Question

Describe the endocrine system's regulation of the anatomy and physiology of the male reproductive system, including maturation at puberty, formation of sperm, and the development and maintenance of secondary sex characteristics.

Answer 1

Ans:-REGULATION OF MALE SEXUAL FUNCTIONS BY ENDOCRINE HORMONES:- A major share of the control of sexual functions in both the male and the female begins with secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus. This hormone in turn stimulates the anterior pituitary gland to secrete two other hormones called gonadotropic hormones: (1) luteinizing hormone (LH) and (2) follicle-stimulating hormone (FSH). In turn, LH is the primary stimulus for the secretion of testosterone by the testes, and FSH mainly stimulates spermatogenesis.

• LH and FSH are glycoproteins. They exert their effects on their target tissues in the testes mainly by activating the cyclic adenosine monophosphate second messenger system, which in turn activates specific enzyme systems in the respective cells.
• Regulation of Testosterone Production by Luteinizing Hormone. Testosterone is secreted by the interstitial cells of Leydig in the testes, but only when they are stimulated by LH from the anterior pituitary gland. Furthermore, the quantity of testosterone that is secreted increases approximately in direct proportion to the amount of LH that is available.
• Regulation of Spermatogenesis by Follicle-Stimulating Hormone and Testosterone Inhibin FSH binds with specific FSH receptors attached to the Sertoli cells in the seminiferous tubules, which causes the Sertoli cells to grow and secrete various spermatogenic substances. Simultaneously, testosterone (and dihydrotes tosterone) diffusing into the seminiferous tubules from the Leydig cells in the interstitial spaces also has a strong tropic effect on spermatogenesis. Thus, both FSH and testosterone are necessary to initiate spermatogenesis.

#MATURATION AT PUBERTY And REGULATION :- it has now been determined that during childhood the hypothalamus does not secrete significant amounts of GnRH. One of the reasons for this is that, during childhood, the slightest secretion of any sex steroid hormones exerts a strong inhibitory effect on hypothalamic secretion of GnRH. Yet, for reasons still not understood, at the time of puberty, the secretion of hypothalamic GnRH breaks through the childhood inhibition and adult sexual life begins.

#SPERMATOGENISIS:-During formation of the embryo, the primordial germ cells migrate into the testes and become immature germ cells called spermatogonia, which lie in two or three layers of the inner surfaces of the seminiferous tubules (a cross section of a tubule is at puberty the spermatogonia begin to undergo mitotic division and continually proliferate and differentiate through definite stages of development to form sperm,

• STEPS OF SPERMATOGENESIS

  Spermatogenesis occurs in the seminiferous tubules during active sexual life as the result of stimulation by anterior pituitary gonadotropic hormones. Spermatogenesis begins at an average age of 13 years and continues throughout most of the remainder of life but decreases markedly in old age.In the first stage of spermatogenesis, the spermatogo nia migrate among Sertoli cells toward the central lumen of the seminiferous tubule. The Sertoli cells are large, with overflowing cytoplasmic envelopes that surround the developing spermatogonia all the way to the central lumen of the tubule.

• Meiosis. Spermatogonia that cross the barrier into the Sertoli cell layer become progressively modified and enlarged to form large primary spermatocytes. Each of these primary spermatocytes, in turn, undergoes meiotic division to form two secondary spermatocytes. After another few days, these secondary sper matocytes also divide to form spermatids that are eventually modified to become spermatozoa (sperm).

#Secondary sexual character:-

i. Effect on muscular growth One of the most important male sexual characters is the development of musculature after puberty. Muscle mass increases by about 50%, due to the anabolic effect of testosterone on proteins. Testosterone accelerates the transport of amino acids into the muscle cells, synthesis of proteins and storage of proteins. Testosterone also decreases the breakdown of proteins.

ii. Effect on bone growth After puberty, testosterone increases the thickness of bones by increasing the bone matrix and deposition of calcium. It is because of the protein anabolic activity of testosterone. Deposition of calcium is secondary to the increase in bone matrix. In addition to increase in the size and strength of bones, testosterone also causes early fusion of epiphyses of long bones with shaft. So, if testes are removed before puberty, the fusion of epiphyses is delayed and the height of the person increases.

iii. Effect on shoulder and pelvic bones Testosterone causes broadening of shoulders and it has a specific effect on pelvis, which results in: a. Lengthening of pelvis b. Funnel-like shape of pelvis. c. Narrowing of pelvic outlet. Thus, pelvis in males is different from that of females, which is broad and round or oval in shape.

iv. Effect on skin Testosterone increases the thickness of skin and ruggedness of subcutaneous tissue. These changes in skin are due to the deposition of proteins in skin. It also increases the quantity of melanin pigment, which is responsible for the deepening of the skin color. Testosterone enhances the secretory activity of sebaceous glands. So, at the time of puberty, when the body is exposed to sudden increase in testosterone secretion, the excess secretion of sebum leads to development of acne on the face. After few years, the skin gets adapted to testosterone secretion and the acne disappears.

v. Effect on hair distribution Testosterone causes male type of hair distribution on the body, i.e. hair growth over the pubis, along linea alba up to umbilicus, on face, chest and other parts of the body such as back and limbs. In males, the pubic hair has the base of the triangle downwards where as in females it is upwards. Testosterone decreases the hair growth on the head and may cause baldness, if there is genetic background.

vi. Effect on voiceAt the time of adolescence, the boys have a cracking voice. It is because of the testosterone effect, which causes: a.Hypertrophy of laryngeal musclesb.Enlargement of larynx and lengtheningc.Thickening of vocal cords. Later, the cracking voice changes gradually into a typical adult male voice with a bossing sound.vii. Effect on basal metabolic rateAt the time of puberty and earlier part of adult life, the testosterone increases the basal metabolic rate to about 5% to 10% by its anabolic effects on protein metabolism.

viii. Effect on electrolyte and water balanceTestosterone increases the sodium reabsorption from renal tubules, along with water reabsorption. It leads to increase in ECF volume.

ix. Effect on bloodTestosterone has got erythropoietic action. So, after puberty, testosterone causes mild increase in RBC count. It also increases the blood volume by increasing the water retention and ECF volume.