Hormone Balance

Hormone Balance 🧬

Your nervous system fires fast messages down nerves. But some jobs — growing up, controlling blood sugar, running a monthly cycle — need slower, steadier control. That is the job of **hormones**: chemical messengers released by glands into the blood. This module runs the whole endocrine control system, with **negative feedback** as the thread tying it together.

The endocrine system 🩸

**Endocrine glands** secrete **hormones** straight into the **blood**, which carries them to their **target organs**. Compared with nerves, hormonal responses are **slower** but **longer-lasting**. The main glands: • **Pituitary** — the **'master gland'** in the brain; its hormones act on other glands. • **Pancreas** — insulin (and glucagon) • **Thyroid** — thyroxine • **Adrenal glands** — adrenaline • **Ovaries** — oestrogen • **Testes** — testosterone

Match gland to hormone

Nerves or hormones?

Compared with a nervous response, a hormonal response is generally…

• Slower to act but longer-lasting
• Faster to act and shorter-lasting
• Carried as electrical impulses along neurones
• Identical in speed and duration

Controlling blood glucose 🍬

The **pancreas** constantly monitors and controls blood glucose: • Glucose **too high** → the pancreas releases **insulin**. Insulin makes cells take up glucose and the **liver** turn excess glucose into **glycogen** for storage. Blood glucose **falls**. • **[HT]** Glucose **too low** → the pancreas releases **glucagon**. Glucagon makes the liver turn **glycogen** back into **glucose**. Blood glucose **rises**. Insulin and glucagon are a matched pair pulling in opposite directions — classic **negative feedback**.

Balance the blood sugar

An interactive activity.

Fill the feedback loop

When blood glucose is high, _____ makes the liver store glucose as _____. When it is low, [HT] _____ makes the liver release glucose again.

When it goes wrong: diabetes 💉

**Diabetes** is a failure of blood-glucose control: • **Type 1** — the pancreas makes little or no **insulin**, so blood glucose can rise dangerously high. Treated with **insulin injections**. • **Type 2** — body cells stop responding properly to insulin (**insulin resistance**). **Obesity** is a major risk factor. Treated with a **carbohydrate-controlled diet**, **exercise**, and medication if needed.

True of type 2 diabetes?

Pick the TWO statements that are true of **type 2** diabetes.

• The body's cells stop responding properly to insulin
• It is often managed with a carbohydrate-controlled diet and exercise
• The pancreas makes no insulin at all
• It always requires insulin injections from birth

The menstrual cycle 🌸

Four hormones run the roughly 28-day cycle: • **FSH** (from the pituitary) — **matures an egg** in the ovary and stimulates the ovary to make oestrogen. • **Oestrogen** (from the ovaries) — **builds up the uterus lining**; it inhibits FSH and triggers a surge of LH. • **LH** (from the pituitary) — **triggers ovulation** (egg release) around day 14. • **Progesterone** (from the ovaries) — **maintains the uterus lining**; when it falls, the lining breaks down (a period).

Match the cycle hormone

Controlling fertility 🛡️

Contraception prevents pregnancy in two broad ways: • **Hormonal** — the **pill**, **injection**, **implant** and **patch** use oestrogen and/or progesterone to inhibit **FSH**, so no egg matures. • **Non-hormonal** — **barrier methods** (condom, diaphragm) stop sperm reaching the egg; plus the **IUD**, **spermicides**, **abstinence** and surgical **sterilisation**. Hormonal methods are very effective but can have side effects; barrier methods also protect against sexually transmitted infections.

Evaluating IVF [Higher tier]

In IVF, **FSH and LH** are given to stimulate egg maturation and release, then eggs are fertilised in the lab. A balanced evaluation of IVF should note that…

• It can help infertile couples conceive, but has a low success rate and can be emotionally and physically stressful
• It always works and has no drawbacks
• It never works and should never be used
• It uses insulin to mature the eggs

Two more controllers ⚙️ [Higher tier]

Two hormones round off the topic (both **Higher tier**): • **Thyroxine** (thyroid) sets the **metabolic rate** and is kept steady by **negative feedback** — low thyroxine triggers its release, high thyroxine shuts it off. • **Adrenaline** (adrenal glands) powers the **'fight-or-flight'** response, boosting heart rate and glucose supply — but it is **NOT** controlled by negative feedback. Also **[Biology-only, HT]**: the kidneys balance the body's water by filtering blood and reabsorbing what is useful, with **ADH** controlling how much water is reabsorbed — another negative-feedback loop.

In the exam 🎓

Balance restored. Grade-9 habits for hormonal coordination: • **Blood glucose**: name the pair — **insulin** lowers (glucose→glycogen), **[HT] glucagon** raises (glycogen→glucose) — and describe the **negative-feedback** loop, don't just name them. • **Menstrual cycle**: sequence the four hormones against the cycle — FSH matures, oestrogen builds + triggers LH, LH ovulates, progesterone maintains. • **IVF**: always give a **balanced** answer — benefit (a pregnancy) vs drawbacks (low success rate, multiple births, emotional/physical stress, cost).