Lecture 23 PDF: Human Reproduction

About This Chapter 26.1 Sex Determination 26.2 Basic Patterns of Reproduction 26.3 Male Reproduction 26.4 Female Reproduction 26.6 Pregnancy and Parturition Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.1 Sex Determination (1 of 2) • Sex organs are three se...

About This Chapter 26.1 Sex Determination 26.2 Basic Patterns of Reproduction 26.3 Male Reproduction 26.4 Female Reproduction 26.6 Pregnancy and Parturition Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.1 Sex Determination (1 of 2) • Sex organs are three sets of structures • Gonads contain germ cells and produce gametes and sex hormones ▪ Male gonads are testes – Produce sperm ▪ Female gonads are ovaries – Produce ova • Internal genitalia – Accessory glands and ducts • gonads, internal genitalia, and external genitalia that connect gonads with outside environment External genitalia – External reproductive structures Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.1 Sex Determination (2 of 2) • Nucleated cells contain 46 chromosomes, diploid – 22 pairs of homologous autosomes – 1 pair of sex chromosomes, X & Y • Eggs and sperms are haploid, 22 autosomes and one sex chromosome • Sex Chromosomes determine genetic sex – XX = female – XY = male ▪ Y is essential for development of the male reproductive organs – Sperm determines sex of zygote – Sexual chromosomal variance, Turner syndrome. XXY: male YO: dies XO: female, but 2 X are needed for normal female reproductive function Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.1 Human chromosomes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Sexual Differentiation Occurs Early in Development (1 of 2) • 2 pairs of accessory ducts Bipotential gonads bc can’t be morphologically ID as male or female derived from embryonic kidney as development proceeds along either male or female, one pair of ducts develops while the other degenerates Internal: Wolffian ducts & Müllerian ducts External: genital tubercle, urethral folds, urethral groove, and labioscrotal differentiate into male and female swellings they reproductive structure as development progress sex-determining region of Y chromosome • Male Embryonic Development (with SRY gene on Y chromosome) – Wolffian ducts develop into epididymis, vas deferens, and seminal vesicle (with testosterone) – Müllerian degenerate, induced by AMH – Testes develop then descend in the scrotum (with testosterone) ▪ Sertoli cells secrete anti-Müllerian hormone (AMH) ▪ Interstitial (Leydig) cells secrete androgens: testosterone and dihydrotestosterone (DHT) – 5a-reductase = testosterone to DHT (DHT external genitalia) despite normal secretion of testosterone, men have inadequate levels of DHT and as a result the male external genitilia and prostate gland fail to develop fully during fetal development Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Sexual Differentiation Occurs Early in Development (2 of 2) • Female embryonic development (without SRY gene) – Müllerian ducts develop into upper portions of the vagina, uterus, and Fallopian tubes (without AMH) – Wolffian ducts degenerate (without testosterone) – External genitalia takes on female characteristics (without DHT) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.2(a) Sexual Development in the Human Embryo Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.2(b) Sexual Development in the Human Fetus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.3 Male embryonic development Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.2 Basic Patterns of Reproduction • Eggs (oocytes) are large cells, nonmotile and must be moved • Sperms are small and use a flagellum to swim • Gametogenesis begins in utrero – Begins with mitosis to increase numbers – Meiosis results in production of haploid cells ▪ DNA duplication into primary spermatocyte or primary oocyte ▪ First meiotic division to produce secondary spermatocyte or secondary oocyte ▪ Second meiotic division to produce gamete • Timing in males and females are different utero Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Male Gametogenesis • At birth males have not progressed past mitosis – Germ cells are spermatogonia • Quiescent until puberty • Mitosis resumes at puberty – Resting pool of spermatogonia • Continuous production of sperms from puberty through life Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Female Gametogenesis • Oögonia complete mitotic stage by 5th month of fetal development – No resting pool of oögonia – Born with all eggs (primary oocytes – primordial follicles) that will be produced • Begin 1st steps of meiosis and arrest until puberty (primary oocytes) • Mature once a month at puberty until menopause – Primary oocytes if selected divide to become egg (secondary oocyte) and first polar body – Ovulation is the releases of the