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,