2.89 - sources, roles and effects of hormones

ADH  - the pituitary gland produces growth hormone and ADH
- this helps physical development in children
- ADH causes kidney tubules to re-absorb more water into the blood

adrenaline - the adrenal glands produce adrenaline
- this is released in times of danger and prepares for "fight or flight" in a dangerous situation
- the effects are increased heart rate, breathing, sweating, hair standing on end (to make the animal look bigger), and glucose released from liver and muscles

insulin - insulin controls the amount of glucose in the blood
- insulin gives us energy

testosterone - is secreted from the testes
- this causes secondary sexual characteristics in boys

estrogen - is responsible for secondary sexual characteristics in girls

progesterone - works together with estrogen to control the menstrual cycle

2.87 - the eye in focusing on near and far objects

- distant objects require less bending, the muscles in the ciliary body relax and the lens is pulled thinner
- near objects need a much more powerful refraction to bend them into focus
- muscles in the ciliary body contract and the lens swells to a more rounded shape
- this makes it more powerful and the rays achieve a more focused image

2.86 - the structure a function of the eye as an receptor

- the eye is the receptor which detects light
- the iris (coloured part) controls the amount of light entering by controlling the size of the hole in the centre
- the cornea bends light rays as they enter to bring a focus on the retina
- the lens provides fine focus to sharpen the image

2.85 - structure and functioning of a simple reflex

- a reflex is a type of response, these are rapid responses that may protect you in some way i.e. hot objects
- the pathway that signals travel along, during a reflex is a reflex arc
- simple reflexes are usually spinal reflexes so the reflexes are processed by the spinal cord, not the brain
- the spinal cord sends signals back to the effector like the muscles or glands
- an example would be touching a hot object

2.84 - stimulation of receptors

- neurons have branched nerve endings to pass on signals
- nerve endings don't touch but there is a small gap between them. when a pulse arrives the chemicals are released and pass along through diffusion
- neutrons are wrapped by a layer of fat and protein which insulates cells and allows impulses to travel faster
- neutrons are usually grouped together in bundles called nerves

2.83 - central nervous system

- the sense organs (skin, tongue, nose, eyes and ears) are connected to the brain, spinal cord, and peripheral nerves to make up the nervous system
- the brain co-ordinates the actions of the body
- signals are sent through the nervous system through electrical impulses
- the types of nerve cells are called neurons
sensory neurons carry signals to the CNS
- motor neurons carry signals to the CNS, controlling how the body responds
- relay neurons connect other neurons together

2.82 - nervous and hormonal communication

- the nervous system includes the brain, spinal cord, peripheral nerves and sense organs such as the eye and ear
- messages are passed by electrical impulses
- the endocrine system uses chemical communication by hormones which are excreted by endocrine glands and cells
- this system helps maintain body functions like metabolism and growth
- this has more long-term effects than the nervous system and its response is less rapid

2.77b - thermoregulation

- a negative feedback loop is the control of our conditions
- for humans, to regulate a temperature of 37/38 degrees celesis the reactor is the hypothalamus in the brain
- if the temp has increased of decreased then the effector would be the skin
- the response would be the increase or decrease of body temp - then it would feedback to the brain
- the control of body temp by the skin would be the sweat glands
- depending on the temp the blood would move closer (hot day) or further away (cold day) from the skin
- sweating on a hot day and hairs are flat
- shivering on a cold day and hairs are raised

2.77a - thermoregulation

- homostatis is the maintenance of a constant internal environment, like a fixed pH
- homeothermic is maintaining the same temp and body water content
- when the temperature of the environment changes then the body temp stays the same
- this is the same idea with the fixed pH

2.76 sensitivity

- sensitivity is how organisms respond to changes in their environment
- these changes may be light, temperature, pressure or chemical
- the receptor identifies the change and the effector responds to the change - an effector may be muscles
- the response is making sure the organism adapts to its new environment