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What are the two criteria that classify the ways that signals are transmitted between animal cells?
- type of secreting cell
- route taken by the signal in reaching its target
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Endocrine Signaling
cell produces signal, which travels through the blood, makes it to target cells, and those with receptor can respond
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Paracrine Signaling
signals released to neighboring cells, only those with receptors can respond
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Neuroendocrine Signaling
specialized neurosecretory cells secrete neurohormones that travel to target cells via the bloodstream
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Autocrine Signaling
the same cell that produces the signal also has a receptor for that signal
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When is paracrine signaling important?
when tissues close to each other need to interact
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Example of Autocrine Signaling
tumor, produces signal for the tumor itself to keep growing
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Main difference between Neuroendocrine & Endocrine/Paracrine Signaling?
- Neuroendocrine- cell that secretes signal is a neuron
- In endocrine/paracrine- regular cell secretes the signal
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What are pheromones?
chemicals that allow members of the same species to send signals to each other
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Functions of pheromones
- marking trails leading to food
- defining territories
- warning of predators
- attracting potential mates
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Endocrine vs. Exocrine glands
- endocrine- secretes stuff inside the body, secrete hormones directly into surrounding fluid
- exocrine- secretes stuff outside the body, have ducts which secrete substances onto body surfaces or into cavities
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The 3 classes of hormones
- polypeptides
- amines
- steroid hormones
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Water-Soluble Hormones vs. Lipid-Soluble Hormones
- Water — can easily travel through bloodstream but has harder time entering/exiting the membrane
- Lipid — no problem exiting the membrane of producing cel, but cannot easily travel through the blood by itself
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Pathway of a Lipid-Soluble Hormone
- Leaves membrane
- Binds to carrier protein in the blood to travel through bloodstream
- Can easily cross membrane when it reaches target cell
- Receptor is more likely to be inside (intracellular) because it can cross the membrane
- Receptor usually tells the cell what to do because it is already inside
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Pathway of a Water-Soluble Hormone
- actively secreted through a vesicle
- easily travels through bloodstream on its own
- stays outside membrane because it cannot pass through
- needs a receptor on the membrane
- Receptor activates signal transduction pathway to deliver signal to the nucleus
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Negative Feedback Loop
inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity
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Positive Feedback Loop
reinforces a stimulus to produce an even greater response
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What role does the hypothalamus play in endocrine regulation
receives info from the nervous system and initiates response through the endocrine system
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Where is the pituitary gland located?
Attached to the hypothalamus
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What are the two hormones released by the posterior pituitary?
- Oxytocin- regulates milk secretion by the mammary glands
- Antidiuretic hormone- regulates physiology and behavior
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What does the ADH target?
kidney tubules
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What type of signaling does the Antidiuretic hormone employ?
Neuroendocrine signaling because neuron releases information into the bloodstream
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How does anterior pituitary work?
- neurosecretory cells of the hypothalamus send signals to anterior pituitary
- Which travels through bloodstream for some distance and target the anterior pituitary, which responds by making more hormones
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What is a hormone cascade pathway?
a hormone can stimulate the release of a series of other hormones, the last of which activates a non endocrine target cell
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Overview of thyroid hormone being released through a hormone cascade pathway
Hypothalamus secretes a hormone, which causes anterior pituitary to produce another hormone, which causes thyroid gland to make another hormone and fix the problem
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Disorders of thyroid function?
- Hypothyroidism: too little thyroid function, can produce symptoms such as weight gain, lethargy, cold intolerance
- Hyperthyroidism: excessive production of thyroid hormone, can lead to high temperate, sweating, weight loss, irritability, and high blood pressure
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How can malnutrition alter thyroid function?
insufficient dietary iodine leads to an enlarged thyroid gland (goiter)
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Where are the adrenal glands located?
adjacent to the kidneys
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Each adrenal gland consists of two glands:
- adrenal medulla (inner portion)
- adrenal cortex (outer portion)
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What does the adrenal medulla secrete?
- (catecholamines)
- epinephrine (adrenaline)
- norepinephrine (noradrenaline)
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What are the catecholamines secreted in response to? & what do they mediate?
- in response to stress-activated impulses from the nervous system
- They mediate various fight or flight responses
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How is adrenal medulla helpful in fight-or-flight response?
- Secretes adrenaline
- which generates sugar, increasing blood pressure and increasing metabolic rate
- gets you ready to make response
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What do epinephrine and norepinephrine do? (3)
- trigger release of glucose and fatty acids
- increase oxygen delivery to body cells
- direct blood towards heart, brain, and muscles
- direct blood away from skin, digestive system, and kidneys
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The release of epinephrine and norepinephrine occurs in response to ________
involuntary nerve signals
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What does the adrenal cortex release?
a family of steroids called corticosteroids
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Humans produce two types of corticosteroids
glucocorticoids and mineralocorticoids
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What are corticosteroids triggered by?
by a hormone cascade pathway via the hypothalamus and anterior pituitary
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What do glucocorticoids do? (ex.)
- influence glucose metabolism and the immune system
- example: cortisol
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What do mineralocorticoids do? (ex.)
- affect salt and water balance
- example: aldosterone
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What does aldosterone control?
water and solute balance
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Long-Term Stress Response
Hypothalamus releases hormone (ACTH), goes through blood, targets adrenal gland, which secretes mineralocorticoids and glucocorticoids that can respond to the stress
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Short-term Stress Response
Hypothalamus signals adrenal medulla through nerve impulses, which then in turn secretes epinephrine and norepinephrine
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How does negative feedback loop come into play in diabetes mellitus?
- Negative feedback loop is broke
- blood glucose level doesn’t drop, it stays high
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Why is the urine sweet in diabetes mellitus?
because blood glucose levels are very high and glucose makes the urine sweet
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Sets of hormones from the hypothalamus, the anterior pituitary, and a target endocrine gland are often organized into a
hormone cascade pathway.
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The anterior pituitary hormones in these hormone cascade pathways are called
tropic hormones
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Function of thyroid hormone
- regulates bioenergetics
- helps maintain normal blood pressure, heart rate, and muscle tone
- and regulates digestive and reproductive functions.
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Describe the process of thyroid regulation
- If the level of thyroid hormone in the blood drops, the hypothalamus responds by initiating a hormone cascade pathway
- The hypothalamus secretes thyrotropin-releasing hormone (TRH), causing the anterior pituitary to secrete a tropic hormone known as either thyroid-stimulating hormone (TSH) or thyrotropin
- TSH stimulates release of thyroid hormone by the thyroid gland, an organ in the neck consisting of two lobes on the ventral surface of the trachea.
- As thyroid hormone accumulates, it increases metabolic rate, while also initiating negative feedback that prevents its overproduction.
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