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36 Cards in this Set
- Front
- Back
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Understand tubular reabsorption and why is it important
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If we didn’t recover most of the substances that make their way into the nephron, homeostasis would be impossible.
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Where does most of the tubular reabsorption take place?
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PCT
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List and define the 2 routes of tubular reabsorption.
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Paracellular reabsorption=passive process that occurs between adjacent tubule cells
Transcellular reabsorption= Movement through an individual cell using a variety of membrane channel and diffusion mechanisms. |
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How may substances be reabsorbed?
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active or passive transport
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Why is sodium important to reabsorption?
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Other substances bind to it so they can be absorbed
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What is transport maximum?
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As filtrate concentration of a particular substance exceeds the amount of available pumps, the transport maximum is reached.
(A group of elevators or escalators in a building can only carry so many people at a time) |
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What substances have a Tm?
What happens if filtrate levels of a substance exceed Tm |
Glucose, phosphate, sulphate, amino acids, organic anions
the rest is excreted in urine |
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How is water reabsorbed?
List and define the two ways |
Obligatory reabsorption of water occurs when it is obliged to follow the solutes as they are reabsorbed
Facultative reabsorption describes variable water reabsorption based upon need |
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Understand tubular secretion and why is it important?
What are some of the common substances secreted? |
The movement of substances from the capillaries which surround the nephron into the filtrate.
To maintain blood PH Some secreted substances include H+, K+, NH4+, urea, and some drugs |
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What is involved in maintaining the body’s pH?
How do lungs contribute How do kidneys contribute |
The lungs eliminate more CO2 by increasing breathing rate. (fast)
The kidneys eliminate more H+ and NH4+ ions and conserve bicarbonate. (slower) |
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Understand how reabsorption take place in the in the PCT
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The product goes from the Filtrate -->Tubule cell--> Basolatereral Membrane --> Interstitial Fluid/Space --> Peritubular Capillary
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What primarily get reabsorbed in the first half of the PCT and what percentage?
What gets secreted? |
The largest amount of solute and water reabsorption from the filtered fluid occurs in the PCT
100% of most filtered organic solutes, Glucose and amino acids 80-90% of filtered HCO3- 65% of water, Na+, and K+ 50% of urea, and Cl- Variable amounts of Ca2+ , Mg2+ , and HPO42- secretes variable amounts of H+, ammonium (NH4+), and urea |
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Why is Na reabsorption important in the PCT?
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Other substances bind to it so they can be absorbed & water follows it
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What is coupled to H+ transport in the PCT?
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Glucose, amino acids, lactic acid, water-soluble vitamins, phosphate, sulfate, and other nutrients
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How are large molecules reabsorbed?
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By passive transport Paracellularly
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How is water reabsorbed in the PCT?
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The movement of these solutes from the tubular fluid into the cells, interstitial fluid, and then blood creates osmotic gradients which pull water along with it
Passive transport/ |
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What are aquaporins and why are they important?
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Where water quickly goes out of the filtrate and in the end of the DCT and the Ducts
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What gets reabsorbed in the second half of the PCT and how?
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electrochemical gradients for Cl-, K+, Ca2+, Mg2+, and urea allow these solutes to passively diffuse down their concentration gradient across the tubular cell membrane using membrane protein channels (transcellular) and in-between the cells (paracellular).
Movement of these substances will also bring water along with them |
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What pump is important for the handling of acids and bases in the PCT
How does the pump work, where does it pump the ions, where do the ions for the pump come from, what enzyme is important for its function, how does bicarb get reabsorbed using this process? |
Na+/H+ antiporters
Sodium is pumped into the tubule cell from the lumen while hydrogen is pumped form the cell into the lumen The PCT tubule cells need a constant supply of hydrogen for the pump to work and it comes from products of carbonic anhydrase on both the apical surface and inside of the tubule cell This also allows for most of the bicarb (HCO3- ) filtered to be reabsorbed |
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Where does ammonia come from?
What does it get converted to? How does the body get rid of it |
it is a poisonous waste product derived from the break-down of amino acids
Hepatocytes of the liver convert most of this dangerous product to urea Small amounts of these wastes are lost through sweat but most are filtered by the glomerulus as well as secreted by the PCT |
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How do the kidneys use a particular amino acid to make more bicarb and excrete more H+ during acidosis?
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by breaking down the amino acid glutamine and producing ammonia as a byproduct
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How are drugs excreted from the kidneys?
