Importance of the Endocrine System

Hormones

• Chemical regulators produced by cells that affect cells in another part of the body.

• Endocrine hormones are produced by endocrine glands and are secreted into the blood.

• Transported by blood to cells in another part of the body.

• By contrast exocrine glands secrete substances through ducts or tubes, onto a body surface or into a cavity (ex. Sweat glands, mucous glands, digestive glands)

Hormones

activation sites of hormones non-target vs. target:

Non-target Target

Location of activation Affect many cells throughout the body

Affect specific cells or target tissues

Examples

Somatotropin- stimulates growth of body (aka growth hormone)

Parathyroid hormone – regulates calcium levels in body

Insulin- regulates blood sugar by increasing permeability of cells to glucose

Gastrin – stimulates cells of stomach to produce digestive enzymes

Epinephrine- produced in times of stress, accelerates body reactions during crisis

Chemical Control Systems• Nervous system & endocrine system work

together to control organs & tissues.

– Nervous system rapid, short-term adjustments. Neurotransmitters

– Endocrine system slower, long-term adjustments. Hormones

Handout 8.1-3

Chemical Control Systems

Nervous system and endocrine system both operating in the hypothalamus…

•The hypothalamus regulates the pituitary gland through nerve signals.

•The pituitary gland stimulates the endocrine glands which secrete hormones that affects the hypothalamus.

Endocrine Glands

Gland Example of Hormones Produced

Hypothalamus • Antidiuretic – H2O regulation• Oxytocin - labourBoth produced in hypothalamus but

released by posterior pituitary

Pituitary“Master Gland”

• Growth hormone • Prolactin• FSH and LH • Thyroid-stimulating hormone

Thyroid • Thyroxine – metabolic rate• Triodothyronine

Parathyroid • Parathyroid hormone (Ca+ and PO43- )

Pancreas • Insulin (high blood sugar)• Glucagon (low blood sugar)

Ovary (female) • Estrogen (devel. 2o sex charac.)• Progesterone (maintains uterine lining)

Testes (male) • Testosterone • Andostrone

Adrenal Gland • Epinephrine (medulla)• Norepinephrine (medulla) • Glucocorticoids (cortex) *Handout 8.1-1*

Chemical Signals: Steroid and Protein Hormones

Steroid Hormones•Made from cholesterol.•Fat soluble diffuses into cell•E.g., sex hormones and cortisol•Hormone-receptor complex acts in nucleus to influence transcription

Protein Hormones•Made from amino acids.•Water soluble – attaches to receptor cell on target cell membrane•Changes activity of enzymes inside cell•E.g., insulin and growth hormones.

*Handout 8.1-4*

Steroid Hormones

1Hormone diffuses from cell and travels through blood stream to interstitial fluid

2Hormone diffuses across cell

membrane into target cell

3Hormone attaches to receptor molecule forming hormone-

receptor complex

4Hormone-receptor complex

attaches to DNA

5Hormone activates a gene initiating transcription of a

specific protein

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Protein Hormones

1Hormone diffuses from cell and travels through blood stream to interstitial fluid

2Hormone (1st messenger) binds to receptor on cell

membrane

3Hormone-receptor complex promotes formation of cyclic

AMP

4cAMP acts 2ndary messenger and activates an enzyme

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The Pituitary Gland

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The Pituitary Gland

• Referred to as the “master gland”.

• Posterior lobe stores and releases hormones produced by the hypothalamus.

• Anterior lobe produces its own hormones, but the release is regulated by the hypothalamus.

*Handout 8.1-5*

Posterior lobe of pituitary gland1) Hypothalamus synthesizes ADH and oxytocin2) specialized nerve cells transport ADH and oxytocin to posterior pituitary3) hormones released into blood stream as needed

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*Handout 8.1-5*

Anterior lobe of pituitary gland1) Hormones secreted by nerve ends of hypothalamus2) Hormones transported in the blood to pituitary gland3) Pituitary gland stimulated to release pituitary hormones, which are carried by blood to target tissues

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*Handout 8.1-5*

*Handout 8.1-2*