Chapter 27 The Reproductive System 1 MDufilho Figure 27.19 Events of oogenesis. Meiotic events Follicle development in ovary Before birth 2n Oogonium (stem cell) Follicle cells Mitosis Oocyte 2n Primary oocyte Primordial follicle Infancy and 2n Primary oocyte Primordial follicle childhood (arrested in prophase I; (ovary functionally present at birth) inactive) 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) Secondary oocyte (arrested in metaphase II) First polar body n Ovulation Meiosis II of polar body Sperm (may or may not occur) Ovulated secondary oocyte Meiosis II completed In absence of fertilization, (only if sperm ruptured follicle becomes n n n n penetrates a corpus luteum and Polar bodies oocyte) ultimately degenerates. (all polar bodies Second Ovum Degenerating degenerate) polar body corpus luteum 2 MDufilho Figure 27.20 Schematic and microscopic views of the ovarian cycle: development and fate of ovarian Slide 1 follicles. Theca 1 Primordial 2 Primary folliculi follicles follicle 3a Secondary Theca folliculi follicle 3b 3a 3b Late secondary Forming 2 Primary follicle antrum 7 oocyte Zona pellucida Antrum Secondary 4 oocyte Secondar 5 6 y 6 oocyte Corona Zona radiata pellucida Antrum 6 Corpus luteum 5 Follicle ruptures; 4 Mature vesicular follicle (forms from ruptured secondary oocyte carries out meiosis I; ready 3 follicle)MDufilho ovulated to be ovulated Ovulation • Ovary wall ruptures, expels secondary oocyte with its corona radiata to peritoneal cavity • Mittelschmerz - twinge of pain sometimes felt at ovulation • 1–2% of ovulations release more than one secondary oocyte, which, if fertilized, results in fraternal twins • Identical twins result from fertilization of one oocyte, then separation of daughter cells 4 MDufilho Figure 27.20 Schematic and microscopic views of the ovarian cycle: development and fate of ovarian Slide 1 follicles. Theca 1 Primordial 2 Primary folliculi follicles follicle 3a Secondary Theca folliculi follicle 3b 3a 3b Late secondary Forming 2 Primary follicle antrum 7 oocyte Zona pellucida Antrum Secondary 4 oocyte Secondar 5 6 y 6 oocyte Corona Zona radiata pellucida Antrum 6 Corpus luteum 5 Follicle ruptures; 4 Mature vesicular follicle MDufilho (forms from ruptured secondary oocyte carries out meiosis I; ready 5 follicle) ovulated to be ovulated Establishing the Ovarian Cycle • During childhood, ovaries grow and secrete small amounts of estrogens that inhibit the hypothalamic release of GnRH • At puberty – Leptin from adipose tissue decreases the estrogen inhibition – GnRH, FSH, and LH are released, act on ovaries – In about four years, an adult cyclic pattern is achieved and menarche occurs 6 MDufilho Hormonal Interactions During a 28-Day Ovarian Cycle • Day 1: GnRH release of FSH and LH – FSH and LH growth of several follicles, and estrogen release – estrogen levels • Inhibit the release of FSH and LH • Stimulate synthesis and storage of FSH and LH • Enhance further estrogen output 7 MDufilho Hormonal Interactions During a 28-Day Ovarian Cycle • Effects of LH surge – Completion of meiosis I (secondary oocyte continues on to metaphase II) – Day 14 – LH Triggers ovulation – Transforms ruptured follicle into corpus luteum 8 MDufilho Hormonal Interactions During a 28-Day Ovarian Cycle • Functions of corpus luteum – Produces inhibin, progesterone, and estrogen – These hormones inhibit FSH and LH release • Declining LH and FSH ends luteal activity and inhibits follicle development • Days 26–28: corpus luteum degenerates and ovarian hormone levels drop sharply – Ends the blockade of FSH and LH – The cycle starts anew 9 MDufilho Figure 27.21 Regulation of the ovarian cycle. Slide 1 Hypothalamus Hypothalamus GnRH 4 Positive 4 feedback exerted GnRH by large in Travels via estrogen output 6 portal blood by maturing follicle. 1 Anterior pituitary 1 4 Progesterone LH surge Estrogens Inhibin FSH LH Ruptured 5 2 2 follicle 6 Thecal cells 2 3 Slightly Androgens elevated 5 estrogen and Granulosa rising inhibin cells levels inhibit 2 Inhibin Mature vesicular FSH Convert androgens follicle Ovulated Corpus luteum secretion. to estrogens secondary 2 oocyte Estrogens Early and Late follicular and luteal phases midfollicular phases Stimulates Inhibits10 MDufilho Uterine (Menstrual) Cycle • Cyclic changes in endometrium in response to ovarian hormones • Three phases 1. Days 1–5: menstrual phase 2. Days 6–14: proliferative (preovulatory) phase 3. Days 15–28: secretory (postovulatory) phase (constant 14-day length) 11 MDufilho Figure 27.23 Correlation of anterior pituitary and ovarian hormones with structural changes of 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 FSH Plasma hormonelevel Plasma Ovulation Corpus Degenerating Ovarian cycle: Structural changes in luteum corpus luteum vesicular ovarian follicles and the corpus Dominant luteum are correlated with changes in the follicle endometrium of the uterus during the uterine cycle (d). Recall that only vesicular follicles (in their antral phase) are hormone dependent —primary and secondary follicles are not. Follicular Ovulation Luteal phase (Day 14) 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). Estrogens Progesterone Plasma hormonelevel Plasma Endometrial Blood vessels The three phases of the uterine cycle: glands • Menstrual: The functional layer of the endometrium is shed. • Proliferative: The functional layer of the endometrium is rebuilt. Menstrual • Secretory: Begins immediately after ovulation. Enrichment of the blood supply and glandular flow secretion of nutrients prepare the endometrium Functional to receive an embryo. layer Both the menstrual and proliferative phases occur Basal layer before ovulation, and together they correspond to the Days 1 5 10 15 20 25 28 follicular phase of the ovarian cycle. The secretory Menstrual Proliferative Secretory phase corresponds in time to the luteal phase of the phase phase phaseMDufilho ovarian cycle. 12 Uterine Cycle • If fertilization does not occur – Corpus luteum degenerates – Progesterone levels fall – Spiral arteries kink and spasm – Endometrial cells begin to die – Spiral arteries constrict again, then relax and open wide – Rush of blood fragments weakened capillary beds and the functional layer sloughs 13 MDufilho Premenstrual Syndrome - PMS • Symtoms – food cravings, headaches, depression, aggression, mood swings, sore breasts, etc. • Cause – excessive response of body to fluctuations of estrogen and progesterone and prostaglandins • Estrogen mimics aldosterone • Relief of PMS???? 14 MDufilho .