Chapter 26a

Reproduction and Development

About this Chapter

• Sex determination and differentiation• Gametogenesis and patterns of reproduction• Male reproductive development and

physiology• Female reproductive development and

physiology• Pregnancy and the birth process• The reproductive system during growth and

aging

Sex Determination

• Sexual dimorphism• Females and males are physically distinct

• Gonads produce gametes and sex hormones• Male gonads = testes sperm• Female gonads = ovaries eggs

• Sex hormones direct development of genitalia• Internal genitalia• External genitalia

Figure 26-1

Sex Determination Is Directed By Our Genome

• Humans have 23 pairs of chromosomes• 22 pairs of autosomes• X and Y = 1 pair of sex

chromosomesNondisjunction• XXX superfemale• XXY Klinefelters• X0 Turners• XYY supermale

Figure 26-2

X and Y Chromosomes Determine Sex

Sexual Differentiation

• Bipotential tissues have not yet differentiated• SRY protein directs development as a male• Gonadal medulla develops into testis• Testicular hormones direct further development

• Absence of SRY protein leads to female development• Gonadal cortex develops into ovarian tissue• Mullerian ducts develop into female organs • Wolffian ducts degenerate

Table 26-1

Sexual Differentiation

Figure 26-3a

Development of Internal Reproductive Organs

FEMALE MALE

Bipotential gonadMüllerian duct

Müllerian duct

Uterus

Uterus

(a) DEVELOPMENT OF INTERNAL ORGANS

Ovary

Vagina

Fallopian tube(from Müllerianduct)

Testis

Testis

ProstateSeminal vesicle

Vas deferens

Wolffianduct

Epididymis

Wolffian duct

Cloacal opening

Kidney

Anti-Müllerianhormone from testiscauses the Müllerianducts to disappear.

Absence of anti-Müllerian hormoneallows theMüllerian ductto become thefallopian tube,uterus, and upperpart of the vagina.

Bipotential stage: 6 week fetusThe internal reproductive organshave the potential to develop intomale or female structures

Testosterone fromtestis converts Wolffianduct into seminalvesicle, vas deferens,and epididymis. DHTcontrols prostatedevelopment.

10 WEEKS

AT BIRTH

Gonadal cortexbecomes ovary in theabsence of SRY protein.

Absence of testosteronecauses Wolffian ductto degenerate.

SRY protein in a maleembryo directs themedulla of thebipotential gonadto develop into testis.

1

2

3

1

2

3

Figure 26-3b

Development of External Genitalia

FEMALE MALE

(b) DEVELOPMENT OF EXTERNAL GENITALIA

Bipotential stage(6 week fetus)

Urethral fold

Urethral fold

Urethral grooveLabioscrotal swelling

Labioscrotalswelling

Labioscrotalswelling

Anus

Genital tubercle

Shaft of penis

Glans penis

Scrotum

Anus

Anus

ClitorisUrethral openingVaginal opening

Anus

Penis

Urethral fold

Clitoris

10 WEEKS

AT BIRTH

In the absenceof androgens,the external genitaliaare feminized.

DHT causesdevelopmentof male externalgenitalia.

The testes descendfrom the abdominalcavity into thescrotum.

1

Anus

1

1

2

Labiamajora

Labiaminora

homologous

Figure 26-4

Control of Male Development

• SRY gene directs male development

Control of Female Development

• The SRY gene and protein are absent• Gonadal cortex develops into ovarian tissue• Mullerian ducts develop into female organs• Vagina• Uterus• Fallopian tubes

• Wolffian ducts degenerate

MALEFEMALE

Spermatids

develop into

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Sisterchromatids

Sisterchromatids

MEIOSIS

Second meioticdivision

Secondary gamete divides.23 chromosomes

(haploid)

First meioticdivision

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

Spermatogonia

Oögonium

Secondaryoocyte(egg)

Disintegrates

Secondpolar body

disintegrates.

Zygote

Sperm

Oögonia

Secondaryspermatocytes

(may notoccur)

Egg releasedfrom ovary at

ovulation.

Primaryspermatocyte

Spermatogonium

One primary spermatocyteyields 4 sperm.

One primary oocyteyields 1 egg.

Primaryoocyte

FERTILIZATION

Unfertilized eggpasses out of body.

