Fisiología Endocrina - INTRO (HORMONAS, ESTRUCTURA, SÍNTESIS, SECRECIÓN)PARTE 1/3 (IG:@doctor.paiva)

Introduction to Endocrinology

Overview of the Class Structure

• The class will cover generalities, types of hormones, synthesis, and secretion of hormones.

• A schedule for the series on endocrine physiology is provided, indicating a structured approach to learning.

Topics to be Discussed

• Future classes will include hormonal transport, feedback mechanisms (positive and negative), and hormonal clearance from blood.

• Specific hormones such as hypothalamic hormones, thyroid hormones (T3 and T4), adrenal cortex hormones (mineralocorticoids and glucocorticoids), insulin, glucagon, parathyroid hormone, calcitonin, sexual hormones (testosterone and estrogen), pregnancy-related hormones (hCG), lactation physiology, and childbirth will be discussed in detail.

Importance of Systematic Study

• Emphasizes the need for systematic study in endocrinology for better comprehension by categorizing by hormone types and functions.

Understanding Hormones

Definition and Functionality

• Hormones are substances synthesized by endocrine cells that enter circulation to act on specific target cells. They serve as chemical messengers within the body.

Types of Hormonal Communication

• Endocrine Hormones: Produced by specialized glands; travel through blood to target cells.

• Neuroendocrine Hormones: Secreted by neurons into the bloodstream affecting distant target cells.

• Paracrine Hormones: Act on neighboring cells after being secreted into interstitial fluid.

• Autocrine Hormones: Affect the same cell that secretes them.

• Cytokines: Peptides secreted by cells that can function as autocrine or paracrine signals.

Hormonal Classification

Types Based on Origin

• Endogenous Hormones: Secreted directly into circulation from a cell to act on effector cells.

• Autocrine Signals: Released by a cell acting upon itself.

• Paracrine Signals: Released by one cell affecting nearby cells.

Additional Concepts

• Discussion includes pheromones in certain animals like ants which influence behavior through airborne signaling.

Hormonal Structure and Synthesis

Overview of Hormones

• The discussion begins with the Atrial Natriuretic Peptide (ANP), highlighting its secretion from various glands including the stomach, kidneys, pancreas, adipose tissue, small intestine, and reproductive organs (testes in men and ovaries in women).

Classification of Hormones

• Hormones are categorized into three main groups based on their structure:

• Peptide or Polypeptide Hormones

• Steroid Hormones

• Tyrosine-Derived Amines (Amine hormones)

Characteristics of Peptide and Polypeptide Hormones

• Most hormones in the body are polypeptides made up of amino acids.

• Proteins contain 100 or more amino acids while peptides have fewer than 100.

• These hormones are hydrophilic (water-soluble), which prevents them from crossing lipid membranes easily; this characteristic is crucial for their storage.

Examples of Polypeptide Hormones

• Common examples include:

• Parathyroid hormone

• Insulin

• Thyroid-stimulating hormone (TSH)

• Follicle-stimulating hormone (FSH)

• Due to their hydrophilicity, these hormones are stored in vesicles within cells until needed.

Synthesis Process of Peptide Hormones

• The synthesis process involves several steps:

• Transcription occurs in the nucleus where DNA is transcribed into mRNA.

• This mRNA exits to the cytoplasm where ribosomes translate it into a precursor protein known as prohormone, which lacks biological activity.

Storage and Secretion Mechanism

• Prohormones move to the Golgi apparatus for packaging into vesicles containing enzymes that convert them into active hormones.

• Upon stimulation (e.g., increased intracellular calcium), these vesicles fuse with cell membranes through exocytosis to release active hormones into circulation.

Steroid Hormones: Structure and Function

Types of Steroid Hormones

• Key steroid hormones include:

• Cortisol and aldosterone from adrenal cortex.

• Testosterone from testes.

• Estrogen and progesterone from ovaries/placenta.

Characteristics of Steroid Hormones

• Steroid hormones are lipophilic (fat-soluble), synthesized primarily from cholesterol. They consist of a unique structure featuring three cyclohexane rings and one cyclopentane ring.

Storage Limitations for Steroid Hormones

• Unlike peptide hormones, steroid hormones cannot be stored in vesicles due to their ability to pass through lipid membranes; instead, they rely on cholesterol esters for synthesis.

Synthesis Location

Hormonal Functions and Classifications

Importance of Cortisol

• Cortisol is a crucial hormone for stress response, often referred to as the "stress hormone." Its synthesis involves pregnenolone and intermediaries leading to cortisol formation.

Hormones Derived from Tyrosine

• Two main groups of hormones derived from the amino acid tyrosine are identified:

• Thyroid hormones (thyroxine and triiodothyronine) secreted by the thyroid gland.

• Adrenal hormones (adrenaline and noradrenaline) secreted by the adrenal medulla.

Solubility Characteristics of Hormones

• Thyroid hormones are liposoluble, while adrenaline and noradrenaline are hydrosoluble. This distinction is vital for understanding their transport mechanisms in the body.

Synthesis and Storage of Thyroid Hormones

• Thyroid hormones are synthesized from iodine stored in colloid within follicular cells. They bind to a transport protein called thyroglobulin, which prevents premature release into capillaries.

Classification of Hormones Based on Structure

• The three primary groups of hormones include:

• Peptides: Stored in secretory vesicles.

• Amines: Such as adrenaline and noradrenaline, which are also hydrosoluble.

• Steroids: Liposoluble; they do not store but have cholesterol precursors available in stress cells.

Mechanisms of Action for Different Hormone Types

Interaction with Cell Receptors

• Hydrosoluble peptides act on extracellular receptors since they cannot penetrate cell membranes. In contrast, liposoluble thyroid hormones enter target cells and interact with intracellular receptors.

Gene Transcription Activation

• Most steroids act through intracellular receptors to influence gene transcription. Specific details will be discussed when examining each hormone individually.

Overview of Endocrinology

Major Endocrine Glands and Their Secretions

• Key glands include:

• Hypothalamus: Secretes various peptide hormones.

• Pituitary Gland: Releases antidiuretic hormone (ADH), oxytocin, etc.

• Thyroid Gland: Produces thyroxine, triiodothyronine, calcitonin.

Additional Hormonal Sources

• Other important sources include:

• Adrenal Cortex: Cortisol and aldosterone secretion.

• Pancreas: Insulin and glucagon production.

• Kidneys: Renin involved in blood pressure regulation.

Future Topics in Endocrinology Studies

Upcoming Discussions on Hormonal Regulation

Introduction to Influential Mentors

Acknowledgment of Key Figures

• The speaker expresses gratitude towards Dr. Osvaldo Santesteban, a close friend from university and an esteemed physician.

• Highlights the impact of Dr. Mauricio Don as another significant mentor in their educational journey.

• Mentions Dr. Migueles Howard Brown as an excellent doctor and educator, emphasizing the valuable lessons learned under his guidance.

• The speaker conveys appreciation for all colleagues and educators who contributed to their professional development.