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Fundamentals of Biology

Lesson 31

The Endocrine System

I. Introduction

    A. Endocrine System.
        1. Definition: the ductless glands of the body.
        2. Purpose: regulate and control the other body systems.
        3. They do this by releasing chemical messengers (hormones) into the blood stream.
        4. The blood carries these hormones to all the other parts of the body.
        5. The effects are slower and longer-lasting than those of the nervous system.

    B. Hormones.
        1. Chemical messengers produced in the endocrine glands and carried by the blood to affect cells in other parts of the body.
        2. Proteins, amines, or sterols (fats).
        3. Carried by the blood.
        4. Specific to one target site.
        5. Secreted in small amounts.
        6. Constantly removed from the blood.
            a. Filtered out by the kidneys.
            b. Deactivated by the liver or other glands.
            c. Thus the endocrine glands must continuously produce hormones to sustain their effect.
        7. Quantity is usually self-regulated by negative feedback mechanisms.

II. The Endocrine Glands.

    A. Secretion.
        1. Hyposecretion: abnormally low level of production.
        2. Hypersecretion: abnormally high level of production.

    B. Thyroid.
        1. In front of the trachea, below the larynx.
        2. Produces thyroxin and calcitonin.
        3. Thyroxin increases metabolism, growth.
        4. Regulated by thyroid stimulating hormone from the anterior pituitary gland.
        5. Calcitonin causes Ca2+ to move from the blood to the bones when blood Ca2+ gets too high.

    C. Parathyroid.
        1. Clusters of cells embedded in tissue around the thyroid gland.
        2. Produces parathyroid hormone.
        3. Causes Ca2+ to move from the bone to the blood.

    D. Anterior pituitary.
        1. In the base of the brain.
        2. Growth hormone stimulates growth.
        3. Thyroid stimulating hormone regulates the thyroid gland.
        4. Adrenocorticotropic hormone acts on the adrenal cortex.
        5. Gonadotropins control hormones secreted by the reproductive organs.
        6. Prolactin stimulates the breasts to produce milk.

    E. Posterior pituitary.
        1. In the base of the brain.
        2. Stores and releases 2 hormones made by the hypothalamus.
        3. Oxytocin causes the smooth muscles to contract (e.g. uterus).
        4. Antidiuretic hormone stimulates the kidneys to reabsorb water..

    F. Islets of Langerhans.
        1. Over 1 million groups scattered throughout the pancreas.
        2. Insulin.
            a. Stimulates cells to take glucose from the blood.
            b. Stimulates conversion of glucose to glycogen.
            c. Increases movement of amino acids into cells.
        3. Glucagon
            a. Stimulates liver to convert glycogen to glucose.
            b. Stimulates breakdown of fats to form glucose.

    G. Adrenal.
        1. On the top of each kidney.
        2. Adrenal medulla (inner part) produces epinephrine and norepinephrine (adrenaline and noradrenaline).
        3. These greatly increase metabolism, enabling stupendous physical feats.
        4. Adrenal cortex produces glucocorticoids.
        5. They stimulate conversion of fats and amino acids to glucose.

    H. Sex hormones.
        1. In males the testes produce androgens, e.g. testosterone.
        2. In females the ovaries produce estrogens and progesterone.
        3. The androgens and estrogens produce secondary sex characteristics.
        4. Progesterone stimulates development of the uterus and the mammary glands.

III. Mind Control.

    A. Man is one creature with two aspects: physical and spiritual.
    B. The brain is part of the physical aspect.
    C. The mind is part of the spiritual aspect.
    D. These two aspects are distinct, yet interrelated.
    E. Thus the mind is related to the brain, but is not identical to the brain.
    F. The mind is a non-physical, spiritual part of man.

IV. Alcohol.

    A. It can be a dangerous and deadly intoxicant.
    B. The Bible warns us against the dangers of indulgence in alcoholic drinks and declares the damnation of drunkards.
    C. However, the Bible also portrays wine and “strong drink” as natural elements of celebrations, notably the Lord’s Supper.
    D. Principles governing the use of alcoholic beverages.
        1. Drunkenness is forbidden.
        2. Illegal use is forbidden (i.e. under 21 yrs. old).
        3. May be served at meals, especially in celebrations, in moderation.
        4. Must never be used in a way that will cause others to stumble.
        5. Care must be taken to avoid dangerous activities (e.g. driving) while drinking alcoholic beverages.
        6. If you are doing something so that you may drink, you are drinking for the wrong reason.

V. Psychotropic Drugs.

    A. Narcotics.
        1. Produce euphoria.
        2. Are physically addictive.
        3. Morphine: derived from opium, the dried sap of the opium poppy.
        4. Heroin: derived from morphine.
        5. Cocaine: derived from the leaves of the coca plant.
        6. Methadone: used to aid withdrawal from other narcotics.
        7. Codeine: pain killer.

    B. Stimulants.
        1. Increase the activity of the central nervous system and often increase metabolism.
        2. Create sense of high energy and greater alertness.
        3. Amphetamines: synthetically produced.
        4. Caffeine.

    C. Depressants.
        1. Slow down the central nervous system.
        2. Memory and thought are impaired.
        3. Barbiturates: synthetically produced.
        4. Tranquilizers: less potent than barbiturates.
        5. Alcohol.

    D. Hallucinogens.
        1. Induce non-existent sensations, visions.
        2. LSD, DMT, STP: synthetic.
        3. Mescaline: derived from a catus; used in some Native American religions.
        4. Marijuana: derived from the Cannabis plant.

    E. Use of psychotropic drugs.
        1. They are illegal.
        2. They are dangerous.
        3. Their benefits are short-lived.
        4. They are a substitute for God, thus idolatrous.

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