Homeostasis

• why is maintaining body temperature, blood glucose concentration and PH levels?

  changes would affect enzyme activity and affect the body's metabolic reactions

  • blood glucose concentration affects water potential
• Temperature:

  • rate of metabolic reaction increases when temp increases -> increase in kinetic energy
• PH:

  • blood PH too high, enzymes denature - hydrogen and ionic bonds broken down
  • equation for PH = -log10()
  • higher amount of hydrogen ions= lower PH + more acidic
• Blood glucose concentration:

  • when too high - water potential decreases, water diffuses out of cell into blood by osmosis and the cell shrivels and dies
  • when too low - cells unable to carry out function since no glucose to produce energy through respiration
• Negative feedback: receptors detect if levels too high or low -> info communicated via N.S or hormonal system to effectors

  • effectors respond to counteract - bring level back to set point
  • can only work if change is not extreme
  • multiple negative feedback mechanisms - more control over change
• Positive feedback: amplifies change

  • effector responds to further increase level from set point
  • isn't involved in homeostasis -> not stabilising internal environment
  • useful to rapidly activate processes in body
• blood glucose monitored by Pancreas

  • hormones controlling blood glucose concentration are secreted from the Islets of Langerhans in the Pancreas
  • B-cells secrete Insulin
  • A-cells secrete Glucagon
• Insulin:

  • lowers blood glucose concentration in blood
  • binds to hepatocytes on muscle and liver receptors on cell membrane
  • membrane becomes permeable to glucose
  • number of channel proteins increase (e,g GLUT4 for skeletal and cardiac muscle)
  • activate glycogenesis
  • more cells respire using glucose in muscle cells
• Glucagon:

  • raises blood glucose concentration
  • binds to receptors on liver cell membranes
  • activates enzyme breaking glycogen into glucose - glycogenolysis
  • forms glucose fro glycerol and amino acids - gluconeogenesis
• Negative feedback of blood glucose concentration: Insulin

  • pancreas detects rise in blood glucose concentration
  • B-cells of islets of Langerhans secrete Insulin
  • Insulin binds to hepatocytes on liver & muscle cell membranes
  • membrane permeable
  • enzymes activated - glycogenesis + more respiration
• Negative feedback of blood glucose concentration: Glucagon

  • pancreas detects fall in blood glucose concentration
  • A-cells of Islets of Langerhans secrete Glucagon
  • Glucagon binds to receptors on liver cell membranes
  • enzymes activated for - glycogenolysis & gluconeogenesis + less respiration of cells
• Adrenaline:

  • secreted by adrenal glands, above kidneys
  • secreted when blood glucose concentration in blood is low
  • binds to receptors on liver cell membrane
  • activates glycogenolysis & inhibits glycogenesis
  • activates glucagon secretion & inhibits insulin secretion
• Second messenger: A molecule that is activated by a signal molecule and then transfers its energy to another molecule
• Second messenger: to activate glycogenolysis

  • Adrenaline and Glucagon bind to specific receptors on liver cell membrane and activare enzyme ADENYLATE CYCLASE
  • Adenylate Cyclase convert ATP into Cyclic AMP (cAMP)- second messenger
  • cAMP activates enzyme Protein Kinase A THAT activates reactions that break down glycogen into glucose
• the kidneys:

  • blood enter kidney through renal artery -> passes through capillaries in cortex of kidney
  • as blood passes through capillaries, substances filtered out of blood into long tubules surrounding capillaries - ultrafiltration
  • glucose & water reabsorbed -> selective reabsorption - unwanted substances pass along bladder and excreted as urine
• Ultrafiltration:

  • blood from renal artery enters smaller arterioles in cortex
  • each arteriole splits into structure glomerulus - a bundle of capillaries looped inside a hollow ball - Bowman capsule
  • Afferent arteriole ->blood into glomerulus
  • Efferent arteriole -> blood filtered blood away from the glomerulus -> smaller diameter
  • blood under high pressure in glomerulus -> forces liquid and small molecules in blood out of capillaries and into Bowman's capsule
  • pass through three layer cell membrane into nephron tubules
  • then through collecting duct and out of kidney along ureter
• selective reabsorption:

  • occurs as glomerular filtrate flows through PCT, through loop of Henle and along DCT
  • epithelial wall of PCT contains microvilli for large SA for absorption
  • glucose reabsorbed along PCT by facilitated diffusion and active transport
• Selective reabsorption:

  • water potential lower in bloodstream - water enters blood by osmosis
  • water reabsorbed from PCT, loop of Henle and DCT and collecting duct
• Urine: 1. Water 2. Urea 3. dissolved salts 4. Creatinine 5. hormones