Key Concepts in Homeostasis and Thermoregulation

• The pituitary gland is often called the 'master gland', as it controls the whole endocrine system. The gland itself produces hormones such as ACTH, ADH and the growth hormone.​

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• Gland: a group of cells or a discrete structure in the body that produces and releases a specific hormone.

• Hormone: a chemical substance that acts on specific cells in another part of the body from where it’s made (called target cells) to alter their function.

• Brain Link: Hypothalamus - monitors internal body conditions like temperature and water balance, signals pituitary gland.

• The main parts of the endocrine system related to the notes are located as follows:

  1. Pituitary Gland: This is often referred to as the "master gland" and is located at the base of the brain, just below the hypothalamus.

  2. Hypothalamus: This gland is located in the brain, situated below the thalamus and above the pituitary gland. It plays a crucial role in monitoring internal body conditions such as temperature and water balance.

  3. Kidneys: These are located in the lower back area, on either side of the spine. They are responsible for filtering blood and regulating water balance through hormones, particularly ADH (antidiuretic hormone).

  The endocrine system is a collection of glands that produce hormones, which are chemical messengers that regulate various bodily functions. Its main purposes include:

  • Regulation of Metabolism: Hormones control the body’s metabolism rate, affecting how energy is used in cells.

  • Growth and Development: Hormones are crucial for normal growth patterns and developmental stages from childhood to adulthood.

  • Homeostasis Maintenance: It helps maintain stable internal conditions, including temperature and water balance. For example, it regulates blood sugar levels and blood pressure.

  • Reproductive Functions: The endocrine system oversees reproductive hormones that influence fertility and behavior.

  • Response to Stress: Hormones like adrenaline prepare the body to respond to stressful situations by increasing heart rate and energy availability.

  • Influencing Behavior and Mood: Hormones can affect mood, emotions, and overall mental health, influencing behaviors such as appetite and sleep.

• Hormone Function: Released into bloodstream, travels to target cells, binds to specific receptors, resulting in a response.

• This response is the body’s automatic reaction to perceived danger and involves both systems:

  Nervous System:

  • Perceives the threat via sensory input (e.g., sight or sound).

  • The hypothalamus in the brain is activated.

  • Signals are sent via the sympathetic nervous system to prepare the body quickly.

  Endocrine System:

  • The hypothalamus signals the adrenal glands.

  • The adrenal medulla releases adrenaline (epinephrine) and noradrenaline.

  • Effects on the body:

    • Increased heart rate

    • Dilated pupils

    • Increased glucose availability

    • Redirection of blood to muscles

    • Slowed digestion

  This prepares the body to fight, flee, or freeze depending on the situation.

• Homeostasis: Ability to maintain stable internal conditions despite changes in the external environment, primarily regulates water and temperature.

• Thermoregulation: Process of maintaining stable body temperature. In mammals, body temp must stay within a narrow range.

• Categories of Animals:

  • Endotherm: Maintains internal temp (e.g., mammals).

  • Ectotherm: Temp varies with environment (e.g., reptiles).

• Water Balance:

  • Controlled via hormones, particularly ADH (antidiuretic hormone).

  • Low water levels → hypothalamus sends signal → pituitary releases ADH → kidneys absorb more water.

  • High water levels → less ADH → kidneys secrete more water.

• Stimulus-Response Model:

  • Stimulus: Environment change (internal/external).

  • Receptor: Specialized cells detect change.

  • Message: Hormonal or nervous response.

  • Effector: Body part responding.

  • Response: Action taken based on stimulus.

• Feedback Mechanisms:

  • Negative Feedback: Counteracts change in system (e.g., sweating to cool down).

  • Positive Feedback: Reinforces change (e.g., blood clotting).

• Success Criteria post-lesson:

  • Describe homeostasis.

  • Identify variables maintained in humans.

  • Explain thermoregulation in endotherms.

  • Use stimulus-response model for thermoregulation.

  • Describe positive and negative feedback loops.

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Homeostasis involves a process that allows the body to maintain stable internal conditions despite changes in the external environment. Here’s a description of how the process works, which can be diagramed:

1. Stimulus: A change in the internal or external environment (e.g., temperature, hydration levels).

2. Receptor: Specialized cells in the body detect this change (e.g., thermoreceptors in the skin detect temperature changes).

3. Message: The receptor sends a signal to the control center (e.g., hypothalamus).

4. Effector: The control center sends a response signal to an effector organ (e.g., sweat glands, blood vessels, kidneys).

   • For high temperature: Sweat glands increase sweat production, blood vessels dilate.

   • For low temperature: Shivering occurs, blood vessels constrict to preserve heat.

5. Response: The action taken (e.g., sweating cools the body, shivering warms it) leads to the restoration of balance.

6. Feedback Mechanism: The change is monitored, and the process continues until homeostasis is restored.

   • Negative Feedback: Opposes the change (e.g., cooling down from sweating).

   • Positive Feedback: Reinforces, amplifies the change if necessary (e.g., blood clotting process)