endocrine signaling

Examples of endocrine signaling in the following topics:

• Forms of Signaling

  • The major types of signaling mechanisms that occur in multicellular organisms are paracrine, endocrine, autocrine, and direct signaling.
  • There are four categories of chemical signaling found in multicellular organisms: paracrine signaling, endocrine signaling, autocrine signaling, and direct signaling across gap junctions .
  • Signals from distant cells are called endocrine signals; they originate from endocrine cells.
  • In chemical signaling, a cell may target itself (autocrine signaling), a cell connected by gap junctions, a nearby cell (paracrine signaling), or a distant cell (endocrine signaling).
  • Paracrine signaling acts on nearby cells, endocrine signaling uses the circulatory system to transport ligands, and autocrine signaling acts on the signaling cell.

• Hormone Functions

  • The endocrine system plays a role in growth, metabolism, and other processes by releasing hormones into the blood.
  • Target cells, those having a receptor for a signal, respond to a hormone when they express a specific receptor for that hormone.
  • Different tissue types may also respond differently to the same hormonal signal.
  • In humans, common endocrine system diseases include thyroid disease and diabetes mellitus.
  • In organisms that undergo metamorphosis, the process is controlled by the endocrine system.

• Hypothalamic-Pituitary Axis

  • The endocrine system uses chemical signals to communicate and regulate the body's physiology.
  • The collection of these glands makes up the endocrine system.
  • The hypothalamus in vertebrates integrates the endocrine and nervous systems.
  • The posterior pituitary receives signals via neurosecretory cells to release hormones produced by the hypothalamus.
  • They are released into the circulatory system via neural signaling from the hypothalamus.

• Brain: Midbrain and Brain Stem

  • The hypothalamus controls the endocrine system by sending signals to the pituitary gland, a pea-sized endocrine gland that releases several different hormones that affect other glands as well as other cells.
  • Motor and sensory neurons extend through the brainstem, allowing for the relay of signals between the brain and spinal cord.
  • The brainstem coordinates motor control signals sent from the brain to the body.

• Humoral, Hormonal, and Neural Stimuli

  • Insulin causes blood glucose levels to drop, which signals the pancreas to stop producing insulin.
  • A number of endocrine glands release hormones when stimulated by hormones released by other endocrine glands.
  • The anterior pituitary, in turn, releases hormones that regulate hormone production by other endocrine glands.
  • In some cases, the nervous system directly stimulates endocrine glands to release hormones, which is referred to as neural stimuli.
  • Here, neuronal signaling from the sympathetic nervous system directly stimulates the adrenal medulla to release the hormones epinephrine and norepinephrine in response to stress.

• Organs with Secondary Endocrine Functions

  • Several organs with specialized non-endocrine functions possess endocrine roles, such as hormone production and release.
  • There are several organs whose primary functions are non-endocrine, but that also possess endocrine functions.
  • The heart possesses endocrine cells in the walls of the atria that are specialized cardiac muscle cells.
  • The endocrine cells are located in the mucus of the GI tract throughout the stomach and small intestine.
  • While the adrenal glands associated with the kidneys are major endocrine glands, the kidneys themselves also possess endocrine function.

• Control of Homeostasis

  • The receptors sense changes in the environment, sending a signal to the control center (in most cases, the brain), which, in turn, generates a response that is signaled to an effector.
  • Homeostasis is controlled by the nervous and endocrine systems in mammals.
  • Specialized cells in the pancreas (part of the endocrine system) sense the increase, releasing the hormone insulin.
  • The hormone oxytocin, made by the endocrine system, stimulates the contraction of the uterus.

• Parathyroid Glands

  • The parathyroid glands are small endocrine glands that produce parathyroid hormone.
  • It also signals the kidneys to reabsorb more of this mineral, transporting it into the blood.
  • PTH can also signal the small intestine to absorb calcium by transporting it from the diet into the blood.

• Intracellular Hormone Receptors

  • Lipid-derived (soluble) hormones such as steroid hormones diffuse across the lipid bilayer membranes of the endocrine cell.
  • The cell signaling pathways induced by the steroid hormones regulate specific genes within the cell's DNA.

• Pancreas

  • It contains both exocrine cells that excrete digestive enzymes and endocrine cells that release hormones.
  • It is sometimes referred to as a heterocrine gland because it has both endocrine and exocrine functions.
  • The endocrine cells of the pancreas form clusters called pancreatic islets or the islets of Langerhans .
  • The islets of Langerhans are clusters of endocrine cells found in the pancreas; they stain lighter than surrounding cells.
  • It is both an endocrine and exocrine gland.