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81 Cards in this Set
- Front
- Back
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1. Identify and describe the functions of the renal system. |
The urinary system has 6 major functions: 1- Waste excretion: based on 3 processes —> filtration, reabsorption and secretion 2- Regulation of blood volume & pressure: controls ECF volume by producing larger or smaller amount of urine. Works with CV system. 3- Regulation of extracellular pH:kidneys vary their secretion of H+ to maintain extracellular pH 4- Regulation of osmolarity: kidneys maintain the concentration of ions to keep osmolarity at ∼290 mOsM 5- Ion balance: kidneys maintain the concentration of Na+, Cl-, K+, Ca2+ andHPO4^2- 6- Hormone production: kidneys produce erythropoietin (EPO; RBC), renin (blood pressure) & vitamin D |
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What is the kidney? |
-lie in the back of the abdomen - only partially protected by the rib cage ---important role of adipose (fat) tissue |
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What parts is the kidney divided into? |
-The cortex (the outer area of the kidney) - the medulla (the inner area of the kidney) |
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What does the cortex contain? |
Renal columns: cortical tissue extending into the medulla (between the pyramids) |
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what does the medulla contain? |
Renal pyramids which end in renal papilla
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how do kidney filtrates reach the bladder? |
proceed through a number of chambers in this order: renal papillae renal pelvis (contains smooth muscle to allow for contraction) ureter: exits kidney and connects to urinary bladder |
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what is a nephron? |
smallest functional unit of the kidney |
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what does a nephron contain? |
1. renal corpuscle (cortex) 2. proximal convoluted tubule (cortex) 3. loop of Henle (cortex and medulla) 4. distal convoluted tubule (cortex) which empties into the 5. collecting duct (medulla) |
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what is the renal corpuscule? |
first part of the nephron |
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what is the function of the renal corpuscule? |
filtration |
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What does the renal corpuscule contain? |
The renal corpuscle contains: 1. Bowman capsule (cortex): chamber made of epithelial cells which surrounds the: 2. glomerulus (cortex, inside the bowmans capsule): a capillary network afferent & efferent arterioles, lined by smooth muscle that control flow |
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how does blood flow through the renal corpuscule? |
afferent (goes in) & efferent (goes out) arterioles, lined by smooth muscle that control flow |
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what is the renal tubule? |
Initial filtrate is modified to urine as it passes through each section of the renal tubule |
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What are the parts of the renal tubule? |
1. Proximal convoluted tubule:- mandatory reabsorption of most solutes & water 2. Loop of Henle:- mandatory reabsorption of water (descending limb) and solutes (ascending limb) 3. Distal convoluted tubule & collecting duct:- reabsorption depends on hormonal signal |
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what is the function of the renal tubule? |
absorption and secretion |
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What is the process of filtration? |
movement of fluid from blood into the nephron |
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what is the process of reabsorption? |
movement of substances from the nephron back into the blood |
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what is the process of secretion? |
selective movement of substances from the blood into the nephron |
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where does filtration happen? |
renal corpuscule |
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where does reabsorption happen? |
all throughout the rest of the nephron |
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where does secretion happen? |
everywhere except the loop of henle |
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How do we figure out how much solute is secreted? |
amount filtered (F)- amount reabsorbed (R) + amount secreted (S) = amount of solute excreted |
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what is a filtrate? |
any fluid filtered into the nephron |
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how much of the plasma entering the bowmans capsule is filtered? |
20 % (180 L/day) |
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how much do we excrete a day? |
1-2 L/day |
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how much of whats filtered is reabsorbed back into the blood? |
99% |
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NOW go over summary in additional slides |
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what is the afferent arteriole? |
where blood enters the renal corpuscle then it goes through the glomerulous (capillaries) where is it filtered |
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what is the efferent arteriole? |
where blood exits the renal corpuscule |
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what is the purpose of the filtration membrane? |
-allows some substances in while others stay in the blood
-During the filtration process, the plasma must go from the capillaries into the lumen of the Bowman’s capsul |
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what are the 3 layers the plasma must cross in the filtration membrane? |
- fenestrated capillary endothelium (has large gaps to facilitate filtration) - basal lamina - Bowman’s capsule’s podocytes (has large gaps [filtration slits] to facilitate filtration) |
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why does urine not contain RBC's or protein? |
the gaps in the capillary endothelium and Bowman’s capsule’s podocytes are large enough to let most plasma components out, but small enough to retain RBCs and proteins in the blood |
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what is the definition of filtration? |
Fluid movement from the flow of blood through the glomerulus and across the filtration membrane to form filtrate
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why is filtration a non-selective process? |
