4: Control of Reproduction Flashcards
Where are the main reproduction hormones released from?
Anterior pituitary
What are the two groups of reproduction hormones?
- Glycoprotein hormones
- Polypeptide hormones
What are the glycoprotein reproduction hormones? (3 things)
- FSH
- LH
- TSH (thyroid stimulating hormone)
Where are FSH and LH produced?
Gonadotrophs in anterior pituitary
What hormones are termed “gonadotropins”
FSH & LH
Where is TSH (thyroid stimulating hormone) released from?
Thyrotrophs in anterior pituitary
What controls FSH and LH release?
Gonadotropin Releasing Hormone (GnRH)
Where is Gonadotropin Releasing Hormone (GnRH) secreted from?
Hypothalamus
What is the purpose of Gonadotropin Releasing Hormone (GnRH)?
Controls secretion of FSH and LH
What are the fuctions of FSH and LH? (2 things)
- Control gamete production
- Stimulate gonadal steroid secretion (testosterone / oestrogen / progesterone)
Where do FSH and LH act?
Gonads
What are the polypeptide reproduction hormones? (3 things)
- Growth Hormone
- ACTH
- Prolactin
Where is Growth Hormone released from?
Somatotrophs in anterior pituitary
Where is ACTH released from?
Corticotrophs in anterior pituitary
Where is prolactin released from?
Lactotrophs in anterior pituitary
What is testosterones effect on GnRH secretion?
Inhibits GnRH secretion
What is oestrogens effect on GnRH secretion?
Inhibits GnRH secretion
What is progesterones effect on GnRH secretion? (2 things)
- ncreasing oestrogens inhibitory effect on GnRH secretion
- Reduces the frequency of pulses
What does a moderate vs high oestrogen concentration do to GnRH secretion?
Moderate oestrogen: causes low amount of GnRH secretion per pulse
High oestrogen: promotes GnRH secretion (surge)
What inhibits the GnRH surge caused by high oestrogen concentration?
Progesterone
What is inhibin?
Hormone that reduces the amount of FSH released in response to GnRH
Where is inhibin released from?
Granulosa cells in ovaries
What are the 3 stages of the Reproductive cycle?
- Preparation
- Ovulation
- Waiting
How long is the Preparation phase of the Reproductive cycle?
12 days
What happens in the Preparation stage of the Reproductive cycle?
- Follicles grow in the ovary
- Uterus prepares for sperm transport and implantation
What is the Preparation stage called in the Ovary?
Follicular stage
What happens in the Follicular (Preparation) phase in the ovary?
Follicles grow in the ovary
What hormone mash up causes the follicles to develop? (3 steps)
- Low oestrogen + progesterone + inhibin –> causes GnRH secretion
- GnRH –> FSH and LH release
- FSH binds to granulosa cells in the ovary and causes:
- Follicular development
- Inhibin Secretion
What hormone mash up causes oestrogen release? (3 steps)
- Low oestrogen + progesterone + inhibin –> causes GnRH secretion
- GnRH –> FSH and LH release
- LH binds to Theca Interna Cells –> help with oestrogen production
What does the oestrogen (released as a result of LH release) do?
Has a negative feedback effect on hypothalamus –> reduces amount of GnRH released
How does the body ensure only 1 follicle develops per cycle?
Inhibin (released as a result of FSH) inhibits FSH –> inhibits further follicular development
What is the Preparation stage called in the uterus?
Proliferative phase
What happens in the Proliferative (Preparation) stage in the uterus?
Uterus prepares for sperm transport and implantation
What is the function of oestrogen in the Preparation stage? (6 things)
- Fimbriae become more motile in fallopian tube
- Thickening of endometrium
- Growh + motility of myometrium
- Thin, alkaline cervical fluid produced
- Vaginal changes
- Changes to skin / hair / metabolism
Visualise it from fallopian tube –> uterus –> cervix –> vagina –> outside body
What happens in the Ovulation Stage of the Reproductive cycle? (2 things)
- Brief period of fertility
- Formation of corpus luteum
When is the corpeus luteum formed?
In the Ovulation (2nd) stage of the Ovarian Cycle
What happens 12-14 days into the cycle?
Oestrogen levels rise enough to cause an LH surge which causes:
- Ovum to be released
- Corpus luteum formed
- Oestrogen levels to decrease
What happens in the Waiting stage of the Reproductive cycle?
Changes occur to prepare for pregnancy
What is the Waiting Stage called in the ovary?
Luteal stage
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What is the Waiting Stage called in the uterus?
Secretory phase
What is the function of progesterone in the Luteal (Waiting) stage? (6 things)
- Thickening & sustaining of endometrium
- Thickening of myometrium
- Thick acidic cervical mucus produced
- Increases body temperature
- Changes in mammary tissue
- Metabolic and electrolyte changes
What happens after 14 days if no implantation occurs?
Corpus Luteum kills himself by:
- Producing prostaglandins –> cuts of own blood supply
What follows the Reproductive cyle if no implantation occurs?
Menstruation
What does the corpus luteum produce?
