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
• All control systems have:

  • Receptors: cells that detect stimuli
  • Coordination centres: process information received from receptors (e.g. brain, spinal cord, pancreas)
  • Effectors: bring about responses to bring conditions in the body back to optimum levels (e.g. muscles, glands)
• The nervous system allows reactions to surroundings and coordinates 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 that take place before thinking are called reflexes
• Synapses are gaps between two neurons
• Reflex arcs allow vital responses to take place quickly without passing through conscious areas of the brain
• Reaction time is how long it takes to respond to a stimulus
• Components of the brain:

  • Cerebral cortex: controls consciousness, intelligence, memory, language
  • Cerebellum: controls fine movement of muscles
  • Medulla: controls unconscious actions like breathing and heart rate
• Investigating brain function and treating brain damage and disease is difficult because:

  • Complex and delicate
  • Easily damaged
  • Drugs may not reach the brain due to surrounding membranes
  • Not fully understood which part of the brain does what
• The eye is a sense organ containing receptors sensitive to light intensity and color
• Structures within the eye are adapted to allow focusing on near or distant objects (accommodation) and to dim light
• Eye defects occur when light cannot focus on the retina
• Examples of eye defects:

  • Short-sightedness (myopia)
  • Long-sightedness (hyperopia)
• Treatment methods for eye defects:

  • Spectacle lenses
  • Contact lenses
  • Laser eye surgery
  • Replacement lens
• The thermoregulatory center in the brain monitors and controls body temperature
• Human body temperature is 37.5 degrees Celsius
• Mechanisms to control body temperature:

  • Sweat production
  • Vasodilation
  • Sweating stops
  • Skeletal muscles contract (shivering)
  • Hairs stand on end
  • Vasoconstriction
• The endocrine system sends hormones around the body to produce responses
• Endocrine system is made up of glands that secrete hormones into the bloodstream
• Pituitary gland is the master gland that secretes hormones into the blood
• Examples of glands and their hormones:

  • Pituitary gland: secretes hormones to have an effect on the body or stimulate other glands
  • Pancreas: secretes insulin to control blood glucose levels
  • Thyroid: secretes thyroxine to control metabolic rate, heart rate, and temperature
  • Adrenal gland: secretes adrenaline involved in the 'fight or flight' response
  • Ovary: secretes estrogen involved in the menstrual cycle and development of female secondary sexual characteristics
  • Testes: secretes testosterone involved in sperm production and development of male secondary sexual characteristics
• Control of blood glucose concentration:

  • Pancreas controls blood glucose levels
  • Insulin reduces blood glucose concentration
  • Glucagon increases blood glucose concentration
  • Blood glucose concentration is kept constant through negative feedback loop
• Osmosis is the process by which water molecules move from high to low concentration
• Kidneys are important in maintaining water and substance balance in the body
• Kidneys filter out waste products and selectively reabsorb useful substances
• Examples of waste products processed by the kidneys:

  • Water
  • Ions
  • Urea
• Water can leave the body through various means

  • Depending on water concentration in the blood, a certain amount is lost as urine
• Ions are taken into the body via food
• If ion concentration is incorrect
• Water loss in the body:

  • A certain amount of water is lost as urine depending on the concentration of water in the blood
  • 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 reaching the kidney tubules increases their permeability to water, leading to less urine production and more concentrated blood
  • ADH release is part of a negative feedback loop to regulate blood concentration
• Kidney failure:

  • Kidneys stop working, leading to harmful waste build-up and eventual death
  • Treatment options include dialysis and kidney transplants
• Dialysis:

  • Blood is filtered through partially permeable membranes with dialysis fluid to remove waste
  • Needs to be done three times a week for 3-4 hours
  • Acts as an artificial kidney while waiting for a transplant