secondary oocyte • If fertilization, then send meiotic division before zygotic program – Secondary oocytes divides into mature gamete and second polar body Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.5 Gametogenesis Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Brain Directs Reproduction (1 of 3) • Both sexes produce androgens and estrogen – Androgens are dominant in males ▪ Most testosterone comes from testes ▪ Aromatase converts androgens to estrogens – Estrogens are dominant in females ▪ Ovary produces estrogens (estradiol and estrone), progestins (porgesterone) and androgens – Adrenal gland secretes small amounts of sex steroids Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Brain Directs Reproduction (2 of 3) • Control pathways • Gonadotropin-releasing hormones (GnRH) from hypothalamus controls secretion of 2 anterior pituitary hormones – Follicle stimulating hormone (FSH) regulates gametogenesis in gonads – Luteinizing hormone (LH) controls production of sex hormones • GnRH regulated by several hypothalamic peptides including kisspeptin • Inhibins inhibit FSH secretion • Activins stimulate FSH secretion and promote spermatogenesis, oocyte maturation, and development of the embryonic nervous system Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.6 Hormonal control of reproduction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Higher concentrations of estrogen can exert either + or - feedback: if estrogen rises rapidly to a threshold level and remains high for at least 36 hours, feedback switches from - to + and gonadotropin release (particularly LH) is stimulated —> significant role in female reproductive cycle —> maybe mediated through estrogen effects on kisspeptin secretion Low levels have no feedback effect Moderate levels: - feedback The Brain Directs Reproduction (3 of 3) When circulating levels of gonadal steroids are low, the pituitary secretes FSH and LH. As steroid secretion increases, - feedback usually inhibits gonadotropin release Androgens always maintain - feedback on gonadotropin release: as androgen levels go up, FSH and LH secretion decreases • Feedback pathways – Positive and negative feedback • Pulsatile GnRH release region of hypothalamus – GnRH pulse generator involved in sexual maturity • Environmental factors influence reproductive – In women: stress, nutrition, daylight and environmental estrogens Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.3 Male Reproduction (1 of 2) • External genitalia – Penis common passageway for sperm and urine (not simultaneously) ▪ Urethra spongy column of tissue surrounding 2 columns of tissue ventral aspect of shaft of penis ▪ Erectile tissue (corpus spongiosum, corpora cavernosa) ▪ Glans tip of penis ▪ Prepuce (foreskin) – Circumcision is surgical removal of the foreskin – Scrotum racole structure ▪ Testes outside abdominal cavity necessary bc normal sperm dev. requires temperature ▪ Lower temperature location that is 2-3 degrees Fahrenheit lower than core body temperature • Cryptorchidism is the failure of both testes to descend Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.3 Male Reproduction (2 of 2) • empty secretions into urethra through ducts • • Male Accessory glands – Prostate gland open directly into urethral lumen – Seminal vesicles – Bulbourethral (Cowper’s) glands Testes produce sperm and hormones – Sperm produced in spermatogonia in seminiferous tubules – Interstitial cells of Leydig produce testosterone – Sertoli cells support sperm production junctions that form an additional barrier between lumen of seminiferous – Blood-testes barrier tight tubule and interstitial fluid outside the basal lamina into seminiferous tubule lumen where it binds – Androgen-binding protein (ABP) secreted testosterone to not diffuse out of the tubule lumen bc less lipophilic Seminiferous tubules leave testicles and join epidydimis then vas single duct that deferens (ductus deferens) forms a tightly coiled passes into abdomen where it eventually empties into urethra cord on surface of testicular capsule Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Sperm Production • Spermatids undergo transformation into sperm – Formation of acrosome needed for fertilization Golgi-derived vesicle flattening out to form a cap over the tip of the nucleus of spermatids that have lost their cytoplasm and developed a flagellated tail • Spermatogenesis requires gonadotropins and testosterone • Male accessory glands contribute secretions to semen – Semen: mixture of accessory gland secretions and mature sperm – 99% volume of semen is fluid Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.7(a) The Male Reproductive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.7(b) The Male Reproductive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.7(c-e) The Male