homeostasis and response

• 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
• 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
• Menstrual cycle

  the monthly cycle of an egg being released in females; controlled by hormones
• Follicle stimulating hormone (FSH)

  a hormone released by the pituitary gland that causes an egg to develop in the ovaries
• Luteinising hormone (LH)

  a hormone that stimulates the release of an egg in the menstrual cycle
• Progesterone

  a hormone that repairs the lining of the uterus after menstruation and prevents it breaking down
• Contraception

  mechanisms that are used to prevent pregnancy occurring as a result of sexual intercourse
• Fertility drug

  a drug that makes it more likely for sexual intercourse to result in pregnancy
• In vitro fertilisation

  a process in which an egg is fertilised by sperm outside of the body
• Tropism

  growth in response to a stimulus, e.g. plants growing towards the light
• Gravitropic

  describes a plant’s growth response to gravity (also called geotropic)
• Phototropic

  describes a plant’s growth response to light
• Auxins

  a group of growth hormones produced in plants
• Gibberellins

  a group of plant hormones
• Ethene

  a gas that acts as a plant hormone