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Reproduction & Development: Sex Determination & Gametogenesis
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REPRODUCTION & DEVELOPMENT Instructor: Mesut Muyan Copyright © 2009 Pearson Education, Inc. • Sex determination and differentiation • Gametogenesis and patterns of reproduction • Male reproductive development and physiology • Female reproductive development and physiology • Procreation and sexual complications • Pregnancy and the birth process • The reproductive system during growth and aging Copyright © 2009 Pearson Education, Inc. Female and Male Sex Organs have three sets of structures: 1. The gonads (Gonos, seed) 2. The internal genitalia 3. The external genitalia The internal genitalia consists of accessory glands and ducts and connect the gonads to the external genitalia Copyright © 2009 Pearson Education, Inc. Sexual development is programmed by the genome. Copyright © 2009 Pearson Education, Inc. Sex Determination Is Directed By Our Genome • Humans have 23 pairs of chromosomes • 22 pairs of autosomes • X and Y = 1 pair of sex chromosomes Copyright © 2009 Pearson Education, Inc. Figure 26-1 The two sex chromosomes designated as X or Y, contain genes that direct the development of internal and external sex organs. The X chromosome is larger than Y and includes many genes that are missing in Y chromosome. Copyright © 2009 Pearson Education, Inc. X and Y Chromosomes Determine Genetic Sex Copyright © 2009 Pearson Education, Inc. Figure 26-2 Abnormal distribution of sex chromosomes: The presence or absence of the Y chromosome determines whether development proceeds as male or female. XXY (Klinefelter syndrome) XO (Turner Syndrome) YO Copyright © 2009 Pearson Education, Inc. Klinefelter syndrome Copyright © 2009 Pearson Education, Inc. Turner syndrome Copyright © 2009 Pearson Education, Inc. Abnormal distribution of of sex chromosomes: The presence or absence of the Y chromosome determines whether development proceeds as male or female. XXY (Klinefelter syndrome) XO (Turner Syndrome) YO Copyright © 2009 Pearson Education, Inc. Sex Determination • Sexual dimorphism • Females and males are physically distinct • Gonads produce gametes and sex hormones • Male gonads = testes → sperm • Female gonads = ovaries → eggs • Sex hormones direct development of genitalia • Internal genitalia • External genitalia Copyright © 2009 Pearson Education, Inc. Sexual Differentiation Copyright © 2009 Pearson Education, Inc. Development of Internal Reproductive Organs Copyright © 2009 Pearson Education, Inc. Development of Female Internal Organs Müllerian duct Wolffian duct Bipotential gonad Kidney Cloacal opening FEMALE Bipotential stage: 6 week fetus The internal reproductive organs have the potential to develop into male or female structures 1 Gonadal cortex becomes ovary in the absence of SRY protein. MALE Müllerian duct Uterus 10 WEEKS AT BIRTH (a) DEVELOPMENT OF INTERNAL ORGANS Copyright © 2009 Pearson Education, Inc. Figure 26-3a (1 of 6) Development of Female Internal Organs Müllerian duct Wolffian duct Bipotential gonad Kidney Cloacal opening FEMALE Bipotential stage: 6 week fetus The internal reproductive organs have the potential to develop into male or female structures 1 Gonadal cortex becomes ovary in the absence of SRY protein. 2 Absence of testosterone causes Wolffian duct to degenerate. MALE Müllerian duct Uterus 10 WEEKS AT BIRTH (a) DEVELOPMENT OF INTERNAL ORGANS Copyright © 2009 Pearson Education, Inc. Figure 26-3a (2 of 6) Development of Female Internal Organs Müllerian duct Wolffian duct Bipotential gonad Kidney Cloacal opening FEMALE Bipotential stage: 6 week fetus The internal reproductive organs have the potential to develop into male or female structures 1 Gonadal cortex becomes ovary in the absence of SRY protein. 