Chapter 10 The Endocrine System

The Endocrine System FIGURE 10.2 The endocrine system. The endocrine system is made up of endocrine glands and of organs that contain some endocrine tissue. Here, the hormones are listed under the endocrine gland or organ that produces them.

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 Come from endocrine glands Circulate in the blood stream Act on specific cells in the body

FIGURE 10.1b Exocrine and endocrine glands. (a) Exocrine glands, such as this oil gland, secrete their products into ducts. (b) Endocrine glands release their products, called hormones, into the fluid just outside cells. The hormones then diffuse into the bloodstream to be transported throughout the body.

Exocrine Gland Figure: 10-01a Title: Exocrine glands. Caption: (a) Exocrine glands secrete their products into ducts that open onto the surface of the body, into the spaces within organs, or into cavities within the body.

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 receptors inside target cells Activate specific genes to produce specific proteins

How Steroid Hormones Act FIGURE 10.3 Mode of action of steroid hormones

Characteristics of Non-steroid 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 FIGURE 10.4 Mode of action of some water-soluble hormones: the second messenger system of cAMP. Because water-soluble hormones cannot cross the plasma membrane, they must affect the activities of target cells indirectly.

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

FIGURE 10.6 The two lobes of the pituitary gland and the hormones they secrete

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

FIGURE 10.5a Location and structure of the pituitary gland. (a) Side view of the pituitary gland. (b) Close-up of the pituitary gland showing how it is attached to the hypothalamus by a short stalk.

FIGURE 10.5b Location and structure of the pituitary gland. (a) Side view of the pituitary gland. (b) Close-up of the pituitary gland showing how it is attached to the hypothalamus by a short stalk.

The Hypothalamus and Anterior Pituitary Gland Connection to hypothalamus: releasing (and inhibiting) hormones from hypothalamus travel to pituitary through pituitary portal vessels No nerve connection to hypothalamus

FIGURE 10.6 The two lobes of the pituitary gland and the hormones they secrete

Neurosecretory Cells From the Hypothalamus Control the Pituitary

True/False Neurosecretory cells have characteristics of both hormone secreting cells and neurons

Hormones of the Pituitary Gland

Hypothalamus and the Posterior Pituitary Gland 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

Oxytocin FIGURE 10.10 The steps by which OT stimulates uterine contractions during childbirth

Oxytocin 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 FIGURE 10.11 The steps by which OT stimulates milk ejection from the mammary glands

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)

FIGURE 10.7 Robert Wadlow, a pituitary giant, was born in 1918 at a normal size but developed a pituitary tumor as a young child. The tumor caused increased production of GH. Robert never stopped growing until his death at 22 years of age, by which time he had reached a height of 8 feet 11 inches.

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

Acromegaly Symptoms 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

FIGURE 10.12a Location and structure of the thyroid gland and parathyroid glands. (a) The thyroid gland lies over the trachea, just below the larynx. (b) Section through thyroid tissue. Note the follicular cells that produce the precursor to thyroid hormone. (c) Diagram showing structure of thyroid tissue. In addition to the follicular cells, note the parafollicular cells, which produce CT.

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 Normal

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.