Hormones and the Endocrine System

Introduction to Endocrine System and Hormones

  • The endocrine system is responsible for coordinating long-term body functions through hormones.
  • Hormones are chemical signals secreted by glands into the bloodstream that regulate various biological processes.

Endocrine Disruptors

  • Definition: Toxic chemicals that interfere with normal hormone function.
  • Examples:
    • Atrazine: Found in herbicides and can contaminate water sources.
    • Bisphenol A (BPA): Commonly used in plastics for food and drink containers.

Comparison of Endocrine and Nervous Systems

  • Endocrine System:

    • Uses hormones for communication.
    • Responses are slower but last longer.

  • Nervous System:

    • Uses electrical signals (nerve impulses).
    • Responses are rapid and short-lived.

Secreted Signaling Molecules

  • Types of chemical signals include:
    • Hormones: Travel through the bloodstream and affect distant target cells.
    • Local Regulators: Chemically signal neighboring cells (e.g., paracrine signals).
    • Neurotransmitters: Chemicals used by neurons to communicate with each other.
    • Neurohormones: Hormones released into the bloodstream by neurosecretory cells.
    • Pheromones: Chemicals released into the environment to communicate with other members of the same species.

Types of Hormones

  • Hormones classified by solubility:
    • Water-soluble hormones (e.g., insulin, epinephrine): Cannot cross cell membranes; act through receptors on the cell surface.
    • Lipid-soluble hormones (e.g., steroid hormones like cortisol): Can diffuse across membranes and bind to intracellular receptors.

Hormone Signaling Mechanisms

  1. Reception: Hormone binds to a specific receptor on the target cell.
  2. Signal Transduction: The signal is converted into a cellular response, often involving relay molecules (e.g., second messengers like cAMP).
  3. Response: The target cell changes behavior (e.g., activating enzymes or gene expression).

Major Endocrine Glands

  • Adrenal Glands: Produce hormones like adrenaline (epinephrine) for stress response.
  • Hypothalamus: Connects nervous and endocrine systems; regulates the pituitary gland.
  • Pituitary Gland: Anterior pituitary secretes hormones that regulate other endocrine glands (e.g., TSH, ACTH).
  • Thyroid Gland: Regulates metabolism and body temperature; produces thyroxine (T4).
  • Gonads (Testes & Ovaries): Produce sex hormones (testosterone, estrogen, progesterone).
  • Pancreas: Regulates blood glucose levels through insulin and glucagon.

Regulation of Blood Glucose Levels

  • Insulin: Lowers blood glucose levels by facilitating cellular uptake.
  • Glucagon: Raises blood glucose levels by promoting glycogen breakdown in the liver.

Diabetes Mellitus

  • Type 1 Diabetes: Autoimmune destruction of insulin-producing beta cells in the pancreas.
  • Type 2 Diabetes: Insulin resistance, often associated with obesity and sedentary lifestyle.

The Effect of Stress on Hormones

  • The adrenal medulla responds to acute stress by releasing epinephrine and norepinephrine.
  • The adrenal cortex releases glucocorticoids (e.g., cortisol) in response to chronic stress, affecting metabolism and immune function.

Hormonal Influence on Behavior

  • Oxytocin: Involved in social bonding and maternal behaviors; levels rise during nurturing interactions (e.g., mother-child bonding, dog-owner interactions).