Hormonal Control of Reproduction Flashcards
What are the 2 groups of hormones?
- Water-soluble
- Fat-soluble
What are water-soluble hormones formed from?
Amino acids
Are water-soluble hormones hydrophilic or hydrophobic?
Hydrophilic
Why can’t water-soluble hormones pass through target cell membranes?
- Cell membranes contain lipid components
- Water-soluble hormone (e.g. FSH) bind to receptor molecules protruding from surface of target cell
- Binding activates enzymes inside cell that regulates biochemical activity of the cell
What does lipophilic mean?
Dissolve in fat
(Fat-soluble hormones are lipophilic)
What are fat-soluble hormones usually formed from?
Cholesterol
Also referred to as steroid hormones
What happens when fat-soluble hormones pass through membrane?
- Binds to a receptor to form a hormone-receptor complex
- HRC moves to nucleus & binds to region of DNA
- Binding causes genes to switch ‘on’ or ‘off’ the activity of enzymes that regulate activity of the cell
What are the 3 principal glands involved in male reproductive hormone production (hypothalamic-pituitary-gonadal axis)?
- Hypothalamus
- Pituitary gland
- Gonads (testes)
What are the 3 principal glands involved in male reproductive hormone production usually referred to?
Hypothalamic-pituitary-gonadal axis (HPG axis)
What type of effects can sex hormones have?
- Organising effects - occur mostly at sensitive
stages of development – e.g. might
determine whether brain & body will
develop m or f characteristics - Activating effects - occur at any time of life & activate a particular response
What are sex limited genes?
- Genes that control most of the differences between m & f
- Present in both sexes but expressed in only 1 sex
- Result = 2 sexes showing different phenotype but have same genotype
- E.g. genes that control milk yield in diary cattle present in both bulls & cows, but only expressed in cow
What are the 6 major hormones involved in male reproduction?
- Gonadotropin Releasing Hormone (GnRH)
- Follicle Stimulating Hormone (FSH)
- Luteinising hormone (LH)
- Androsterone
- Testosterone
- Sex Hormone-Binding Globulin (SHBG)
What is dihydrotestosterone (DHT)?
- A more potent form of testosterone
- Androsterone can be directly converted to it
What is testosterone synthesised from?
Cholesterol
Are SHBG (sex hormone-binding globulin) levels higher in males or females?
Females
Does testosterone increase or decrease as men age?
Decrease
What are 4 side effects of testosterone & anabolic steroid abuse?
- Testicular atrophy
- Infertility
- Prostate enlargement
- Liver damage
The cyclic changes that occur in the female oestrus/menstrual cycle are initiated & regulated by hormones from where?
- Hypothalamus
- Pituitary
- Ovaries
- The hypothalamic-pituitary-ovarian (HPO) axis
What is the results of an increase in oestrogen?
(3 points)
- Initiates morphological changes in uterus & vagina
- Triggers oestrous behaviour
- Suppresses the release of GnRH (LHRH) by the hypothalamus & inhibits pituitary
secretion of LH and FSH (negative
feedback)
What happens once oestrogen levels peak?
- Inhibition of LHRH & gonadotrophin secretion ceases
- Results in surge in LHRH/GnRH & subsequent surge in LH
- This triggers ovulation- the Graafian follicle ruptures & egg is released
When does progesterone levels start to increase?
During pro-oestrus & peak during ovulation
Following ovulation, what does progesterone & oestrogen inhibit?
LH & FSH secretion
What does the corpus luteum secrete for pregnancy?
Progesterone
What does the body release if fertilisation doesn’t occur & why?
- Prostaglandins
- Causes corpus luteum to break down
What happens as progesterone levels begin to fall?
FSH levels begin to rise & cycle begins again
What happens if fertilisation occurs?
- Zygote moves from oviduct to uterus under control of oestrogen
- Progesterone prepares uterus for pregnancy by:
• Decreasing muscular activity of uterus
• Thickening the uterus lining
• Producing nutrients to feed zygote
How does progesterone prepare the uterus for pregnancy?
- Decreasing muscular activity of uterus
- Thickening the uterus lining
- Producing nutrients to feed zygote
In mammals that have oestrus cycles, what happens to the endometrium if conception does not occur?
It is reabsorbed
What does the combined oral contraceptive pill contain?
- Synthetic oestrogen (Estrogen)
- Synthetic progesterone (Progestogen)
How does the combined pill work?
- Inhibits FSH and LH production in pituitary to prevent follicular development & ovulation
- Progesterone thins endometrium, making it difficult for a fertilised egg to implant
- Thickens mucus in cervix, so it is
harder for sperm to move up the tract to reach an egg
What does the mini pill contain?
Progesterone only
How does the mini pill work?
- Takes every day with no break
- Suppresses ovulation (but not consistently)
- Thickens cervical mucus to stop sperm
reaching an egg - Thins endometrium to
prevent implantation
What is the morning after pill?
- E.g. Levonelle
- Progesterone-only hormone pill
- Delays release of an egg from an ovary,
therefore preventing pregnancy
What are the 2 types of IUD?
- Non-hormonal ones that contain copper
- Hormonal ones that slowly release a low dose of a synthetic hormone called levonorgestrel
How do copper IUD’s work?
- T-shaped piece of plastic wrapped in copper wire with a dabbling ‘tail’ of threads
- Produces an inflammatory reaction that is toxic to sperm & eggs, preventing pregnancy
