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28 Cards in this Set
- Front
- Back
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describe location of kidneys
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-retroperitoneal; 11th or 12th rib
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describe the renal blood flow
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-total renal blood flow is .4% total body weight, 1/4 CO
-afferent arterioles are short, direct, low resistance vessels contributing to high glomerular hydrostatic pressure which promotes filtration -glomerulus is leaky with high hydrostatic pressure, 180L/D of fluid filters into interstitium of Bowman's -peritubular capillary has low hydrostatic pressure and high colloidal osmotic pressure, promoting reabsorption |
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describe the innervation of the kidneys
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-sensory connections from pain receptors
-sympathetic noradrenergic neurons to afferent and efferent arterioles, JG apparatus and many portions of tubule. influences renal blood flow and pressure, renin secretion and possibly reabsorptive processes of tubules -no parasympathetic innervation and some dopamine containing neurons |
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what is overall function of renal corpuscle; describe the permeability characteristics of it; what does filtrate contain
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-serves to produce high volume ultra filtrate of plasma; consists of plasma water and its non-protein constituents
-3 layers- capillary endothelium, basement membrane and specialized epithelium -primary filtration barrier is basement membrane -neg charged glycoproteins in basement membrane repel anionic macromolecules, impeding/slowing their passage -allows material with MW up to 70,000 -filtrate contains- no cellular elements of blood, no plasma globulins, possibly trace albumin and hemoglobin, many small molecules -permeability is NOT subject to physiological regulation but often altered in renal disease |
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describe net filtration values of hydrostatic pressure and oncotic pressure between arterioles in glomerular capillary and Bowmans space
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Pg is 60 afferent 58 mmHg efferent
pbs is 0 does not change Pbs is -15 does not change pg is -28 to -35 overall positive filtration wanting to move fluid into Bowman's |
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what factors determine magnitude of GFR
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1. filtration coefficient- glomerular capillary permeability per meter squared multiplied by SA available for filtration
2. net filtration pressure as established by Starling's forces 3. glomerular capillary blood flow -overall resistance in afferent dec GFR and RBF; resistance in efferent inc GFR, dec RBF -dilating efferent but maintaing flow in afferent leads to dec in hydrostatic pressure causing overall dec in GFR |
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what range of MAP can kidneys maintain GFR, how?
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90-180 MMHG via intrinsic, intrarenal mechanisms controlling renal hemodynamics
-arteriolar smooth muscle tissue- myogenic mechanisms, pressure sensitive -tubuloglomerulo-feedback, NaCl sensitive, to glomerular arterioles to correct GFR by macula densa cells at cortical thick ascending limb of henle -adenosine constricts afferent; inc Na+ inc ATPase causing release of adenosine which leads to Ca release causing constriction of afferent arteriole -NO dilates -macula densa also inc systemic levels of renin and angiotensin 2 leading to vasoconstriction of glomerular arterioles (mainly efferent, inc glomerular hydrostatic pressure to inc GFR) |
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describe extrarenal mechanisms- autonomic and hormonal control
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-sympathetic neurons with alpha 1 adrenergic receptors on glomerular arterioles causes vasoconstriction and inc vascular resistance causing dec renal blood flow, GFR and urine output
-at high levels of angiotensin 2- constricts both afferent and efferent arterioles causing renal blood flow and GFR to dec -prostaglandins, bradykinin and NO dampen vasoconstrictor effects of sympathetic input and angiotensin 2 |
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define filtration fraction
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fraction of the total renal plasma flow that is filtered from the glomerulus into the tubule
=GFR/RPF -normally .16 to .2 -greater this fraction (the amount of protein-free water removed from plasma that flows through glomerulus), greater the concentration of plasma proteins in blood entering peritubular capillaries and hence larger will be the oncotic pressure promoting reabsorption of tubular fluid by peritubular capillaries |
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describe pathological disturbances of glomerular function
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-nephrotic syndrome- noninflammatory damage to glomerular capillary wall
-nephritic syndrome is caused by inflammation -glomerular disease is a common cause of chronic renal failure requiring dialysis or renal transplantation -clinical manifestations include proteinuria, hematuria, oliguria, azotemia, hypertension and edema |
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define reabsorption and secretion
