Hormones and the Endocrine System

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A hormone

casade

pathway

Cold

Pathway

Stimulus

Hypothalamus secretes thyrotropin-releasing hormone (TRH )

Negative feedback

Example

Sensory neuron

Neurosecretory cell

Blood vessel

Anterior pituitary secretes thyroid-stimulating hormone (TSH or thyrotropin )

Target cells

Response

Body tissues

Increased cellular metabolism

–

Thyroid gland secretes thyroid hormone (T3 and T4 )

–

Slide 53

Tropic Hormones

A tropic hormone regulates the function of endocrine cells or glands.

The four strictly tropic hormones are:

Thyroid-stimulating hormone (TSH)

Follicle-stimulating hormone (FSH)

Luteinizing hormone (LH)

Adrenocorticotropic hormone (ACTH)

Slide 54

Nontropic Hormones - target nonendocrine tissues.

Nontropic hormones produced by the anterior pituitary are:

Prolactin (PRL)

Melanocyte-stimulating hormone (MSH)

Prolactin stimulates lactation in mammals but has diverse effects in different vertebrates.

MSH influences skin pigmentation in some vertebrates and fat metabolism in mammals.

Slide 55

Growth Hormone

Growth hormone (GH) is secreted by the anterior pituitary gland and has tropic and nontropic actions.

It promotes growth directly and has diverse metabolic effects.

It stimulates production of growth factors.

An excess of GH can cause gigantism, while a lack of GH can cause dwarfism.

Slide 56

Endocrine signaling regulates metabolism, homeostasis, development, and behavior.

Endocrine glands respond to diverse stimuli in regulating metabolism, homeostasis, development, and behavior

Slide 57

Thyroid Hormone: Control of Metabolism and Development

The thyroid gland consists of two lobes on the ventral surface of the trachea.

It produces two iodine-containing hormones: triiodothyronine (T3) and thyroxine (T4).

Proper thyroid function requires dietary iodine for thyroid hormone production.

Slide 58

Thyroid hormones stimulate metabolism and influence development and maturation.

Hyperthyroidism, excessive secretion of thyroid hormones, causes high body temperature, weight loss, irritability, and high blood pressure.

Graves’ disease is a form of hyperthyroidism in humans.

Hypothyroidism, low secretion of thyroid hormones, causes weight gain, lethargy, and intolerance to cold.

Slide 59

Parathyroid Hormone and Vitamin D: Control of Blood Calcium