© 2010 Pearson Education, Inc. Reproduction and Development Unifying Comcepts of Animal...

Reproduction and Development

Unifying Comcepts of Animal Reproduction

Human Reproduction

Reproductive Health

Human Development

Reproductive Technologies

UNIFYING CONCEPTS OF ANIMAL REPRODUCTION• Reproduction is the creation of new individuals from existing

Asexual Reproduction• Asexual reproduction creates offspring that are genetically

identical to the parent.

• Budding, a type of asexual reproduction, produces offspring by the outgrowth and eventual splitting off of a new individual from the parent.

Figure 26.1

• During the asexual process of fission, a parent separates into two or more offspring of about equal size.

Figure 26.2

• Fragmentation is the breaking of a parent body into several pieces.

• Regeneration

– Typically follows fragmentation

– Is the regrowth of a whole animal from the pieces

Number of chromosomesin body cells

Indian muntjac deer

Species

Opossum

Giraffe

Buffalo

Red viscacha rat

Duck-billed platypus

Figure 8.2

• Asexual reproduction

– Allows a population to perpetuate itself if its individual members are isolated from one another

– Permits organisms to multiply quickly

• However, asexual reproduction produces genetically identical offspring, which limits a population’s chance to survive periods of environmental change.

• Sexual reproduction involves

– The fusion of gametes (sperm and egg) from two parents

– The formation of a zygote

Sexual Reproduction

• Sexual reproduction increases the

– Genetic variability among offspring

– Chances that some of the variants can survive and reproduce

• Some animals can reproduce both

– Sexually and

– Asexually

Twooffspringarising fromasexualreproductionby fission

Figure 26.3

• Some species are hermaphrodites, individuals with

– Male and

– Female reproductive systems

• The mechanics of fertilization play an important part in sexual reproduction.

– Aquatic animals typically

– Use external fertilization

– Discharge their gametes into the water

Figure 26.4

– Most terrestrial organisms deposit sperm directly from the male into the female.

HUMAN REPRODUCTION• Both sexes of humans have

– A pair of gonads that produce gametes

– Ducts to store and deliver the gametes

Male Reproductive Anatomy• The penis

– Contains erectile tissue that fills with blood

– Becomes erect during sexual arousal

• The male gonads are the testes, which

– Are enclosed in a sac called the scrotum

– Produce sperm

Side view

Rectum

Seminalvesicle

Vasdeferens

SpermductProstategland

Anus Vas deferensEpididymisTestisScrotum

Urinary bladder

Pubic bone

Erectiletissue

Urethra

Prepuce

Urinarybladder

Prostategland

Erectiletissueof penis

Vasdeferens

Epididymis

Testis

Front view

Seminalvesicle(behind bladder)

Urethra

Scrotum

Glans ofpenis

Figure 26.5

• During an ejaculation, the seminal vesicles and prostate gland add fluid that

– Nourishes the sperm

– Provides protection from the natural acidity of the vagina

• Semen consists of

– This fluid and

– Sperm

Female Reproductive Anatomy• The outer features of the female reproductive tract are the

vulva, consisting of the

– Vagina, or birth canal

– Labia majora, fatty ridges that protect the entire genital region

– Labia minora, inner folds bordering the openings

– Hymen, partially covering the vaginal opening

– Clitoris, which becomes erect upon sexual arousal

Urinary bladder

Front view

Endometrium(lining of uterus)

Uterus

Cervix(“neck” of uterus)Vagina

OviductOvaries

Follicles

Wall of uterus

Corpus luteum

Side view

Cervix

Vagina

Rectum

Vaginal opening

Uterus

Oviduct

Urethra

Pubic bone

Labia majora

Labia minora

ClitorisPrepuceGlans

Urinary bladder

Side view

Cervix

Vagina

Rectum

Vaginal opening

Uterus

Oviduct

Urethra

Pubic bone

Labia majora

Labia minora

ClitorisPrepuceGlans

Figure 26.6

• The ovaries

– Are the sites of gamete production

– Contain follicles consisting of a single egg surrounded by layers of cells that nourish and protect it

• The follicles also produce estrogen, the female sex hormone.

