Key Takeaways for Hormonal Coordination in Humans

1. The Human Endocrine System

  • Hormones: Chemical messengers secreted by glands into the bloodstream. They act on target organs to regulate processes like growth, metabolism, and reproduction.
  • Key Glands & Hormones:HormoneGlandTarget OrganFunctionADHPituitaryKidneysControls water concentration in urine.InsulinPancreasLiverLowers blood glucose by converting it to glycogen.GlucagonPancreasLiverRaises blood glucose by breaking down glycogen.AdrenalineAdrenal glandsHeartPrepares body for “fight or flight” (↑ heart rate, blood glucose).ThyroxineThyroidBody cellsRegulates metabolic rate, protein synthesis, and hormone sensitivity.OestrogenOvariesUterusControls puberty, menstrual cycle, and thickens uterine lining.TestosteroneTestesReproductiveControls puberty, sperm production, and male secondary characteristics.
  • Pituitary Gland: The “master gland” that secretes hormones to regulate other glands (e.g., TSH stimulates the thyroid).

2. Blood Glucose Regulation

  • Homeostasis: Maintains blood glucose at ~90 mg/dL.
    • Insulin: Secreted when blood glucose is too high. Converts glucose → glycogen (stored in liver/muscles).
    • Glucagon: Secreted when blood glucose is too low. Converts glycogen → glucose.
    • Negative Feedback: Adjustments reverse changes (e.g., high glucose → insulin release → glucose ↓).
  • Diabetes:
    • Type 1: Autoimmune destruction of insulin-producing cells. Treated with insulin injections, diet, and exercise.
    • Type 2: Insulin resistance (often due to obesity). Managed via diet, exercise, and medication.
    • Graph Analysis: Diabetic patients (e.g., Patient B) show higher blood glucose peaks and slower return to baseline.

TIP:

  • INsulin puts glucose IN storage.
  • GlucaGON releases glucose when it’s GONE.

3. Water & Nitrogen Balance

  • ADH (Anti-diuretic hormone):
    • Produced by the pituitary gland.
    • Controls water reabsorption in kidneys.
    • Dehydration → ↑ ADH → concentrated urine.
      Overhydration → ↓ ADH → dilute urine.
  • Kidney Function:
    1. Filtration: Blood filtered in nephrons (removes urea, ions, water).
    2. Reabsorption: Useful substances (glucose, some water/ions) reabsorbed.
    3. Excretion: Urea and excess water/ions expelled as urine.
  • Kidney Failure Treatments:
    • Dialysis: Machine filters blood (time-consuming, temporary).
    • Transplant: Permanent solution; requires donor match to prevent rejection.

Example Calculation:
If total water input = 2500 cm³:
Water from food=2500−1400 (drink)−300 (metabolic)=800 cm3Water from food=2500−1400(drink)−300(metabolic)=800cm3

4. Hormones in Reproduction

  • Menstrual Cycle (28 days):HormoneSourceFunctionFSHPituitaryStimulates egg maturation and oestrogen production.OestrogenOvariesThickens uterine lining; inhibits FSH, stimulates LH.LHPituitaryTriggers ovulation (day 14).ProgesteroneCorpus luteumMaintains uterine lining; inhibits FSH/LH.
  • Negative Feedback: High oestrogen inhibits FSH; high progesterone inhibits LH/FSH.

Graph Tip: Uterine lining thickness peaks around day 14 (ovulation) and sheds during menstruation (days 1–5).

5. Contraception & Fertility

  • Contraception Methods:
    • Hormonal: Pill (oestrogen + progesterone), implant, patch. Prevent ovulation by inhibiting FSH.
    • Barrier: Condoms (also prevent STIs), diaphragms.
    • Surgical: Vasectomy (sperm ducts cut), tubal ligation (fallopian tubes cut).
  • IVF (In Vitro Fertilisation):
    1. FSH/LH injections stimulate egg production.
    2. Eggs fertilised in lab → embryos implanted into uterus.
      Ethical Issues: Disposal of unused embryos; cost; multiple births.

6. Negative Feedback Examples

  1. Blood Glucose: Insulin/glucagon balance.
  2. Water Balance: ADH regulation.
  3. Menstrual Cycle: Oestrogen/progesterone control.
  4. Thyroxine: TSH stimulates thyroxine; low iodine → goitre (enlarged thyroid).

Adrenaline Exception: No negative feedback—released rapidly for short-term “fight or flight”.

Key Revision Tips

  1. Mnemonics: “INsulin IN, GlucaGON GONE”.
  2. Diagrams: Draw flowcharts for hormone interactions (e.g., menstrual cycle).
  3. Tables: Memorise hormone sources, targets, and functions using Table 12.1.
  4. Graph Practice: Interpret blood glucose curves (diabetic vs non-diabetic).
  5. Compare & Contrast: Type 1 vs Type 2 diabetes; dialysis vs transplant.

Exam Focus: Expect questions on interpreting data, explaining hormonal pathways, and evaluating treatments (e.g., IVF ethics).

50 GCSE Biology Questions on Hormonal Coordination

Section 1: The Endocrine System

  1. Define the term hormone.
  2. Name the gland that produces ADH.
  3. What is the function of thyroxine?
  4. Which hormone prepares the body for “fight or flight”?
  5. Why is the pituitary gland called the “master gland”?

Section 2: Blood Glucose Regulation

  1. Explain how insulin reduces blood glucose levels.
  2. What is the role of glucagon?
  3. Describe negative feedback in blood glucose control.
  4. Patient A’s blood glucose peaks at 144 mg/dL after eating, while Patient B’s peaks at 223 mg/dL. Which patient likely has diabetes? Why?
  5. Compare Type 1 and Type 2 diabetes in terms of causes and treatments.

