Chapter 11 - Reproductive Behaviour Flashcards
Describe androgens and estrogens.
Androgens and estrogens are steroid hormones. A moderate amount of cholesterol is necessary for generating these hormones.
Steroids exert their effect by:
1. They bind to membrane receptors, like neurotransmitters, exerting rapid effects
2. They enter cells and activate certain kinds of proteins in the cytoplasm
3. They bind to receptors that bind to chromosomes, where they activate or inactivate certain genes
Androgens and estrogens are categories of chemicals, not specific chemicals. Testosterone is an androgen and estradiol is an estrogen.
Androgens promote the development of typically masculine features. Estrogens promote typically female features. These hormones also influence. Activity in many brain areas with some areas bigger in the male brain. However, some of the differences are directly controlled by the X and Y chromosomes, independent of the hormones.
What are Müllerian ducts, Wolffian ducts and gonads?
Male and female mammals start with the same anatomy.
The male’s Y chromosome includes the SRY (sex determining region of the Y chromosome) gene which causes the gonads to develop into testes. The testes produce androgens. These hormones encourage the continued growth of testes and the Wolffian ducts to become seminal vesicles (saclike structures that store semen) and the vas deferents (a duct from the testis into the penis). The testes also produce zmullerian inhibiting hormone (MIH) which cause the Müllerian ducts to degenerate.
Because the females do not have the SRY gene, their gonads develop into ovaries and their Wolffian ducts degenerate. With no MIH, the Müllerian ducts develop and mature into oviducts, uterus and the upper vagina.
What are the organising effects of sex hormones?
The organising effects produce long lasting structural effects. The most prominent effects occur during a sensitive stage of early development. The time before birth, just after birth and puberty.
What are the activating effects of hormones?
These are more temporary, when a hormone increases some activity that lasts only while the hormone is present. Activating effects occur at any time in life. The distinction between organising and activating effects is not absolute as a hormone can produce a combination.
What causes the organisation effects on the development of genitals?
It is dependent on testosterone levels. A high level of testosterone causes male genitals, a low level leads to female genitals. It promotes the male pattern and inhibits the female pattern. Estradiol produces important on the internal organs but has little effect on the external genitals.
What drugs tend to feminise or fe masculine early development?
Alcohol, marijuana, cocaine. Male development is also vulnerable to estradiol like compounds found in the linings of plastic bottles and cans.
Describe the overall mechanism of early development.
Nature’s default setting is to make every mammal a female. Add early testosterone and the individual becomes a male, without testosterone it becomes female regardless of anything else. Remember that this is a generalisation.
How do sex hormones influence the hypothalamus?
Early in life, they influence development in parts of the hypothalamus, amygdala, and other brain areas. Eg. One area in the anterior hypothalamus, known as the sexually dimorphic nucleus, is larger in males and contributes to control of male sexual behaviour. Parts of the female hypothalamus generate a cyclic pattern of hormone release, as in the human men’s trail cycle.
How do hormones within the mother’s body influence toy choice of the children?
Girls exposed to higher levels of testosterone in prenatal life showed slightly elevated preference for boy’s toys. Sons of women with high phthalate levels showed less interest in boys’ toys and more interest in girls’ toys.
Activating effects, please note
At any time in life levels of testosterone and estradiol exert activating effects, modifying behaviour. Changes in hormonal secretions influence sexual behaviour within 15 mins. Behaviours can also influence hormonal secretions.
How do hormones impact on non sexual behaviour?
Testosterone decreases pain, anxiety, and estrogens probably do to. Decreases in sex hormones lead to impairments of memory. Estrogens directly stimulate parts of the prefrontal cortex that are important for working memory. Testosterone decreases trust
How does testosterone impact on sexual behaviour?
Among men levels of testosterone correlate positively with sexual arousal and the drive to seek sexual partners. Married and committed men tend to have lower testosterone. Single women also has higher testosterone. These were not causal sowe don’t know if marriage impacts on hormone levels or if those with low levels get married. High testosterone is linked with additional sex partners, whilst low decreases sexual activity.
Low testosterone is not the basis of impotence, it is impaired blood circulation.
Testosterone reduction has been used as a means of controlling sex offenders. Issues, they refuse to take the tablet. Side effects include weight gain, diabetes, depression
Describe the processes involved in the menstrual cycle
A woman’s hypothalamus and pituitary interact with the ovaries to produce the me steal cycle.
- After the end of the menstrual period, the anterior pituitary releases follicle stimulating hormone (FSH) which promotes the growth of a follicle in the ovary.
- The follicle nurtures the ovum (egg cell) and produces several types of estrogen, including estradiol.