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filtered by the glomerulus but are also secreted by the PCT cells into the tubule filtrate fluid
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Understand reabsorption in the loop of Henle
What gets reabsorbed and in what percentage? What is secreted? |
reabsorbs about;
~15% of the filtered water 20-30% of filtered Na and K ~35% of filtered Cl 10-20% of filtered Bicarbonate Variable amounts of calcium and magnesium secrets: variable amounts of urea |
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What is absent from the tubular fluid as it enters the loop of henle?
What is the osmolarity of the fluid? |
Glucose, amino acids, and other solutes are no longer present under normal conditions
osmolarity of the fluid is equal to that of the normal blood (300mOsm) |
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How is water, Na, and Cl absorbed
Where does the reabsorption of these take place in the loop of henle? |
Descending limb= H2O can leave via osmosis
solutes cannot leave Ascending limb= H2O cannot leave due to the ascending limb being relatively impermeable to water. However, certain solutes can Thin segment – passive Na+ movement Thick segment – Na+-K+-2Cl- symporter and Na+-H+ antiporter; some passes by paracellular route |
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Understand reabsorption in the early DCT
What is reabsorbed and in what percentage How is Na and Cl absorbed? |
absorbs;
about 10-15% of the filtered water 5% filtered Na and Cl Transport into the tubule cell uses Na/Cl cotransporter Transports both Na and Cl into the cell |
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What does parathyroid hormone do in the early DCT?
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Early DCT is site of action for parathyroid hormone
Stimulates reabsorption of calcium |
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Understand reabsorption and secretion in the terminal DCT and collecting ducts
What cell types are present? Why are they important? What do each absorb? What do each secrete? |
Principal cells
Absorb Na+ and secrete K+ across the apical surface via diffusion through ion specific leak channels Pump Na+ from the cell to the interstitial fluid and K+ from the interstitial fluid into the cell using Na+-K+ ATPases; Maintains ionic gradients that promote diffusion across the apical channels ; Important in maintaining proper K+ balance for body fluids Main source of K+ excretion for urine Intercalated cells Absorb K+ and HCO3- Secrete H+ |
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Why does water reabsorption vary in the terminal DCT and collecting ducts?
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final amount of water reabsorption depends upon body’s need
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Understand each of the 5 hormones involved in tubular reabsorption and secretion:
What are these key to maintaining? |
hormones affect the extent of Na+, Cl–, Ca2+, and water reabsorption as well as K+ secretion by the renal tubules.
key to maintaining homeostasis of not only renal blood flow and B.P., but systemic blood flow and B.P. |
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Understand why renin is secreted and the steps involved in the activation of angiotensin II
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When blood volume and blood pressure decrease or the sympathetic NS is stimulated, the walls of the afferent arterioles are stretched less, and the cells of the JGA secrete renin in response
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What are the 3 main effects of angiotensin II
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Vasoconstriction which decreases GFR.
Enhances reabsorption of Na+, Cl-, and water in the PCT by stimulating the activity of the Na+/H+ antiporters. Thus it increases blood volume by increasing reabsorption of water and electrolytes in the PCT. It stimulates the adrenal cortex to release aldosterone |
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Where does aldosterone have an effect?
What is it’s function? What does it promote? How does it increase Na and water reabsorption and increase K secretion? |
Targets collecting ducts (principal cells) and distal DCT
Function – increase blood pressure; decrease the extracellular fluid K+ levels Promotes synthesis of apical Na+ and K+ channels, and basolateral Na+-K+ ATPases for Na+ reabsorption (The osmotic consequence of reabsorbing more Na+ is that more water is reabsorbed, which increases blood volume and blood pressure.) Reabsorbing more Na+ by the Na+-K+ ATPase means that more K+ is secreted into the tubule fluid |
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Where is ADH released from?
Where does it work, what does it do, and how? |
by posterior pituitary gland
Causes principal cells of collecting ducts to insert aquaporins in apical membranes -->increases water reabsorption As ADH levels increase = increased water reabsorption |
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Where is ANP secreted from?
Under what conditions would it be secreted? Where does it work, what does it do, and how? What hormones can it suppress the release of? |
Released by cardiac atrial cells if blood volume or pressure elevated
Reduces blood Na+ by inhibiting Na+ reabsorption in the PCT and collecting duct = more Na+ in urine (natriuresis) Less Na+ reabsorbed means less water reabsorbed and increased urine volume production (diuresis) This leads to decreased blood volume and blood pressure the release of aldosterone and ADH |
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Where is parathyroid hormone released from?
Where does it work, what does it do, and how? |
Released by the parathyroid glands
Acts on DCT to increase Ca2+ reabsorption Acts on the PCT to inhibit phosphate reabsorption thereby increasing phospahte excretion |
