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319 Cards in this Set
- Front
- Back
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What are three types of capillaries found in the body?
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Continuous, fenestrated, and discontinuous
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What are continuous capillaries and where are they found?
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Capillaries with tight junctions that have low water and protein permeability; common in muscle nerve
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What are fenestrae?
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Circular pathways through cells that allow passage of water and protein (create specialized barrier)
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Where are fenestrae most common? Most rare?
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Common in liver and intestine; rare in brain and CNS
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What are podocytes?
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Interdigitating fingers that block large molecules from passing thorough fenestrae
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What organ contains podocytes? Why?
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Kidney so that water can pass but proteins cannot be excreted
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What is a glial cell?
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Supportive cells in capillaries that modulate permeability
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What are discontinuous capillaries?
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Capillaries with a gap that allows very high permeability to both water and proteins
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Where are discontinous capillaries found?
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Liver, bone, and spleen
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What is the major mode of transport across in transcapillary exchange?
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Diffusion
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What is the driving force for diffusion?
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Concentration gradient
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What molecules are most easily diffused?
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Lipid-soluble, oxygen, carbon dioxide
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How do water soluble molecules diffuse?
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Through pores and around cells
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What percentage of the capillary surface comprises pores?
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0.02%
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Describe bulk flow.
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Water flows through large pores; accounts for only a small fraction of exchange
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What type of flow is bulk flow? What is its driving force
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Poiseuille; hydrostatic pressure
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True or false, water will drag solute through pores during bulk flow?
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True
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What is pinocytosis?
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Vesicular transport across endothelium that involves encapsulation of EC solution
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In what organ does active transport play a role in transcapillary exchange? Why?
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Brain; BBB blocks other types of exchange (except for lipids)
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What molecules are actively transported in the brain?
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Glucose, amino acids, Na+, K+, H+
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What is a caveolus?
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Specialized site for signal transduction that associate with NOS; may form channels
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What is the equation for Fick’s Law
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Flux = DA ΔC/ΔX
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True or false, all variables of Fick’s law are under physiological control?
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True
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What is the relationship between metabolism and capillary perfusion
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As metabolism increases so does capillary perfusion
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As flow increases oxygen extraction by tissues…
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Decreases
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What two things must increase to increase oxygen consumtion in skeletal muscles?
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Oxygen extraction efficiency and blood flow
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What is Starling’s equation?
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Water flux = k[(Pc-Pi)-(∏p-∏i)]
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What are the two driving forces for water movement?
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Hydrostatic pressure and osmotic pressure
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What is the typical hydrostatic pressure gradient?
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~32 mmHg at arterial end
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What is the colloid osmotic pressure?
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Osmotic pressure contributed by proteins
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What is the Gibbs-Donnan equilibrium?
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The association of small ions with large negatively charged proteins
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What is the effective COP?
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~27 mmHg
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True or false, increase in arterial pressure influences hydrostatic pressure more?
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False – venous pressure more greatly influences capillary hydrostatic pressure
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When hydrostatic pressure > COP…
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Filtration ↑ and there is net water efflux
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When hydrostatic pressure < COP…
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Absorption ↑
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Normally what percentage of volume is filtered out of capillaries, and of that portion what is reabsorbed?
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2%; 85%
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If arterioles dilate…
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Hydrostatic pressure ↑ and filtration ↑
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If arterioles constrict…
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Hydrostatic pressure ↓ and absorption ↑h
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If COP falls what is the long term effect?
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Edema - ↑ in interstitial fluid
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Define lymphatic system.
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Tubular, blind-ended, ramifying vessel system that returns excess water filtered in the capillaries (water not reabsorbed)
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What are the 4 main functions of they lymphatic system?
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Return interstitial fluid to CS, return proteins, absorb lipids from GI and transport them to CS, immune functions
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How is lymph moved back to heart?
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Vasoconstriction and VSM pumping; also constriction of skeletal muscles
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What are the 3 connective loops?
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CO, capillary absorption/filtration, lymph
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What is vasodilatory reserve?
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Magnitude of capacity to ↑ blood flow
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What percent of CO does the brain receive?
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15-20%
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What is the most important mediator for cerebral autoregulation? Less important?
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pCO2; pO2 (↑ CO2 = ↑ flow)
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Describe SNS influence in brain?
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Very little – local mechanisms easily override SNS effects
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What are common metabolic vasodilators in the brain?
