Sexual growth and development

DR NILESH KATE
MBBS,MD
PROFESSOR
ESIC MEDICAL COLLEGE, GULBARGA.
DEPT. OF PHYSIOLOGY
Sexual Growth
and Development

OBJECTIVES
 PRE-PUBERTAL SEXUAL GROWTH AND
DEVELOPMENT
 Sex determination
 Sex differentiation
 Disorders of sexual development
Friday, June 19, 2020

SEX DETERMINATION
 Human chromosomes
 Human gametes
 Genetic sex determination
 Formation of Barr body

Sex determination
(Genetic differentiation)
 Genotype of the fetus,
whether male or
female.
 Determined by the
presence of sex
chromosomes,
 So also known as
chromosomal sex
differentiation

Human chromosomes
 Each cell in a normal adult male and female
possesses 46 chromosomes (44 autosomes +
2 sex chromosomes)
 Except ovum and sperm

Gametogenesis
Primitive
germ cells
oogonia
Meiosis
Reduction
division
Ova
22X
Primitive germ
cells
Spermatogonia
Meiosis
Reduction
division
Sperm
22Y

Genetic sex determination
 Occurs during
fertilization, i.e.
penetration of the
ovum by the sperm.

Formation of Barr body
 One of X chromosomes of
somatic cells in the female
embryo becomes inactive
while the other remains
active.

Formation of Barr body
 The inactive X
chromosome of each
somatic cell forms a
condensed mass called sex
chromatin or Barr body

Significance of Barr body
• By cytological tests.Identification
of sex
genotype
• In abnormal cells with 3
or more x chromosomes,
there are 2 or more barr
bodies.
Identification
of abnormal
genotype.

Sex differentiation

Gonadal Differentiation
 Gonadogenesis
 Formation of gonads, i.e. testes in males and
ovaries in females.
 Dependent on the genotype of the embryo.

Genital Ridge
 Condensation of
mesenchymal tissue
present on each side near
the adrenal glands.
 Proliferation of both
germinal and non-germinal
cells migrated to genital
ridge leads to formation of
bipotential gonads.

Bipotential Gonads
 Primordial or primitive or
indifferent or ambisexual
gonads.
 Up to 6 weeks of gestation
the bipotential gonads are
identical in both sexes

Structure.
 Consists of a medulla, a
cortex and primordial
germ cells.
 The germ cells are
embedded in the layer
of cortical epithelium
surrounding a core of
medullary
mesenchymal tissue

Testicular Differentiation
 At about 6th week
 At about eighth week
 At about ninth week
 At about the 35th week

At about 6th week
 Begins with the
appearance of primitive
seminiferous cords (sex
cords) from the
germinal epithelium
covering the medulla of
bipotential gonad

At about eighth week
 Leydig (interstitial) cells
appear in the interstitial
spaces of seminiferous
tubules and continue to
proliferate.

At about eighth week
 The membrane of Leydig cells has receptors
for human chorionic gonadotropins (HCG)
and for luteinizing hormone (LH).

At about ninth week
 The Leydig cells synthesize and secrete
testosterone in response to HCG secreted by
placenta.

At about the 35th week
 Occurs descent of testes through inguinal
canal into scrotum.
 Final stage of testicular differentiation.

Role of Y chromosome in
testicular differentiation
 Y chromosome contains
2 transcription genes,
 For Testicular
differentiation
 For the formation of
Mullerian duct inhibitory
substance (MIS)

Gene for testicular
differentiation
 Called SRY gene (Sex-determining region of
the Y chromosome)
 Encodes the testis-determining factor (TDF) -
triggers the testicular differentiation.
 The TDF gene product causes Sertoli cell
differentiation.

Ovarian Differentiation
 By 10th week occurs in the absence of TDF.

