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 _____.

Where the glands are

Knowing what each gland makes is half the job. The other half is finding it on a diagram of the body, which exam questions ask for directly. The pituitary gland hangs just under the middle of the brain. The thyroid wraps around the front of the neck. The pancreas lies across the upper abdomen, behind and just below the stomach. An adrenal gland sits on top of each kidney, like a cap. The ovaries are low in the abdomen, one on each side, and the testes sit in the scrotum, outside the abdomen. Every one of them releases its hormones into the blood, which is why a gland can sit a long way from its target organ.

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.

Put each gland in its place

Tap the name of a gland, then tap the pin where it sits in the body.

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).

What fails without each one

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

Name each line on the graph

Tap a label, then tap the pin on the line, or the part of the cycle, that it names.

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).