Endocrine System

• Endocrine System


  • Plays a role in growth, metabolism, and sexual development
  • Controls body processes through the production, secretion, and regulation of hormones
• Hormones


  Chemical "messengers" functioning in cellular and organ activity and, ultimately, maintaining the body's homeostasis
• Types of Hormones


  • Lipid-derived
  • Amino acid-derived
  • Peptide (peptide and proteins)
• Lipid-Derived Hormones


  • Derived from cholesterol
  • Insoluble in water
  • Transported by transport proteins in blood
  • Remain in circulation longer than peptide hormones
• Steroid hormones


  • Estradiol (estrogen)
  • Testosterone (androgen)
  • Aldosterone and cortisol (released by adrenal glands)

  
• Amino Acid-Derived Hormones


  • Water soluble and insoluble in lipids
  • Derived from amino acids tyrosine and tryptophan
• Amino Acid-Derived Hormones


  • Epinephrine and norepinephrine (synthesized in adrenal glands)
  • Thyroxine (produced by thyroid gland)
  • Melatonin (secreted by pineal gland)

  
• Peptide Hormones


  • Polypeptide chain (chain of amino acids)
  • Water soluble and insoluble in lipids
  • Larger than those derived from cholesterol or amino acids
• Peptide Hormones


  • Antidiuretic hormone and oxytocin (produced in brain, released into blood in posterior pituitary)
  • Growth hormones (produced by pituitary)
  • Follicle-stimulating hormone (large glycoproteins produced by pituitary)

  
• How Hormones Work


  • Hormones mediate changes in target cells by binding to specific cellular hormone receptors
  • Receptor binding alters cellular activity and results in an increase or decrease in normal body processes
  • Up-regulation (increase in number of receptors in response to rising hormone levels)
  • Down-regulation (decrease in number of receptors in response to rising hormone levels)

  
• Intracellular Hormone Receptors


  • Residing in the cytoplasm or in the nucleus
  • Forms a complex with the hormone (hormone-receptor complex)
  • DNA sequence which triggers gene transcription and translation

  
• Plasma Membrane Hormone Receptors

  • Receptors on the outer surface of the plasma membrane that binds with lipid insoluble hormones
  • Binding results in activation of a signaling pathway

  
• Endocrine Glands


  • Hypothalamus
  • Pituitary Gland
  • Thyroid Gland
  • Parathyroid Glands
  • Adrenal Glands
  • Pancreas
  • Pineal Gland
  • Gonads

  
• Hypothalamus


  • Located in the diencephalon of the brain
  • Receives input from the body and other brain areas and initiates endocrine responses to environmental changes
  • Synthesizes and secretes regulatory hormones that control the endocrine cells in the anterior pituitary gland
  • Produces antidiuretic hormone (ADH) and oxytocin

  
• Pituitary Gland


  • Sometimes called the "master gland"
  • Located at the base of the brain
  • Attached to the hypothalamus via a stalk
  • Has two distinct regions: anterior pituitary and posterior pituitary

  
• Anterior Pituitary gland (Adenohypophysis)


  • Surrounded by a capillary network that extends from the hypothalamus
  • Produces seven hormones regulated by the hypothalamus

  
• Posterior Pituitary (+ infundibulum = neurohypophysis)

  • Significantly different in structure from the anterior pituitary
  • Contains mostly nerve fibers and neuroglial cells
  • Does not produce hormones
  • Stores hormones produced by the hypothalamus and releases them into the blood stream

  
• Thyroid Gland


  • Located in the neck, just below the larynx and in front of the trachea
  • Butterfly-shaped gland with two lobes connected by the isthmus
  • Made up of many spherical thyroid follicles which store the glycoprotein thyroglobulin
  • Thyroid follicle cells synthesize the hormones thyroxine (T4) and triiodothyronine (T3)
  • Parafollicular cells produce calcitonin

  
• Parathyroid Glands


  • Located on the posterior surface of the thyroid gland
  • Produce parathyroid hormone (PTH) which increases blood calcium concentrations when calcium ion levels fall below normal
• Adrenal Glands


  • Located on top of each kidney
  • Consist of an outer adrenal cortex and an inner adrenal medulla
  • Adrenal cortex produces mineralocorticoids, glucocorticoids, and small amounts of androgens
  • Adrenal medulla produces epinephrine and norepinephrine

  
• Pancreas


  • Contains both exocrine cells that excrete digestive enzymes and endocrine cells that release hormones
  • Islets of Langerhans contain alpha cells that produce glucagon and beta cells that produce insulin
• Pineal Gland


  • Pea shaped gland located in the mid-line of the brain
  • Produces melatonin, which is affected by the photoperiod and involved in biological rhythms

  
• Gonads


  • Testes produce the steroid hormone testosterone
  • Ovaries produce the steroid hormones estradiol and progesterone

  
• Adrenal Insufficiency occurs when the adrenal glands do not produce sufficient amounts of steroid hormones, primarily cortisol
• Congenital Adrenal Hyperplasia (CAH) is a group of inherited genetic disorders that affect the adrenal glands, resulting in a lack of enzymes needed to produce hormones
• Nonclassic CAH is a more mild form of congenital adrenal hyperplasia, with symptoms including rapid growth, acne, excess facial/body hair, irregular menstrual periods, infertility, male-pattern baldness, and enlarged penis but small testicles
• Hyperaldosteronism is a disease where the adrenal glands make too much aldosterone, leading to hypertension and low blood potassium levels
• Osteoporosis is the deterioration of bone tissue and reduction of bone strength, making bones fragile, and can be triggered by hormone-related disorders
• Pituitary disorders involve abnormal growths that develop in the pituitary gland, resulting in too many hormones that regulate important body functions

  
• Thyroid disorders include hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid)