PUBERTY

OBJECTIVES To discus the terms: thelarche, pubarche, menarche and adrenarche To understand secondary sexual characteristics( physiologic effects of sex hormones) To understand control of onset of puberty To understand precocious delayed or absence of puberty

Puberty (PU–-ber-te¯) The time of life during which: the secondary sex characteristics begin to appear and the capability for sexual reproduction is possible. usually occurs between the ages of 8 to13 in girls and 9 to 14 years in boys Secondary sex characteristic : A characteristic of the male or female body that develops at puberty under the influence of sex hormones ; examples are distribution of body hair, voice pitch, body shape, and muscle development etc.

Puberty, strictly defined, is the period when the endocrine and gametogenic functions of the gonads have first developed to the point where reproduction is possible ( Review of medical Physiology-21st edition by Ganong) Puberty means the onset of adult sexual life [Guyton] In girls, the first event is thelarche, the development of breasts, followed by pubarche, the development of axillary and pubic hair, and then by menarche, The age at the time of puberty is variable. In Europe and the United States, it has been declining at the rate of 1-3 months per decade for more than 175 years. In the United States in recent years, puberty generally occurs between the ages of 8 and 13 in girls and 9 and 14 in boys.

TERMS Thelarche :is the first physical change of puberty in about 60% of girls. It is a result of rising levels of estradiol. When thelarche occurs at an unusually early age, it may be the first manifestation of precocious puberty. Pubarche : refers to the first appearance of pubic hair in a child. It is a result of rising levels of androgens. When pubarche occurs prematurely it is referred to as premature pubarche.

Types of Hairs Hair follicles develop at about twelve weeks after fertilization. Usually by the fifth month of development, the follicles produce very fine, nonpigmented, downy hairs called lanugo (la-NOO-go¯ wool ) that cover the body of the fetus. Prior to birth, the lanugo of the eyebrows, eyelashes and scalp are shed and replaced by long, coarse, heavily pigmented hairs called terminal hairs.

Types of Hairs The lanugo of the rest of the body are replaced by vellus hairs (VEL-us fleece), commonly called “peach fuzz,” which are short, fine, pale hairs that are barely visible to the naked eye. During childhood, vellus hairs cover most of the body except for the hairs of the eyebrows, eyelashes, and scalp, which are terminal hairs. In response to hormones (androgens) secreted at puberty, terminal hairs replace vellus hairs in the axillae (armpits) and pubic regions of boys and girls , on the face, limbs, and chests of boys, which leads to the formation of a mustache, beard, hairy arms and legs, and a hairy chest. During adulthood, about 95% of body hair on males is terminal hair and 5% is vellus hair. on females, about 35% of body hair is terminal hair and 65% is vellus hair.

TERMS (contd) Menarche : is the first menstrual cycle or first menstrual bleeding. From both social and medical perspectives, it is often considered the central event of female puberty as it signals the possibility of fertility. Adrenarche is an early sexual maturation stage. During adrenarche the adrenal cortex secretes increased levels of adrenalandrogens. It occurs at age 8-10 years in girls and age 10-12 years in boys

TERMS (contd) Precocious puberty : describes puberty occurring at an unusually early age. Early development of secondary sexual characteristics without gametogenesis is caused by abnormal exposure of immature males to androgen or females to estrogen. This syndrome should be called precocious pseudopuberty to distinguish it from true precocious puberty due to an early but otherwise normal pubertal pattern of gonadotropin secretion from the pituitary

Constitutional precocious puberty—ie, precocious puberty in which no cause can be determined—is more common in girls than in boys. In both sexes, tumors or infections involving the hypothalamus cause precocious puberty.

Delayed puberty with exceptions :when an organism has passed the usual age of onset of puberty with no physical or hormonal signs that it is beginning. Puberty may be delayed for several years and still occur normally, in which case it is considered constitutional delay, a variation of healthy physical development. Delay of puberty may also occur due to malnutrtion, many forms of systemic disease, or to defects of the reproductive system(hypogonadism)or the body's responsiveness to sex hormones.

