Chapter 8 Hormones + Sex

Question 1

What are hormone and endocrine glands?

Answer 1

Hormones are chemicals that enter the blood stream and act on target organs or tissues.

Endocrine glands are glands that secrete hormones. Examples include: pituitary gland, thyroid, adrenal gland, gonads etc.

Question 2

What are the different classes of hormones?

Answer 2

Peptide Hormones: made of short strings of amino acids, are small protiens. e.g. oxcytocin

Amine Hormones: single amino acids

Steroid Hormones: derived from cholesterol and bind to receptors inside the cells (they can move freely through cell membranes. e.g. estrogen, progesterone, androgens (e.g. testosterone).

Protein hormones bind to receptors outside the cell and trigger changes in the cell through a second messenger system. They operate slightly faster than steroid hormones.

Steroid hormones bind to receptors inside the cell and then the steroid receptor complex enters the cell’s nucleus to bind with the DNA/ Here in controls gene expression. Takes longer than other hormone processes.

Question 3

How do hormones manage an integrated effect on their target tissue?

Answer 3

Hormones can act on more than one target tissue (having a different effect at each one.) Multiple hormones can act on a single tissue providing an integrated effect.

Question 4

How are hormones regulated?

Answer 4

Hormones are regulated through a negative feedback loop that can have two basic structures:

Brain Regulation –> They hypothalamus becomes aware that a hormone is required and it triggers the endocrine cells to release their hormone, the hormones enter the blood stream and go to their target cells, producing a biological response, the biological response triggers the hypothalamus that the hormone is no longer required.

Brain, pituitary regulation –> The hypothalamus releases the “releasing hormone” to the anterior pituitary which releases a tropic hormone to the endocrine cells which release a hormone that travels to the target cells and produces a biological effect. Meanwhile the releasing of the endocrine cell hormone is tracked by the pituitary and the hypothalamus and it triggers them to stop the production of the releasing and tropic hormone.

Question 5

What are neuroendocrine cells?

Answer 5

These are cells that operate like neurons except that an action potential triggers the release of a hormone instead of a neurotransmitter.

Question 6

What is the hypothalamic-pituitary portal system?

Answer 6

This is the system through which the hypothalamus triggers the pituitary system to produce it’s tropic hormones.

The neuroendocrine axons from the hypothalamus converge in the median eminence just above the pituitary stalk (the thread that connects the hypothalamus with the anterior pituitary). they release releasing hormones into the localized blood stream (the blood vessels and capillaries are specific to the hypothalamus and pituitary region. The releasing hormones trigger the anterior pituitary to release their own tropic hormones into the general blood stream (which target cells in the endocrine system triggering the release of their own hormones etc.). The secretion rate of the releasing hormones control the secretion rate of the tropic hormones.

Question 7

What hormone does the hypothalamus release to trigger the release of what two tropic hormones for the gonads?

Answer 7

The hypothalamus releases gonadotropin-releasing hormone (GnRH) which triggers the anterior pituitary to release either or both Follicle stimulating hormone (FSH) and/or the luteinizing hormone (LH)

Question 8

What affect do FSH and LH have on females?

Answer 8

FSH stimulates the growth and maturation of the egg containing follicles in the ovaries which secrete estrogen.

LH stimulates the follicles of the ovary to rupture and release their egg and transform into structures called corpora lutea which secretes progesterone.

Question 9

What affect do FSH and LH have on Males?

Answer 9

FSH: governs sperm production
LH: stimualtes the testes to produce testosterone.

Question 10

What are the two basic functions of the gonads?

Answer 10

To produce hormones (m: testosterone, f: estrogens/progesterone)

To produce gametes (m: sperm, F: egg)

Question 11

What is the reproductive hormone system in males?

Answer 11

The hypothalamus releases the gonadotropin-releasing hormone. The anterior pituitary releases FSH which triggers the sertoli cells in the testes to produce sperm. It also releases LH which triggers the leydig hormones to produce testosterone which is released into the general circulatory system to travel to it’s target cells.