the filtrate is a solution of water, small molecules and ions that can pass through the filtration membrane —>excludes proteins (healthy filtrate contains 0.03% proteins) and blood cells from entering the Bowman’s capsu |
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what drives filtration across the walls of the glomerular capillaries? |
Difference of pressure between the glomerulus and the Bowman’s capsule Pglomerulus> Pbowmans capsule |
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what is filtration pressure? |
pressure gradient responsible for filtration |
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how many different pressures is filtration pressure dependent on? |
3 |
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what is the first one? |
1. Hydrostatic pressure (PH): blood pressure (BP) inside the glomerulus capillaries tends to move fluid out of capillary into Bowman’s capsule High capillary BP because diameter of afferent arterioles > the diameter of efferent arterioles PH = 55 mm Hg **this is an OUTWARD force toward bowmans capsule |
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what is the second one? |
2- Hydrostatic fluid pressure (Pfluid): accumulation of filtrate in the lumen of the Bowman’s capsule creates a pressure Pfluid (15 mm Hg) < hydrostatic pressure (55 mm Hg) because the filtrate is constantly moving through the PCT and the rest of the renal tubule **this is an INWARD force towards the glomerulus |
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what is the third one? |
3. Colloid osmotic pressure (π): osmotic pressure caused by the presence of proteins in the blood —> favours fluid movement into the glomerulus from the lumen ↑ [protein]glomerulus = ↑π π = 30 mm Hg **this is an INWARD force toward the glomerulus |
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what is the filtration pressure formula? |
PH (55 mm Hg) – Pfluid (15 mm Hg) – π (30 mm Hg) = 10 mm Hg |
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how much volume of fluid is filtered into the bowmans capsule? |
Renal blood flow rate = cardiac output x renal fraction = 5,600 mL/min x 21% = 1,176 mL/min ∼1 L per minute renal plasma flow rate = renal blood flow rate x 55% = ~650 mL/min Glomerular filtration rate (GFR) = amount of filtrate produced every minute = 650 mL/min x 0.19 = 123.5 mL/min ∼ 125 mL per minute 19% of the plasma is removed from the blood during filtration —>180 L of filtrate is produced daily!!! |
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how many times a day do our kidneys filter our entire plasma volume? |
60 |
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what is GFR? |
Glomerular filtration rate (GFR) = amount of filtrate produced every minute = 650 mL/min x 0.19 = 123.5 mL/min ∼ 125 mL per minute |
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What 2 ways is GFR regulated? |
auto regulation and sympathetic regulation |
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if MAP changes, does GFR change also? |
no, MAP can increase or decrease while GFR stays the same |
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what is autoregulation? |
changes in the diameter of the afferent arteriole |
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what happens during autoregulation? |
Dilation of afferent arterioles = ↑ blood flow into glomerulus = ↑ blood pressure (PH) in the glomerulus = ↑ filtration pressure = ↑ GFR Constriction of afferent arterioles = ↓ blood flow into glomerulus = ↓ blood pressure (PH) in the glomerulus = ↓ filtration pressure = ↓ GFR |
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whats one way afferent arterioles constrict and dilate? |
A. Myogenic response: smooth muscle cells around the afferent arterioles have stretch receptors. ↑ BP = activate stretch receptor = open Ca2+ channels in smooth muscle cells = Ca2+ flows into the cell = depolarization = constriction ↓ BP = relaxed smooth muscle cells = dilation |
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whats another way afferent arterioles constrict and dilate? |
B. Tubuloglomerular feedback: local pathway where cells in the loop of Henle influences GFR through: macula densa cells: cells of the loop of Henle located between the afferent and efferent arterioles able to detect flo |
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Memorize tuboglomular feedback diagram- slide 36 |
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What is the second way that GFR is regulated? |
2. Sympathetic control: Intense sympathetic stimulation (e.g. intense exercise, shock, severe dehydration) leads to constriction of smooth muscle in small renal arteries and afferent arterioles leads to decreased renal blood flow & decreased formation of filtrate helps maintain blood volume and blood pressure in emergency situation |
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go over summary on slide 38 |
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define tubular reabsorption |
return to the blood of water and solutes filtered from the blood at the renal corpuscl -second step of urine formation |
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where does tubular reabsorption occur? |
the PCT (+++), the loop of Henle, the DCT and the collecting duc |
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how does tubular reabsorption occur? |
simple diffusion, facilitated diffusion, active transport, symport & osmosis |
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what does tubular reabsorption lead to? |
99% of water, inorganic salts and small organic molecules are returned to the blood |
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Why does our body go through all the troubles of forming 180 L filtrate each day and then reabsorb 99% of it? What are the advantages? |
1. Foreign substances are filtered easily, but not reabsorbed, so high filtration rate ensures that we clear foreign substances from the plasma quickly. 2. Filtering ions and water into the tubule makes their regulation easier. It is difficult to regulate at the filtration step (because it is non-specific), so it is easier to regulate at the reabsorption stage |
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How does reabsorption happen in the PCT? **watch the last slideshow |
For reabsorption, components must move from the PCT lumen —> inside of cell —> extracellular fluid must cross 2 membranes: apical membrane: on the tubule side basolateral membrane: on the ECF side |
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describe Na+ reabsorption in PCT |
