5.6 Chemical Coordination and Integration

The Endocrine System

• A system of ductless glands that secrete hormones directly into the bloodstream.
• Hormones are non-nutrient chemicals that act as intercellular messengers.

Hypothalamus & Pituitary Gland

• Hypothalamus: The "master control center," controls the pituitary gland.
• Pituitary Gland: The "master gland."
  • Anterior Pituitary: Produces GH, PRL, TSH, ACTH, LH, FSH.
  • Posterior Pituitary: Stores and releases Oxytocin and ADH (Vasopressin).

Key Pituitary Hormones & Disorders

• Growth Hormone (GH):
  • Hyposecretion: Dwarfism
  • Hypersecretion: Gigantism, Acromegaly
• Antidiuretic Hormone (ADH):
  • Hyposecretion: Diabetes Insipidus

Thyroid & Parathyroid Glands

• Thyroid Gland:
  • Hormones: Thyroxine (T4), Triiodothyronine (T3), Calcitonin.
  • Functions: Regulates metabolism and blood calcium.
  • Disorders: Goiter, Cretinism, Grave's Disease.
• Parathyroid Gland:
  • Hormone: Parathyroid Hormone (PTH).
  • Function: Increases blood calcium levels (hypercalcemic).

Adrenal Gland

• Adrenal Medulla (Inner):
  • Hormones: Adrenaline, Noradrenaline (Catecholamines).
  • Function: "Fight or Flight" response.
• Adrenal Cortex (Outer):
  • Hormones: Glucocorticoids (Cortisol), Mineralocorticoids (Aldosterone).
  • Function: Regulate metabolism, water/electrolyte balance.
  • Disorder: Addison's Disease.

Pancreas & Gonads

• Pancreas (Islets of Langerhans):
  • Insulin (β-cells): Decreases blood glucose.
  • Glucagon (α-cells): Increases blood glucose.
  • Disorder: Diabetes Mellitus.
• Gonads:
  • Testis: Testosterone (male characteristics, spermatogenesis).
  • Ovary: Estrogen (female characteristics), Progesterone (supports pregnancy).

Other Endocrine Tissues

• Pineal Gland: Melatonin (regulates diurnal rhythms).
• Thymus: Thymosins (immune system development).
• Gastrointestinal (GI) Tract: Gastrin, Secretin, CCK, GIP.

Mechanism of Hormone Action

• Peptide/Protein Hormones (e.g., Insulin, Glucagon):
  • Bind to cell surface receptors.
  • Act via second messengers (e.g., cAMP).
• Steroid Hormones (e.g., Cortisol, Testosterone):
  • Lipid-soluble, enter the cell.
  • Bind to intracellular receptors.
  • Regulate gene expression directly.