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Hormones & Homeostasis

Hormones & Homeostasis. Introduction to the Endocrine System. Homeostasis: A Review. The body’s ability to maintain stable internal conditions even though the outside world changes constantly. Why is it so important to maintain a state of dynamic equilibrium ?. Homeostasis Vocabulary.

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Hormones & Homeostasis

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  1. Hormones & Homeostasis Introduction to the Endocrine System

  2. Homeostasis: A Review • The body’s ability to maintain stable internal conditions even though the outside world changes constantly. • Why is it so important to maintain a state of dynamic equilibrium?

  3. Homeostasis Vocabulary

  4. Maintaining Homeostasis • The body keeps a stable environment by using negative feedback mechanisms, which reduce or shut-off a stimulus. • Example… think about your home thermostat. • What happens when it gets hot in the house? • What happens when it gets cold? • Biological examples… body temperature, blood [glucose], pH, blood pressure, etc.

  5. Control Systems:Endocrine vs. Nervous • Both play a necessary role in maintaining homeostasis: • Nervous • Fast • uses electrical impulses that travel along nerve cells • Activates muscles and glands • Short, immediate responses • Endocrine • Slow • uses hormones that travel in the blood • Activates other organs • generates slower, but longer responses

  6. Hormones • Chemical messengers that are released by glands into the bloodstream, and regulate the metabolic activity of other body cells. • Only effect Target Cells – which have specific protein receptors for that hormone • 2 Major Types: • Non-steroid– amino acid derivatives • Include proteins, peptides, amines • Steroids – lipid (cholesterol) derivatives • Sex hormones – made from ovaries & testis • Hormones from the adrenal cortex

  7. Role of Hormones in Negative Feedback Mechanisms • Glands release hormones in response to a stimulus • The blood [hormone] increases and they alter the cellular activity of their target organs (effector) • The increased levels of product “feed back” to the original gland, which reduces the release of the hormone.

  8. 3 Types of stimuli • Hormonal – endocrine organs are stimulated by other hormones • Ex. hormones from the hypothalamus stimulate the pituitary gland to secrete its hormones.

  9. As hormones from the final target glands increase in the blood, they “feed back” to inhibit the release of the pituitary hormones

  10. Humoral– ions and nutrients circulating in the blood • Ex. The secretion of calcitonin by the thyroid gland and PTH by the parathyroid gland is determined by blood [calcium].

  11. Blood [calcium] is regulated by this negative feedback mechanism

  12. Neural– nerve cells stimulate hormone release • Ex. The adrenal gland is stimulated by neurons of the sympathetic nervous system, which triggers the secretion of epinephrine and norepinephrine. These hormones are involved in the “fight-or flight” response.

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