Transcript Conception, Embryonic Development, and Birth

Meiosis patterns in mammals differ for
males and females



Gametogenesis, the production of gametes by
meiosis, differs in females and males
Sperm are small and motile and are produced
throughout the life of a sexually mature male
Spermatogenesis is production of mature sperm
Fig. 46-12b
Epididymis
Seminiferous tubule
Sertoli cell
nucleus
Spermatogonium
Primary spermatocyte
Testis
Cross section
of seminiferous
tubule
Secondary spermatocyte
Spermatids
(two stages)
Lumen of
seminiferous tubule
Sperm
Fig. 46-12c
Primordial germ cell in embryo
Mitotic divisions
Spermatogonial
stem cell
2n
Mitotic divisions
Spermatogonium
2n
Mitotic divisions
Primary spermatocyte
2n
Meiosis I
Secondary spermatocyte
n
n
Meiosis II
Early
spermatid
n
n
n
n
n
n
Differentiation (Sertoli
cells provide nutrients)
Sperm
n
n
Fig. 46-12d
Fig. 46-12a
Epididymis
Seminiferous tubule
Testis
Cross section
of seminiferous
tubule
Primordial germ cell in embryo
Mitotic divisions
Sertoli cell
nucleus
Spermatogonial
stem cell
2n
Mitotic divisions
Spermatogonium
2n
Mitotic divisions
Primary spermatocyte
2n
Meiosis I
Lumen of
seminiferous tubule
Secondary spermatocyte
n
n
Meiosis II
Neck
Tail
Midpiece
Head
Spermatids
(at two stages of
differentiation)
Early
spermatid
n
n
n
n
n
n
Differentiation
(Sertoli cells
provide nutrients)
Plasma membrane
Mitochondria
Sperm
Nucleus
Acrosome
n
n


Eggs contain stored nutrients and are much larger
Oogenesis is development of mature oocytes (eggs)
and can take many years
Fig. 46-12f
Ovary
Primary
oocyte
within
follicle
Growing
follicle
Ruptured
follicle
Ovulated
secondary oocyte
Corpus luteum
Mature follicle
Degenerating
corpus luteum
Fig. 46-12g
In embryo
Primordial germ cell
Mitotic divisions
2n
Oogonium
Mitotic divisions
Primary oocyte
(present at birth), arrested
in prophase of meiosis I
2n
First
polar
body
Completion of meiosis I
and onset of meiosis II
n
n
Secondary oocyte,
arrested at metaphase of
meiosis II
Ovulation, sperm entry
Completion of meiosis II
Second
polar n
body
n
Fertilized egg
Fig. 46-12e
Ovary
Primary
oocyte
within
follicle
In embryo
Growing
follicle
Primordial germ cell
Mitotic divisions
2n
Oogonium
Mitotic divisions
2n
First
polar
body
Primary oocyte
(present at birth), arrested
in prophase of meiosis I
Completion of meiosis I and
onset of meiosis II
n
n
Secondary oocyte,
arrested at metaphase of
meiosis II
Ovulation, sperm entry
Mature follicle
Ruptured
follicle
Ovulated
secondary oocyte
Completion of meiosis II
Second
polar n
body
Corpus luteum
n
Fertilized egg
Degenerating
corpus luteum

Spermatogenesis differs from oogenesis:
 In
oogenesis, one egg forms from each cycle of meiosis; in
spermatogenesis four sperm form from each cycle of
meiosis
 Oogenesis ceases later in life in females; spermatogenesis
continues throughout the adult life of males
 Oogenesis has long interruptions; spermatogenesis
produces sperm from precursor cells in a continuous
sequence
The interplay of tropic and sex hormones
regulates mammalian reproduction



Human reproduction is coordinated by hormones
from the hypothalamus, anterior pituitary, and
gonads
Gonadotropin-releasing hormone (GnRH) is secreted
by the hypothalamus and directs the release of FSH
and LH from the anterior pituitary
FSH and LH regulate processes in the gonads and
the production of sex hormones


The sex hormones are androgens, estrogens, and
progesterone
Sex hormones regulate:
 The
development of primary sex characteristics during
embryogenesis
 The development of secondary sex characteristics at
puberty
 Sexual behavior and sex drive
Hormonal Control of the Male
Reproductive System




