Glossary:
the part of the nervous system where information is processed. It is made up of the brain and spinal cord.
areas (usually muscles or glands) that bring about responses in the body.
the glands that produce the hormones that control many aspects of the development and metabolism of the body, and the hormones they produce.
chemicals produced in one area of the body of an organism that have an effect on the functioning of another area of the body. In animals hormones are produced in glands.
basic cells of the nervous system that carry minute electrical impulses around the body.
endocrine ‘master gland’ found in the brain that secretes a number of different hormones into the blood in response to different conditions to control other endocrine glands in the body.
cells that detect stimuli – changes in the internal or external environment.
a disorder where the pancreas fails to produce sufficient insulin.
a disorder where the body cells no longer respond to the insulin produced by the pancreas.
Homeostasis maintains optimal conditions for enzyme action and all cell functions.
In the human body, these include control of:
• blood glucose concentration
• body temperature
• water levels.
These automatic control systems may involve nervous responses or chemical responses.
All control systems include:
• cells called receptors, which detect stimuli (changes in the environment)
• coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors
• effectors, muscles or glands, which bring about responses which restore optimum levels.
B5: Homeostasis and Response
The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
Information passes:
The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream.
The blood carries the hormone to a target organ where it produces an effect.
Compared to the nervous system the effects are slower but act for longer.
Blood glucose concentration is monitored and controlled by the pancreas.
If the blood glucose concentration is too high, the pancreas produces the hormone insulin that causes glucose to move from the blood into the cells. In liver and muscle cells excess glucose is converted to glycogen for storage.
(HT only) If the blood glucose concentration is too low, the pancreas produces the hormone glucagon that causes glycogen to be converted into glucose and released into the blood.
Hormones in Human Reproduction
Oestrogen is the main female reproductive hormone produced in the ovary.
At puberty eggs begin to mature and one is released approximately every 28 days. This is called ovulation.
Testosterone is the main male reproductive hormone produced by the testes and it stimulates sperm production.
Several hormones are involved in the menstrual cycle of a woman.
• Follicle stimulating hormone (FSH) causes maturation of an egg in the ovary.
• Luteinising hormone (LH) stimulates the release of the egg.
• Oestrogen and progesterone are involved in maintaining the uterus lining.
Fertility can be controlled by a variety of hormonal and non-hormonal methods of contraception.
B5: Homeostasis and Response