PHYSIOLOGICAL CHANGES DURING PUBERTY & MENOPAUSE

Dr. Amel Eassawi

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OBJECTIVES

Define puberty. List the factors that affect time of onset of puberty in

females and males. Describe the hormonal changes that take place during

puberty in females and males. Outline the functions of pituitary and gonadal hormones

during puberty. Define Menopause and Andropause. Distinguish the hormonal changes that takes place during

menopause.

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PUBERTYPuberty is defined as the stage of physical maturation in which an individual becomes physiologically capable of sexual reproduction.

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ENDOCRINE REGULATION OF REPRODUCTION

Hypothalamus releases GnRH into hypothalamo-hypophyseal portal vessels.

Anterior pituitary secretes: LH (luteinizing hormone). FSH (follicle-stimulating hormone).

Primary effects of LH and FSH on gonads:Stimulation of spermatogenesis and oogenesis.Stimulation of gonadal hormone secretion.Maintenance of gonadal structure.

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ENDOCRINE REGULATION OF REPRODUCTION

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ONSET OF PUBERTY

Wide variation in the onset of puberty:–  Males vs. females.–  Ethnic and racial groups.–  Individual difference(genetic factor).

On average It usually begins between the ages of Males 10-16 years and females 8-14 ( two years earlier in females than males )

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NORMAL TIME RANGES OF PUBERTAL EVENTS (USA)

1. Female pubertal changes usually begin with breast budding followed by pubic hair & menarche.

2. Male pubertal changes usually begin with testicular enlargement followed by pubic hair and penile growth.

FEMALES

MALES

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ONSET OF PUBERTY

While control of the onset of puberty is not clear, two factors are believed to contribute:

1. An intrinsic brain timing mechanism(Agonadal subjects demonstrate increase gonadotropins in the pubertal time periods with both males and females).

2. Changes in hypothalamic sensitivity to gonadal steroid feedback regulation.This mechanism has been called the “Hypothalamic gonadostat “ theory.

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THE HYPOTHALAMIC “GONADOSTAT”[Gonadal Steroids]……Low………………Low……………..….High (Adult level)

[Feedback]…………Sensitive ……Decreasing in Sensitivity …..Adult Sensitivity

[Gonado-tropins] …….Low …………Increasing ………………..High (Adult level)

HYPOTHALAMUS

LH FSH LH LHFSH FSH

Gonad Gonad Gonad

GnRH GnRH GnRH

Puberty is initiated by decreased Gonadostat sensitivity to sex steroid feedback inhibition of gonadotropin secretion

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ONSET OF PUBERTY

1. Increase gonadotropins in the pubertal time: FSH and LH secretion is high in newborn, but falls

to low levels in few weeks.

At puberty secretion of GnRH,FSH,& LH increases and become pulsatile.

Pulsatile pattern of hypothalamo pituitary axis is required for normal reproductive functions.

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ONSET OF PUBERTY2. Changes in hypothalamic sensitivity to gonadal steroid feedback regulation.During childhood , the hypothalamus is extremely sensitive to the negative feedback exerted by the small quantities of estradiol & testosterone produced by the child's ovaries or testes.

As puberty approaches , the sensitivity of the hypothalamus is decreased and subsequently , it increase the pulsatile GnRH secretion initially at night .

The anterior pituitary responds by progressive secretion of FSH and LH associated with increased secretion of growth hormone .

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DEVELOPMENT OF THE PITUITARY-HYPOTHALAMIC AXIS

1. Development of the hypothalamic-pituitary – gonadal axis is a continuous process and from birth through sexual maturity.

2. The first measurable evidence of the impeding onset of puberty is a nocturnal rise in LH.

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GONADOTROPINS & ESTROGEN LEVELS DURING SEXUAL MATURATION

1. Blood gonatotropins levels rise throughout prepubertal years.

2. The rate of gonadotropin rise increases as puberty is approached.

3. Ovarian estradiol secretion shows a threshold response to gonadotropin blood levels.

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INDUCTION OF PUBERTAL GROWTH

1. Gonadal steroids (estrogen + testosterone) induce bone growth and epiphyseal closure.

2. The active agent for this induction in males may be estrogen.

3. GH elevation at puberty is induced by gonadal steroids.

4. Local bone cell secretion of IGF may play a role.

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CIRCADIAN RHYTHM OF LH SECRETION FROM PREPUBERTY TO ADULTHOOD

A major nighttime surge of LH is characteristic of puberty in girls and boys

Smaller nocturnal surges of LH continue through the adult years

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PUBERTY IN FEMALE

The ovaries respond to the increase Gonadotrophin secretion by follicular development & estrogen secretion.

Estrogen causes development of the genital organs and the appearance of the secondary sexual characters .

With increased estrogen secretion, menarche occurs.

