Student KINS 1131 Lec 2 Endocine System

Endocrine System Overview

• Introduction

  • Focus on the study of the Endocrine System and its processes.

Lecture Outline: Part I

• Introduction

• Endocrinology

• Functions of the Endocrine System

• Nervous System vs Endocrine System

• Control of Secretion

• Hormones

• Hormones vs Local Chemical Messengers

• Receptor Regulation

• Chemical Classes

• Mechanism of Action

• Interactions

Endocrinology

• Arnold Berthold

  • Conducted the first recorded endocrine experiments.

  • Proposed that the endocrine system regulates the internal milieu of an organism through internal secretions that travel via the bloodstream to distant target cells.

Functions of the Endocrine System

1. Regulation of Body Functions

• Maintains chemical composition and volume of extracellular fluid.

• Regulates metabolism and energy balance.

• Influences smooth and cardiac muscle contractions.

• Controls glandular secretions.

• Modulates some immune system activities.

2. Growth and Development Control

3. Reproductive System Regulation

4. Circadian Rhythm Establishment

Homeostasis

• Describes the body's ability to maintain constant internal conditions despite external changes.

Control Systems in the Body

• Homeostasis Maintenance - Primarily through the Nervous and Endocrine Systems:

  • Nervous System: Acts quickly (milliseconds), short-term effects.

  • Endocrine System: Acts over seconds to hours, longer-lasting effects.

Nervous System vs. Endocrine System

• Nervous System:

  • Fast response with short-term effects.

  • Uses electrochemical impulses via neurons.

  • Overrides endocrine controls for rapid adjustments.

• Endocrine System:

  • Slow response with long-term effects.

  • Utilizes hormones transported through the bloodstream.

Control of Hormone Release

1. Humoral Stimuli:

• Hormone release triggered by changes in blood levels of ions/nutrients.

• Example: Parathyroid glands monitor blood calcium levels.

2. Neural Stimuli:

• Nerve fibers directly stimulate hormone release, e.g., epinephrine from the adrenal medulla.

3. Hormonal Stimuli:

• Hormones released in response to other hormones, e.g., anterior pituitary hormones regulated by the hypothalamus.

Hormones vs Local Chemical Messengers

• Hormones:

  • Act on distant targets via the bloodstream.

• Local Chemical Messengers:

  • Autocrines: Act on the same cells that secrete them.

  • Paracrines: Affect nearby cells.

Receptor Regulation

• Target cell activation depends on:

• Blood levels of hormones and the number of receptors on the target cells.

• Up-regulation: Occurs under low hormone concentration, increasing receptor number.

• Down-regulation: Occurs under high hormone concentration, leading to desensitization and fewer receptors.

Hormones: Chemical Classes

• Lipid-Soluble Hormones:

  • Steroid hormones (derived from cholesterol).

  • Thyroid hormones (T3, T4).

  • Examples: Nitric Oxide.

• Water-Soluble Hormones:

  • Amine hormones (e.g., catecholamines).

  • Peptide and protein hormones (e.g., insulin).

  • Eicosanoid hormones (e.g., prostaglandins).

Hormones: Transport & Mechanism of Action

• Hormones circulate in two forms:

  • Free Hormones: Unbound form that can diffuse into tissues.

  • Bound Hormones: Attached to transport proteins.

• Hormone action on target cells:

  1. Alters plasma membrane permeability.

  2. Stimulates protein synthesis.

  3. Activates/deactivates enzyme systems.

  4. Induces secretory activity.

  5. Stimulates mitosis.

• Hormonal interactions include:

  • Permissiveness, Synergism, and Antagonism.

Hypothalamus Overview

• The hypothalamus controls the autonomic nervous system and integrates functions such as emotional responses, drinking, and sleep-wake cycles.

• Hormones released by hypothalamus target the pituitary gland, affecting its hormone secretion.

Anterior and Posterior Pituitary Hormones

• Anterior Pituitary Hormones include:

  • Growth Hormone: Cell growth and tissue repair.

  • Thyroid Stimulating Hormone: Stimulates synthesis/secretion of thyroid hormones.

  • Adrenocorticotropic Hormone (ACTH): Stimulates corticosteroid release.

  • Follicle Stimulating Hormone: Involved in gamete production.

  • Luteinizing Hormone: Stimulates sex hormone secretion and ovulation.

• Posterior Pituitary Hormones include:

  • Oxytocin: Stimulates uterine contractions and milk secretion.

  • Antidiuretic Hormone (ADH): Regulates urine formation and response to dehydration.

Thyroid Gland

• Located inferior to the larynx; produces T3 and T4, which regulate metabolism and body temperature.

• Calcitonin: Decreases blood calcium levels by promoting calcium uptake into bones.

Parathyroid Gland

• Produces Parathyroid Hormone: crucial for increasing blood calcium levels by stimulating osteoclast activity and promoting absorption in intestines and kidneys.

Adrenal Glands

• Adrenal Cortex secretions include:

  • Aldosterone: Regulates sodium and fluid balance.

  • Cortisol: Involved in stress response, increasing blood sugar and suppressing immune function.

• Adrenal Medulla produces catecholamines like epinephrine which intensify sympathetic nervous system activity.

Pancreas

• Functions as both exocrine and endocrine gland:

  • Glucagon: Raises blood sugar levels.

  • Insulin: Lowers blood sugar levels by facilitating glucose uptake.

Ovaries and Testes

• Ovaries: Produce estrogens and progesterone influencing female characteristics and reproductive cycles.

• Testes: Produce testosterone influencing male characteristics and sperm production.

Pineal Gland

• Produces Melatonin, involved in regulating circadian rhythms and sleep cycles, linked to Seasonal Affective Disorder (SAD).

Summary of Concepts

• Understand the regulation by various hormones and their interactions within the endocrine system.

• Recognize hormonal functions, control mechanisms, and physiological impacts on homeostasis and body systems.