1. Chapter 46
Animal Reproduction

3. Concept 46.1: Both asexual and sexual reproduction occur in the animal kingdom
Asexual reproduction is creation of offspring whose genes all come from one parent
Sexual reproduction is creation of offspring by fusion of male gametes (sperm) and female gametes (eggs) to form zygotes

5. In budding, two new individuals arise from outgrowths of existing ones
Fragmentation is breaking of the body into pieces, some or all of which develop into adults
Fragmentation must be accompanied by regeneration, regrowth of lost body parts

6. Reproductive Cycles and Patterns
Most animals exhibit reproductive cycles related to changing seasons
Reproductive cycles are controlled by hormones and environmental cues
Animals may reproduce asexually or sexually, or they may alternate these methods

7. Parthenogenesis is a process in which an egg develops without being fertilized
Several genera of fishes, amphibians, and lizards reproduce only by a complex form of parthenogenesis

8. LE 46-3 Ovary size Ovulation Ovulation Estrogen Progesterone Hormone
level
Time
Behavior
Female-
like
Male-
like
Female-
like
Male-
like

9. Sexual reproduction is a special problem for organisms that seldom encounter a mate
One solution is hermaphroditism, in which each individual has male and female reproductive systems
In sequential hermaphroditism, an individual reverses its sex during its lifetime

11. Concept 46.2: Fertilization depends on mechanisms that help sperm meet eggs of the same species
In external fertilization, eggs shed by the female are fertilized by sperm in the external environment
Eggs

12. In internal fertilization, sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract
Internal fertilization requires behavioral interactions and compatible copulatory organs

13. Ensuring the Survival of Offspring

14. Female Reproductive Anatomy
The female external reproductive structures include the clitoris and 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
Animation: Female Reproductive Anatomy

15. LE 46-9a Oviduct Ovary Uterus (Urinary bladder) (Rectum) (Pubic bone)
Cervix
Urethra
Vagina
Shaft
Glans
Clitoris
Bartholin’s gland
Prepuce
Labia minora
Vaginal opening
Labia majora

16. LE 46-9b Oviduct Ovaries Follicles Corpus luteum Uterine wall Uterus
Endometrium
Cervix
Vagina

17. 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 surrounded by one or more layers of follicle cells

18. Ovulation expels an egg cell from the follicle
The remaining follicular tissue grows within the ovary, forming a mass called the corpus luteum
The corpus luteum secretes hormones, depending on whether pregnancy occurs

19. 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

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

21. Mammary Glands
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

22. Male Reproductive Anatomy
In most mammals, the male’s external reproductive organs are the scrotum and penis
Internal organs are the gonads, which produce sperm and hormones, and accessory glands
Animation: Male Reproductive Anatomy

23. LE 46-10b (Urinary Seminal vesicle bladder) (Rectum) (Public bone)
Vas deferens
Erectile
tissue of
penis
Ejaculatory duct
Prostate gland
Urethra
Bulbourethral gland
Vas deferens
Glans penis
Epididymis
Testis
Prepuce
Scrotum

24. LE 46-10a Seminal vesicle (behind bladder) (Urinary bladder)
Prostate gland
Bulbourethral
gland
Urethra
Erectile tissue
of penis
Scrotum
Vas deferens
Epididymis
Glans penis
Testis

25. Testes
The male gonads, or testes, consist of highly coiled tubes surrounded by connective tissue
Sperm form in these seminiferous tubules
Production of normal sperm cannot occur at the body temperatures of most mammals
The testes of many mammals are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity

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

27. Glands
Three sets of accessory glands add secretions to the semen, the fluid that is ejaculated
The two seminal vesicles contribute about 60% of the total volume of semen

28. 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

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

30. Human Sexual Response Two reactions predominate in both sexes:
Vasocongestion, the filling of tissue with blood
Myotonia, increased muscle tension
The sexual response cycle has four phases: excitement, plateau, orgasm, and resolution

31. Oogenesis is development of mature ova
Concept 46.4: 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
Oogenesis is development of mature ova
Spermatogenesis is production of mature sperm

32. LE 46-11 Ovary Primary germ cell in embryo Differentiation Oogonium
in ovary
Oogonium
Mitotic
division
Primary
oocyte
within
follicle
Primary
oocyte
Completion of meiosis I
and onset of meiosis II
Growing
follicle
Secondary
oocyte
First polar body
Ovulation
Entry of sperm
triggers
completion
of meiosis II
Mature follicle
Ruptured
follicle
Second polar body
Ovum
Ovulated
secondary oocyte
Corpus luteum
Degen-
erating corpus luteum

33. LE 46-12 Epididymis Seminiferous tubule Testis Cross section
of seminiferous
tubule
Spermatogonium
Mitotic division, producing
large numbers of spermatogonia
Sertoli cell
nucleus
Differentiation and onset of meiosis I
Primary spermatocyte
(in prophase of meiosis I)
Meiosis I completed
Secondary spermatocyte
Meiosis II
Lumen of
Seminiferous tubule
Early
spermatids
Spermatids
(at two stages of
differentiation)
Differentiation
Sperm cells
Neck
Head
Midpiece
Tail
Plasma membrane
Acrosome
Nucleus
Mitochondria

