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Questions and Answers
Which type of hormone cannot pass through the cell membrane?
How do steroid hormones reach target cells?
Which of the following is a function of hormones?
What role does the hypothalamus play in the endocrine system?
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Which hormone showcases a quick onset time due to its peptide nature?
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Which statement about nerve signals is true?
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What distinguishes tropic hormones from others?
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Which gland is primarily responsible for the secretion of thyroid-stimulating hormone (TSH)?
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Hormones secreted by the endocrine glands travel directly into what?
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What is a common characteristic of peptide hormones?
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Which organ does not have cells with an endocrine function?
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Which substance accumulates in areas of tissue disturbance or injury?
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When a hormone binds to a receptor, which of the following does NOT occur?
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What happens when an amino-acid-based hormone acts on a target cell?
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If cyclic AMP acts as a 'second messenger,' what would be the 'first messenger'?
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Which is an example of an amino-acid-based hormone?
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Which of the following statements is TRUE regarding amino-acid-based hormones?
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What characteristic of steroid hormones allows them to pass through cell membranes?
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Which organ is responsible for removing hormones from the blood and breaking them down?
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Why is the pituitary gland no longer considered the 'master gland' of the endocrine system?
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Study Notes
Endocrine System
- The endocrine system is made up of glands that secrete hormones directly into the blood.
Hormones
- Hormones are chemical substances secreted directly into the blood by ductless glands.
- They can be classified into two groups:
- Peptide Hormones: Formed from proteins, have a quick onset time, cannot pass cell membrane, and are hydrophilic. Examples include insulin and growth hormone.
- Steroid Hormones: Formed from fats, can enter the cell membrane, are hydrophilic, and have a slower onset than peptide hormones. Examples include estrogen, progesterone, and testosterone.
Tropic Hormones
- Tropic hormones are hormones that stimulate other glands to release hormones.
- They have a far-reaching effect because they can trigger a cascade of hormonal release.
- Example: The anterior pituitary releases thyroid-stimulating hormone (TSH), which then stimulates the thyroid gland to produce thyroxine.
Hypothalamus
- The hypothalamus acts as a bridge between the endocrine and nervous systems.
- It functions both as part of the nervous system and as an endocrine gland:
- Nervous System Function: During stress, the hypothalamus sends electrical signals to the adrenal gland to release adrenaline.
- Endocrine Gland Function: It produces oxytocin and antidiuretic hormone, which are stored in the posterior pituitary.
- Regulatory Function: The hypothalamus also regulates temperature, hunger, thirst, and coughing.
Pituitary Gland
- The pituitary gland releases several hormones, including FSH and LH.
Functions of Hormones
- Hormones control the body's response to stress.
- They regulate metabolism and growth and development.
- Hormones do not trigger rapid, short-term responses; this function is carried out by the nervous system.
Hormone Action
- For a hormone to work, it must reach its target cells, be produced and released, and enter the bloodstream or fluids around cells.
- Hormones do not travel through ducts.
- Hormones bind to receptor proteins on the surface of target cells, triggering a cascade of events that ultimately lead to the desired change in cell function.
Nervous System vs. Endocrine System
- Nervous signals are much faster than hormonal messages but have shorter-lasting effects.
- Nerve transmissions reach many cells at once, while hormonal messages can be more targeted.
Endocrine Glands
- All endocrine glands secrete hormones directly into the bloodstream or the fluid around cells.
- Not all hormones affect every cell near the gland.
- Hormones are not always lipid molecules.
Organs with Endocrine Function
- The brain, stomach, small intestine, and lungs all contain cells that have an endocrine function.
Prostaglandins
- Prostaglandins are hormone-like substances that accumulate in areas of tissue disturbance or injury.
Hormone Binding
- When a hormone binds to a receptor, the receptor protein changes shape, which then triggers a series of chemical reactions inside the cell, ultimately leading to a change in cell activity.
- Hormones do not enter the cell by endocytosis.
Amino-Acid-Based Hormones
- Amino-acid-based hormones bind to receptors in the cell membrane, triggering the activation of a second messenger like cyclic AMP.
- They do not pass through the cell membrane; they activate a chain reaction to cause a change inside the cell.
Steroid Hormones
- Steroid hormones are fat-soluble and can pass through the cell membranes of their target cells.
- They are not always bound to fat receptor molecules.
- They can influence gene expression in target cells.
Hormone Regulation
- The liver plays a role in feedback by removing hormones from the blood and breaking them down.
Anterior Pituitary Gland
- The anterior pituitary gland secretes several tropins, including follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH).
- It does not produce antidiuretic hormone (ADH).
Pituitary Gland Regulation
- Hormones produced by the pituitary gland are regulated by secretions from the hypothalamus.
- They control the activity of other endocrine glands and affect many organs and tissues.
- The pituitary gland does not primarily regulate metabolic rate; this is primarily regulated by the thyroid gland.
Hypothalamus-Pituitary Relationship
- The hypothalamus acts as the regulatory center of the endocrine system, controlling the activity of the pituitary gland.
- It does not control other glands by acting through the pituitary gland; instead, it directly controls other glands or indirectly through the pituitary.
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