GCSE | BIOLOGY /5/ Homeostasis and Response

• Homeostasis is the maintenance of a constant internal environment
• Mechanisms are in place to keep optimum conditions despite internal and external changes
• Homeostasis controls:

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Nervous and hormonal communication is involved in automatic control systems
• Control systems have:

  • Receptors: cells that detect stimuli
  • Coordination centres: process information from receptors
  • Effectors: bring about responses to bring conditions back to optimum levels
• The Human Nervous System:

  • Allows reaction to surroundings and coordinate actions in response to stimuli
• Receptor cells convert a stimulus into an electrical impulse
• Electrical impulse travels along sensory neurons to the central nervous system (CNS)
• Information is processed in the CNS and appropriate response is coordinated
• Automatic responses before thinking are reflexes
• Reflex arc allows vital responses to take place quickly
• Synapses are gaps between neurons
• Reaction time is how long it takes to respond to a stimulus
• The Brain:

  • Controls complex behavior
  • Made up of connected neurons
  • Different regions control different functions
• Components of the brain:

  • Cerebral cortex
  • Cerebellum
  • Medulla
• Investigating brain function and treating brain damage is difficult
• The Eye:

  • Contains receptors sensitive to light intensity and color
  • Adapted to change shape to focus on objects
• Retina: layer of light-sensitive cells at the back of the eye
• Optic nerve: carries impulses from retina to the brain
• Iris: muscles that surround the pupil
• Ciliary muscles and suspensory ligaments hold the lens in place
• Eye defects occur when light cannot focus on the retina
• Control of Body Temperature:

  • Thermoregulatory center in the brain monitors and controls body temperature
• Human body temperature is 37.5 degrees Celsius
• Mechanisms to regulate body temperature:

  • Sweat production
  • Vasodilation
  • Skeletal muscle contraction
  • Hair standing on end
  • Vasoconstriction
• Hormonal Coordination in Humans:

  • Endocrine system sends hormones around the body
• Endocrine system made up of glands that secrete hormones into the bloodstream
• Control of Blood Glucose Concentration:

  • Pancreas controls blood glucose levels
  • Insulin and glucagon regulate blood glucose concentration
  • Negative feedback loop maintains blood glucose levels
• Diabetes types and treatments:

  • Type 1: pancreas cannot produce enough insulin
  • Type 2: body cells do not respond to insulin
• Maintaining Water and Nitrogen Balance in the Body:

  • Osmosis is the process by which water molecules move
• Kidneys are important in maintaining the balance of water and substances in the body
• Kidneys filter out waste products and selectively reabsorb useful substances
• Examples of waste products processed by the kidneys include water, ions, and urea
• Water balance in the body:

  • Depending on the concentration of water in the blood, a certain amount of water is lost as urine
  • Ions are taken into the body via food
  • Incorrect ion concentration can lead to too little or too much water entering body cells, altering the water potential of the blood
  • Ions are lost in sweat
  • In the kidneys, certain amounts of ions are reabsorbed into the blood after filtration to maintain blood concentration
• Urea:

  • Amino acids from protein digestion are deaminated in the liver to form ammonia, which is converted to urea
  • Urea is lost in sweat
  • In the kidneys, urea is filtered out of the blood
• Anti-diuretic hormone (ADH):

  • Released by the pituitary gland into the bloodstream to control water loss as urine
  • Increased ADH increases kidney tubule permeability to water, leading to less urine production and less concentrated blood
  • Negative feedback loop regulates ADH secretion based on blood concentration
• Kidney failure:

  • Kidneys stop working, leading to harmful waste build-up and eventual death
  • Treatments: Dialysis (artificial kidney) and Kidney transplants (only cure)
• Contraception methods:

  • Hormonal methods: contraceptive pill (mixed and progesterone only), patch, implant, injection
  • Non-hormonal methods: spermicides, condoms, diaphragms, copper IUD
  • Surgical methods: male and female sterilisation, abstaining from intercourse
• Hormones in Human Reproduction:

  • Testosterone (male) stimulates sperm production
  • Oestrogen (female) produces physical changes and is involved in the menstrual cycle
  • Menstrual cycle prepares the body for potential pregnancy through hormonal control
• Negative Feedback:

  • Thyroxine regulates metabolic rate and growth, controlled by negative feedback
  • Adrenaline stimulates 'fight or flight' response in times of stress