The endocrine system consists of cells, tissues, and organs that secrete hormones critical to homeostasis. The body coordinates its functions through two major types of communication: neural and endocrine. Neural communication includes both electrical and chemical signaling between neurons and target cells. Endocrine communication involves chemical signaling via the release of hormones into the extracellular fluid. From there, hormones diffuse into the bloodstream and may travel to distant body regions, where they elicit a response in target cells. Endocrine glands are ductless glands that secrete hormones. Many organs of the body with other primary functions—such as the heart, stomach, and kidneys—also have hormone-secreting cells.
autocrine
chemical signal that elicits a response in the same cell that secreted it
endocrine gland
tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion
endocrine system
cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes
exocrine system
cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts
hormone
secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body
paracrine
chemical signal that elicits a response in neighboring cells; also called paracrine factor
Visit this link to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. What is the secondary messenger made by adenylyl cyclase during the activation of liver cells by epinephrine?
cAMP
1. Endocrine glands ________.
A) secrete hormones that travel through a duct to the target organs
B) release neurotransmitters into the synaptic cleft
C) secrete chemical messengers that travel in the bloodstream
D) include sebaceous glands and sweat glands
C
2. Chemical signaling that affects neighboring cells is called ________.
A) autocrine
B) paracrine
C) endocrine
D) neuron
B
1. Describe several main differences in the communication methods used by the endocrine system and the nervous system.
The endocrine system uses chemical signals called hormones to convey information from one part of the body to a distant part of the body. Hormones are released from the endocrine cell into the extracellular environment, but then travel in the bloodstream to target tissues. This communication and response can take seconds to days. In contrast, neurons transmit electrical signals along their axons. At the axon terminal, the electrical signal prompts the release of a chemical signal called a neurotransmitter that carries the message across the synaptic cleft to elicit a response in the neighboring cell. This method of communication is nearly instantaneous, of very brief duration, and is highly specific.
2. Compare and contrast endocrine and exocrine glands.
Endocrine glands are ductless. They release their secretion into the surrounding fluid, from which it enters the bloodstream or lymph to travel to distant cells. Moreover, the secretions of endocrine glands are hormones. Exocrine glands release their secretions through a duct that delivers the secretion to the target location. Moreover, the secretions of exocrine glands are not hormones, but compounds that have an immediate physiologic function. For example, pancreatic juice contains enzymes that help digest food.
3. True or false: Neurotransmitters are a special class of paracrines. Explain your answer.
True. Neurotransmitters can be classified as paracrines because, upon their release from a neuron’s axon terminals, they travel across a microscopically small cleft to exert their effect on a nearby neuron or muscle cell.