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Excretory systems control __
volume, concentration, and composition of the extracellular fluid & excrete wastes
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Cell volume depends on __, which depends on __
- water movement to or from extracellular fluid;
- differences in solute concentrations
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osmolarity
number of moles of active solutes per liter of solvent
more solutes in solution = higher osmolarity
The osmolarity of the extracellular fluid must be maintained for cellular water balance.
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Excretory organs control osmolarity and volume of extracellular fluids by excretion of __ & conserving __
- solutes that are in excess, such as NaCl;
- valuable solutes or solutes in short supply, such as glucose & amino acids
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__ is the output of the excretory system
Urine (filled with waste products)
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Excretory systems have 3 processes in common:
- filtration: extracellular fluid is filtered to contain no cells or large molecules (size filter)
- secretion: modifies the filtrate
- reabsorption: concentrates the urine
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Terrestrial animals must conserve __ & freshwater animals must conserve __
- salts & water;
- salts but excrete excess water
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metabolic waste products that are easily excreted
Carbs and fats end as water and CO2
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__ & __ contain nitrogen so metabolism produces __
Proteins; nucleic acids; nitrogenous waste
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Mammals secrete mostly __ as their nitrogenous wastes.
urea
Humans are ureotelic but also excrete uric acid (from metabolism of nucleic acids and caffeine) & ammonia (regulates pH of extracellular fluid by buffering urine)
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The __ is the main excretory organ and the __ is the main functional unit of that organ.
kidney; nephron
kidneys > ureters > urinary bladder > urethra
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function of nephrons
filter large volumes of blood & achieve bulk reabsorption
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main function of the kidney
filter blood & produce urine
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From the renal artery, blood flows through the __ in the cortex then to the __ surrounded by a __. This is where __ occurs. The blood continues to the __ to the __ & down the __ in the medulla and back up and out through the renal vein.
- afferent arteriole;
- glomerulus (fenestrated capillaries with leaky pores);
- Bowman's capsule;
- filtration (size filter - large stay in blood, small enter the nephron);
- efferent arteriole;
- peritubular capillaries (surround the tubule)
- vasa recta (surrounds the loop of Henle)
The peritubular capillaries and the vasa recta serve as exchange sites.
(page 14 on slide)
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Filtration:__ stay in the blood and __ enter __
- RBCs and proteins;
- small molecules such as ions, amino acids, water, urea, glucose, and small toxins;
- Bowman's capsule (start of the nephron)
Glucose, amino acids, and valuable solutes will need to be reabsorbed.
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__ are capsule cells that contact the glomerular capillaries.
Podocytes
Podocytes have fine processes that wrap around the capillaries.
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Blood is filtered in the __ Tubular reabsorption occurs mainly in the __
- glomerulus (to Bowman's capsule)
- proximal convoluted tubule (of glucose, amino acids, and valuable solutes)
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The rate of filtration is high in the glomerulus due to __
- high capillary blood pressure;
- high permeability of glomerular capillaries and their podocytes
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3 parts of the filtration membrane
- fenestrations (pores)
- basal lamina
- foot processes of podocyte
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From the Bowman's capsule, __ enter the __ of the nephron where __ are reabsorbed into the interstitial fluid. The nephron continues down the __ and up the __ to the __ to the __.
- small molecules;
- proximal convoluted tubule;
- glucose & valuable solutes;
- descending loop of Henle;
- ascending look of Henle;
- distal convoluted tubule;
- collecting duct
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__ are membrane proteins abundant in highly water-permeable areas.
Aquaporins
not found in the ascending loop of Henle
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The proximal convoluted tubule is responsible for the __ of water & solutes - osmolarity __
- isosmotic reabsorption;
- does not change
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The PCT cells have __ to increase surface area & have mitochondria. They actively transport __.
- microvilli;
- Na+, glucose, and amino acids (Water follows the transport of solutes.)
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Concentration of urine is due to a __ mechanism in the loops of Henle.
countercurrent multiplier
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As the loop of Henle descends down the medulla, the osmolarity of the fluid inside the nephron increases due to __. In the thin ascending limb, __. In the thick ascending limb, __. In the distal convoluted tubule, __. Down the collecting duct, __, resulting in a __
- diffusion of H2O from the descending loop to the interstitial fluid via aquaporins (transfers indirectly to the vasa recta);
- due to no aquaporins, no H2O leaves, but NaCl leaves, decreasing osmolarity;
- osmolarity continues to decrease as no H2O leaves and membrane proteins transport out NaCl into the interstitial fluid;
- osmolarity has decreased greatly
- osmolarity increases again as H2O leaves, because of the increasing solute concentration in the interstitial fluid down into the medulla;
- concentrated urine with very high osmolarity (up to 1200 mOsm/L)
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Renal failure results in:
- salt and water retention (high bp)
- urea retention (uremic poisoning)
- decreasing pH (acidosis)
Dialysis treatments passes blood through membrane channels bathed in a plasma-like solution to remove wastes.
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