Hormone Balance

Hormone Balance

Some jobs, such as growing up, controlling blood sugar and running a monthly cycle, need slower and steadier control than nerves can give. That is the job of **hormones**: chemical messengers secreted by **endocrine glands** straight into the **blood**, which carries them to their **target organs**. The glands to know: **pituitary** (the master gland, whose hormones act on other glands), **pancreas** (insulin and glucagon), **thyroid** (thyroxine), **adrenal** (adrenaline), **ovaries** (oestrogen) and **testes** (testosterone). The two control systems compare like this:

Match gland to hormone

Tell them apart

A nervous response travels as an electrical impulse along a _____, so it is very _____ and its effect is short-lived. A hormonal response travels as a chemical in the _____, so it is slower to start but its effect is _____.

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

Follow blood glucose through a full negative-feedback loop after a meal.

• You eat a sugary meal and blood glucose rises. Which organ detects this, and what does it release?
• Insulin reaches the liver. What does the liver do with the excess glucose?
• Hours later you have not eaten and blood glucose drops too low. [HT] Which hormone restores it?

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, and the two types fail in different places:

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, and an evaluation question wants a point from each column rather than a list from one:

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

Order the cycle

Put the four menstrual-cycle hormones into the order they act, starting from the beginning of the cycle.

• FSH matures an egg in the ovary and stimulates oestrogen production
• Oestrogen builds up the uterus lining and inhibits FSH
• A surge of LH triggers ovulation, around day 14
• Progesterone maintains the lining, and when it falls the lining breaks down

Name the controller

The hormone that sets your metabolic rate, and is itself held steady by negative feedback, is _____. The hormone behind fight-or-flight, which is NOT controlled by negative feedback, is _____. The hormone controlling how much water the kidneys reabsorb is _____, and the type of control loop that keeps a level steady by reversing any change is called _____ feedback.

Describe the loop

A person eats a large meal and their blood glucose rises sharply. Describe how negative feedback brings it back to normal, and then what happens if it falls too low.

• Name the organ that detects the change and the hormone it releases when glucose is high
• Say what that hormone makes the liver and muscle cells do to the glucose
• Then take the opposite case: which hormone is released, and what it does to the stored glycogen

In the exam

Three higher-tier controllers round the topic off: • **Thyroxine** (thyroid) sets the **metabolic rate**, kept steady by **negative feedback**: low thyroxine triggers its release, high thyroxine shuts it off. • **Adrenaline** (adrenal glands) powers **fight-or-flight**, boosting heart rate and glucose supply, and is **NOT** controlled by negative feedback. • **[Biology-only]** **ADH** controls how much water the kidneys reabsorb: another negative-feedback loop. 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 rather than just naming them. • **Menstrual cycle**: sequence the four hormones. FSH matures, oestrogen builds and triggers LH, LH ovulates, progesterone maintains. • **IVF**: always give a **balanced** answer. Benefit (a pregnancy) against drawbacks (low success rate, multiple births, emotional and physical stress, cost).