Lecture 6 - HPG, Puberty And Menstrual Cycle Flashcards
What organs make up the HPG axis?
Hypothalamic-Pituitary-gonadal axis
Hypothalamus
Pituitary
Gonads
How do hormones that are produced by the hypothalamus reach the pituitary ?
Travel down the infundibulum and goes through the hypophyseal hypothalamic portal system
What hormone is important in the HPG axis that’s produced by the hypothalamus?
GnRH (Gonadotropin releasing Hormone)
What part of the pituitary gland is involved in the HPG axis?
Anterior pituitary
What hormones does the anterior pituitary gland produce in response to GnRH?
FSH
LH
How is GnRH released from the anterior pituitary?
In a pulsatile way (isn’t released continuously
What is the function of FSH in males?
fSh = Sertoli cells (s for sertoli)
Stimulates Sertoli cells:
- carry out spermatogenesis and produce inhibin
-Inhibin inhibits the production of FSH (-ve feedback on anterior pituitary)
What is the function of LH in males?
Lh = L for Leydig
Stimulates Leydig cells
-produce testosterone (has a negative feeback effect on the hypothalamus and anterior pituitary
Generally what happens in males when GnRH is made?
Stimulates Ant pituitary to make FSH and LH
FSH and LH are gonadal hormones which go onto to the gonads
FSH stimulates Sertoli cells = Spermatogenesis + inhibin production
LH stimulates Leydig cells = testosterone release
What part of the testes are Sertoli cells located in?
What part of the testes are leydig cells found in?
Seminferous tubules = Sertoli cells
Interstitial tissue = leydig cells
Where are granulosa cells and theca interna cells located?
Surrounding the oocyte
What is the role of FSH in women’s HPG axis?
Stimulates granulosa cells stimulating follicular development
What is the role of LH in women’s HPG axis?
Stimulates theca interna cells to release androgens
What cells in the woman convert androgens to oestrogen?
What cells produce the androgens?
Granulosa cells convert
Theca interna cells produce
What level does oestrogen have to be in for it to start causing positive feedback on the hypothalamus and pituitary?
When oestrogen is very high
In women what do very high levels of oestrogen lead to?
+ve feedback leading to a surge of LH being produced leading to Ovulation
Go to the last slide and label the image
1 = oocyte
2 = antrum
3 = zona pellucida
4 = zona granulosa
5 = theca interna
Go to the last slide and label the image
1 = oocyte
2 = antrum
3 = zona pellucida
4 = zona granulosa
5 = theca interna
What is puberty?
The point in which the HPG axis gets turned on where the individual can reproduce
How do levels of GnRH change as individuals go through puberty?
Increased frequency and amplitude of pulsation GnRH which first occurs at night and then progressively happens throughout the day
How do levels of FSH and LH change through puberty?
FSH and LH steadily rise
What is gonadarche?
Activation of gonads
What is adrenarche?
The awakening of the adrenal glands causing pubic/axillary hair and oily skin
What is Thelarche?
Onset of breast development occurring the beginning of puberty in girls
What is menarche?
Onset of menstruation at puberty
What is pubarche?
The onset of the growth of pubic hair
What factors can affect the timing of puberty?
Pineal gland
Body weight (critical weight for menses is 47kg)
Leptin levels (deficient in leptin = puberty doesn’t begin)
Environment (economic factors may lead to stress)
Genetics
What is the normal age of puberty in boys?
9-14yrs
What are the stages of puberty in boys from first to last?
Genital development (scrotum + testes enlarge)
Pubic hair growth
Spermatogenesis
Growth spurt
What are some male secondary sexual characteristics?
Inc and thickend hair on pubis, trunk, Axillae and face
Increased laryngeal size (Adams apple)
Deeping of voice
Increased bone mass
Increased muscle mass and strength
What hormone leads to the fusion of the epiphyseal plates ending the growth spurt in puberty?
Oestrogen
Why can going through puberty early lead to being short in adult life?
Less time for bone growth
Once the growth spurt occurs and the oestrogen is made to end it, the epiphyseal growth plates fuse preventing further growth
Essentially hey get less time growing
What is the scale used to measure puberty progression?
Tanner scale
What does the Tanner scale assess in boys?
Scrotum + testes development
Pubic hair development
Penis growth
What is the normal range for puberty in girls?
8-13 years
What are the 4 stages of puberty in girls from start to end?
Thelarche (breast bud)
Adrenarche (pubic hair growth)
Growth spurt
Menarche (menstrual cycle)
What are some female secondary sexual characteristics?
Pubic and axillary hair
Enlargement labia minora and majora
Increased fat in hips/thighs (men get more muscle)
Keratinisation of vaginal mucosa
Uterine enlargement
How does the growth spurt stage differ in girls and boys in puberty?
Happens earlier in the process in women but is shorter
Men it happens later and is a longer process so men are larger
What ends the growth spurt stage in men and women?
Oestrogen (fuses epiphyseal plates)
What hormones cause growth spurts?
Growth hormone
IGF (insulin like growth factor)
What is the point of the menstrual cycle?
Prepares for potential fertilisation and implantation
What are the 2 simultaneous stages to the menstrual cycle?
Ovarian cycle
Uterine cycle
What are the 3 phases to the uterine cycle?
Menstrual phase
Proliferation phase
Secretory phase
What are the 2 phases of the ovarian cycle?
Follicular phase
Luteal phase
What key event occurs between the follicular phase and the luteal phase of the ovarian cycle?
What day does this happen on?
Ovulation
Day 14
What happens on day 14 of the menstrual cycle?
Ovulation
How long is the Luteal phase of the menstrual cycle (ovarian cycle)?
14 days
Go to the last slide and label the menstrual cycle:
1 = LH (Lutenising Hormone)
2 = FSH (Follicle-stimulating hormone)
3 = oestrogen
4 = progesterone
5 = follicular phase
6 = luteal phase
7 = 14 days
What happens during the early follicular phase of the ovarian cycle?
No ovarian hormones made yet
Granulosa cells make activin
Activin increases FSH production
FSH stimulates follicle growth
Theca interna makes androgens which the granulosa cells convert to oestrogen
1 follicle becomes dominant so granulosa cells produce inhibin instead of activin
What happens during the late follicular phase?
The increasing oestrogen leads to more FSH receptors on follicle (causing negative feed back on FSH production)
Inc LH receptors on granulosa
Increasing levels of Inhibin reduces FSH production preventing other follicles from developing
What triggers ovulation to occur on day 14 in the ovarian cycle of the menstrual cycle?
Surge in LH
What causes the surge of LH that leads to ovulation occurring?
Oestrogen has risen enough to high enough levels to now exert a positive feedback affect on the hypothalamus and pituitary
Why do levels of FSH not surge as a result of oestrogen now acting in a positive feeback way?
Inhibin prevents FSH levels increasing
At ovulation what stage of meiosis is the oocyte in?
Meiosis I completed
Meiosis II begun but not complete
Arrests at metaphase II
When does Meiosis II complete in the oocyte?
After fertilisation
What happens to the follicle once the oocyte breaks free from it after ovulation has occured?
What hormone stimulates this?
High levels of LH stimulates follicle to develop into the Corpus Luteum
What hormones is the Corpus Luteum responsible for producing lots of?
Oestrogen
Progesterone
What occurs in the luteal phase of the ovarian cycle?
LH stims empty follicle to become the corpus luteum
Corpus luteum makes lost of oestrogen and progesterone
How long is the luteal phase of the ovarian cycle (how long does the corpus luteum survive for)?
14 days
What generally happens in each stage of the uterine cycle?
Menstrual = shedding of endometrium
Proliferative = lignin of uterus builds up
Secretory phase = uterus prepares for implantation
What are the 3 uterine layers from the inner most layer outwards?
Endometrium
Myometrium
Perimetrium
What makes up the endometrium?
Functional layer (layer that gets shed, responds to hormones)
Basal layer
What is the main hormone produced by the corpus luteum in the Luteal phase?
