Hormonal coordination in humans — AQA GCSE Biology

Revision notes

11 short notes, in the order of the specification. Each one in short:

1. The human endocrine system

   The endocrine system is made of glands that secrete hormones directly into the bloodstream. The blood carries each hormone to a target organ, where it produces an effect. Compared with the nervous system, its effects are slower but act for longer. The pituitary gland is a master gland: its hormones stimulate other glands to release hormones.

2. Control of blood glucose concentration

   Blood glucose concentration is monitored and controlled by the pancreas. If the concentration is too high, the pancreas produces the hormone insulin, which causes glucose to move from the blood into the cells. In liver and muscle cells, excess glucose is converted to glycogen for storage, so the blood glucose concentration falls back to the normal level.

3. Type 1 and Type 2 diabetes

   Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin, causing uncontrolled high blood glucose levels. It is normally treated with insulin injections. In Type 2 diabetes the body cells no longer respond to the insulin produced by the pancreas. Treatments are a carbohydrate controlled diet and an exercise regime; obesity is a risk factor.

4. Water balance and the effect of osmosis on cells

   Triple only

   Water balance means controlling how much water the body loses. Water leaves via the lungs when we breathe out, and water, ions and urea are lost in sweat, but only the kidneys can adjust the amounts lost, removing excess water, ions and urea in urine. Cells that gain or lose too much water by osmosis do not function efficiently.

5. The kidneys and urea

   Triple only

   The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances. Water, glucose, ions and urea are filtered out of the blood, then all of the glucose, some ions and some water are reabsorbed. The urea, excess ions and excess water leave the body in the urine, so healthy urine contains no glucose.

6. ADH and water level

   Triple onlyHigher tier

   ADH is a hormone released by the pituitary gland when the blood is too concentrated. It acts on the kidney tubules, making them more permeable to water, so more water is reabsorbed into the blood and a small volume of concentrated urine is produced. This is negative feedback: when the water level returns to normal, less ADH is released.

7. Kidney failure: dialysis and transplant

   Triple only

   Kidney failure can be treated by dialysis or by an organ transplant. In dialysis, the blood flows next to a partially permeable membrane, and urea and excess ions diffuse into the dialysis fluid, while glucose stays in the blood. A transplant is a long-term treatment, but donor kidneys are in short supply and the body may reject the new kidney.

8. Hormones in human reproduction

   Reproductive hormones cause secondary sex characteristics to develop during puberty. Oestrogen, made by the ovary, is the main female reproductive hormone. Testosterone, made by the testes, is the main male reproductive hormone and stimulates sperm production. In the menstrual cycle, FSH causes an egg to mature, LH stimulates its release, and oestrogen and progesterone maintain the uterus lining.

9. Contraception

   Contraception controls fertility using hormonal or non-hormonal methods. Oral contraceptives contain hormones that inhibit FSH production so that no eggs mature, and injections, implants or skin patches slowly release progesterone. Non-hormonal methods include condoms and diaphragms, which prevent sperm reaching an egg, spermicidal agents, which kill or disable sperm, and surgical sterilisation, which is permanent.

10. The use of hormones to treat infertility

    Higher tier

    Infertility can be treated with a fertility drug containing FSH and LH, so a woman may then become pregnant normally. In IVF, FSH and LH make several eggs mature. The eggs are collected and fertilised by sperm in the laboratory, and one or two embryos are inserted into the uterus. IVF is stressful and success rates are not high.

11. Adrenaline, thyroxine and negative feedback

    Higher tier

    Adrenaline is a hormone produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for flight or fight. Thyroxine from the thyroid gland stimulates the basal metabolic rate, and its level is controlled by negative feedback.