2 Absence of testosterone causes Wolffian duct to degenerate. MALE Müllerian duct Uterus 10 WEEKS Ovary 3 Absence of antiMüllerian hormone allows the Müllerian duct to become the fallopian tube, uterus, and upper part of the vagina. Fallopian tube (from Müllerian duct) Uterus Vagina AT BIRTH (a) DEVELOPMENT OF INTERNAL ORGANS Copyright © 2009 Pearson Education, Inc. Figure 26-3a (3 of 6) Development of Male Internal Organs Müllerian duct Wolffian duct Bipotential gonad Kidney Cloacal opening FEMALE MALE Bipotential stage: 6 week fetus The internal reproductive organs have the potential to develop into male or female structures 1 Gonadal cortex becomes ovary in the absence of SRY protein. Testis 2 Absence of testosterone causes Wolffian duct to degenerate. 1 SRY protein in a male embryo directs the medulla of the bipotential gonad to develop into testis. Wolffian duct Müllerian duct Uterus 10 WEEKS Ovary 3 Absence of antiMüllerian hormone allows the Müllerian duct to become the fallopian tube, uterus, and upper part of the vagina. Fallopian tube (from Müllerian duct) Uterus Vagina AT BIRTH (a) DEVELOPMENT OF INTERNAL ORGANS Copyright © 2009 Pearson Education, Inc. Figure 26-3a (4 of 6) Development of Male Internal Organs Müllerian duct Wolffian duct Bipotential gonad Kidney Cloacal opening FEMALE MALE Bipotential stage: 6 week fetus The internal reproductive organs have the potential to develop into male or female structures 1 Gonadal cortex becomes ovary in the absence of SRY protein. Testis 2 Absence of testosterone causes Wolffian duct to degenerate. Wolffian duct Müllerian duct 1 SRY protein in a male embryo directs the medulla of the bipotential gonad to develop into testis. 2 Anti-Müllerian hormone from testis causes the Müllerian ducts to disappear. Uterus 10 WEEKS Ovary 3 Absence of antiMüllerian hormone allows the Müllerian duct to become the fallopian tube, uterus, and upper part of the vagina. Fallopian tube (from Müllerian duct) Uterus Vagina AT BIRTH (a) DEVELOPMENT OF INTERNAL ORGANS Copyright © 2009 Pearson Education, Inc. Figure 26-3a (5 of 6) Development of Male Internal Organs Müllerian duct Wolffian duct Bipotential gonad Kidney Cloacal opening FEMALE MALE Bipotential stage: 6 week fetus The internal reproductive organs have the potential to develop into male or female structures 1 Gonadal cortex becomes ovary in the absence of SRY protein. Testis 2 Absence of testosterone causes Wolffian duct to degenerate. Wolffian duct Müllerian duct 1 SRY protein in a male embryo directs the medulla of the bipotential gonad to develop into testis. 2 Anti-Müllerian hormone from testis causes the Müllerian ducts to disappear. Uterus 10 WEEKS Ovary 3 Absence of antiMüllerian hormone allows the Müllerian duct to become the fallopian tube, uterus, and upper part of the vagina. Prostate Seminal vesicle Fallopian tube (from Müllerian duct) Uterus Vagina Vas deferens Testis AT BIRTH 3 Testosterone from testis converts Wolffian duct into seminal vesicle, vas deferens, and epididymis. DHT controls prostate development. Epididymis (a) DEVELOPMENT OF INTERNAL ORGANS Copyright © 2009 Pearson Education, Inc. Figure 26-3a (6 of 6) Development of External Genitalia Copyright © 2009 Pearson Education, Inc. Figure 26-3b Development of Female External Genitalia Genital tubercle Urethral groove Labioscrotal swelling Urethral fold Anus FEMALE Bipotential stage (6 week fetus) Clitoris MALE Urethral fold Labioscrotal swelling Anus 10 WEEKS 1 In the absence of androgens, the external genitalia are feminized. Labia majora Clitoris Urethral opening Labia minora Vaginal opening Anus AT BIRTH (b) DEVELOPMENT OF EXTERNAL GENITALIA Copyright © 2009 Pearson Education, Inc. Figure 26-3b (1 of 3) Development of Male External Genitalia Genital tubercle