Homeostasis

• Homeostasis


  The regulation of internal physiological processes in response to a stimulus at hand. A network of cells, tissues and organisms that regulate and maintain the internal environment.
• Homeostasis


  • Uses biochemical pathways and physiological processes
  • Involves feedback controls and feedback loops
  • Has counterresponses to maintain equilibrium
• Positive feedback loop


  Amplifies the response to a stimulus
• Negative feedback loop


  Counteracts changes and brings the body back to equilibrium
• Homeostasis process


  1. Stimulus detected

  2. Receptor detects change

  3. Sends message to control center

  4. Control center determines response

  5. Effector regulates or propagates response

  6. Homeostasis maintained
• Central regulation


  • Control of processes through the central nervous system and endocrine system
  • Involuntary control of bodily functions like breathing, fight-or-flight, rest and digest
• Local regulation


  • Involves autonomic reflexes and chemical factors within tissues and organs to maintain stability
• Examples of homeostasis


  • Normal body temperature (36-37°C)
  • Blood pressure regulation
• Set point for homeostasis

  The balanced physiological value for a variable
• Body temperature regulation


  1. Body detects rise/fall in temperature

  2. Receptors send signal to hypothalamus

  3. Hypothalamus activates effectors to retain or lose heat
• Blood pressure regulation


  1. Brain receives signals from pressure sensors (baroreceptors)

  2. Brain adjusts heart rate, blood vessel diameter, and cardiac output

  3. Sympathetic system increases heart rate and constriction if pressure is low

  4. Parasympathetic system decreases heart rate and promotes dilation if pressure is high
• Local blood pressure regulation

  1. Cells in blood vessel walls release chemicals in response to changes in blood flow

  2. Chemicals like nitric oxide cause blood vessel dilation, reducing pressure

  3. During exercise, tissues release substances causing local blood vessel dilation to increase blood flow
• Water homeostasis regulation


  1. Kidneys detect increase in water retention/dehydration

  2. Kidneys send signals to pituitary and adrenal glands

  3. Hormones like ADH increase water retention

  4. Kidneys sense reduction in water, triggering release of hormones to increase water retention
• Blood glucose regulation


  1. Pancreas detects high blood glucose

  2. Pancreas releases insulin to increase glucose uptake by cells

  3. Liver stores excess glucose as glycogen

  4. Low blood glucose triggers release of glucagon to increase blood glucose
• Positive feedback examples


  • Baby's head stimulus and oxytocin release causing uterine contractions
  • Platelet plug formation to stop bleeding
• Physiological acclimation


  Permanent or reversible organ changes to adapt to a new environmental setting for optimal function
• Types of physiological acclimation

  • Altitude (lungs, heart, muscles, red blood cells)
  • Heat (sweat glands, vasodilation)
  • Starvation (metabolism, protein catabolism)
• Homeostasis


  The regulation of internal physiological processes in response to a stimulus
• Homeostasis


  1. Stimulus

  2. Receptor detects change

  3. Sends message via information pathway to control center

  4. Control center determines what will happen

  5. Effector regulates, counteracts, or propagates a response
• Feedback controls


  • Negative feedback loop - counteracts changes to bring body back to equilibrium
  • Positive feedback loop - amplifies response to stimulus

  
• Negative feedback examples


  • Normal body temperature
  • Blood glucose levels

  
• Positive feedback examples


  • Labor contraction in pregnancy
  • Platelet plug formation
• Physiological acclimation


  Permanent or reversible changes in organs to adapt to a new environmental setting for optimal function
• Types of physiological acclimation

  • Altitude
  • Heat
  • Starvation
• Endocrine system


  A complex system of glands and organs that use hormones to control and coordinate body's metabolism, energy levels, reproduction, growth, development, stress response, thermoregulation, and homeostatic regulation
• Hormones


  An integral part of the endocrine system that help with physiological regulation and homeostasis
• Hormone signaling pathways


  • Humoral - through bloodstream in response to changes in extracellular fluid
  • Neural - based on signals from nervous system
  • Hormonal - release of hormones in response to other hormone signaling

  
• Ways hormone signalling can occur

  • Humoral
  • Neural
  • Hormonal

  
• Humoral pathway


  Release of hormones in response to changes in extracellular fluid levels of certain ions and nutrients

  
• Neural pathway


  Release of hormones based on signals from the nervous system. Nerve impulses generated by the nervous system trigger neural pathway. As a response certain hormones are released by the CNS, particularly the hypothalamus and autonomic nervous system.
• Hormonal pathway


  Release of hormones from response to other hormone signalling. Hypothalamus will secrete hormones which will stimulate effector organ such as pituitary gland which will secrete hormones to activate specific endocrine glands to make more hormones.
• Fat soluble hormones


  Smaller than water soluble hormones, can diffuse through cell membrane, go into cell and signal a various cascade of effects within the cell, have to be transported through blood circulation with plasma protein, can enter nucleus and influence gene expression
• Water soluble hormones


  Have receptors on entrance of cell, result in physiological changes to the cell such as enzyme activation or inhibition or ion channels opening and closing

  
• Negative feedback


  The body detects a high presence of a hormone in the bloodstream, sends a signal to the control centre (hypothalamus) to inhibit further release of that hormone
• Positive feedback


  A substance (e.g. ghrelin) detects a hormone (e.g. HGH) and signals the control centre (hypothalamus) to increase release of that hormone
• Antagonistic hormones


  Hormones that have opposite effects on one another, e.g. calcitonin and parathyroid hormone
• Nervous system


  • Consists of the brain, spinal cord and complex network of nerves
  • Sends messages back and forth
• Afferent pathways


  Transmit impulses from sensory receptors in peripheral organs to the central nervous system
• Efferent pathways


  Transmit impulses from the central nervous system to peripheral organs to cause an effect or action

  
• Divisions of the nervous system

  • Somatic nervous system
  • Autonomic nervous system