FSH promotes the activity of Sertoli cells, which
nourish developing sperm and are located within the
seminiferous tubules
LH regulates Leydig cells, which secrete testosterone
and other androgen hormones, which in turn promote
spermatogenesis
Testosterone regulates the production of GnRH, FSH,
and LH through negative feedback mechanisms
Sertoli cells secrete the hormone inhibin, which
reduces FSH secretion from the anterior pituitary
Fig. 46-13
–
Hypothalamus
GnRH
–
–
FSH
LH
Leydig cells
Sertoli cells
Inhibin
Spermatogenesis
Testis
Testosterone
Negative feedback
Negative feedback
Anterior pituitary
The Reproductive Cycles of Females




In females, the secretion of hormones and the
reproductive events they regulate are cyclic
Prior to ovulation, the endometrium thickens with
blood vessels in preparation for embryo
implantation
If an embryo does not implant in the endometrium,
the endometrium is shed in a process called
menstruation
Hormones closely link the two cycles of female
reproduction:
 Changes
in the uterus define the menstrual cycle (also
called the uterine cycle)
 Changes in the ovaries define the ovarian cycle
The Ovarian Cycle





The sequential release of GnRH then FSH and LH
stimulates follicle growth
Follicle growth and an increase in the hormone estradiol
characterize the follicular phase of the ovarian cycle
The follicular phase ends at ovulation, and the
secondary oocyte is released
Following ovulation, the follicular tissue left behind
transforms into the corpus luteum; this is the luteal
phase
The corpus luteum disintegrates, and ovarian steroid
hormones decrease
The Uterine (Menstrual) Cycle

Hormones coordinate the uterine cycle with the ovarian
cycle
Thickening of the endometrium during the proliferative phase
coordinates with the follicular phase
 Secretion of nutrients during the secretory phase coordinates
with the luteal phase
 Shedding of the endometrium during the menstrual flow
phase coordinates with the growth of new ovarian follicles




A new cycle begins if no embryo implants in the endometrium
Cells of the uterine lining can sometimes migrate to an
abnormal, or ectopic, location
Swelling of these cells in response to hormone stimulation
results in a disorder called endometriosis
Menstrual Versus Estrous Cycles

Menstrual cycles are characteristic of humans and
some other primates:
 The
endometrium is shed from the uterus in a bleeding
called menstruation
 Sexual receptivity is not limited to a timeframe

Estrous cycles are characteristic of most mammals:
 The
endometrium is reabsorbed by the uterus
 Sexual receptivity is limited to a “heat” period
 The length and frequency of estrus cycles varies from
species to species
(a)
Control by hypothalamus
+
Inhibited by combination of
estradiol and progesterone
Stimulated by high levels
of estradiol
–
Inhibited by low levels of
estradiol
–
Hypothalamus
GnRH
Anterior pituitary
LH
FSH
Pituitary gonadotropins
in blood
(b)
LH
FSH
FSH and LH stimulate
follicle to grow
LH surge triggers
ovulation
Ovarian cycle
(c)
Growing follicle
Corpus
luteum
Maturing
follicle
Ovulation
Follicular phase
Days
Fig. 46-14a
|
|
|
0
5
10
|
|
14 15
Degenerating
corpus luteum
Luteal phase
|
|
20
25
|
28
Fig. 46-14b
(d)
Ovarian hormones in
blood
Estradiol
Peak causes
LH surge
Progesterone
Ovulation
Estradiol level
very low
(e)
Progesterone and estradiol promote thickening
of endometrium
Uterine (menstrual) cycle
Endometrium
Days
Menstrual flow phase Proliferative phase
|
0
|
|
5
10
Secretory phase
|
|
14 15
|
|
20
25
|
28
Control by hypothalamus
(a)
GnRH
1
Anterior pituitary
2
(b)
+
Inhibited by combination of
estradiol and progesterone
Stimulated by high levels
of estradiol
–
Inhibited by low levels of
estradiol
–
Hypothalamus
FSH
LH
Pituitary gonadotropins
in blood
6
LH
FSH
3
(c)
FSH and LH stimulate
follicle to grow
Ovarian cycle
7
Growing follicle
Maturing
follicle
Ovarian hormones in
blood
Degenerating
corpus luteum
Corpus
luteum
Ovulation
Luteal phase
Estradiol secreted
by growing follicle in
increasing amounts
4
(d)
LH surge triggers
ovulation
8
Follicular phase
Progesterone and
estradiol secreted
by corpus luteum
Peak causes
LH surge
5
10
9
Progesterone
Estradiol
Progesterone and estradiol promote thickening
of endometrium
Estradiol level
very low
Uterine (menstrual) cycle
(e)
Endometrium
Secretory phase
Menstrual flow phase Proliferative phase
Days
Fig. 46-14
|
0
|
|
5
10
|
|
14 15
|
|
20
25
|
28
Menopause