Progesterone
How does the endometrium change in the early prolfierative stage to the late proliferative stage of the uterine cycle?
Early = sparse glands and straight glands
Late proliferative = thicker functional layer, glands become coiled
What changes in the endometrium in the secretory stage of the uterine cycle?
What hormone controls this stage?
Endometrial thickness at max
Glands and Arterioles very coiled
Progesterone
What happens to the corpus luteum if fertilisation doesn’t occur?
Dies and becomes the corpus albicans lead to a dramatic fall in the levels of oestrogen, progesterone and inhibin leading to menstrual bleeding
What happens to levels of FSH once the corpus luteum becomes the corpus albicans and why?
FSH slowly starts rising since the corpus luteum is no loner producing high levels of oestrogen, progesterone and inhibin so the negative feedback is lost
How is the corpus luteum kept alive if fertilisation occurs?
Syncytiotrophoblasts produce HCG (Human Chorionic Gonadotropin) which extends the lifespan of the corpus luteum ensuring oestrogen and progesterone levels are maintained preventing menstruation
What is the main hormone in the follicular phase?
Oestrogen
What is the main hormone in the Luteal phase?
Progesterone
What does oestrogen do?
Thickening and proliferation of endometrium
Fallopian tube function
Growth and motility of myometrium
Thin alkaline cervical mucus
Vaginal changes
Changes skin, hair and metabolism
What does progesterone do?
Produces secretory endometrium
Thickens myometrium and reduction of motility
Thick acidic cervical mucus
Development of breast tissue
Inc body temp
Metabolic changes
Electrolyte changes
What can disrupt the menstrual cycle?
Physiological factors like pregnancy
Lactation
Emotional stress
Body weight (weight loss or excess exercise)
Infertility
How can precocious puberty by caused by intracranial pathology like meningitis?
Inflammation of meninges can lead to premature release of GnRH making CNS lesions
Look at the last slide:
Early follicular phase before ovulation:
What Hormone should be in place 1, what type of feedback effect does this have (2)?
What hormones should be in place 3, what type of feedback effect does this have (4)?
1 = oestrogen
2 = -ve feedback effect
3 = inhibin (stops FSH surging), progesterone
4 = -ve feedback effect
Look at the last slide:
During ovulation:
What Hormone should be in place 1, what type of feedback effect does this have (2)?
What hormones should be in place 3, what type of feedback effect does this have (4)?
1 = oestrogen
2 = +ve feedback
3 = inhibin
4 = -ve feedback
Look at the last slide:
Luteal phase after ovulation:
What Hormone should be in place 1, what type of feedback effect does this have (2)?
What hormones should \be in place 3, what type of feedback effect does this have (4)?
1 = oestrogen
2 = -ve feeback
3 = progesterone
4 = -ve feedback
What affect does oestrogen have on the hypothalamus during the early follicular phase?
Oestrogen is at low levels so has a negative(inhibitory) feeback affect on Gonadotropin release
What affect does oestrogen have on the hypothalamus during ovulation?
Rising levels of oestrogen produces positive feedback affect enhancing LH release promoting ovulation
What affect does oestrogen have on the hypothalamus during the Luteal phase?
Corpus luteum makes lots of oestrogen and progesterone
High oestrogen with high progesterone has a negative/inhibitory feedback affect on hypothalamus and pituitary.
How may you delay puberty?
Weight loss, exercise
Drugs that block androgens
GnRH analogue
What is an example of a drug that blocks androgens?
Medroxyprogesterone
How can you tell whether its a central cause (hypothalamus/pituitary) for delayed puberty?
FSH and LH low (GnRH low)
How can you tell whether its a peripheral/gonadal cause for delayed puberty?
High FSH and LH (GnRH high)
The gonads aren’t responding to the FSH/LH this leads to more GnRH being produce which further increases the levels of FSH and LH
What cells make androgens?
What cells convert androgens to oestrogen?
Making androgens = theca interna
Converting androgens = granulosa
