Human body systems, Year 11: hormones and blood glucose

A hormone

提示Insulin and adrenaline are two examples.

为什么The glands that make these chemicals form the endocrine system. Each messenger circulates everywhere, but only its target organ responds to it, which is how one chemical can bring about one particular effect.

slower; longer

提示Compare how quickly you blink with how gradually the body changes during puberty.

为什么A nerve impulse reaches its effector in a fraction of a second and the effect stops just as quickly. A hormone has to be made, released and carried to its target organ, so it takes more time to act, but it goes on acting for as long as it stays in the blood.

pituitary

提示It is nicknamed the 'master gland'.

为什么This pea-sized gland responds to conditions in the body by secreting hormones into the blood. Several of those hormones do not act on the body directly: their targets are other glands, such as the ovaries, which then release their own hormones.

neck; kidney

提示One is just below the voice box; the other organ filters the blood.

为什么GCSE asks you to find six glands on a diagram of the body: the pituitary at the base of the brain, the thyroid, the pancreas just below the stomach, the two adrenal glands, and the ovaries or the testes.

blood

提示It is the body's transport system, pumped by the heart.

为什么Endocrine glands have no tube leading away from them. The hormone passes straight from the gland's cells into the vessels running through it, and the circulation then carries it to every organ, including the one that responds.

Glucose moves out of the blood and into the body's cells

提示Ask where the sugar has to go for its level in the bloodstream to fall.

为什么The pancreas both monitors blood glucose and controls it. When the level is too high it releases insulin, and insulin makes cells take glucose in, so the concentration in the blood falls back towards normal.

glycogen

提示Its name begins 'gly-', and it does for animals what starch does for plants.

为什么Insulin makes cells take up glucose, and liver and muscle cells join the excess glucose molecules into a large insoluble molecule that can be stored. The store can be turned back into glucose later, when the level in the blood falls.

The pancreas does not produce enough insulin; it is treated with insulin injections

提示The treatment replaces the very thing that is missing.

为什么Without enough insulin, glucose stays in the blood after a meal and its level can rise dangerously high. Injecting insulin does the job the pancreas cannot, so the person has to match each dose to what they eat and how active they are.

Body cells no longer respond to insulin; a carbohydrate-controlled diet and regular exercise

提示Here the hormone is still being made, so the treatments are changes to lifestyle.

为什么In Type 2 the pancreas still makes insulin, but the body's cells have stopped responding to it properly, so glucose stays in the blood. Controlling how much carbohydrate is eaten and taking exercise both help to keep the level down. Obesity is a risk factor for this type.

Glucagon; it causes stored glycogen to be converted into glucose, which is released into the blood

提示It has the opposite effect to insulin, and it acts on the store in the liver.

为什么The pancreas makes two hormones with opposite effects. Insulin lowers blood glucose after a meal; this second hormone raises it between meals or during exercise by releasing glucose from the body's store.

Any change away from the normal level triggers a response that reverses the change

提示Think of a thermostat switching the heating off when the room gets too warm, and on when it gets too cold.

为什么If blood glucose rises, insulin is released and brings it down; if it falls, glucagon is released and brings it up. In both cases the response cancels out the change that caused it, so the level keeps returning to normal.

Adrenaline

提示Its name is taken from the glands that make it.

为什么When you are frightened or under stress, the two glands above the kidneys release this hormone into the blood. Its effects are felt within seconds: a pounding heart and a body ready for sudden effort.

It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles

提示Think about what hard-working tissues need more of, and what carries it to them.

为什么Muscles and brain cells release energy by respiration, which needs glucose and oxygen. A faster heartbeat sends more blood to them each minute, so they are supplied for a burst of action, whether that is to face the danger or to run from it.

metabolic

提示It is the adjective for the sum of all the chemical reactions in the body.

为什么The basal rate is the speed at which the body's reactions run when it is at rest. Thyroxine sets that speed. Because it affects how quickly cells work everywhere, it also matters for normal growth and development.

thyroid

提示The hormone's name comes from the gland's name; the gland is in the neck.

为什么This gland lies at the front of the neck. It releases thyroxine into the blood continuously, and the amount it releases is adjusted so that the level in the blood stays close to normal.

The rise is detected and less thyroxine is released, so the level falls back to normal

提示The response has to cancel out the change that set it off.

为什么Thyroxine is controlled like a thermostat. If the level is too high, release is cut back; if it is too low, more is released. A diagram of the loop always shows the change leading to a response that reverses it.