Endocrine System Overview

Endocrine System Function

• Coordinates and integrates body activity through chemical signaling (hormones) produced by glands.
• Composed of glands and their secreted hormones.

Hormone Classification

• Endocrine: Released into the bloodstream, acting on distant target cells.
• Local: Acts locally, without entering the bloodstream.
  • Paracrine: Acts on neighboring cells.
  • Autocrine: Acts on the secreting cell itself.

Hormone Types

• Steroid Hormones: Lipid-soluble.
• Amino Acid-Based Hormones:
  • Proteins
  • Peptides
  • Amines

Target Cells and Receptors

• Target Cells: Specific cells or tissues affected by a hormone.
• Receptors: Proteins on target cell membranes where hormones bind.

Stimuli for Endocrine Organs

• Hormonal: Stimulated by other hormones.
• Neural: Stimulated by nerve fibers.
• Humoral: Stimulated by changes in blood levels of ions or nutrients.

Glands: Endocrine vs. Exocrine

• Endocrine: Ductless glands releasing hormones directly into the bloodstream.
• Exocrine: Release products through ducts onto body surfaces or into body cavities.

Major Endocrine Glands

• Pituitary Gland (Hypophysis): Walnut-sized gland inferior to the hypothalamus.
• Thyroid Gland:
• Parathyroid Glands: Located on the posterior surface of the thyroid.
• Adrenal Glands: Bean-shaped glands atop the kidneys.
  • Adrenal Cortex: Outer layer.
  • Adrenal Medulla: Inner layer.
• Pancreas: Dual function endocrine and exocrine gland.
• Pineal Gland:
• Thymus:

Anterior Pituitary Hormones

• Hypothalamic Releasing Hormones: Stimulate release of other anterior pituitary hormones.
  • GHRH (Growth Hormone Releasing Hormone)
  • TRH (Thyrotropin Releasing Hormone)
  • GnRH (Gonadotropin Releasing Hormone)
  • PRH (Prolactin Releasing Hormone)
  • CRH (Corticotropin Releasing Hormone)
• Hypothalamic Inhibiting Hormones: Inhibit release of other anterior pituitary hormones.
  • GHIH (Growth Hormone Inhibiting Hormone)
  • PIH (Prolactin Inhibiting Hormone)

Anterior Pituitary Hormones (Continued)

• Growth Hormone (GH): Converts amino acids to proteins.
• Ghrelin: Hormone signaling hunger.
• Prolactin (PRL): Stimulates and maintains milk production.
• Adrenocorticotropic Hormone (ACTH): Regulates adrenal cortex.
• Thyroid-Stimulating Hormone (TSH): Regulates thyroid gland activity.
• Gonadotropic Hormones: Regulate gonads.
  • FSH (Follicle-Stimulating Hormone): Female: follicle development; Male: sperm development
  • LH (Luteinizing Hormone): Female: ovulation; Male: testosterone production.

Posterior Pituitary Hormones

• Oxytocin: Released significantly during childbirth and nursing.
• Antidiuretic Hormone (ADH) / Vasopressin: Prevents excessive urine production.

Posterior Pituitary Conditions

• Polyuria: Excessive urination.
• Polydipsia: Excessive thirst.
• Bedwetting: Incontinence in children.
• Dehydration: Loss of body water.

Pituicytes

• Neuroglia associated with axon terminals of hypothalamic neurons.

Thyroid Gland Hormones

• Thyroxine (T4): Regulates metabolism, heart rate, and body temperature.
• Triiodothyronine (T3): More potent form of thyroid hormone.
• Calcitonin: Regulates calcium homeostasis.

Parathyroid Gland Hormone

• Parathyroid Hormone (PTH): Key regulator of blood calcium.

Adrenal Gland Hormones

• Mineralocorticoids: Regulate mineral balance (e.g., sodium, potassium) in the blood.