Prophase I; Crossovers tetrads form form by synapsis of homologues Figure 43.1 Events of meiosis involving one pair of homologous chromosomes. Prophase I; tetrads form by synapsis of homologues Crossovers form Anaphase I; homologues separate Daughter cells of Meiosis I Anaphase II; sister chromatids separate Daughter cells of Meiosis II

Figure 43.2a Spermatogenesis. Spermatogonium (2n) Mitosis Primary spermatocyte (2n) Growth phase Primary spermatocyte (2n) Meiosis I (DNA replicated before division) Secondary spermatocyte (n) Meiosis II (DNA not replicated before division) Spermatids (n) Spermiogenesis Functional sperm (n) 2

Figure 42.2 Structure of the testis. Interstitial endocrine cells Immature sperm Spermatic cord Blood vessels and nerves Seminiferous tubule Ductus (vas) deferens Head of epididymis Efferent ductule Spermatogenic cells Rete testis Lobule Straight tubule Septum Tunica albuginea Body of epididymis Spermatic cord Tunica vaginalis Duct of epididymis Cavity of tunica vaginalis Tail of epididymis Epididymis Testis 4

Figure 43.2b Spermatogenesis. Spermatogonia Primary spermatocytes Spermatids Immature sperm in lumen Sustentocytes (of testis) 5

Figure 42.5 Cross section of epididymis (120). Pseudostratified columnar epithelium Spermatozoa Stereocilia 6

Figure 42.3 Transverse section of the penis (3). Corpora cavernosa Venous cavities Tunic albuginea (surrounds corpora) Lumen of urethra Corpus spongiosum 7

Fluid medium of semen Tail Midpiece Sperm Head with acrosome Figure 43.3 Sperm in semen. Fluid medium of semen Tail Midpiece Sperm Head with acrosome 8

Figure 43.4 Oogenesis. 11 Meiotic events Follicle development in ovary Before birth 2n Oogonium (stem cell) Follicle cells Mitosis Oocyte 2n Primary oocyte Primordial follicle Infancy and childhood (ovary functionally inactive) 2n Primary oocyte (arrested in prophase I; present at birth) Primordial follicle Each month from puberty to menopause Primary follicle 2n Primary oocyte (still arrested in prophase I) Secondary follicle Spindle Vesicular (antral) follicle Meiosis I (completed by one primary oocyte each month in response to LH surge) First polar body n Secondary oocyte (arrested in metaphase II) Ovulation Meiosis II of polar body (may or may not occur) Sperm Ovulated secondary oocyte Meiosis II completed (only if sperm penetration occurs) In absense of fertilization, ruptured follicle becomes a corpus luteum and ultimately degenerates. n n n n Polar bodies (all polar bodies degenerate) Second polar body Ovum Degenerating corpus luteum 11

Figure 43.5 Anatomy of the human ovary. Tunica albuginea Secondary follicle Cortex Granulosa cells Late secondary follicle Degenerating corpus luteum (corpus albicans) Mesovarium and blood vessels Germinal epithelium Vesicular (antral) follicle Primary follicles Antrum Secondary oocyte Ovarian ligament Zona pellucida Theca folliculi Medulla Ovulated secondary oocyte Corpus luteum Corona radiata Developing corpus luteum 12

Figure 42.9 Cross-sectional view of the uterine tube (12). Serosa Smooth muscle Highly folded mucosa Lumen 16

Figure 42.8 Cross-sectional view of the uterine wall. Endometrium Myometrium Serosa 17

Figure 43.6 Endometrial changes during the menstrual cycle. Necrotic (areas of dead and dying cells) fragments of functional layer of endometrium Elaborated glands Endometrium Glands Endometrium Myometrium Functional layer Basal layer Myometrium 18

Figure 43.7 Correlation of anterior pituitary and ovarian hormones with structural changes in the ovary and uterus. Fluctuation of gonadotropin levels: Fluctuating levels of pituitary gonadotropins (follicle-stimulating hormone and luteinizing hormone) in the blood regulate the events of the ovarian cycle. LH Plasma hormone level FSH Ovarian cycle: Structural changes in the ovarian follicles during the ovarian cycle are correlated with (d) changes in the endometrium of the uterus during the uterine cycle. Primary follicle Secondary follicle Vesicular follicle Ovulation Corpus luteum Degenerating corpus luteum Follicular phase Ovulation (Day 14) Luteal phase Fluctuation of ovarian hormone levels: Fluctuating levels of ovarian hormones (estrogens and progesterone) cause the endometrial changes of the uterine cycle. The high estrogen levels are also responsible for the LH/FSH surge in (a). Plasma hormone level Estrogens Progesterone The three phases of the uterine cycle: Endometrial glands Blood vessels Menstrual: The functional layer of the endometrium is shed. Approximately days 1–5. Proliferative: The functional layer of the endometrium is rebuilt under influence of estrogens. Approximately days 6–14. Ovulation occurs at the end of this phase. Secretory: Begins immediately after ovulation under the influence of progesterone. Enrichment of the blood supply and glandular secretion of nutrients prepare the endometrium to receive an embryo. Menstrual flow Functional layer Basal layer Days 1 5 10 15 20 25 28 Menstrual phase Proliferative phase Secretory phase 19

Figure 43.2 Spermatogenesis. Spermatogonium (2n) Mitosis Spermatogonia Primary spermatocyte (2n) Growth phase Primary spermatocytes Primary spermatocyte (2n) Meiosis I (DNA replicated before division) Spermatids Secondary spermatocyte (n) Meiosis II (DNA not replicated before division) Immature sperm in lumen Spermatids (n) Spermiogenesis Functional sperm (n) Sustentocytes (of testis) 20