Endocrine system Complete Exam Study Guide_ Guaranteed Success 2023 latest

Endocrine system - An animal hormone is a chemical signal that is secreted into the extracellular fluid, circulates in the blood or hemolymph, and communicates regulatory messages within the body. ○ A hormone may reach all parts of the body, but only specific target cells have the receptors that enable a response. ○ A given hormone traveling in the bloodstream elicits specific responses— such as a change in metabolism—only from its target cells while other cells are unaffected. - Chemical signaling by hormones is the function of the endocrine system, one of two basic systems for communication and regulation throughout the body. - The other major communication and control system is the nervous system, a network of specialized cells called neurons that transmit signals along dedicated pathways. - Hormones secreted by endocrine cells regulate reproduction, development, energy metabolism, growth, and behavior. - Because signaling by neurons can regulate the release of hormones, the nervous and endocrine systems often overlap in function. - Hormones convey information via the bloodstream to target cells throughout the body. - Other chemical signals—local regulators—transmit information to target cells near the secreting cells. - Pheromones carry messages to different individuals of a species. Intercellular Communication Communication between animal cells via secreted signals is often classified by two criteria: 1. The type of secreting cell 2. The route taken by the signal in reaching its target. Endocrine Signaling In endocrine signaling, hormones secreted into extracellular fluid by endocrine cells reach target cells via the bloodstream (or hemolymph). - One function of endocrine signaling is to maintain homeostasis. Hormones regulate properties that include blood pressure and volume, energy metabolism and allocation, and solute concentrations in body fluids. Endocrine signaling also mediates responses to environmental stimuli, regulates growth and development, and triggers physical and behavioral changes underlying sexual maturity and reproduction. Paracrine and Autocrine Signaling - Many types of cells produce and secrete local regulators, molecules that act over short distances and reach their target cells solely by diffusion. Once secreted, local regulators act on their target cells within seconds or even milliseconds. - Local regulators include cytokines, which enable communication between immune cells and growth factors, which promote the growth, division, and development of many types of cells. - Depending on the target cell, signaling by local regulators can be either paracrine or autocrine. • In paracrine signaling (from the Greek para, to one side of), target cells lie near the secreting cell. • In autocrine signaling (from the Greek auto, self), the secreting cells themselves are the target cells. - Paracrine and autocrine signaling play roles in many physiological processes, including blood pressure regulation, nervous system function, and reproduction. - Local regulators that mediate such signaling include the prostaglandins, so named because they were first discovered in prostate gland secretions that contribute to semen. • In the reproductive tract of a female, prostaglandins introduced in semen stimulate the smooth muscles of the uterine wall to contract, helping sperm reach an egg. At the onset of childbirth, prostaglandins produced by the placenta cause the uterine muscles to become more excitable, helping to induce labor. • Prostaglandins also act in the immune system, promoting inflammation and the sensation of pain in response to injury. That is why drugs that block prostaglandin synthesis, such as aspirin and ibuprofen, have both anti-inflammatory and pain-relieving effects. • Prostaglandins also help regulate the aggregation of platelets, one step in the formation of blood clots. Because blood clots in vessels that supply the heart can block blood flow, causing a heart attack, some physicians recommend that people at risk for a heart attack take aspirin on a regular basis. Synaptic and Neuroendocrine Signaling - Secreted molecules are crucial for two types of signaling by neurons. • In synaptic signaling, neurons form specialized junctions called synapses with target cells, such as other neurons and muscle cells. At most synapses, neurons secrete molecules called neurotransmitters that diffuse a very short distance and bind to receptors on the target cells. Neurotransmitters are central to sensation, memory, cognition, and movement. • In neuroendocrine signaling, specialized neurons called neurosecretory cells secrete neurohormones, which diffuse from nerve cell endings into the bloodstream. One example of a neurohormone is antidiuretic hormone, which is essential to kidney function and water balance. Many neurohormones function in the regulation of endocrine signaling. Signaling by Pheromones - Not all secreted signaling molecules act within the body. Members of a particular animal species sometimes communicate with each other via pheromones, chemicals that are released into the external environment. • For example, when a foraging ant discovers a new food source, it marks its path back to the nest with a pheromone. Ants also use pheromones for guidance when a colony migrates to a new location. - Pheromones serve a wide range of functions that include defining territories, warning of predators, and attracting potential mates. Classes of Local Regulators and Hormones Classes of Local Regulators • The prostaglandins, are modified fatty acids. • Many other local reg