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among the most important wastes are what?
nitrogenous breakdown products of proteins and nucleic acids
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what do some animals convert ammonia (NH3) to prior to excretion?
less toxic compounds
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animals that excrete nitrogenous wastes as ammonia need a lot of what?
- water
- They release ammonia across the whole body surface or through gills
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The liver of mammals and most adult amphibians converts ammonia to less toxic what?
urea
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the circulatory system carries urea to where? from there it is excreted
to the kidneys
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excretion of urea requires what?
Conversion of ammonia to urea is energetically expensive; excretion of urea requires less water than ammonia
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Insects, land snails, and many reptiles, including birds, mainly excrete what?
uric acid
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uric acid is largely what in water and can be secreted as a what with little water loss
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Uric acid is more energetically expensive to produce than what?
urea
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The kinds of nitrogenous wastes excreted depend on what?
an animal’s evolutionary history and habitat
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The amount of nitrogenous waste is coupled to the animal’s what?
energy budget
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Excretory systems regulate solute movement between what and what?
internal fluids and the external environment
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Most excretory systems produce urine by refining a what?
filtrate derived from body fluids
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what are the key functions of most excretory systems?
- –Filtration
- –Reabsorption
- –Secretion
- –Excretion
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what is filtration?
pressure-filtering of body fluids
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what is reabsorption
reclaiming valuable solutes
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what is secretion?
adding toxins and other solutes from the body fluids to the filtrate
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what is excretion?
removing the filtrate from the system
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what is a protonephridium? (flatworm excretion)
a network of dead-end tubules connected to external openings
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what is a flame bulb? function? (flatworm excretion)
- The smallest branches of the network (protonephridium) are capped by a cellular unit
- These tubules excrete a dilute fluid and function in osmoregulation
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earthworms have what?
Each segment of an earthworm has a pair of open-ended metanephridia
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metanephridia consist of what?
consist of tubules that collect coelomic fluid and produce dilute urine for excretion
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Malpighian tubules do what?
- In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation
- Insects produce a relatively dry waste matter, an important adaptation to terrestrial life
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The mammalian excretory system centers on what?
paired kidneys
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where is the principle site of water balance and salt regulation in mammals?
in the kidneys
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each kidney is supplied with blood by a what and is drained by a what?
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Urine exits each kidney through a duct called the what?
ureter
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both ureters drain into a common what and urine is expelled through a what?
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what is a nephron?
the functional unit of the vertebrate kidney, consists of a single long tubule and a ball of capillaries called the glomerulus
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what is the Bowman's capsule?
Bowman’s capsule surrounds and receives filtrate from the glomerulus
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Filtration occurs as blood pressure forces fluid from the what in the glomerulus into the what of Bowman’s capsule (glomerular capsule)
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Filtration of small molecules is what?
Filtration of small molecules is nonselective
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The filtrate contains what 6 things?
salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules
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From Bowman’s capsule, the filtrate passes through three regions of the nephron
- the proximal tubule,
- the loop of Henle (ansa nephroni),
- and the distal tubule
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Fluid from several nephrons flows into a what duct, all of which lead to the what, which is drained by the ureter
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Cortical nephrons are confined to the what?
renal cortex
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juxtamedullary nephrons have what?
loops of Henle that descend into the renal medulla
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what takes place in the proximal tubule?
reabsorption of ions, water and nutrients
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molecules are transported actively and passively from the what into the interstitial fluid and then the capillaries?
- the filtrate
- some toxic materials are secreted into the filtrate and the filtrate volume decreases
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aquaporin proteins do what? (descending limb of the loop of henle)
form channels to allow reabsorption of water to continue
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the movement in aquaporin proteins is driven by the high what of the interstitial fluid, which is what to the filtrate?
- osmolarity
- hyperosmotic
- the filtrate becomes increasingly concentrated
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what does the distal tubule regulate?
- k+ and NaCl concentrations of body fluids
- the controlled movement of ions contributes to pH regulation
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the collecting duct carries what through the medulla to where?
- filtrate
- to the renal pelvis
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what happens in the collecting duct?
water is lost as well as some salt and urea and the filtrate becomes more concentrated
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urine is what to body fluids
hyperosmotic
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