Urethral groove Labioscrotal swelling Urethral fold Anus FEMALE MALE Bipotential stage (6 week fetus) Clitoris Penis Urethral fold Urethral fold Labioscrotal swelling Labioscrotal swelling Anus Anus 10 WEEKS 1 In the absence of androgens, the external genitalia are feminized. Labia majora Clitoris Urethral opening Labia minora Vaginal opening 1 DHT causes development of male external genitalia. Anus AT BIRTH (b) DEVELOPMENT OF EXTERNAL GENITALIA Copyright © 2009 Pearson Education, Inc. Figure 26-3b (2 of 3) Development of Male External Genitalia Genital tubercle Urethral groove Labioscrotal swelling Urethral fold Anus FEMALE MALE Bipotential stage (6 week fetus) Clitoris Penis Urethral fold Urethral fold Labioscrotal swelling Labioscrotal swelling Anus Anus 10 WEEKS 1 In the absence of androgens, the external genitalia are feminized. 1 DHT causes development of male external genitalia. Glans penis Labia majora Clitoris Urethral opening Labia minora Vaginal opening Anus Shaft of penis Scrotum Anus AT BIRTH 2 The testes descend from the abdominal cavity into the scrotum. (b) DEVELOPMENT OF EXTERNAL GENITALIA Copyright © 2009 Pearson Education, Inc. Figure 26-3b (3 of 3) • SRY gene directs male development Copyright © 2009 Pearson Education, Inc. Figure 26-4 Sexual Differentiation Copyright © 2009 Pearson Education, Inc. Table 26-1 Control of Female Development Take home message • The SRY gene is silent and protein is absent • Gonadal cortex develops into ovarian tissue • Mullerian ducts develop into female organs • Vagina • Uterus • Fallopian tubes • Wolffian ducts degenerate Copyright © 2009 Pearson Education, Inc. Gametogenesis Begins In Utero • Germ cells exist within the embryonic gonad • Mitotic divisions increase the number of germ cells • Meiosis • Primary gamete • Secondary gamete • Haploid gamete • Different timing of meiosis in males and females Copyright © 2009 Pearson Education, Inc. Gametogenesis Differs in Males and Females Copyright © 2009 Pearson Education, Inc. Mitosis: Germ Cell Proliferation FEMALE Oögonium MALE 1 MITOSIS Germ cell proliferation Spermatogonium Embryo 46 chromosomes per cell (only two shown here) Copyright © 2009 Pearson Education, Inc. 46 (diploid) Spermatogonia Reproductive adult Reproductive adult Oögonia Embryo STAGE OF CELL DIVISION Figure 26-5, step 1 Meiosis: DNA Replicates FEMALE Oögonium MALE 1 MITOSIS Germ cell proliferation Spermatogonium Embryo 46 chromosomes per cell (only two shown here) 46 (diploid) Oögonia Sister chromatids DNA replicates but no cell division. Sister chromatids Reproductive adult 46 chromosomes, duplicated Primary spermatocyte Reproductive adult Copyright © 2009 Pearson Education, Inc. Spermatogonia MEIOSIS 2 Primary oocyte Embryo STAGE OF CELL DIVISION Figure 26-5, steps 1–2 First Meiotic Division FEMALE Oögonium MALE 1 MITOSIS Germ cell proliferation Spermatogonium Embryo 46 chromosomes per cell (only two shown here) 46 (diploid) Oögonia 2 Sister chromatids DNA replicates but no cell division. Reproductive adult First meiotic division Primary gamete divides into two secondary gametes. 23 chromosomes, duplicated Reproductive adult Secondary oocyte (egg) Sister chromatids 46 chromosomes, duplicated 3 Copyright © 2009 Pearson Education, Inc. Spermatogonia MEIOSIS Primary oocyte First polar body Embryo STAGE OF CELL DIVISION Primary spermatocyte Secondary spermatocytes Figure 26-5, steps 1–3 Second Meiotic Division FEMALE Oögonium MALE 1 MITOSIS Germ cell proliferation Spermatogonium Embryo 46 chromosomes per cell (only two shown here) 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 Primary oocyte Sister chromatids DNA replicates but no cell division. Disintegrates Egg released from ovary at ovulation. Reproductive adult (may not occur) First meiotic division Primary gamete divides into two secondary gametes. 