Welcome to Hormonal Coordination!

In this chapter, we are going to explore how your body sends "chemical text messages" to keep everything running smoothly. While the nervous system uses fast electrical signals, the hormonal system (or endocrine system) uses chemicals to coordinate long-term changes like growing up, managing your energy, and even controlling your mood. It’s all part of homeostasis—the way your body keeps its internal environment stable, no matter what is happening outside!

1. The Human Endocrine System

The endocrine system is made of glands. These glands secrete (release) chemicals called hormones directly into your bloodstream. The blood then carries these hormones to a target organ where they produce an effect.

Hormones vs. Nerves:
Don't worry if you get these mixed up! Just remember: Nervous responses are lightning-fast but short-lived. Hormonal responses are usually slower but their effects last much longer.

The "Master Gland"

The pituitary gland, located in the brain, is known as the "master gland." It secretes several hormones into the blood in response to body conditions. These hormones can act on other glands, telling them to release even more hormones to bring about specific effects.

Key Glands You Need to Know:

  • Pituitary Gland: In the brain (The Boss).
  • Thyroid: In the neck (Controls metabolism).
  • Adrenal Gland: Just above the kidneys (The "Flight or Fight" center).
  • Pancreas: Near the stomach (Controls blood sugar).
  • Ovaries (Female): Produce oestrogen.
  • Testes (Male): Produce testosterone.

Quick Review: The endocrine system uses hormones in the blood to send slow, long-lasting messages to target organs.

2. Control of Blood Glucose

Your body needs glucose (sugar) for respiration, but too much or too little in the blood is dangerous. The pancreas is the organ in charge of monitoring this.

If Blood Sugar is TOO HIGH:

  1. The pancreas produces the hormone insulin.
  2. Insulin causes glucose to move from the blood into the cells.
  3. In liver and muscle cells, excess glucose is converted to glycogen for storage.

(Higher Tier Only) If Blood Sugar is TOO LOW:

  1. The pancreas produces the hormone glucagon.
  2. Glucagon causes the stored glycogen in the liver to be converted back into glucose.
  3. This glucose is released into the blood.

Memory Trick:
When the glucose is gone, you need glucagon!

Diabetes

Sometimes the body can't control blood sugar levels correctly. This is called diabetes.

  • Type 1 Diabetes: The pancreas fails to produce enough insulin. It is usually treated with insulin injections.
  • Type 2 Diabetes: The body cells no longer respond to insulin. Obesity is a major risk factor. It is usually treated with a carbohydrate-controlled diet and regular exercise.

Key Takeaway: The pancreas uses insulin to lower blood sugar and glucagon (HT) to raise it, keeping you in a healthy balance.

3. Maintaining Water and Nitrogen Balance (Biology Only)

Your cells work best when they aren't too "watery" or too "salty." If cells lose or gain too much water by osmosis, they won't function efficiently.

How we lose water:

  • Lungs: During exhalation (breathing out).
  • Skin: Through sweat (this also loses ions and urea). Note: The body cannot control how much water we lose this way.
  • Kidneys: Through urine. This IS controlled by the body!

(Higher Tier Only) The Liver and Urea

When you eat too much protein, the excess amino acids must be excreted safely. In the liver, these are deaminated to form ammonia. Because ammonia is toxic, the liver immediately converts it to urea, which is then sent to the kidneys.

Kidney Function

The kidneys produce urine by filtration of the blood and then selective reabsorption of useful things like glucose, some ions, and the right amount of water.

(Higher Tier Only) ADH and Water Control

The amount of water in your blood is controlled by a hormone called ADH, released by the pituitary gland.

  • If blood is too concentrated (not enough water), MORE ADH is released. This makes the kidney tubules more permeable, so more water is reabsorbed back into the blood.
  • This is a negative feedback cycle.

Treating Kidney Failure

If kidneys stop working, people can be treated by:

  1. Dialysis: A machine filters the blood artificially.
  2. Transplant: A healthy kidney is put into the patient's body.

Quick Review: The kidneys filter the blood. ADH (HT) tells the kidneys how much water to keep or let go.

4. Hormones in Reproduction

During puberty, reproductive hormones cause secondary sex characteristics to develop (like facial hair in men or breasts in women).

  • Testosterone: Produced by the testes. It stimulates sperm production.
  • Oestrogen: Produced by the ovary. It is the main female reproductive hormone.

The Menstrual Cycle

There are four main hormones you need to know:

  1. FSH (Follicle Stimulating Hormone): Causes an egg to mature in the ovary.
  2. LH (Luteinising Hormone): Stimulates the release of the egg (ovulation).
  3. Oestrogen & Progesterone: Involved in maintaining the uterus lining.

(Higher Tier Only) Hormone Interactions:
FSH stimulates the ovaries to produce oestrogen. Oestrogen then stops (inhibits) FSH and starts the release of LH.

Common Mistake: Don't confuse FSH and LH! Remember: FSH comes First to make the egg grow. LH makes the egg Leave the ovary.

5. Contraception

Fertility can be controlled in several ways:

  • Hormonal: Oral contraceptives (the pill), injections, or implants. These use hormones to inhibit FSH so no eggs mature.
  • Barrier methods: Condoms or diaphragms (these also prevent STIs!).
  • IUDs: Prevent embryos from implanting or release hormones.
  • Spermicides: Kill or disable sperm.
  • Surgical: Sterilisation (permanent).

6. Treating Infertility (Higher Tier Only)

Sometimes couples need help to have a baby.

  • Fertility Drugs: Giving a woman FSH and LH to help her mature and release eggs.
  • IVF (In Vitro Fertilisation):
    1. Mother is given FSH and LH to mature several eggs.
    2. Eggs are collected and fertilised by father's sperm in a lab.
    3. The fertilised eggs develop into embryos.
    4. One or two embryos are inserted into the mother's uterus.

Note: IVF is stressful, has low success rates, and can lead to multiple births.

7. Adrenaline and Thyroxine (Higher Tier Only)

These two hormones are great examples of how the body reacts to the world.

Adrenaline

Produced by the adrenal glands in times of fear or stress. It increases your heart rate to boost delivery of oxygen and glucose to your brain and muscles. This is the "flight or fight" response!

Thyroxine

Produced by the thyroid gland. It stimulates your basal metabolic rate (how fast your body uses energy) and is important for growth and development. Its levels are controlled by negative feedback.

Did you know? Negative feedback is like a see-saw. If a level gets too high, the body works to bring it down. If it gets too low, the body works to bring it up. This keeps you in the "Goldilocks zone"—just right!

Key Takeaway: Adrenaline prepares you for action, while Thyroxine keeps your body's "engine" idling at the right speed.