After about 500 cycles, human females undergo
menopause, the cessation of ovulation and
menstruation
Menopause is very unusual among animals
Menopause might have evolved to allow a mother to
provide better care for her children and
grandchildren
Conception, Embryonic Development, and
Birth




An egg develops into an embryo in a series of
predictable events
Conception, fertilization of an egg by a sperm,
occurs in the oviduct
The resulting zygote begins to divide by mitosis in a
process called cleavage
Division of cells gives rise to a blastocyst, a ball of
cells with a cavity
Fig. 47-3-5
Sperm plasma
membrane
Sperm
nucleus
Fertilization
envelope
Acrosomal
process
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Actin
filament
Cortical
Fused
granule
plasma
membranes
Perivitelline
Hydrolytic enzymes
space
Vitelline layer
Egg plasma
membrane
EGG CYTOPLASM
Fig. 47-UN1
Sperm-egg fusion and depolarization
of egg membrane (fast block to
polyspermy)
Cortical granule release
(cortical reaction)
Formation of fertilization envelope
(slow block to polyspermy)
Fig. 46-15
3
Cleavage
Cleavage
continues
4
Ovary
2
Fertilization
The blastocyst
implants
5
Uterus
1
Ovulation
(a) From ovulation to implantation
Endometrium
Endometrium
Inner cell mass
Cavity
Blastocyst
(b) Implantation of blastocyst
Trophoblast
Fig. 47-6
(a) Fertilized egg
(b) Four-cell stage
(c) Early blastula
(d) Later blastula
Fig. 47-16-5
Endometrial
epithelium
(uterine lining)
Uterus
Inner cell mass
Trophoblast
Expanding
region of
trophoblast
Maternal
blood
vessel
Epiblast
Hypoblast
Blastocoel
Expanding
region of
trophoblast
Amniotic
cavity
Epiblast
Hypoblast
Yolk sac (from
hypoblast)
Extraembryonic
mesoderm cells
(from epiblast)
Chorion (from
trophoblast)
Trophoblast
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolk sac
Extraembryonic
mesoderm
Allantois
Fig. 46-UN1
Gametogenesis
Oogenesis
Spermatogenesis
Primary
spermatocyte
2n
Primary
oocyte
2n
n
n
Secondary
spermatocytes
n
n
n
n
n
n
n
n
n
n
Secondary
oocyte
Spermatids
Sperm
n
n
Polar body
Fertilized
egg
Polar
body




After blastocyst formation, the embryo implants into
the endometrium
The embryo releases human chorionic
gonadotropin (hCG), which prevents menstruation
Pregnancy, or gestation, is the condition of carrying
one or more embryos in the uterus
Duration of pregnancy in other species correlates
with body size and maturity of the young at birth
First Trimester






Human gestation can be divided into three trimesters of
about three months each
The first trimester is the time of most radical change for
both the mother and the embryo
During implantation, the endometrium grows over the
blastocyst
During its first 2 to 4 weeks, the embryo obtains nutrients
directly from the endometrium
Meanwhile, the outer layer of the blastocyst, called the
trophoblast, mingles with the endometrium and eventually
forms the placenta
Blood from the embryo travels to the placenta through
arteries of the umbilical cord and returns via the umbilical
vein
Fig. 46-16
Maternal
arteries
Maternal
veins
Placenta
Maternal
portion
of placenta
Umbilical cord
Chorionic villus,
containing fetal
capillaries
Maternal blood
pools
Uterus
Fetal arteriole
Fetal venule
Umbilical cord
Fetal
portion of
placenta
(chorion)
Umbilical
arteries
Umbilical
vein




