CHAPTER 27 Reproduction and Embryonic Development Modules 27.4 – 27.8

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

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

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

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

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

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

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

(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

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

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

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

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

27.7 Connection: Sexual activity can transmit disease Table 27.7

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

Table 27.8