1. Chapter 46
Animal Reproduction

2. Asexual and Sexual Reproduction
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 a male gamete (sperm) and a female gamete (egg) to form a zygote
Animals may reproduce exclusively asexually or sexually or they may alternate between the two

3. 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

4. Asexual Reproduction Budding Fragmentation
In which new individuals arise from outgrowths of existing ones
Fragmentation
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
Hydra
Planaria

5. Reproductive Cycles and Patterns

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. Some animals reproduce by parthenogenesis
A process in which an egg develops without being fertilized
The resulting organism is haploid and may produce haploid eggs without meiosis
Male honeybees are produced by parthogenesis

8. Parthenogenesis
Among vertebrates, several genera of fishes, amphibians, and lizards, including whiptail lizards (photo) reproduce exclusively parthenogenesis
Ovulation is stimulated by mating behavior in this all female species. These lizards having evolved from species with 2 sexes still need certain sexual stimuli for maximum reproductive success
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.
There is a doubling of chromosomes after meiosis to create a diploid “zygote”

9. One solution to the problem is hermaphroditism
Sexual reproduction presents a special problem for certain organisms that seldom encounter a mate
One solution to the problem is hermaphroditism
In which each individual has both male and female reproductive systems
Some hermaphrodites can mate with themselves, but most must find a partner (as with mating earthworms where both donate and receive sperm)

10. Hermaphroditism
Sequential hermaphroditism: where an individual reverses its sex during its lifetime
Some species are male-first, other species are female-first
male
female
Caribbean bluehead wrasse.
All members of this species are born female, but the oldest, largest fish complete their life as males
female

11. Mechanisms of Fertilization

12. External Fertilization
Some species have external fertilization, in which
Eggs shed by the female are fertilized by sperm in the external environment
Eggs

13. Internal fertilization
Some species have internal fertilization
Sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract

14. 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

15. Ensuring the Survival of Offspring
All species produce more offspring than the environment can handle
But the proportion that survives is quite small
The more of your offspring that survive to reproduce …the greater the influence of your genes on the next generation

16. Ensuring the Survival of Offspring
The embryos of many terrestrial animals develop in shelled eggs that can withstand harsh environments
Many animals retain the embryo, which develops inside the female
Many different types of animals exhibit parental care to ensure survival of offspring
Egg brooding in Giant Water Bug

17. Gamete Production and Delivery
Animals must have systems that produce gametes to reproduce sexually
The least complex reproductive 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

18. Many animals with relatively simple body plans possess highly complex reproductive systems
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

19. 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.

20. Human Reproductive System

21. Female Reproductive Anatomy
Prepuce
(Rectum)
Cervix
Vagina
Bartholin’s gland
Vaginal opening
Ovary
Oviduct
Labia majora
Labia minora
(Urinary bladder)
(Pubic bone)
Uterus
Urethra
Shaft
Glans
Clitoris

22. Female Reproductive Anatomy
Vagina
Uterus
Cervix
Ovaries
Oviduct
Uterine wall
Endometrium
Follicles
Corpus luteum

23. 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

24. 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

25. Cilia in the tube help draw the ovulated egg into the tube
Oviducts
The egg cell is released into the abdominal cavity near the opening of the oviduct, or fallopian tube
Cilia in the tube help draw the ovulated egg into the tube
Cilia also convey the egg to the uterus
Fertilization usually occurs in the oviduct
The oviduct is the site of ectopic (tubal) pregnancies

26. Lining is the endometrium
Uterus
A thick muscular organ
Lining is the endometrium
Cervix is the neck of the uterus that opens into the vagina
Vagina
Uterus
Cervix
Ovaries
Oviduct
Uterine wall
Endometrium
Follicles
Corpus luteum

27. 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
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

28. Mammary Glands
Not part of the reproductive system but are obviously important to mammalian reproduction
Within the glands small sacs of epithelial tissue produce and secrete milk
High levels of estrogen during pregnancy stimulate growth and development of mammary glands

29. Male Reproductive Anatomy
External reproductive organs in most mammalian species are the scrotum and penis
The internal organs
gonads, which produce sperm and hormones
accessory glands

30. Male Reproductive Anatomy
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

31. Male Reproductive Anatomy
Erectile tissue
of penis
Prostate gland
(Urinary bladder)
Bulbourethral gland
Vas deferens
Epididymis
Testis
Seminal
vesicle
(behind
bladder)
Urethra
Scrotum
Glans penis

32. The male gonads, or testes
Consist of many highly coiled tubes (seminiferous tubules ) surrounded by several layers of connective tissue
Sperm is formed in the seminiferous tubules
Testosterone is produced in the interstitial cells (cells of Leydig)

33. 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
A testicle not in the scrotum is a cryptorchid

34. 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

35. Glands
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
Prostate gland
Secretes its products directly into the urethra through several small ducts
Bulbourethral gland
Secretes a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra

