endocrine

Unit 4 Study Guide: Endocrine System and Reproductive System

Hormones

• Definition:

  • Hormones are chemical substances secreted by cells into the extracellular fluids that travel in the blood or lymph to target cells.

Activation of Hormones

• Mechanism of Action:

  • Hormones activate functions in the body by binding to specific receptors on or in target cells.

• Factors Influencing Activation:

  • Number of Hormones: The concentration of hormones present.

  • Number of Receptors: The amount of hormone receptors available on target cells.

  • Sensitivity of Receptors: How responsive the receptors are to hormone binding.

Stimuli for Hormone Release

• Types of Stimuli:

  • Humoral Stimuli:

  • Fluid-based stimuli affecting hormone release.

  • Neural Stimuli:

  • Signals from the nervous system leading to hormone release.

  • Hormonal Stimuli:

  • Hormones that trigger the release of other hormones.

Pituitary Gland

• Lobes:

  • Adenohypophysis: Glandular tissue (anterior lobe).

  • Neurohypophysis: Neural tissue (posterior lobe).

Hormones Secreted by the Pituitary Gland

• Neurohypophysis (Posterior Lobe):

  • Oxytocin

  • Antidiuretic Hormone (ADH)

• Adenohypophysis (Anterior Lobe):

  • Growth Hormone (GH)

  • Thyroid-Stimulating Hormone (TSH)

  • Adrenocorticotropic Hormone (ACTH)

  • Follicle-Stimulating Hormone (FSH)

  • Luteinizing Hormone (LH)

  • Prolactin (PRL)

Antidiuretic Hormone (ADH)

• Cells Involved:

  • Synthesized in the supraoptic nuclei of the hypothalamus.

• Storage Location:

  • Stored in the posterior pituitary.

• Feedback Mechanism:

  • ADH is released through a negative feedback system to maintain homeostasis.

Oxytocin

• Cells Involved:

  • Primarily produced by neuroendocrine cells in the paraventricular nucleus of the hypothalamus.

• Storage Location:

  • Stored in the pituitary gland.

• Feedback Mechanism:

  • Release is an example of a positive feedback system.

Tropic Hormones

• Definition:

  • Tropic hormones are hormones from the anterior pituitary that stimulate target glands to secrete their own hormones.

Growth Hormone Disorders

• Gigantism:

  • Hypersecretion of growth hormone prior to puberty, leading to tall stature and thin body.

• Acromegaly:

  • Hypersecretion of growth hormone after puberty, resulting in thickened bones and features.

• Dwarfism:

  • Hyposecretion of growth hormone leading to stunted growth.

Adrenal Cortex

• Layers and Secretions:

  • Zona Glomerulosa: secretes aldosterone.

  • Zona Fasciculata: secretes cortisol.

  • Zona Reticularis: secretes dehydroepiandrosterone (DHEA).

Aldosterone

• Function:

  • Signals kidneys to reabsorb more sodium and water back into the bloodstream, while excreting potassium and hydrogen ions, which helps to raise blood volume and blood pressure, as well as maintaining electrolyte balance and blood pH.

Mechanisms of Aldosterone Secretion

• Renin-Angiotensin-Aldosterone System (RAAS):

  • Triggered by low blood pressure leading to the release of renin, which converts angiotensinogen to angiotensin I, then to angiotensin II, stimulating aldosterone secretion to increase sodium and water reabsorption, thus raising blood pressure.

• Potassium Levels:

  • High potassium levels in the blood trigger an increase in aldosterone secretion.

• Adrenocorticotropic Hormone (ACTH):

  • Stimulates aldosterone secretion due to stress-related signals sent from the hypothalamus.

• Atrial Natriuretic Peptide (ANP):

  • Released in response to increased blood pressure, inhibits excess aldosterone secretion.

Aldosteronism vs Addison’s Disease

• Aldosteronism:

  • Overproduction of aldosterone leading to high blood pressure, low potassium, and normal sodium.

• Addison’s Disease:

  • Underproduction of cortisol and aldosterone leading to low blood pressure, low sodium, high potassium levels, fatigue, and skin pigmentation changes.

Cortisol

• Mechanism of Action:

  • Released as a response to stress, increasing blood glucose, fatty acids, and amino acids. Its main function is gluconeogenesis (conversion of fats and proteins into glucose).

Cushing’s Disease

• Definition:

  • Hypersecretion of cortisol; symptoms include elevated blood sugar, weight gain, and easy bruising.

Catecholamines

• Source:

  • Secreted by chromaffin cells.

• Effects:

  • Increases blood pressure, heart rate, and blood glucose levels during stress.

Hormonal Responses to Stress

• Short-Term Stress:

  • Involves epinephrine and norepinephrine; leads to the fight or flight response characterized by increased heart rate and blood pressure.

• Long-Term Stress:

  • Involves cortisol; results in immune suppression, elevated blood pressure, and weight gain.

Thyroid Hormones

• Production Location:

  • Produced in the follicular cells of the thyroid gland (T3/T4).

• Colloid:

  • A protein-rich substance filling thyroid follicles.

• Comparison of T4 and T3:

  • T4 (Thyroxine): Most secreted thyroid hormone with four iodine atoms; 90% of T4 is converted into T3.

  • T3 (Triiodothyronine): The active hormone used by the body, containing three iodine atoms.

Thyroid Hormone Synthesis Steps

1. Production of thyroglobulin.

2. Iodide absorption and oxidation to iodine.

3. Iodine attachment to tyrosine.

4. Formation of thyroglobulin.

5. Endocytosis of colloid combining with lysosomes.

6. Lysosomal enzymes cleave T3 and T4 from the colloid.

7. Transport in the blood via thyroxine-binding globulins.

Thyroid Disorders

• Hyperthyroidism:

  • Overactive thyroid producing excess hormones causing weight loss, rapid heartbeat, and anxiety.

• Hypothyroidism:

  • Underactive thyroid producing insufficient hormones causing fatigue, weight gain, and a puffy face.

• Goiter:

  • Enlargement of the thyroid gland, often due to iodine deficiency.

Calcitonin and Parathyroid Hormone (PTH)

• Calcitonin:

  • Lowers blood calcium levels by inhibiting osteoclast activity, promoting calcium storage in bone, increasing calcium excretion in urine, and reducing intestinal absorption of calcium.

• PTH:

  • Raises blood calcium levels by stimulating osteoclast activity leading to calcium release into the bloodstream