Chapter at a Glance

Sexual Reproduction 634

Sex Determination 634

Formation of Testes and Ovaries 635 Development of Accessory Sex Organs and External Genitalia 637 Disorders of Embryonic Sexual Development 639

Endocrine Regulation of Reproduction 640

Interactions Between the Hypothalamus, Pituitary Gland, and Gonads 640 The Onset of Puberty 641 Pineal Gland 643 The Human Sexual Response 643

Male Reproductive System 644

Control of Gonadotropin Secretion 644 Testosterone Derivatives in the Brain 644 Testosterone Secretion and Age 645 Endocrine Functions of the Testes 645 Spermatogenesis 646 Sertoli Cells 647 Hormonal Control of

Spermatogenesis 648 Male Accessory Sex Organs 649 Erection, Emission, and Ejaculation 650 Male Fertility 652

Female Reproductive System 654

Ovarian Cycle 655 Ovulation 657 Pituitary-Ovarian Axis 658

Menstrual Cycle 659

Phases of the Menstrual Cycle: Cyclic Changes in the Ovaries 660

Follicular Phase 660 Ovulation 661 Luteal Phase 661 Cyclic Changes in the Endometrium 662 Contraceptive Methods 663 Contraceptive Pill 663 Rhythm Method 664 Menopause 664

Fertilization, Pregnancy, and Parturition 665

Fertilization 666

Cleavage and Blastocyst Formation 667

Embryonic Stem Cells and Cloning 668 Implantation of the Blastocyst and Formation of the Placenta 669 Chorionic Gonadotropin 670 Chorionic Membranes 670 Formation of the Placenta and Amniotic Sac 670

Exchange of Molecules Across the Placenta 672 Endocrine Functions of the Placenta 673 Pituitary-like Hormones from the

Placenta 673 Steroid Hormones from the Placenta 674 Labor and Parturition 674 Lactation 677

Concluding Remarks 679 Interactions 680

Summary 681 Review Activities 682 Related Websites 683

■ Pituitary Gland 299

Autocrine and Paracrine Regulation 316

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Humam Phsiology

Clinical Investigation

Gloria, a second-year college student, goes to the student health center complaining of amenorrhea of several months' duration. Before that, her periods had always been normal. Gloria's body weight is below average for her height, but she exhibits normal development of secondary sexual characteristics. She had been diagnosed a few years earlier as hypothyroid, and thyroxine pills were prescribed for this condition. Gloria teaches an aerobics class at a local gym, and she exercises at least an hour a day. She states that she is not taking birth control pills.

A pregnancy test is performed and is negative. Blood is drawn, and the subsequent laboratory report indicates normal thyroxine levels; in fact, all measurements are within the normal range (her blood cholesterol is even on the low side).What is the most likely cause of Gloria's condition? What should she do about it?

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