Genital Differentiation
 Differentiation of
internal genitalia
 Differentiation of
external genitalia

Differentiation Of Internal
Genitalia
 During 6th week - neutral sex anlagen develops
along with the development of bipotential gonad.
 The primordia consists of 2 ducts
 Paired set of Wolffian (male) ducts
 Paired set of Mullerian (female) ducts.
 By seventh week of gestation, the embryo has both
male and female primordial ducts

Differentiation Of Male
Internal Genitalia
 Leydig cells secrete
testosterone –stimulate
wolffian duct & forms
epididymis, vas
deferens & seminal
vesicles.
 The MIS causes
regression of the
Mullerian ducts by
apoptosis.

Differentiation Of Female
Internal Genitalia
 In the absence of MIS,
the female ducts
(Mullerian ducts)
proliferate and form
oviduct (uterine tubes),
uterus and upper two
thirds of vagina.
 In the absence of
testosterone, Wolffian
ducts degenerate.

Differentiation Of External
Genitalia
 Develop from common
anlagen, which are the
urogenital sinus, the
genital sinus, the genital
tubercle, the genital
swelling and the genital
(urethral) folds

Differentiation Of External
Genitalia
 The external genitalia are bipotential till
eighth week of gestation,
 i.e. it can develop along either male or female
lines.

Psychological Differentiation
 It is determined by the effect of androgens
on the development of brain in the
embryonic stage.

Disorders Of Sexual
Development
 Chromosomal abnormalities.
 Hormonal abnormalities.

Chromosomal Abnormalities
 Trisomy
 Monosomy

Trisomy
 During gametogenesis
due to non-disjunction
of sex chromosomes.
 The presence of extra
X or Y chromosome
(Trisomy)

XXY pattern of chromosomes
 Klinefelter syndrome
 Characteristic features
 Poor development of testis
with hyalization of
seminiferous tubules, leading
to sterility. (seminiferous
dysgenesis.)
 Patient has normal male
internal and external
genitalia.

XXY Pattern Of Chromosomes
 Patients are usually tall
(due to growth of lower
body segment) and
obese.
 Gynaecomastia
(development of breast
in male).
 The secondary sex
characters are poorly
developed.

XXX (Genotype) Pattern Of
Chromosomes
 poor sexual development
(infantile), scanty
menstruation and mental
retardation.
 Low or normal plasma
testosterone level,
 High plasma level of
gonadotropins (LH and FSH),
 High plasma level of
oestradiol
 Positive sex chromatin test

Monosomy
 Turner’s syndrome.
 (karyotype) is 44 + XO
 ovarian dysgenesis because of XO karyotype.
 Puberty is delayed, scanty menstruation,
amenorrhoea (no menstruation), primary
infertility and amastia.

Turner Syndrome
 mental retardation
 Dwarfism.
 Webbed neck (folds of skin
on the side of the neck
 face is peculiar with low
hair line, ptosis (drooping
of eyelids),
 epicanthus (low set ears),
micrognathia (small jaw)
and co-arctation of aorta

Diagnosis Of Chromosomal
Abnormalities
 Amniocentesis - by inserting a needle into
the amniotic cavity through anterior
abdominal wall.
 Chorionic villus sampling - by a needle
biopsy of chorionic villi.

Hormonal Abnormalities
 Pseudohermaphroditism - individual
having genotype (gonads) of one sex (either
testes or ovaries) and genitalia of other sex.
 True hermaphroditism - gonads of both
sexes are present; its rare.

Pseudohermaphroditism
 Female – Genotypically
–female.
 Gonads and internal
genitalia are feminine
like (ovaries, oviduct
and uterus are present),

 But at pre-pubertal
age masculinization
occurs in the form of
diamond-shaped
pubic hair growth and
development of penis.
 Increased plasma
levels of testosterone
and androgens

 Male
 Androgen resistance – gynaecomastia
 Testicular feminising syndrome
 Defective testicular development.
 Congenital 17α hydroxylase deficiency –
deficient testosterone.
 Congenital blockade of pregnenolone
formation

Sexual growth and development

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