•
Splitting of the embryo during the first month of
development results in genetically identical twins
Release and fertilization of two eggs results in fraternal
and genetically distinct twins
The first trimester is the main period of organogenesis,
development of the body organs
All the major structures are present by 8 weeks, and the
embryo is called a fetus
Changes occur in the mother
Growth of the placenta
 Cessation of ovulation and the menstrual cycle
 Breast enlargement
 Nausea is also very common

Fig. 46-17a
(a) 5 weeks
Fig. 46-17b
(b) 14 weeks
Fig. 46-17c
(c) 20 weeks
Fig. 46-17
(a) 5 weeks
(b) 14 weeks
(c) 20 weeks
Second Trimester

During the second trimester
 The
fetus grows and is very active
 The mother may feel fetal movements
 The uterus grows enough for the pregnancy to become
obvious
Third Trimester


During the third trimester, the fetus grows and fills
the space within the embryonic membranes
A complex interplay of local regulators and
hormones induces and regulates labor, the process
by which childbirth occurs
Fig. 46-18
from
ovaries
Oxytocin
+
from fetus
and mother’s
posterior pituitary
Positive feedback
Estradiol
Induces oxytocin
receptors on uterus
Stimulates uterus
to contract
Stimulates placenta
to make
Prostaglandins
Stimulate more
contractions
of uterus
+
Fig. 46-19-1
Placenta
Umbilical cord
Uterus
Cervix
1
Dilation of the cervix
Fig. 46-19-2
2
Expulsion: delivery of the infant
Fig. 46-19-3
Uterus
Placenta
(detaching)
Umbilical
cord
3
Delivery of the placenta
Fig. 46-19-4
Placenta
Umbilical cord
Uterus
Cervix
1
2
Dilation of the cervix
Expulsion: delivery of the infant
Uterus
Placenta
(detaching)
Umbilical
cord
3
Delivery of the placenta



Birth, or parturition, is brought about by a series of
strong, rhythmic uterine contractions
First the baby is delivered, and then the placenta
Lactation, the production of milk, is unique to
mammals
Contraception and Abortion


Contraception, the deliberate prevention of
pregnancy, can be achieved in a number of ways
Contraceptive methods fall into three categories:
 Preventing
release of eggs and sperm
 Keeping sperm and egg apart
 Preventing implantation of an embryo

A health-care provider should be consulted for complete
information on the choice and risks of contraception
methods
Fig. 46-20
Male
Method
Female
Event
Production of
sperm
Event
Production of
primary oocytes
Vasectomy
Sperm transport
down male
duct system
Method
Oocyte
development
and ovulation
Combination birth
control
pill (or injection,
patch, or
vaginal ring)
Abstinence
Abstinence
Condom
Female condom
Coitus
interruptus
(very high
failure rate)
Sperm
deposited
in vagina
Capture of the
oocyte by the
oviduct
Tubal ligation
Sperm
movement
through
female
reproductive
tract
Transport
of oocyte in
oviduct
Spermicides;
diaphragm;
cervical cap;
progestin alone
(as minipill,
implant,
or injection)
Meeting of sperm and oocyte
in oviduct
Union of sperm and egg
Implantation of blastocyst in
endometrium
Morning-after
pill; intrauterine
device (IUD)



The rhythm method, or natural family planning, is
to refrain from intercourse when conception is most
likely; it has a pregnancy rate of 10–20%
Coitus interruptus, the withdrawal of the penis before
ejaculation, is unreliable
Barrier methods block fertilization with a pregnancy
rate of less than 10%
A
A
condom fits over the penis
diaphragm is inserted into the vagina before
intercourse


Intrauterine devices are inserted into the uterus and
interfere with fertilization and implantation; the
pregnancy rate is less than 1%
Female birth control pills are hormonal
contraceptives with a pregnancy rate of less than
1%

Sterilization is permanent and prevents the release
of gametes
 Tubal
ligation ties off the oviducts
 Vasectomy ties off the vas deferens



Abortion is the termination of a pregnancy
Spontaneous abortion, or miscarriage, occurs in up to
one-third of all pregnancies
The drug RU486 results in an abortion within the first
7 weeks of a pregnancy
Sexually Transmitted Diseases

