Chapter 10

The Endocrine System

The Endocrine System

• 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 System Characteristics

• Hormones:– Come from endocrine glands

– Circulate in the blood stream

– Act on specific cells in the body

Endocrine Functions: Hormones

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 receptors inside target cells– Activate specific genes to produce specific

proteins

How Steroid Hormones Act

• 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

Characteristics of Non-steroid Hormones

How water-solublehormones 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):

A. Receptors are useful but not essential

B. 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

• Anterior pituitary– Connection to hypothalamus: releasing (and

inhibiting) hormones from hypothalamus travel to pituitary through pituitary portal vessels

– No nerve connection to hypothalamus

The Hypothalamus and Anterior Pituitary Gland

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

• 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

Hypothalamus and the Posterior Pituitary Gland

Oxytocin

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

Oxytocin and ADH (antidiuretic hormone)

A. Are synthesized and released from the anterior pituitary gland

B. Are synthesized and released from the posterior pituitary gland

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

Posterior Pituitary Disorder

• 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

Anterior Pituitary Disorders

Acromegaly Symptoms

• Bony changes alter facial features: – The brow and lower

jaw protrude– Spacing of the teeth

increases– Enlarged jaw

(prognathism), lips, nose & tongue

AcromegalySymptoms

• 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

• 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)

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

Disorders of the Thyroid Gland

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:

A. Too little iodide in the diet

B. Too much iodide in the diet

Too little iodide in the diet causes a goiter because:

A. Not enough T3/T4 is produced

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

C. Excess secretion of TSH (Thyroid Stimulating Hormone)

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

excess:

A. Iodide

B. T3/T4

C. 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

NormalHyperthyroid

Hypothyroidism and Cretinism

Cretinism is characterized by mental retardation, dwarfism and delayedsexual development and is caused by undersecretion of thyroid hormone during fetal life or infancy.