Module 5.1.1- Communication and homeostasis

• Homeostasis


  the maintenance the internal environment in a constant state despite external changes, so enzymes can work at an optimum
• Example of internal environment factors

  - blood glucose concentration- internal temperature- water potential- cell pH
• Example of external environment factors


  - humidity

  - external temperature

  - light intensity

  - new or sudden sound

  These fluctuate
• Why must different organs be coordinated

  In order to maintain a relatively constant internal environment (homeostasis)
• The need for communication systems in multicellular organisms

  - for coordination
• What is cell signaling?

  communication between cells using chemical messengers. cell releases chemical which has an effect on another cell (target cell)important for maintaining homeostasis
• Example of cell signalling over short distances

  Neurotransmitter over a synapse
• Example of cell signalling over long distances

  using hormones. e.g. ADH to the kidneys to maintain water balance in the body
• Since plants do not have a nervous system like animals, how do they respond to internal and external temperatures

  Through use of plant hormones e.g. plant stems towards a light source to maximise their rate of photosynthesis
• Receptors


  Special structures that allow living organisms to detect the change in conditions of their internal or external environment.
• Effectors


  They bring about a change in response to a stimulusCause responses that alter conditions in the internal environment
• Negative feedback system


  Work to reverse the initial stimulus. Effectors work to reverse the change and restore conditions to their base level. e.g. controlling blood glucose levels

  
• Positive feedback system


  a process that results in a response that enhances the original stimulus Effectors are stimulated to reinforce that change and increase the response
• Example of a positive feedback system


  Blood clotting Childbirth
• Example of a negative feedback system


  Regulation of body temperature Regulation of blood glucose level Maintenance of water balance of the body
• Thermoregulation


  the maintenance of body temperature within a range that enables cells to function efficiently.
• Factors of heating and cooling down

  - exothermic reactions- latent heat of evaporation- radiation- convection - conduction
• Ectotherm


  An animal who uses their surroundings to warm their bodies. Their core body temperature is heavily dependent on their environment.Relies on external sources
• Why do many ectotherms living in water not need to thermoregulate?

  Water has a high specific heat capacity so temperature does not change
• Why is living on land problematic for an ectotherm?

  The temperature of the air can dramatically change between seasons. Even from day to night
• Endotherm


  An organism that relies on its metabolic processes to internally warm them up. They maintain a stable core body temp regardless of the external temperature. They are adapted and have a 5x higher metabolic rate than ectotherms
• Behavioral responses of ectotherms


  - bask in sun- conduction by pressing their bodies against the ground- orientate body to get more SA exposed to sun- moving into shade- increasing breathing movements
• Physiological responses of ectotherms


  - dark colours absorb more radiation; lizards living in colder climates tend to be darker- colour may change (chameleons)- able to alter heart rate (increase/decrease metabolism)
• Peripheral temperature receptors


  Located in the skin and detect changes in the surface temperature
• Hypothalamus temperature receptors


  The thermoregulatory centre in the hypothalamus monitors blood temperature and detects any changes in the core body temperature.
• Behavioural responses of endotherms

  - hibernation- aestivation (sleeping during the day)- wearing clothes- houses

  Very similar to ectotherms
• Physiological responses of endotherms when hot enviroment

  - sweating

  - panting

  - hairs lie flat on surface

  - vasodilation

  - increased metabolic reactions
• Cooling Down - Vasodilation


  Arterioles near surface of skin dilate (when temp increases) forcing blood through the capillary networks close to the surface of the skin. Skin flushes, heat loss.

  
• Cooling Down- Increased sweating

  Rate of sweating increases. Sweat evaporates and heat is lost.
• Cooling Down- Reducing the insulating effect of hair or feathers


  The hair erector pili muscles relax and lie flat to prevent trapping any insulating layer of air
• Warming Up- Vasoconstriction


  Arterioles near the surface of skin constricts. Little blood flows through the capillary networks close to the surface of the skin. Little radiation/heat loss so warm blood kept well below the surface

  
• Warming Up- Decreased Sweating


  rate of sweating decreases. reduces cooling by evaporation
• Warming Up- Raising body hairs or feathers


  hair erector pili muscles contract, trapping insulating layer of air therefore reducing cooling through the skin
• Warming Up- Shivering


  Rapid, involuntary contracting and relaxing of the large voluntary muscles in the body. Metabolic heat from the exothermic reactions warm up the body
• Warming Up- adaptations


  - small SA- insulating layer of fat
• What are the 2 control centres

  The heat loss centre the heat gain centre
• Heat loss centre (of the hypothalamus)


  centre of the hypothalamus which is activated when blood temperature (flowing through) increases. It sends impulses through autonomic motor neurones to effectors in the skin and muscles.
• Heat gain centre (of the hypothalamus)


  centre of the hypothalamus which is activated when blood temperature (flowing through) decreases. It sends impulses through the autonomic nervous system to effectors in the skin and muscles.
• Advantages of ectotherms

  - less food used in respiration therefore can be used for growth- need less food and can survive long periods of time without eating
• Disadvantages of ectotherms

  - less active in cooler temperatures- more susceptible to global warming- surviving in winter is difficult