Introduction to human sexual behaviors Differentiation, quick review of internal and external organs, hormones and related disorders

1. Introduction
to Sexual Behaviors
Sofia Balali, BSc
SUNY

2. Why do we
reproduce?
 Reproduction increases
the variation in the gene
pool
 Quick evolutionary
adaptation to environment
 Correction of genetic
errors & mutations

3. Sex Determination
Presence or
absence of Y
chromosome
Types of
gonads
Sex
hormones
Internal
genitalia
External
genitalia

4. Sex differentiation Stages
1.embryological stage(conception-8th week)
2. fetal stage (9th week until birth)
3. later life( e.g. puberty)
Differentiation
between the sexes
of the sex
organs(internal and
external) occurs
throughout:

5. Sexual Characteristics
Primary sex characteristics
changes to the sexual organs (uterus, vagina, penis, ,testes)
Secondary sex characteristics
visible changes that mark adult maturation (height, body shape,
body hair and so on)

6. Sex Determination
chromosomes
Sexual differentiation begins at chromosomes
At fertilization a chromosome from the sperm cell (X or Y) fuses with the X
chromosome in the egg cell
Y chromosome factors (SRY gene) trigger male development
Females do not have the SRY gene (Do not forget there are only XX)
Males XYFemales XX

7. Sex determination
gonads

8. Internal Differentiation
 Around 7 weeks
 Strong hormonal influence
Male
Mesonephric Duct->
Wolffian Duct
SRY
gene
Gonads
testes
Androgens, testosterone
anti-Mullerian hormone
Female
Paramesonephric Duct->
Mullerian Duct
No SRY
gene
Gonads
ovaries
Estrogens

9. Internal Genitalia
Male
Mullerian
inhibiting
hormone
causes
Mullerian
Ducts to
regress
Female
Wolffian
Ducts regress
in the
absence of
Androgens
https://basicmedicalkey.com/structure-and-function-of-the-reproductive-systems/

10. External Differentiation
 Around 8-12 weeks
 Further sex differentiation of the external genitalia occurs at puberty
Male
penis
scrotum
epididymis
testes
Female
vulva or pudendum includes:
Mons pubis Labia Majora
Labia minora
clitoris
Vestibule
perineum

11. Sex Determination
hormones
Organizing effects: determine sex characteristics
Activating effects: activate particular response
promote development of features
influence brain activity
influence neuronal survival

12. Other hormones
Estrogen: primary female sex hormone, responsible for the
development and regulation of the female reproductive system and
secondary sex characteristics (estrone, estradiol, and estriol)
Prolactin: released after birth for milk production
Vasopressin: for long-term bond and olfactory recognition

13. Other hormones
 In the absence of sex hormones the genitalia will develop to be female-like
 However extra estradiol seems to have no effect on the looks
Oxytocin: love hormone
FSH :follicle stimulating hormone, women release their
eggs and men produce sperm
Testosterone: primary male sex hormone and anabolic
steroid, responsible for the development of male
reproductive tissues such as testes and prostate and
secondary sexual characteristics

14. Some Disorders
 Turner's Syndrome
a chromosomal condition that affects development in females
 Klinefelter syndrome,
a boy is born with an extra X chromosome (XXY)
 Androgen insensitivity syndrome
appear to be female at birth, but do not have a uterus, fallopian tubes
or ovaries
 Intersex
several variations in sex characteristics, discrepancy between the
external genitals and the internal genitals (the testes and ovaries

15. Extra information
https://embryology.med.unsw.edu.au/embryology/index.ph
p/Embryonic_Development
https://www.gfmer.ch/Books/Reproductive_health/Human_
sexual_differentiation.html
https://basicmedicalkey.com/structure-and-function-of-
the-reproductive-systems/#s0030
https://www.nature.com/scitable/topicpage/genetic-
mechanisms-of-sex-determination-314/