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-transport of a substance from tubular lumen into peritubular blood
-secretion- into lumen to be excreted |
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describe structure of epithelium of nephron
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-tubular epithelial cells are held together by tight junctions, below cells are separated by lateral intercellular spaces
-apical (lumen side) membrane, epithelial cell, basolateral (blood side) membrane -across cells- transcellular, 2 steps to cross each membrane -between- paracellular by solvent drag (solutes dissolved in water are carried by flow of water through leaky tight junctions) or diffusion -transtubular potential- between lumen and interstitial fluid; between luminal and basolateral membrane; cell interior is negative to lumen and interstitial fluid; drives paracellular diffusion |
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describe reabsorption of small organic molecules
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-such as glucose, AA, organic ions (citrate, lactate, acetoacetate), etc occurs in early proximal tubule
-via secondary active transport as cotransport with Na from lumen into epithelial cell -via facilitated facilitated diffusion from epithelial cell to blood with Na being actively pumped out and K in -glucose uses SGLT2 on lumen side and GLUT2 on basolateral membrane in early proximal tubule; SGLT1 and GLUT1 in late proximal tubule |
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describe reabsorpotion of polypeptides and small proteins
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-essentially completed in early proximal tubule
-small peptides via carrier mechanisms, larger proteins by endocytosis; both are degraded intracellulary to their constiuent AA -some oligopeptides may be degraded in lumen and free AA constituents are reabsorbed -constieunt AA returned to peritublar blood |
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describe path of metabolic by-products and foreign substances
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-tubule helps to eliminate compounds that cannot adequately be disposed of by glomerular filtration or metabolism alone by secreting them into tubular fluid
-secretion occurs primarily in proximal tubule from interstitial space into epithelial cell and across to lumen -via secondary active transport- counter transport with Na -active secretory pathways for organic anions and cations in proximal tubule have relatively low specificity- accounds for ability to effectively excrete so many drugs and foreign chemicals -weak acids or weak bases are many of substances secreted -couple transporters OATs/OCTs- organic anion/cation transporters; can be coupled or facilitated -imp secretion of end products of metabolism (hippurates, oalates, urate); substances bound to plasma proteins which cannot be filtered easily or in large amounts; foreign substances or drugs |
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describe use of para-amino hippuric acid (PAH)
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-almost all PAH is excreted therefore can be used to measure renal plasma flow
-substances secreted tend to reach higher concentrations in urine than other compounds -radio-opaque contrast agents are used to visualize the lower urinary tract to xray are aggressively secreted -drugs can be designed to compete for same tubular transport pathways and therefore interfere with each other's excretion, limiting it- eg penicillin |
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describe regulation of water, electrolyte and urea excretion in proximal tubule in general and Na specifically
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-largest adjustments in volume and electrolyte composition of filtrate
-Na is actively pumped across basolateral membranes then passively enters epithelial cell from tubule via cotransport with organic nutrients or countertransport with H -early PCT Na transported with organic substances -late PCT Na/H exchanger companied with Cl- counter transport (Cl follows Na) and diffusion with Na through tight junctions |
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describe reabsorption of K and Cl and HCO3-
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-K largely occurs via solvent drag early and diffusion late through paracellular spaces in PCT
-early PCT, HCO3- is reabsorbed with Na -later in PCT Cl reabsorption predominates by transcellular and paracellular routes |
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describe water reabsorption
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-filtrate remains isotonic
-in proximal tubular epithelium the spaces between the cells are long and narrow while luminal end is bounded by tight junctions -Na reabsorption creates osmotic gradients which pull water from lumen through brush border of epithelial cells (transcellular pathways) or through tight junctions (paracellular) into intercellular spaces -water can then be removed from interstitium by peritubular capillaries, a process promoted by elevated colloidal osmotic pressure and low hydrostatic pressure of peritubular blood -approx 70-80 percent of filtered water is reabsorbed in proximal tubule |
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describe reabsorption of urea
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-urea is freely filtered at glomerulus
-50 percent reabsorbed in PCT -in PCT, predominantly reabsorbed via solvent drag |
