国外动物学34.PPT

Chemical Coordination Chapter 34 Hormones A hormone is a chemical signal that is secreted into the circulatory system and communicates regulatory messages within the body. Hormones may reach all parts of the body, but only certain types of cells, target cells, are equipped to respond. Systems of Internal Communication Animals have two systems of internal communication and regulation: The nervous system The endocrine system Systems of Internal Communication The nervous system conveys high-speed electrical signals along specialized cells called neurons. The endocrine system, made up of endocrine glands, secretes hormones that coordinate slower but longer-acting responses to stimuli. Hormones Advantages of using chemical messengers: Chemical molecules can spread to all tissues through the blood. Chemical signals can persist longer than electrical ones. Many different kinds of chemicals can act as hormones; different hormones can target different tissues. Glands Many hormones are secreted by ductless endocrine glands. Obtain raw materials from and secrete hormones directly into the bloodstream. Exocrine glands have ducts for discharging secretions onto a free surface. Sweat glands, salivary glands, enzyme-secreting glands in the digestive tract. Hormones Hormones convey information via the bloodstream to target cells throughout the body. Pheromones carry messages outside the body – to other individuals. Hormones Three major classes of molecules function as hormones in vertebrates: Proteins and peptides Amines derived from amino acids Steroids Hormones Signaling by any of these molecules involves three key events: Reception Signal transduction Response Hormones The hypothalamus regulates the neuroendocrine system, maintaining homeostasis in the body. The hypothalamus can use motor nerves to send short-lived electrical messages or hormones to send chemical messages with a longer duration. The Chain of Command The hypothalamus produces seven different “releasing” hormone