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Adenosine, and K+
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Define autoregulation.
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Ability of organ to regulate blood flow independently of arterial pressures
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What organ receives the largest % of CO?
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Kidney – 20-25% - processes blood
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In the kidney oxygen extraction is …
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Very low – 5-10%
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What are two autoregulation regulations of the kidney?
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Myogenic and tubuloglomerular feedback (excellent autoregulation)
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What is splanchnic circulation?
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Blood flow through GI tract and liver
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What are local vasodilators in the GI tract?
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Histamine, bradykinin, vasoactive intestinal peptide, gastrin, cholecystokinin
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What percent of total blood volume is in the splanchnic circulation?
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20-25%
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What is the effect of vagal stimulation on the GI tract?
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↑ in Q due to ↑ metabolism and local hormone release
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In the GI tract autoregualtion is…
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Moderate
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What occurs after a meal in GI circulation?
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Local hormones ↑ and blood flow ↑
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What are the major factors influencing coronary blood flow?
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A-V pressure gradient, compression by ventricular contraction, metabolic activity of myocardium, activity of SNS and PNS
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The heart has a very ____ oxygen reserve.
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Small (already extracting large % at rest)
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Coronary blood flow ____ during systole.
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Decreases
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To increase oxygen the heart….
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Increases vasdilatory perfusion
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What effect does heart rate have on diastole and blood flow?
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Decreases time for diastole and increases need for blood flow
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What does an intraaortic balloon do during the heart cycle?
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Inflates during diastole to ↑ driving force and deflates during systole to ↓ afterload; effective in ↑ coronary perfusion
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What is the major factor that can increase in skeletal muscle?
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Vasodilatory reserve (can ↑ 20X)
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Control is _____ dominant at rest and _____ dominant during exercise.
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Neural (SNS); local metablolic
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What are vasodilators in skeletal muscles?
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K+, adenosine, and prostaglandins
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What is skin’s most important function?
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Thermoregulation
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What part of the brain controls skin thermoregulation?
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Hypothalamus
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What are the two types of resistance vessels for thermoregualation?
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Normal arterioles and A-V shunts
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Sympathetic cholinergic stimulation causes sweat gland to release what?
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Proteins which form bradykinin
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What is bradykinin?
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Vasodilator
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Skin autoregulation is…
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Very poor – very poor metabolic control
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Increased body temp causes what response?
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↓ SNS which relaxes VSM and opens A-V shunts, also vessels dilate and sweat gland activity ↑
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What problems does standing upright cause?
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↑ hydrostatic pressure at feet, transmural pressure ↑, small venous pressure ↓ causing a ↓ in driving force to heart, ↑ capillary filtration due to hydrostatic pressure ↑
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How does the body compensate for standing upright?
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↑ TPR, ↑ skeletal muscle pumps, ↑ venous return, ↓ venous compliance,
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What part of the brain receives signals on cardiovascular changes?
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Medullary
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An increase in SNS activity results in what?
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↑ heart rate, ↑ contractility, ↑ TPR, ↓ stroke volume, ↓ CO, ↓ vascular capacitance
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After standing what occurs when a person starts walking?
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All the values are reversed (CO↑, SV↑, RAP↑, HR ↓)
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Sitting causes hydrostatic pressure to…
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Increase
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What is anticipation?
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↑ SNS activity by “central command” before exercise begins
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Where does blood flow ↓ during exercise?
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Splanchnic and renal
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What two areas compete for blood flow during exercise?
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Active skeletal muscle and cutaneous
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Why does resistance ↓ in active muscle even though SNS ↑?
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Local metabolites cause vasodilation
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Why does net TPR decrease?
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Active muscle metabolic vasodilation > inactive muscle SNS vasoconstriction
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What role does the adrenal play in exercise?
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Adrenal hormones Epi and NE support increased in heart rate and contractility
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During exercise MAP…
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Increases
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Respiratory pump action is __ by exercise.
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Enhanced
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Small increase in MAP is a result of what type of changes in CO and TPR?
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CO increases 5x while TPR decreases 80% (4/5) results in slight increase in MAP
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What 2 things send signals to the medullary CV brain center?
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Muscle and joint stretch receptors and muscle chemoreceptors
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During exercise the ↑ in CO is linearly related to what?
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Heart rate
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Workload is linearly related to what?
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O2 consumption and extraction
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What drops rapidly post exercise?
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HR and CO and therefore MAP
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What remains elevated for some time post exercise?
