12
Birth, or Parturition

Transition between prenatal and postnatal
periods of life

Stages of labor (Figure 33-20)
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Stage one—period from onset of uterine
contractions until cervical dilation is complete
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Stage two—period from maximal cervical dilation
until the baby exits through the vagina

Stage three—process of expulsion of the placenta
through the vagina
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Slide 13
Birth, or Parturition

Multiple births—birth of two or more infants
from the same pregnancy; twins are most
common (Figure 33-21)
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Identical twins result from the splitting of embryonic
tissue from the same zygote early in development

Fraternal twins result from the fertilization of two
different ova by two different spermatozoa
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Slide 14
Postnatal Period

Begins at birth and continues until death;
commonly divided into a number of periods
(Figure 33-22)

Infancy begins at birth and lasts until
approximately 18 months
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Neonatal period—first 4 weeks of infancy; dramatic
changes occur at a rapid rate (Figure 33-23)

Changes allow the infant to become totally
self-supporting, especially respiratory and
cardiovascular systems (Figure 33-24)
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Slide 15
Postnatal Period

Childhood extends from end of infancy to sexual
maturity, or puberty
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Early childhood—growth continues at a rapid pace
but slows down
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By age 6, child looks more like a preadolescent than
an infant or toddler
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Nervous and muscular systems develop rapidly
during middle years of childhood
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Deciduous teeth are lost during childhood, beginning
at approximately 6 years of age
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Permanent teeth have erupted by age 14, except for
third molars (wisdom teeth)
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Slide 16
Postnatal Period
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Adolescence and adulthood
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Adolescence is considered to be the teenage years (from 13 to
19); marked by rapid and intense physical growth, resulting in
sexual maturity
• Puberty—stage of adolescence during which a person becomes
sexually mature
• Changes triggered by increases in reproductive hormones (Figure
33-25)
• Primary sexual characteristics—maturity of gonads and reproductive
tract
• Secondary sexual characteristics—fat and hair distribution, skeletal
changes, etc. (Figure 33-26)

Adulthood—characterized by maintenance of existing body
tissues
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Slide 17
Postnatal Period
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Older adulthood and senescence
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As a person grows older, a gradual decline occurs in
every major organ system in the body
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Gerontologists theorize a number of different aging
mechanisms, all of which may be involved in the
processes of aging:
• Limit on cell reproduction
• Environmental factors
• Viruses
• Aging genes
• Degeneration of mitochondria—perhaps progressive
damage by oxygen free-radicals (Figure 33-27)
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Slide 18
Effects of Aging—Common Degenerative
Changes That Frequently Characterize
Senescence (Figure 33-28)
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Skeletal system (Figure 33-29)
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Bones decrease in bone mineral density (BMD ) and
thus change in texture, degree of calcification, and
shape
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Lipping occurs, which can limit range of motion

Decreased bone size and density lead to increased
risk of fracture

Decreased BMD can be avoided (at least partly) by
exercise and adequate calcium intake
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Slide 19
Effects of Aging—Common Degenerative
Changes That Frequently Characterize
Senescence (Figure 33-28)

Muscular system (Figure 33-30)

Muscle mass decreases to about 90% by age 50
and around 50% by age 80

The number of muscle fibers decreases as
humans age but can be offset by an increase in
muscle fiber size through exercise

Ratio of “fast” to “slow” functioning in muscle fibers
decreases, slowing the function of muscle organs
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Slide 20
Effects of Aging—Common Degenerative
Changes That Frequently Characterize
Senescence (Figure 33-28)

Integumentary system (skin)

Skin becomes dry, thin, and inelastic

Pigmentation changes and thinning hair are
common problems associated with aging
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Slide 21
Effects of Aging—Common Degenerative
Changes That Frequently Characterize
Senescence (Figure 33-28)

Urinary system
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Number of nephron units in the kidney decreases
by almost 50% between the ages of 30 and 75

Decreased blood flow through kidneys reduces
overall function and excretory capacity

Diminished muscle tone in bladder results in
decreased capacity and inability to empty, or void,
completely
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Slide 22
Effects of Aging—Common Degenerative
Changes That Frequently Characterize
Senescence (Figure 33-28)

Respiratory system
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Costal cartilages become calcified
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Respiratory efficiency decreases

Decreased strength of respiratory muscles
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Slide 23
Effects of Aging—Common Degenerative
Changes That Frequently Characterize
Senescence (Figure 33-28)

Cardiovascular system

Degenerative heart and blood vessel disease—one
of the most common and serious effects of aging

Atherosclerosis—build-up of fatty deposits on blood
vessel walls narrows the passageway for blood

Arteriosclerosis—“hardening” of the arteries

Hypertension—high blood pressure
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Slide 24
Effects of Aging—Common Degenerative
Changes That Frequently Characterize
Senescence (Figure 33-28)
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Special senses

Sense organs—gradual decline in performance and
capacity with aging
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Presbyopia—far-sightedness due to hardening of lens

Cataract—cloudy lens, which impairs vision

Glaucoma—increased pressure within the eyeball; if
left untreated, often results in blindness

Decreased hearing

Decreased taste
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Slide 25
Effects of Aging—Common Degenerative
Changes That Frequently Characterize
Senescence (Figure 33-28)

Reproductive systems

Mechanism of sexual response may change

Fertility decreases

In females, menopause occurs between ages of 45
and 60
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Slide 26
Causes of Death

In developed countries such as the United
States, heart disease, cancer, and stroke
(CVA) are among the leading causes of death
(Figure 33-31)

In developing countries, heart disease and
stroke are also leading causes of death,
along with infectious diseases such as
HIV/AIDS, diarrheal disorders, and malaria
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Slide 27