Module 5

• Multicellular organisms


  As animals and plants became more complex, the need to coordinate responses to changes in internal and external environment became more important to their survival
• Cell signalling


  Cells communicate intracellularly, with adjacent cells and distant cells using different methods
• Methods of cell communication

  • Chemical signalling: Autocrine signalling
  • Chemical signalling: Paracrine signalling
  • Chemical signalling: Endocrine signalling
• Homeostasis


  Maintenance of a dynamic steady internal environment
• Stimulus


  Any change in the environment that can evoke a response in an organism
• Examples of stimuli


  • Changes in temperature
  • Increased blood glucose
  • Sounds
  • Changes in colours
• Receptors


  Cells that detect stimuli
• Effectors


  Cells that produce a response
• Negative feedback


  Homeostatic mechanism in which the response acts in the opposite direction to the stimulus
• Positive feedback


  Homeostatic mechanisms in which the response acts in the same direction to the stimulus
• Thermoregulation


  Ability of an organism to control their own body temperature via behavioural and physiological responses
• Ectothermic organisms


  Unable to physiologically control their own body temperature
• Endothermic organisms


  Maintain a constant internally controlled body temperature, regardless of environmental changes in temperature
• Thermoreceptors


  Stimulated in response to an increase or decrease in body temperature
• Thermoregulation in endotherms


  1. Vasodilation in the skin and sweating in response to an increase in temperature

  2. Vasoconstriction in the skin and rapid muscle contraction (shivering) in response to a decrease in temperature
• Thermoregulation in ectotherms


  1. Expand ribcage and use frill to expand surface area to absorb more heat from the sun

  2. Increase abdominal breathing movements to increase water loss when hot
• Behavioural responses of ectotherms for thermoregulation

  • Expose body to sun to absorb more heat
  • Orientate body towards sun to expose larger surface area
  • Hide in burrows to prevent heat absorption
• Behavioural responses of endotherms for thermoregulation

  • Move into shade or hide in burrow
  • Orientate body to decrease surface area exposed to sun
  • Remain inactive and spread out limbs to increase surface area
  • Move into sunlight
  • Orientate body to increase surface area exposed to sun
  • Move about to generate heat in muscles
  • Roll into a ball and keep still to decrease surface area
• Excretion


  Removal of metabolic waste from the body
• Main types of metabolic waste

  • Carbon dioxide
  • Nitrogen compounds
• Liver


  Largest gland in the body, weighing about three pounds in an adult, divided into two primary lobes: a large right lobe and a much smaller left lobe
• Hepatocytes, bile canaliculi, and hepatic sinusoids

  Main components of the liver
• Glucose metabolism and role of glycogen in the Liver

  1. When blood sugar is high, insulin is released from the pancreas, stimulating glucose uptake by many tissues and glycogen synthesis

  2. When blood sugar is low, the pancreas releases glucagon, triggering the stimulation of glycogen breakdown, leading to increased glucose-6-phosphate levels
• The Ornithine Cycle (conversion of ammonia to urea)

  1. Within the liver, ammonia is converted into urea, which is less soluble and less toxic than ammonia so it can be passed back into the blood to the kidneys

  2. The kidneys filter out the urea from the blood and store it as urine in the bladder
• Kidney


  A pair of bean-shaped structures located just below and posterior to the liver in the peritoneal cavity, with the adrenal glands sitting on top of each kidney
• Nephron


  The functional unit of the kidney, with the glomerulus and convoluted tubules located in the kidney cortex, and collecting ducts located in the pyramids of the medulla
• Osmoregulation


  The regulation of the water potential of the blood by the kidneys
• Control of water reabsorption

  1. Osmoreceptors in the hypothalamus monitor water potential of the blood

  2. When water potential decreases, osmoreceptors transmit a signal to the hypothalamus, which then sends a signal to the posterior pituitary gland to release antidiuretic hormone (ADH)

  3. ADH causes the walls of the collecting duct and DCT to become more permeable to water, allowing more water to be reabsorbed from these tubules into the blood by osmosis
• Kidney failure


  Inability to remove waste and maintain fluid balance in the system, can lead to death if not treated
• Treatments for kidney failure

  • Hemodialysis
  • Peritoneal dialysis
  • Kidney transplant
• Receptors


  Specific, respond to only one kind of stimulus, stimulation induces potential difference across membrane leading to generation of an action potential
• Pacinian Corpuscle


  Present in the skin, detect pressure and vibration by being compressed, encapsulated dendrites of sensory neurons
• Retina


  The main photosensitive layer in the human eye which mediates vision, contains special light detecting cells called photoreceptors
• Types of photoreceptors


  • Rods
  • Cones
• Cones


  Detect color, three types with different optical pigments (red, green, blue)
• Rods


  More sensitive to light, allow us to see in dim light
• Fovea


  Region of the retina with highest density of rods and cones, most photosensitive
• Vision


  The ability to detect light patterns from external environment and interpret them into images
• Retina


  The main photosensitive layer in the human eye which mediates vision
• Photoreceptors in the retina

  • Rods
  • Cones