Chapter 26a Reproduction and Development
Feb 23, 2016
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