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• Homeostasis


  The biological process by which an organism maintains a stable internal environment despite changes in the external environment
• Homeostasis


  • Involves a set of physiological mechanisms that work together to regulate and balance various internal variables such as body temperature, blood sugar levels, pH balance, and water balance
  • Is essential for the survival of all living organisms as it ensures that the cells of the body can function properly within a narrow range of optimal conditions
• Negative feedback


  1. A change in a physiological variable triggers a response that counteracts or reverses the initial change, restoring the variable to its original set point or target value

  2. Serves to maintain stability or homeostasis in a system
• Steps of negative feedback

  1. A change occurs (stimulus) and this causes a change or imbalance in the body

  2. The change is detected by a receptor

  3. The receptor sends a signal to an effector regarding the change

  4. The effector responds in such a way as to reverse the change

  5. The imbalance is corrected and homeostasis is restored
• Systems where negative feedback is used to maintain homeostasis

  • Thyroid hormones
  • Glucose control
  • Osmoregulation
  • Salt and CO levels
  • Thermoregulation
• Negative feedback


  The levels of TSH (thyroid stimulating hormone) and thyroxin are tightly regulated in the body through negative feedback mechanisms
• Thyroid stimulating hormone (TSH)


  • Produced by the pituitary gland
  • Plays a critical role in regulating the production of thyroxin by the thyroid gland
• Negative feedback inhibition


  1. When there is an excess of thyroxin in the bloodstream, it signals the pituitary gland to reduce the production of TSH

  2. As TSH production decreases, the thyroid gland receives less stimulation and produces less thyroxin which helps to restore balance

  
• Negative feedback loop


  1. When there is a deficiency of thyroxin in the bloodstream, the pituitary gland increases the production of TSH

  2. This stimulates the thyroid gland to produce more of this hormone
• The negative feedback loop between TSH and thyroid hormones plays a critical role in maintaining normal thyroid function and ensuring that the levels of thyroid hormones in the body remain within a healthy range
• If the thyroid gland constantly secretes too little thyroxin, the individual will be diagnosed with hypothyroidism
• If the thyroid continually secretes too much thyroxin, they will be diagnosed with hyperthyroidism

  
• Figure 1: Hypothyroidism vs hyperthyroidism

  
• Negative feedback process


  1. Normal thyroxin levels

  2. Pituitary detects increase in thyroxin

  3. Thyroxin levels drop

  4. Pituitary detects drop in thyroxin

  5. Thyroxin levels rise

  6. Thyroxin levels drop

  7. Thyroxin levels rise

  8. Secretes more TSH

  9. Stop secreting TSH

  10. Thyroid produces less thyroxin

  11. Thyroid produces more thyroxin

  
• Chromatin - DNA + proteins, condensed into chromosomes during mitosis/meiosis
• Nucleolus - site of ribosome synthesis
• The nucleus is the control center of the cell.
• Ribosomes are made up of RNA & protein
• Lysosomes contain enzymes to break down waste materials within cells.
• Ribosomes are responsible for protein synthesis.
• Ribosome - site where amino acids are assembled together to form polypeptides
• Mitochondria are organelles that produce energy through respiration.
• Cytoskeleton - network of protein fibres that gives cells their shape and allows them to move
• Mitochondria is where cellular respiration occurs
• Nucleus - contains genetic material (DNA) which controls all cellular activities
• Lysosomes contain enzymes that break down waste products
• Mitochondria produce ATP through aerobic respiration
• Golgi apparatus modifies and packages proteins for transport to other parts of the cell or outside the cell
• Cell membrane controls what enters/leaves the cell
• Cell membrane regulates what enters/exits the cell
• Nucleus is the control centre of the cell containing DNA which controls all activities of the cell
• Lysosomes contain digestive enzymes which break down waste material inside the cell
• Vacuoles store water, nutrients, and wastes inside the cell.
• Chloroplasts are organelles found in plant cells that convert sunlight into chemical energy.
• Mitochondria produce ATP through aerobic respiration.
• Ribosome synthesises protein molecules using instructions from mRNA
• Glucose control


  The processes by which the body maintains a stable level of glucose (sugar) in the blood

  
• Glucose


  • The primary source of energy for the body's cells
  • Its concentration in the blood must be tightly regulated to avoid harmful effects

  
• Insulin


  A hormone produced by the pancreas that promotes the uptake of glucose

  
• Glucagon


  A hormone produced by the pancreas that promotes the release of glucose and increases blood glucose levels