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67 Cards in this Set
- Front
- Back
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What makes up the extracellular fluid?
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Interstitial fluid, plasma and transcellular fluid
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What percentage of mammals is water?
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60%
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What portion of the internal environment is ECF and ICF?
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ECF 1/3
ICF 2/3 |
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How much more water do neonates typically need?
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About double the amount
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Define osmolality
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The aggregated amounts of osmotivally active particles in 1 kg of water
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How can one measure osmolality in the clinical setting?
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Refractometer
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What is the dominant osmotic cation in the ECF?
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Sodium
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For fluid replacement, what should be used?
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Something isotonic with the ECF, like 0.9% Saline
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In basic terms, how is osmolality defended?
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Changes are detected by osmoreceptors, and adjustments are made in water retention by the kidney and thirst
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(BIG ONE!) 9 functions of the kidney!
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1. Regulation of acid/base
2. Conservation of water and glucose from glomerular filtrate 3. Stability of ECF by controlling SODIUM 4. Excretion of wastes (urea, creatinine, ammonia) 5. Excretion of exogenous compounds (antibiotics) 6. Regulation of electrolyte balance and osmolality 7. Erythropoiesis 8. Production of CALCITRIOL 9. Production of GLUCOSE by gluconeogenesis during prolonged starvation |
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What is the functional unit of the kidney?
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The nephron
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What are the two types of nephrons?
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Cortical and Juxtamedullary
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What is responsible for ultrafiltration in the kidney?
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Glomerulus
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Discuss charge component of filter.
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Has a negative charge, which repels most molecules, especially proteins like albumin
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What is the GFR?
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Glomerular filtration rate, or how fast blood is filtered
Note: each glomerulus filters 0.1 mL daily in avg person |
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What is the main function of the glomerular filter?
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To recover sodium and glucose
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Where does most selective reabsorption occur in the kidney?
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In the proximal tubule - 65% of water, anions and cations recovered
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What methods does the proximal tubule use to transfer material from the tubule to bloodstream?
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Sodium-Potassium ATPase pumps and leaky tight junctions
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Why is the flow of water out of the leaky tight junctions?
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Because water follows the electrolytes out osmotically
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Where does the remaining reabsorption occur in the kidneys?
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In the distal tubule
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What occurs in the late distal tubule?
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Site of exchange of sodium, K+, etc under control of ALDOSTERONE and ADH
NOTE: 5% of Sodium recovered here |
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What is tubuloglomerular feedback (TGF)?
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The ability of the kidney to carefully monitor if the bulk recovery process is going well - ie not too much or too little sodium
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What is the term for the structural and functional elements of the TGF?
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The Juxtaglomerular apparatus
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What parts make up the juxtaglomerular apparatus?
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Macula Densa
Juxtaglomerular Cells Extraglomerular Mesengial (Lacis) Cells |
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What is the macula densa?
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Chemoreceptors that monitor volume flow in the distal tubule
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What are juxtaglomerular cells?
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Modified smooth muscle cells in afferent arteriole that release the enzyme RENIN
Note: Also called "granular cells" |
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What are extraglomerular mesengial cells?
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Located at macula densa and afferent arteriole and play a role in mediating TGF response
Note: Also the origin of erythropoietin |
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How does aldosterone help recover sodium?
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It stimulate sodium uptake by upregulating sodium channels and pumps
Note: Angiotensin II helps to release aldosterone when low bp is detected |
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How does ANP play a role in sodium recovery?
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Released in response to HYPERVOLAEMIA and acts to prevent sodium recovery
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What is different about the regulation of K+ from sodium?
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K+ can be secreted INTO the tubule
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Where are the principle cells located that secrete K+ and reabsorb Na+?
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Late DCT
Collecting duct |
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Explain a dietary K+ deficit.
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Intercalated cells reabsorb K+ using H+/K+ ATPASE
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Explain a dietary K+ excess.
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Aldosterone released, principle cells secrete K+
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What does aldosterone do in regard to K+?
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It stimulates expression of K+ channels and sodium pumps in principle cells.
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How are dietary fluctuations of K+ controlled?
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By the large reservoir in the ICF - but only until the kidney has time to secrete the excess.