• During ovulation an egg is

– Ejected from a follicle

– Collected into the oviduct, where fertilization typically occurs

• The remains of the follicle grow to form a solid mass, the corpus luteum, which releases hormones during the reproductive cycle.

• The uterus

– Is the actual site of pregnancy

– Is lined by a thick blood-rich layer of tissue, the endometrium, where an embryo implants and grows

• A developing human is called

– An embryo for the first nine weeks

– A fetus from the 9th week until birth

• The cervix

– Is the narrow neck at the bottom of the uterus

– Opens into the vagina

• Annual Pap smears:

– Sample cervical cells

– Can detect cervical cancer early, when treatment is more likely to be successful

Gametogenesis• Gametogenesis produces gametes, haploid cells, by meiosis.

• In females, it’s called oogenesis. Most eggs are formed before birth

• In males, it’s called spermatogenesis and continues from puberty to death

Spermatogenesis• Spermatogenesis

– Is the formation of sperm cells

– Occurs in seminiferous tubules inside the testes

• Primary spermatocytes are diploid cells that undergo meiosis and produce secondary spermatocytes.

Seminiferoustubule

Testis

TestisScrotum

Epididymis

Crosssection ofseminiferous tubule

Mature sperm released intocenter of seminiferous tubule

Differentiation andonset of meiosis

Diploid cell

Meiosis

Meiosis completed (diploid)

(haploid)

Secondary spermatocyte

Primary spermatocyte

Developing sperm cells

Differentiation

(haploid)Sperm cells

Figure 26.7

Oogenesis• Oogenesis is the development of eggs within the ovaries.

• Meiosis I produces

– A secondary oocyte

– A polar body

• Meiosis II produces

– A mature ovum

– A polar body

Differentiation and onset of

meiosis

Diploid cell in embryo

(diploid)

(haploid)

Secondary oocyte

Primary oocyte

Completion of meiosis

and onset of meiosis

Entry ofsperm triggerscompletion of

meiosis n

arrested at prophase of meiosis ; present

at birth

arrested at metaphase of meiosis

(haploid)

Mature egg (ovum)

Firstpolar body

Secondpolar body

Secondary oocyte Ovary

A secondary oocyte beingreleased during ovulation

Degeneratingcorpus luteum

Corpus luteum

Ovulatedsecondary oocyte

Rupturedfollicle

Mature follicle

Growing follicle

Primaryoocytewithin follicle

Figure 26.8

• Human females have a reproductive cycle, a recurring series of events that

– Produces gametes

– Makes females available for fertilization

– Prepares the body for pregnancy

• The female reproductive cycle is actually two cycles in one:

– The ovarian cycle controls the growth and release of an egg.

– The menstrual cycle prepares the uterus for possible implantation of an embryo.

• Hormones regulate the ovarian and menstrual cycle.

The Female Reproductive Cycle

• Menstruation is

– Uterine bleeding

– Caused by the breakdown of the endometrium

REPRODUCTIVE HEALTH• Two issues of human reproductive health are

– Contraception, the deliberate prevention of pregnancy

– Sexually transmitted diseases (STDs)

Contraception• Contraception comes in many forms with varying degrees of

effectiveness.

• Barrier methods prevent sperm from meeting an egg. These include

– Diaphragms, a dome-shaped rubber cap that covers the cervix

– Condoms, sheaths usually made of latex, that fit

– Over the penis or

– Within the vagina

• Barrier devices are usually used with spermicides, sperm-killing chemicals.

Table 26.1b

• Birth control hormones include

– Oral contraceptives, or birth control pills, which have been used by millions of women since the 1960s

– Morning-after pills (MAPs), which are about 75% effective at preventing pregnancy when taken within three days of intercourse

– RU-486, which can induce abortions

Figure 26.10

Spermicide

Diaphragm

Condom

Birth control pill

Table 26.1

Sexually Transmitted Diseases• Sexually transmitted diseases (STDs) are

– Contagious diseases

– Spread by sexual contact

• Viral STDs

– Cannot be cured but can be controlled by medications

– Include

– AIDS

– Genital herpes

– Genital warts

Herpes simplex virusTable 26.2e

PapillomavirusesTable 26.2f

• STDs caused by bacteria, protozoans, and fungi are generally curable with drugs.

