INTRODUCTION TO ENDOCRINOLOGY

Page 1: Hormone Classification

  • Hormones classified based on structure and function.

Page 2: Introduction to Glands

  • Two Types of Glands:

    • Exocrine Glands: Secrete products into ducts.

    • Endocrine Glands: Secrete hormones directly into the bloodstream.

Page 3: Exocrine Glands

  • Secretion Methods:

    • Into body cavities

    • Into the lumen of organs

    • To the outer body surface

  • Examples of Exocrine Glands:

    • Sweat glands

    • Sebaceous (oil) glands

    • Mucous glands

    • Digestive glands

Page 4: Endocrine Glands

  • Definition:

    • Pour secretions into interstitial fluid, hence termed ductless glands.

  • Process:

    • Hormones diffuse into capillaries, with blood transporting them to target cells.

Page 5: Hormone Action

  • Mechanism:

    • Hormones secreted into blood only affect target cells with specific receptors.

  • Action:

    • Without receptor: No response

    • With receptor: Response initiated

Page 6: Exceptions in Hormone Secretion

  • Organs with Hormonal Function:

    • Hypothalamus, Thymus, Pancreas, Ovaries, Testes, Kidneys, Stomach, Liver, Small Intestine, Skin, Heart, Adipose Tissue, Placenta.

Page 7: Introduction to Endocrinology

  • Coordination:

    • Nervous and endocrine systems collaborate for body functions.

  • Functions:

    • Nervous: Conducts impulses via neurotransmitters.

    • Endocrine: Releases hormones into blood affecting distant target cells.

Page 8: Neuroendocrine Hormones

  • Secreted by neurons into blood, influencing target cells at different body locations.

Page 9: Characteristics of Endocrine Glands

  • Response Speed:

    • Usually slower than nervous responses, taking minutes.

  • Effects Duration:

    • Longer-lasting effects compared to the nervous system.

Page 10: Definition of Hormones

  • Hormones:

    • Chemicals released from cells, glands, or organs to regulate activities in other body regions.

  • Example:

    • Norepinephrine acts as a neurotransmitter and a hormone.

Page 11: Functions of Hormones

  • a) Regulate metabolic processes (e.g., thyroid hormones).

  • b) Control chemical reaction rates (e.g., growth hormone).

  • c) Aid transport across membranes (e.g., insulin, glucagon).

  • d) Regulate water and electrolyte balance (e.g., ADH, calcitonin, aldosterone).

  • e) Vital in reproduction, growth, and development (e.g., estrogens, progesterone, testosterone).

Page 12: Major Endocrine Organs

  • Included Organs:

    • Pineal gland, Hypothalamus, Pituitary gland,

    • Thyroid gland, Parathyroid glands, Thymus,

    • Adrenal glands, Pancreas, Ovaries, Testes.

Page 13: Chemistry of Hormones

  • Types of Hormones:

    • a) Protein Hormones:

      • Amino acid chains, water-soluble, not membrane-diffusible except gonadal/adrenal hormones.

    • b) Steroid Hormones:

      • Fatty acids derived from cholesterol, fat-soluble, membrane-diffusible.

Page 14: Amino Acid Derivatives

  • Examples:

    • Thyroxine and triiodothyronine (from thyroid)

    • Epinephrine and norepinephrine (from adrenal medulla).

Page 16: Endocrine Glands, Hormones, and Their Functions

  • Examples:

    • Glucagon: Increases glucose levels (Peptide).

    • Parathyroid Hormone: Regulates calcium (Peptide).

    • Testosterone: Promotes male characteristics (Steroid).

Page 17: Hormone Action Steps

  1. Gland synthesizes hormone.

  2. Hormone diffuses into capillaries.

  3. Transported by blood/lymph to target cells.

  4. Hormone diffuses out of capillaries at target, eliciting effects.

Page 18: Step Specificity in Hormone Action

  • Highly controlled by endocrine and circulatory systems:

    • Synthesis, secretion, transport, and interaction with target cell are precise.

Page 19: Effects on Target Cells

  • Results of hormone action:a) Altered cell membrane permeability (e.g., insulin).b) Changed chemical reaction rates (e.g., growth hormone).c) Enzyme activation (e.g., epinephrine).d) Activation of secretion (e.g., MSH).

Page 20: Sequence of Steroid Hormone Action

  • Detailed processes involved in steroid hormone action, leading to gene activation.

Page 22: Mechanism of Steroid Hormone Action

  • Hormones diffuse across the membrane, bind to receptors in cytoplasm/nucleus, influence mRNA synthesis, leading to produced proteins that exert effects.

Page 23: Sequence of Protein Hormone Action

  • Overview of protein hormone action involving receptor binding and subsequent activation of a signaling cascade.

Page 24: Action of Protein Hormones

  1. Transported without a receptor.

  2. Binds to membrane receptors, initiating cascade reactions.

  3. Produces secondary messenger effects.

Page 26: G Protein-Linked Hormone Receptors

  • Structure:

    • Seven trans-membrane segments with trimeric G proteins.

  • Activation:

    • Hormone binding activates G proteins for intracellular signaling.

Page 34: Control of Hormone Secretion

  • Mechanisms:

    • a) Negative Feedback:

      • Inhibitory signals regulate secretion.

    • b) Nervous Control:

      • Nerve impulses influence gland secretion.

  • Hormonal Types:

    • Nontropic: Directly affect target cells.

    • Tropic: Stimulate other glands.

Page 37: Example of Blood Glucose Regulation

  • Insulin Mechanism:

    • High blood glucose -> Insulin release -> Increased glucose uptake by cells -> Reduced blood glucose to set point.

Page 38: Hormone Half-Life

  • Peptides and catecholamines: short half-life (seconds to minutes).

  • Steroids and thyroid hormones: longer half-life (hours).