Chapter 10: SEXUAL DEVELOPMENT Flashcards
What a sexually dimorphic behavior?
A behaviour that has different forms or that occurs with different probabilities or under different circumstances in males and females.
What is intersex?
A variety of combinations of biologically male and female characteristics, such as an individual born with external female genitalia and internal male sex organs.
What does the process of meiosis do?
- production of gametes (ova and sperms)
- Produces cells that contain on set of each of the pairs of chromosomes
What happens at the time of fertilization?
- A person’s genetic sex is determined
- A single sperm and ovum join, sharing their 23 single chromosomes to reconstitute the 23 pairs.
How does the determination of genetic sex happen?
- 22 of the 23 pairs of chromosomes determine the organism’s physical development independent of its sex.
- Last pair consists of 2 sex chromosomes which contain genes that determine the sex.
What pair of sex chromosomes do genetic females have?
- XX
- All ova of a female contain an X chromosome
What pair of sex chromosomes does a male have?
- XY
- Some sperms contain an X some others contain a Y
- A Y-bearing sperm produces a XY ovum so a male.
- A X-bearing sperm produces a XX ovum do a female.
What do the Y chromosomes control in genetic sexual development?
the development of the glands that produce the male sex hormones.
What are the three general categories of sex organs?
Gonads, internal sex organs and external genitalia.
What are the first sex organs to develop?
Gonads (testes or ovaries)
What is the dual function of the gonads?
- produce ova or sperms
- secrete hormones
At which week of prenatal development do foetuses start to form their gonads?
6th week
What factor controls the development of gonads?
- The SRY gene, a single gene on the Y chromosomes
- It acts only when the the undifferentiated gonad is to become testes.
- If the SRY gene is not present, the testes is to become ovaries.
In what case can a XX male be produced?
-SRY gene becomes translocated from the Y chromosome to the X chromosome.
What are the organizational effects of reproductive hormones?
- The effect of a hormone on tissue differentiation and development of sex organs and brain.
- Permanent effect
- Persist throughout person’s life
- Effects occur during prenatal period
What are the activational effects of sex hormones?
- Different effects for each sex
- Occurs at puberty
- May depend on organisms prior exposure to the organizational effects of hormones
- Not permanent.
How can we characterize the internal sex organs in early embryonic development?
- bisexual
- embryos contain precursors for both male and female sex organs
- 3rd month of gestation: only 1 precursor develops.
What is the precursor of the internal female sex organs?
Müllerian system
What the Müllerian system develop into?
- fimbriae
- fallopian tubes
- uterus
- inner two-thirds of the vagina
What is the precursor of the internal male sex organs?
Wolffian system
What does the Wolffian system develop into?
epididymis, vas deferens, seminal vesicles.
What does the development of internal sex organs of a foetus depend on?
presence or absence of hormones that are secreted by the testes.
What are the two types of hormones secreted by testes?
- peptide hormone: anti-Müllerian hormone
- set of steroid hormones: androgens
What does the anti-Müllerian hormone do?
prevents Müllerian system from developing
What do androgens do?
- stimulates the development of the Wolffian system
- masculinizing effect
what are the two androgens responsible for masculinization?
- testosterone
- dihydrotestosterone
How is testosterone converted into dihydrotestosterone?
enzyme called 5a reductase
How is the growth of epididymis, vas deferens and seminal vesicles promoted in the Wolffian system?
- androgen receptors coupled to cellular mechanisms that promote growth and division
- molecules of androgens bind to these receptors
What two genetic disorders illustrate the fact that the internal sex organs of the human embryo could develop as either male or female?
- androgen insensitivity syndrome
- persistent Müllerian duct syndrome
What is the cause of androgen insensitivity syndrome?
congenital lack of functioning androgen receptors
What does androgen insensitivity syndrome cause in a person with XY chromosomes?
- development of a female with testes but no internal organs
- secrete both anti-Müllerian hormones and androgens
What is persistent Müllerian duct syndrome caused by?
-failure to produce anti-Müllerian hormone, or absence of receptors for this hormone
What happens when persistent Müllerian duct syndrome occurs in genetic males?
- androgens have their masculinizing effect
- defeminization does not occur
- person is born with both sets of internal sex organs
What is the Turner syndrome ?
