Endocrine o4ungouewrbng

• Balance - homeostasis


  A relatively constant internal environment that supports cell functioning and life processes
• Imbalance - loss of homeostasis


  As cells function they use up nutrients and produce biproducts
• Examples of imbalance


  • growth
  • reproduction
  • exercise
  • stress
  • illness
• Negative feedback control loops

  • Keep a regulated variable within its normal range, around its set-point
  • If the variable goes up, negative feedback brings it down
  • If the variable goes down, negative feedback brings it up
• Regulated variable


  A variable for which there is a sensor and a system to ensure the variable is kept within a normal range, around a set-point
• Examples of regulated physiological variables

  • Core temperature
  • Plasma glucose concentration
  • Plasma calcium concentration
  • Basal metabolic rate
• Hormones from these glands/organs are involved in homeostasis of plasma calcium and glucose concentration, growth and cell metabolism, immunity and stress management, and endocrine disorders and disease

  
• Plasma [Ca2+] Homeostasis


  There needs to be enough Ca2+ calcium in the blood for cells to use it when they need it
• Ca2+ in the body

  • Interacts with vesicles to facilitate release of neurotransmitter
  • Interacts with myofilaments in sarcomeres to facilitate cross-bridge formation
  • More than 99% of Ca2+ in the body is stored in bones (as hydroxyapatite)
• How Ca2+ enters or exits the blood plasma


  • Ca2+ absorbed into blood from digestive tract
  • Ca2+ reabsorbed back into blood by kidneys
  • Ca2+ filtered out of blood by kidneys
  • Ca2+ removed from blood and deposited into bone
  • Ca2+ resorbed into blood from bone broken down
• Glands/organs and hormones involved in plasma [Ca2+] homeostasis

  • Parathyroid glands (secrete PTH)
  • Kidneys (secrete Calcitriol)
  • Thyroid gland (secretes Calcitonin)
  • Digestive system (absorbs Ca2+)
  • Bones (osteoblasts and osteoclasts)

  
• How the body corrects hypocalcemia - low plasma [Ca2+]

  1. Parathyroid glands detect low Ca2+, release more PTH

  2. Kidneys convert more vitamin D to Calcitriol

  3. Digestive tract absorbs more Ca2+

  4. Bone resorbs more Ca2+ into plasma
• How the body corrects hypercalcemia - high plasma [Ca2+]

  1. Parathyroid glands detect high Ca2+, release less PTH

  2. Kidneys convert less vitamin D to Calcitriol

  3. Digestive tract absorbs less Ca2+

  4. Bone deposits more Ca2+ from plasma
• Calcitonin has minimal effect, the primary hormone that controls plasma [Ca2+] is Parathyroid hormone (PTH)
• Plasma [glucose] Homeostasis


  There needs to be enough glucose in the blood for cells to use it when they need it
• How glucose enters blood plasma

  - absorbed into blood from digestive tract

  - Released into blood by liver (from glycgen breakdown or new glucose )
• Glands and gland cell involved in plasma [glucose] homeostasis


  • Pancreas
  • Alpha islet
  • Beta islet
• Plasma [glucose] regulated


  Because there needs to be enough glucose in the blood for cells to use it when they need it
• How glucose enters or exits the blood plasma

  1. Carbohydrates in food enter digestive tract

  2. Glucose absorbed into blood from digestive tract

  3. Glucose removed from blood by all body cells

  4. Excess glucose removed from blood and stored in liver and skeletal muscle as glycogen

  5. Excess glucose removed from blood and stored in adipose as fat

  6. Glucose released into blood by liver (new or from glycogen breakdown)
• Glands/organs and hormones involved in plasma [glucose] homeostasis

  • Pancreas
  • Alpha islet cells secrete glucagon
  • Beta islet cells secrete insulin

  
• How the body corrects hypoglycemia - low plasma [glucose]

  1. Alpha islet cells of the pancreas detect low glucose, compare to set-point and release glucagon

  2. Glucagon signals to the liver to release glucose into plasma

  3. By creating new glucose

  4. By breaking down glycogen into glucose
• How the body corrects hyperglycemia - high plasma [glucose]

  1. Beta islet cells of the pancreas detect high glucose, compare to set-point and release insulin

  2. Liver, skeletal muscle & adipose (fat) cells take excess glucose from blood to store as glycogen or fat
• All body cells use glucose as the main substrate for making ATP
• Glucose is also used to make other substances essential for body functioning (e.g. glycoproteins)
• Glucose is stored in the form of glycogen (long chains of glucose molecules) or fat
• Glycogen is formed by linking glucose molecules together in long chains
• If glucose is stored as glycogen in skeletal muscle, meat is not a good source of glucose because glycogen is broken down very rapidly after an animal dies