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56 Cards in this Set
- Front
- Back
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filtration
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-glomerulus
- all but proteins and cells |
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resorption
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takes stuff from ultrafiltrate back into blood
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secretion
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takes stuff from blood into ultrafiltrate which turns into urine
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bulk resorption of urine
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-proximal tubulus
- iso-osmotic resorption eg ~ 2/3 NaCal, H2O and 100% amino acids, glucose |
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dilution/ concentration of urine
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-loop of henle
- low tubular and high interstitial osmotic P are preconditions for final adjustment |
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final adjustment of urine formation
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-distal tubule and collecting duct
-adjusts urine volume and concentration |
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glomerular filtrate vs plasma
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-glomerular filtrate is almost the same as plasma except for no significant amount of protein
- more than 99 % of the ultrafiltrate is reabsorbed in the tubular system of the nephron |
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medullas of nephron
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-loops of Henle of cortical nephrons remain in the outer medulla
- only loops of the juxtaglomerular nephrons descend into the inner medulla |
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transport processes in the proximal tubule
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-most of the valuable solutes reabsorbed: Na, K, Ca, Mg, Cl, glucose, aa's, lactate, sulfate
- wastes are excreted into tubule: H, organic acids/ bases, antiobiotica -H20 reabsorbed by osmosis -driven by electrochemical gradients and active transport |
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transport processes in the loop of Henle
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-resorption of high amounts of Na and Cl from the ascending loop with related water from the descending loop results in:
1. decrease in total volume 2. increase in osmotic P in interstitium 3. decrease in osmolarity of tubular fluid: important precondition to the final adjustment of urine in the distal tubule and collecting duct |
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transport processes in the distal tubule and collecting duct
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-transport of key solutes like Na and water regulated by hormones
- urine volume and concentration adjusted to needs - eg: body fluid volume or Na increase results in decreased resorption with help of ADH (inc. H2O res), ANF (inc. Na excretion) and/or aldosterone =excretion of higher urine volume or concentration |
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role of macula densa
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-regulates filtration into Bowman's and thus the flow speed in the tubular system and total resorption
- eg: dec. filtration and flow speed causes fluid to remain in tubule longer = more time for resorption |
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osmotic pressure in the cortex and medulla
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1. cortex: 290 mOsm/ L
2. outer medullar: 600 mOsm/ L 3. inner medulla: 1200 mOsm/ L -high osmotic P in the medullary interstitium is a precondition to concentrating the tubular fluid in the collecting duct -fluid leaves the duct as urine -Loop of Henle generates these pressures |
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resorption in the loop of Henle
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-resorbs ~2/3 of the water and NaCl entering the descending loop
-OsM of the tubular fluid entering the loop = OsM blood = 290 mOsm -leaves loop with lower osmolality= 220mOsm |
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generation of high interstitial OsM P of Loop of Henle
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-generates high interstitial OsM P in the medulla which are essential for the resorption of water from the collecting duct
- preconditions for high OsM P: 1. only descending limb is permeable to water 2. only the ascending limb is equipped with Na/K pumps |
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principle 1 countercurrent of the loop of Henle
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1. tubular fluid from the proximal tubule enters the loop,
2. through the descending limb 3. to outer / inner medulla 4. returns through the thick ascending limb to the cortex 5. to distal tubule |
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principle 2 countercurrent of the loop of Henle
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Na concentration of the tubular fluid entering the loop equals the blood Na concentration
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principle 3 countercurrent of the loop of Henle
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-ascending limb Na is transported from the tubular fluid into the interstitium
- consequently, the Na concentration in the tubular fluid decreases and OsM P in the interstitium increases -tubular fluid then leaves the ascending limb with an oncotic P lower than blood |
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principle 4 countercurrent of the loop of Henle
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-due to the high interstitial P, water diffuses out the water-permeable descending limb
- Na cannot follow so it concentration in the tubular fluid increases along the descending limb, reaching a maximum turning point |
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principle 5 countercurrent of the loop of Henle
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-increase in Na in the descending limb triggers a (+) feedback cycle in the ascending limb:
1. uphill pumping by Na/K pump is limited to a maximum [] difference 2. as tubular fluid enters the ascending limb, already with a higher [], the starting level for the pumps is also higher 3. thus the pumps are able to further increases the interstitial [] 4. in turn, water resorption increases, which again increases the concentration in the tubular fluid... |
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Resorption of Na
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~2/3 of the Na filtered into Bowman's is immediately resorbed from the proximal tubule (isotonic resorption)
- only 10% of the filtered amount reaches the distal tubule -depending on the hormonal status, 0.5-5% is finally excreted |
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resorption of Cl
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-main source of Cl is cooking salt in the diet
- excretion closely linked to that of Na - main transport mechanisms are symport with Na and diffusion |
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Hormones which regulate NaCl resorption
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-increase:
1. aldosterone 2. angiotensin -decrease: 1. ANF |
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aldosterone
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-distal tubule, collecting duct
-increases NaCl and H2O resorption - decreases K resorption |
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angiotensin II
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-proximal tubule, thick ascending loop of Henle, distal tubule
-increases NaCl and H2O resorption - decreases H resorption |
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antidiuretic hormone
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-distal tubule, collecting duct
- increases H2O resorption |
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atrial natriuretic factor
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-distal tubule, collecting duct
- decreases NaCl resorption |
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parathyroid hormone