- Towards the middle of the cycle, the follicle builds up more and more receptors to FSH, so even though the actual concentration of FSH in the blood is decreasing, it’s effects on the follicle increases. As a result the follicle produces increasing amounts of estradiol
- The increased release of estradiol causes an increase of luteinizing hormone (LH) from the anterior pituitary
- FSh and LH combine to cause the follicle to release the ovum.
- The remnant of the follicle releases the hormone progesterone, which prepares the uterus. For the implantation of a fertilised ovum.
- Progesterone also inhibits further release of LH. Towards the end of the menstrual cycle the levels of LH, FSh, estradiol and progesterone all decline.
- If the ovum is not fertilised, the lining of the uterus is cast off and the cycle begins again
- If the ovum is fertilised, the levels of estradiol and progesterone increase gradually during pregnancy
What causes the nausea during pregnancy?
High steadily and progesterone levels fluctuates the activity
At the serotonin 3 receptor
How do birth control pill work?
They interfere with the usual feedback cycle between the ovaries and the pituitary.
The most widely used birth control pill, the combination pill, containing estrogen and progesterone, prevents the surge of FSH and LH that would otherwise release the ovum. The estrogen-progesterone combination also thickens the mucus of the cervix, making it harder for a sperm to reach the egg, and prevents an ovum, if released, from implanting in the uterus
What is the periovulatory period?
It is the days around the middle of the menstrual cycle when fertility is at max levels, as is the estrogen level. Studies have found that women not on birth control pills initiate more sexual activity during this time. Other studies found that lap dancers earns more money at this time. Women are also more attentive to sexual related stimuli at this time (can distinguish between make and female faces faster)
Outline how oxytocin is important for reproductive behaviour
Oxytocin is a pituitary hormone. It stimulates the contractions of the uterus during the delivery of the baby. It stimulates the mammary glands to produce milk. Sexual pleasure releases oxytocin, especially after orgasm. This hormone causes the relaxed feeling, the calmness and lack of anxiety experienced after orgasm. When people inhale a nasal spray containing oxytocin, they become more accurate at recognising familiar faces. It can make you more attentive to ones you love.
Are hormonal changes necessary to install human parental behaviours?
No
What is sexual selection?
Part of Darwin’s theory of evolution was that genes that make an individual more appealing to the other sex will increase the probability of reproduction, and therefore the next generation will resemble those who had the favourable genes.
In animals this is not always practical because it may be no good for survival eg. Brighter colours also makes you more vulnerable to attack.
In humans however, to some extent women have evolved based on what appeals to men and men have evolved based on what appeals to women.
What are the benefits of having multiple partners?
Males - more men seek casual sex relationships than women. Why? The theory is to spread one’s genes.
Women - benefits of multiple partners may appear if your partner is infertile, may provide additional support to herself and her children, trading up
What do males and females seek in a mate?
Almost all seek romance, healthy, wealthy, honest and physically attractive.
Women - want a mate who is a good provider. A woman is much more likely to reject a man because of his smell. Research has found that a woman tends to be less sexually responsive to a man whose immune genes and therefore body door are too similar to her own. This may be a way of avoiding inbreeding
Men - prefer young partners (more likely to be fertile for longer. Also men remain file for longer so this is not a requirement for females)
Why do men tend to be more jealous?
If a man is to pass on his genes he needs to be sure that the children he supports are his own. An unfaithful wife threatens that certainty.
What is gender identity?
This is how we identify sexually and what we call ourselves. Biological differences are sexual differences but differences that result from people’s thinking about themselves are gender differences. Gender identity is a human characteristic.
What are hermaphrodites?
Individuals who appear to be a mixture of male and female.
- People with XX chromosomes may have either an ovary and a testis, or two testis, or a mixture of ovaries and testis tissue on each side.
- An atypical hormone pattern like a genetic male with low levels of testosterone or a deficiency of testosterone receptors may develop female or intermediate appearance. A genetic female whi is exposed to high levels of testosterone can appear partially masculinised.
- The most common form of this is congenital adrenal hyperplasia (CAH) meaning overdevelopment of the adrenal glands at birth
What is a congenital adrenal hyperplasia?
The overdevelopment of the adrenal glands from birth.
Ordinarily, the adrenal gland has a negative feedback relationship with the pituitary gland. The pituitary gland secretes adrenocorticoptropic hormone (ACTH), which stimulates the adrenal gland. Cortisol, one of the hormones from the adrenal gland, feeds back to decrease the release of ACTH. Without this feedback mechanism from the cortisol, the pituitary continues secreting ACTH, causing the adrenal to secrete larger amounts of its other hormones, including testosterone. In a male this causes no issues, in genetic females they develop varying degrees of masculinisation of their external genitals. After birth these children are given medical treatments to bring their adrenal hormones within normal levels. Some are given surgery to alter their appearance.
