Copy of Lab 8 Mini Lesson Learning Guides

Mini Lesson 1: General Characteristics of Hormones and Hormonal Signaling

Definitions and Relationships

• Autocrine signaling – A cell releases a chemical messenger that acts on the same cell that secreted it.

• Paracrine signaling – A cell releases a chemical messenger that acts on nearby cells.

• Neurotransmitter signaling – A neuron releases a neurotransmitter that binds to receptors on another neuron or effector cell.

• Endocrine signaling – Endocrine glands secrete hormones into the bloodstream to act on distant target cells.

• Exocrine signaling – Glands secrete substances (e.g., enzymes, sweat) into ducts that lead outside the body or into internal cavities.

• Neurocrine signaling – A neuron releases a chemical messenger that enters the bloodstream (neurohormones).

• Hormone – A chemical messenger secreted by endocrine glands that travels in the bloodstream to regulate distant target cells.

• Neurohormone – A hormone secreted by neurons (e.g., oxytocin, vasopressin).

Properties of Protein/Peptide Hormones

• Structure – Made of chains of amino acids.

• Solubility – Water-soluble (hydrophilic).

• Synthesis – Synthesized as larger inactive precursors (prohormones) in the rough ER.

• Storage – Stored in secretory vesicles.

• Secretion – Released via exocytosis.

• Transport – Dissolved in plasma.

• Receptor location – On the target cell membrane.

• Biologic response – Activates second messenger pathways.

• Onset of effect – Rapid (seconds to minutes).

• Lifetime – Short (minutes).

Examples of Steroid Hormones and Their Sources

• Cortisol – Adrenal cortex

• Aldosterone – Adrenal cortex

• Testosterone – Testes

• Estrogen & Progesterone – Ovaries

• Vitamin D-derived hormones – Skin/liver/kidney

Properties of Steroid Hormones

• Base molecule – Derived from cholesterol.

• Solubility – Lipid-soluble (hydrophobic).

• Synthesis – Synthesized on demand in the smooth ER.

• Storage – Not stored (diffuses out as soon as synthesized).

• Secretion – Diffuses across the membrane.

• Transport – Bound to plasma proteins in the blood.

• Receptor location – Intracellular (cytoplasm or nucleus).

• Biologic response – Alters gene expression.

• Onset of effect – Slow (hours to days).

• Lifetime – Long (hours to days).

Examples of Amine Hormones and Their Sources

• Catecholamines (epinephrine, norepinephrine, dopamine) – Adrenal medulla

• Thyroid hormones (T3, T4) – Thyroid gland

Properties of Amine Hormones

• Base molecule – Derived from tyrosine or tryptophan.

• Solubility –

  • Catecholamines – Water-soluble.

  • Thyroid hormones – Lipid-soluble.

• Synthesis & Storage –

  • Catecholamines – Stored in vesicles.

  • Thyroid hormones – Stored in the thyroid follicle.

• Secretion – Exocytosis (catecholamines), diffusion (thyroid hormones).

• Transport –

  • Catecholamines – Dissolved in plasma.

  • Thyroid hormones – Bound to plasma proteins.

• Receptor location –

  • Catecholamines – On the membrane.

  • Thyroid hormones – Intracellular.

• Biologic response –

  • Catecholamines – Second messenger pathways.

  • Thyroid hormones – Alters gene expression.

• Onset of effect –

  • Catecholamines – Rapid.

  • Thyroid hormones – Slow.

• Lifetime –

  • Catecholamines – Short.

  • Thyroid hormones – Long.

Four Possible Fates of a Hormone After Secretion

1. Bind to a receptor on a target cell and cause a response.

2. Be metabolized into an inactive form by enzymes in the blood or tissues.

3. Be excreted in urine or bile.

4. Be stored temporarily in the bloodstream by binding to transport proteins.

Mini Lesson 2: Functional Roles of Hormones

Hormone Receptor Characteristics

• Specificity – Hormones bind only to their specific receptors.

• Sensitivity – Receptors have different affinities for their hormones.

• Amplification – One hormone molecule can activate many intracellular molecules.

• Up-regulation – Increased receptor number in response to low hormone levels.

• Down-regulation – Decreased receptor number in response to high hormone levels.

• Permissiveness – One hormone enhances the action of another (e.g., thyroid hormone increases responsiveness to epinephrine).

Three Categories of Inputs That Influence Hormone Secretion

1. Changes in ions or nutrients – Example: Insulin is secreted in response to high glucose levels.

2. Neural signals – Example: Sympathetic nerves stimulate epinephrine release.

3. Other hormones – Example: TSH stimulates the release of thyroid hormones.

Tropic vs. Trophic Hormones

• Tropic hormones – Regulate the secretion of another hormone (e.g., ACTH stimulates cortisol release).

• Trophic hormones – Promote the growth and maintenance of target tissues (e.g., TSH maintains the thyroid gland).

• Some hormones are both tropic and trophic – Example: TSH stimulates thyroid hormone release and promotes thyroid gland growth.

Four General Categories of Endocrine Disorders

1. Hyposecretion (primary) – Gland does not produce enough hormone.

2. Hyposecretion (secondary) – Insufficient stimulation from tropic hormones.

3. Hypersecretion (primary) – Gland overproduces hormone.

4. Hypersecretion (secondary) – Excessive stimulation from tropic hormones.

Mini Lesson 3: Hypothalamus and Pituitary Gland

Inputs Integrated by the Hypothalamus

• Neural signals from the brain

• Sensory input (light, temperature, pain)

• Blood-borne signals (hormones, nutrients, osmolarity)

Anatomical and Functional Relationships

• Anterior Pituitary (Adenohypophysis) – Connected by hypothalamo-hypophyseal portal vessels; regulated by hypothalamic hormones.

• Posterior Pituitary (Neurohypophysis) – Connected by axons; releases neurohormones synthesized in the hypothalamus.

Neurohormones Secreted by the Posterior Pituitary

1. Oxytocin – Peptide hormone; stimulates uterine contractions and milk ejection.

2. Vasopressin (ADH) – Peptide hormone; regulates water balance.

• Synthesis – In the hypothalamus.

• Storage – In the posterior pituitary.

• Secretion – Released into the bloodstream upon neural signals.

Control of Anterior Pituitary Hormone Secretion

• Regulated by hypophysiotropic hormones from the hypothalamus via the portal system.

Hormones Involved in Hypothalamus → Anterior Pituitary Signaling

• CRH → ACTH → Cortisol

• TRH → TSH → Thyroid Hormones

• GnRH → FSH/LH → Sex Hormones

• GHRH → GH → IGF-1

• Dopamine (DA) → Inhibits Prolactin

Hypothalamus-Pituitary-Endocrine Gland Axis Model

• Uses negative feedback loops to maintain homeostasis.