Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Reproductive system

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormonal Regulation of Reproduction  Hypothalamus: pulse generator  Gonadotropin releasing hormone (GnRH)  Anterior pituitary  Luteinizing hormone (LH)  Follicle stimulating hormone (FSH)  Gonads produce steroid and peptide hormones  Gonads are the main source of sex steroids  Peptide hormones: inhibin and activin

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Feedback Loops Control Gonadotropin Release Internal and environmental stimuli CNS Hypothalamus Anterior pituitary Steroid and peptide hormones Gamete production GnRH Short-loop negative feedback Long-loop feedback may be negative or positive Stimulus Integrating center Efferent pathway Effector Tissue response LH Endocrine cells FSH Gonads (ovaries or testes) KEY Females only

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Synthesis Pathways for Steroid Hormones Cholesterol Progesterone Testosterone Dihydro- testosterone (DHT) aromatase EstradiolCorticosteroneCortisol Aldosterone Intermediate steps

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Male Reproductive System Figure 27.1

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Testes protection - Testicular Thermoregulation  Sperms are not produced at core body temperature  In the scrotum, the testes are kept 2-3°C cooler than in the pelvic cavity. This is essential for sperm production.  Cooling mechanisms  The cremaster muscle contains strips of the internal abdominal oblique muscle around the spermatic cord.  It can elevate or lower the testes.  The dartos muscle is a subcutaneous layer of smooth muscle that wrinkles skin reducing surface area of scrotum. Can lifts testis upwards  The pampiniform plexus is an extensive network of veins that surround the testicular artery in the spermatic cord, keeping the testes cooler countercurrent heat exchange that cools arterial blood entering testis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cells in the testes – 3 types  2 populations found in the Seminiferous tubule  Germinal epithelium – lines the lumen of the tubules  consisting of several layers of germ cells in the process of becoming sperm  Sustentacular (Sertoli) cells.  Between the seminiferous tubules are clusters of interstitial (Leydig) cells, the source of testosterone (will be discussed later with hormonal control).

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The functions of Sertoli cells and BTB  Sertoli cells protect the germ cells and promote their development. Tight junctions between adjacent sustentacular cells form a blood-testis barrier (BTB)  The fluid inside the tubules contains high levels of androgens, potassium and amino acids  The BTB prevents the immune system from attacking the developing spermatozoa (contain specific Ag that are not found on any other cell)  Sertoli cell supply nutrients to the developing sperms  Phagocytize cytoplasm shed by spermatids  Secrete inhibin - negative feedback loop for FSH  Secrete androgen-binding-protein (ABP) – binds testosterone inside tubules to maintain high levels

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermatogenesis  Cells making up the walls of seminiferous tubules are in various stages of cell division  These spermatogenic cells give rise to sperms in a series of events  Mitosis of spermatogonia, forming spermatocytes  Meiosis forms spermatids from spermatocytes  Spermiogenesis – spermatids to sperm

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings MALEFEMALE Spermatids develop into MITOSIS STAGE OF CELL DIVISION 46 (diploid) Sister chromatids MEIOSIS Second meiotic division Secondary gamete divides. 23 chromosomes (haploid) First meiotic division Primary gamete divides into two secondary gametes. 23 chromosomes, duplicated Spermatogonia Oögonium Secondary oocyte (egg) Disintegrates Second polar body disintegrates. Zygote Sperm Oögonia Secondary spermatocytes (may not occur) Egg released from ovary at ovulation. Primary spermatocyte Spermatogonium One primary spermatocyte yields 4 sperm. One primary oocyte yields 1 egg. Primary oocyte FERTILIZATION Unfertilized egg passes out of body. First polar body Germ cell proliferation 46 chromosomes per cell (only two shown here) DNA replicates but no cell division. 46 chromosomes, duplicated Embryo Reproductive adult Figure 26-5, steps 1–6 Ovulation with Fertilization Is Followed by Final Step of Meiosis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings spermatogenesis spermiogenesis  Spermiogenesis – spermatids lose excess cytoplasm and form a tail, becoming sperm Spermiogenesis: Spermatids to Sperm

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mitosis of Spermatogonia  Spermatogonia – outermost cells in contact with the epithelial basal lamina  Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells  Type A cells remain at the basement membrane and maintain the germ line  Type B cells move toward the lumen and become primary spermatocytes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermatogenesis Spermatogonium (2n) Primary spermatocyte (2n) Primary spermatocyte Division – 1 st meiosis secondary spermatocyte (n) Spermatid (n) differentiation 2 nd meiosis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermiogenesis spermatozoa