Chlamydia trachomatis

Neisseria gonorrhoeae

Treponema pallidum

Herpes simplex virus

Papillomaviruses

Trichomonas vaginalis

Candida albicans

Table 26.2

HUMAN DEVELOPMENT• Embryonic development begins with fertilization, the union of

sperm and egg to form a zygote.

Fertilization• Sexual intercourse releases hundreds of millions of sperm into

the vagina.

– Only a few hundred survive the trip to the egg.

– Only one will fertilize it.

• The shape of a human sperm is streamlined, which helps it swim through fluids in the

– Vagina

– Uterus

– Oviduct

Plasma membrane

Acrosome

Head(carries genetic material)

Flagellum(used for swimming)

Mitochondrion(produces energy)

Nucleus

Figure 26.11

• Fertilization by a sperm involves many steps.

NucleusAcrosome

Follicle cell

Jellycoat

Acrosomalenzymes

Plasmamembrane

Eggnucleus

Egg cell

nCytoplasm

Zygotenucleus

Spermnucleus

The spermsqueezesthrough cellsleft over fromthe follicle.

The sperm’sacrosomalenzymes digestthe jelly coatsurrounding theegg. The plasma

membranes of thesperm and egg fuse.

The sperm nucleus entersthe egg cytoplasm.

The sperm andegg chromosomesintermingle.

Figure 26.12

Basic Concepts of Embryonic Development• The key to development is that each stage of development takes

place in a highly organized fashion.

• Development begins with cleavage, a series of rapid cell divisions that results in a multicellular ball.

• Cleavage continues as the embryo moves down the oviduct toward the uterus.

• A blastocyst

– Forms about 6–7 days after fertilization

– Consists of a fluid-filled hollow ball with:

– About 100 cells

– A small clump of inner cells called the inner cell mass, which eventually forms the fetus

• About 9 days after conception, the embryo

– Undergoes gastrulation, an organized migration of cells

– Changes to a gastrula stage with three main tissue layers that establish the basic body plan:

– Ectoderm is the outer layer that forms the nervous system and skin.

– Mesoderm is the middle layer that forms the heat, kidneys, and muscles.

– Endoderm is the innermost layer the becomes the lining of the digestive tract.

Many cells(solid ball)

2 cellsZygote

4 cells

8 cells

Blastocyst (hollow ball)

Cross section of blastocyst

Gastrula (cross section)

EndodermMesodermEctoderm Gastrulation

Cleavage

Inner cellmass

Figure 26.13

• Tissues and organs take shape in a developing embryo as a result of many different changes in the cells.

• In the process called induction, one group of cells influences the development of an adjacent group of cells.

• Programmed cell death:

– Selectively kills cells to reshape the embryo

– Is used to form the fingers of the human hand

Figure 26.14

• Pregnancy, or gestation, is

– The carrying of developing young within the female reproductive tract

– Measured as 40 weeks from the start of the last menstrual cycle in humans

Pregnancy and Early Development

• The early stages of human development begin in the oviduct with

– Fertilization

– Cleavage

Oviduct

Ovulation releasessecondary oocyte,which entersoviduct.

Uterus

The blastocystimplants in theendometrium.

Endometrium

The embryodevelops into ablastocyst.

Cleavage (cell division)of embryo starts.

Mature egg (ovum)is fertilized by asperm, forming azygote.

Figure 26.15-5

• About one week after conception

– The embryo has become a blastocyst.

– The blastocyst implants in the uterine wall.

