AP Biology—Unit 9

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Definition: maintaining a stable internal environment.
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Fluctuates within the bounds of “normal.”
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Feedback mechanisms to control homeostasis

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Positive Feedback—an increase in a variable triggers a mechanism that amplifies the variable
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Negative Feedback—an increase in a variable triggers a response that counteracts the initial change

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Thermoregulation—regulation of body temperature
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By what feedback loop do animals regulate body temperature, positive or negative?
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What are some adaptations that help organisms regulate their temperature?

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Define the following types of
INTERCELLULAR COMMUNICATION:
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Endocrine Signaling
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Paracrine
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Synaptic

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Endocrine System—sum of all the cells and tissues that secrete hormones
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Endocrine Glands—secrete hormones directly into body fluids. They do not have ducts.
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Hormones—chemical signals that cause a response in a target cell.
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Water-Soluble (Hydrophilic)—cannot go through plasma membrane, so bind to receptor proteins
Lipid-Soluble (Hydrophobic)—diffuse through plasma membrane and bind to intracellular receptor

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Both an Endocrine and Exocrine gland
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Endocrine—_________________________________
(i.e. pituitary, thyroid, etc.)
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Exocrine—secretes “stuff” that goes into a duct
(i.e. liver, salivary gland)

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Exocrine—Secretes Pancreatic Juice through the
Pancreatic Duct to the Small Intestines
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Pancreatic Juice Contains—
 Bicarbonate—buffers stomach acid
 Digestive Enzymes

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Endocrine—regulate blood glucose by negative feedback
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Beta cells—make Insulin
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Insulin tells cells to take in sugar
Increased insulin causes decrease in blood sugar
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Alpha Cells—make Glucagon
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Glucagon tells cells to convert glycogen to glucose
Increased glucagon causes increase in blood sugar

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Steps:
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Eat—Blood sugar increases
Insulin increases—cells take in glucose which decreases blood sugar
Liver converts excess glucose to glycogen
Blood sugar decreases, and so insulin decreases
As blood sugar begins to dip, glucagon increases and tells liver to convert glycogen to glucose
Blood glucose increases

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Homeostasis: Regulating Blood Sugar Movie
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Draw a diagram of the feedback system that controls blood sugar levels!

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Prostagladins (local regulators) and Estradiol and Oxytocin (hormones) regulate the contractions of the uterus
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Oxytocin forms a positive feedback loop— uterine contractions stimulate the secretion of more oxytocin

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Kidneys—filter blood; maintain water balance
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Parts of Nephron—functional unit of kidney
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Glomerulus / Bowman’s Capsule
Proximal & Distal Convoluted Tubules
Loop of Henle
Collecting Duct
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Processes
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Filtration
Reabsorption
Secretion
Excretion

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Antidiuretic Hormone (ADH)
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Produced by hypothalamus
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Receptor cells in hypothalamus sense osmolarity in the blood (more solutes/salts = higher osmolarity)
If osmolarity increases, ADH is released
ADH binds to receptor proteins on the cells in the collecting duct of nephron
This increases permeability of these cells for water— causing water to be reabsorbed into the blood
Result = more water in blood = decrease in osmolarity

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Aldosterone
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Produced in Adrenal Glands
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Stimulated by cascade of events between renin and angiotensin when blood pressure and / or blood volume decreases in artioles that supply blood to glomerulus
Aldosterone acts on distal tubule and collecting duct
Increases reabsorption of Na + and water = increase in blood volume = increase in blood pressure