Reproduction and Development Chapter 26a Reproduction and Development

Sex determination and differentiation About this Chapter Sex determination and differentiation Gametogenesis and patterns of reproduction Male reproductive development and physiology Female reproductive development and physiology Pregnancy and the birth process The reproductive system during growth and aging

Gonads produce gametes and sex hormones 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

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 Nondisjunction XXX superfemale XXY Klinefelters X0 Turners XYY supermale Figure 26-1

X and Y Chromosomes Determine Sex Figure 26-2

Sexual Differentiation Bipotential tissues have not yet differentiated SRY protein directs development as a male Gonadal medulla develops into testis Testicular hormones direct further development Absence of SRY protein leads to female development Gonadal cortex develops into ovarian tissue Mullerian ducts develop into female organs Wolffian ducts degenerate

Sexual Differentiation Table 26-1

Development of Internal Reproductive 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. 1 SRY protein in a male embryo directs the medulla of the bipotential gonad to develop into testis. Testis 2 Absence of testosterone causes Wolffian duct to degenerate. 2 Anti-Müllerian hormone from testis causes the Müllerian ducts to disappear. Wolffian duct Müllerian duct Uterus 10 WEEKS Ovary 3 Testosterone from testis converts Wolffian duct into seminal vesicle, vas deferens, and epididymis. DHT controls prostate development. 3 Absence of anti- Müllerian 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) Vas deferens Uterus Testis AT BIRTH Epididymis Vagina (a) DEVELOPMENT OF INTERNAL ORGANS Figure 26-3a

Development of External Genitalia Genital tubercle homologous Urethral groove Labioscrotal swelling Anus Urethral fold FEMALE MALE Bipotential stage (6 week fetus) Clitoris Penis Urethral fold Urethral fold Labioscrotal swelling Labioscrotal swelling Anus Anus 1 DHT causes development of male external genitalia. 10 WEEKS 1 1 In the absence of androgens, the external genitalia are feminized. Glans penis Labia majora Clitoris Shaft of penis Urethral opening Labia minora Vaginal opening Scrotum 2 The testes descend from the abdominal cavity into the scrotum. Anus Anus AT BIRTH (b) DEVELOPMENT OF EXTERNAL GENITALIA Figure 26-3b

Control of Male Development SRY gene directs male development Figure 26-4

Control of Female Development The SRY gene and protein are absent Gonadal cortex develops into ovarian tissue Mullerian ducts develop into female organs Vagina Uterus Fallopian tubes Wolffian ducts degenerate

Gametogenesis Differs in Males and Females STAGE OF CELL DIVISION MALE Oögonium 1 MITOSIS Spermatogonium Germ cell proliferation 46 chromosomes per cell (only two shown here) Embryo Embryo 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicates but no cell division. Primary oocyte Sister chromatids Sister chromatids Primary spermatocyte 46 chromosomes, duplicated 3 First meiotic division First polar body Secondary oocyte (egg) Primary gamete divides into two secondary gametes. Reproductive adult Secondary spermatocytes (may not occur) 23 chromosomes, duplicated Reproductive adult 4 Second meiotic division Disintegrates Spermatids Egg released from ovary at ovulation. Secondary gamete divides. develop into 23 chromosomes (haploid) Sperm 6 FERTILIZATION One primary oocyte yields 1 egg. One primary spermatocyte yields 4 sperm. 5 Second polar body disintegrates. Unfertilized egg passes out of body. Zygote Figure 26-5

Mitosis: Germ Cell Proliferation FEMALE STAGE OF CELL DIVISION MALE Oögonium 1 MITOSIS Spermatogonium Germ cell proliferation 46 chromosomes per cell (only two shown here) Embryo Embryo 46 (diploid) Oögonia Spermatogonia Reproductive adult Reproductive adult Figure 26-5, step 1

Meiosis: DNA Replicates FEMALE STAGE OF CELL DIVISION MALE Oögonium 1 MITOSIS Spermatogonium Germ cell proliferation 46 chromosomes per cell (only two shown here) Embryo Embryo 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicates but no cell division. Primary oocyte Sister chromatids Sister chromatids Primary spermatocyte 46 chromosomes, duplicated Polar bodies Reproductive adult Reproductive adult Figure 26-5, steps 1–2