34. Oogenesis differs from spermatogenesis in three major ways:
During meiotic divisions, cytokinesis is unequal, with almost all of the cytoplasm in one daughter cell, the secondary oocyte
Unlike sperm, eggs are not produced continuously throughout life
Oogenesis has long “resting” periods, whereas sperm are produced in uninterrupted sequence

35. 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 after the endometrium has started to thicken in preparation for implantation

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

37. The Human Female Reproductive Cycle: A Closer Look
The female reproductive cycle is one integrated cycle involving two organs: the uterus and ovaries
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 positive and negative feedback
Animation: Ovulation
Animation: Post Ovulation

38. LE 46-13 Control by hypothalamus Inhibited by combination of
estrogen and progesterone
Hypothalamus
Stimulated by high levels
of estrogen
GnRH
Anterior pituitary
Inhibited by low levels of
estrogen
FSH LH
Pituitary gonadotropins
in blood LH
FSH
FSH and LH stimulate
follicle to grow
LH surge triggers
ovulation
Ovarian cycle
Corpus
luteum
Degenerating
corpus luteum
Growing follicle
Mature
follicle
Follicular phase
Ovulation
Luteal phase
Estrogen secreted
by growing follicle in
increasing amounts
Progesterone and
estrogen secreted
by corpus luteum
Ovarian hormones
in blood
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
Days 5 10 14 15 20 25 28

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

40. 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

41. Menopause
After about 450 cycles, human females undergo menopause, the cessation of ovulation and menstruation

42. 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 controlled by hypothalamic and pituitary hormones
Animation: Male Hormones

43. LE 46-14 Stimuli from other areas in the brain Hypothalamus GnRH
Anterior
pituitary
Negative
feedback
FSH LH
Leydig cells
make
testosterone
Primary and
secondary sex
characteristics
Sertoli cells
Spermatogenesis
Testis

44. Concept 46.5: 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
Duration of pregnancy in other species correlates with body size and maturity of the young at birth

45. Conception, Embryonic Development, and Birth
Conception, fertilization of an egg by a sperm, occurs in the oviduct
After fertilization, the zygote undergoes cleavage and develops into a blastocyst before implantation in the endometrium

46. LE 46-15a Cleavage starts Cleavage continues Ovary
Fertilization occurs
The blastocyst implants
Uterus
Ovulation
Endometrium
From ovulation to implantation

47. Implantation of blastocyst
LE 46-15b
Endo-
metrium
Inner cell mass
Cavity
Trophoblast
Blastocyst
Implantation of blastocyst

48. 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
The first trimester is the main period of organogenesis, development of the body organs

49. LE 46-16 Maternal arteries Maternal veins Placenta Maternal portion
of placenta
Umbilical cord
Chorionic villus
containing fetal
capillaries
Fetal portion of
placenta (chorion)
Maternal blood
pools
Uterus
Umbilical arteries
Fetal arteriole
Fetal venule
Umbilical vein
Umbilical cord

50. LE 46-17
5 weeks.
14 weeks.
20 weeks.

51. 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

52. 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

53. Estrogen Oxytocin from ovaries from fetus and mother’s
LE 46-18
Estrogen
Oxytocin
from
ovaries
from fetus
and mother’s
posterior pituitary
Induces oxytocin
receptors on uterus
Positive feedback
Stimulates uterus
to contract
Stimulates
placenta to make
Prostaglandins
Stimulate more
contractions
of uterus

54. LE 46-19 Placenta Umbilical cord Uterus Placenta (detaching) Uterus
Cervix
Umbilical
cord
Dilation of the cervix
Expulsion: delivery of the infant
Delivery of the placenta

55. Contraception and Abortion
Contraception, the deliberate prevention of pregnancy, can be achieved in a number of ways
Some general contraceptive methods:
Preventing release of eggs and sperm
Keeping sperm and egg apart
Preventing implantation of an embryo
Abortion is the termination of a pregnancy

56. Meeting of sperm and oocyte Implantation of blastocyst
LE 46-20
Male
Female
Method
Event
Event
Method
Production of
viable sperm
Production of
viable oocytes
Vasectomy
Combination birth control
pill (or injection, patch, or
vaginal ring)
Sperm transport
down male
duct system
Ovulation
Abstinence
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)
Sperm
movement
through
female
reproductive
tract
Transport
of oocyte in
oviduct
Meeting of sperm and oocyte
in oviduct
Morning-after
pill (MAP)
Union of sperm and egg
Progestin alone
Implantation of blastocyst
in properly prepared
endometrium
Birth

57. Modern Reproductive Technology
Recent advances are addressing 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
Modern technology can help infertile couples by in vitro fertilization

58. LE 46-21
Head
Head
Body
Body