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Front
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Back
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Things to Remember That We Already Know
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- Homeostasis
- Osmosis
- Osmolarity
- Regulators
- Conformers
- Solutes
- Ions
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Saltwater-Freshwater Transitions
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- Some fish migrate between saltwater & freshwater (diadromous fish)
- Catadromous: Migrating down rivers to the sea to spawn
- Live in freshwater, migrate to saltwater to spawn (i.e., eels)
- Live in saltwater, migrate to freshwater to spawn (i.e., salmon)
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Ionic & Osmotic Challenges
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- Marine environments: Animals tend to gain salts & lose water
- Freshwater environments: Animals tend to lose salts & gain water
- Terrestrial environments: Animals tend to lose water
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- Organisms are mostly water (70-80%)
- Chemical reactions take place in water
- Salt balance equally important
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- Isotonic solutions: Cells retain their normal size & shape in isotonic solutions (same solute/water concentration as inside cells; water moves in & out)
- Hypertonic solutions: Cells lose water by osmosis & shrink in a hypertonic solution (contains a higher concentration of solutes than are present inside the cells)
- Hypotonic solutions: Cells take on water by osmosis until they become bloated & burst (lyse) in a hypotonic solution (contains a lower concentration of solutes than are present in cells)
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Sources of Water & Solutes
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- Water
- Dietary water
- Water preformed in plant & animal tissue
- Metabolic water
- Water generated as result of oxidative phosphorylation
- Drinking
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Animals use different combinations of tissues to control ion & water balance in various internal & external environments: - Osmotic regulation
- Ionic regulation
- Nitrogen excretion
- Nitrogen: Constituent of organic compounds found in all living tissues
- Example: Urea (a nitrogenous compound) is a waste product made when liver breaks down protein
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Ionic & Osmotic Regulation
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- Strategies to meet osmotic challenges
- Osmoconformer: Similar internal & external osmolarity (i.e., marine invertebrates)
- Osmoregulator: Osmolarity constant regardless of external environment (i.e., most vertebrates)
- Strategies to meet ionic challenges
- Ionoconformer: Exert little control over ion profile within extracellular space (i.e., marine animals)
- Ionoregulator: Control ion profile of extracellular space (i.e., most vertebrates)
- Ability to cope w/ external salinities
- Stenohaline: Can tolerate only narrow range
- Euryhaline: Can tolerate wide range
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- Epithelial tissues form boundary between animal & environment
- External surfaces (i.e., skin)
- Internalized surfaces (i.e., lumen of digestive & excretory systems)
- Digestive epithelia
- Water & salts from drinking & food transported across digestive epithelium
- Absorbed water & salts enter blood
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Integument
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- Integument: A tough outer protective layer in animals or plants
- Animals change flux of water across body surface by mediating permeability of integument
- Aquaporin proteins increase water permeability 100-fold
- Typically, animals need to reduce water flux
- Cover external surfaces w/ layer of hydrophobic molecules
- Mucus - A slimy substance, typically not miscible w/ water, secreted by mucous membranes & glands for lubrication, protection, etc.
- Keratin - A fibrous protein forming the main structural constituent of hair, feathers, hoofs, claws, horns, etc.
- Chitin - A fibrous substance consisting of polysaccharides & forming the major constituent in the exoskeleton of arthropods & the cell walls of fungi
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Features of Transport Epithelia
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- Solutes selectively transported across membrane via membrane transporters
- Epithelial cells use 2 main routes of transport
- Transcellular transport: Movement through the cell across membranes
- Paracellular transport: Movement between cells
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Nitrogen Excretion
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- Ammonia produced during amino acid breakdown is toxic & must be excreted
- Ammonia nitrogen excreted in 3 forms:
- Ammonia (ammonioteles)
- Uric acid (uricoteles)
- Urea (ureoteles)
- Type of nitrogen compound excreted is related to the animal's environment
- Aquatic animals usually excrete ammonia
- Terrestrial animals usually excrete urea or uric acid
- Many animals change mode of nitrogen excretion in response to water availability
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The kidneys play several important roles in maintaining homeostasis: - Maintaining the proper blood volume
- Maintaining the proper ion balance
- Removing nitrogenous wastes from the blood
Vertebrate kidneys have 6 roles in homeostasis: - Ion balance
- Osmotic balance
- Blood pressure
- pH balance
- Excretion of metabolic wastes & toxins
- Hormone production
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- The kidney primarily accomplishes its tasks by filtering impurities, metabolic wastes, & salt from the blood
- Mammalian kidney has 2 layers
- Outer cortex
- Inner medulla
- Urine leaves kidney via ureter
- Ureters empty into urinary bladder
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The Nephron
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- Functional unit of the kidney
- There are ~1,000,000 nephrons in each human kidney
- Produces urine in the process of removing waste & excess substances from the blood
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