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormonal Regulation of Testicular Function  The hypothalamus releases gonadotropin-releasing hormone (GnRH)  GnRH stimulates the anterior pituitary to secrete FSH and LH  FSH causes sustentacular cells to release androgen- binding protein (ABP)  LH stimulates interstitial cells to release testosterone  ABP binding of testosterone enhances spermatogenesis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings LH GnRH Hypothalamus Anterior pituitary Inhibin Testes Leydig cells Testosterone (T) To body for secondary effects FSH Sertoli cell Cell products Second messenger Sertoli cell ABPT Androgen-binding protein (ABP) Spermatogonium Spermatocyte Figure (9 of 9) Testosterone Inhibits the Hypothalamus and Anterior Pituitary

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Testosterone  The principal androgen (male sex hormone) is testosterone.  This steroid is manufactured by the interstitial (Leydig) cells of the testes.  Secretion of testosterone increases sharply at puberty and is responsible for the development of the secondary sexual characteristics of men.  Testosterone is also essential for the production of sperm.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 22.2 Effects of Androgens gonads and Secondary Sex Characteristics

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Accessory Glands Contribute to Semen

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Ovaries  Ovaries contain the ovarian follicles  Each follicle consists of an immature egg (oocyte)  Cells around the oocyte are called:  Follicle cells (one cell layer thick)  Granulosa and theca cells (when more than one layer is present)  The follicles and the oocytes are going through cyclic development – ovarian cycle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Combination of follicles and oocyte development  Divided to 2 major periods (phases)  Follicular phase – period of follicle growth (days 1–14)  Luteal phase – period of corpus luteum activity (days 14– 28)  The 2 phases are “separated” by Ovulation (release of the secondary oocyte from a tertiary follicle) The ovarian cycle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Follicular phase Luteal phase ovulation

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Follicular development - Folliculogenesis  The folliculogenesis occurs during follicular phase  Primordial Follicle –flattened granulosa cell layer, basement membrane, oocyte  Primary Follicle – growth of oocyte, zona pellucida formation, cuboidal granulosa cells  Secondary Follicle – add layers of granulosa cells, formation of theca cells

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Folliculogenesis  Early Tertiary Follicle – antrum formation, zona pellucida thickens, theca interna and theca externa form, basement membrane is still present between theca and granulosa cells, blood vessels are in the theca cell layer but not in follicle  Tertiary/pre-ovulatory/Graffian – full size follicle ready to ovulate; oocyte surrounded by corona radiata (granulosa cells) and attached to follicular wall by the comulus oophorus

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Follicular Phase  A few follicles begin to develop from primordial follicle  Oocyte grows, granulosa cells proliferate  Zona pellucida and antrum form

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Follicular Phase  Dominant follicle continues development, rest regress  Corona radiata develops  Graafian follicle = mature follicle  Ovulation

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Photomicrograph of an early tertiary follicle

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Luteal Phase  After ovulation, the ruptured follicle collapses, granulosa cells enlarge, and along with internal thecal cells, form the corpus luteum  The corpus luteum secretes progesterone and estrogen  If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving a scar (corpus albicans)  If pregnancy does occur, the corpus luteum produces hormones until the placenta takes over that role (at about 3 months)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Luteal Phase  Ruptured follicle  gland = corpus luteum  Corpus luteum secretes mostly progesterone  Corpus luteum reaches max activity 10 days, then degenerates

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Corpus luteum  The fate of the corpus luteum depends on fertilization:  If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving a scar (corpus albicans)  If pregnancy occurs, the corpus luteum produces hormones until the placenta takes over that role (at about 3 months)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Ovarian Cycle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings MALEFEMALE Spermatids develop into MITOSIS STAGE OF CELL DIVISION 46 (diploid) Sister chromatids MEIOSIS Second meiotic division Secondary gamete divides. 23 chromosomes (haploid) First meiotic division Primary gamete divides into two secondary gametes. 23 chromosomes, duplicated Spermatogonia Oögonium Secondary oocyte (egg) Disintegrates Second polar body disintegrates. Zygote Sperm Oögonia Secondary spermatocytes (may not occur) Egg released from ovary at ovulation. Primary spermatocyte Spermatogonium One primary spermatocyte yields 4 sperm. One primary oocyte yields 1 egg. Primary oocyte FERTILIZATION Unfertilized egg passes out of body. First polar body Germ cell proliferation 46 chromosomes per cell (only two shown here) DNA replicates but no cell division. 46 chromosomes, duplicated Embryo Reproductive adult Oogenesis – oocyte development

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Ovum production  Occurs monthly in ovarian follicles  Part of ovarian cycle  Happens during the Follicular phase (preovulatory) Oogenesis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Oogenesis  Production of female sex cells by meiosis  In the fetal period, oogonia (2n ovarian stem cells) multiply by mitosis and store nutrients  Primordial follicles appear as oogonia are transformed into primary oocytes  Primary oocytes begin meiosis but stall in prophase I

