PUBERTY and pubertal changes of human.pptx

about the changes happening during the puberty

1. PUBERTY

2. Definitions of puberty and adolescence vary. Puberty is the physiological phenomenon of attainment of sexual maturity . T he onset of adult sexual life Adolescence is the broader period of time including puberty and extending until a person attains full adult height.

3. 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. The hypothalamic-pituitary-gonadal axis is activated The events of puberty occur in the same sequence in all individuals, but the age at which they occur varies widely

4. Age of Onset of Puberty The age of onset of puberty varies depending on various factors like socioeconomic and environmental conditions and genetic constitutions. In general, in developed countries, puberty occurs earlier than in the developing countries. In advanced nations, it occurs between the age of 8–13 in girls and 9–14 in boys. In developing nations, the age of onset of puberty is 11–16 years in girls and 13–18 years in boys

5. Puberty represents the earliest time that reproduction is possible. The ability to reproduce is attained with puberty and ceased with menopause. In females, reproducibility totally stops at menopause, whereas in males reproducibility continues

6. Total rates of secretion of gonadotropic hormones throughout the sexual lives of female and male

7. Another event that occurs in humans at the time of puberty is an increase in the secretion of adrenal androgens. The onset of this increase is called adrenarche . It occurs at age 8–10 years in girls and age 10–12 years in boys. Dehydroepiandrosterone (DHEA) values peak at about age 25 in women and slightly later than that in men. They then decline slowly to low values in old age. The rise appears to be due to an increase in the activity of 17α-hydroxylase

8. Stages of Puberty

9. In Boys The pubertal development in males occurs in five stages. Usually it is completed within 2 to 4 years from its onset . Stage 1 This is the preadolescent stage . There is no enlargement of external genitalia (penis, scrotum and testes). No pubic hair is present. However, secretion of adrenal androgen is increased ( adrenarche ). Stage 2 Testes enlarge to more than 2.5 cm, which occurs due to growth of seminiferous tubules. 1. Though this occurs due to the secretion of adrenal androgen ( adrenarche ), testicular androgen also contributes. 2. Testicular testosterone secretion increases significantly. 3. Pubic hairs appear in scanty at the root of the penis .

10. Stage 3 Penis enlarges in length . Scrotum and testes are further enlarged. Pubic hairs become darker and coarser above the pubis. Sperm first appears in the morning sample urine ( spermarchy ). Stage 4 Penis enlarges in width and further in length. Scrotal and testicular enlargement continues. Pubic hair becomes adult type. Ejaculation of sperm occurs either in dreams, or on masturbation or by sexual act. Stage 5 Full adult pattern of sexual features develops

11. In Girls The pubertal development in females also described in five. Usually, it is completed within 2 to 5 years from its onset . Stage 1 This is the preadolescent stage . There is no breast development. No pubic hair is present. However, secretion of adrenal androgen is increased ( adrenarche ). Stage 2 Breast development starts ( thelarche ). Breast paillae is elevated and the diameter of areola is increased. Secretion of estrogen from ovary increases significantly. Sparse hairs appear along the labia majora .

12. Stage 3 Breast enlarges with enlargement of areola. Pubic hairs develop , grow and become dark ( pubarche ). Hairs appear in axilla. Stage 4 Breast further enlarges with areola and papillae projecting out of it. Pubic hair becomes adult type, but covers smaller area . Menstrual cycle starts ( menarche ), but irregular at the beginning . Stage 5 Full adult pattern of breasts and pubic hairs develop. Menstrual cycle occurs regularly

13. Mechanism of Onset of Puberty

14. 1. Dehydroepiandrosterone (DHEA) secreted from adrenal gland plays some role in the maturation of hypothalamic neurons . 2. The adipose tissue via secretion of leptin also plays some role in the determination of the time of onset of puberty. 3 . Normally, the secretion of GnRH , LH and FSH is not pulsatile before the onset of puberty. It is clear that until puberty the release of GnRH is non-pulsatile , which prevents puberty to occur.

15. Role of Leptin Body fat is crucial to a female’s ability to sustain the caloric demands of pregnancy and lactation, so girls and women don’t ovulate if they have too little of it. A girl must attain about 17% body fat before she can begin to ovulate and menstruate, and adult women commonly cease if they drop below 22% fat.

16. How does the brain know if fat reserves are adequate for reproduction? Leptin , the hormone secreted by fat cells, acts as an adiposity signal to the brain. If the leptin level is too low, the hypothalamus doesn’t secrete gonadotropin-releasing hormone ( GnRH ). Puberty is therefore delayed in undernourished girls, unusually thin girls, and in other girls with low body fat due to such vigorous and habitual physical activity as gymnastics and ballet . Ovulation and menstruation may cease even in adult women who become underweight.

17. Abnormalities of Puberty

18. Precocious Puberty 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

19. Classification of the causes of precocious sexual development in humans

20. The youngest mother known to history was Lina Medina of Peru, who began menstruating at 8 months of age, was impregnated at age 4 , and gave birth at age 5 , in 1939.

21. Delayed or Absent Puberty 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 .

22. 1. It occurs usually due to panhypopituitarism that causes failure of maturation of gonads. 2 . It is also associated with chromosomal abnormality of XO pattern or gonadal dysgenesis . 3. Puberty may be delayed in spite of presence of normal gonads , which is called eunuchoidism in males and primary amenorrhea in girls.

23. References GUYTON AND HALL TEXTBOOK OF MEDICAL PHYSIOLOGY, THIRTEENTH EDITION Ganong’s Review of Medical Physiology TWENTY-FIFTH EDITION Comprehensive Textbook of Medical Physiology Human Anatomy & Physiology, TENTH edition, Elaine N. Marieb, Katja Hoehn ANATOMY & PHYSIOLOGY, Ninth Edition, KENNETH S. SALADIN.

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