Homeostasis and control flashcards

Homeostasis is the maintenance of a stable internal environment within narrow limits, despite changes in external conditions. It is essential for enzyme activity and cell function. Control systems involve receptors detecting changes from a set point, a coordination centre processing the information, and effectors producing a response. Most homeostatic mechanisms use negative feedback, where a deviation from the set point triggers responses that reverse the change. Key examples include the regulation of blood glucose concentration through insulin and glucagon, thermoregulation in mammals, and the control of water potential in the blood through osmoregulation. Students must understand how the liver and pancreas interact in glucose regulation, how the hypothalamus and skin act in temperature control, and how the kidneys adjust urine concentration via ADH. The distinction between ectotherms and endotherms is also important.

1. Card 1

   What is homeostasis?

   Homeostasis is the maintenance of a stable internal environment within narrow limits, allowing cells and enzymes to function optimally.

2. Card 2

   What are the three components of a homeostatic control system?

   A receptor detects a stimulus, a coordination centre processes the signal, and an effector produces a corrective response.

3. Card 3

   How does negative feedback maintain homeostasis?

   Negative feedback reverses a deviation from the set point; when a variable rises or falls, responses are triggered to bring it back to normal.

4. Card 4

   Which organ detects changes in blood glucose concentration?

   The islets of Langerhans in the pancreas detect blood glucose changes; alpha cells sense low glucose and beta cells sense high glucose.

5. Card 5

   How does insulin lower blood glucose concentration?

   Insulin is released by beta cells; it increases glucose uptake by cells and promotes glycogenesis (conversion of glucose to glycogen) in the liver.

6. Card 6

   How does glucagon raise blood glucose concentration?

   Glucagon is released by alpha cells; it stimulates glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis in the liver.

7. Card 7

   What is the role of the hypothalamus in thermoregulation?

   The hypothalamus acts as the thermoregulatory centre; it detects blood temperature directly and receives nerve impulses from peripheral thermoreceptors in the skin.

8. Card 8

   Name two responses that reduce body temperature in mammals.

   Vasodilation of skin arterioles increases heat loss by radiation, and sweating increases evaporative cooling from the skin surface.

9. Card 9

   Name two responses that conserve or generate heat in mammals.

   Vasoconstriction reduces blood flow to the skin surface, and shivering generates heat through rapid involuntary muscle contractions.

10. Card 10

    What is the difference between an ectotherm and an endotherm?

    An ectotherm relies on external heat sources to regulate body temperature, whereas an endotherm generates heat internally through metabolic processes.

11. Card 11

    How does ADH regulate water potential of the blood?

    ADH (antidiuretic hormone) increases the permeability of the collecting duct in the kidney, allowing more water reabsorption and producing more concentrated urine.

12. Card 12

    What triggers increased ADH release from the pituitary gland?

    Osmoreceptors in the hypothalamus detect a fall in blood water potential (e.g. through dehydration) and stimulate the posterior pituitary to release more ADH.

• Many students confuse glycogenesis (glucose to glycogen) with glycogenolysis (glycogen to glucose), leading to errors when explaining the roles of insulin and glucagon.
• A common misconception is that ectotherms are cold-blooded and therefore always have a low body temperature, when in fact they can achieve similar body temperatures to endotherms by using behavioural strategies.
• Students often incorrectly state that ADH is produced by the pituitary gland, when it is actually synthesised in the hypothalamus and only stored and released from the posterior pituitary.

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