First Meiotic Division FEMALE STAGE OF CELL DIVISION MALE Oögonium 1 MITOSIS Spermatogonium Germ cell proliferation 46 chromosomes per cell (only two shown here) Embryo Embryo 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicates but no cell division. Primary oocyte Sister chromatids Sister chromatids Primary spermatocyte 46 chromosomes, duplicated Polar bodies 3 First meiotic division First polar body Secondary oocyte (egg) Primary gamete divides into two secondary gametes. Reproductive adult Secondary spermatocytes 23 chromosomes, duplicated Reproductive adult Figure 26-5, steps 1–3

Second Meiotic Division FEMALE STAGE OF CELL DIVISION MALE Oögonium 1 MITOSIS Spermatogonium Germ cell proliferation 46 chromosomes per cell (only two shown here) Embryo Embryo 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicates but no cell division. Primary oocyte Sister chromatids Sister chromatids Primary spermatocyte 46 chromosomes, duplicated Polar bodies 3 First meiotic division First polar body Secondary oocyte (egg) Primary gamete divides into two secondary gametes. Reproductive adult Secondary spermatocytes (may not occur) 23 chromosomes, duplicated Reproductive adult 4 Second meiotic division Disintegrates Spermatids Egg released from ovary at ovulation. Secondary gamete divides. develop into 23 chromosomes (haploid) Sperm One primary spermatocyte yields 4 sperm. Figure 26-5, steps 1–4

Ovulation Without Fertilization FEMALE STAGE OF CELL DIVISION MALE Oögonium 1 MITOSIS Spermatogonium Germ cell proliferation 46 chromosomes per cell (only two shown here) Embryo Embryo 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicates but no cell division. Primary oocyte Sister chromatids Sister chromatids Primary spermatocyte 46 chromosomes, duplicated Polar bodies 3 First meiotic division First polar body Secondary oocyte (egg) Primary gamete divides into two secondary gametes. Reproductive adult Secondary spermatocytes (may not occur) 23 chromosomes, duplicated Reproductive adult 4 Second meiotic division Disintegrates Spermatids Egg released from ovary at ovulation. Secondary gamete divides. develop into 23 chromosomes (haploid) Sperm One primary oocyte yields 1 egg. One primary spermatocyte yields 4 sperm. 5 Unfertilized egg passes out of body. Figure 26-5, steps 1–5

Ovulation with Fertilization Is Followed by Final Step of Meiosis FEMALE STAGE OF CELL DIVISION MALE Oögonium 1 MITOSIS Spermatogonium Germ cell proliferation 46 chromosomes per cell (only two shown here) Embryo Embryo 46 (diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicates but no cell division. Primary oocyte Sister chromatids Sister chromatids Primary spermatocyte 46 chromosomes, duplicated Polar bodies 3 First meiotic division First polar body Secondary oocyte (egg) Primary gamete divides into two secondary gametes. Reproductive adult Secondary spermatocytes (may not occur) 23 chromosomes, duplicated Reproductive adult 4 Second meiotic division Disintegrates Spermatids Egg released from ovary at ovulation. Secondary gamete divides. develop into 23 chromosomes (haploid) Sperm 6 FERTILIZATION One primary oocyte yields 1 egg. One primary spermatocyte yields 4 sperm. 5 Second polar body disintegrates. Unfertilized egg passes out of body. 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

Synthesis Pathways for Steroid Hormones Cholesterol Progesterone * Dihydro- testosterone (DHT) Testosterone aromatase Corticosterone Cortisol Estradiol KEY * 5-reductase Aldosterone Intermediate steps Figure 26-6

Hormonal Regulation of Reproduction Anterior pituitary Luteinizing hormone (LH) Follicle stimulating hormone (FSH) Gonads produce steroid and peptide hormones Gonads are the main source of sex steroid

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 FSH Tissue response Gonads (ovaries or testes) Females only Endocrine cells Gamete production Steroid and peptide hormones Figure 26-7

Consequences of Feedback Table 26-2