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-proximal tubule, thick ascending loop of Henle, distal tubule
-increases Ca resorption -decreases phosphate resorption |
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intracellular fluid
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63% of total body water
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extracellular fluid
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-37% of total body water
- 27% interstitial fluid - 7% blood plasma - 3% transcellular fluid: synovial, peritoneal, pericardial, pleural, cerebrospinal, and intraocular spaces |
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main control of blood and extracellular fluid volume
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-effect of BV on arterial P
-effect of arterial P on urinary excretion of Na and water |
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blood volume and extracellular fluid volume
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-intensive, continuous exchange of water and electrolytes between blood and extracellular fluid
-impossible to control BV without controlling the extracellular fluid V at the same time |
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main inorganic constituents of body fluids
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1. water
2. sodium (NaCl) 3. K 4. Ca and P 5. Mg |
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aldosterone and ECF volume
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-controls excretion of Na and Cl
eg inc in NaCl --> inc in thirst and H2O intake --> plasma V increases --> inc blood aldosterone ---> inc NaCl and H2O excretion --> plasma V reduced to normal levels |
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antidiuretic hormone and ECF volume
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-controls excretion of H2O
-eg. drinking water --> dec. osmolarity of plasma -if deviates more than 1% from 290 mOsm the less ADH is released and blood level decreases --> inc. excretion of H2O until the normal osmolarity is acheived again |
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ADH and collecting duct
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-without ADH: collecting duct cells are "water-tight"
-preformed water channels allow influx of H2O into hypertonic environment (cell, interstitium, plasma) |
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interstitium and fluid
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-acts as an overflow release valve, preventing over-filling of the circulatory system
- if ECF rise >30-50% above normal, almost all of excess fluid fills interstitial spaces, causing edema |
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dehydration
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-excessive sweating and respiration causes loss of hypotonic fluid
-osmolality increases: > 285 mmol/kg - ADH released from the hypothalamus causes max water retention and thirst - decrease in plasma V causes Na retention (renin-angiotensin-aldost) -interstitial and cytoplasmic osmolality increases--> cells shrink - functional disturbances develop: confusion, hallucinations, convulsions |
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drinking seawater?!
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-seawater contains 450 mmol Na/L but excretion by kidneys is limited to a max 300 mmol/ L
-excretion of 1 L of seawater requires 1.5 L of urine |
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Na balance general rule
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any increase or decrease of Na results in an increase or decrease of EC V
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Na balance
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-most important EC cation for control of ECF V
- normal []= 140mmol/L - level controlled through filling circulatory system: atrial v receptors, arterial baroreceptors --> ADH, ANF - closely linked to Cl |
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Na resorption
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-<1% of Na from ultrafiltrate excreted:
-70% reabsorbed in prox. tubule -20-25% reabsorbed in the l of Henle - aldosterone controls final reabsorption in distal tubule and collecting duct |
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glomerular filtration of NaCl and H2O
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-glomerular filtration per day:
1. humans: 180 L H2O, 1500g NaCl, and 660g Na 2. cattle: 500 L H2O, 4000g NaCl, 1760g Na |
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edema
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-increase in Na causes an increase in BV
- when the capacity of the circulatory system is exceeded, fluid is shifted into the extracellular space, which acts as a fluid reservoir -overfilling = edema |
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K homeostasis
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maintained by:
1. Na/K pump 2. K permeability of the cell membrane 3. Na/K antiport -disturbances can cause life-threatenings shifts in ICS and ECS: bradycardia, arrhythmia and even heart arrest -kidney regulates K metabolism |
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urinary K excretion
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-most important regulating factors:
1. EC [K]: normally 4.1 mM, increase beyond causes excretion 2. plasma [aldosterone] |
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K in EC and IC
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-EC: only 2% K
- disturbance of Na/K pump or membrane permeability results in major changes eg releasing only 1% of the IC K to the ECF would almost double the EC K |
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K and acid/base balance
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-Na/K pump activity effected by IC pH: low pH decreases activity, vice versa
- acidosis (low pH): K accumulation in ECF -alkalosis (high pH): K depletion in ECF |
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urea and NaCl
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1. distal tubule and proximal collecting duct are impermeable to urea, but not water
2. H2O resorption causes high [urea] 3. driven by this gradient, urea diffuses back from distal collecting duct to ascending loop 4. interstitial osmotic P rises which drives NaCl back into blood therefore recycling urea saves NaCl |
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glucose
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-glucose filtered freely in glomerulus
- resorption capacity is limited - if [glucose] in plasma rises too high, the resorption system becomes saturate and glucose appears in urine =diabetes mellitus |
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H excretion
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-mainly exchanged for Na ions
- active transport: 1.secreted into lumen 2. excreted by collecting duct type A cells 3. alkalosis: type A turns to type B cells which reverse transport from lumen back into blood |
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bicarbonate
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-90% bicarbonate resorbed in the proximal tubule
- H secretion drives this - carbonic anhydrase catalyzes breakdown of H2O and CO2 to bicarb and H -bicarb returns to blood by a symport with Na and CO3- |
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Na-K pump general
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motor for urine formation via chemical, osmotic and electrical gradients
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ATP general
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fuel for formation of urine
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Bulk resorption
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takes place in the proximal tubule and loop of Henle:
88% of filtered H2O, 90% NaCl, 100% glucose |
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final urine composition
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-determined by hormones: ADH, ANF, aldosterone, angiotensin II, parathyroid
- control mainly resorption in the distal tubule and the collecting duct, but some in the proximal tubule and Loop of Henle |
