Homeostasis Part 1

• Homeostasis


  The body's tendency to maintain a relatively constant internal environment
• The human body works best at a temperature of 37C, with a blood pH level of 7.4 and a blood sugar level of 100 mg/dL
• Homeostasis


  • It is critical for survival because other vertebrates, the human body can survive only within a narrow range of conditions
  • It is a dynamic process and information about body temperature, blood glucose levels, and blood oxygen levels may rise and fall during the day, but still be considered in balance
• Feedback systems


  They have 3 functional components: sensor, control centre, and effector
• Feedback systems


  1. Sensor detects change in internal environment and sends a signal to the control centre

  2. Control centre sets the range of values within which a variable should be maintained, receives information from the sensor and sends a signal to the effectors when needed

  3. Effector receives signals from the control centre and responds, resulting in a change to an internal variable
• Negative feedback systems


  Mechanisms that make adjustments to bring the body back within an acceptable range
• Positive feedback systems


  They are less common in the body and are designed to reinforce change, moving the controlled variable even further away from a steady state
• Thermoregulation


  The ability of an organism to maintain a constant internal body temperature
• Endotherms


  • Regulate their temperature internally, "warm-blooded" (e.g. human, dog)
• Ectotherms


  • Regulate their temperature externally, "cold-blooded" (e.g. lizard, turtle)
• How mammals deal with heat stress

  1. Sweating occurs - sweat evaporates, taking heat with it

  2. Blood vessels dilate - this brings blood closer to the surface of the skin, allowing heat to escape
• Endocrine Glands


  • Pineal Gland
  • Hypothalamus
  • Pituitary Gland
  • Thyroid Gland
  • Parathyroid Glands
  • Thymus
  • Adrenal Glands
  • Pancreas
  • Ovaries (Female)
  • Testis (male)
• How mammals deal with cold stress

  1. Shivering occurs - shivering exercises the muscles, creating heat as a by-product of cellular respiration

  2. Blood vessels constrict - this brings blood away from the surface of the skin, in the attempt to retain heat in the body

  3. Hair stands on end - this creates a "web" that traps heat closer to the body
• Mammalian diving reflex


  Upon exposure of the face to cold water, in the attempt to conserve oxygen, blood is diverted away from the extremities and towards the blood-brain circuit, causing the pulse to drop
• Ice is destructive to cells because water expands as it freezes. The cell is a bit elastic so it can withstand some expansion, but ice crystals that form outside the cell are more dangerous as they can puncture the cell.
• Some animals are able to survive freezing because they often have cryoprotectants or other anti-freeze chemicals in their blood to prevent freezing, e.g. painted turtle hatchlings, wood frogs, Upis beetles, Arctic ground squirrels.
• Nervous system


  Elaborate communication system (>100 billion nerve cells in the brain alone!) that responds to stimuli (external or internal) by controlling the actions of the body through electrochemical messages
• Main divisions of the nervous system

  • Central Nervous System (CNS) - brain and spinal cord, coordinating system
  • Peripheral Nervous System (PNS) - nerves that carry info between organs and CNS, subdivided into somatic (skeletal muscle, bones and skin) and autonomic (internal organs)
• Neurons


  • Functional units of the nervous system, can be sensory (sense and relay info from the environment to CNS), motor (relay information to effectors), or interneurons (link neurons in the body)
• Parts of a neuron

  • Dendrites - receive info from sensory receptors
  • Axon - projects nerve impulses from the cell body
  • Myelin sheath - covers many axons, insulates the neurons, preventing loss of charged ions from nerve cell
  • Nodes of Ranvier - areas between sections of myelin sheath, nerve impulses jump from one node to another, speeding up the process
  • Neurilemma - surrounds the axon and promotes re-generation of a damaged axon
• Reflex arc


  Simplest nerve pathway, occurs without brain coordination, has 5 components: receptor, sensory neuron, interneuron, spinal cord, motor neuron and effector
• Resting neuron


  A neuron that is not conducting signals, contains potential energy resulting from an electrical charge difference between the inside and outside of the plasma membrane
• Action potential


  If an axon is stimulated sufficiently, it will trigger an impulse down the length of the axon - an all-or-none response
• Synapse


  The tiny gap between neurons where neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron
• Hormones


  Chemicals released by cells that affect cells in other body parts by speeding up or slowing down bodily processes
• Steroid hormones


  • Made from cholesterol, diffuse from capillaries into interstitial fluid then into target cells, combine with receptor molecules in the cytoplasm and the hormone-receptor complex moves to the nucleus to activate a gene
• Protein hormones


  • Chains of amino acids, combine with specific receptors on the cell membrane, this complex activates the production of an enzyme called adenylyl cyclase which causes the cell to convert ATP into cAMP (cyclic adenosine monophosphate), cAMP functions as a messenger activating enzymes in the cytoplasm to carry out normal functions
• Pituitary gland


  The "master" endocrine gland, connected by a stalk to the hypothalamus, produces and stores hormones that regulate other endocrine glands
• Hormones produced by the anterior pituitary

  • Thyroid stimulating hormone (TSH)
  • Follicle-stimulating hormone (FSH)
• Protein


  Made from amino acids
• Steroid hormone


  Made from cholesterol, requires conversion of ATP to cAMP, creates genes to make proteins
• Anterior pituitary


  Regulated through blood vessels connected to hypothalamus, produces and releases hormones directly into bloodstream, bigger in size
• Posterior pituitary


  Regulated through nerves connected to hypothalamus, stores and releases hormones produced by hypothalamus, smaller in size, promotes other glands to secrete