Firstpolarbody

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

DNA replicatesbut no cell division.46 chromosomes,

duplicated

Embr

yoEm

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

2

3

4

5

6

Figure 26-5

Gametogenesis Differs in Males and Females

MALEFEMALE

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Spermatogonia

Oögonium

Oögonia

Spermatogonium

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

Embr

yoEm

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

Figure 26-5, step 1

Mitosis: Germ Cell Proliferation

MALEFEMALE

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Sisterchromatids

Sisterchromatids

MEIOSISSpermatogonia

Oögonium

Oögonia

Primaryspermatocyte

Spermatogonium

Primaryoocyte

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

DNA replicatesbut no cell division.46 chromosomes,

duplicated

Embr

yoEm

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

2

Figure 26-5, steps 1–2

Meiosis: DNA Replicates

Polar bodies

MALEFEMALE

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Sisterchromatids

Sisterchromatids

MEIOSIS

First meioticdivision

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

Spermatogonia

Oögonium

Secondaryoocyte(egg)

Oögonia

Secondaryspermatocytes

Primaryspermatocyte

Spermatogonium

Primaryoocyte

Firstpolarbody

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

DNA replicatesbut no cell division.46 chromosomes,

duplicated

Embr

yoEm

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

2

3

Figure 26-5, steps 1–3

First Meiotic Division

Polar bodies

Figure 26-5, steps 1–4

Second Meiotic Division

MALEFEMALE

Spermatids

develop into

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Sisterchromatids

Sisterchromatids

MEIOSIS

Second meioticdivision

Secondary gamete divides.23 chromosomes

(haploid)

First meioticdivision

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

Spermatogonia

Oögonium

Secondaryoocyte(egg)

Disintegrates

Sperm

Oögonia

Secondaryspermatocytes

(may notoccur)

Egg releasedfrom ovary at

ovulation.

Primaryspermatocyte

Spermatogonium

One primary spermatocyteyields 4 sperm.

Primaryoocyte

Firstpolarbody

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

DNA replicatesbut no cell division.46 chromosomes,

duplicated

Embr

yoEm

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

2

3

4

Polar bodies

Figure 26-5, steps 1–5

Ovulation Without Fertilization

MALEFEMALE

Spermatids

develop into

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Sisterchromatids

Sisterchromatids

MEIOSIS

Second meioticdivision

Secondary gamete divides.23 chromosomes

(haploid)

First meioticdivision

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

Spermatogonia

Oögonium

Secondaryoocyte(egg)

Disintegrates

Sperm

Oögonia

Secondaryspermatocytes

(may notoccur)

Egg releasedfrom ovary at

ovulation.

Primaryspermatocyte

Spermatogonium

One primary spermatocyteyields 4 sperm.

One primary oocyteyields 1 egg.

Primaryoocyte

Unfertilized eggpasses out of body.

Firstpolarbody

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

DNA replicatesbut no cell division.46 chromosomes,

duplicated

Embr

yoEm

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

2

3

4

5

Polar bodies

MALEFEMALE

Spermatids

develop into

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Sisterchromatids

Sisterchromatids

MEIOSIS

Second meioticdivision

Secondary gamete divides.23 chromosomes

(haploid)

First meioticdivision

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

Spermatogonia

Oögonium

Secondaryoocyte(egg)

Disintegrates

Secondpolar body

disintegrates.

Zygote

Sperm

Oögonia

Secondaryspermatocytes

(may notoccur)

Egg releasedfrom ovary at

ovulation.

Primaryspermatocyte

Spermatogonium

One primary spermatocyteyields 4 sperm.

One primary oocyteyields 1 egg.

Primaryoocyte

FERTILIZATION

Unfertilized eggpasses out of body.

Firstpolarbody

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

DNA replicatesbut no cell division.46 chromosomes,

duplicated

Embr

yoEm

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

2

3

4

5

6

Figure 26-5, steps 1–6

Ovulation with Fertilization Is Followed by Final Step of Meiosis

Polar bodies

Steroid Synthesis Pathways

• Steroid hormones are similar to each other• Production of sex steroids differs between

men and women• Ovary• Estrogen and progesterone

• Testis• Testosterone and dihydrotestosterone (DHT)

• Adrenal gland secretes small amounts of sex steroids

Figure 26-6

Synthesis Pathways for Steroid HormonesCholesterol

Progesterone

TestosteroneDihydro-

testosterone(DHT)

aromatase

EstradiolCorticosterone Cortisol

Aldosterone

*

* 5-reductaseKEY

Intermediate steps

Hormonal Regulation of Reproduction

• Anterior pituitary• Luteinizing hormone (LH) • Follicle stimulating hormone (FSH)

• Gonads produce steroid and peptide hormones• Gonads are the main source of sex steroid

Figure 26-7

General Pattern of Hormonal Control of Reproduction

Internal andenvironmental

stimuliCNS

Hypothalamus

Anteriorpituitary

Steroid andpeptide hormones

Gameteproduction

GnRHShort-loop negative feedback

Long-loop feedbackmay be negative

or positive

Stimulus

Integrating center

Efferent pathway

Effector

Tissue responseLH

Endocrinecells

FSH

Gonads(ovaries or testes)

KEY

Females only

Table 26-2

Consequences of Feedback