Chem 5, College of the Desert

Antagonist: A substance that blocks or inhibits the normal biochemical response of a receptor.

Agonist: A substance that interacts with a receptor to cause or prolong the receptors normal biochemical response.

Drug: Any substance that alters body function when it is introduced from an external source.

Steroid: A lipid who's structure is based on the following tetracyclic (four-ring) carbon skeleton: 3 cyclohexanes, 1 cyclopentane

Second Messanger: Chemical messanger released inside a cell when a hydrophylic hormone or neurotransmitter interacts with a receptor on the cell surface.

• Indirect control through release of regulatory hormones: In the most common control mechanism, regulatory hormones from the hypothalomus stimulate or inhibit the release of hormones by the anterior gland. Many of these pituitary hormones in turn stimulate release of still other hormones by their own target tissue.
• ie:
• Hypothalomus->(releasing factor)->Pituitary Gland->Thyrotropin(regulatory hormon)->Thyroid gland-> Thyroid hormones.
• Thyroid hormones are targeted to cells throughout the body: they affect oxygen availability, blood pressure, and other endocride tissues.

• Direct release of Hormones: Hormones move from the hypothalamus to the posterior pituitory gland, where they are stored untill needed.
• ie:
• Hypothalamus -> Antidiuretic hormone
• Antidiuretic hormone which is stored in the posterior pituitary gland, targets the kidneys and causes retention of water and elivation of blood pressure.

Endocrine System: A system of specialized cells, tissues, and ductless glands that excretes hormones and shares with the nervouse system the resposability for maintaining constant internal body conditions and responding to changes in the enviornment.

Hormone: A chemical messanger secreted by cells of the endocrine system and transported through the bloodstream to target cells with appropriate receptors where it elicits a response.

• Direct Neural Control: A nervouse system message from the hypothalamus initiates release of hormones by the adrenal gland.
• ie:
• Hypothalamus -> (nerve message) -> Adrenal Gland -> Epinephrine.
• Epinephrine is targeted to many cells; it increases heart rate, blood pressure, and glucose availability.

Neurotransmitter: A chemical messanger that travels between a neuron and a neighboring neuron or other target cell to transmit a nerve impulse.

Receptor: A molecule or proton of a molecule with which a hormone, neurotransmitter, or other biochemically active molecule interacts to initiate a response in a target cell.