1. Chapter 46
Animal Reproduction

2. Overview: Doubling Up for Sexual Reproduction
Each worm produces both sperm and eggs, which will fertilize
A population transcends finite life spans
Only by reproduction

3. Both asexual and sexual reproduction occur in the animal kingdom
Asexual reproduction is the creation of new individuals
Whose genes all come from one parent
Sexual reproduction is the creation of offspring
By the fusion of male and female gametes to form a zygote
The female gamete is the egg
The male gamete is the sperm

4. Mechanisms of Asexual Reproduction
Many invertebrates reproduce asexually by fission
The separation of a parent into two or
more individuals of approximately the
same size
Also common in invertebrates is budding
In which two new individuals arise from
outgrowths of existing ones
Another type of asexual reproduction is fragmentation, which
Is the breaking of the body into several pieces, some or all of which develop into complete adults
Must be accompanied by regeneration, the regrowth of lost body parts

5. Sexual reproduction results in genetic recombination, which provides potential advantages:
An increase in variation in offspring, providing an increase in the reproductive success of parents in changing environments
An increase in the rate of adaptation
A shuffling of genes and the elimination of harmful genes from a population

6. Reproductive Cycles and Patterns
Most animals exhibit cycles in reproductive activity
Often related to changing seasons
Reproductive cycles
Are controlled by hormones and environmental cues

7. Animals may reproduce exclusively asexually or sexually
Or they may alternate between the two
Some animals reproduce by parthenogenesis
A process in which an egg develops without being fertilized

8. Reproduce exclusively by a complex form of parthenogenesis
Among vertebrates, several genera of fishes, amphibians, and lizards, including whiptail lizards
Reproduce exclusively by a complex form of parthenogenesis
Figure 46.3a, b
Time
Ovary size
Hormones
Behavior
Ovulation
Progesterone
Estrogen
Female- like
Male- like
(a) Both lizards in this photograph are C. uniparens females. The one on top is playing the role of a male. Every two or three weeks during the breeding season, individuals switch sex roles.
(b) The sexual behavior of C. uniparens is correlated with the cycle of ovulation mediated by sex hormones. As blood levels of estrogen rise, the ovaries grow, and the lizard behaves like a female. After ovulation, the estrogen level drops abruptly, and the progesterone level rises; these hormone levels correlate with male behavior.

9. Sexual reproduction presents a special problem for certain organisms
That seldom encounter a mate
One solution to this problem is hermaphroditism
In which each individual has both male and female reproductive systems
Another remarkable reproductive pattern is sequential hermaphroditism
In which an individual reverses its
sex during its lifetime

10. Some species have external fertilization, in which
Fertilization depends on mechanisms that help sperm meet eggs of the same species
Some species have external fertilization, in which
Eggs shed by the female are
fertilized by sperm in the external
environment
Other species have internal fertilization, in which
Sperm are deposited in or near the
female reproductive tract, and
fertilization occurs within the tract

11. In either situation, fertilization requires critical timing
Often mediated by environmental cues, pheromones, and/or courtship behavior
Internal fertilization
Requires important behavioral interactions between male and female animals
Requires compatible copulatory organs
Pheromones

12. Ensuring the Survival of Offspring
All species produce more offspring than the environment can handle
But the proportion that survives is quite small
The embryos of many terrestrial animals
Develop in eggs that can withstand harsh environments
Instead of secreting a shell around the embryo
Many animals retain the embryo, which develops inside the female
Exhibit parental care to ensure
survival of offspring

13. Gamete Production and Delivery
To reproduce sexually
Animals must have systems that produce gametes
The least complex systems
Do not even contain distinct gonads, the organs that produce gametes in most animals
The most complex reproductive systems
Contain many sets of accessory tubes and glands that carry, nourish, and protect the gametes and the developing embryos

14. Many animals with relatively simple body plans
Possess highly complex reproductive systems
Figure 46.7
Male organs:
Female organs:
Genital pore
(Excretory pore)
Seminal
receptacle
(Digestive tract)
Testis 1
Vas efferens 2
Sperm duct (vas deferens) 3
Seminal vesicle 4
Ovary
Oviduct
Yolk duct
Yolk gland
Uterus

15. Most insects Have separate sexes with complex reproductive systems
Ovary 1
Accessory gland 4
Ejaculatory duct 1
Testis
Oviduct
Spermatheca 2 5
Penis
Vas deferens
Vagina 3 3
Seminal vesicle
Accessory gland
(a) Male honeybee. Sperm form in the testes, pass through the sperm duct (vas deferens), and are stored in the seminal vesicle. The male ejaculates sperm along with fluid from the accessory glands. (Males of some species of insects and other arthropods have appendages called claspers that grasp the female during copulation.)
(b) Female honeybee. Eggs develop in the ovaries and then pass through the oviducts and into the vagina. A pair of accessory glands (only one is shown) add protective secretions to the eggs in the vagina. After mating, sperm are stored in the spermatheca, a sac connected to the vagina by a short duct.
Figure 46.8a, b

