bio paper 2

• Homeostasis


  Physiological control systems to maintain your internal environment within set restricted limits
• Examples of homeostasis


  • Maintaining the core body temperature
  • Maintaining the blood pH
• Homeostasis involves


  Negative feedback
• Negative feedback


  Any deviation from the normal values (too high or too low) has mechanisms put in place to bring the conditions back to their original level
• Negative feedback involves


  • The nervous system
  • Hormones
• Blood glucose concentration


  Example of homeostasis
• Regulation of blood glucose

  1. Blood glucose increases after eating carbohydrates

  2. Pancreas detects changes in blood glucose

  3. Pancreas releases insulin when blood glucose is too high

  4. Insulin causes liver to store glucose as glycogen

  5. Blood glucose decreases when not eating carbohydrates or exercising

  6. Pancreas releases glucagon when blood glucose is too low

  7. Glucagon causes liver to break down glycogen into glucose
• Insulin


  Hormone released by pancreas that reduces blood glucose levels
• Glucagon


  Hormone released by pancreas that increases blood glucose levels
• Action of insulin


  1. Binds to receptors on target cells

  2. Increases permeability of cells to glucose

  3. Activates enzymes to convert glucose to glycogen
• Action of glucagon


  1. Binds to receptors on target cells

  2. Activates second messenger system

  3. Activates enzymes to hydrolyse glycogen into glucose
• Second messenger model


  Mechanism by which hormones like glucagon and adrenaline act to increase blood glucose levels
• Processes involving the liver

  • Glycogenesis (converting glucose to glycogen)
  • Glycogenolysis (breaking down glycogen to glucose)
  • Gluconeogenesis (producing glucose from other molecules)
• Type 1 diabetes


  Inability to produce insulin, usually starts in childhood, caused by autoimmune disease
• Type 2 diabetes


  Cells become resistant to insulin, usually develops in adults, often due to obesity and poor diet
• Osmoregulation


  Regulation of water potential of blood
• Hypertonic blood


  Blood with too low water potential, causes cells to shrivel
• Hypotonic blood


  Blood with too high water potential, causes cells to burst
• Regulation of water potential

  1. Hypertonic blood: more water reabsorbed from nephron, less dilute urine

  2. Hypotonic blood: less water reabsorbed from nephron, more dilute urine
• Nephron


  • Long tubule in kidney surrounded by capillaries
  • Where blood is filtered and selective reabsorption occurs
• Filtration and reabsorption in nephron

  1. Blood flows into glomerulus, water and small molecules filtered into renal capsule

  2. Filtrate passes through proximal convoluted tubule, glucose and other useful substances reabsorbed

  3. Filtrate passes through loop of Henle, ions reabsorbed to create osmotic gradient

  4. Filtrate passes through distal convoluted tubule and collecting duct, more water reabsorbed
• Regulation of water potential by hypothalamus and pituitary

  1. Osmoreceptors in hypothalamus detect changes in blood water potential

  2. Hypothalamus releases more/less ADH when blood is hypo/hypertonic

  3. ADH increases/decreases permeability of distal convoluted tubule and collecting duct to water
• Aerobic respiration has 4 key stages: glycolysis, link reaction, Krebs cycle, oxidative phosphorylation
• Glycolysis


  First stage of aerobic respiration, occurs in cytoplasm, produces some ATP
• Steps of glycolysis


  1. Glucose is phosphorylated using 2 ATP

  2. Glucose phosphate is split into 2 triose phosphates

  3. Triose phosphates are oxidized to produce 4 ATP and reduced NAD
• Glycolysis


  1. Glucose is phosphorylated to glucose phosphate

  2. Glucose phosphate is converted into trios phosphate

  3. Trios phosphate is oxidated to form pyruvate
• Glucose phosphorylation uses two molecules of ATP
• Oxidation of trios phosphate produces four ATP and reduced NAD
• Pyruvate


  Three carbon compound produced from glycolysis
• Link reaction


  1. Pyruvate is oxidized further to make acetate

  2. Acetate combines with coenzyme A to create acetyl CoA

  3. Acetyl CoA enters the Krebs cycle
• For every glucose molecule, two pyruvates are created, so the link reaction happens twice
• Krebs cycle


  1. Acetyl CoA combines with a four carbon molecule

  2. Series of redox reactions occur

  3. Generates reduced coenzymes, a small amount of ATP, and carbon dioxide
• The products per Krebs cycle are three reduced NAD, one reduced FAD, one ATP, and two carbon dioxides
• For every glucose molecule, the Krebs cycle happens twice
• Oxidative phosphorylation


  1. Reduced coenzymes release hydrogen which is transported along the electron transfer chain

  2. Energy from the electron transfer chain is used to transport protons into the intermembrane space

  3. Protons flow through ATP synthase to phosphorylate ADP and create ATP
• Oxidative phosphorylation produces 34 ATP molecules
• Oxygen is the final electron acceptor, forming water
• Anaerobic respiration


  1. Pyruvate is reduced to lactate in animals

  2. Pyruvate is reduced to ethanol and carbon dioxide in plants and microbes
• Anaerobic respiration re-oxidizes NAD so glycolysis can continue
• Anaerobic respiration produces lactic acid or ethanol, which can be harmful