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Key internal conditions controlled in humans

Homeostasis and response • Homeostasis

Key concepts

What you'll likely be quizzed about

  • A rise in blood glucose after a meal is detected by the pancreas, which increases insulin secretion.
  • Insulin prompts liver and muscle cells to convert glucose into glycogen and stimulates cellular uptake of glucose, causing blood glucose concentration to fall.
  • Conversely, a drop in blood glucose during fasting or exercise signals the pancreas to release glucagon.
  • Glucagon triggers the breakdown of glycogen into glucose in the liver, raising blood glucose levels back to normal.
  • The insulin-glucagon system functions via negative feedback.
  • Insufficient or excessive control can lead to disorders like diabetes, where regulation fails and blood glucose remains elevated.

Flashcards

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Define homeostasis.

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Homeostasis is the maintenance of a constant internal environment to keep conditions optimal for cell and enzyme function.

Key notes

Important points to keep in mind

Homeostasis maintains internal variables within narrow limits for enzyme function.

Negative feedback reverses deviations from normal and prevents runaway changes.

High blood glucose → insulin → glycogen formation → blood glucose falls; low blood glucose → glucagon → glycogen breakdown → blood glucose rises.

Core temperature rises → vasodilation and sweating → increased heat loss; core temperature falls → vasoconstriction and shivering → heat conservation and production.

Low blood water concentration → increased ADH → kidneys reabsorb more water → urine volume decreases.

The nephron filters blood, selectively reabsorbs useful substances, and excretes excess water, salts, and urea.

Failure of organs involved in regulation disrupts homeostasis and causes clinical conditions.

Enzyme activity limits temperature tolerance; extreme temperatures produce fever, hypothermia, or hyperthermia.

Blood-borne hormones act more slowly but usually have longer-lasting effects than nerve impulses.

Regular revision of cause → effect chains enhances recall for regulation processes (sensor → control center → effector → response).

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