Hepatitis
A
- Sewage-contaminated drinking water
B
- Sexual contact
C
- Post-transfusion
HIV, the AIDS Virus
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Genital Warts
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360
270
180
90
0
1966
1972
1978
1984
1990
Year
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1996
2002
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320
240
160
80
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1966
1972
1978
1984
1990
Year
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1996
2002
Gonorrhea
57
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400
300
200
100
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1945
1955
1965
1975
Year
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1985
1995
2005
Syphilis
58
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a.
c.
b.
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c: © Science VU/Visuals Unlimited;
Detecting Disorders During Pregnancy



Amniocentesis and chorionic villus sampling are
invasive techniques in which amniotic fluid or fetal
cells are obtained for genetic analysis
Noninvasive procedures usually use ultrasound
imaging to detect fetal condition
Genetic testing of the fetus poses ethical questions
and can present parents with difficult decisions
Treating Infertility



Modern technology can provide infertile couples
with assisted reproductive technologies
In vitro fertilization (IVF) mixes eggs with sperm in
culture dishes and returns the embryo to the uterus at
the 8 cell stage
Sperm are injected directly into an egg in a type of
IVF called intracytoplasmic sperm injection (ICSI)
You should now be able to:
1.
2.
3.
4.
Distinguish between asexual and sexual
reproduction
Explain how hermaphroditism may be
advantageous to animals that have difficulty
encountering a member of the opposite sex
Describe various ways in which animals may protect
developing embryos
Using diagrams, identify and state the function of
each component of the male and female
reproductive systems
5.
6.
7.
8.
Describe oogenesis and spermatogenesis; describe
three major differences between them
Explain how the uterine and ovarian cycles are
synchronized and describe the functions of the
hormones involved
List the various methods of contraception, how each
works, and how effective each is
Describe techniques that allow us to learn about the
health and genetics of a fetus
If a hermaphrodite self-fertilizes, will the
offspring be identical to the parent?
a.
b.
c.
d.
Yes.
No, the parent will use sperm stored from a previous
mating.
No, random assortment and crossing over during meiosis
will ensure a unique combination of genes upon
fertilization.
No, interactions of the offspring with their environment
will cause changes in their genetic makeup, making each
unique.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings.
What advantage does internal fertilization
have compared to external fertilization?
a.
b.
c.
d.
Internal fertilization allows animals to reproduce
sexually.
Generally, internal fertilization requires much less
expenditure of resources.
Usually internal fertilization produces more offspring,
ensuring rapid population growth.
Internal fertilization prevents the drying out of gametes
in a dry environment.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings.
Suppose a man’s two vas deferens were sealed
off. Which of the following would be missing
from his ejaculate?
a.
b.
c.
d.
Semen
Sperm
Citrate
bulbourethral fluid
Copyright © 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings.
Which of the following organs is unnecessary
for a woman to conceive and reproduce
(the natural way)?
a.
b.
c.
d.
e.
Clitoris
Uterus
Oviducts
Cervix
vagina
Copyright © 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings.
In humans, how do spermatogenesis and
oogenesis differ?
a.
b.
c.
d.
Oogenesis produces one haploid cell and
spermatogenesis produces four.
Oogenesis begins at the onset of puberty.
Spermatogenesis begins in the embryonic stage of
development.
Oogenesis produces one functional ovum and
spermatogenesis produces four functional spermatozoa.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings.
Many birth-control pills contain low levels
of estrogen and progesterone. What effect
does this have on a woman’s ovarian cycle?
a.
b.
c.
d.
e.
stimulates LH and FSH secretion by the anterior pituitary,
thus inhibiting follicle development
inhibits secretion of GnRH by the hypothalamus, thus
inhibiting secretion of LH and FSH
inhibits secretion of LH and FSH by the anterior pituitary,
thus inhibiting follicle development
a and b
b and c
Copyright © 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings.
You are a lab tech testing hormone levels in
a blood sample taken from a woman in her 20s.
You find high levels of estrogen, progesterone,
hCG, and prolactin. Which of these hormones
is not being produced by the woman?
a.
b.
c.
d.
Estrogen
Progesterone
hCG
prolactin
Copyright © 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings.
An infant suckling on the breasts of a woman
who has recently given birth sends a nerve
impulse to the pituitary gland. The pituitary gland
then secretes oxytocin, which stimulates the
mammary glands in the breasts to release milk.
What type of hormonal feedback is this?
a.
b.
negative feedback
positive feedback
Copyright © 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings.