1. Human Reproduction and Development
Chapter 42

2. Modes of Reproduction
1. Sexual reproduction
Meiosis (gamete formation) followed by fertilization
Offspring show genetic variation
2. Asexual reproduction
Mitosis
Single parent produces offspring
Offspring are genetically identical
3. Hermaphrodites
-produce eggs and sperm, some can self-fertilize
Ex.-Tapeworms…why is this an advantage?
Parasite, lives in a animal’s gut, doesn’t see another of the same species very often to mate

3. Cost of Sexual Reproduction
Specialized cells and structures must be formed (to deliver/receive sperm)
Reproductive timing; pheromones,
Visual signals, special courtship, and parental behaviors can be costly
Nurturing developing offspring, either in egg or body, requires resources from mother
Reproductive timing: sperm and egg must mature at same time, requires hormonal regualtion, reponsiveness to environmental cues

4. Costs of Sexual Reproduction

5. Gamete Formation

6. The Reproductive System
Gonads – primary sex organs
Testes in males
Ovaries in females
Gonads produce gametes (sex cells) and secrete hormones
Sperm – male gametes
Ova (eggs) – female gametes

7. Male Reproductive System
Accessory organs(Seminal vesicle, Prostate gland, Bulbourethral gland)
External genitalia (penis, Scrotum: testes, epididymis)

8. Testes Spermatogenesis Seminiferous tubules Tightly coiled structures
Function as sperm-forming factories
Sperm travels from testes to epididymis
Produce testosterone
Figure 16.1

9. Epididymis Comma-shaped, tightly coiled tube
Function: to mature and store sperm cells (at least 20 days)
Expels sperm with the contraction of muscles in the epididymis walls to the vas deferens

10. Vas Deferens Carries sperm from epididymis to the ejaculatory duct
Vasectomy – cutting of the vas deferens at the level of the testes to prevent transportation of sperm

11. Urethra
Extends from the base of the urinary bladder to the tip of the penis
Carries both urine and sperm
Sperm enters from the ejaculatory duct

12. Semen Mixture of sperm and accessory gland secretions
Advantages of accessory gland secretions
Seminal Vesicles: Fructose provides energy for sperm cells
Prostate Gland: raises pH of semen helps neutralize the acidic environment of vagina
Bulbourethral gland: lubricating mucus clears urethra of urine
Semen inhibits bacterial multiplication
Elements of semen enhance sperm motility

13. External Genitalia Scrotum Penis
Divided sac of skin outside the abdomen
Maintains testes at 3°C lower than normal body temperature to protect sperm viability
Penis
Delivers sperm into the female reproductive tract
Internally, three areas of spongy erectile tissue around the urethra

14. Sperm Formation: Seminiferous Tubules

15. Spermatogenesis Production of sperm cells
Begins at puberty and continues thru-out life
In the seminiferous tubules (inside testes)
Spermatogonium (2n) divides by mitosis to form primary spermatocyte (2n)
Meiosis produces haploid spermatids
Spermatids mature to become sperm
Spermatogenesis takes 64 to 72 days

16. Sperm Formation (in seminferous tubule in testes)
head
midpiece with mitochondria
tail with core of microtubules

17. Anatomy of Mature Sperm
The only human flagellated cell
DNA is found in the head
Little cytoplasm
48-72 hour lifespan (up to 5 days)
Figure 16.5b

18. Testosterone Production
Produced in Testes
Functions of testosterone
Stimulates reproductive organ development
Underlies sex drive
Causes secondary sex characteristics
Deepening of voice
Increased hair growth
Enlargement of skeletal muscles
Thickening of bones

19. Regulation of Male Androgens (Sex Hormones)

20. Female Reproductive System
Ovaries
Duct System
Uterine tubes (fallopian tubes)
Uterus
Vagina
Urethra is NOT part of reproductive system in females
External genitalia

21. Female Reproductive Organs

22. Female Reproductive Organs

23. Ovaries
Produces eggs
Composed of ovarian follicles (sac-like structures)
Ovulation –
egg is mature and
the follicle ruptures
Occurs every 28 days
Ruptured follicle is transformed into a corpus luteum
Figure 16.7

24. Fallopian Tubes (Oviducts)
Receive the ovulated oocyte
Cilia move the oocyte towards the uterus (takes 3–4 days)
Provide a site for fertilization
Attaches to the uterus
Does not physically attach to the ovary

25. Uterus
Hollow organ
Cervix – narrow outlet that protrudes into the vagina
Functions of the uterus
Receives a fertilized egg
Retains the fertilized egg
Nourishes the fertilized egg
Endometrium
Inner layer
Allows for implantation of a fertilized egg
Sloughs off if no pregnancy occurs (menses)

26. Vagina Extends from cervix to exterior of body
Serves as the birth canal
Receives sperm during sexual intercourse

27. Oogenesis Making eggs Total supply of eggs are present at birth
Ovulation begins at puberty
Many eggs “die off” in earlier stages of development, before ovulation occurs
Reproductive ability ends at menopause
Oocytes are matured in developing ovarian follicles

28. Oogenesis
Girl is born with 2 million primary oocytes already in ovaries
Each oocyte has entered meiosis I and stopped
Meiosis resumes, with the first menstrual cycle
Meiosis completed only after fertilization
Unfertilized egg: lifespan 24 hours

29. Ovarian Cycle

30. Oogenesis
Figure 16.10

31. Menstrual Cycle
Function: produce an environment that is hospitable to the growing embryo
Lining of uterus builds up cyclically
Bleeding is a by-product resulting from no pregnancy
The fertile period for a human female occurs on a cyclic basis

32. Menstrual Cycle Cyclic changes of the endometrium
Regulated by cyclic production of estrogens and progesterone
Menstrual cycle lasts about 28 days
Day 1: first day of bleeding
Ovulation around day 14
Stages of the menstrual cycle
Menses: endometrium is sloughed
Follicular phase: prior to ovulation
Luteal phase: after ovulation

33. Hormonal Control of the Ovarian and Uterine Cycles
Figure 16.12a, b

34. Hormonal Control of the Ovarian and Uterine Cycles
Figure 16.12c, d

35. Menstrual Cycle Overview

36. Hormone Production by the Ovaries
Estrogens
Produced by follicle cells
Cause secondary sex characteristics
Enlargement of accessory organs
Development of breasts
Appearance of pubic hair
Increase in fat beneath the skin
Widening and lightening of the pelvis
Onset of menses

37. Hormone Production by the Ovaries
Progesterone
Produced by the corpus luteum
Production continues until LH diminishes in the blood
Helps maintain pregnancy

38. Female Hormonal Control

39. Cycle Overview
GnRH secretion affects LH and FSH secretion by pituitary
LH and FSH affect follicle maturation
Estrogen and progesterone from ovary affect uterus

40. Probability of Pregnancy
10 days…that’s about 2 weeks after the start of her period.
Wilcox, A. J et al. BMJ 2000;321:
What day on a regular cycle is there the highest probability of pregnancy?
Copyright ©2000 BMJ Publishing Group Ltd.

41. Fertilization Sperm penetrates to egg cytoplasm
Secondary oocyte undergoes meiosis II; forms mature egg
Egg nucleus and sperm nucleus fuse to form diploid zygote

42. Birth Control Options