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Maintaining Homeostasis
Maintaining Homeostasis
The Endocrine System overlaps with the Nervous System in transmitting regulatory signals throughout the body. While the CNS and PNS utilize neuronal cells to send electrical and chemical signals, endocrine cells release hormones into the bloodstream, allowing for more long-term physiological changes.
Hormones
Hormones
Hormones often begin a signaling pathway following their release. They target a specific endocrine gland, and interact with receptors on endocrine cells to cause a physiological response within the body. Hormones fall into three classes: polypeptides, steroids, and amines. Water-soluble hormones (polypeptides and most amines) are secreted by axocytosis and bind to extracellular receptors, initiaing a signal transdcution. Lipid-soluble hormones (steroids) are able to diffuse across cell membranes.
Posterior Pituitary
Posterior Pituitary
Stores and secretes hormones that are made in the hypothalamus, specifically antidiuretic hormone (ADH) and oxytocin.
Hypothalamus
Hypothalamus
Receives information from nerves throughout the body and initiates the right neuroendocrine signals.
Anterior Pituitary
Anterior Pituitary
Produces and release hormones under the regulation of the hypothalamus, controlling more diverse endocrine processes.
Important Hormones in the Marine Iguana
Important Hormones in the Marine Iguana
Testosterone: Produced in the gonads and found in much higher levels in male marine iguanas, as it stimulates the development of male secondary sex characterizes. Produced by the ovaries in female marine iguanas, testosterone levels in females rise significantly and reach a maximum level during mating season when aggression is most common. Testosterone levels in females also rise significantly during the nesting stage, when female to female aggression is common.
Estradiol: A metabolite of testosterone, estradiol promotes aggression in female reptiles.
Progesterone: Produced in the gonads and found in much higher levels in female marine iguanas, this hormone stimulates the development of female secondary sex characteristics. Progesterone may influence aggression in some instances of female behavior but can also suppress it.
Corticosterone: Suppresses female aggression in marine iguanas. Levels are lower during mating season than in nesting season.
Rubenstein and Wikelski 2005
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