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Total periphery resistance
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What occurs if venous return is not enhanced by movement post exercise?
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Fainting due to rapid MAP decrease (< 50 mmHg)
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Hemorrhage – loss of ____ of blood vol
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10%
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What occurs due to an ↑ in Angiotensin II?
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Vasoconstriction (response to hemorrhage)
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↑ renin results in what?
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Decreased urine flow
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↑ AVP results in what?
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Increase water retention
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Effects of SNS and adrenals after blood loss results in what?
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↑TPR, ↑CO, and ↑MAP
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In what organ is blood flow environmentally controlled?
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Skin
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In what organ does vasoconstriction not occur during hemorrhage?
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Heart – due to ↑ in HR and contractility
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What % of the body is water?
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60%
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Lean people will have ___ body water than fat people
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More
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What tissues of the body have the greatest % of water?
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Muscle (76%), brain (74%), skin (72%), intestine (74%), and blood (83%)
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What tissue contributes the most water to the total body %?
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Muscle
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What tissue has the lowest water content?
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Adipose
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What compartments is body water distributed to?
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Plasma, interstitial fluid, transcellular fluid, and intracellular fluid
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What are the 4 colligative properties?
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Vapor pressure, freezing point, boiling point, and osmotic pressure
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When measuring osmotic pressure it is defined as…
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The hydrostatic force required to prevent water flux
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What causes non-ideal osmotic behavior?
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Ionized salts
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What is the equation you use to find the osmotic pressure of a non-ideal solution?
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π = RT(φiC) φ = osmotic coefficient
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What is the osmolarity equation?
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Osmolarity = φiC
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Osmotic pressure can only occur in what circumstances concerning solute/solvent?
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The permeability of the solute must be less than the solvent
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What is the “reflection coefficient (σ)”?
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The relative solute to solvent permeabilities
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Protein σ = ?
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1
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Small solute σ = ?
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0
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What small solutes are not restrained by the capillary wall?
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Glucose, Na, K, Cl,
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How is water distributed in the body?
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60:40:20 (60% body water with 40% ICF and 20% ECF)
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What is the equation to determine volume from a diluted indicator?
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Volume = tracer quantity injected
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What is the tracer for total body water?
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HTO or D2O
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What is the tracer for ECF?
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Inulin or radio-sodium
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What is the tracer for plasma?
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131I-albumin or Evans blue
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What is the tracer for blood(plasma + RBC)?
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51Cr-RBC’s
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How is interstitial volume determined?
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ECF – plasma
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How is ICF determined?
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TBW – ECF
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What is inulin?
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Plant starch with β-linkage that cannot be digested (can’t get in cell)
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What 3 things contribute to water intake?
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Drinking, eating, cellular metabolism
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What 4 things contribute to water output?
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Urine, fecal, insensible, sweat
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What is insensible water loss?
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Evaporative water loss through lungs and across skin
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True or false water input is driven by water output?
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True
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What occurs to water loss during exercise or hot weather?
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Sweat and insensible losses greatly ↑ while urine losses ↓
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What type of solution causes water to leave the cell?
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Hypertonic
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What type of solution causes water to enter the cell?
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Hypotonic
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What are the units for osmolarity?
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Osmoles/liter
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What are the units for osmolality?
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Osmoles/kg
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What are the 3 simplifying assumptions for body fluid calculations?
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Osmotic equilibrium between compartments, solutes remain in original compartment, no hydrostatic gradient
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Water distributes ___ ECF and ___ ICF
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1/3 ; 2/3
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Total osmolytes = ?
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TBW(liters) X osmolality (milliosmoles/L)
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Where would an NaCl solution distribute?
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ECF
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How would the intake of 4 liters of water affect the ECF and ICF? (or loss of 2 liters)
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1/3 would distribute to the ECF (1.5L) and 2/3 would go to the ICF (2.5L) (= for loss)
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How would the loss of 2 liters of blood affect ECF and ICF?
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ECF would lose 1 liter (due to plasma ↓) and ICF would lose 1 liter (due to RBC ↓)
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What occurs during isotonic expansion?
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ECF↑, Hct↓, ICF no change, ECF osmolarity no change
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What occurs during isotonic contraction?
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ECF↓, Hct↑, ICF no change, ECF osmolarity no change
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What occurs during hypertonic expansion?
