Chapter 10
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Chapter 10. The Endocrine System. The Endocrine System. Endocrine System Characteristics. Each hormone acts only on specific cells (target cells) Only target cells have receptors for specific hormones Endocrine control slower than nervous system

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Chapter 10

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Chapter 10

The Endocrine System

The Endocrine System

Endocrine System Characteristics

  • Each hormone acts only on specific cells (target cells)

  • Only target cells have receptors for specific hormones

  • Endocrine control slower than nervous system

  • Endocrine and nervous systems complement each other

Endocrine Functions: Hormones

  • Hormones:

    • Come from endocrine glands

    • Circulate in the blood stream

    • Act on specific cells in the body

Exocrine Gland

Classification of Hormones: Steroid Hormones

Lipid-soluble and water-soluble hormones interact differently with target cells

  • Steroid Hormones:

    • Lipid soluble, chemically derived from cholesterol

    • Bind to receptorsinside target cells

    • Activate specific genes to produce specific proteins

How Steroid Hormones Act

Characteristics of Non-steroid Hormones

  • Nonsteroid hormones:

    • Water soluble

    • Bind to receptors on target cell membranes

    • Work through intermediate mechanisms (second messengers) to activate existing enzymes

    • Faster action than steroid hormones; time to action = seconds to minutes

How water-soluble

hormones act

Hormone Receptors

  • All hormones work through receptors

  • Target cells (and only target cells) for a hormone contain receptors for that hormone

  • Example: Estrogen Receptor Knockout (ERKO) mouse (and human)

In order for a hormone to work on a cell (or tissue):

  • Receptors are useful but not essential

  • Receptors for that hormone must be present

Feedback mechanisms regulate the secretion of hormones

  • Refer to in-class worksheet

Hypothalamus and Pituitary Glands

  • Hormones from the hypothalamus regulate the pituitary gland

  • Neurosecretory cells: part neuron; part endocrine organ

  • Pituitary hormones often prompt other glands to release hormones

The Hypothalamus and Anterior Pituitary Gland

  • Anterior pituitary

    • Connection to hypothalamus: releasing (and inhibiting) hormones from hypothalamus travel to pituitary through pituitary portal vessels

    • No nerve connection to hypothalamus

Neurosecretory Cells From the Hypothalamus Control the Pituitary


Neurosecretory cells have characteristics of both hormone secreting cells and neurons

Hormones of the Pituitary Gland

Hypothalamus and the Posterior Pituitary Gland

  • Posterior pituitary

    • Connection to hypothalamus: hormones made in hypothalamus, stored in posterior pituitary

    • Neurosecretory cells project to post. pit.

Hypothalamus and the Posterior Pituitary Gland

  • Posterior pituitary Hormones (protein)

    • Antidiuretic hormone (ADH): conserves water in kidneys, regulates water balance in body

    • Regulated by:

      • High/Low water intake

      • Alcohol

Hypothalamus and the Posterior Pituitary Gland

  • Posterior pituitary Hormones (protein)

    • Oxytocin induces:

      • Uterine contractions during labor

      • Milk ejection through neuroendocrine reflex

      • Behavioral Effects: Love/Trust/Bonding



  • Human Sexual Response:

    • Oxytocin may have a role in sexual arousal, orgasm & sexual satiety/satisfaction

  • CNS: Penile erection, copulatory behavior

  • Trust/Love

    • Pair bonding

  • Maternal Behavior:

    • Oxytocin induces maternal behavior in female rats


Oxytocin and ADH (antidiuretic hormone)

  • Are synthesized and released from the anterior pituitary gland

  • Are synthesized and released from the posterior pituitary gland

Posterior Pituitary Disorder

  • Diabetes Insipidus: hyposecretion of ADH, inability to conserve water appropriately

Anterior Pituitary Disorders

  • Gigantism: hypersecretion of growth hormone (during growth phase)

  • Pituitary Dwarfism: hyposecretion of growth hormone (during growth phase)

Anterior Pituitary Disorders

  • Acromegaly: hypersecretion of growth hormone after bones have stopped growth

Acromegaly Symptoms

  • Bony changes alter facial features:

    • The brow and lower jaw protrude

    • Spacing of the teeth increases

    • Enlarged jaw (prognathism), lips, nose & tongue


  • Enlarged hands and/or feet

    • Soft tissue swelling of the hands & feet is often an early feature, with patients noticing a change in ring or shoe size

  • Widened fingers or toes due to skin overgrowth with swelling, redness, & pain

Why is Growth Hormone an Abused Drug?

  • Role of GH in Normal Adults

    • Increases muscle growth

    • Decreases fat stores

Thyroid Gland

Thyroid Gland

  • Secretes thyroid hormones:

    • Thyroxine (T4) and Triiodothyronine (T3)

Thyroid Gland

  • Secretion: regulated by hypothalamus (TRH) & pituitary (TSH) hormones

  • Action of T4 & T3

    • Increase metabolic rate & heat prodn.

    • Development of fetal nervous system (cretinism results from lack of T4 & T3)

Disorders of the Thyroid Gland

  • Hypothyroidism:

    • Children: cretinism

    • Adults: myxedema

    • Low BMR, Lethargy, Weight gain, Low body temp.

  • Hyperthyroidism: Graves Disease

    • Increased BMR

    • Hyperactivity, nervousness, agitation

    • Weight loss

    • Exophthalmos

  • Hypothyroidism and Goiter

    • Causes of Goiter

      • Low iodide intake

      • Genetic mutation

      • Diet

    • Direct cause is

    • excess TSH secretion

    Low Iodide Goiter

    Goiters can be caused by:

    • Too little iodide in the diet

    • Too much iodide in the diet

    Too little iodide in the diet causes a goiter because:

    • Not enough T3/T4 is produced

    • Not enough negative fdbk of T3/T4 on the pituitary/hypothalamus

    • Excess secretion of TSH (Thyroid Stimulating Hormone)

    The factor that most often is the direct stimulus that causes a goiter is excess:

    • Iodide

    • T3/T4

    • TSH (Thyroid Stimulating Hormone)

    Exophthalmos and Hyperthyroidism

    Exophthalmos is caused by oversecretion of the thyroid hormone which leads to accumulation of fluid behind the eyes causing the eyes to bulge out.

    Hyperthyroidism Patient



    Hypothyroidism and Cretinism

    Cretinism is characterized by mental retardation, dwarfism and delayed

    sexual development and is caused by undersecretion of thyroid hormone during fetal life or infancy.

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