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CHAPTER

25

The Gonads: Development

& Function of the

Reproductive System

OBJECTIVES

After studying this chapter, you should be able to:

■

Name the key hormones secreted by Leydig cells and Sertoli cells of the testes and

by graafian follicles and corpora lutea of the ovaries.

■

Outline the role of chromosomes, hormones, and related factors in sex determina-

tion and development.

■

Summarize the hormonal changes that occur at puberty in males and females.

■

Outline the hormonal changes and their physiologic effects during perimeno-

pause and menopause.

■

List the physiologic stimuli and the drugs that affect prolactin secretion.

■

Outline the steps involved in spermatogenesis and the mechanisms that produce

erection and ejaculation.

■

Know the general structure of testosterone, and describe its biosynthesis, trans-

port, metabolism, and actions.

■

Describe the processes involved in regulation of testosterone secretion.

■

Describe the physiologic changes that occur in the female reproductive organs

during the menstrual cycle.

■

Know the general structures of 17

β

-estradiol and progesterone, and describe their

biosynthesis, transport, metabolism, and actions.

■

Describe the roles of the pituitary and the hypothalamus in the regulation of ovar-

ian function, and the role of feedback loops in this process.

■

Describe the hormonal changes that accompany pregnancy and parturition.

■

Outline the processes involved in lactation.

INTRODUCTION

Modern genetics and experimental embryology make it clear

that, in most species of mammals, the multiple differences

between the male and the female depend primarily on a sin-

gle chromosome (the Y chromosome) and a single pair of

endocrine structures, the testes in the male and the ovaries in

the female. The differentiation of the primitive gonads into

testes or ovaries in utero is genetically determined in

humans, but the formation of male genitalia depends on the

presence of a functional, secreting testis; in the absence of

testicular tissue, development is female. Evidence indicates

that male sexual behavior and, in some species, the male pat-

tern of gonadotropin secretion are due to the action of male

hormones on the brain in early development. After birth, the

gonads remain quiescent until adolescence, when they are

activated by gonadotropins from the anterior pituitary. Hor-

mones secreted by the gonads at this time cause the appear-

ance of features typical of the adult male or female and the

onset of the sexual cycle in the female. In human females,

ovarian function regresses after a number of years and sexual

cycles cease (the menopause). In males, gonadal function