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Oogenesis: Puberty  At puberty, one activated primary oocyte produces two haploid cells  The first polar body  The secondary oocyte  The secondary oocyte arrests in metaphase II and is ovulated  If fertilized, the second oocyte completes meiosis II, yielding:  One large ovum (the functional gamete)  A tiny second polar body

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Oogenesis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Oogonia (multiple by mitosis until 5 th month of fetal development) Arrested development (until shortly before birth) Primary oocytes (arrest in prophase I) ___________________________________________________________ Puberty Oocyte in Graafian follicle – complete meiosis I Secondary oocyte first polar body Arrested in metaphase II If fertilization occur Complete meiosis II Ovum second polar body

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Actions of Estrogens from growing follicle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Actions of Progesterone from the Corpus luteum

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 Repeating series of changes in the endometrium  Menses  Degeneration of the endometrium  Menstruation  Proliferative phase  Restoration of the endometrium  Secretory phase  Endometrial glands enlarge and accelerate their rates of secretion Uterine cycle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Beginning of new cycle - Menstrual Phase of the Uterus  If fertilization does not occur, the corpus luteum degenerates and estrogen and progesterone levels decrease.  The lack of estrogen and progesterone leads to the collapse of the endometrium, which in turn leads to menstruation.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Menstrual and prolifarative phases (corresponds Follicular Phase of Ovary)  FSH and LH increase during follicular phase because progesterone concentration is low and therefore negative feedback on these pituitary hormones is low.  FSH and LH stimulate primary follicles (containing primary oocytes) to grow and stimulate their theca cells to produce estrogen.  Estrogen leads to a thickening of the endometrium.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  The one dominant follicle (Graafian follicle) survives because  it is hyperresponsive to FSH and can maintain itself even under low FSH  it also becomes sensitive to LH.  LH surge appears because increased estrogen exerts a positive feedback effect on the LH releasing mechanism of pituitary.  LH surge leads to release of the primary oocyte (ovulation) Menstrual and prolifarative phases (corresponds Follicular Phase of Ovary)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Secretory Phase of the Uterus (corresponding to Luteal Phase of Ovary )  The now empty follicle, corpus luteum, starts secreting progesterone that exert a negative feedback on secretion from LH and FSH, preventing new follicles from maturing.  Progesterone converts the endometrium into a secretory tissue full of glycogen and blood vessels, ready to receive a fertilized egg.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure (2 of 2) The Uterine Cycle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings DAYS /0 Follicular Phase Ovulation Luteal Phase Phases of the Uterine Cycle Phases of the Ovarian Cycle Basal body temperature (–C) Uterine cycle Ovarian hormone levels Ovarian cycle Gonadotrophic hormone levels Primary follicle Theca Ovulation Corpus luteum formation Mature corpus luteum Corpus albicans Progesterone MENSES PROLIFERATIVE PHASE SECRETORY PHASE Inhibin Estrogen Antrum LH FSH Figure (4 of 4) Corpus Luteum Degenerates and Ceases Hormone Production

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings LHFSH GnRH Androgens Estrogens (a) Early to mid-follicular phase Follicle Granulosa cells Thecal cells Corpus luteum Progesterone Ovum LH FSH Follicle Estrogen Inhibin Pituitary Hypothalamus Figure (1 of 4) Hormonal Control of the Menstrual Cycle: Follicular Phase

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings LHFSH GnRH Androgens Estrogens (a) Early to mid-follicular phase Follicle Granulosa cells Thecal cells (b) Late follicular phase and ovulation (d) Late luteal phase FSHLH New follicles begin to develop Corpus luteum dies Tonic secretion resumes Corpus luteum Progesterone Ovum LH FSH Follicle Estrogen and progesterone FSHLH Corpus luteum (from ovulated follicle) Estrogen Progesterone Inhibin GnRH secretes (c) Early to mid-luteal phase Estrogen Inhibin Follicle Granulosa cells Thecal cells Inhibin High estrogen output Small amount of progesterone Androgens LHFSH GnRH Pituitary Hypothalamus Figure (4 of 4) Hormonal Control of the Menstrual Cycle: Late Luteal Phase

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Menstrual phase Proliferetive phase Secretory phase Follicular/preovulatory phaseLuteal/postovulator y phase Days Hormones All lowHigh estrogen; low progesterone High progesterone; low estradiol Endometrium Necrotic tissue falls away from the uterine wall Repaired and become thicker Very well vascularized. Thick Glands Not developed. SimpleGland proliferateGlands increase in size and secrete nutritional substances Follicles Primordial follicles develop into primary and then secondary follicles One follicle continue to grow into Graafian follicle and ovulate by the end of this phase No follicular development. Corpus luteum is present Oocyte/s First meiosis; arrested in prophase IFirst meiosis completed; secondary oocyte arrested in metaphase II ovulates If fertilization occur second meiosis is completed