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describe loop of henle
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-thin descending- low permeability to solutes and lacks any mechanism for active solute transport but is highly permeable to water- reabsorbs 10% filtered water which moves in response to hyperosmolality of interstitium
-thin ascending impermeable to water and highly permeable to Na/Cl to be reabsorbed and (slight to urea which is secreted) -thick ascending- impermeable to water and can actively transport Na, K, and Cl from lumen; 1Na:1K:2Cl cotransporter via large gradient favoring Na entry; Na out by NA/K ATPase and K and Cl out passively; some K returns from blood to lumen via specific channels; cations are also passively reabsorbed -more solute is reabsorbed than water creating medullary hypertonicity |
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describe diuresis
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-loop or high ceiling diuretics bind Cl binding site, inhibiting Na:K:Cl cotransporter in thick ascending limb
-osmotic diuretics also disrupts Na and water reabsorption link -impairs concentrating ability of kidney and produce a diuresis |
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describe distal tubule
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-15% of filtered water reabsorbed
-early segment is highly convoluted, reabsorbs ions but impermeable to water- diluting segment; Na/Cl cotransporter (inhibited by thiazide diuretics but not loop diuretics) -later segment contains principal cells that contains channel to reabsorb Na via facilitated diffusion (diuretics amiloride and triamterene block); aldosterone stimulates -later K reabsorption via K/H/ATPase in intercalated cells of late DT and DC; secretion of K via Na/K/ATPase; aldosterone antagonist reduce K secretion |
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describe regulation of H2O and urea excretion
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-water an urea permeability of collecting duct are regulated by vasopressin
-ADH- water permeability is high preventing establishment of any osmotic gradient and tubular fluid volume shrinks -increases permeability to urea in innermost collecting duct; promotes diffusion out of tubular fluid into interstitium -in absence of ADH collecting duct is relatively impermeable to water and volume of tubular fluid will remain constant throughout entire ascending, distal tubule and collecting duct |
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describe characteristics of K
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-2% extracellular, modest changes produce marked alterations in excitability of muscle and nerve with serious medical consequences
-plasma K is largely determined by dietary intake, K uptake into cells and K excretion -intracellular compartment serves imp first line of defense in response to either increases or dec in extracellular K, serving as an overlfow site of K -regulation of renal excretion occurs in late distal tubule and collecting duct where principal cells have capacity to secrete large quantities of K into lumen -secretion by Na/K ATPase influenced by extracellular concentration of K, tubular flow rate and aldosterone (inc luminal permeability to K and stimulates ATPase) -most of filtered K is reabsorbed in PCT (70%) and loop of Henle (20) as 5-20 is secreted in distal tubule and collecting duct -15-30% is filtered -inc ECF H causes dec in K secretion due to inhibition of Na/K pump |
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describe characteristics of urea excretion
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-with normal protein intake, urea contributes approx 40% osmolaltiy of medullary interstitium
-loop of henle, late distal tubule and early collecting duct urea permeability is low and becomes concentrated in urine -in medullary collecting duct, urea permeability inc and it diffuses out driven by its concentration gradient -medullary collecting duct urea permeability is inc by vasopressin |
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describe excretion of other electrolytes
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-Ca excretion primarily through feces; 50% of Ca plasma is unbound and available for filtration; 99% reabsorbed- 70 in PCT, 20 ascending Henle, 9 in distal tubule; parathyroid hormone (and plasma phosphate via PTH), metabolic acidosis and 1,25 dihydroxycholecalciferol stimulates reabsorption
-most of body phosphate is in bone but 99 percent of plasma phosphate is available for filtration; 80% is reabsorbed in PCT 10 in proximal straight tubule; PTH inhibits PCT reabsorption -Mg 50% stored in bone, little Mg in plasma but 70% available for filtration; almost all reabosrobed- 30 in PCT 60 in ascending Henle |
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describe pathological disturbances of tubular function
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-tubulointerstitial diseases- can be rapid (acute tubular necrosis or acute interstitial nephritis) resulting in rapid renal failure that is usually reversible
-acute usually caused by renal ischemia or toxic substances -tubulointerstitial caused by bacterial infection, drug-induced hypersensitivity, and toxic reactions, renal ischemia, intratubular obstruction, urinary tract obstruction and cyst formation -signs/symptoms- impaired ability to concentrate urine resulting in polyuria and noturia, salt wasting, metabolic acidosis, glucosuria, aminoaciduria |
