biology

• Homeostasis


  The tendency to maintain a balanced internal environment
• Homeostasis


  The process by which our body maintains internal stability and balance despite external fluctuations or changes in the environment
• To survive and function optimally, organisms must regulate the composition of fluids surrounding cells and maintain appropriate concentrations of nutrients, oxygen and other gases, ions, etc.
• Factors that trigger homeostatic response

  • Temperature
  • Water–solute concentration
  • Blood glucose level
• Any variation of these factors from normal condition will trigger homeostatic response
• Normal conditions or set points that are kept constant or within narrow physiological limits

  • Glucose: 70–100 mg/dL of blood
  • Temperature: 36.5–37.5⁰C
  • Blood pressure: < 120/80 mmHg
  • pH: 7.32–7.42 (↓↓ acidosis, ↑↑ alkalosis)
  • O2 level: 75–100 mmHg
• Homeostatic mechanisms


  Multi-organ systems response, coordinated via communication system, typically involve negative feedback loops
• Negative feedback mechanism


  A control mechanism in which an information about a change is fed back into the system resulting in opposite responses to revert to the normal condition
• Components of a feedback mechanism

  • Stimulus
  • Receptor
  • Relay
  • Effector
  • Response
  • Feedback
• Set point


  Normal value / range for a particular factor
• Stimulus


  A trigger / change from the set point
• Receptor


  Cells / tissues that detect the stimulus
• Relay


  The transmission of signals via nervous or endocrine systems (or both) from receptors to effectors
• Effector


  Cells / tissues (usually glands or muscles) involved in a response
• Response


  An action, at cell / tissue / whole organism level which would not have occurred without the stimulus
• Feedback


  The consequence of the response on the stimulus (may be positive or negative)
• Homeostasis provides stability and adaptation, allowing organisms to live in a wider range of habitats and with variable conditions
• Homeostasis provides efficiency, allowing thousands of reactions to occur simultaneously within each cell and the rate of metabolic reaction to be accurately coordinated based on needs
• Glycemic regulation


  The control of blood glucose level
• Glucose is central to many metabolic processes and the normal blood glucose level is ~90 mg / 100 ml blood
• Hyperglycemia leads to loss of water from tissues, while hypoglycemia leads to low blood pressure, fatigue, and coma
• Glucose can be converted to CO2 and H2O via cellular respiration, stored as glycogen, or stored as fat

  
• Pancreas


  An organ that contains two types of cells: beta cells that secrete insulin, and alpha cells that secrete glucagon

  
• Insulin

  A hormone that promotes the oxidation of glucose to CO2 and H2O, and the conversion of glucose to glycogen and fat for storage

  
• Glucagon

  A hormone that inhibits the formation of glucose from glycogen and non-carbohydrate sources, and promotes the formation of glucose from stored glycogen
• Glucose regulation


  1. Falling sugar level: Pancreas alpha cells release glucagon, which promotes the conversion of glycogen to glucose in the liver

  2. Normal sugar level

  3. Rising sugar level: Pancreas beta cells release insulin, which promotes the conversion of glucose to glycogen in the liver

  
• Without glycemic regulation, conditions like hyperglycemia, hypoglycemia, and diabetes mellitus can occur
• Diabetes mellitus


  The most common endocrine disorder, leading to cardiovascular disease, blindness, nerve diseases, kidney disorders and gangrene

  
• Main types of diabetes mellitus

  • Type 1 (insulin deficiency)
  • Type 2 (insulin resistance)

  
• Type 1 diabetes

  Caused by an autoimmune disease that destroys the beta cells in the pancreas, leading to insulin deficiency

  
• Type 2 diabetes


  Caused by insulin resistance, where the target cells do not bind to insulin effectively

  
• Thermoregulation


  The regulation of body temperature, which is crucial for metabolic activities
• Types of animals based on thermoregulation

  • Endotherms (warm-blooded)
  • Ectotherms (cold-blooded)
• Endotherms


  Animals (birds and mammals) that maintain a constant body temperature independent of the environment, primarily through physiological processes
• Ectotherms


  Animals (reptiles, amphibians, fishes, and invertebrates) that have a varying body temperature dependent on the environment, and control it through behavioral changes
• Thermoregulation in endotherms


  1. Falling temperature: Brain triggers skeletal muscles to start shivering

  2. Normal temperature

  3. Rising temperature: Brain triggers sweat glands to open
• Endothermy has high metabolic costs to maintain a constant body temperature, while ectothermy allows organisms to survive in locations with scarce food and allocate more energy to reproduction and growth
• Ectotherms can regulate their body temperature through behaviors like migration, hibernation, basking in the sun, and seeking shade, as well as physiological changes like changing skin color
• Osmoregulation


  The maintenance of salt and water balance in organisms, primarily via the urinary system

  
• Types of osmoregulators


  • Osmoregulators (aquatic vertebrates, bony fishes)
  • Osmoconformers (marine invertebrates, cartilaginous fishes)