Endocrine Glands Flashcards
endocrine system
comprised of ductless glands that release chemicals into the blood to regulate body functions
hormone
chemical messenger that is transported indiscriminately via the bloodstream to act on distant target cells
- are specific and will only activate cells or tissues that possess the appropriate target receptor
where do endocrine glands secrete their product
secrete products directly into the bloodstream, rather than through a duct
steroid horomones
lipophilic (fat-loving) – meaning they can freely diffuse across the plasma membrane of a cell
- bind to receptors in either the cytoplasm or nucleus of the target cell, to form an active receptor-hormone complex
- activated complex will move into the nucleus and bind directly to DNA, acting as a transcription factor for gene expression
- Examples of steroid hormones include those produced by the gonads
peptide hormones
hydrophilic and lipophobic (fat-hating) – meaning they cannot freely cross the plasma membrane
- bind to receptors on the surface of the cell, which are typically coupled to internally anchored proteins
- receptor complex activates a series of intracellular molecules called second messengers, which initiate cell activity
- process is called signal transduction, because the external signal (hormone) is transduced via internal intermediaries
- Peptide hormones include insulin, glucagon, leptin, ADH and oxytocin
hypothalamus
section of the brain that links the nervous and endocrine systems in order to maintain homeostasis
- receives information from nerves throughout the body and other parts of the brain and initiates endocrine responses
- secretes neurochemicals (called releasing factors) into a portal system which target the anterior lobe of the pituitary gland
- secretes hormones directly into the blood via neurosecretory cells that extend into the posterior pituitary lobe
pituitary gland
lies adjacent to the hypothalamus and is in direct contact due to a portal blood system. anterior and posterior
anterior lobe
hypothalamus produces releasing factors, which are released into portal vessels by neurosecretory cells
- The releasing factors cause endocrine cells in the anterior pituitary to release specific hormones into the bloodstream
- An example of a releasing factor is GnRH, which triggers the release of LH and FSH from the anterior pituitary
posterior lobe
releases hormones produced by the hypothalamus itself
- These neurosecretory cells extend into the posterior lobe from the hypothalamus and release hormones into the blood
what do pituitary hormones control
- metabolism
- adult development
- reproduction
- growth
- equilibrium
somatotropin (growth hormone)
anabolic peptide hormone that stimulates growth
- acts directly to reduce the formation of adipose cells
- acts indirectly via insulin growth factor (IGF) – produced by the liver – to increase muscle mass and bone size
lactation
production and secretion of milk by maternal mammary glands following growth
prolactin
responsible for the development of the mammary glands and the production of milk
- secreted by the anterior pituitary in response to the release of PRH (prolactin releasing hormone) from the hypothalamus
- effects of prolactin are inhibited by progesterone, which prevents milk production from occurring prior to birth
oxytocin
responsible for the release of milk from the mammary glands
- It is produced in the hypothalamus and secreted by neurosecretory cells that extend into the posterior pituitary
- Oxytocin release is triggered by stimulation of sensory receptors in the breast tissue by the suckling infant
- This creates a positive feedback loop that will result in continuous oxytocin secretion until the infant stops feeding