23 chromosome, 4 Second meiotic division Secondary gamete divides. 23 chromosomes (haploid) Reproductive adult Secondary oocyte (egg) Sister chromatids 46 chromosomes, duplicated 3 First polar body Embryo STAGE OF CELL DIVISION Primary spermatocyte Secondary spermatocytes Spermatids develop into Sperm One primary spermatocyte yields 4 sperm. Copyright © 2009 Pearson Education, Inc. Figure 26-5, steps 1–4 Ovulation Without Fertilization FEMALE Oögonium MALE 1 MITOSIS Germ cell proliferation Spermatogonium Embryo 46 chromosomes per cell (only two shown here) 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 Primary oocyte Sister chromatids DNA replicates but no cell division. Reproductive adult (may not occur) Disintegrates Egg released from ovary at ovulation. One primary oocyte yields 1 egg. First meiotic division Primary gamete divides into two secondary gametes. 23 chromosomes, duplicated 4 Second meiotic division Secondary gamete divides. 23 chromosomes (haploid) Reproductive adult Secondary oocyte (egg) Sister chromatids 46 chromosomes, duplicated 3 First polar body Embryo STAGE OF CELL DIVISION Primary spermatocyte Secondary spermatocytes Spermatids develop into Sperm One primary spermatocyte yields 4 sperm. 5 Unfertilized egg passes out of body. Copyright © 2009 Pearson Education, Inc. Figure 26-5, steps 1–5 Ovulation with Fertilization Is Followed by Final Step of Meiosis FEMALE Oögonium MALE 1 MITOSIS Germ cell proliferation Spermatogonium Embryo 46 chromosomes per cell (only two shown here) 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 Primary oocyte Sister chromatids DNA replicates but no cell division. Reproductive adult (may not occur) Disintegrates Egg released from ovary at ovulation. First meiotic division Primary gamete divides into two secondary gametes. 46 chromosomes, 4 Secondary gamete divides. 23 chromosomes (haploid) 6 One primary oocyte yields 1 egg. Second meiotic division FERTILIZATION Reproductive adult Secondary oocyte (egg) Sister chromatids 46 chromosomes, duplicated 3 First polar body Embryo STAGE OF CELL DIVISION Primary spermatocyte Secondary spermatocytes Spermatids develop into Sperm One primary spermatocyte yields 4 sperm. 5 Second polar body disintegrates. Unfertilized egg passes out of body. Copyright © 2009 Pearson Education, Inc. Zygote Figure 26-5, steps 1–6 Steroid Synthesis Pathways • Steroid hormones are similar to each other • Production of sex steroids differs between men and women • Ovary • Estrogen and progesterone • Testis • Testosterone and dihydrotestosterone (DHT) • Adrenal gland secretes small amounts of sex steroids Copyright © 2009 Pearson Education, Inc. Synthesis Pathways for Steroid Hormones Cholesterol Progesterone Testosterone * Dihydrotestosterone (DHT) aromatase Corticosterone Cortisol Estradiol KEY * Aldosterone Copyright © 2009 Pearson Education, Inc. 5-reductase Intermediate steps Figure 26-6 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 © 2009 Pearson Education, Inc. General Pattern of Hormonal Control of Reproduction Internal and environmental stimuli CNS GnRH Hypothalamus Short-loop negative feedback KEY Stimulus Anterior pituitary Integrating center Efferent pathway Effector Long-loop feedback may be negative or positive LH Tissue response FSH Gonads (ovaries or testes) Endocrine cells Steroid and peptide hormones Copyright © 2009 Pearson Education, Inc. Gamete production Figure 26-7 Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc. General Pattern of Hormonal Control of Reproduction Copyright © 2009 Pearson Education, Inc. Hypothalamus Is Stimulated by Multiple Stimuli CNS Hypothalamus Internal and environmental stimuli GnRH GnRH Pulse Generator KEY Stimulus Anterior pituitary Integrating center Efferent pathway Effector Tissue