GCSE Biology: Hormonal coordination and homeostasis

Justina: You may have heard of hormones in relation to the way people behave.

Georgina: They are the chemical messengers created in glands throughout the body, that travel in your blood to a variety of tissues and organs.

Justina: They then create chemical reactions in the target organs, to create a physiological response.This could be to make your heart beat faster or to regulate the water levels in your body.

Georgina: Let’s start by taking a closer look at adrenaline as an example.

Justina: Adrenaline is released by the adrenal glands in response to stressful, exciting, dangerous or threatening situations and stimuli.

Georgina: It has several effects that prepare the body to deal with those sorts of situation.

Justina: it increases the heartrate, which in turn, increases cardiac output, so more oxygen reaches respiring cells.

Georgina: it increases blood pressure by constricting blood vessels so the blood moves around your body even faster.

Justina: it increases your breathing rate, which raises the volume of oxygen entering the respiratory system, that then diffuses into the bloodstream.

Georgina: And the liver converts glycogen into glucose, providing more glucose for respiration so more energy is released.

Justina: All of this primes the body for action….Whether that be to face the situation…

Georgina: Or run away from it.Fight or flight.

Justina: The adrenal glands are part of a much larger system of glands located throughout the body.The endocrine system.

Georgina: Each gland is responsible for producing different hormones that have different roles to play in the body.The pituitary gland is known as the master gland, as it controls several other glands in the body.

Justina: Another hormone you may have heard of is insulin.Insulin is released by the pancreas when blood sugar levels are too high.Insulin helps promote the conversion of glucose in the blood, into glycogen by enzymes, which is then stored in the liver.If blood sugar levels are too low, glucagon is released by the pancreas, which enables the glycogen stored in the liver to be changed back into glucose.

Georgina: This is an example of homeostasis.Homeostasis is the self-regulating process that maintains stability in biological systems by responding to internal and external conditions.

Justina: For humans to live, we need a balance in our bodies.Water levels, temperature or blood sugar levels must all be kept constant.The endocrine system and the nervous system are the control systems our bodies use.

Georgina: And these control systems are examples of homeostasis.They work through what is known as a negative feedback mechanism.Let’s take a look at body temperature to illustrate tis.

Justina: Body temperature is controlled by the hypothalamus in the brain.If it detects that the body is too hot, one response is that the body begins to produce more sweat.Sweat is warm – 37 Degrees Celsius – and as it evaporates, it takes heat energy away from the body, cooling the body.Once the body’s temperature gets back to the correct level, less sweat is produced.If the body is too cold, one of the responses is that the body begins to shiver, to raise the temperature back to the correct level.

Georgina: The endocrine system works in a similar way to this.The thyroid gland produces hormones such as thyroxine, which controls our metabolism.Too much thyroxine in the bloodstream can lead to symptoms including weight loss, tiredness and irritability.Too little can lead to weight gain, reduced appetite and fatigue, amongst other things.

Justina: The hypothalamus, the pituitary gland and the thyroid gland work to maintain a constant thyroxine level in the blood through a negative feedback mechanism as well.Another example of homeostasis in effect.

Georgina: Hormones are so important for keeping your bodies in balance.

Justina: And going back to adrenaline, it’s not just used for the fight or flight mechanism.It’s also very important for maintaining cardiovascular homeostasis, as it diverts blood to areas of the body that are under stress.

Georgina: For example, if someone has a heart attack, adrenaline helps maximise the volume of blood flowing through the coronary artery.

Justina: Our bodies are pretty amazing.