1. Animal Reproduction

2. 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

3. Mechanisms of Asexual Reproduction
Many invertebrates reproduce asexually by fission, separation of a parent into two or more individuals of about the same size
Video: Hydra Budding

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-estrus-heat
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. 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

9. Video: Hydra Releasing Sperm
Fertilization depends on mechanisms that help sperm meet eggs of the same species
The mechanisms of fertilization, the union of egg and sperm, play an important part in sexual reproduction
In external fertilization, eggs shed by the female are fertilized by sperm in the external environment
Video: Hydra Releasing Sperm

10. LE 46-5
Eggs

11. In internal fertilization, sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract
Fertilization requires critical timing, often mediated by environmental cues, pheromones, and/or courtship behavior
Internal fertilization requires behavioral interactions and compatible copulatory organs

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, amniotic eggs
Many animals retain the embryo, which develops inside the female, placentals
In many animals, parental care helps ensure survival of offspring, altricial

14. Gamete Production and Delivery
To reproduce sexually, animals must have systems that produce gametes
The least complex systems do not contain distinct gonads, organs that produce gametes
The most complex systems contain many sets of accessory tubes and glands that carry, nourish, and protect gametes and developing embryos
Many animals with relatively simple body plans have highly complex reproductive systems

15. Genital pore (Digestive tract) Male organs: Female organs: Uterus
LE 46-7LE 46-8
Genital
pore
(Digestive tract)
Male organs:
Female organs:
Uterus
Seminal
vesicle
Yolk gland
Yolk duct
Sperm duct
(vas deferens)
Oviduct
Ovary
Vas efferens
Seminal
receptacle
Testis
(Excretory pore)

16. Oviduct Ovary Uterus (Urinary bladder) (Rectum) (Pubic bone) Cervix
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

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
The vagina is a thin-walled chamber that is the repository for sperm during copulation and serves as the birth canal

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. (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. Seminal vesicle (behind bladder) (Urinary bladder) Prostate gland
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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
Produce fructose for sperm energy

28. The prostate gland secretes its products directly into the urethra through several small ducts. Neutralizes acidity of vagina
The bulbourethral gland secretes a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra

29. Semen in the Female Reproductive Tract
Within the female reproductive tract, a number of processes, including contractions of the uterus, help move the sperm up the uterus

30. 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

33. 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

34. The Reproductive Cycles of Females
In females, the secretion of hormones and the reproductive events they regulate are cyclic
FSH LH
ESTROGEN
PROGESTERONE
GNRH

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: In estrous 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. Female Reproductive Cycle
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

40. 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

41. 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

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

43. 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

44. In 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. The blastocyst implants
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Cleavage starts
Cleavage continues
Ovary
Fertilization occurs
The blastocyst implants
Uterus
Ovulation
Endometrium
From ovulation to implantation

47. Implantation of blastocyst
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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

49. During its first 2 to 4 weeks, the embryo obtains nutrients directly from the endometrium
Meanwhile, the outer layer of the blastocyst 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

50. 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

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

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

53. 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

54. 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

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

57. LE 46-21
Head
Head
Body
Body

58. Video: Ultrasound of Human Fetus 1 Video: Ultrasound of Human Fetus 2