Endocrine System

  • Chapt. 14

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    I. Introduction

  • A. Endocrine glands are ductless glands that secrete specific chemicals called hormones directly into the blood.
  • 1. The blood then transports these hormones to target tissues, where they perform precise functions.

    2. The endocrine system, along with the nervous system, functions in regulating and integrating organ systems in order to maintain homeostasis.

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    • Comparison of the Endocrine System
    and the Nervous System

  • Endocrine System

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  • Nervous System

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    II. Location

    III. Kinds of Hormones

  • A. All steroids contain a complex set of carbon rings and are synthesized from cholesterol.
  • 1. Basic structure of steroids -->

    Cyclopentanoperhydro-

    phenanthrene nucleus

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    2. Steroids are a type of lipid.

  • a. Therefore, they are fat soluble and can pass through the cell membrane with ease.
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    3. Some examples of steroid hormones include: cortisol, cortisone, estrogen, progesterone, androstenedione, and testosterone.

    B. Proteins (Polypeptides)

  • 1. Protein hormones are composed of long chains of amino acids.

    2. Protein hormones are not fat soluble.

    3. Protein hormones include: calcitonin, insulin, and parathyroid hormone.

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    C. Amines

  • 1. Amines are derived from amino acids.
  • a. Examples include: epinephrine, norepinephrine, and thyroxine.
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    • IV. Endocrine Glands

  • A. Pituitary (Hypophysis)
  • 1. Composed of 2 parts:
  • a. Anterior Pituitary (Adenohypophysis)

    b. Posterior Pituitary (Neurohypophysis)

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    • 2. Hormones

  • a. Anterior Pituitary
  • 1) Growth Hormone (GH) - causes an increase in cell division.

    2) Thyroid-stimulating Hormone (TSH) - stimulates the thyroid gland to release its hormones.

    3) Adrenocorticotropic Hormone (ACTH) - promotes normal functioning of the adrenal cortex.

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    Hormones of the anterior pituitary (continued):

    4) Follicle-stimulating Hormone (FSH) - In males, it stimulates sperm production. In females, it stimulates development of an oocyte (immature egg) and its surrounding follicle cells.

    5) Luteinizing Hormone (LH) - In the female, LH works with FSH in bringing about ovulation and stimulates the formation of the corpus luteum.

    Hormones of the anterior pituitary (continued):

  • 6) Prolactin - Functions only in females following parturition (childbirth).
  • a) Prolactin stimulates milk production in the mammary glands.
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    7) Melanocyte-stimulating hormone (MSH)- Causes dispersal of pigment granules within melanocytes.

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    b. Posterior Pituitary

  • 1. Oxytocin - Increases contractions during labor and results in the "let-down" reflex in the mammary glands.

    2. Antidiuretic Hormone (ADH) - Causes the kidneys to conserve water.

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    • B. Thyroid Gland

  • 1. Hormones:
  • a. Thyroxine (T4) and Triiodothyronine (T3) - These hormones regulate metabolism by controlling the rate of carbohydrate metabolism and protein synthesis.

    b. Calcitonin - (a minor hormone) - inhibits the release of calcium from bone.

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    • C. Parathyroid Glands

  • 1. The parathyroid glands are embedded in the posterior side of the thyroid gland.

    2. They secrete the hormone, Parathyroid Hormone, which causes an increase in blood calcium levels.

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    D. Pancreas

  • 1. The pancreas is both an exocrine and an endocrine gland.

    2. The endocrine portion of this gland consists of clusters of cells called the Pancreatic islets.

    3. The islets consist of two types of cells:

  • a. alpha cells - secrete glucagon.
  • 1) Glucagon - causes the blood glucose levels to rise.
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    b. beta cells - secrete insulin.

  • 1) Insulin - Acts on almost all of the cells of the body. It causes a decrease in blood glucose concentration by allowing the cells of the body to take up glucose.
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    • 4. Diabetes mellitus - deficiency of insulin.

  • a. Type I (juvenile onset) - Caused by insufficient insulin.

    b. Type II (adult onset) - levels of insulin are normal or above normal.

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    • E. Adrenal (Suprarenal) Glands

  • 1. Composed of two parts:
  • a. adrenal cortex - outer part

    b. adrenal medulla - deeper portion composed of modified postganglionic sympathetic fibers.

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    2. Adrenal Cortex

  • a. Over 30 hormones have been identified from the adrenal cortex.
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    • b. These many hormones are divided into 3 types:

  • 1) Mineralocorticoids
  • 2) glucocorticoids
  • 3) Gonadocorticoids
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