16. Reproductive organs produce and transport gametes: focus on humans

17. Female Reproductive Anatomy
The female external reproductive structures include
The clitoris
Two sets of labia
The internal organs are a pair of gonads
And a system of ducts and chambers that carry gametes and house the embryo and fetus

18. Reproductive anatomy of the human female
Prepuce
(Rectum)
Cervix
Vagina
Bartholin’s gland
Vaginal opening
Ovary
Oviduct
Labia majora
Labia minora
(Urinary bladder)
(Pubic bone)
Uterus
Urethra
Shaft
Glans
Clitoris
Figure 46.9

19. Vagina
Uterus
Cervix
Ovaries
Oviduct
Uterine wall
Endometrium
Follicles
Corpus luteum

20. Ovaries The female gonads, the ovaries Lie in the abdominal cavity
Each ovary
Is enclosed in a tough protective capsule and contains many follicles
A follicle
Consists of one egg cell surrounded by one or more layers of follicle cells
The process of ovulation
Expels an egg cell from the follicle
The remaining follicular tissue then grows within the ovary
To form a solid mass called the corpus luteum, which secretes hormones, depending on whether or not pregnancy occurs

21. The egg cell is released into the abdominal cavity
Oviducts and Uterus
The egg cell is released into the abdominal cavity
Near the opening of the oviduct, or fallopian tube
Cilia in the tube
Convey the egg to the uterus

22. The vagina is a thin-walled chamber
Vagina and Vulva
The vagina is a thin-walled chamber
That is the repository for sperm during copulation
That serves as the birth canal through which a baby is born
The vagina opens to the outside at the vulva
Which includes the hymen, vestibule, labia minora, labia majora, and clitoris

23. The mammary glands are not part of the reproductive system
But are important to mammalian reproduction
Within the glands
Small sacs of epithelial tissue secrete milk

24. Male Reproductive Anatomy
In most mammalian species
The male’s external reproductive organs are the scrotum and penis
The internal organs
Consist of the gonads, which produce sperm and hormones, and accessory glands

25. Reproductive anatomy of the human male
Figure 46.10
Erectile tissue
of penis
Prostate gland
(Urinary bladder)
Bulbourethral gland
Vas deferens
Epididymis
Testis
Seminal
vesicle
(behind
bladder)
Urethra
Scrotum
Glans penis

26. Seminal vesicle
(Rectum)
Vas deferens
Ejaculatory duct
Prostate gland
Bulbourethral gland
(Urinary
bladder)
(Pubic bone)
Erectile
tissue of
penis
Urethra
Glans penis
Prepuce
Epididymis
Testis
Scrotum

27. The male gonads, or testes
Consist of many highly coiled tubes surrounded by several layers of connective tissue
The tubes are seminiferous tubules
Where sperm form
Production of normal sperm
Cannot occur at the body temperatures of most mammals
The testes of humans and many mammals
Are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity

28. From the seminiferous tubules of a testis
Ducts
From the seminiferous tubules of a testis
The sperm pass into the coiled tubules of the epididymis
During ejaculation
Sperm are propelled through the muscular vas deferens, the ejaculatory duct, and exit the penis through the urethra

29. Three sets of accessory glands
Add secretions to the semen, the fluid that is ejaculated
A pair of seminal vesicles
Contributes about 60% of the total volume of semen
The prostate gland
Secretes its products directly into the urethra through several small ducts
The bulbourethral gland
Secretes a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra

30. Semen in the Female Reproductive Tract
Once in the female reproductive tract
A number of processes, including contractions of the uterus, help move the sperm up the uterus

31. Penis The human penis During sexual arousal
Is composed of three cylinders of spongy erectile tissue
During sexual arousal
The erectile tissue fills with blood from the arteries, causing an erection
Baculum

32. Two types of physiological reactions predominate in both sexes
Human Sexual Response
Two types of physiological reactions predominate in both sexes
Vasocongestion, the filling of tissue with blood
Myotonia, increased muscle tension
The sexual response cycle can be divided into four phases
Excitement, plateau, orgasm, and resolution

33. The process of gametogenesis
In humans and other mammals, a complex interplay of hormones regulates gametogenesis
The process of gametogenesis
Is based on meiosis, but differs in females and males

