The Endocrine System Overview GR 10 A

Endocrine Organs Endocrine system is series of organs and glands in body that secrete chemical messengers into blood stream Exocrine glands, like sweat glands, secrete substances that leave the body, but are not part of endocrine system that secrete into body Organs like the heart and small intestine also secrete hormones, but they are not a part of the endocrine system

Hormones Chemical messengers released by endocrine glands are called hormones Hormones are released into blood stream and travel all over body, some affecting millions of cells simultaneously; effects last for minutes or even hours or possibly days Many hormones are secreted all the time, with amount secreted changing as needed

Hormones Hormones work by binding to receptors on target cells; they bind to not only sites outside cell, like neurotransmitters, but also to sites inside cell If hormones bind to outside of cell, they can have several different effects, either changing cellular permeability or sending target cell a message that changes enzyme activity inside cell

Hormones Hormones can stimulate the cell to start production of a protein They can stimulate the cell to turn off production of a protein The target cell changes what it has been doing in response to the hormone

Steroids Are a powerful hormone because they can bind to sites inside cells Steroids are lipid molecules that can pass easily through target cell membrane, allowing them to interact directly with cell’s DNA to change cell activity They must be carefully regulated because only small amounts needed to perform their task

Test Your Knowledge What chemical, when secreted into the bloodstream, controls the metabolic process of target cells? – Hormone (C) Steroid hormones are very powerful because they: – interact directly with DNA (c) Which of the following is true of hormones? – They affect distant targets (c)

Control of Hormones Amount of hormone secreted changes based on situational demands in order to maintain homeostasis. Many of chemical and physical characteristics of body have standard level, or set-point, that is ideal level for that particular value; blood pressure, blood oxygen, heart rate, and blood sugar are examples

Control of Hormones Control systems (endocrine and nervous system) work to keep levels at or near ideal There is a way for body to measure, remember and correct variable levels; for example, hypothalamus stores ideal set-point for temperature

Control of hormones If any body characteristic becomes seriously abnormal, negative feedback counteracts the change Negative feedback is used to maintain appropriate hormone levels in the body. Example: if blood pressure rises, body works to bring it down to normal set-point; if blood pressure falls, body works to raise it back up to normal Hormones work same way; if hormone levels rise, negative feedback will turn off endocrine organ that is secreting hormone

Control of the Endocrine System When a body characteristic changes, positive feedback increases magnitude of change This kind of process also known as vicious cycle Positive feedback is not a way to regulate body, since positive feedback increases change away from set-point

Controlling hormone levels Hormone levels in the body can be controlled in 3 ways: Neural-controlled by the nervous system Hormonal-controlled by other hormones Humoral-controlled by body fluids, such as blood

Controlling hormone levels Neural control is when stimulation of the nervous system results in the release of a particular hormone.

Controlling hormone levels Hormonal control Hormones are part of a hierarchy. – One gland is controlled by the release of hormones from another gland higher up the chain – Negative feedback controls the flow of orders from one part of the chain to the next. When enough hormone has been produced, the “ordering” gland stops sending orders

Controlling hormone levels Humoral control The endocrine organs directly monitor the body’s internal environment by monitoring the body fluids

Test Your Knowledge Which of the following in not a way that hormone levels are regulated? – Positive feedback (c) The “ideal” value for a body characteristic is called the: – Set point (a) ____________ feedback enhances a change in body chemistry. – Positive (b)

Pharmacology Hormone replacements and analogues Synthroid: synthetic thyroid hormone used to treat hypothyroidism Hydrocortisone: used to replace cortisol in Addison’s disease Prednisone: drug that acts like corticosteroid – Used in patients with corticosteroid deficiency as hormone replacement – Used in patients with normal cortisol levels to decrease inflammation, treat severe allergies Growth hormone: may be given by injection to children with deficiencies

Pharmacology Diabetic medications Insulin – Used to replace insulin in cases of deficiency – Can be administered in variety of ways including, injections, pumps, and inhaled aerosols Pills – Potentiate effects of body’s own insulin in Type-2 diabetes Example drug: Glucophage

Pharmacology Medications that inhibit natural hormones Mitotane: cortisol inhibitor used to treat some kinds of Cushing’s syndrome Somatostatin analogues: can be used to decrease growth hormone production in acromegaly

Label the diagram 1. Pituitary and pineal 2. Thyroid 3. Parathyroid 4. Thymus 5. Adrenals 6. Pancreas 7. Testes (male) 8. Ovaries (female)