国外动物学34.PPT
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1、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 Int
2、ernal 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
3、 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
4、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, sal
5、ivary 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:
6、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 m
7、otor 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” hormones that travel to the pituitary gland. Each releasing hormone stimulates the pituitary to release a corre
8、sponding hormone which travels to an endocrine gland and causes it to start producing a particular endocrine hormone.,Membrane-Bound Receptors,Many hormones are too large, or too polar, to pass through plasma membranes. Bind to transmembrane proteins that act as receptor sites on target cell membran
9、es. Hormone is first messenger. Causes activation of a second messenger in the cytoplasm. cAMP,Nuclear Receptors,Steroid hormones are lipid soluble molecules that bind to hormone receptors in the cytoplasm of the target cell. Site of activity is the nucleus. Steroids are manufactured from cholestero
10、l. Estrogen, progesterone, testosterone, cortisol.,Nuclear Receptors,Thyroid hormones and insect-molting hormone (ecdysone) also act through nuclear receptors. Binds to transmembrane protein that uses ATP to move it into the cell.,Control Pathways and Feedback Loops,A common feature of control pathw
11、ays is a feedback loop connecting the response to the initial stimulus. Negative feedback regulates many hormonal pathways involved in homeostasis.,Invertebrate Hormones,Ecdysone regulates molting in insects. Juvenile hormone favors the retention of juvenile characteristics.,The Pituitary,The pituit
12、ary gland is located below the hypothalamus. Nine major hormones are produced here. These hormones act primarily to influence other endocrine glands.,The Pituitary,The posterior lobe of the pituitary regulates water conservation, milk letdown, and uterine contraction in women. The anterior lobe regu
13、lates the other endocrine glands.,The Anterior Pituitary,Thyroid stimulating hormone (TSH) stimulates the thyroid gland to produce thyroxine which stimulates oxidative respiration. Luteinizing hormone (LH) plays an important role in the menstrual cycle. It also stimulates the production of testoster
14、one in males.,The Anterior Pituitary,Follicle-stimulating hormone (FSH) plays an important role in the menstrual cycle. In males, it causes the testes to produce a hormone that regulates sperm production. Adrenocorticotropic hormone (ACTH) stimulates the adrenal gland to produce steroid hormones. So
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