Reproductive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.7(f-g) The Male Reproductive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Androgens Influence Secondary Sexual Characteristics • Primary sex characteristics are internal organs and external genitalia that distinguish males from females • Secondary sex characteristics are other traits that distinguish males from females – Body shape – Beard and body hair – Muscular development – Lowering of voice – Libido • Anabolic steroids are used illegally by athletes promote protein synthesis side effects: liver tumours, infertility, excessive agression, addictiveness —> withdrawal can lead to depression, psychosis, aggression Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.8 Hormonal control of spermatogenesis Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.4 Female Reproduction (1 of 2) • External genitalia Majora: folds of skin that arise from the same embryonic tissue as the scrotum Minora: derived from embryonic tissues that in the male give – Vulva (pudendum) rise to the shaft of the penis ▪ Labia majora and labia minora bud of erectile, sensory tissue at the anterior of vulva, enclosed by the labia minora and an additional fold of – Clitoris small tissue equivalent to the foreskin of the penis – Urethra lies between clitoris and vaginal opening Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.4 Female Reproduction (2 of 2) • • Internal organs – Vagina where sperm are deposited ▪ Hymen thin ring of tissue of uterus that protrudes slightly int the upper end of the vagina – Cervix neck cervical canal is is lined with mucous glands whose secretions create a protective barrier between the vagina and uterus – Uterus ▪ Myometrium thick middle layer of smooth muscle of epithelial lining alternately ▪ Endometrium – changes during menstruation cells proliferate and slough off, accompanied by inner layer, epithelium with glands that dip into a connective tissue layer below a small amount of bleeding in the process of menstruation Two fallopian tubes lead to ovaries – where fertilization takes place – Fimbriae fingerlike projections Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.9(a) The Female Reproductive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.9(b) The Female Reproductive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.9(d-e) The Female Reproductive System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Ovary Produces Eggs and Hormones (1 of 2) • Organization of the ovary – Outer connective tissue and inner connective tissue (stroma) – Cortex contains follicles – Medulla blood vessels and nerves • Primordial follicle – Primary oocyte surrounded by granulosa cell – If unselected for maturation, will undergo atresia hormonally regulated cell death • Primary follicles – Primary oocyte grows – Granulosa cells divide Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Ovary Produces Eggs and Hormones (2 of 2) • Secondary follicles – Follicles grow larger (multiplying granulosa cells) – Theca begins to form – Some fail program and become atretic • Tertiary follicle – Formation of a large fluid filled cavity (antrum) – A follicle that remains from pool becomes the dominant follicle – Releases egg Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.10 Follicular development Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved A Menstrual Cycle Lasts One Month • Menstrual cycles with 3-7 days of menses (menstruation) • Changes in the follicle, ovarian cycle, and changes in the endometrium, the uterine cycle • Ovarian cycle 1. Follicular phase period of follicular growth for ovary 2. Ovulation one or more follicles have ripened, very releases ovocyte(s) of a ruptured follicle into a corpus luteum (yellow 3. Luteal phase with corpus letuem transformation pigment and lipid deposits) that secretes hormones that continue • the preparations for pregnancy and if it does not occur, it ceases to function after about 2 weeks and the ovarian cycle begins again Uterine cycle 1. Menses beginning of follicular phase : bleeding from uterus part of the ovary’s follicular phase: endometrium adds a new layer of cell in anticipation of 2. Proliferative phase latter pregnancy 3. Secretory phase After ovulation, hormones from corpus luteum convert the thickened endometrium into a secretory structure: luteal phase of ovarian cycle corresponds to it If no pregnancy, superficial layers of secretory endometrium are lost during menstruation as the uterine cycle begins again Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hormonal Control of the Menstrual Cycle Is Complex (1 of 3) • Early follicular phase – FSH → growth of tertiary follicles – Granulosa cells and theca produce steroid hormones – Estrogen blocks FSH and LH – AMH, no development of other follicles in this cycle – Endometrium proliferates because