response Gonads (ovaries or testes) Copyright © 2009 Pearson Education, Inc. Figure 26-7 (1 of 6) A GnRH Pulse Ördög T et al. Am J Physiol Endocrinol Metab 1998;274:E665-E676 Copyright © 2009 Pearson Education, Inc. Hypothalamus Is Stimulated by Multiple Stimuli CNS Hypothalamus Internal and environmental stimuli GnRH KEY Stimulus Anterior pituitary Integrating center Efferent pathway Effector Tissue response Gonads (ovaries or testes) Copyright © 2009 Pearson Education, Inc. Figure 26-7 (1 of 6) GnRH Stimulates Release of LH and FSH Internal and environmental stimuli CNS GnRH Hypothalamus KEY Stimulus Anterior pituitary Integrating center Efferent pathway Effector LH Tissue response FSH Gonads (ovaries or testes) Copyright © 2009 Pearson Education, Inc. Figure 26-7 (2 of 6) FSH Stimulates Gamete Production Internal and environmental stimuli CNS GnRH Hypothalamus KEY Stimulus Anterior pituitary Integrating center Efferent pathway Effector LH Tissue response FSH Gonads (ovaries or testes) Gamete production Copyright © 2009 Pearson Education, Inc. Figure 26-7 (3 of 6) LH Stimulates Steroid Synthesis Internal and environmental stimuli CNS GnRH Hypothalamus KEY Stimulus Anterior pituitary Integrating center Efferent pathway Effector LH Tissue response FSH Gonads (ovaries or testes) Endocrine cells Steroid and peptide hormones Copyright © 2009 Pearson Education, Inc. Gamete production Figure 26-7 (4 of 6) Feedback Loops Control Gonadotropin Release Internal and environmental stimuli CNS GnRH Hypothalamus KEY Stimulus Anterior pituitary Integrating center Efferent pathway Effector Long-loop feedback may be negative or positive LH Tissue response FSH Gonads (ovaries or testes) Endocrine cells Steroid and peptide hormones Copyright © 2009 Pearson Education, Inc. Gamete production Figure 26-7 (5 of 6) Feedback Loops Control Gonadotropin Release Internal and environmental stimuli CNS GnRH Hypothalamus Short-loop negative feedback KEY Stimulus Anterior pituitary Integrating center Efferent pathway Effector Long-loop feedback may be negative or positive LH Tissue response FSH Gonads (ovaries or testes) Endocrine cells Steroid and peptide hormones Copyright © 2009 Pearson Education, Inc. Gamete production Figure 26-7 (6 of 6) Consequences of feedback • Sex steroids feedback to control hormone release (long-loop feedback) • GnRH release by the hypothalamus • LH and FSH release by the anterior pituitary • Gonadotropins also feedback to control hormone release (short-loop feedback) • GnRH release by the hypothalamus Copyright © 2009 Pearson Education, Inc. Consequences of Feedback Copyright © 2009 Pearson Education, Inc. Table 26-2 Male Reproductive Structures • External genitalia • Penis and scrotum • Common passageway • Urethra • Accessory glands and ducts • Prostate gland • Seminal vesicle • Bulbourethral gland Copyright © 2009 Pearson Education, Inc. Male Reproductive Structures - Overview Copyright © 2009 Pearson Education, Inc. Figure 26-8 (1 of 2) Male Reproductive Structures - Erectile Tissues Copyright © 2009 Pearson Education, Inc. Figure 26-8 (2 of 2) Male Reproductive Structures • Testes (sperm production) • Seminiferous tubules • Epididymis (sperm maturation) • Vas deferens (aka “ductus deferens”, a passageway into abdomen and delivery to the urethra) Copyright © 2009 Pearson Education, Inc. Male Reproductive Structures - Sagittal View ANATOMY SUMMARY THE MALE REPRODUCTIVE SYSTEM Ureter Urinary bladder Seminal vesicle Rectum Prostate gland Bulbourethral gland Pubic symphysis Vas deferens Ejaculatory duct Urethra Penis Epididymis Testis Scrotum Copyright © 2009 Pearson Education, Inc. (a) Figure 26-9a Male Reproductive Structures - Scrotal Structures ANATOMY SUMMARY THE MALE REPRODUCTIVE SYSTEM Head of epididymis Seminiferous tubule Epididymis Vas deferens (b) Copyright © 2009 Pearson Education, Inc. Scrotal cavity Figure 26-9b Testes •Each lobule contains one to four seminiferous tubules –Tightly coiled structures –Function as sperm-forming factories –Empty sperm into the rete testis •Sperm travels through the rete testis to the epididymis •Interstitial (Leydig) cells produce androgens such as testosterone Copyright © 2009 Pearson Education, Inc. Seminiferous Tubule - Cross-Section ANATOMY SUMMARY THE MALE REPRODUCTIVE SYSTEM Capillary Sertoli cell Leydig cell Spermatogonium (c) Copyright © 2009 Pearson Education, Inc. Figure 26-9c Sertoli Cells •Extend from basement membrane to the fluid filled luman •Joined together by tight junctions •Remove any damaged germ cells in the tubules •Form a blood testes barrier, which develops at puberty just before spermatogenesis takes place and prevents many substances from entering of leaving the tubules via the blood: –Some hormones –Ions –Drugs –Keeps the sperm from entering the blood -immunogenic •Secrete most of the fluid in the lumen of the tubules –Proteins, enzymes nutrients, androgens and certain ions –Fluid produced provides a force for flushing the sperm into the epididymis Copyright © 2009 Pearson Education, Inc. Spermatogenesis in the Testes • Seminiferous tubules • Sertoli cells surround and support developing sperm • Spermatogonia divide and produce all sperm cells • Primary and secondary spermatocytes (I. and II. Meiotic cell division) • Spermatids • Spermatozoa • Interstitial tissues support spermatogenesis • Leydig cells → testosterone • Capillaries deliver nutrients and remove wastes Copyright © 2009 Pearson Education, Inc. Formation of Sperm •Takes place inside the tubules called spermatogenesis •Primitive germ cells are called spermatogonia are present in the testes during embryonic development and childhood •Prior to puberty spermatogonia divide by mitosis to produce more •Mature sperm production begins at puberty and does not end •The process of spermatogenesis takes 70 to 80 days •All stages of sperm development are present in the tubules at any given time Copyright © 2009 Pearson Education, Inc. Seminiferous Tubule - Detail ANATOMY SUMMARY THE MALE REPRODUCTIVE SYSTEM Lumen of seminiferous tubule Spermatids Secondary spermatocyte Primary spermatocyte Spermatogonium Tight junction between Sertoli cells Fibroblast (d) Copyright © 2009 Pearson Education, Inc. Spermatozoa Sertoli cells Basal lamina Capillary Leydig cells Figure 26-9d Spermatozoa Structure Head Acrosome contains enzymes Mid piece Nucleus Centrioles Mitochondrial spiral Tail (flagellum) Microtubules Copyright © 2009 Pearson Education, Inc. Figure 26-10 Epididymis •Comma-shaped, tightly coiled tube •Found on the superior part of the testis and along the posterior lateral side •Functions to mature and store sperm cells (at least 20 days) •Expels sperm with the contraction of muscles in the epididymis walls to the vas deferens Copyright © 2009 Pearson Education, Inc. •Sperm move from the tubules through the rete testis and into the epididymis as a result of pressure created by the formation of fluid in the tubules •The epididymis lies along the back portion of each testis and is lined with smooth muscle. The muscle undergoes rhythmic peristalsis, which transports the sperm through the epididymis and toward the vas deferens •When sperm enter the epididymis they are immature non-motile, and incapable of fertilization •The epididymis secretes a fluid containing nutrients, enzymes, and hormones that aid in sperm maturation •Sperm take two weeks to pass through the epididymis, during which time they become mature and mobile •From the epididymis sperm enters the vas deferens. As the sperm pass through the epididymis approximately 90% of the fluid surrounding them is reabsorbed, hence concentrating