Na+ enters cell through membrane proteins, moving down electrochemical gradient Na+ is pumped out of the basolateral side of the cell by the Na+K+ ATPase Important concepts: - Na+/K+ ATPase at the basolateral membrane: Na+ is actively pumped out of the cell —> concentration gradient between the tubule & ICF allows: Na+ to enter the cell (apical side) passively through protein channel |
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describe Na+ dependent reabsorption in the PCT **watch video |
Na+ concentration gradient between the tubule & ICF allows: - apical side: glucose is transported against its concentration gradient through a Na+ symporter by 2ary active transport - basolateral side: glucose is transported with its concentration gradient by facilitated diffusio |
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Glucose reabsorption in the PCT is dependent upon what 2 types of transport? |
secondary active transport and facilitated diffusion |
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what do both require? |
protein carriers |
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what are they both susceptible to? |
saturation |
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What are the take home messages about glucose reabsorption in the PCT? |
- When [glucose]plasma < threshold, all filtered glucose gets reabsorbed - When [glucose]plasma > threshold, glucose carriers are saturated, transport maximum is reached, and glucose is excreted in the uri |
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another way to look at it? |
glucose excretion is 0 until renal threshold is reached formula: filtration-reabsorption= excretion |
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Describe Na+ dependent reabsorption in the PCT in terms of concentration gradient |
- Na+ concentration gradient between the tubule & ICF- allows reabsorption of -organic & nutrient solutes (e.g. amino acids, lactate) - other electrolytes (e.g. PO4-, Ca2+, M g2+) -water!!! |
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How does H2O get reabsorbed in the PCT? |
- Na+ concentration gradient between the tubule & extracellular fluid leads to - osmotic gradient between the PCT & ECF —> H2O moves from the PCT lumen to the interstitial fluid by osmosis |
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How does fluid get from the interstitium to the blood? |
Peritubular capillaries: blood vessels that surround the nephron tubule For movement to occur between the interstitium to the blood: - colloid osmotic pressure (π) in the interstitium > hydrostatic pressure (PH) in the peritubular capillaries π (30 mm Hg) > PH (10 mm Hg) |
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Read slide 58 for PCT summary |
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If We know: - that up to 99% of fluid & solutes gets reabsorbed in the nephron- 65% of fluid & solutes gets reabsorbed in the PCT Where and how does the rest of the reabsorption take place?? |
loop of Henle, DCT, collection duct |
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Describe reabsorption from the loop of henle |
Descending limb: high permeability to water leads to: Reabsorption of water ONLY (by osmosis Filtrate volume is reduced by 15% in the descending limb. B. Ascending limb: is water-impermeable, but solute-permeable leads to: Reabsorption of solutes ONLY (by active transport Volume does not change in the ascending limb. An additional 25% Na+ is reabsorbed |
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How does reabsorption from the loop of henle work? |
B. Ascending limb: is water-impermeable, but solute-permeable leads to: Reabsorption of solutes ONLY (by active transport) Volume does not change in the ascending limb. An additional 25% Na+ is reabsorbed **tight junctions prevent movement of water |
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describe water permeability being variable |
Water permeability is variable and depends on hormonal signal main hormone: anti-diuretic hormone (ADH)- when secreted: water permeability —> water reabsorption by osmosis & some solutes reabsorption by diffusion —> small volume of concentrated urine- when not secreted: water impermeability —> water & solutes remain in the nephron —> large volume of dilute urin |
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Describe how 1) the osmolarity in the renal cortex and the medulla and 2) the countercurrent flow in the vasa recta helps maintain water and solute movement throughout the nephr |
The kidneys can produce urine with a concentration ranging from 50 mOsM to 1200 mOsM ^this is essential to maintain homeostasis it is dependent on: 1. antidiuretic hormone (ADH) that controls the water permeability of the DCT and collecting ducts 2- maintenance of high concentration of solutes in the medulla (up to 1200 mOsm/kg) 3- countercurrent functions of the loop of Henle |
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how does the the countercurrent flow in the vasa recta helps maintain water and solute movement throughout the nephron? |
Vasa recta: specialized sets of capillaries associated with the nephrons
-The vasa recta is permeable to both water and solutes along its entire length -is essential for: Countercurrent mechanism: blood flow in the vasa recta is opposite the filtrate flow in the nephron -which allows for: Removal of excessive water and solutes from the medulla without changing the high concentration of solutes in the medulla |
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describe counter current flow is descending loop of henle |
As the filtrate goes through the descending limb of the loop of Henle: - water moves from the nephron to the interstitium via osmosis (with its concentration gradient) - water moves from the interstitium to the vasa recta via osmosis (with its concentration gradient) |
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describe counter current flow is ascending loop of henle |
As the filtrate goes through the ascending limb of the loop of Henle: - solutes move from the nephron to the interstitium via active transport (against its concentration gradient) - solutes move from the interstitium to the vasa recta with their concentration gradient |
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do activity on slide 62 |
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1. Define secretion and give examples of secreted solute |
Secretion: Movement of substances (e.g. K+, H+, anions, drugs) from the blood into the filtrate — mostly via active transport -takes place in PCT, DCT and collecting ducts |
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read summary on slide 65 |
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