Module 13 - The Endocrine System

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What does the endocrine system consist of?
- glands that secrete chemicals (hormones) into the blood
- the hormones then travel throughout body to their target site to initate their effect
What are the major organs of the endocrine system?
- hypothalamus
- pituitary gland
- parathyroid glands (on dorsal aspect of thyroid gland)
- thyroid gland
- adrenal glands
- pancreas
- ovaries (female)
- testes (male)
What is the function of the endocrine system?
- maintenance of internal environment, adaptation to stress, control of growth and metabolism, and control of reproduction
How does the endocrine system contrast with the nervous system?
- actions are slower to take effect yet last longer and are more widespread throughout body
- it indirectly affects organs at a distance by secreting chemicals into body
What is a gland?
- a group of specialized cells that synthesize, store, and release hormones into blood
How do hormones work?
- they are released into the blood stream and circulate throught body to target cells that have receptors for hormone
- either stimulates or inhibits activity of cell
What are the three catagories of hormones based on chemical makeup?
- hormones derived from amino acid Tyrosine (thyroxine, triiodothyronine), secreted from thyroid gland
- hormones derived from proteins: calcitonin, parathyroid hormone, pituitary and pancreatic hormones, hormones from hypothalamus
- steroid hormones: cortisol, aldosterone, estrogen, progesterone, testosterone - all derived from cholesterol
How are protein hormones carried in the blood? How do they act on target cells?
- they circulate freely in blood but cannot diffuse through cell membrane (both because they are hydrophilic)
- receptors must be located on cell membrane of target cell
How are steroid and thyroid hormones carried in the blood? How do they act on target cells?
- they require a protein carrier to circulate blood and they diffuse easily through cell membrane (both because they are hydrophobic)
- receptors are located inside target cells
How are hormones secreted into the blood?
- in "pulses" by specific stimulus (neural or blood borne)
Are they present in large or small concentrations in the blood after being secreted?
- very small concentrations
What is a receptor?
- in or on a cell - it interacts with hormones in a particular way
- a specific hormone binds to a specific receptor
- the interaction triggers a response in the cell
What is a receptor?
- in or on a cell - it interacts with hormones in a particular way
- a specific hormone binds to a specific receptor
- the interaction triggers a response in the cell
What is a receptor?
- in or on a cell - it interacts with hormones in a particular way
- a specific hormone binds to a specific receptor
- the interaction triggers a response in the cell
Explain receptors for hydrophobic hormones.
- located in cytoplasm or nucleus
- hormone is released by carrier protein and then enters cell where it binds with its receptor
- new hormone/receptor complex will the bind to the DNA within the nucleus to eventually alter various activities of cell (increase or decrease production of proteins)