Who are intersects?
People whose sexual development is intermediate are called intersexes.
How to raise an intersex child?
For many years most intersex people were raised as girls based on the assumption that surgery could make them look like normal girls and that they would develop behaviours corresponding to how they were reared.
Results - girls were intermediate in their preference for girls and boys without CAH in terms of their preferences for toys. A study a adolescent girls found their interests to be intermediate to those of typical boys and girls. In adulthood they show more physical aggression than most women and are less interested in infants.
What is androgen insensitivity?
This is also called testicular feminization. This person has the XY chromosomes and produces the normal amount of androgens (including testosterone) however they lack the receptors that enable androgen to activate genes in a cell’s nucleus. Thus development proceeds as if the level of testosterone is low.
In some cases no one suspects that the person is anything other than a female until puberty. The breasts and hips develop but internally the person has internal testis instead of a uterus and ovaries, therefore no menstruation.
How should CAH children , and the like, be raised?
Many were originally raised as girls but they found huge issues as the person grew. For boys who had small penises removed, they still had male interests even though they were brought up as girls. For girls with CAH, they often wished that they had their original enlarged clitorus instead of the mutilated, insensitive structure, their enlarged vaginas provided them with no sensations and definitely no orgasms. And mostly they all resented being deceived.
Suggestions - be honest, be consistent with rearing but be prepared for change, do not perform surgery.
What causes sexual orientation?
Homosexual behaviour happens in many animal species. Genetics, prenatal environment and as yet un identified aspects of experience impact on homosexuality. It is probably different for different people. Feminine behaviours in childhood and adolescence are strong correlations for homosexual men but early masculine behaviours are poor indicators of female homosexuality.
More women than men feel some attraction to both sexes and women can switch from homosexuality to heterosexuality and back. Men rarely switch.
How do homosexual and heterosexual people differ biologically?
Heterosexual men are slightly taller and heavier. When giving directions women and homosexual men are more likely to use landmarks to do so than to use compas directions.
Genetics- stronger concordance for monozygotic twins. We can reasonably infer that genetics contribute to sexual orientation but we can’t be sure the size of the contribution. It is inconclusive whether the maternal or paternal relatives have more influence.
If certain genes promote a homosexual orientation, why hasn’t evolution selected strongly against these genes?
Hypothesis 1 - genes for homosexuality are maintained by kin selection. These homosexuals may do a great job of looking after nieces and nephews.
Hypothesis 2 - genes that produce homosexuality in males produce advantageous effects in their sisters and other female relatives, increasing their probability of passing on the gene.
Hypothesis 3 - certain genes lead to homosexuality in men homozygous for the gene but produce reproductive advantages in men heterozygous for the gene.
Hypothesis 4 - homosexuality relates to the activation or inactivation of genes
Does the prenatal environment influence sexual orientation?
Adult hormone levels do not explain sexual orientation. However, it is possible for it to be related to testosterone levels during a sensitive period if brain development. It has also been reported that homosexuality in males is higher for those will more older brothers. They hypothesis that this is due to a mother’s immune system sometimes reacts against a protein in a son and then attacks subsequent sons enough to alter their development.
Prenatal stress alters sexual development in animals. People who were exposed to prenatal stress AND alcohol had decreased male sexual behaviours. Stress releases endorphins which can antagonise the effects of testosterone on the hypothalamus. Stress also elevates levels of the adrenal hormone corticosterone which decreases testosterone release. Long term effects of either prenatal stress or alcohol include several changes in the structure of the nervous system, making the affected males anatomy closer to that of females.
Outline the differences in the brain anatomy go homosexual vs heterosexual people.
- On average the left and right hemispheres are nearly equal in size in heterosexual females (and homosexual males), whereas the right hemisphere is bigger in heterosexual males, with homosexual females somewhere in between.
- The left amygdala has more widespread connections than the right in heterosexual females (and homosexual males), whereas heterosexual males have a right amygdala with more widespread connections, homosexual females are somewhere in between.
- The anterior commissure is larger in heterosexual women than heterosexual males and often even larger in homosexual men
- The SCN is larger in homosexual men than heterosexual men
- The third interstitial nucleus of the anterior hypothalamus (INAH-3) is an area that has more cells with androgen receptors in men than in women. Research found this area to be twice as large in heterosexual men than hero sexual women (or homosexual men)
- Non of these findings show causality.