-presence of only one sex chromosome X.
What is the Turner syndrome characterized by?
-lack of ovaries but normal female sex organs
Does the external genitalia require female sex hormones to become female?
No (eg. Turner syndrome)
In what condition will the external genitalia become male?
presence of dihydrotestosterone
What does the development of a person’s external genitalia depend on?
The presence or absence of an androgen.
Figure 10.4
summary
What do the primary sex characteristics include?
gonads, internal sex organs, external genitalia.
What do the secondary sex characteristics include?
- enlarged breasts, widened hips or beard and deep voice
- influenced by the activational effects of hormones and do not appear until puberty.
When does the onset of puberty occur?
- when cells in the hypothalamus secrete gonadotropin-releasing hormones (GnRH)
- stimulates the production and release of gonadotropic hormones by anterior pituitary gland
- stimulate gonads that produce their hormones which are responsible for sexual maturation.
what is the gonadotropic releasing hormone?
Hypothalamic hormone that stimulates the anterior pituitary gland to secrete gonadotropic hormone.
What is a gonadotropic hormone?
A hormone of the anterior pituitary gland that has a stimulating effect on cells of the gonads.
What are the two gonadotropic hormones?
- follicle stimulating hormone(FSH)
- luteinizing hormone (LH)
What does the follicle stimulating hormone (FSH) do ?
The hormone of the anterior pituitary gland that causes development of an ovarian follicle and the maturation of an ovum.
What does the luteinizing hormone do?
A hormone of the anterior pituitary gland that causes ovulation and the development of the ovarian follicle into a corpus luteum.
What is kisspeptin?
- A peptide produced by neurons in the arcuate nucleus of the hypothalamus under the control of leptin receptors.
- controls the secretion of GnRH
- essential for initiation of puberty and maintenance of reproductive ability.
What steroid sex hormone do ovaries produce?
- estradiol
- part of estrogens (class of hormones)
What steroid sex hormones do testes produce?
- testosterone
- part of androgens
What does estradiol cause in females?
breast development, growth of the lining of the uterus, changes in the disposition of body fat, maturation of the female genitalia
What does androgen do in males?
- stimulates growth of facial, axillary (underarm) and pubic hair
- lowers the voice
- alters the hairlines on he head
- stimulates muscular development
- causes genital growth
Table 10.2
Summary
Do X-linked diseases occur more often in male or female?
More often in men
What is the Klinefelter syndrome?
extra X chromosome in a male (XXY genotype)
How prevalent is Turner syndrome?
Affects 1 in 2500 females
How is Turner syndrome most often treated?
- growth hormones during childhood
- hormones to induce pubertal development
- HRT throughout adulthood
How prevalent is Klinefelter syndrome?
Affects 1 in 500 to 1000 males
What is a typical treatment for Klinefelter Syndrome ?
testosterone supplementation
Is SRY the only gene involved in sex determination?
No
What are the stages of prenatal development?
- 0 months: genetic sex
- 2 months: gonadal/hormonal sex
- 5 months: genital sex
What does Androgen Insensitivity syndrome cause?
- X-linked disorder
- causes those with an XY karyotype to develop a female phenotype
What is the cause of Androgen Insensitivity Syndrome?
- Mutations in the androgen-receptor genes
- Which cause a lack of androgen receptors
What physical aspects does androgen insensitivity syndrome cause?
- Prevent the body tissue from masculinizing to some degree
- But tissue does respond to estrogen
What does an individual with CAIS look like and what sexuality do they tend to have?
- Complete Androgen insensitivity
- Female genitals
- Tend to identify as heterosexual
What does an individual with PAIS look like ?
- Partial Androgen Insensitivity
- intermediate characteristics, with differing degrees of genital masculinization.
What does Congenital Adrenal Hyperplasia cause?
- causes individuals to be exposed to high levels of androgens before birth
- causes varying degrees of virilization in female genitals
how prevalent is CAH?
-Affects about 1 in 5000-1500
What do the genitals of people affected by 5-Alpha-Reductase deficiency look like at birth?
- Female-typical external genitalia
- Male internal genitals
What is 5-RT caused by?
enzyme deficiency