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ECF↑, ICF↓, ECF osmolarity↑, Hct↓, ECF [Na+]↑
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What occurs during hypertonic contraction?
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ECF↓, ICF↓, ECF osmolarity↑, Hct↑, ECF[Na+] ↑
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What occurs during hypotonic contraction?
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ECF↓, ICF↑, ECF osmolarity↑, Hct↑, ECF[Na+]↓
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What occurs during hypotonic expansion?
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ECF↑, ICF↑, ECF osmolarity↓, Hct↑, ECF[Na+]↓
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Expansion always results in what?
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ECF increase
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Contraction always results in what?
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ECF decrease
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Hypertonic always refers to what?
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ICF decrease and ECF[Na+] increase
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Hypotonic always refers to what?
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ICF increase and ECF[Na+] decrease
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What causes isotonic volume expansion?
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Isotonic NaCl infusion
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What causes isotonic volume contraction?
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Diarrhea – loss of ECF
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What causes hypertonic volume expansion?
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Concentrated NaCl infusion
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What causes hypertonic volume contraction?
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Sweating, fever, diabetes insipidus
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What causes hypotonic volume contraction?
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Adrenal insufficiency – loss of salt
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What causes hypotonic volume expansion?
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Syndrome of inappropriate ADH
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Why don’t cells stay at an electrochemical equilibrium?
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Na-K pump makes sodium functionally impermeant
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What is mannitol? What is it used for?
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Monosaccharide that causes diuresis in the kidney; used to ↓ intercranial pressures
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What occurs during a regulatory volume increase(RVI)?
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Cell shrinking activates ion transporters and NaCl enters the cell followed by water for an increase to normal cell volume
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What 2 transporters are activated by RVI?
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Na/K/2Cl cotransporter and Na-H exchanger
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What occurs during a regulatory volume decrease (RVD)?
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Cell swelling activates ion pathways and KCl exits the cell followed by water for a decrease to normal cell volume
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What pathways are activated by RVD?
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KCl cotransporter, K+channel and Cl-channel
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What are the 5 main functions of the renal system?
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H2O and salt excretion, excretion of wastes, acid-base regulation, endocrine functions
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What is renin?
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Hormone that forms angiotensin
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What is erythropoietin?
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Hormone that stimulates RBC production
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The outer portion of the kidney is called…
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Cortex
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The inner portion of the kidney is called…
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Medulla
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Medulla is segmented into areas called…
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Pyramids
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What is a nephron?
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Functional unit of the kidney consisting of filtering glomerulus and tubule
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What is the role of the mesangium in the glomerulus?
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Forms supporting matrix for capillaries and salvages leaked macro-molecules; may control distribution of blood flow
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What are the 3 layers of the filtration barrier?
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Capillary endothelium, basement membrane, podocytes
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What 3 things make up the juxtaglomerular apparatus (JGA)?
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Macula densa, afferent arteriole, extraglomerular mesangium
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What is the stimulus of the JGA?
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↑ flow in the proximal tubule sensed by the macula densa
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What is the effect of stimulus in the JGA?
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↑ resistance in the afferent arteriole to ↓ filtration rate of the glomerulus
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Where in the JGA is renin stored?
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Granular or juxtaglomerular cells
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What are the 2 types of nephrons?
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Cortical and juxtamedullary
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Where portion of the kidney is contains only juxtamedullary nephrons?
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Inner medulla
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Which nephron has an ↑ filtration rate?
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Juxtamedullary
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What type of capillaries are associated with cortical nephrons?
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Peritubular
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Vascular bundles and vasa recta are components of what type of nephron?
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Juxtamedullary
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Differentiate the proximal convoluted tubule from the proximal straight tubule.
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PCT has a well developed brush border and is less involved in transport
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In what part of the nephron are thick cells with ↑ mitochondria found?
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Distal tubule and loop of Henle due high rates of transport
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What changes are seen in hydrostatic pressures across the glomerular capillaries?
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No change; hydrostatic pressure is maintained relatively constant
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What % of renal plasma flow is filtered?
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20%
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What are the 2 mechanisms of autoregulation for the kidney?
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Myogenic and tubuloglomerular feeback
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What is involved in myogenic autoregulation?
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Glomerular arterioles prevent changes in blood flow despite arterial pressure change
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What is involved in tubuloglomerular feedback?
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Distal tubule flow is the signal for the JGA to regulate glomerular filtration
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What molecules are used for transferring JGA signal to the afferent arteriole?
