Homeostasis
- In order to function properly and efficiently, organisms have different control systems that ensure their internal conditions are kept relatively constant
- Physiological control systems maintain the internal environment within restricted limits through a process known as homeostasis
- Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function
- Sensory cells can detect information about the conditions inside and outside of the body
- Examples of physiological factors that are controlled by homeostasis in mammals include:
- Core body temperature
- Metabolic waste (eg. carbon dioxide and urea)
- Blood pH
- Concentration of glucose in the blood
- Water potential of the blood
- Concentration of the respiratory gases (carbon dioxide and oxygen) in the blood
- Homeostatic mechanisms in mammals require information to be transferred between different parts of the body
- There are two coordination systems in mammals that do this:
- The nervous system
- The endocrine system
The nervous system
- The human nervous system consists of:
- The central nervous system (CNS) – the brain and the spinal cord
- The peripheral nervous system (PNS) – all of the nerves in the body
- It allows us to make sense of our surroundings and respond to them and coordinate and regulate body functions
- Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones
- A bundle of neurones is known as a nerve
- Neurones coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands
The human nervous system
The endocrine system
- A hormone is a chemical substance produced by an endocrine gland and carried by the blood
- They are chemicals which transmit information from one part of the organism to another and bring about a change
- They alter the activity of one or more specific target organs
- Hormones are used to control functions that do not need instant responses
- The endocrine glands that produce hormones in animals are known collectively as the endocrine system
- A gland is a group of cells that produces and releases one or more substances (a process known as secretion)
The major endocrine glands in the body
- Endocrine glands have a good blood supply as when they make hormones they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about a response
- Hormones only affect cells with receptors that the hormone can bind to
- These are either found on the cell surface membrane, or inside cells
- Receptors have to be complementary to hormones for there to be an effect
Hormones are synthesized and released into the bloodstream from a gland (such as the pituitary gland) and circulate in the bloodstream, affecting target cells