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GCSE Biology: Homeostasis and Hormonal Coordination

Hormonal Coordination in Humans

Human Endocrine System (5.3.1)

  • The human body has two communication systems: the nervous system and the endocrine system.

    • The endocrine system sends hormones (chemical messengers) throughout the body.

    • Hormones are secreted by glands directly into the bloodstream.

Key Glands and Their Functions:

  • Pituitary Gland

    • Known as the master gland.

    • Secretes hormones that affect the body and stimulate other glands.

  • Pancreas

    • Secretes insulin to control blood glucose levels.

  • Thyroid

    • Secretes thyroxine, regulating metabolic rate, heart rate, and temperature.

  • Adrenal Gland

    • Secretes adrenaline, involved in the 'fight or flight' response.

  • Ovary

    • Secretes oestrogen, involved in the menstrual cycle and female secondary sexual characteristics.

  • Testes

    • Secretes testosterone, involved in sperm production and male secondary sexual characteristics.

  • The hormonal system is slower than the nervous system but has longer-lasting effects.

Control of Blood Glucose Concentration (5.3.2)

  • Blood glucose levels must be maintained for cellular respiration.

  • High Glucose Levels:

    • Pancreas produces insulin.

    • Insulin facilitates glucose uptake by muscle cells and converts excess glucose to glycogen in the liver.

  • Low Glucose Levels:

    • Pancreas produces glucagon.

    • Glucagon prompts the liver to convert glycogen back to glucose, raising blood glucose levels.

  • Blood glucose regulation operates through a negative feedback loop.

Diabetes:

  1. Type 1 Diabetes:

    • Pancreas fails to produce enough insulin.

    • Treated with insulin injections and dietary management.

  2. Type 2 Diabetes:

    • Body cells become resistant to insulin.

    • Managed through diet, exercise, and medication.

Maintaining Water and Nitrogen Balance in the Body (5.3.3)

  • Osmosis:

    • Water moves from high to low concentration.

    • Imbalance can cause cells to burst or shrink.

The Kidneys:

  • Essential for maintaining water and substance balance.

  • Functions include:

    • Filtering waste products.

    • Selectively reabsorbing useful substances (glucose, ions, water).

Key Processes:

  • Water:

    • Lost through urine, lungs, and sweat.

  • Ions:

    • Regulated to maintain proper water balance in cells.

  • Urea:

    • Formed from deaminated amino acids in the liver and filtered by kidneys.

Anti-diuretic Hormone (ADH):

  • Regulates water loss in urine.

  • Released when blood is too concentrated, increasing kidney tubule permeability to water.

Kidney Failure Treatments:

  1. Dialysis:

    • Artificially filters blood.

    • Requires regular sessions and strict dietary control.

  2. Kidney Transplants:

    • Provides a healthy kidney from a donor.

    • Risks include rejection and the need for immunosuppressant drugs.

Hormones in Human Reproduction (5.3.4)

  • Reproductive hormones released during puberty lead to secondary sexual characteristics and egg maturation.

Key Hormones:

  • Testosterone:

    • Produced by testes; stimulates sperm production.

  • Oestrogen:

    • Produced by ovaries; regulates menstrual cycle and physical changes.

The Menstrual Cycle:

  • Involves hormonal regulation and preparation for potential pregnancy.

  • Key hormones include:

    1. Follicle Stimulating Hormone (FSH): Matures eggs and stimulates oestrogen production.

    2. Oestrogen: Promotes uterine lining growth and regulates FSH and LH.

    3. Luteinising Hormone (LH): Triggers ovulation.

    4. Progesterone: Maintains uterine lining and inhibits FSH and LH.

Contraception (5.3.5)

Hormonal Methods:

  • Contraceptive Pill:

    • Contains oestrogen and progesterone; prevents egg maturation.

  • Contraceptive Patch and Implant:

    • Releases hormones to prevent ovulation and thicken cervical mucus.

  • Contraceptive Injection:

    • Similar effects to the implant; lasts for 2-3 months.

Non-Hormonal Methods:

  • Chemical Methods: Spermicides kill or disable sperm.

  • Barrier Methods: Condoms and diaphragms prevent sperm from reaching the egg.

  • Surgical Methods: Permanent sterilization through cutting and tying tubes.

  • Abstinence: Prevents fertilization by avoiding intercourse.

The Use of Hormones to Treat Infertility (5.3.6)

  • Fertility Drugs: Increase chances of pregnancy by using FSH and LH.

  • In Vitro Fertilisation (IVF): Eggs are matured, fertilized in a lab, and implanted in the uterus.

Benefits and Cons of IVF:

  • Provides a chance for infertile couples to have children.

  • Physically and emotionally stressful with a low success rate (26%).

Negative Feedback (5.3.7)

  • Negative feedback maintains homeostasis by returning factors to original levels.

  • Thyroxine: Regulates metabolic rate; controlled by TSH and negative feedback.

  • Adrenaline: Triggers 'fight or flight' response during stress.

Plant Hormones (5.4 - Biology Only)

Control and Coordination (5.4.1)

  • Hormones coordinate plant growth and responses (e.g., phototropism and gravitropism).

  • Auxin: Promotes growth towards light and away from gravity.

Use of Plant Hormones (5.4.2)

  • Auxin:

    • Used in weed killers and rooting powders.

  • Ethene: Controls fruit ripening, reducing waste.

  • Gibberellins: Stimulate seed germination, flowering,