Which is the main one and what do they do? |
Main: Adenosine (here it acts as a vasoconstrictor)
ATP, NO, prostaglandins - these induce vasodilation |
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What are the 2 capillary beds of the cortical nephron?
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Glomerular capillaries and peritubular capillaries
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Colloid osmotic pressure ____ as fluid progresses through the glomerulus.
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Increases
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What is Starling’s formula for the glomerulus?
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GFR = Kf [(Pc-PBS) – COPx]
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What favors filtration at the glomerulus?
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Capillary hydrostatic pressure and Bowman’ capsule osmotic pressure
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Compare systemic capillary pressure to glomerular capillary pressure?
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Systemic pressure is lower and changes as fluid moves across
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If efferent pressure ↑ than GFR will ___?
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Increase
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If afferent pressure ↑ than GFR will ___?
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Decrease
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As renal blood flow ↑ the GFR will ___?
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Increase but be less of the filtered volume
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The glomerular filtration barrier repels what molecules of what charge?
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Negative; barrier has strong negative charges which attract + charged molecules
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What occurs during nephrotic serum nephritis?
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Negative charge of filtration barrier is lost and anion filtering increases
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For substance the body needs to conserve the clearance will be ___.
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Low
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What is the definition of renal clearance?
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Volume of plasma that is completely cleared by the kidney per unit time
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What three things contribute to the amount of a substance excreted in the kidney?
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Glomerular filtration, tubule reabsorption and tubule secretion
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The excreted amount = ?
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Urine concentration X rate of urine flow
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The amount filtered = ?
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Glomerular filtration X plasma concentration
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What are the 4 requirements for a GFR marker?
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Freely filtered, not reabsorbed or secreted, not metabolized or bound, can be measured
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What are 2 common GFR markers?
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Inulin and creatinine
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For inulin renal clearance is ____ GFR
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Equal to
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As plasma creatinine ↑, GFR ___
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Decreases
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At what % of normal GFR does renal failure begin to occur?
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25%
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Aging causes the # of nephrons to ___
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Decrease
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During pregnancy GFR ___ and PCr ___
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Increases; decreases
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Amount reabsorbed = ?
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Amount filtered – amount excreted
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Amount secreted = ?
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Amount excreted – amount filtered
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PAH is totally ____ by the kidney.
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Secreted
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What is fractional clearance?
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Ratio of “x” renal clearance to inulin
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If fractional clearance = 1.0 then …
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There is no net absorption or secretion
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If fractional clearance > 1.0 then…
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There is net secretion
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If fractional clearance < 1.0 then…
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There is net absorption
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What is the tubular transport maximum (Tm)?
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The maximum rate of reabsorption observed for organic solutes
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What are 2 clinical situations in which the Tm for glucose is exceeded?
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Type I diabetes (due to ↑ blood glucose) and pregnancy (due to ↑ GFR)
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When does secretion = excretion for PAH?
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At low plasma concentrations
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Why is PAH only actually 85% excreted?
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Some blood bypasses proximal tubules
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U/PInulin increases as ….
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Water is reabsorbed
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If U/PInulin = 2.0 then water reabsorption =?
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50%
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What is free-water clearance?
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The volume of plasma that is completely cleared of pure water per unit time
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When is positive free-water clearance observed?
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When hyposmotic urine is formed and net free water is removed
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When is negative free-water clearance observed?
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When hyperosmotic urine is formed and net free water is “virually” gained due to excretion of osmolytes
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Total body [K] ___ total body [Na]
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Greater than
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What is located on the basolateral membrane of cells along the nephron?
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Sodium-potassium pump and potassium channels
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The Na-K pump acts like the ____ for electrolyte transport.
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Battery or electromotive force
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What causes a short-circuit in the epithelium?
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Paracellular leaky tight junctions
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What transports Na across the proximal tubule membrane in the nephron?
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Na-H exchanger and Na-glucose contransporter and leaky tight junctions
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What is isosmotic fluid reabsorption and where does it occur?
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Absorption of water and Na in equal proportions so that osmolality remains constant; occurs in the proximal tubule
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What % of water and Na is absorbed in the proximal tubule?
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67%
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What other molecules are reabsorbed in the proximal tubule?
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Bicarbonate ,amino acids, glucose, potassium, chloride, urea, etc…
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In the kidney O2 consumption is directly related to what?
