The Gonads
Like the pancreas, the gonads are both endocrine and exocrine. Their exocrine products are eggs and sperm, and their endocrine products are the gonadal hormones, most of which are steroids.
Each follicle of the ovary contains an egg cell surrounded by a wall of granulosa cells (fig. 17.12a). The granulosa cells produce an estrogen called estradiol in the first half of the menstrual cycle. After ovulation, the corpus luteum secretes estradiol and progesterone for 12 days or so, or for 8 to 12 weeks in the event of pregnancy. The functions of estradiol and progesterone are discussed in chapter 28. In brief, they contribute to the development of the
Figure 17.12 The Gonads. (a) Histology of the ovary; (b) histology of the testis. The granulosa cells of the ovary and interstitial cells of the testis are endocrine cells.
Figure 17.12 The Gonads. (a) Histology of the ovary; (b) histology of the testis. The granulosa cells of the ovary and interstitial cells of the testis are endocrine cells.
Saladin: Anatomy & 17. The Endocrine System Text © The McGraw-Hill
Physiology: The Unity of Companies, 2003 Form and Function, Third Edition
652 Part Three Integration and Control reproductive system and feminine physique, they promote adolescent bone growth, they regulate the menstrual cycle, they sustain pregnancy, and they prepare the mammary glands for lactation. The follicle and corpus luteum also secrete inhibin, which suppresses FSH secretion by means of negative feedback inhibition of the anterior pituitary.
The testis consists mainly of microscopic seminiferous tubules that produce sperm. Nestled between them are clusters of interstitial cells (fig. 17.12b), which produce testosterone and lesser amounts of weaker androgens and estrogen. Testosterone stimulates development of the male reproductive system in the fetus and adolescent, the development of the masculine physique in adolescence, and the sex drive. It sustains sperm production and the sexual instinct throughout adult life. Sustentacular (Sertoli21) cells of the testis secrete inhibin, which suppresses FSH secretion and thus homeostatically stabilizes the rate of sperm production.
Post a comment