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PUBERTY IN FEMALES

The sequence of events in girls are as follows:I. THELARCHE: The development of breast 2. PUBARCHE: The development of axillary and pubic hairs.

3. MENARCHE: The first menstrual period.

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PUBERTY IN FEMALESCharactrstic of Puberty in Females:Folliculogenesis proceedsOvulation for first timeIncrease of Estradiol and progesteroneSecondary sexual characteristics:

– Broadening of hips.– Subcutaneous fat( buttocks, breast, thighs).– Growth of external genitalia.– Pubic hair.– Increased sebaceous gland secretions (adrenal

androgens).

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PUBERTY IN MALES

The testis respond to the increase Gonadotropin secretion by increase in testicular size and increase testosterone secretion.

Testosterone causes development of the genital organs and the appearance of the secondary sexual characters.

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PUBERTY IN MALES

Puberty Changes in Males:Spermatogenesis initiatesIncreased androgen secretionGrowth of accessory sex structures

– Prostate– External genitalia

Male secondary sex characteristics– Facial and body hair– Growth of larynx( deepening of voice)

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CHANGES IN TIME OF ONSET OF MENARCHE (US & WESTERN EUROPE)

1. Early onset of puberty is associated with improved socioeconomic status, nutrition and health.

2. Delayed puberty is associated with chronic disease and malnutrition.

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FACTORS INFLUENCING THE TIME OF PUBERTY

Genetic Factors– Although the interaction of multiple genes on

the timing of puberty is recognized, little is known of the specific gene loci involved.

Environmental Factors– Socioeconomic status– Nutritional status– Health status– Geography– Altitude

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FACTORS INFLUENCING THE TIME OF PUBERTY

The mechanism underlying the pulsatile GnRH secretion  remain unclear The Theories Proposed are: 1. Melatonin secretion by pineal gland. 2. Leptin secretion by adipose tissue. 

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FACTORS INFLUENCING THE TIME OF PUBERTYMELATONIN ROLE

Melatonin is secreted by pineal gland .Secretion decreases by exposure to light and

increses during exposure to dark. It is suggested that , there is observed decrease in

rate of melatonin secretion at puberty (particularly at night).

When peak in GnRH secretion first occur is the trigger for onset of puberty.

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FACTORS INFLUENCING THE TIME OF PUBERTY

ROLE OF LEPTIN

• A satiety producing hormone.• Secreted by adipose tissue.• May play role in hypothalamic maturation at puberty ( delayed onset of puberty in lean or caloric deprived girls).

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FACTORS INFLUENCING THE TIME OF PUBERTYROLE OF LEPTIN

Leptin secreted by adipocytes appears to exert a permissive effect on the timing of puberty and is not considered a metabolic trigger for the event

This effect occurs both directly through receptors on the pulse generator neurons secreting GnRH and indirectly through neural network influences

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MENOPAUSE

• Cessation of woman’s menstrual cycle(Absence of menstrual cycle for at least 12 consecutive months)• Usually occurs between ages of 45 and 55.

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MENOPAUSE 

Preceded by period of progressive ovarian failure characterized by:

– Increasingly irregular cycles.– Declining estrogen levels.

• Loss of estrogen primarily affects skeleton and cardiovascular system.

• Period of transition from sexual maturity to cessation of reproductive capability is called the climacteric or perimenopause.

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MENOPAUSE Characteristic of Menopause:

• Cessation of menstrual cycle

• Loss of ovarian function

• Infertility

• Drop in ovarian steroids (estrogen and progesterone)

• Rise in gonadotropin hormones

• Decrease in ovarian inhibin production

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MENOPAUSE

Symptoms of Menopause:• Hot flashes/flushes.• Mood swings.• Vaginal dryness.• Depression.• Incontinence.• Change in sex drive.• Risk of cardiovascular diseases and

osteoporosis increases.

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MENOPAUSE

What Causes Menopause: • Midlife hypothalamic changes may trigger

onset of menopause.

• limited supply of ovarian follicles present at birth. Once this reservoir is depleted ovarian cycle and menstrual cycle ceases – Follicular reserve provides an exhaustible source of

oocytes that is established around the time of birth.

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MENOPAUSE

Hormone Replacement Therapy in Menopause:

• Estrogen is taken on a daily basis while progesterone is taken less regularly.

• Helps alleviate symptoms such as hot flashes, vaginal dryness and mood swings.

• Slows the progress of osteoporosis; decreased rate of fractures.

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ANDROPAUSE• Male reproductive aging.

• Very gradual compared to menopause.

• Gradual decrease in sperm production and in testosterone production.

• May occur after 45 to 50 years. • Results from degenerative changes in small testicular

blood vessels.

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REFERENCES Human physiology, Lauralee Sherwood, seventh

edition. Text book physiology by Guyton &Hall,11th

edition. Text book of physiology by Linda .s Contanzo,

third edition. Physiology by Berne and Levy, sixth edition.