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Rate of sodium transport
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What contributes to sodium transport across the TAL membrane in the nephron?
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Na, K, 2Cl cotranporter, inward K channel, tight tight junctions (only allow Na to pass)
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What is on the apical membrane of the distal convoluted tubule epithelial cells?
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Na-Cl cotransporter that is Thiazide sensitive
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What is on the apical membrane of the cortical collecting duct epithelial cells?
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Outward sodium channels (ENaC) and inward K channels
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What is the effect of a carbonic anhydrase inhibitor?
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Reduced the effectiveness of Na-H pump in the early PT and ↓ HCO3- reabsorbed
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What is effected by amiloride?
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ENaC channels in CT; K-saving diuretic
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What 3 things does aldosterone cause in the epithelial cells of the kidney?
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↑ in Na-K pumps, ↑ in ENaC (Na channels), ↑ mito ATP production
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What 2 things stimulate aldosterone release
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Angiotensin II and ↑ in plasma [K]
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What is the net result of ↑ aldosterone?
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↑ Na reabsorption and ↓ K reabsorption
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What does NE released by renal sympathetic nerves activate in the kidney?
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Na-H exchanger in apical mem and Na-K pump in basolateral mem of proximal tube
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What does angiotensin II increase in the kidney?
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Na-H exchanger in apical mem of proximal tubule; ENaC channels in distal tubule; aldosterone secretion
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What is the effect of AVP in the kidney?
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In TAL stimulates Na/K/2Cl cotransporter and K channels; in principle cells ↑ ENaC channels
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What is AVP sensitive to changes in?
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Osmotic pressure (mainly) and volume
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What is the glomerulotubular balance?
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Intrinsic ability of proximal tubule to reabsorb a constant fraction filtered Na and water load despite GFR changes
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What occurs when the efferent arteriole pressure increases?
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Filtration fraction ↑ causing COP to ↑ and Pc to ↓ leading to ↑ reabsorption of fluid
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As GFR increases Na-couple solute transport ____.
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Increases
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True or false, sodium has a Tm?
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False, sodium can diffuse passively
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The distal nephron will do what as sodium load increases?
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Increase sodium reabsorption
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What action does atrial natriuretic peptide have on the kidney?
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↓ activity of non-selective cation channels in inner medullary collecting duct via cGMP; ↑ Na excretion
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What does prostaglandin do to the kidney (opposite action of AVP)?
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Inhibits apical K channels in TAL which depolarized the membrane and ↓ paracellular cation reabsorption;
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What does bradykinin and prostaglandin do to the kidney?
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Inhibit the apical ENaC channels in the cortical collecting tubule
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What the effect of nitric oxide in the kidney?
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Inhibits Na-H cotransporter in proximal tubule and Na/K/2Cl cotransporter in TAL
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What effect does hyperkalemia have on the EKG?
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Indiscernible P wave with widened QRS
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What is the effect of hypokalemia on the EKG?
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Flattened T wave merges with U wave
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What % of potassium is reabsorbed in the proximal tubule despite any change in [K]?
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80%
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What % of K is reabsorbed in the TAL despite any change in [K]?
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10%
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With a normal-high K diet what occurs in the distal tubule?
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20-180% of K is secreted into the lumen
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With a low K diet what occurs in the distal tubule?
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2% of K is reabsorbed by α-intercalated cells’ H-K exchanger
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What’s the normal % of K excreted?
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10-15%
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What occurs in the collecting duct with a normal to high K diet?
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20-40% of K is reabsorbed
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What occurs in the collecting duct with a low K diet?
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6% of K is reabsorbed (lower b/c K is also absorbed in the distal tubule)
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What is the % of K excreted with a low K diet?
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1-3%
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Why is it more important to monitor K balance in diet than Na?
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Ability to alter the excretion % is greater with Na (~0%) than with K (1-3%)
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How is K absorbed in the proximal tubule?
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Passively via paracellular pathways
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How is K absorbed in the TAL?
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Paracellularly and Na/K/2CL cotransport
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How is K absorbed in the cortical collecting tubule?
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H+-K+ countertransport in the α-intercalated cells
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How is K secreted in the cortical collecting tubule?
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Uptake across basolateral by Na-K pump, diffusion via K channels across apical
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What affect would aldosterone have on potassium excretion?
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It would ↑ excretion by ↑ secretion by ↑ Na-K pumps in basolateral membrane
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What affect does ↑ distal flow rate have on K secretion?
