Hormones complete

Endocrine System

  • The endocrine system interacts with the nervous system to coordinate and integrate body activities through hormones.

  • Endocrine tissues and organs secrete hormones into body fluids (mainly blood and lymph) directly through diffusion.

Major Functions of Hormones

  1. Regulation of Metabolism

    • Example: Thyroid hormones regulate metabolic activities in the body.

  2. Control of Chemical Reactions

    • Example: Growth hormone controls various chemical processes, including growth and development.

  3. Regulation of Blood Glucose Levels

    • Example: Insulin lowers blood glucose levels while glucagon raises them.

  4. Regulation of Water and Electrolyte Balance

    • Examples: Antidiuretic hormone, calcitonin, and aldosterone assist in maintaining body fluid balance.

  5. Role in Reproduction, Growth, and Development

    • Examples: Estrogens, progesterone, and testosterone are crucial for reproductive functions.

Classification of Hormones

  • Hormones may be classified based on their chemical composition, solubility properties, location of receptors, and the nature of hormonal signals.

Types of Hormones

  1. Amine Hormones

    • Simple molecules derived from amino acids.

  2. Protein Hormones

    • Composed of amino acids linked by peptide bonds (fat insoluble; cannot diffuse across cell membranes).

  3. Steroid Hormones

    • Derived from fatty acids using cholesterol (fat-soluble; can diffuse into target cells).

Hormone Types based on Action

  1. Nontropic Hormones

    • Directly secreted by endocrine glands to target cells.

  2. Tropic Hormones

    • Secreted by one gland (e.g., pituitary gland) to stimulate another gland to secrete hormones.

Hormone Action Mechanism

  • Hormone action follows a defined sequence:

  1. Synthesis in the endocrine gland.

  2. Diffusion into capillaries.

  3. Transport via blood/lymph to target cells.

  4. Diffusion out of capillaries into target tissue, inducing an effect.

Actions of Steroid Hormones

  1. Bind to protein transporters in blood.

  2. Diffuse into target cells and through the nuclear envelope.

  3. Bind to specific DNA receptors, altering genetic information.

  4. New mRNA is produced and translated into proteins or enzymes, leading to cellular effects.

Actions of Protein Hormones

  1. Transported independently in blood (no transporter).

  2. Bind to membrane receptors on target cells.

  3. Activate cascade reactions resulting in secondary messengers like cAMP, IP3, Ca²⁺.

  4. Cause effects within the target cell without direct DNA interaction.

Signal Transduction Pathways

  1. Involvement of 1st and 2nd Messengers

    • Example: Protein hormones often utilize cAMP as a second messenger to propagate signaling.

  2. Calcium and Phosphoinositide Signaling

    • Hormones like acetylcholine and angiotensin II initiate pathways affecting calcium levels leading to various cellular responses.

Hormones from the Hypothalamus and Anterior Pituitary

  • Hypothalamic Hormones regulate anterior pituitary hormone production:

  1. GnRH → LH and FSH for reproduction.

  2. CRH → ACTH for stress response.

  3. GHRH and Somatostatin → GH secretion regulating growth.

  4. TRH → TSH stimulating thyroid hormones.

  5. Dopamine → regulates prolactin affecting milk production.

The Pituitary Gland

  • Structure: The pituitary gland is the "master gland" regulating other hormone-secreting glands through anterior and posterior lobes.

  • Anterior Pituitary Hormones: TSH, ACTH, FSH, LH, GH, and Prolactin.

  • Posterior Pituitary Hormones: Oxytocin and ADH (vasopressin) stored and released as needed.

Key Hormones and Their Functions

Thyroid-stimulating Hormone (TSH)

  • Stimulates production of T3 and T4; vital for metabolism and nervous system activities.

  • Imbalances: Overproduction leads to hyperthyroidism; lack leads to hypothyroidism.

Adrenocorticotropic Hormone (ACTH)

  • Stimulates adrenal gland to release cortisol during stress, regulates blood pressure and inflammation.

  • Imbalances lead to Cushing's syndrome or adrenal insufficiency.

Follicle-stimulating Hormone (FSH) and Luteinizing Hormone (LH)

  • Gonadotropins crucial for reproductive hormone regulation and gamete maturation.

  • Abnormal levels can cause reproductive issues.

Growth Hormone (GH)

  • Important for growth, stimulates protein synthesis, and affects fat and carbohydrate metabolism.

  • Disorders: Deficiency causes dwarfism; excess leads to acromegaly and gigantism.

Antidiuretic Hormone (ADH)

  • Regulates kidney water retention, constricts blood vessels. Low levels cause diabetes insipidus.

Oxytocin

  • Stimulates childbirth contractions and lactation.

Thyroid Hormones (T3 and T4)

  • Synthesized in the thyroid gland; regulate metabolic rate, growth, and CNS function.

Synthesis Process

  • Involves iodide trapping, oxidation, incorporation into thyroglobulin, and release into circulation.

Disorders

  • Hypothyroidism is characterized by weight gain and fatigue; hyperthyroidism by weight loss and anxiety.

The Pancreas

  • Functions as both an endocrine (hormone secretion) and exocrine (digestive fluid) gland.

  • Produces insulin (β cells), glucagon (α cells), somatostatin (D cells), and pancreatic polypeptide (F cells).

  • Hormones regulate blood glucose levels and energy storage post-meal.

Insulin

Structure

  • Composed of two chains linked by disulfide bridges; derived from proinsulin.

Function

  • Promotes glucose uptake and storage, protein synthesis, and overall growth.

Deficiency and Diabetes Mellitus

  • Hyperglycemia results in various symptoms and complications; diabetes can be type 1 (insulin deficiency) or type 2 (insulin resistance).

Glucagon

  • Secreted by alpha cells, it raises blood glucose by stimulating glycogenolysis and gluconeogenesis in the liver.

  • Works antagonistically with insulin to maintain glucose levels.

Adrenal Glands

Structure

  • Composed of adrenal cortex (producing various hormones) and adrenal medulla (producing stress hormones).

Cortisol

  • A glucocorticoid managing metabolism, inflammation, and stress response; low levels cause Addison’s disease; high levels can lead to Cushing’s Syndrome.

Aldosterone

  • A mineralocorticoid influencing blood pressure and electrolyte balance. Imbalances can lead to hyperaldosteronism or hypoaldosteronism.

Epinephrine and Norepinephrine

  • Produced during stress; affect heart rate, blood flow, and metabolism to provide energy in emergencies.

Pheochromocytoma

  • A condition causing excess adrenal secretion leading to persistent high blood pressure and other symptoms.