1. CHAPTER 27 Reproduction and Embryonic Development
Modules 27.4 – 27.8

2. 27.4 The formation of sperm and ova requires meiosis
Spermatogenesis
Produces sperm in the male
Oogenesis
Produces ova in the female

3. Spermatogenesis Increases genetic variation
Primary spermatocytes are produced throughout a male’s reproductive years
Diploid cells undergo meiosis to form four haploid sperm

4. Differentiation and onset of MEIOSIS I Seminiferous tubule
Epididymis
Testis
Penis
Scrotum
Diploid cell
Testis
Differentiation and onset of MEIOSIS I
Seminiferous tubule
Cross section of seminiferous tubule
PRIMARY SPERMATOCYTE
(in prophase of MEIOSIS I)
MEIOSIS I completed
SECONDARY SPERMATOCYTE
(haploid; double chromatids)
MEIOSIS II
Developing sperm cells (haploid; single chromatids)
Differentiation
SPERM CELLS
Center of seminiferous tubule
(haploid)
Figure 27.4A

5. Oogenesis Most of the process occurs within the ovaries
Lifetime supply of primary oocytes is present at birth
One primary oocyte matures each month to form a secondary oocyte
If the secondary oocyte is fertilized, it completes meiosis and becomes a haploid ovum

6. Diploid cell
In embryo
Differentiation and onset of MEIOSIS I
PRIMARY OOCYTE,
arrested in prophase of MEIOSIS I
Present at birth
Completion of MEIOSIS I and onset of MEIOSIS II
SECONDARY OOCYTE,
First polar body
arrested at metaphase of MEIOSIS II; released from ovary
Entry of sperm triggers completion of MEIOSIS II
OVUM
Second polar body
(haploid)
Figure 27.4B

7. Development of an ovarian follicle
Degenerating corpus luteum
Start:
PRIMARY OOCYTE
within follicle
CORPUS LUTEUM
Growing follicles
Mature follicle
SECONDARY OOCYTE
Ovary
OVULATION
Ruptured follicle
Figure 27.4C

8. 27.5 Hormones synchronize cyclical changes in the ovary and uterus
Table 27.5

9. (1) (2) CONTROL BY HYPOTHALAMUS
Inhibited by combination of estrogen and progesterone
Hypothalamus
Stimulated by high levels of estrogen
Releasing hormone
Anterior pituitary
FSH LH
(2)
PITUITARY HORMONES IN BLOOD
LH peak triggers ovulation and corpus luteum formation LH
FSH
FSH LH
Figure 27.5

10. Degenerating corpus luteum
(3)
OVARIAN CYCLE
Corpus luteum
Degenerating corpus luteum
Growing follicle
Mature follicle
Ovulation
Pre-ovulatory phase
Post-ovulatory phase
Estrogen
Progesterone and estrogen
(4)
OVARIAN HORMONES IN BLOOD
Estrogen
Progesterone
Estrogen
Progesterone and estrogen
(5)
MENSTRUAL CYCLE
Endometrium
Days
Figure 27.5 (continued)
Menstruation

11. 27.6 The human sexual response occurs in four phases
Excitement
Sexual passion builds
Penis and clitoris become erect
Testes, labia, nipples swell
Vagina secretes lubricating fluid
Muscles of arms and legs tighten

12. Plateau Orgasm Continuation of excitement responses
Increase in breathing and heart rates
Orgasm
Rhythmic contraction of the reproductive structures
Extreme pleasure
Ejaculation by the male

13. Resolution Reverse previous phase responses
Structures return to normal size
Muscles relax
Passion subsides

14. 27.7 Connection: Sexual activity can transmit disease
Table 27.7

15. 27.8 Connection: Contraception prevents unwanted pregnancy
Contraception prevents pregnancy in one of three ways
Blocking the release of gametes
Preventing fertilization
Preventing implantation
Figure 27.8

16. Table 27.8