Section 3: Water & Nitrogen Balance

  1. How does ADH affect urine concentration?
  2. Calculate the volume of water gained from food if total input is 2500 cm³, drink is 1400 cm³, and metabolic water is 300 cm³.
  3. Outline the three steps in kidney filtration.
  4. Why might a kidney transplant fail?
  5. Compare dialysis and transplants as treatments for kidney failure.

Section 4: Reproductive Hormones

  1. Name the four hormones involved in the menstrual cycle.
  2. What triggers ovulation?
  3. How does progesterone maintain pregnancy?
  4. Describe two secondary sexual characteristics caused by testosterone.
  5. Explain why the menstrual cycle stops during pregnancy.

Section 5: Contraception & IVF

  1. How does the contraceptive pill prevent pregnancy?
  2. What is a vasectomy?
  3. Why are condoms more effective than diaphragms at preventing STIs?
  4. Outline the steps in IVF.
  5. Give two ethical concerns about IVF.

Section 6: Negative Feedback

  1. Give three examples of negative feedback in hormonal control.
  2. How does TSH regulate thyroxine production?
  3. Explain why iodine deficiency causes a goitre.
  4. Why is adrenaline not regulated by negative feedback?

Section 7: Data Interpretation

  1. A blood glucose graph shows a slow return to baseline after eating. Is this Type 1 or Type 2 diabetes? Explain.
  2. In Table 12.5, if sweat output increases to 1000 cm³, how would the body adjust urine output?

Section 8: Extended Response

  1. Evaluate the advantages of insulin pumps over injections for Type 1 diabetes.
  2. Explain how FSH and LH interact during the menstrual cycle.
  3. Why might a person with Type 2 diabetes not use insulin injections?

Section 9: Calculations

  1. If a dialysis session removes 500 mg of urea, and the patient’s blood has 200 mg/dL urea, how many sessions are needed to reduce it to 50 mg/dL?

Section 10: Ethical & Practical Applications

  1. Why might an ethics committee deny IVF to Couple X (wanting a son)?
  2. Explain one economic argument against NHS-funded IVF.
  3. What is “three-person IVF”, and why is it controversial?

Answers

  1. Hormone: A chemical messenger secreted by glands into the bloodstream to regulate specific body functions.
  2. ADH is produced by the pituitary gland.
  3. Thyroxine regulates metabolic rate, protein synthesis, and hormone sensitivity.
  4. Adrenaline (from adrenal glands) prepares the body for “fight or flight”.
  5. The pituitary gland controls other glands (e.g., TSH stimulates the thyroid).
  6. Insulin converts glucose → glycogen in the liver, lowering blood glucose.
  7. Glucagon breaks down glycogen → glucose, raising blood glucose.
  8. Negative feedback: High glucose → insulin release → glucose ↓; Low glucose → glucagon release → glucose ↑.
  9. Patient B has diabetes. Their blood glucose remains elevated (223 → 138 mg/dL over 6 hours vs. 144 → 82 mg/dL in Patient A).
  10. Type 1: Autoimmune destruction of pancreatic cells (insulin injections). Type 2: Insulin resistance (diet/exercise).
  11. ADH increases water reabsorption in kidneys → concentrated urine.
  12. Water from food=2500−1400−300=800 cm3Water from food=2500−1400−300=800cm3
  13. Kidney steps: Filtration (blood → nephron), reabsorption (glucose/ions retained), excretion (urea/water expelled).
  14. Transplant failure due to immune rejection or donor mismatch.
  15. Dialysis: Temporary, time-consuming. Transplant: Permanent but requires immunosuppressants.
  16. FSH, LH, oestrogen, progesterone.
  17. LH surge triggers ovulation (~day 14).
  18. Progesterone maintains the uterine lining and inhibits FSH/LH.
  19. Testosterone causes deepening voice, muscle growth, facial hair.
  20. High progesterone during pregnancy inhibits menstruation.
  21. The pill inhibits FSH (prevents ovulation) and thickens cervical mucus.
  22. Vasectomy: Cutting/blocking sperm ducts to prevent ejaculation of sperm.
  23. Condoms block bodily fluid exchange; diaphragms do not.
  24. IVF steps: FSH injections → egg retrieval → lab fertilisation → embryo implantation.
  25. Ethical issues: Embryo disposal, “designer babies”, cost.
  26. Examples: Blood glucose, ADH, menstrual hormones, thyroxine.
  27. TSH stimulates thyroxine release; low thyroxine → ↑ TSH (negative feedback).
  28. Iodine deficiency → ↓ thyroxine → ↑ TSH → thyroid enlarges (goitre).
  29. Adrenaline is released rapidly for short-term emergencies (no feedback).
  30. Type 2 diabetes (slow insulin response).
  31. Urine output decreases to maintain water balance: 2500−1000−100=1400 cm3 urine2500−1000−100=1400cm3 urine.
  32. Insulin pumps provide continuous dosing, improving glucose control.
  33. FSH matures eggs and stimulates oestrogen; LH triggers ovulation.
  34. Type 2 patients often have insulin resistance; diet/exercise improve sensitivity.
  35. Sessions needed: 200−50500/100=3 sessions500/100200−50​=3sessions.
  36. Gender selection is ethically controversial (non-medical preference).
  37. Cost: IVF cycles (~£5,000 each) strain NHS budgets.
  38. Three-person IVF uses mitochondrial DNA from a donor; critics argue ethical risks of genetic modification.

Revision Tip: Practice graphing blood glucose data and hormone interaction flowcharts!