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↑ K secretion by washing away K and ↑ Na entry which ↑ electrical gradient for K exit
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What affect does apical Na entry have on K secretion?
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↑ K secretion by ↑ the electrochemical gradient for K exit
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How does alkalosis affect K secretion?
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↑ K secretion by ↑ cell uptake – results in an ↑ gradient for secretion in principle cells
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How does aldosterone affect K secretion?
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↑ K secretion by ↑ Na-K pumps in basolateral, ↑ ENaC in apical, ↑ K channels in apical
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How does a high K diet affect K secretion?
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↑ K secretion by ↑ aldosterone, ↑ distal flow, and ↑ Na delivery
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K secretion is _____ dependent on flow.
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Highly
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What effects do insulin and epinephrine have on K secretion?
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↑ K secretion by ↑ Na-K pump and K channels in apical membrane
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What effects does acidosis have on K secretion?
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↓ K secretion due to loss from the ECS and ICS and inhibition of the Na-K pump
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What acts as a K buffer after meals?
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Cells which take in large amounts of K
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K wasting diuretics affect what area of the nephron?
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Any area upstream of principle cells
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Where are K sparing diuretics effective?
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At the principle cells
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What are 3 K wasting diuretic examples?
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Lasix, carbonic anhyrase inhibitor, thiazide
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What is a K sparing diuretic?
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Amiloride
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What % of urea is reabsorbed in the proximal tubule?
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50% ; obligatory reabsorption
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What happens to urea in the loop of Henle?
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60% is secreted
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What % of urea is reabsorbed in the inner medullary collecting duct?
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70%
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What % of filtered load of urea is excreted
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40%
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How is urea reabsorbed in proximal tube?
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Passively through paracellular pathway
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How is urea secreted in the TDL?
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UT2 transporter?
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How is urea secreted in the TAL?
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Unknown transporter
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How is urea absorbed by the collecting duct?
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UT1 transporter in the apical membrane and UT4 transporter in the basolateral
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Urea excretion rate varies with what?
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Urine flow rate
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How does dehydration affect urea concentrations in blood?
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BUN/creatinine ↑ due to decreased urine production and decreased urea excretion
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Urea excretion is _____ filtered load.
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Proportional to; Uurea • V α GFR • Purea
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Where is the transport work to make dilute urine done?
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distal portion of the nephron (isosmotic urine is delivered to distal portion)
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What is necessary to maintain a large sodium gradient in the distal nephron?
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Tight tight junctions and tubular epithelium with low water production
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What makes the collecting duct permeable to water?
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Arginine vasopressin
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In diuresis what is reabsorbed in the collecting duct?
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NaCl
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In an anti-diuretic state what is reabsorbed in the collecting duct?
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Water via aquaporins
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What must be present for water to be reabsorbed (an anti-diuretic state)?
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Arginine vasopressin
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What % of water is reabsorbed in the proximal tubule?
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67% (the same as sodium)
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What % of water is reabsorbed in the loop of Henle?
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15%
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What % of water is reabsorbed in the distal tubule and collecting ducts?
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8-17% - all collecting duct because distal tubule is impermeable to water
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What volume of urine is indicative of renal failure?
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<0.5 liters/day
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What creates the large osmotic gradient in the renal medulla?
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Loop of Henle – functional counter current multiplier
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Why is it necessary for a large osmotic gradient to exit?
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Collecting duct uses the gradient to reabsorb water
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What gradient is the TAL capable of creating?
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200 mOsm
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What role does the vasa recta play in creating the osmotic gradient?
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Travels in parallel with loop of Henle and passively absorbs NaCl carrying it to tip
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As you go deeper in the kidney what happens to [urea], [Na], [Cl]?
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All increase
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What is reabsorbed/secreted in the descending loop of Henle?
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Water is reabsorbed, urea and NaCl don’t move b/c descending loop is impermeable
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What is reabsorbed/secreted in the ascending loop of Henle?
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NaCl is reabsorbed – passively in ThinAl and actively in ThickAl
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What agents inhibit AVP action?
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Protaglandins, calcium, protein kinase C
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How does AVP ↑ aquaporins in the apical membrane of the collecting tubule cells?
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Binds to receptor→ G-protein/kinase cascade→ gene transcription of AQP2
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What concentration of water enters the collecting ducts?
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120 mOsm
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What is the concentration of urine during an anti-diuretic state?
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1200 mOsm
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