Biol2302_Chapter16 (1)

Chapter 16: The Endocrine System

16.1: Cell-Cell Communication

• SENDING CELL → TARGET CELL: Cell signaling for maintaining homeostasis.

Types of Signaling

• Autocrine Signaling: Cell signals to itself, releasing ligands that bind to its own receptors.

• Paracrine Signaling: Cells near one another communicate via chemical messengers.

• Endocrine Signaling: Hormones produced in one body area travel through circulation to distant target cells.

Types of Glands

1. Exocrine Glands:

   • Produce non-hormonal substances (e.g., sweat, saliva).

   • Have ducts that carry secretions to surfaces.

   • Examples: sweat glands, salivary glands.

2. Endocrine Glands:

   • Ductless, produce hormones.

   • Hormones secreted directly into extracellular fluid.

   • Examples: pituitary, thyroid, adrenal, pineal glands.

Long Distance Communication

• Neuronal Signaling: Rapid, direct transfer of electric signals via neurons.

• Endocrine Signals: Slower chemical signaling through hormones.

Comparison of Nervous and Endocrine Systems

• Nervous System:

  • Rapid initiation and short-duration responses.

  • Acts through action potentials and neurotransmitters.

• Endocrine System:

  • Slower initiation and longer-duration responses.

  • Hormones act at diffuse locations throughout the body.

Functions of the Endocrine System

• Major processes controlled include:

  • Reproduction, growth and development.

  • Maintenance of electrolyte, water, and nutrient balance.

  • Regulation of metabolism and energy balance.

  • Mobilization of body defenses.

Hormones and Their Functions

• Hormones: Chemical messengers that regulate metabolic functions.

• Response Time: Varies from minutes to days after hormone binding.

16.2: Types of Hormones

• Amino Acid-Derived: Includes amines, peptides, and proteins (e.g., water-soluble).

• Lipid-Derived: Includes steroid hormones (e.g., lipid-soluble).

• Eicosanoids: Localized actions, not classified strictly as hormones.

Water-Soluble vs. Lipid-Soluble Hormones

• Water-soluble:

  • Derive from amino acids, cannot cross plasma membrane.

  • Act via receptors on plasma membrane.

• Lipid-soluble:

  • Derive from cholesterol, can pass through plasma membrane.

  • Act via intracellular receptors.

16.3: Pathways of Hormone Action

• Binding to Receptors: Hormones bind either at the plasma membrane or inside the cell.

• Target Cell Alteration: Hormones change activity by altering cellular processes.

Responses of Target Cells

• Target cells only respond if they have specific receptors for the hormone.

• Changes may include:

  • Synthesis of proteins, enzyme activation, permeability alteration, etc.

16.4: Regulation of Hormone Secretion

• Negative Feedback: Most common mechanism, hormone levels regulate their own secretion.

• Positive Feedback: Less common, hormone output is enhanced by its own effects.

16.5: Half-Life of Hormones

• Duration for hormone levels in blood to decrease by half varies (e.g., minutes to hours).

• Water-soluble hormones typically have shorter half-lives.

16.6: Pituitary Gland and Hypothalamus

• Hypothalamus secretes hormones that regulate the pituitary.

• Pituitary has anterior (glandular) and posterior (neural tissue) lobes.

• Hormones of the Posterior Pituitary: Oxytocin and Antidiuretic Hormone (ADH).

16.7: Thyroid Gland

• Regulates metabolism and affects growth.

• Produces Thyroxine (T4) and Triiodothyronine (T3).

• Negative Feedback for TSH Regulation: T3 and T4 can inhibit TSH release.

16.8: Parathyroid Glands and Calcium Balance

• Parathyroid Hormone (PTH): Crucial for calcium levels in the blood.

• Opposes calcitonin actions to maintain necessary calcium levels.

16.9: Adrenal Glands

• Adrenal cortex produces corticosteroids; adrenal medulla produces catecholamines.

• Cortisol and aldosterone are key hormones influencing stress responses.

16.10: Pineal Gland

• Secretes melatonin, regulating sleep-wake cycles and possibly affecting puberty timing.

16.11: Pancreas

• Functions as both exocrine (digestive) and endocrine (insulin and glucagon) gland.

• Insulin and Glucagon: Control blood glucose levels.

Clinical Imbalances

• Diabetes Mellitus: Results from insulin issue (Type 1 or Type 2).

• Cushing’s Syndrome: Hypersecretion of glucocorticoids impacts health.

Environmental and Developmental Aspects

• Hormonal functions can be disrupted by environmental pollutants.

• Aging affects function of many endocrine organs and hormone levels.