5. Homeostasis

• Hormones are chemical messages that are produced by glands and travel through the bloodstream to target organs
• Hormones do a similar job to neurons of the nervous system but there are some differences
• Neurons are fast
• Hormones are slow
• Neurones take a short time
• Hormones take a long time
• Neurons have a specific target
• Hormones don't have a specific target
• Neurons are electrical impulses
• Hormones are chemical
• Hormones are transported in the blood plasma
• The pituitary gland is the master gland
• Negative feedback systems work to maintain a steady state. An important example of negative feedback is seen in control of thyroid hormone secretion
• Pancreas produces insulin and it lowers the blood sugar levels
• Ovary produces oestrogen and controls puberty, stimulates the production of LH and supresses the production of FSH in the pituitary gland
• Ovary also produces progesterone which maintains the linin follicle and prevents the release of the egg
• pituitary gland produces FSH and triggers the egg ripening and oestrogen production in the ovaries
• Testes produce testosterone which controls puberty in males
• 1. Normal blood glucose concentration
  2. Blood concentration becomes too high
  3. Pancreas releases insulin which causes cells to absorb glucose
  4. Liver and muscles convert glucose into glycogen to be stored
  5. Normal blood glucose concentration
• The menstrual cycle occurs in females every 28 days
• The control of water and mineral slats within the body is called osmoregulation
• Water leaves the body via the lungs during exhalation
• Water, ions and urea are lost from the skin from swear
• Excess water, ions and urea are removed via the kidneys in the urine
• Plants make many different hormones that result in responses. A tropism is where a plant grows towards or away from the stimulus
• Phototropism - a plant responses to light

  Positive - towards light

  Negative - away from light
• Plant hormones are called auxins
• In shoots, auxins are more concentrated on the dark side and make the cells elongate and grow towards the light
• In roots, auxins are more concentrated on the lower part of the root but this time stop the growth of cells in the area
• Ethene (gas) is used in the food industry to control ripening of fruit during storage and transport
• Gibberellins can be used to end seed dormancy, promote flowering and increase fruit size
• Cerebral cortex - controls conscious activities and other functions including memory, intelligence, language, and sensation
• Cerebellum - controls muscle coordination
• Medulla - controls unconscious functions including heat beating and breathing
• Cornea - refracts light into the eye
• Iris - controls how much light is entering the pupil
• Lens - focuses light onto the retina of the eye.
• Retina - contains two types of cells: rods and cones.
• Optic nerve - carries impulses from the eye to the brain along a bundle of sensory neurons
• Accommodation is the process of changing the shape of the lens to focus on near or distant objects