36. Semen in the Female Reproductive Tract
Once in the female reproductive tract
A number of processes, including contractions of the uterus, thinning of cervical mucus, and swimming of the spermatozoa, help move the sperm up the uterus

37. Penis The human penis During sexual arousal
Is composed of three cylinders of spongy erectile tissue (distensible blood spaces)
During sexual arousal
The erectile tissue fills with blood from the arteries, causing an erection
Viagra works by increasing blood flow to the genital region

38. 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

39. The process of gametogenesis
Is based on meiosis, but differs in females and males

40. Primary germ cell in embryo
Oogenesis
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

41. Secondary spermatocyte
Spermatogenesis
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
Acrosome

42. Oogenesis differs from spermatogenesis
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

43. The Reproductive Cycles of Females
The secretion of hormones and the reproductive events they regulate are cyclic

44. Menstrual Versus Estrous Cycles
Two different types of cycles occur in females
Humans and other primates have menstrual cycles
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

45. Menstrual Versus Estrous Cycles
In menstrual 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
In estrous animals that bleed (dogs & cats), it is due to high estrogen that accompanies receptive period

46. The Human Female Reproductive Cycle
The female reproductive cycle
Is one integrated cycle involving two organs, the uterus and ovaries
Cyclic secretion of GnRH from the hypothalamus
And of FSH and LH from the anterior pituitary orchestrates the female reproductive cycle

47. Reproductive cycle of the human female
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
Refer back to this figure to integrate your thinking of ovarian and uterine events

48. In the Follicular Phase of the ovarian cycle
The female has a set of primary follicles containing primary oocytes that have become arrested in early meiosis
With each cycle a small # of primary follicles are stimulated by FSH to grow and mature (generally one follicle completes maturation)
In the Follicular Phase of the ovarian cycle
FSH stimulates follicle growth
The growing follicle secretes ever increasing amounts of estrogen (which ultimately leads to the LH surge)

49. Ovulation
A surge in LH levels results in ovulation

50. In the Luteal Phase of the ovarian cycle
The follicular tissue left behind transforms into the corpus luteum
The corpus luteum secretes progesterone and estrogen
Over time the corpus luteum regresses and sex hormone production declines. This leads to menstruation

51. 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

52. The Uterine (Menstrual) Cycle
The classic 28-day cycle
Menstruation (days 1-5)
Regression of the C.L. from the previous cycle results in low hormone levels and shedding of the endometrium
Proliferative Phase (days 6-13)
Estrogen from the growing ovarian follicle stimulates growth of the endometrium
Ovulation (day 14)
Secretory Phase (days 15-28)
Progesterone from the C.L. stimulates development of uterine glands
Estrogen and Progesterone levels continue to thicken the endometrium

53. After about 450 cycles, human females undergo menopause
The cessation of ovulation and menstruation
Due to decrease in sensitivity of the ovary to FSH?

54. Hormonal Control of the Male Reproductive System
Testosterone and other androgens are directly responsible for the primary and secondary sex characteristics of the male

55. 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

56. Embryo Growth in Placental Mammals

57. Conception, Embryonic Development, and Birth
In humans and most other placental mammals
Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus
After fertilization
The zygote undergoes cleavage and develops into a blastocyst before implantation in the endometrium

58. 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
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

59. First Trimester Human gestation The first trimester
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

60. 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

61. Blood flow at the placenta
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

62. Organogenesis
The first trimester is the main period of organogenesis (the development of the body organs)
(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.

63. 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

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

65. Labor
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

66. Three stages of labor
Birth, or parturition is brought about by a series of strong, rhythmic uterine contractions
Placenta
Umbilical
cord
Uterus
Cervix
Dilation of the cervix
Expulsion: delivery of the infant
(detaching)
Delivery of the placenta 1 2 3
Cervical dilation
Expulsion
Placenta delivery

67. 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 (sterilization, the pill)
Prevent fertilization by keeping sperm and egg apart (barrier methods)
Prevent implantation of an embryo (IUD)

68. RU486 (Mifepristone)
RU-486 is the name commonly used for an artificial steroid that blocks progesterone. This hormone is needed to continue a pregnancy
When taken alone, RU-486 causes a complete abortion only about 60% of the time.
A second drug, a prostaglandin, is given 48 hours later to increase its effectiveness. The prostaglandin causes uterine contractions to help expel the embryo

69. Morning After Pill
The active ingredients in morning-after pills are similar to those in birth control pills, except in higher doses. Some morning-after pills contain only one hormone, progestin (Plan B), and others contain two, progestin and estrogen.
The morning-after pill is designed to be taken within 72 hours of intercourse with a second dose taken 12 hours later.

70. Mechanisms of some contraceptive methods
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
A lot of stuff here. Take a look at this figure in your textbook.

71. Modern Reproductive Technology
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
Modern technology can help infertile couples by ART (assisted reproductive technology)
in vitro fertilization
Etc.

72. Ultrasound
Noninvasive procedures usually use ultrasound imaging to detect fetal condition
Head
Body