H.S.B

• Excretion


  The process by which matabolic waste and harmful substances, produced by chemical reactions occurring inside body cells, i.e. the body's metabolism, are removed from the body
• Importance of excretion


  • It prevents toxic metabolic waste substances from building up in the body and damaging or killing cells
  • It helps to keep the environment within the body constant
• Egestion


  The removal of undigested dietary fibre and other materials from the body as faeces
• 5 Metabolic waste excreted by humans


  • Carbon dioxide
  • Water
  • Urea (nitrogenous waste)
  • Bile pigments, e.g. bilirubin
  • Heat
• Excretory organs


  • Kidneys
  • Lungs
  • Skin
  • Liver
• Functions of the kidneys

  • To excrete metabolic waste, mainly urea, from the body
  • To regulate the volume and concentration of blood plasma and body fluids by regulating the amount of water they contain, a process known as osmoregulation
• Urine production in the nephrons

  1. Ultra-filtration or pressure filtration

  2. Selective reabsorption
• Ultra-filtration


  Small molecules are forced from the blood into Bowman's capsule forming filtrate
• Selective reabsorption


  Useful substances are reabsorbed from the filtrate back into the blood travelling through the capillaries wrapped around each nephron
• Renal dialysis


  When nephrons stop functioning properly so that they are unable to remove waste from the blood and regulate the volume and composition of blood plasma and body fluids, kidney failure occurs. Harmful waste, especially urea, builds up in the blood and can reach toxic levels resulting in death. Kidney failure can be treated by a kidney transplant or renal dialysis.
• Layers of the skin

  • Epidermis
  • Dermis
  • Subcutaneous layer
• Functions of skin structures

  • Epidermis protects the body
  • Sebaceous glands secrete sebum
  • Nerve endings detect stimuli
  • Hairs and hair erector muscles
  • Arterioles and capillary networks regulate body temperature
  • Sweat glands produce sweat
  • Subcutaneous layer protects against heat loss and damage
• Homeostasis


  Maintaining a constant internal environment. Conditions surrounding cells must be very carefully controlled, including water content or concentration of blood plasma and body fluids, levels of carbon dioxide in the blood, body temperature and blood sugar levels.
• Negative feedback mechanisms


  If the level of something in the body changes, receptors in the body detect the change and send messages to the appropriate effectors causing them to respond and return the level to normal, i.e. the effectors exert an opposite or negative effect.
• Osmoregulation


  The regulation of the water content of blood plasma and body fluids. Their water content must be kept constant to prevent water moving into and out of body cells unnecessarily.
• Regulation of body temperature

  1. Skin produces sweat, water evaporates removing heat

  2. Vasodilation occurs, arterioles supplying the capillaries in the skin dilate, increasing blood flow through them and heat loss

  3. Respiration slows, especially in liver and muscle cells, decreasing heat production

  4. Skin stops producing sweat

  5. Vasoconstriction occurs, arterioles supplying the capillaries in the skin constrict, decreasing blood flow through them and heat loss

  6. Respiration speeds up, especially in liver and muscle cells, increasing heat production

  7. Shivering occurs to generate heat
• Heat and temperature


  Heat is the total amount of energy an object contains, measured in joules. Temperature is a measure of how hot or how cold an object is, measured in degrees Celsius.
• Regulation of carbon dioxide levels

  Receptors, mainly in the medulla of the brain, detect changes in pH and send messages to the intercostal muscles and diaphragm to adjust the rate and depth of breathing
• Regulation of blood sugar (glucose) levels

  1. If the blood glucose level rises, the pancreas secretes insulin. Insulin stimulates body cells to absorb glucose for respiration and the liver cells to convert excess glucose to glycogen, which it stores.

  2. If the blood glucose level falls, the pancreas secretes glucagon. Glucagon stimulates liver cells to convert stored glycogen to glucose, which enters the blood.
• Diabetes mellitus


  A condition where a person is unable to regulate their blood glucose levels such that they remain too high
• Ultra-filtration


  The first step in urine production, where the kidneys filter the blood to remove waste and extra water
• Selective reabsorption


  The second step in urine production, where the kidneys reabsorb certain substances from the filtered fluid and put them back into the bloodstream
• Negative feedback mechanisms


  Processes that help maintain balance in the body by detecting changes and responding to them. When the level of something in the body changes, receptors detect the change and send messages to the appropriate effectors, which respond by exerting an opposite or negative effect to return the level to normal.
• Receptors


  Cells, tissues, or organs that detect changes in the body and send messages to the appropriate effectors in response to negative feedback mechanisms.
• Osmoregulation


  The regulation of the water content of blood plasma and body fluids to prevent water from moving into and out of body cells unnecessarily.
• Blood plasma


  The liquid component of blood that carries cells, hormones, nutrients, and waste products throughout the body.
• Melanin protects skin for harmful ultra violet rays(to prevent against skin cancer)
• Osmosis is the movement of water particles from an area of high water potential to an area of of low water potential, through a semi permeable
• Simple diffusion is the movement of particles from an area of high concentration to an area of low concentraion
• Living organisms

  Made of cells
• Cells


  Microscopic, basic structural and functional unit of all living organisms
• Characteristics of living organisms

  • Nutrition (feeding)
  • Respiration
  • Excretion
  • Growth
  • Irritability (sensitivity)
  • Movement
  • Reproduction
• Nutrition (feeding)


  Process by which living organisms obtain or make food. Animals are heterotrophs, plants are autotrophs.
• Respiration


  Process by which energy is released from food by all living cells. Aerobic respiration requires oxygen, anaerobic respiration does not.
• Excretion


  Process by which waste and harmful substances produced by metabolism are removed from the body
• Growth


  Permanent increase in the size and complexity of an organism
• Irritability (sensitivity)


  Ability of organisms to detect and respond to changes in their environment or within themselves
• Movement


  Change in the position of a whole organism or parts of an organism. Animals can move their whole bodies, plants and some animals can only move parts.
• Reproduction


  Process by which living organisms generate new individuals of the same kind. Sexual reproduction involves fusion of gametes, asexual reproduction does not.
• Cell


  Basic structural and functional unit of all living organisms, possessing all 7 characteristics of life