Question 12

What is the reproductive hormone system in females?

Answer 12

The hypothalamus releases gonadotropin-releasing hormones. The anterior pituitary relases FSH which stimulates the ovarian follicles to grow and secrete estrogen. The estrogen is secreted into the blood stream and travels to it’s target cells. It also releases LH which stimulates the ovarian follicles to rupture, release their egg, and form the corpus luteum which secretes progesterone, enters the general bloodstream and travels to its target cells.

Question 13

What do androgens promote in males?

Answer 13

the development and maintenance of male reproductive organs.

the development of male secondary sex characteristics such as body form, larynx, and facial hair.

Question 14

What do estrogen and progesterone promote in females?

Answer 14

Estrogen: promotes the development and maintenance of female reproductive organs and female secondary sex characteristics such as breasts.

Progesterone: prepares the uterus for implantation of fertilized eggs and the breasts for milk secretion.

Question 15

How does birth control affect the hormone system of females.

Answer 15

oral contraceptives contain small amounts of synthetic hormones which exert a negative feedback on the hypothalamus, inhibiting the release of gonadotropin-releasing hormone which prevents the release of FSH and LH therefore stopping the release of an egg to be fertilized.

Question 16

What are reciprocal effects in our hormone systems?

Answer 16

Reciprocal effects are the phenomenon where our experiences, behaviour, and hormones influence one another. Hormones change behaviour which changes our experiences which change our hormones and the cycle continues.

Question 17

What are the four stages of sexual behaviour and their characteristics?

Answer 17

Stage 1: Sexual Attraction –> this stage brings potential mates together in the same space. In humans this could be “going out” or to be on the nose, joining a singles club. In animals like the fossa, this could be the temporary sharing of territory between genders during mating season. In almost all cases, movement to the next stages depends on mutual agreement between all involved parties.
Stage 2: Appetitive behaviour –> this stage is intended to maintain and promote sexual interaction. Females who engage in appetitive behaviour are considered receptive. In humans this could be flirting behaviour. In birds, this could include a certain call, or (e.g. in peacocks and birds of paradise) more elaborate dances. In rats the females wiggle their ears and do a sort of hopping dance.
Stage 3: Copulation –> involves intromission followed by variable amounts of stimulation. When stimulation reaches a threshold, the male will ejaculate. In rats the male will grasp the females flanks and thrust his pelvis. If receptive, a female will exhibit lordis and then, after thrusting, the male will back off. This is repeated ~7x until the male ejaculates.
Stage 4: post copulatory behaviour –> varies significantly across species. In rats they separate and groom, in dogs they engage in a copulatory lock, in cats they roll.

Question 18

What are the roles of hormones during copulation?

Answer 18

Steroids activate sexual behaviour.

In males, testosterone creates sexual interest. Testesoterone does not however, have a linear relationship with sexual interest (i.e. more testosterone does not = more sexual interest)

Estrogen controls the proceptivity and receptivity of females. Without estrogens, rats do not exhibit lordis.

Question 19

What is the refractory phase of copulation? The Coolidge effect?

Answer 19

The refractory phase: where males will not mate again immediately after copulation. This can last minutes to months depending on the species.

The Coolidge effect is the shortening of the refractory phase by presenting the male with multiple different mates.

Question 20

What is the neural circuitry of sex in female rats?

Answer 20

The ventromedial hypothalamus –> the periaqueductal region of the midbrain –> Medullary reticular formation of the brain stem –> reticulospinal tract –> spinal cord.

Question 21

What is the neural circuitry of sex in male rats?

Answer 21

Important to understand that PGN (Serotonin in pons inhibits the erection reflex in males on a regular basis.

The Vomeronasal organ responds to the external stimuli of pheromones –> the olfactory organ –> medial amygdala –> Medial Preoptic area –> ventral midbrain –> basal ganglia –> spinal cord. This pathway leads to the inhibition of the inhibitory PGN on the erection reflex.

This pathway is not implicated in sexual interest but rather copulation behaviour only (e.g. mounting, erection etc.)

Question 22

What is the one most understand fact about human sexual behaviour?

Answer 22

IT IS DIVERSE

Question 23

What is the typical male sexual response cycle?

Answer 23

Desire rises into arousal where it plateaus until it spikes suddenly into orgasm before rapidly falling into resolution. The period between orgasm and resolution is the male refractory period.

Question 24

What are the typical female sexual response cycles?

Answer 24

There are three:

A: looks very similar to male. Desire rises to arousal and then it plateaus before spiking into orgasm and then falling into resolution. Sometimes this cycle involves multiple orgasms before fully falling into resolution.

B: Desire rises to arousal and then up into orgasm without a plateau. The orgasm may last longer before dropping rapidly in resolution.

C: desire rises to arousal and then plateaus for extended periods of time, fluctuating up and down only slightly before falling into a slow resolution. There is no orgasm.

Question 25

What is the relationship between hormones and human sexual behaviour?

Answer 25

Hormones play a permissive role only, they have to be there to stimulate sexual interest but they are not the main contributor to sexual behaviour. How other hormones (beyond testosterone) affect sexual behaviour is still unclear.

Question 26

What is the difference in the role of pheromones in animals versus humans?

Answer 26

In animals pheromones allow for communication about information like identity, sexual attractiveness and receptivity, and status. They can influence the behaviour of others.

In humans there may be some communication but it is very different than in animals and, although the obvious function would be to enhance reproduction, how it does so is unclear. Example pheromones may result in the synchronization of menstrual cycles in woman living in close proximity but there is no clear reproductive benefit from this.

Question 27

What is sexual differentiation?

Answer 27

the process by which individuals develop male or female sex characteristics and behaviours.

Question 28

How do indifferent gonads develop into sex-specific gonads?

Answer 28

The default path of development is for the indifferent gonads to develop into ovaries. The external cells of the indifferent gonads will proliferate.

If there is a Y chromosome, there is a sex determining region (the SRY gene). This encodes proteins that direct the internal core cells of the indifferent cell to proliferate, developing the indifferent gonads into testes.

Question 29

What are the basic structures of an early fetus that sexually differentiate? What happens to these structures during masculinization? Feminization?

Answer 29

The early fetus has a

1. ) genital bump that differentiates into either the clitoris or the penis (if exposed to testosterone)
2. ) Wolffian Duct: If exposed to testosterone, this system develops into the epididymis, vas deferens, and seminal vesicles. If not exposed to testosterone, than it degenerates.
3. the Mulllerian Ducts: if exposed to anti-mullerian hormone, it degenerates; if not exposed to AMH, it develops into oviducts (fallopian tubes) uterus, and inner vagina.

Question 30

What other structures (besides the main three) are masculinized? How does this occur? What if the masculinizing forces are not present?

Answer 30

Testosterone is not strong enough to masculinize all structures in the body but it can be converted into a more potent androgen called dihydrotestosterone (DHT) by the 5-alpha-enzyme.

DHT masculinizes the external genitalia to form the penis, prostrate gland, and scrotum.

Without any androgens, a labia and fully formed clitoris develop.

Question 31

What is Turner’s Syndrome?

Answer 31

A syndrome in which the individual is born with a single X chromosome and no other chromosome.

Because there is no SRY gene, the individual has a largely feminized system. The wolffian system degenerates and the mullerian system remains. The external genitalia form into labia and clitoris. The ovaries are underdeveloped but recognizable.

Individuals with Turner’s syndrome often have consistent physical markers such as :

• a short stature,
• low hairline
• fold of skin on neck
• small finger nails
• brown spots on the skin
• distinct eye shape
• cardiac issues
• poor breast development
• elbow deformities

Question 32

What is Congenital Adrenal Hyperplasia?

