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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: ADH, FSH and LH
Hormones are chemical messengers that travel in the bloodstream and control various body functions. In this session, we'll focus on three important hormones: ADH, FSH and LH. These hormones help regulate water balance and reproduction in the human body.
Key Definitions:
ADH is produced by the hypothalamus (a part of the brain) and stored in the pituitary gland. Its main job is to control the amount of water in your body by affecting how much water your kidneys reabsorb.
When your blood becomes too concentrated (meaning there's not enough water), the hypothalamus detects this and triggers the release of ADH from the pituitary gland. ADH travels through the bloodstream to the kidneys, where it makes the collecting ducts more permeable to water. This allows more water to be reabsorbed back into the blood, resulting in less water in your urine (more concentrated urine).
ADH works through a negative feedback system. When blood water concentration returns to normal, the hypothalamus stops stimulating ADH release. If you drink lots of water, your blood becomes more dilute and ADH secretion decreases. This means less water is reabsorbed by the kidneys, resulting in more dilute urine.
Diabetes insipidus is a condition where the body doesn't produce enough ADH or the kidneys don't respond to it properly. People with this condition produce large volumes of dilute urine (up to 20 litres per day!) and feel extremely thirsty. It's different from diabetes mellitus (type 1 or 2), which involves insulin problems. Treatment often involves ADH replacement therapy.
FSH is produced by the pituitary gland and plays crucial roles in both male and female reproductive systems. Its name comes from its role in stimulating follicles in the ovaries.
In females, FSH stimulates the development of follicles in the ovaries. Each follicle contains an immature egg cell (oocyte). FSH also triggers the follicles to produce oestrogen, which is important for the development of female secondary sexual characteristics and preparing the uterus for pregnancy.
In males, FSH stimulates the Sertoli cells in the testes. These cells support sperm development (spermatogenesis). FSH is essential for the production of healthy, mature sperm cells, though it doesn't directly cause sperm production.
Doctors can measure FSH levels in the blood to investigate fertility issues. High FSH levels in women might indicate that the ovaries aren't working properly (as the body tries to stimulate them more). In men, high FSH could suggest problems with sperm production.
Like FSH, LH is produced by the pituitary gland and is crucial for reproduction. It works alongside FSH but has different specific functions in males and females.
In females, LH triggers ovulation - the release of a mature egg from the ovary. After ovulation, LH helps transform the empty follicle into the corpus luteum, which produces progesterone to maintain the uterine lining in case of pregnancy. The sharp rise in LH (known as the "LH surge") is what ovulation predictor kits detect.
In males, LH stimulates the Leydig cells in the testes to produce testosterone. Testosterone is essential for sperm production and the development of male secondary sexual characteristics like facial hair, deeper voice and muscle development.
The menstrual cycle is a perfect example of how hormones work together in a complex feedback system. FSH and LH play crucial roles throughout the cycle.
Understanding FSH and LH is crucial for fertility treatments. In procedures like IVF (in vitro fertilisation), synthetic FSH is often given to stimulate multiple follicles to develop. Then, an injection of LH or similar hormones triggers the final maturation of eggs before they're collected. This knowledge of reproductive hormones has helped millions of people worldwide overcome fertility issues.
Many contraceptive methods work by affecting FSH and LH levels. The combined contraceptive pill contains synthetic versions of oestrogen and progesterone, which prevent FSH and LH from being released. This stops ovulation from occurring, making pregnancy impossible.
| Hormone | Produced by | Target organs | Main functions |
|---|---|---|---|
| ADH | Hypothalamus (stored in pituitary) | Kidneys | Water reabsorption, blood concentration regulation |
| FSH | Pituitary gland | Ovaries (females), testes (males) | Follicle development, oestrogen production (females); supports sperm production (males) |
| LH | Pituitary gland | Ovaries (females), testes (males) | Triggers ovulation, forms corpus luteum (females); testosterone production (males) |
Questions about ADH often focus on the negative feedback mechanism and how it responds to different scenarios (dehydration, excessive water intake). For FSH and LH, make sure you can explain their roles in both males and females and how they change during the menstrual cycle. Diagrams are often helpful for explaining these hormone pathways!
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