- Progesterone –> inhibits FSH and LH
- Oestrogen
- Inhibin
What does the death of the Corpus Luteum cause? (3 things)
- Reduced progesterone + oestrogen
- Triggers menstrual menses (bleeding)
- Inhibition of FSH & LH releaved –> cycle repeated
What happens if implantation occurs?
Implanted embryo develops a placenta –> secretes Human Chorionic Gonadotropin (hCG)
What does hCG secreted by the placenta do?
Preserves the Corpus Luteum
How does the Corpus Luteum help in pregnancy?
Secretes oestrogen and progesterone –> suppors early weeks of pregancy and suppresses ovarian cycle
What are the 2 categories of Testosterone effects?
- Determinative Effects
- Regulatory Effects
Which of the types of testosterone effects is more reversible?
Regulatory effects (highly reversible)
The determinative effects are only partially reversible
What are the determinative effects of testosterone?
Mostly secondary sexual characteristics e.g deepening of voice
What do the regulatory effects of testosterone rely on for maintenance?
Continous hormonal stimulation
What are the regulatory effects of testosterone? (3 things)
- Maintenace of male internal genitalia
- Metabolic effects (anabolic action)
- Behavioural effects (aggression / sexual activity)
What is the feedback control of gonadal steroids in males?
Testosterone reduces GnRH secretion
What is the feedback control of gonadal steroids in females? (6 points)
- Moderate oestrogen concentration –> reduces GnRH (negative feedback)
- High oestrogen concentration –> increases GnRH secretion (positive feedback)
- High oestrogen concentration –> LH surge
- Progesterone prevents positive feedback and surge
- Oestrogen affects amount of GnRH released per pulse
- Progesterone affects frequency of pulses
What is puberty?
A sequence of events called Tanner stages
What is puberty controlled by?
HPG axis activation
What are the 5 Tanner stages?
- Hormone release begins
- First physical changes noticeable
- Growth spurts, Physical change progression
- Key functional events
- Adult physical appearance & function
What happens in the first Tanner stage?
Hormone release begins
But NO physical changes
What happens in the 2nd Tanner stage?
First physical changes visible:
Girls: breast bud
Boys: testes and scrotum enlargement
What happens in the 3rd Tanner Stage?
Growth spurts, Physical change progression:
Girls: Fat deposits on hips
Boys: Voice cracking and nocturnal ejaculations
What happens in the 4th Tanner stage?
Key functional events
Girls: Menarche (first period)
Boys: Spermatogenesis
What happens in the 5th Tanner stage?
Adult physical appearance and function
Girls: Regular periods and ovulation
Boys: Facial hair and musculature
What is early puberty called?
Precocious puberty
What happens in Precocious puberty?
Signs of puverty before age of 8 (girls) and 9 (boys)
What are the causes of Precocious puberty? (2 things)
- Neurological issues impact central maturation signalling
- Pineal tumours
- Meningitis - Uncontrolled gonadotropin / steroid release
- Hormone secreting tumours of pituitary / gonads
What is the treatment for Precocious puberty?
Blocking gonadotropin release from pituitary
What is Delayed puberty?
No testicular development in boys by age 14
No breast development in girls by 13 or menarche by 15
What are the causes of Delayed puberty? (3 things)
- Malnutrition and chronic illness
- Issues with gonads / thyroids / pituitary glands
- Genetic conditions (Androgen insensitivity / Klinefelters syndrome)
What is the treatment for Delayed puberty?
Pulsative GnRH infusions
What age is pre-menopause?
40’s
What changes to the menstrual cycle occur in Pre-menopause?
- Follicular phase shortens (ovulation occurs early / absent)
- Reduced oestrogen secretion
- Increased FSH & LH because reduced negative feedback
- Reduced fertility
What is menopause?
Cessation of menstrual cycle
What is the usual age of menopause?
49-50 years old
What happens to oestrogen levels in menopause?
Oestrogen levels drop a lot
What happens to FSH and LH levels in menopause and why?
Increase a lot
Because there is no negative feedbak via gonadal steroids and inhibin
What are vascular changes that occur at menopause?
Hot flushes caused by because increased skin temperature
What are the hot flushes of menopause relieved by?
Oestrogen treatment
What changes occur to the uterus at menopause? (2 things)
- Regression of the endometrium
- Shrinkage of the myometrium
What happens to the cervix at menopause?
Becomes thinner
What happens to breast tissue at menopause?
Shrinks
What other changes occur at menopause?
Skin and bladder changes
How are bones changes at menopause? (3 things)
- Bone mass declines by 2.5% per year
- Increased reabsorption relative to production
- Oesteoporosis –> increased risk of fractures
How can the changes to bone at menopause be limited?
Oestrogen therapy
When does Post-menopause start?
After there hasn’t been any periods for 12 consecutive months
What are the benefits of Hormone Replacement Surgery?
- Relieves menopause symptoms
- Increases well being
- Limits osteoporosis
What are the risk factors of Hormone Replacement Surgery?
- Increased risk of malignancy (especially in breast tissue because they are stimulated to grow by oestrogen)
- Women who have NOT had hysterectomies should NOT be given oestrogen only preparations because risk of endometrial thickening