The normal variation in the age at which adolescent changes occur is so wide that puberty cannot be considered to be pathologically delayed until the menarche has failed to occur by the age of 17 or testicular development by the age of 20 In some individuals, puberty is delayed even though the gonads are present and other endocrine functions are normal. In males, this clinical picture is called eunuchoidism. In females, it is called primary amenorrhea

Control of the Onset of Puberty Initiation of the onset of puberty has long been a mystery. But it has now been determined that during childhood the hypothalamus simply 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.

Control of the Onset of Puberty (contd) During the first decade of life, the reproductive system is in a juvenile state. At about age 10, hormone-directed changes start to occur in both sexes. The onset of puberty is marked by pulses or bursts of LH and FSH secretion, each triggered by a pulse of GnRH. Most pulses occur during sleep. As puberty advances, the hormone pulses occur during the day as well as at night. The pulses increase in frequency during a three- to four-year period until the adult pattern is established.

Control of the Onset of Puberty (contd) The stimuli that cause the GnRH pulses are still unclear, but a role for the hormone leptin [the satiety-producing hormone secreted by fat cells] is starting to unfold. Just before puberty, leptin levels rise in proportion to adipose tissue mass. Interestingly, leptin receptors are present in both the hypothalamus and anterior pituitary. EVIDENCE: Mice that lack a functional leptin gene from birth are sterile and remain in a prepubertal state. Giving leptin to such mice elicits secretion of gonadotropins, and they become fertile. Leptin may signal the hypothalamus that long-term energy stores (triglycerides in adipose tissue) are adequate for reproductive functions to begin.

Secondary sexual characteristics Male: Spermatogenesis Growth and development of primary sex organs Secondary sexual character -Spurt of growth-increase the length and girth of the long bone -Increase protein synthesis-that is muscular growth is brought about, males are more muscular

Secondary sexual characteristics (contd) Increase in size of external genitalia Scrotum becomes pigmented & rugose Seminal vesicles enlarge & begin to secrete fructose; prostate & bulbourethral glands enlarge & secrete Skin-becomes more rough, increase in sebaceous glands more prone for acne

Secondary sexual characteristics (contd) Bass Voice [Voice becomes deeper & low pitched due to enlargement of larynx & lengthening & thickening of vocal cords ] Male body conformation-broad shoulder, narrow pelvis Hair pattern & Baldness : hairline on scalp recedes, beard appears, axillary hair appears, general body hair increases at pubis, upward along the linea alba of the abdomen sometimes upto umblicus and above with apex-up-triangle pattern—on face, chest, sometime on back. Mental changes -more aggressive behavior, interest in opposite sex

Secondary sexual characteristics (contd) FEMALE: Changes in bone-causes increase osteoblastic activity, fast growth but earlier unity of epiphyses Board pelvis and narrow shoulder Growth spurt in around 13-15years Development of breast

Secondary sexual characteristics (contd) Deposition of fat in specific region-Thigh,hip,breast,buttocks Development of Hair-Pubic and axila Carrying angle:In male the hands are close to the body and in female its away from the body Skin becomes soft and smooth Voice high pitch Menses

Hypogonadism in the male: Loss of testes before puberty Have infantile sex organs with infantile sexual characteristics throughout life State of Eunuchism ensues Height of an adult eunuch is slightly greater then that of normal male. Voice is childlike No Masculine hair distribution

If the testes are removed there is permanent sterility; owing to absence of testosterone the usual pubertial changes do not occur and the accessory organs of reproduction do not develop; the penis, scrotum, vesiculae seminales, and prostate remain small. There is no growth of hair on face, trunk or axillae; the pubic hair is of the female type, the outline being concave upwards; the growth of larynx is arrested.

There may be abnormal deposition of fat; accumulations may be found on the buttocks, hips, pubis and breasts. The muscles are soft and poorly developed. There is some delay in the union of the epiphyses, but no regular tendency to gigantism; some eunuchs are short, others are tall, and on the whole they show the same range of variations as do normal people. The skin is pale and tans poorly when exposed to sun.

When a man is castrated after puberty Secondary sexual characteristics revert to those of a child The Sexual organs regress slightly in size Voice regresses from the bass only slightly Loss of thick masculine hair, bone and muscle Sexual desires are decreased Erection can still occur with less Ease

OUT COMES Define Puberty Explain the terms thelarche, pubarche, menarche and adrenarche State secondary sexual characteristics and role of hormones(What changes occur in males and females at puberty? ) Explain the terms precocious delayed or absence of puberty