Sex Differences

Question 1

What is the difference between gender and sex?

Lecture 1

Answer 1

Gender refers to how one identifies and cultural aspects, while sex is biological

Question 2

How is sex determined in mammals?

Lecture 1

Answer 2

Sex is determined by the combination of sex chromosomes inherited from the mother and father: XX for females and XY for males

Question 3

What determines the babies chromosomal sex?

Lecture 1

Answer 3

The presence or absence of Y chromosomes

Question 4

What is the SRY gene and where is it located?

Lecture 1

Answer 4

SRY is located on the Y chromosome and is responsible for turning fetal gonads into testes, which is the determining factor for male development. When SRY is absent, the gonad becomes an ovary.

Question 5

What are the two types of hormones produced by early testes and what do they do?

Lecture 1

Answer 5

1. Anti-Mullerian Hormone:
   * Defeminising
   * Inhibits the development of the Mullerian system
2. Androgens:
   * Masculinising
   * Required for development of the Wolffian system

They both contribute to the development of male sexual characteristics.

Question 6

What are the precursors of male and female sex organs?

Lecture 1

Answer 6

1. Wolffian system (Male sex organs)
2. Mullerian system (Female sex organs)

Question 7

How does a gene mutation affecting anti-Mullerian hormone production impact sex organ development?

Lecture 1

Answer 7

If anti-Mullerian hormone isn’t produced due to a gene mutation but androgens are still present, both male and female internal anatomies can develop

Question 8

What androgen is external genitalia dependent on?

Lecture 1

Answer 8

External genitalia are dependent on the androgen DHT (Dihydrotestosterone) for their development. When DHT is present male external genitalia will develop, when it is not female external genitalia will develop.

Question 9

What are the two types of effects hormones can have on development?

Lecture 1

Answer 9

1. Organizational effects: permanent and occur during sensitive periods.
2. Activational effects: reversible depending on hormone presence

Question 10

What are the characteristics of Persistent Mullerian Duct Syndrome (PMDS)

Lecture 2

Answer 10

PMDS involves the presence of male external genitalia, testes, and both male and female internal genitalia due to incomplete regression of the Mullerian ducts

Question 11

Describe the resulting external genitalia in people with Androgen Insensitivity Syndrome (AIS)

Lecture 2

Answer 11

AIS results in female external genitalia despite having XY chromosomes and testes due to impaired response to androgens (DHT)

Question 12

Explain the difference between organizational and activational effects of hormones

Lecture 2

Answer 12

Organizational effects permanently shape the body during sensitive periods, while activational effects temporarily influence behavior and physiology

Question 13

What is the purpose of Androstenedione

Lecture 2

Answer 13

Androstenedione is responsible for pubic and auxillary hair in both male and female puberty

Question 14

What is a secondary sexual characteristic?

Lecture 2

Answer 14

Any physical characteristic developing at puberty which distinguishes between the sexes but is not directly involved in reproduction

Question 15

What starts puberty?

Lecture 2

Answer 15

Still a mystery however we do know some things
* Genetic component (similar onset to parents/siblings)
* Sex - girls start puberty earlier than boys
* Environment e.g. fat levels Study: In 1840s avg. age of onset:17, whilst in 1960s:13. In both cases on avg. onset occurred when girls were about 47kg (7st 6lbs).

Question 16

What neuroendocrinological processes trigger the onset of puberty?

Lecture 2

Answer 16

1. During childhood, GABA/NPY neurons in the hypothalamus are highly active. These GABA/NPY neurons inhibit KNDy neurons from releasing kisspeptin (their neurotransmitter) and stimulatiing GnRH neurons.
2. As puberty approaches, the activity of GABA/NPY neurons decreases.
3. This reduction in GABA/NPY neuron activity allows KNDy neurons to release kisspeptin and stimulate GnRH neurons
4. This leads to the release of GnRH and subsequent activation of the reproductive axis.
5. The specific cause of this shift in neuron activity during puberty onset remains a mystery

Question 17

neuroendocrinological processes during the onset of puberty

During childhood, which neurons in the hypothalamus are highly active?

