BMN 1002 Cell Biology - Lecture 25

BMN 1002 Cell Biology - Lecture 25: Introduction to Endocrinology

• Lecture focused on the introduction to endocrinology
• Recommended textbook: "The Endocrine System" by Joy Hinson, Peter Raven, and Shern Chew (2nd Edition) and "Human Physiology" by Dee Unglaub Silverthorn (4th Edition)
• Learning outcomes include defining the endocrine system and hormones, listing different hormone classes and their properties, explaining hormone action via receptors and feedback mechanisms regulating hormone secretion.

Mode of Communication

• Gap junctions: message transmitted directly between cells; specificity depends on anatomical location (e.g., heart).
• Synaptic: message transmitted across the synaptic cleft; specificity depends on anatomical location and receptors.
• Paracrine/Autocrine: message transmitted locally by diffusion in interstitial fluid; specificity depends on receptors.
• Endocrine: message transmitted by circulating body fluids (bloodstream); specificity depends on receptors.

Endocrine Glands and Hormones

• Endocrine glands produce hormones for both local and distant effects.
• Classical endocrine glands: pineal, hypothalamus, pituitary, thyroid, parathyroids, thymus, adrenals, pancreas, ovaries, testes
• Non-classical endocrine producers: kidney, heart muscle, adipocytes, endothelium, platelets.
• The endocrine system involves the release of hormones into the bloodstream acting on distant cells.
• Hormones are chemical messengers synthesized by specialized cells in small amounts to regulate cellular function in target organs.

Hormones, Receptors, and Actions

• Hormones act on specific receptors located on the cell surface or within the cell.
• High affinity: hormones are effective at low concentrations.
• Synergistic: two hormones have a greater combined effect than one alone.
• Permissive: presence of one hormone is necessary for another to have a full effect.
• Antagonistic: two hormones oppose each other's effects; hormones compete for the same receptor.
• Competitive: two hormones similar in structure compete for the same receptor.

Classifications of Hormones

• Hormones classified into three groups based on chemical structure:
  • Steroids: synthesized from cholesterol; act on intracellular receptors, slow but long-lasting effects
  • Peptides/Proteins: synthesized from amino acids; act on cell surface receptors.
  • Amino acids: e.g., thyroid hormone; synthesized from tyrosine, variable mechanisms of action in the cell

Hormone Signaling-Peptide and Amino acid Hormones

• Action via second messengers like cAMP, IP3 pathways triggering rapid or long-term responses.
• Includes catecholamines, ACTH, FSH, LH, and others
• Mechanisms for hormone release include continuous (e.g., thyroid hormones), pulsatile (e.g., growth hormone), circadian (e.g., melatonin), and exocytosis on stimulus (e.g. insulin).
• Hormone activation includes structural alteration (e.g. vitamin D), degradation, receptor down-regulation, termination of intracellular effects, and negative feedback.
• Mechanisms of negative feedback involve the regulated metabolite (like glucose and insulin) , the hormone itself (like cortisol), and the trophic hormone from the pituitary.

Hormone Signaling-Steroid Hormones

• Steroids pass through the plasma membrane (lipid-soluble) and act on intracellular receptors, which bind to DNA and regulate gene transcription resulting in slow but long-lasting effects.
• Include examples like corticosteroids and sex hormones.

Action on receptors and 2nd messengers: Peptide and amino acid hormones : cAMP and IP3.

• Receptors have different signaling pathways depending on the hormones involved resulting in both short and long term effects

Mechanisms for hormone release, activation, and feedback control

• Feedback mechanisms regulate hormones ensuring homeostasis

Integrated and Complex Systems

• The hypothalamic-pituitary-axis forms the centre of the complex system for integrating hormonal functions involving both short and long-loop feedback systems.

Attempt questions in VEVOX during the session

Explore the fundamentals of endocrinology in this lecture focused on the endocrine system and hormones. Learn to define the endocrine system, differentiate hormone classes, and understand hormone action through various mechanisms. This quiz is essential for grasping the basics of cell signaling and its implications in biology.