Session 4

Question 1

What is puberty?

Answer 1

Puberty is the preparation for sexual maturity, to enable us to reproduce. it creates sexual dimorphism (distinct differences between male and female sexes). It results with morphologicial, physiological and behavioural development.

Question 2

Define primary sexual characteristics

Answer 2

Sexual characteristics at birth ie before puberty has begun. This includes the anatomy of internal and external genitalia.

Question 3

Define secondary sexual characteristics

Answer 3

Sexual characteristics that develop during/after puberty; ie pubic hair, breast or genital development or enlargement, and menstruation in females.

Question 4

When do girls start puberty?

Answer 4

Girls typically start puberty before boys, between ages 9-13.

Question 5

When do boys start puberty?

Answer 5

boys typically begin puberty slightly later than girls, around age 10-14.

Question 6

Define Thelarche

Answer 6

Thelarche refers to ‘breast bud’ development, which is the first sign of puberty in girls

Question 7

Define Menarche

Answer 7

Menarche is the initiation of the menstrual cycle, with a girl’s first period.

Question 8

Describe the sequence of events for girls when they go through puberty

Answer 8

Thelarche

Pubic hair
Pubic hair starts to develop under the influence of testosterone, in both boys and girls. This is the next stage.

Growth spurt
The growth spurt happens next over a wide age range.

Menarche

Pubic hair
Pubic hair will then become coarser, with further anatomical spread until the adult pattern of pubic hair distribution is reached.

Breast development
This is the final stage, with further growth of breast tissue until adult breast enlargement is reached.

Question 9

Describe the sequence of events for male puberty

Answer 9

Genital development
The first sign of puberty occurring in boys is testicular volume enlargement.

Pubic hair growth
As with girls, under the influence of testosterone, pubic hair starts to develop.

Spermatogenesis
This process begins next, however it is difficult to determine exactly when the timing of this occurs.

Growth spurt
This happens much later in boys

Genital enlargement
The testes and external male genitalia continue to increase in size and volume until adult external genitalia has developed.

Pubic hair
Similarly to girls, the coarseness and pattern of pubic hair will change until an adult distribution has occurred.

Question 10

In puberty, which comes first: Hormonal or physical changes?

Answer 10

Hormonal changes and then they drive the physical changes.

Question 11

How is puberty started?

Answer 11

Light, Leptin and weight are factors which affect the onset of puberty. The median emminance of the brain detects leptin and light levels and has projections into the hypothalamus and those projections undergo an increase in electrical excitability which activtes the hypothalamus which beginsthe initial nocturnal release of Gonadotrophin Releasing Hormone (GnRH) which travels through a portal system to the pituitary to start hormone release. GnRH is the critical signalling molecule that triggers the start of puberty. Critical weight must also be reached.

Question 12

Describe the release of Gonadotrophin Releasing Hormone and its effect

Answer 12

Paracrine secretion from the hypothalamus. It has a pulsatile release, i.e. it is not secreted consistently. Every 1-3 hours. Mainly nocturnal.
GnRH causes release of Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) in both males and females from gonadotrophs in the anterior pituitary. Regulates its own receptor.

Question 13

How are cells in the seminiferous tubules affected by Luteinizing Hormone and Follicle Stimulating Hormone

Answer 13

Sertoli cells produce Sperm under the influence of FSH

Leydig cells produce testosterone under the influence of LH

Question 14

How are cells in the ovaries affected by Luteinizing Hormone and Follicle Stimulating Hormone

Answer 14

GranuloSa cells respond to FSH

THeca cells respond to L_H_

Question 15

Describe the feedback mechanism that the Hypothalamic Pituitary Gonadal Axis follows

Answer 15

Like most hypothalamic-pituitary axes, this cycle is subject to negative feedback. Raising levels of androgen/oestrogen causes negative feedback on the hypothalamus, which then stops the release of GnRH.

(Slightly more complicated in women)

Question 16

When is Inhibin produced and what does it do?

Answer 16

When ‘follicles’ (gametes) are stimulated (i.e. sperm production in males and formation of a primary oocyte in females), the granulosa cells of the corpus luteum (women and the sertoli cells (men) releases inhibin, which specifically causes negative feedback on FSH only to prevent further sperm production or maturation of any more follicles.

Question 17

Why does release of the oocyte need to be periodic?

Answer 17

In the female, it takes time to prepare the uterus for implantation of a fertilised oocyte. Therefore, release of this oocyte needs to be periodic, otherwise even if fertilisation occurs, the uterus will not be able to sustain it

Question 18

How long does a typical menstrual cycle take?

Answer 18

21-35 days

Question 19

Describe the negative feedback mechanism in males for production of testosterone

Answer 19

Typical ‘negative feedback’ loop; where hormones are released to stimulate LH and FSH release, which will increase levels of testosterone as the gonad is stimulated, and the high levels of testosterone cause an inhibitory effect on the hypothalamus and anterior pituitary.

Question 20

Why is it important that GnRH is released in pulses?

Answer 20

Release of GnRH in a pulsatile nature is key in fertility, as receptors can become desensitised if they are over exposed to this hormone.

Question 21

What does FSH do?

Answer 21

This is as its name suggests; it acts at the ovary to allow the follicles to develop at the start of the menstrual cycle (the first day of menstruation) in order to nurture and sustain the development of the gamete. The follicles also produce oestrogen and a hormone called inhibin, which is selectively involved in negative feedback of FSH at the anterior pituitary.

Question 22

What does LH do?

Answer 22

This hormone is responsible for ovulation, as the ‘LH surge’ is the key factor that drives ovulation.

Question 23

What is the ovarian cycle?

Answer 23

The ovarian cycle describes the changes that affect the ovaries during the menstrual cycle. This can be divided into two halves; the first half is called the follicular phase and the second half is called the luteal phase.

Question 24

Describe the follicular phase of the ovarian cycle

Answer 24

This phase is all about preparing a follicle to be ready for ovulation.

At the start of the cycle, a small number of follicles will begin to develop. There is no inhibition on the hypothalamus or anterior pituitary, therefore FSH levels start to rise. Under the influence of FSH, the number of granulosa cells increases, and causes the development of the theca interna and externa cells. The follicle will now produce oestrogen from both the granulosa cells and the theca cells, therefore oestrogen levels rise. At these lower levels of oestrogen, it exerts a negative feedback effect on the hypothalamus and anterior pituitary.

The follicles will then develop into a Graafian follicle with a large antrum, ready to be released at ovulation. As the follicle develops, oestrogen levels rise further, and at higher levels of
oestrogen it exerts a positive feedback effect on the hypothalamus and anterior pituitary, to allow levels of LH to rise. Importantly, as the follicle develops, inhibin also rises, to prevent FSH stimulating more than one dominant follicle. Therefore under this positive feedback, the amount of LH rises considerably more than the levels of FSH prior to ovulation. Despite FSH inhibition oestrogen continues to be produced as follicle has essentilly become autonomous and can produce the oestrogen without prompt from FSH.

This phase can be variable in length and therefore the precise timing of ovulation can vary from individual to individual. Roughly 2 weeks long

Question 25

Describe the luteal phase of the ovarian cycle

Answer 25

This phase happens after ovulation, and it is the stage of the cycle where the reproductive system is waiting to see if fertilization and implantation has occurred.
‘Lutein’ refers to a yellow/gold pigmentation, which describes what happens visually to the follicle after ovulation when the granulosa and theca cells become the corpus luteum whose endocrine function is to produce oestrogen and progesterone. The high levels of oestrogen alone would cause positive feedback to the hypothalamus and anterior pituitary, however the presence of progesterone promotes the negative feedback of oestrogen at the hypothalamus and anterior pituitary so LH falls. The main purpose of high levels of oestrogen and progesterone is for its effect on the endometrium.

The corpus luteum has a set lifespan of 14 days, while it waits to see if implantation of a fertilized oocyte has occurred. Without it, it regresses; levels of oestrogen, progesterone, and inhibin drop, allowing the cycle to start again. The luteal phase is therefore always constant, typically 14 days long.

Question 26

What is the uterine cycle?

Answer 26

The uterine cycle describes the effects on the uterus during the menstrual cycle, and can be divided into the proliferative phase prior to ovulation and the secretory phase after ovulation.

Question 27

Describe the proliferative phase of the uterine cycle

Answer 27

At the start of the cycle, the endometrium will proliferate and thicken in response to oestrogen produced by the ovary. There are simple, straight glands within the endometrium but as this part of the cycle continues and the endometrium continues to develop, the glands become coiled and the functional layer doubles in size.

Question 28

Describe the myometrium and endometrium

Answer 28

The myometrium is the muscular wall of the uterus and the endometrium is the epithelial lining of the uterine cavity. The endometrium can be further divided into the functional layer and basal layer; the functional layer is the layer that sheds during menstruation and the basal layer allows this to regrow at the start of a new cycle.

Question 29

Describe the secretory phase of the uterine cycle

Answer 29

Once ovulation has occurred, the glands that have been produced in the proliferative stage then become secretory under the influence of progesterone. Towards the end of this stage, when the hormones from the corpus luteum begin to fall, the glands then lose their structure and the endometrium becomes ready to shed its functional layer if implantation has not occurred.

Question 30

What happens in the secretory phase of the uterine cycle if implantation occurs?

Answer 30

The embryonic tissue of the outer cell mass (trophoblast) produces hCG (human chorionic gonadotrophin); it acts as a gonadotrophin and has the same function as LH. hCG will maintain the corpus luteum, which will therefore maintain the pregnancy by producing oestrogen and progesterone. Later this function will be taken over by the placenta

Question 31

Describe the basic functions of oestrogen on the reproductive tract

Answer 31

The effect of oestrogen on the reproductive tract is intended to promote fertilisation: 

Proliferation of endometrium 

Proliferation of myometrium 

Fallopian tube motility 

Promote growth of thin, alkaline cervical mucus

Question 32

Describe the basic functions of progesterone on the reproductive tract

Answer 32

The effect of progesterone on the reproductive tract is intended to sustain a viable pregnancy:

Secretory function of endometrium 

Reduction of motility of myometrium (assumes fertilisation has occurred)

Promote growth of thick, acidic cervical mucus to prevent further entry of sperm

Question 33

What is endometriosis?

Answer 33

Endometriosis is a condition where ectopic endometrial tissue can develop, leading to significant pain. Giving continuous GnRH to such patients can ‘switch the axis off’ to alleviate their symptoms. It can also be given in situations such a precocious puberty when you want to temporarily halt this axis.

Question 34

What is precocious puberty?

Answer 34

Precocious puberty is the appearance of signs of pubertal development at an abnormally early age. In girls this has traditionally been considered to be before 8 years, and in boys before age 9.

Question 35

Why can precocious puberty cause a shorter stature?

Answer 35

Early onset (precocious) puberty can lead to levels of oestrogen rising earlier, and can therefore result in short stature.

Question 36

What are they key overall changes during puberty?

Answer 36

Accelerated somatic growth

Maturation of primary sexual characteristics (Gonads and Genitals)

Appearence of secondary sexual characteristics (pubic and axillary hair, female breast development, male voice changes)

Menstruation and spermatogenesis begin

Question 37

What is the Tanner scale?

Answer 37

Scale from pre-puberty to end puberty in various stages characterised by size and development of penis and testis along with pubic hair development for men; and breast bud appearence, breast development and pubic hair development for women

Question 38

Define adernache

Answer 38

First appearence of an increase in production of androgens resulting in accelerated growth, pubic hair, body odour and skin oiliness/acne

Question 39

Why are men taller than women on average?

Answer 39

Although growth starts later for boys, it lasts longer so they grow taller. Closing of epiphyseal plates which stops growth is caused by oestrogen. Men can convert testosterone into oestrogen in a process called aromatisation and this is done in the peripheral tissues and in and around the epiphyseal plates. The concentration of oestrogen in men is lower than that of women so the epiphyseal plates take longer to close.

Question 40

How can weight affect menarche?

Answer 40

In girls the critical weight to have menarche and upkeep the menstaual cycle is 47kg. Girls often get to this weight earlier in modern times so the age of menarche has decreased.

Question 41

What is the HPG axis?

Answer 41

Hypothalmic Pituitary Gonadal axis

Communication between Hypothalamus and Pituitary gland regulate the Gonadal development and homeostasis.

Question 42

Why would a tumour of the pineal gland affect puberty

Answer 42

It secretes melatonin which is involved in circadian rhythm regulation and GnRH release is closely tied to your circadian rhythm

Question 43

What is the gene that codes for Gonadotrophin Releasing Hormone?

Answer 43

GnRH - 1 which is exclusively expressed in the hypothalamus

Question 44

What is another name for the anterior pituitary?

Answer 44

Adenohypophysis

Question 45

How is the hypothalaumus and anterior pituitary connected

Answer 45

Superior hypophyseal artery

Question 46

What are the 6 peptide hormones produced by the anterior pituiatry? Which ones are most signficant in reproduction?

Answer 46

Prolactin, Growth Hormone (GH), Thyroid Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH)

FSH, LH and Prolactin are most significant for reproduction

Question 47

Describe testosterone production

Answer 47

Produced from cholesterol by leydig cells in the testis. Once production starts, in the medium long term testosterone production levels remain constant. Most produced early in the morning as part of your circadian rhythm.

Question 48

What do sertoli cells do?

Answer 48

Found in the interstitium of the testis, they provide nutrition and hormonal support to germ cells allowing sperm formation. Secrete Inhibin which inhibits FSH production

Question 49

How do oestrogen and progesterone affect FHS and LH secretion?

Answer 49

Pogesterone increases inhibitory effects of small/moderate amounts of oestrogen.

Progesterone prevents positive feedback of high oestrogenpreventing the LH surge.

Oestrogen reduces GnRH per pulse whereas progesterone affects the frequency of the pulse

Question 50

How do hormonal changes cause a growth spurt?

Answer 50

Growth hormone secreted from pituitary results in bone growth. There’s also an increase in TSH which increases metabolic rate which promotes tissue growth. An increase in androgen production results in retention of minerals in the body to support bone and muscle growth

Question 51

What is Leptin and what does it do?

Answer 51

Adipocyte derived protein hormone. It signals information about energy stores to the CNS.

It has an important role in reguating neuroendocrine function.

Reproductive dysfunction is associated with leptin deficiency.

Leptin can accelerate the onset of reproductive function.

Leptin has a pulsatile release pattern sigificanty associated with the variations in LH.

Leptin can regulate GnRH levels as its related to body weight.

Question 52

Why is it important hat GnRH is released intermittently? How can this mechanism be used in realtion to endometriosis?

Answer 52

If GnRH receptors are exposed to continuous presence of GnRH they will become desensitised causing FSH and LH to drop so gonadal steroid production stops which can lead to infertility.

This can be used however to treat endometriosis by giving a GnRH agonist to relieve symptoms by reducing gonadal steroid production

Question 53

In women, how does FSH lead to inhibin production

Answer 53

FSH binds to granulosa cells

• Follicular development continues
• Theca interna appears
• Follicle now capable of oestrogen secretion
• Inhibin secretion begins

Question 54

How do the glands change in the uterus over the menstrual cycle?

Answer 54

Early proliferative: Glands sparse, straight

Late proliferative: Functional layer has doubled, glands now coiled

Early secretory: Endometrium at max thickness, very pronounced coiled glands

Late secretory: Glands adopt characteristic saw-tooth appearence

These glandular secretions help to prepare for implantation and help support that after.