Lecture 2

Answer 17

GABA/NPY neurons

Question 18

neuroendocrinological processes during the onset of puberty

What neurotransmitter do KNDy neurons utilize?

Lecture 2

Answer 18

Kisspeptin

Question 19

neuroendocrinological processes during the onset of puberty

What role do GABA/NPY neurons play in inhibiting KNDy neurons?

Lecture 2

Answer 19

GABA/NPY neurons inhibit KNDy neurons, preventing them from stimulating GnRH neurons.

Question 20

neuroendocrinological processes during the onset of puberty

How does the reduction in GABA/NPY neuron activity influence the stimulation of GnRH neurons?

Lecture 2

Answer 20

The reduction in GABA/NPY neuron activity allows KNDy neurond to release kisspeptin which stimulates GnRH neurons, leading to the release of GnRH and subsequent activation of the reproductive axis

Question 21

What is GnRH and what is its role in puberty?

Lecture 2

Answer 21

• GnRH stand for Gonadotropin Releasing Hormone
• GnRHs move from the hypothalamus to capillaires in the stalk of the pituitary gland (entering the bloodstream).
• The anterior pituitary gland is made up of secretory cells. When these detect the GnRH in the bloodstream they release Gonadotropin hormones, which will then also enter the bloodstream.
• Gonadotropin hormones bind to receptors in gonads

Question 22

What hormones begin being secreted by the anteriour pituitary gland during puberty? What are the two types?

Lecture 2

Answer 22

Gonadotropins:

1. Follicle Stimulating Hormone (FSH)
2. Luteinising Hormone (LH)

Question 23

How does FSH (Follicle Stimulating Hormone) affect males and females?

Lecture 2

Answer 23

Males: Sperm production
Females: Cause follicles to ripen

Question 24

How does LH (Luteinising Hormone) affect males and females?

Answer 24

Males: Testosterone production

Females: Induces ovulation and formation of Corpus Luteum

Question 25

Recreate the diagram of the negative-feedback loop showing the regulation of gonadal hormones in males and explain what is happening at each stage

Lecture 2

Answer 25

Diagram - see notes
Brain -> Hypothalamus (releases GnRH) -> Anterior Pituitary (release of Gonadotropins) -> Gonads (releases androgens testosterone from testes) -> Anterior pituitary (testosterone binds to receptors here) -> Hypothalamus ((testosterone binds to receptors here)

This is a negative feedback loop:
1. If testosterone levels go high, it will suppress release of GnRH (which means less FSH and LH).
2. Less LH means less testosterone production, which means testosterone levels go down, which in turn removes this inhibition of testosterone production etc. This is how testosterone levels are controlled in this negative feedback loop.

Question 26

Gonadal hormones in women - The Menstral Cycle
What are the steps?

Lecture 2

Answer 26

1. End of Menstral Flow: At the end of your period there is an increase in FSH causing small spheres of cells called ovarian follicles to begin to grow around individual egg cells (ova)
2. Follicular: The follicles begin to releaser estrogens such as estradiol
3. End of Follicular: The estrogens stimulate the hypothalamus to increase the release of LH and FSH from the anterior pituitary gland
4. Ovulation: In response to the LH surge, one of the follicles ruptures and releases its ovum
5. Luteal: The ruptures follicle under the influence of LH develops into a corpus luteum (yellow body) and begins to release progesterone, which prepares the lining of the uterus for the implantation of a fertilised ovum
6. Premenstural: Meanwhile the ovum is moved into the fallopian tube by the rowing action of ciliated cells. If the ovum is not fertilised, progesterone and estradiol levels fall and the wall of the uterus are cloughed off as menstural flow and the cycle repeats. If the ovum is fertilised the featus would take over the production of progesterone and estradiol.