Physiological Changes D uring P uberty & Menopause
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Transcript of Physiological Changes D uring P uberty & Menopause
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Physiological Changes During Puberty & Menopause
Dr.Mohammed Sharique Ahmed QuadriAssistant professor physiology
Al Maarefa College
بسم الله الرحمن الرحيم
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Objectives • Define puberty
• List the factors that affect time of onset of puberty in boys and girls
• Describe the hormonal changes that take place during puberty in boys and girls
• Outline the functions of pituitary, gonadal and adrenal hormones during puberty
• Define menopause
• Distinguish the hormonal changes that takes place during menopause
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Definition of Puberty:
Puberty is the stage of physical maturation in which an individual becomes physiologically capable of sexual reproduction.
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Onset of Puberty
• Wide variation in the onset and duration of puberty– Males vs. females– Ethnic and racial groups– Individual difference(genetic factor)
• On average It usually begins between the ages of 10-14 years,( two years earlier in females than males )
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Endocrine Regulation of Reproduction
• Hypothalamus releases LHRH (GnRH) into hypothalamo-hypophyseal portal vessels.
• Anterior pituitary secretes:– LH (luteinizing hormone). – FSH (follicle-stimulating hormone).
• GnRH Secreted in pulsatile fashion to prevent desensitization and down regulation of receptors.
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Endocrine Interactions
• Anterior pituitary secretes LH and FSH.• Secretion of LH and FSH stimulated by LHRH
(GNRH).– 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
• Negative feedback:– Inhibits GnRH from
hypothalamus.– Inhibits anterior pituitary
response to GnRH.• Inhibin secretion inhibits
anterior pituitary release of FSH.
• Female: – Estrogen and
progesterone.• Male:
– Testosterone.
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Onset of Puberty
• 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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How does puberty begin ?
• 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 .
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• 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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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 Girls
• The sequence of events in girls are as follows
I. THELARCHE: The development of breast II. PUBARCHE: The development of axillary and
pubic hairs
III. MENARCHE: The first menstrual period
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Pubertal Changes in Females
• Folliculogenesis proceeds• Ovulation for first time• Increase of Estradiol and progesterone• Secondary 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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In Males
• The testis respond to the increase Gonadotrophin 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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Pubertal Changes in Males
• Spermatogenesis initiates• Increased androgen secretion• Growth 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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CHRONOLOGICAL ASPECT(changes in boys and girls at puberty)
GIRLS• Acceleration of growth
rate • Development of breasts
and pubic hair• Axillary hair • Menarche
BOYS• Increase of testicular
volume• Increase of penile
length• Pubic hair• Increased growth rate• Axillary hair• Deepening of the voice
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• What causes initiation of puberty in humans ?• The mechnismunderlyig the pulsatile
GnRH secretion remain unclear. The theories proposed are –Melatonin secretion by pineal gland –Leptin secretion by adipose tissue
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Factors responsible for initiating pubertyMelatonin secretion
• 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 responsible for initiating pubertyLeptin secretion
• 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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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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What Causes Menopause
• Midlife hypothalamic change 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
• Preceded by period of progressive ovarian failure characterized by – Increasingly irregular cycles– Dwindling 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 (Reproductive Decline)
• 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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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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Hormone Replacement Therapy
• 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 by Lauralee Sherwood, seventh edition
• Text book physiology by Guyton &Hall,11th edition
• Text book of physiology by Linda .s contanzo,third edition