physiology of puberty

1. Physiology of Puberty
Dr. Ramadan Saad

2. Learning 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

3. Reproductive System

4. • Gonads
– primary reproductive organs
– testes (testicles)
– site in which gametes (sperm) are made
• Sperm
– male haploid cells that can fertilize an egg to form a zygote
• Accessory reproductive organs
– needed for sperm maturation and delivery of sperm to the
female
– include external genitalia – penis and scrotum
– include internal structures – epididymes, prostate, 2
seminal glands, and the 2 bulbourethral glands.
• Scrotum
– pouch of skin that hangs outside the body that contains
the 2 testes and associated ducts
– externally located to keep the testes at a cooler temp to
maximize sperm production
Male Reproductive Overview

5. • The ovaries
– oocyte
• egg cell
– ovulation
• release of egg from the ovary
• Ducts of the female
reproductive system
– uterine tubes
• connect ovary to uterus
• Uerus–womb
– endometrium
– cervix
Female Reproductive System Overview
• Vagina
– birth canal
• External genitalia
– labia–majora and minora
– clitoris
• Mammary glands
– lactation

6. 6

7. Definition of Puberty:
Puberty is the stage of physical maturation in which an individual
becomes physiologically capable of sexual reproduction.
On average It usually begins between the ages of 10-14 years,
(two years earlier in females than males)

8. 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.
• 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.

9. 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.
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.
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.

10. What causes initiation of puberty
in humans?
• The mechanism underlying the
pulsatile GnRH secretion remain
unclear. The theories proposed
are
– Melatonin secretion by pineal
gland
– Leptin secretion by adipose tissue
10
Melatonin secretion
• Melatonin is secreted by pineal
gland.
• 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.
Leptin 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).

11. Physical Growth…At the beginning of adolescence, however,
the pituitary gland and hypothalamus
release additional hormones.
Adolescent hormones cause an…
A. overall growth spurt, including increased size, strength, and stamina;
adolescents may experience clumsiness adjusting to rapidly growing bodies.
B. increased activity in sebaceous (oil-producing) glands which can cause skin
breakouts
C. Increased activity in sweat glands which can cause stronger body odor.

12. MALE Changes During adolescence, the
testes in males start
producing more
testosterone.
Enlargement of the testes
and scrotum, followed about
a year later by growth of the
penis.
The first ejaculation,
(emission of semen) may
occurs during sleep.
These first emissions usually
do not contain fertile sperm.
The heart, lungs, prostate gland, and seminal vesicles also
increase in size; boys produce more red blood cells than
girls.
These changes normally begin to occur between the ages of
9-14 years and are completed between ages 12 and 16 years.

13. At the beginning of the
adolescent period, the
ovaries in females produce
more estrogens.
Enlargement of the labia and
clitoris, as well as the
development of the uterus
and vagina.
The first menstrual cycle, or
menarche occurs at the age
of 12 – 12 ½.
The first ovulation of an egg
occurs a year or more later.
FEMALE Changes

14. BOTH Secondary sex characteristics also develop
during adolescence. These are physical
changes that do not directly affect
reproduction, but are associated with
sexual maturation.
Secondary sex characteristics in males
include pubic, underarm, and facial hair
growth, deepening of the voice, and the
ability to increased muscular development.
Secondary sex characteristics in
females include fat deposits on
breasts and hips, a widening of the
pelvic bowl, and growth of underarm
and pubic hair.

15. Summary

16. Try to answer the following questions
In a young boy diagnosed
with precocious puberty,
puberty is best delayed by
the administration of a long-
lasting preparation of which
of the following?
A. Estrogen receptor
antagonist
B. FSH receptor antagonist
C. GnRH receptor agonist
D. Growth hormone receptor
antagonist
E. Testosterone receptor
agonist
In experiments designed to
accomplish male contraception,
immunization to produce antibodies
capable of both binding and
neutralizing the bioactivity of human
FSH is being investigated. Men
immunized in this manner would be
expected to exhibit which of the
following?
A. Depressed hypothalamic GnRH
secretion
B. Depressed serum inhibin levels
C. Depressed serum testosterone
levels
D. Elevated serum LH
E. Enhanced secretion of growth
factors by Sertoli cells
A 24-year-old male has been
lacking the production of
testosterone since early
childhood and has not been
treated. He will likely exhibit
which of the following signs?
A. Be somewhat taller than
average
B. Have a deep voice
C. Have abundant chest hair
D. Have no pubic or axillary
hair
E. Undergo premature
baldness

17. Take home message
• Puberty onset is due to pulsatile secretion of GnRH
• Hypothalamic pituitary gonadal axis is the main controller of
reproductive functions
• Adrenal androgens are responsible for the very early puberty
signs
• Nutrition is an important factor in puberty besides other
factors

18. 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