Chemical Control and Coordination in Biology

Chemical Control and Coordination in Biology

• Chemical control and coordination in organisms regulates physiological processes primarily via hormones, chemical messengers traveling through the bloodstream.
• Endocrine glands, lacking ducts, release hormones directly into the bloodstream.
• The endocrine system and nervous system work together; hormones have slower, longer-lasting effects than nerve impulses.

Types of Hormones

• Hormones are categorized by chemical composition:
  • Steroid hormones, derived from cholesterol, are lipid-soluble and bind to intracellular receptors. Examples include testosterone, estrogen, and aldosterone.
  • Non-steroidal hormones, derived from amino acids, are less lipid-soluble and typically bind to membrane-bound receptors. Examples include insulin, glucagon, and epinephrine.

Mechanisms of Hormone Action

• Hormones bind to specific receptors, forming hormone-receptor complexes.
  • These complexes trigger intracellular signaling cascades, altering target cell activities.
  • Hormone effects vary depending on the hormone and target cell.

The Endocrine System

• Major endocrine glands include the pituitary, thyroid, adrenal, pancreas, ovaries, and testes.
  • The pituitary gland regulates other endocrine glands via tropic hormones, hence often called the "master gland".
  • The thyroid gland controls metabolic rate.
  • The adrenal glands manage stress response and electrolyte balance.
  • The pancreas regulates blood sugar.
  • Ovaries and testes produce sex hormones, influencing sexual development and reproduction.

Endocrine Glands and Their Functions

• Pituitary Gland: Anterior (growth hormone, TSH, ACTH) and posterior (ADH, oxytocin) pituitary regulate other endocrine glands through tropic hormones.
• Thyroid Gland: Produces thyroxine (T4) and triiodothyronine (T3) to influence metabolic rate.
• Adrenal Glands: Adrenal medulla (epinephrine, norepinephrine) for stress response; adrenal cortex (corticosteroids) for metabolism and mineral balance.
• Pancreas: Islets of Langerhans secrete insulin (lowering blood sugar) and glucagon (raising blood sugar).
• Ovaries: Produce estrogen and progesterone, affecting female sexual characteristics and reproductive cycles.
• Testes: Produce testosterone, regulating male sexual characteristics and spermatogenesis.

Homeostasis and Feedback Mechanisms

• Homeostasis maintains a stable internal environment, with the endocrine system playing a key role.
  • Negative feedback loops are common, where a hormone's effect inhibits its own production.

Disorders of Chemical Control and Coordination

• Hormone production or function irregularities cause various disorders.
  • Examples include diabetes (insulin issues), hypothyroidism (low thyroid hormone), hyperthyroidism (high thyroid hormone), and growth disorders.

Factors Affecting Hormone Secretion

• Hormone secretion is influenced by:
  • Environmental factors (stress)
  • Circadian rhythms
  • Blood levels of other hormones
  • Nervous system input, and more.

Chemical Messengers Beyond Hormones

• Neurotransmitters, fast-acting chemical messengers, transmit signals across synapses in both plants and animals.
• Plant hormones (phytohormones) regulate plant growth, development, and environmental responses.