34. Secondary spermatocyte
Spermatogenesis is the production of mature sperm
Epididymis
Seminiferous tubule
Testis
Cross section
of seminiferous
tubule 2n
Spermatogonium
Mitotic division,
producing large numbers
of spermatogonia
Sertoli cell
nucleus
Differentiation and onset of meiosis I 2n
Primary spermatocyte
(in prophase of meiosis I)
Meiosis I completed n n
Secondary spermatocyte
Meiosis II
Lumen of
Seminiferous tubule n n n n
Early
spermatids
Spermatids
(at two stages of
differentiation)
Differentiation
(Sertoli cells provide
nutrients) n n n
Sperm cells n
Neck
Head
Midpiece
Tail
Plasma membrane
Mitochondria
Nucleus
Figure 46.12
Acrosome

35. Primary germ cell in embryo
Oogenesis is the development of mature ova
Ovary
Primary germ cell in embryo
Differentiation
Oogonium
in ovary
Mitotic
division
Primary oocyte,
arrested in prophase
of meiosis I
(present at birth)
Completion of meiosis I
and onset of meiosis II
Primary
oocyte
within
follicle
Secondary oocyte,
arrested at meta-
phase of meiosis II
First
polar
body
Ovulation
Entry of
sperm triggers
completion of
meiosis II
Ovum
Growing
Mature follicle
Ruptured
Ovulated
secondary oocyte
Corpus luteum
Degenerating
corpus luteum 2n n
Figure 46.11

36. Oogenesis differs from spermatogenesis
In three major ways
First, during the meiotic divisions of oogenesis
Cytokinesis is unequal, with almost all the cytoplasm monopolized by a single daughter cell, the secondary oocyte
Second, sperm are produced continuously throughout a male’s life
Which is not the case in oogenesis
Third, oogenesis has long “resting” periods
While spermatogenesis produces sperm in uninterrupted sequence

37. Concept 46.5: 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

38. 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

39. The Reproductive Cycles of Females
In females
The secretion of hormones and the reproductive events they regulate are cyclic
Two different types of cycles occur in females
Humans and other primates have menstrual cycles
While other mammals have estrous cycles
In both cases ovulation occurs at a time in the cycle
After the endometrium has started to thicken in preparation for implantation

40. In menstrual cycles In estrous cycles
The endometrium is shed from the uterus in a bleeding called menstruation
Sexual receptivity is not limited to a specific timeframe
In estrous cycles
The endometrium is reabsorbed by the uterus
Sexual receptivity is limited to a “heat” period

41. The Human Female Reproductive Cycle: A Closer Look
The female reproductive cycle
Is one integrated cycle involving two organs, the uterus and ovaries

42. Cyclic secretion of GnRH from the hypothalamus
And of FSH and LH from the anterior pituitary orchestrates the female reproductive cycle
Five kinds of hormones
Participate in an elaborate scheme involving both positive and negative feedback

43. Control by hypothalamus Uterine (menstrual) cycle
The reproductive cycle of the human female
Figure 46.13a–e
Control by hypothalamus
Inhibited by combination of
estrogen and progesterone
Stimulated by high levels
of estrogen
Inhibited by low levels of
estrogen
Hypothalamus
Anterior pituitary
GnRH
FSH LH
Pituitary gonadotropins
in blood
FSH and LH stimulate
follicle to grow
LH surge triggers
ovulation
Ovarian cycle
Growing follicle
Mature
follicle
Corpus
luteum
Degenerating
corpus luteum
Estrogen secreted
by growing follicle in
increasing amounts
Progesterone and
estrogen secreted
by corpus luteum
Follicular phase
Luteal phase
Ovulation
Ovarian hormones
Peak causes
LH surge
Estrogen
Progesterone
Estrogen level
very low
Progesterone and estro-
gen promote thickening
of endometrium
Uterine (menstrual) cycle
Endometrium
Menstrual flow phase
Proliferative phase
Secretory phase 5 10 14 15 20 25 28
Days 1
(a)
(b)
(c)
(d)
(e) 3 6 7 8 4 2 9

44. The Ovarian Cycle In the ovarian cycle Following ovulation
Hormones stimulate follicle growth, which results in ovulation
Following ovulation
The follicular tissue left behind transforms into the corpus luteum

45. The Uterine (Menstrual) Cycle
Cycle after cycle
The maturation and release of egg cells from the ovary are integrated with changes in the uterus
If an embryo has not implanted in the endometrium by the end of the secretory phase
A new menstrual flow commences

46. After about 450 cycles, human females undergo menopause
The cessation of ovulation and menstruation

47. Hormonal Control of the Male Reproductive System
Testosterone and other androgens
Are directly responsible for the primary and secondary sex characteristics of the male
Androgen secretion and sperm production
Are both controlled by hypothalamic and pituitary hormones
Stimuli from other
areas in the brain
Hypothalamus
GnRH from the
hypothalamus reg-
ulates FSH and LH
release from the
anterior pituitary.
FSH acts on the
Sertoli cells of the
seminiferous
tubules, promoting
spermatogenesis.
LH stimulates the
Leydig cells to make
testosterone, which
in turn stimulates
sperm production.
Anterior
pituitary
Negative
feedback
Leydig cells
make
testosterone
Primary and
secondary sex
characteristics
Sertoli cells
Spermatogenesis
Testis

