Homeostasis

• Homeostasis


  the process of keeping the internal conditions of the body constant
• Receptors

  cells found in sense organs, e.g. eyes, ears, nose
• Effectors


  part of the body (e.g. a muscle or a gland) that produces a response to stimuli
• Negative feedback


  a set of events that detects a variable and then corrects any change in the variable away from a set value
• Thermoregulatory centre


  the part of the brain responsible for maintaining a constant body temperature in warm-blooded animals
• Vasodilation


  occurs when blood vessels in the skin become wider so that more blood flows close to the surface of the skin to increase heat loss
• Vasoconstriction


  occurs when blood vessels in the skin become narrower so that less blood flows close to the surface of the skin
• Central nervous system (CNS)


  the part of the nervous system made up of the brain and spinal cord
• Synapse


  the gap between two neurones
• Cerebral cortex


  the area at the top of the brain that is responsible for intelligence and initiating movements
• Cerebellum


  part of the brain, at the rear, that is responsible for balance and controlling movements
• Medulla


  the area of the brain that controls heartbeat and breathing
• Retina


  the layer at the back of the eye that contains the lightsensitive receptors
• Optic nerve


  a collection of neurones that pass nerve impulses from the eye to the brain
• Sclera


  the tough white coating to the eye
• Cornea


  the transparent membrane that covers the eyeball
• Iris


  the coloured part of the eye that changes the size of the pupil in response to different light intensities
• Pupil


  the opening at the front of the eye that lets light enter
• Ciliary muscles


  muscles in the eyes that can change the shape of the lens for accommodation
• Suspensory ligaments


  structures that attach the ciliary muscle to the lens in the eye
• Accomodation


  process that occurs to enable the eye to change so that objects at different distances can be focused on the retina
• Refract

  to bend / change the direction of a light ray (commonly performed by a lens)
• Myopia


  the condition that stops a person’s eyes from focusing on distant objects clearly
• Hyperopia


  the condition that stops a person’s eyes from focusing on near objects clearly
• Endocrine system


  a system of glands that release hormones directly into the bloodstream
• Hormone


  a chemical messenger produced by a gland that travels in the blood to its target organ
• Pituitary gland


  a small gland at the base of the brain that produces hormones; known as the ‘master gland’
• Adrenaline

  hormone released from the adrenal gland, which prepares the body for ‘fight or flight’
• Thyroxine


  a hormone released from the thyroid gland that controls the metabolic rate of the body
• Type 1 diabetes

  a condition where not enough insulin is produced by the pancreas
• Type 2 diabetes


  a condition where insulin is produced but the cells of the body do not respond to it
• Urea


  a waste product from the breakdown of proteins formed in the liver and excreted in urine
• Deamination


  the breakdown of excess amino acids in the liver
• Selective reabsorption


  the process of active transport that reabsorbs useful molecules back into the blood from the kidney tubules
• Tubules


  small tubes in the kidney, where blood is filtered, selective reabsorption takes place, and urine is produced
• ADH


  hormone released from the pituitary gland, which acts on the kidneys causing more water to be reabsorbed back into the blood
• Dialysis


  the artificial removal of urea and excess material from the blood (used when the kidneys fail)
• Oestrogen


  a hormone secreted by the ovaries that inhibits the production of FSH and triggers the production of LH
• Ovulation


  the release of an egg (ovum) from the ovary into the fallopian tube
• Testosterone


  a hormone produced by the testes that controls the male sexual characteristics