of estrogen • Mid- to Late Follicular phase – High estrogen becomes positive feedback – LH and FSH surge – Uterus prepares for implantation, endometrium thickens Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hormonal Control of the Menstrual Cycle Is Complex (2 of 3) • • Ovulation – Inflammatory reaction attracts leukocytes that secrete prostaglandins – Mature follicle secretes matrix metalloproteinases (MMPs) – Follicle ruptures, releasing mature oocyte Early to mid-luteal phase – Granulosa and theca cells differentiate into luteal cells – Luteal cells secrete inhibin and progesterone ▪ – Negative feedback on hypothalamus Endometrium prepares for implantation ▪ Deposits lipids and glycogen increase in endometrial cells – – Provide nutrients for embryo while placenta develops Cervical mucus thickens Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hormonal Control of the Menstrual Cycle Is Complex (3 of 3) • Late luteal phase and menstruation – No pregnancy, corpus luteum degenerates into corpus albicans – Progesterone and estrogen levels drop and FSH and LH are secreted – Endometrium sloughs off → menstruation • Hormones influence female secondary sex characteristics – Estrogens control breast development and fat distribution – Androgens control pubic and axillary hair growth and libido Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.11 The menstrual cycle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.12 Hormonal control of the menstrual cycle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26.6 Pregnancy and Parturition • Fertilization requires capacitation • Capacitation is the final maturation step – Enables sperm to fertilize an egg change in lipids and proteins of sperm head membrane – Occurs in the female reproductive tract • Fertilization in the Fallopian tubes capacitated sperm release powerful enzymes from the acrosome in the sperm head protective glycoprotein coat – Zona pellucida and acrosomal reaction – Fusion of sperm and egg triggers the cortical reaction excludes other sperm ▪ Cortical granules released ▪ Prevents polyspermy more than 1 sperm fertilizes an egg – Nuclear fusion creates a diploid cell • Gestation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.14(a-b) Fertilization Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.14(c) Fertilization Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.14(d) Fertilization Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Developing Embryo Implants in the Endometrium • Developing embryo forms a hollow blastocyst when it reaches the uterus • Extraembryonic membranes – Chorion forms the placenta – Amnion, secretes amniotic fluid – Allantois, umbilical cord – Yolk sac degenerates early • Chorionic villi of placenta surrounded by maternal blood, nutrients, gases, and wastes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Placenta Secretes Hormones during Pregnancy • Human chorionic gonadotropin (hCG) – “maintenance” of corpus luteum – Basis of pregnancy tests • Human chorionic somatomammotropin (hCS) – Also called human placental lactogen (hPL) – Necessary for breast development and milk production (lactation) – Affects maternal metabolism • Estrogen and progesterone – Estrogen helps develop milk-secreting ducts in the breasts – Progesterone maintains endometrium ▪ Placenta takes over progesterone production → corpus luteum degenerates Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Class stopped here Figure 26.15 The placenta Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pregnancy Ends with Labor and Delivery Accouchement naturel • Parturition begins with labor – Signals from mother or fetus or both • Prior to labor, the cervix softens – Relaxin peptide hormone secreted by ovaries and placenta • Positive feedback loop – Uterine contractions → cervical stretch → oxytocin → prostaglandins → contractions • Delivery • Placenta detaches and is expelled Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.16(a-c) Parturition: The birth process Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.16(d) Parturition: The birth process Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Mammary Glands Secrete Milk during Lactation • Puberty – • Pregnancy – • Estrogen influences breast development Estrogen, growth hormone, and cortisol stimulate further gland development Late pregnancy – Progesterone converts duct epithelium into secretory structure – Prolactin is not inhibited by prolactin-inhibiting hormone (PIH) and glands begin to produce milk • Mammary glands initially produce colostrum • Let-down reflex – Oxytocin initiates smooth muscle contraction in breast tissue and plays a role in involution (uterus returning to pre-pregnancy size) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 26.17 Lactation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved