Lecture 14: Reproductive 1

Question 1

Describe how the hypothalamus helps to control the posterior pituitary gland

Answer 1

Hypothalamus neurosecretory cells have long axon tracts which pass into the posterior pituitary. From there neurosecretory peptide hormones are made in the hypothalamus and stored in vesicles at the axon terminals. Nerve impulses trigger the opening of these vesicles.

Question 2

Describe how the hypothalamus helps to control the anterior pituitary gland

Answer 2

For the Anterior there are hypothalamic neurosecretory cells that produce releasing and inhibiting hormones which are sent to axon terminus. When nerve impulses cause the vesicles to be released they are secreted into the hypophyseal portal vessels where they act on specific anterior pituitary secretory cells.

Question 3

What are the two main functions of the gonads

Answer 3

To produce gametes and to produce reproductive hormones

Question 4

How is gonadotrophin secretion regulated in the pathway to produce sex steroid hormones. which are the positive and negative pathways.

Answer 4

The hypothalamus releases GnRH (Gonadotrophin releasing hormone) - (a positive signal)which acts on the Gonadotrophs (secretory cells) of the anterior pituitary. This causes it to produce FSH and LH which act on the gonads which bring about the production of sex steriod hormones. These steroid hormones contribute to a negative feedback system on the hypothalamus.

Question 5

What are the key reproductive hormones and what are the two chemical classes they are under

Answer 5

Water soluble : Peptides and proteins such as GnRH, FSH, LH and Oxytocin as well as Lipid soluble: Steroid sex hormones such as Oestrogens, Progestagens, Androgens

Question 6

Where are the lipid soluble sex hormones produced vs the water soluble sex hormones produced

Answer 6

Lipid soluble are in the gonads- Androgens are in testes while others are in ovaries.
Water soluble hormones are mostly from the Ant. Pituitary (LH and FSH). Oxytocin is Post. Pituitary and GnRH is hypothalamus

Question 7

What are the main androgens and what are the key properties

Answer 7

Testosterone, 5-a- Dihydrotestosterone. These promote and maintain male sex development, spermatogenesis, sexual behaviour (also in females) and muscle development

Question 8

What are the 3 oestrogens, where are they produced

Answer 8

Oestradiol- the main hormone produced by granulosa cells of growing follicle, in puberty onwards Oestrone- produced throughout life, from fat tissue, produced by men and dominant post menopause. Oestriol- produced by the placenta prior to labour helping the softening of the cervix.

Question 9

What are the key properties of oestrogens

Answer 9

They promote and maintain female sex development and fertility. They regulate the menstrual cycle and are involved in the growth of endometrium and bone growth.

Question 10

What are the main progestagens and what are the key properties

Answer 10

Progesterone is the major steroidal hormone of the corpus luteum and of the placenta. It is associated with the preparation and maintenance of a pregnancy

Question 11

What is sex determination vs sex differentiation

Answer 11

Sex determination is the commitment of bipotential gonad to testis or ovary in the genotype whereas Sex differentiation is the phenotypic development of the genital structures due to the action of hormones produced by the gonad present.

Question 12

How does sex determination happen

Answer 12

There is a sex determining region on the Y chromosome (SRY) that provides a pathway for the testes to develop. The presence of a testis drives the sexual fate of the embryo against the basic feminine trend. In absence or mutation of SRY the embryo develops into a female

Question 13

What are the key events of sex differentiation for internal genitalia for females

Answer 13

Ovary will produce oestrogens and progestagens. There is spontaneous regression of the wolffian ducts. The mullerian ducts persist, developing to give rise to fallopian tubes, uterus, cervix and upper vagina.

Question 14

What are the key events of sex differentiation for internal genitalia for males

Answer 14

The testes will produce sertoli cells which produce Anitmullerian hormone. This drives the regression of the female system. Leydig cells secrete testosterone which actively maintain the wolffian ducts and leads to development of epididymis, vas deferens, and seminal vesicles.

Question 15

What is the kind of time difference between development of the internal organs of males and females

Answer 15

Female differentiation lags behind Male organogenesis as male one is a driven process. The testis descends from its internal position to the scrotum usually after the 7th month.

Question 16

Describe the main external features of the bipotential precursor (undifferentiated stage)

Answer 16

Outer layer is the labioscrotal swelling, with the urethral folds and a urethral groove in the middle and on top, a gential tubercle

Question 17

What are the key events of sex differentiation for external genitalia for males

Answer 17

The shaft of the penis is made from urethral folds fusing together to enclose a urethral tube.
The scrotum comes from the labioscrotal swellings fusing at the midline.
The glans penis is formed when the genital tubercle swells

Question 18

What are the key events of sex differentiation for external genitalia for females

Answer 18

The labia minora (inner) is formed from urethral folds staying separate and the labia majora (outer) are formed by the labioscrotal swellings staying separate. The clitoris forms from the genital turbercle.

Question 19

What is puberty

Answer 19

The physical and behavioural changes associated with the sexual transition from childhood to adulthood where the reproductive endocrine systems are reawakened from when they were first active in the development of the embryo

Question 20

What is the first endocrine sign of puberty and what causes it.

Answer 20

An increase in LH plasma levels due to the increase in GnRH release from the hypothalamus acting on the pituitary. As a result there is a rise in sex steroid hormones.

Question 21

When does the first endocrine sign of puberty happen throughout puberty

Answer 21

In early puberty GnRH, and therefore LH (+FSH) levels increase during sleep. In late puberty daytime LH pulses also increase

Question 22

What is the purpose of the (Tanner stage) staging criteria of secondary sexual characteristics

Answer 22

These characteristics develop at different chonological ages in different individuals but their sequence is usually the same so this allows abnomalities to be detected and comparisons to be made between individuals

Question 23

What is the sequence of the 4 major events during puberty for females

Answer 23

1st: development of breasts
2nd: Pubic hair
3rd: Peak height spurt
4th: Menarche

Question 24

Describe the development of the breast- when does it first start, what hormones involved

Answer 24

Starts age ~10-11.
First Oestrogen causes a breast bud to start, followed by the breast mound.
Full breast development then happens when ovulation causes the release of progesterone

Question 25

Describe the development of sexual hair in females- when does it first start, what hormones involved

Answer 25

It starts within 6 months of the appearance of the breast bud (~10/11)
This is due to exposure of hair follicles to androgens.
Axillary (armpit) hair follows 1 year after pubic hair

Question 26

What is indicated by pubic hair before breasts in females

Answer 26

An androgen disorder.

Question 27

Describe the development of the Growth Spurt in females- when does it first start, what hormones involved

Answer 27

Peak growth occurs in girls age 11,12. This is stimulated by both steroid hormones. This growth process is then slowed steeply over time with epiphyseal closure of the bony ends caused by oestrogen.

Question 28

Describe the development of Menarche and Ovulation- when does it first start, what hormones involved

Answer 28

Menarche starts at 12-13 years, and ovulation doesn’t take place until 6-9 months after menarche because the positive feedback mechanisms of oestrogen haven’t developed

Question 29

When are regular ovulatory cycles established

Answer 29

1-2 years are first menstrual bleed

Question 30

What is the sequence of the 4 major events during puberty for males

Answer 30

1: Growth of the Testis- testicular and penile enlargement
2: Pubic hair
3: Growth of Penis
4: Height spurt

Question 31

Describe Testicular and penile enlargement- when does it first start, what hormones involved

Answer 31

Starts 10-13.5. Caused by Leydig cells enlarging and secreting testosterone giving rise to increased testicular size. Testosterone causes elongation and enlargement of the penis begins within a year of testicular enlargement

Question 32

Describe the development of sexual hair growth in boys when does it first start, what hormones involved

Answer 32

Starts about 6 months after the beginning of testicular enlargement, with axillary hair beginning 18 months later and facial hair later. Caused by androgens

Question 33

Describe the event of spermache- when does it occur

Answer 33

This is the beginning of spermatogenesis. Motile sperm is seen in urine at 13-14 years. The first ejaculation occurs soon after.

Question 34

What is spermache the equivalent to in females

Answer 34

ovulation

Question 35

What is the trend in the timing of Menarche?

Answer 35

There is a trend towards earlier ages of Menarche. this may be because a critical weight (~47kg) must be attained before the activation of the hypothalamo-pituitary-gonadal axis can occur. This signifies that sufficient storage is required to sustain pregnancy and lactation.

Question 36

Define precocious puberty

Answer 36

The appearance of physical and hormonal signs of puberty before
7 in girls
9 in boys.

Question 37

What are causes of precocious puberty

Answer 37

This is due to release of GnRH, in extreme cases caused by hypothalamic tumour.

Question 38

Define delayed puberty

Answer 38

The lack of appearance of physical and hormonal signs of puberty at
13 in girls
14 in boys

Question 39

What are the causes of delayed puberty

Answer 39

The gonadotrophin signals from the pituitary are inadequate for sex steroid secretion

Question 40

How is the point of Menopause measured in time

Answer 40

The last menstrual bleed

Question 41

Why does menopause occur and when does it occur

Answer 41

Menopause happens because the ovaries run out of viable follicles. This occurs between 50-52

Question 42

What are the 5 different phases of end of reproductive life as a woman

Answer 42

Premenopause, menopausal transition, post menopause, ovarian senescence and perimenopause

Question 43

Describe Pre-menopause phase

- where does it start and end

Answer 43

Starts from early 40s until ~46. During this period she still has regular periods

Question 44

Describe Menopausal Transition

- where does it start and end

Answer 44

Starts from ~46 til 50/52 (Menopause). During this time her periods become irregular as some follicles may not respond. Cycles can become longer.

Question 45

Describe Post Menopause

Answer 45

This is from 50-52 years onwards after the last menstrual bleed

Question 46

Describe Ovarian senescence - where does it start and what happens because of it

Answer 46

~ 1 year after menopause the ovaries stops producing hormones. This means that oestrogen production reduces to 1/10 of what it used to be. The main source of oestrogen is now from Oestrone produced in stromal cells of adipose tissue.

Question 47

Describe the phase of perimenopause

Answer 47

Refers to the time ‘around menopause starting at menopausal transition until ovarian senescence. During this period perimenopausal symptoms of oestrogen deprivation occur

Question 48

List the main perimenopausal symptoms

Answer 48

Vasomotor: fluctuations in blood vessels leading to overheating- hot flushes/night sweats

Genitourinary: Vaginal dryness due to reduced secretion, and atrophic changes

Bone Metabolism:
- increased risk of bone disease and weakness

Behavioural and Psychological:
-Depression, tensions, anxiety, mental confusion and loss of libido