Chapter 9 outline

Chapter 9: The Endocrine System

• Second-Messenger System:

  • A crucial communication mechanism in the body that is slow-acting but long-lasting.

• Endocrinology:

  • The scientific study of hormones, their effects, and the organs that secrete them.

• Homeostasis:

  • The endocrine system maintains homeostasis by releasing hormones into the blood.

• Major Hormonal Processes Controlled:

  • Reproduction

  • Growth and development

  • Mobilization of body defenses

  • Maintenance of homeostasis

  • Regulation of metabolism

Hormone Overview

• Production & Secretion:

  • Hormones are produced by specialized cells

  • Secretion occurs into extracellular fluids

  • Blood transports hormones to their target sites with specificity

• Regulatory Function:

  • Hormones regulate the activity of other cells and sometimes prompt the release of other hormones.

Types of Chemical Messengers

• Autocrines:

  • Affect the same cells that secrete them.

• Paracrines:

  • Affect cells other than those that secrete them.

• Hormones:

  • Travel via blood or lymph and regulate distant targets.

The Chemistry of Hormones

• Classification:

  • Amino Acid-Based Hormones: Includes proteins, peptides, and amines

  • Steroids: Derived from cholesterol, including sex hormones and adrenal cortex hormones.

  • Eicosanoids: Derived from 20-carbon fatty acids like arachidonic acid.

Mechanisms of Hormone Action

• Target Cells:

  • Hormones affect specific target cells with specific protein receptors.

• Binding Effects:

  • Hormone binding alters cellular activity, leading to diverse outcomes.

• Effects Caused by Hormones:

  • Changes in plasma membrane permeability or electrical state.

  • Promotion of secretory activity.

  • Protein synthesis.

  • Enzyme activation/inactivation.

  • Stimulation of mitosis.

Two Mechanisms of Hormone Action

1. Direct Gene Activation (Steroid Hormone Action):

   • Hormones diffuse through the plasma membrane and bind to specific proteins in the nucleus.

   • The binding activates genes leading to new protein synthesis.

2. Second-Messenger System (Non-Steroid Hormone Action):

   • Hormones bind to membrane receptors initiating reactions within the cell that activate enzymes and produce second-messenger molecules.

Control of Hormone Release

• Regulation:

  • Hormone levels are maintained primarily through negative feedback mechanisms.

• Stimulus Types:

  • Hormonal: Activating factors from other hormones.

  • Humoral: Changes in levels of ions or nutrients in the blood.

  • Neural: Nerve impulses trigger hormone release.

Types of Endocrine Gland Stimuli

• Hormonal:

  • E.g., activation of endocrine glands by other hormones.

• Humoral:

  • E.g., changes in blood ion levels stimulate hormone release (e.g., insulin).

• Neural:

  • Nerve impulses lead to hormone release (e.g., epinephrine from adrenal medulla).

Major Endocrine Organs

• Pituitary gland

• Thyroid gland

• Parathyroid glands

• Adrenal glands

• Pineal gland

• Thymus gland

• Pancreas

• Gonads (Ovaries and Testes)

• Hypothalamus

Pituitary Gland

• Structure:

  • A pea-sized gland connected to the hypothalamus.

  • Has two functional lobes (anterior and posterior).

  • Often called the "master endocrine gland" due to its regulatory functions.

Hypothalamus-Pituitary Relationships

• The posterior lobe is a neural connection from the hypothalamus.

• Synthesizes and transports neurohormones like oxytocin and ADH for release in the posterior pituitary.

Posterior Pituitary

• Stores and releases ADH and oxytocin in response to nerve impulses.

• Oxytocin's Role: Stimulates Uterine contractions and milk ejection.

• Antidiuretic Hormone (ADH):

  • Responds to blood solute concentration.

  • Promotes water reabsorption in kidneys and affects blood pressure.

  • Alcohol inhibits ADH release leading to increased urine output.

Anterior Pituitary

• Structure:

  • Originates from oral mucosa and employs the hypophyseal portal system.

• Hormonal Functions:

  • Six hormones produced: GH, Prolactin, TSH, ACTH, FSH, LH.

  • Functions as tropic hormones stimulating other endocrine glands.

  • All anterior pituitary hormones are proteins or peptides acting through second-messenger systems and regulated by hormonal stimuli.

Growth Hormone (GH)

• Functions to direct growth, primarily affecting skeletal muscles and long bones.

• Regulated by GHRH and GHIH from the hypothalamus.

• GH Disorders:

  • Dwarfism: GH underproduction during childhood.

  • Gigantism: GH overproduction in childhood.

  • Acromegaly: GH overproduction in adulthood.

Prolactin (PRL)

• Stimulates and maintains milk production post childbirth.

Other Anterior Pituitary Hormones

• Adrenocorticotropic Hormone (ACTH):

  • Regulates adrenal cortex activities.

• Thyroid-Stimulating Hormone (TSH):

  • Influences the thyroid gland's growth and function.

• Gonadotropic Hormones:

  • Control gonad activity; includes FSH and LH which stimulate reproductive system processes.

Thyroid Gland

• Location: Located at the base of the throat with two lobes.

• Function:

  • Regulates metabolism through thyroid hormones T3 and T4.

• Calcitonin:

  • Decreases blood calcium levels, opposing parathyroid hormone (PTH).

Thyroid Hormone Disorders

• Goiter: Enlargement from iodine deficiency, leading to excessive TSH production.

• Congenital Hypothyroidism (Cretinism): Caused by thyroxine deficiency in childhood leading to stunted growth.

• Myxedema: Due to adult hypothyroidism, resulting in sluggishness and puffy appearance.

• Hyperthyroidism: Often due to a tumor, characterized by weight loss and agitation.

Parathyroid Glands

• Function:

  • Secretion of PTH in response to low calcium levels, its primary action is to increase calcium blood concentration.

• Homeostatic Imbalances:

  • Hyperparathyroidism: leads to bones softening and kidney stones.

  • Hypoparathyroidism: results in muscle spasms and respiratory complications.

Adrenal Glands

• Structure:

  • Comprised of cortex and medulla, with distinct hormone functions.

Adrenal Cortex Hormones

• Mineralocorticoids (e.g., Aldosterone):

  • Regulate blood mineral content, primarily targeting kidneys.

• Glucocorticoids (e.g., Cortisol):

  • Help manage stress and metabolism by increasing blood glucose.

• Gonadocorticoids:

  • Involve sex hormone production influencing secondary characteristics.

Disorders of the Adrenal Cortex

• Addison's Disease:

  • Low hormone production leads to fatigue and skin darkening.

• Cushing's Syndrome:

  • characterized by excess cortisol leading to weight gain and hypertension.

• Masculinization:

  • Hypersecretion of sex hormones leading to premature traits in children.

Adrenal Medulla Hormones

• Secretes catecholamines (e.g., Epinephrine, Norepinephrine) that prepare the body for stress (