the sperm entering the vas deferens Copyright © 2009 Pearson Education, Inc. Regulation of Spermatogenesis Copyright © 2009 Pearson Education, Inc. GnRH Stimulates Gonadotropin Release Hypothalamus Anterior pituitary Copyright © 2009 Pearson Education, Inc. GnRH FSH LH Figure 26-11 (1 of 9) FSH Stimulates Sertoli Cells Hypothalamus Anterior pituitary Testes GnRH FSH LH Sertoli cell Sertoli cell Copyright © 2009 Pearson Education, Inc. Figure 26-11 (2 of 9) Sertoli Cells Stimulate Spermatogenesis Hypothalamus Anterior pituitary GnRH FSH LH Spermatogonium Spermatocyte Testes Sertoli cell Copyright © 2009 Pearson Education, Inc. Second messenger Sertoli cell Cell products Figure 26-11 (3 of 9) Roles of Inhibin and Androgen-Binding Protein GnRH Hypothalamus Anterior pituitary FSH LH Spermatogonium Inhibin Testes Sertoli cell Spermatocyte Second messenger Cell products Androgen-binding protein (ABP) Copyright © 2009 Pearson Education, Inc. Sertoli cell ABP T Figure 26-11 (4 of 9) LH Stimulates Leydig Cells GnRH Hypothalamus Anterior pituitary FSH LH Spermatogonium Inhibin Testes Sertoli cell Spermatocyte Second messenger Sertoli cell Cell products Androgen-binding protein (ABP) Copyright © 2009 Pearson Education, Inc. Leydig cells ABP T Figure 26-11 (5 of 9) Leydig Cells Produce Testosterone GnRH Hypothalamus Anterior pituitary FSH LH Spermatogonium Inhibin Testes Sertoli cell Testosterone (T) Spermatocyte Second messenger Sertoli cell Cell products Androgen-binding protein (ABP) Copyright © 2009 Pearson Education, Inc. Leydig cells ABP T Figure 26-11 (6 of 9) Testosterone Stimulates Sertoli Cells GnRH Hypothalamus Anterior pituitary FSH LH Spermatogonium Inhibin Testes Sertoli cell Testosterone (T) Spermatocyte Second messenger Sertoli cell Cell products Androgen-binding protein (ABP) Copyright © 2009 Pearson Education, Inc. Leydig cells ABP T Figure 26-11 (7 of 9) Testosterone Binds to Androgen-Binding Protein GnRH Hypothalamus Anterior pituitary FSH LH Spermatogonium Inhibin Testes Sertoli cell Testosterone (T) Spermatocyte Second messenger Sertoli cell Cell products Androgen-binding protein (ABP) Copyright © 2009 Pearson Education, Inc. Leydig cells ABP T Figure 26-11 (8 of 9) Testosterone Inhibits the Hypothalamus and Anterior Pituitary GnRH Hypothalamus Anterior pituitary FSH LH Spermatogonium Inhibin Testes Sertoli cell Testosterone (T) Spermatocyte Second messenger Sertoli cell To body for secondary effects Cell products Androgen-binding protein (ABP) Copyright © 2009 Pearson Education, Inc. Leydig cells ABP T Figure 26-11 (9 of 9) Regulation of Spermatogenesis • Hormones control the production of sperm • GnRH stimulates the release of LH and FSH • LH → Leydig cells → testosterone • FSH → Sertoli cells → cell products • Sertoli cell products • Paracrine signals needed for sperm development • Androgen binding protein (ABP) • Inhibin • GnRH and LH/FSH secretion are inhibited by negative feedback Copyright © 2009 Pearson Education, Inc. Accessory Glands Contribute to Semen • Accessory glands contribute 99% of semen volume, as well as the following • Seminal vesicles – fructose, vitamin C, prostaglandins • Prostate gland – buffers, citric acid, enzymes • Bulbourethral gland – mucus, buffers Copyright © 2009 Pearson Education, Inc. Accessory Glands Contribute to Semen Copyright © 2009 Pearson Education, Inc. Table 26-3 Male Secondary Sexual Characteristics • Secondary sexual characteristics are traits, other than genitalia, that distinguish males from females • General body shape, including pattern of muscle development • Body hair and beard • Deep voice • Male sexual behavior (libido) • Androgens (called anabolic steroids) are often used illegally by athletes Copyright © 2009 Pearson Education, Inc.
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