– The outer embryonic cell layer, the trophoblast, starts to form part of the placenta, the organ that

– Provides nourishment and oxygen to the embryo

– Helps dispose of metabolic waste

Endometrium

Inner cell mass

January

Day 31

Day 10Day 6

Cavity

TrophoblastUterine cavity

(a) Day 6: Before implantation (b) Day 10: Implantation under way

Endometrium

Futureyolk sac

Uterine cavity

Blood vessel(maternal)

Trophoblast

Multiplying cells of trophoblast(future placenta)

Embryo

(c) Day 31: The embryo and its life-supportequipment

Chorionicvilli

Yolk sac

Mother’sbloodvessels

Allantois (formspart of theumbilicalcord)

Chorion

Amnion

Embryo

Placenta

Figure 26.16

• About a month after conception

– The placenta has fingerlike chorionic villi that promote exchanges between the embryo’s and mother’s blood

– Four life-supporting membranes have formed:

– Amnion, a fluid-filled sac that protects the embryo

– Yolk sac, which produces the first blood cells

– Allantois, which helps form the umbilical cord

– Chorion, which contributes to the placenta

The Stages of Pregnancy• Pregnancy is divided into three trimesters about 3 months each.

The First Trimester• About 5 weeks after fertilization, the embryo

– Has formed a brain and spinal cord

– Has developed four stumpy limb buds

– Has a short tail

– Has pharyngeal pouches

– Has genitals that can be examined to determine the sex by an ultrasound device

14 weeks (98 days)9 weeks (63 days)5 weeks (35 days)

Amnion

Umbilical cordPlacenta

Figure 26.17a

• About 9 weeks after fertilization:

– The embryo has all of its organs and major body parts.

– The limb buds have become tiny arms and legs with fingers and toes.

20 weeks (140 days) At birth (280 days)

Figure 26.17b

Figure 26.18

The Second Trimester• At about 14 weeks of development, the fetus

– Is about 2.4 inches long

– Starts to look distinctly human

• At about 20 weeks of development, the embryo

– Is now called a fetus

– Mostly reveals an increase in

– Size

– Detail

5 weeks (35 days)Figure 26.17c

• At 20 weeks, the fetus

– Is about 19 cm (7.6 in.) long

– Weighs about half a kilogram (1 lb)

– Has the face of an infant

9 weeks (63 days)

Amnion

Umbilical cordPlacenta

Figure 26.17d

The Third Trimester• The third trimester

– Is a time of rapid growth

– Includes many important physical changes

• At birth, a typical baby

– Is about 50 cm (20 in.) long

– Weighs 2.7–4.5 kg (6–10 lb)

14 weeks (98 days)Figure 26.17e

20 weeks (140 days)Figure 26.17f

At birth (280 days)Figure 26.17g

Childbirth• The birth of a child is brought about by a series of strong,

rhythmic contractions of the uterus called labor.

• Hormones such as oxytocin, a powerful stimulant of the smooth muscle walls in the uterus, play a key role in inducing labor.

• Labor involves three stages:

– (1) Dilation:

– The longest stage of labor

– Increases the opening of the cervix

– (2) Expulsion results in the delivery of the child

– (3) Delivery of the placenta, about 15 minutes after the birth of the baby

Dilation of the cervix

Cervix

Uterus

Placenta

Umbilical cord

Expulsion: delivery ofthe infant

Delivery of the placenta

UterusPlacenta(detaching)

Umbilical cord

Figure 26.19

Infertility• Infertility is

– The inability to have children after one year of trying

– Most often due to problems in the man, such as underproduction of sperm or impotence

– Sometimes caused by impotence (erectile dysfunction), the inability to maintain an erection

• Female infertility can result from

– A lack of eggs

– A failure to ovulate

• There are technologies available to help treat the many forms of infertility.

In Vitro Fertilization• In vitro fertilization (IVF) begins with

– The surgical removal of eggs

– The collection of sperm

• Fertilization happens under artificial, laboratory conditions.

In vitro fertilization

Zygote

Implantation

Collectedegg

Collectedsperm

Earlyembryo

Figure 26.20

• IVF

– Offers choices that nature does not

– Raises many moral and legal issues

The Ethics of IVF

Evolution Connection: The “Grandmother Hypothesis”• Around age 50, human females undergo menopause, the

cessation of ovulation and menstruation.

• How might menopause be adaptive?

• Menopause might increase a woman’s fitness by allowing her to invest more time and energy in her children and grandchildren instead of having more children.

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