Answer 32

When a female fetus (XX) is exposed to higher than normal levels of androgens due to overactive adrenal glands. They do not have the SRY gene nor enough testosterone to fully masculinize however. This results in an intersex appearance where the phallus will be intermediate between a penis and clitoris and the skin folds will be intermediate between a scrotum and labia.
The individual will have ovaries and NOT testes due to a lack of the SRY gene however. This means that even if the genitalia are more masculine in form, the scrotum will be empty.

Question 33

What is Androgen Insensitivity?

Answer 33

The androgen receptor gene is mutated resultign in malfunctioning androgen receptors. The individual has XY chromosomes and will develop normal testes BUT

• depsite the testes producing testosterone, the body is insensitive to it and so the wollfian system degenerates.
• the testes produce AMH so the mullerian system also degenerates.
• being unable to detect testosterone, the individual develops a labia and clitoris and breasts (at puberty)
• they do not mensturate (no uterus or ovaries)
• they look and behave like woman (despite having XY)

Question 34

What is Guevedoces?

Answer 34

Guevedoces means having a genetic mutation that disables the 5-alpha-reductase enzyme, preventing testosterone from turning into dihydrotestosterone.

A lack of DHT means that the individual will develop normal testes and internal male reproductive systems but will have unmasculinized external genitalia that give the appearence of a clitoris and labia without the vaginal opening.

At puberty, there is a enough testosterone to compensate for the lack of DHT and the external genitalia will develop into a scrotum and penis.

In an area of the Dominic Republic, this condition is relatively common. For the first half of their lives, the individuals will present as female and then at puberty will change their presentation to male.

Question 35

What do abnormalities in sexual differentiation tell us about the role of nature versus nurture in gender?

Answer 35

• The two are so closely tied that it is difficult (arguably impossible) to pull it apart. It is clear that it is more than simply having an XX or XY that makes someone a man or woman. For example, individuals with Turner’s syndrome (who only have 1 X) reliably identify as woman as do women with androgen insensitivity (who actually have XY. We cannot reliably point to hormones as the determiner either. For example. it is not simply having testosterone that makes someone male (consider individuals with Guevedoces, they have testosterone all their life but begin with identifying as female) Likewise, woman with Congenital Adrenal Hyperplasia still identify as woman despite having higher than normal exposure to androgens however they do demonstrate some more male-typical behaviour, they are often described as tom-boys, tend to demonstrate male cognitive skills, and are more likely to be sexually attracted to females. So while hormones are not the only factor, they do obviously play a role.

But again, we cannot disregard the role that socialization plays. For example, do those with Guevedoces transition from female to male during puberty because of hormonal changes that affect their physical body and presentation or is it because such a transition is not only culturally accepted but also encouraged? Are the male typical behaivours seen in AIS due to socialization exaggerating such behaviours. (e.g. growing up being called a tom-boy could affect how individuals present themselves)

Question 36

How is the brain masculinized?

Answer 36

Testosterone is aromatized (converted into estrogen in the cells of the brain via the enzyme aromatase). This means that it is actually estrogen that masculinizes the brain.

Woman do not have a masculinized brain because an alpha-fetoprotein sequesters the estrogen, preventing from entering the brain.

Question 37

What two areas of the brain are sexually dimorphic?

Answer 37

In Rats, two main areas display sexual dimorphism.
- the preoptic area of the hypothalamus is larger in rats exposed to testosterone during development.
i the spinal nucleus of the bulbocavernosus (SNB). These nerves inervate the muscles at the base of the penis/clitoris. before birth, male and female rats have an equal number of nerves here. After birth, most SNB cells die off in female rats. In humans, females will still have SNB nerves but not as many as their male counterparts.

Question 38

How does socialization affect sexual differentiation in rats?

Answer 38

In rats, grooming by the mother can affect sexual differentiation. Males pups who are groomed more have larger SNB regions than pups who are groomed less. Female pups who are groomed more have more higher estrogen and oxytocin sensitivity which tends to make them more responsive mothers themselves.