48. Conception, Embryonic Development, and Birth
In humans and other placental mammals, an embryo grows into a newborn in the mother’s uterus
Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus

49. From ovulation to implantation Implantation of blastocyst
Fertilization of an egg by a sperm, conception
Occurs in the oviduct
Cleavage (cell division)
begins in the oviduct
as the embryo is moved
toward the uterus
by peristalsis and the
movements of cilia. 3
Cleavage continues.
By the time the embryo
reaches the uterus,
it is a ball of cells.
It floats in the uterus for
several days, nourished by
endometrial secretions. It
becomes a blastocyst. 4
Figure 46.15a, b
Ovary
Uterus
Endometrium
From ovulation to implantation
Inner cell mass
Cavity
Blastocyst
Trophoblast
(a)
Implantation of blastocyst
(b)
Fertilization occurs. A sperm
enters the oocyte; meiosis of
the oocyte finishes; and the
nuclei of the ovum and sperm
fuse, producing a zygote. 2
Ovulation releases a
secondary oocyte, which
enters the oviduct. 1
The blastocyst implants
in the endometrium
about 7 days after conception. 5

50. After fertilization
The zygote undergoes cleavage and develops into a blastocyst before implantation in the endometrium

51. During its first 2 to 4 weeks of development
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 its first 2 to 4 weeks of development
The embryo obtains nutrients directly from the endometrium
Meanwhile, the outer layer of the blastocyst
Mingles with the endometrium and eventually forms the placenta

52. Blood from the embryo
Travels to the placenta through arteries of the umbilical cord and returns via the umbilical vein
Placenta
Umbilical cord
Chorionic villus
containing fetal
capillaries
Maternal blood
pools
Uterus
Fetal arteriole
Fetal venule
Maternal portion
of placenta
Fetal portion of
placenta (chorion)
Umbilical arteries
Umbilical vein
Maternal
arteries
veins
Figure 46.16

53. The first trimester is the main period of organogenesis
The development of the body organs
Figure 46.17a–c
(a) 5 weeks. Limb buds, eyes, the heart, the liver, and rudiments of all other organs have started to develop in the embryo, which is only about 1 cm long.
(b) 14 weeks. Growth and development of the offspring, now called a fetus, continue during the second trimester. This fetus is about 6 cm long.
(c) 20 weeks. By the end of the second trimester (at 24 weeks), the fetus grows to about 30 cm in length.

54. 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

55. During the third trimester
The fetus continues to grow and fills the available space within the embryonic membranes

56. A complex interplay of local regulators and hormones
Induces and regulates labor, the process by which childbirth occurs
Estrogen
Oxytocin
from
ovaries
from fetus
and mother's
posterior pituitary
Induces oxytocin
receptors on uterus
Stimulates uterus
to contract
Stimulates
placenta to make
Prostaglandins
Stimulate more
contractions
of uterus
Positive feedback
Figure 46.18

57. The process of labor has three stages
Placenta
Umbilical
cord
Uterus
Cervix
Dilation of the cervix
Expulsion: delivery of the infant
(detaching)
Delivery of the placenta 1 2 3
Birth, or parturition
Is brought about by a series
of strong, rhythmic uterine
contractions
The process of labor has three
stages

58. The Mother’s Immune Tolerance of the Embryo and Fetus
A woman’s acceptance of her “foreign” offspring
Is not fully understood
May be due to the suppression of the immune response in her uterus

59. Contraception and Abortion
Contraception, the deliberate prevention of pregnancy
Can be achieved in a number of ways
Some contraceptive methods
Prevent the release of mature eggs and sperm from gonads
Prevent fertilization by keeping sperm and egg apart
Prevent implantation of an embryo

60. Mechanisms of some contraceptive methods
Figure 46.20
Male
Female
Method
Event
Production of
viable sperm
viable oocytes
Vasectomy
Combination
birth control
pill (or injection,
patch, or
vaginal ring)
Sperm transport
down male
duct system
Ovulation
Abstinence
Condom
Coitus
interruptus
(very high
failure rate)
Sperm
deposited
in vagina
Capture of the
oocyte by the
oviduct
Tubal ligation
Spermicides;
diaphragm;
cervical cap;
progestin alone
(minipill, implant,
or injection)
movement
through
female
reproductive
tract
Transport
of oocyte in
Meeting of sperm and oocyte
in oviduct
Morning-after
pill (MAP)
Union of sperm and egg
Implantation of blastocyst
in properly prepared
endometrium
Birth
Progestin alone

61. Modern Reproductive Technology
Recent scientific and technological advances
Have made it possible to deal with many reproductive problems
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
in vitro fertilization
Head
Body