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Where is Calcium reabsorbed?
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2/3 reabsorbed in PCT, and undergoes regulated absorption in DCT and collecting ducts under control of PTH
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What are the 3 contributions to calcium homeostasis?
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Low plasma calcium = PTH release =
1. calcium released from bone 2. increased absorption from gut 3. increated absorption from kidneys |
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Explain the structure of the collecting duct.
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Divided into inner medullary and outer medullary portions - passes through medulla allowing regulated reabsorption of water under control of ADH.
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What is the function of the collecting duct?
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Final site for excretion of toxic ions and the production of urine.
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Why is the regulation of water recovery from ducts important?
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It is part of the body's defense of osmolality
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How is water recovery regulated?
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A HYPERTONIC MEDULLARY INTERSTITIUM is created by the LOOP OF HENLE.
NaCl is reabsorbed w/out water in the thick ascending limb of the loop - "SINGLE OSMOTIC EFFECT" |
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How is urea recycled?
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Some urea diffuses into the ascending limb and adds to that already there - therefore is redelivered to collecting ducts and a higher concentration.
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What occurs in dehydration?
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A hyperosmotic plasma is detected by osmoreceptors in the hypothalamus.
ADH is secreted by the posterior pituitary and the cells of duct stimulated to insert preformed aquaporin-2 into apical membrane Therefore - H2O reabsorbed into hypertonic medulla. |
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What is a normal blood pH range?
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7.35-7.45
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How does pH affect the CNS?
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Acidaemia depressed the CNU while alkalaemia leads to hyperexcitability of it.
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What is the most important blood buffer?
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Carbonic acid/bicarbonate buffer
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What does the carbonic acid/bicarbonate buffer do?
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Acts to limit pH change due to metabolic production of acid.
More complex than other buffers because it has a volatile acid and 3 equilibria to be considered |
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What does metabolic CO2 do and how is it fixed?
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It acidifies the blood by adding to the acid component. This is quickly rectified by the lungs.
However, this leaves a bicarb deficit which must be fixed by the kidneys. |
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Where does the kidney recover bicarb?
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From the filtrate in the proximal tubule.
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How and why does the kidney produce bicarb?
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Even though it recovers bicarb from the filtrate, it must produce some to make up the deficit.
It uses phosphate to buffer protons released from carbonic acid. This allows the plasma level to correct. |
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What happens in chronic acidosis?
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The kidney will also use ammonia in place of phosphate to allow excretion of excess protons.
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What is the bicarb to acid ratio?
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20:1
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The renal blood flow is how much of the cardiac output?
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25% (and 90% of that is to the cortex)
NEED TO MAINTAIN GLOMERULAR FILTER!! |
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Explain the flow of blood through the kidneys.
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Go through the glomeruli through the afferent arterioles and exit via the efferent arterioles. They enter a 2nd capillary network (PERITUBULAR CAPILLARIES, which run alongside the tubule) and exit via the RENAL TUBULES.
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What is the major role of the Renin-Angiotensin-Aldosterone System (RAAS)?
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Regulation of blood pressure.
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What is renin released in response to?
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Released from the juxtaglomerular apparatus in response to either
1. decrease in Na+ conc 2. decrease in bp 3. decrease in distension of renal afferent arterioles |
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Once in circulation, what does RENIN do?
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It catalyses conversion of ANGIOTENSINOGEN to form ANGIOTENSIN 1 (ANG1), which is cleaved by converting enzyme ACE to form ANGIOTENSIN 2 (ANGII).
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Explain the renin negative feedback loop.
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ANGII inhibits further renin release.
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What are the 2 alternative pathways for ANGII formation that do not rely on renin?
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1. Tissue plasminogen activator (TPA) forms ANGII directly from angiotensinogen.
2. Enzymes like chymase form ANGII from ANGI via an ACE-independant mechanism. |
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What are the two types of ANG11 receptors?
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AT1 (AT1a and AT1b) - found throughout most tissues, binding results in actions of ANGII
AT2 - little known |
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What are the 5 effects of binding ANGII?
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1. Constriction of renal efferen arterioles to preserve filtration during hypotension.
2. Stimulating exchange of H+ for Na+ w/in PCT. 3. Promoting release of aldosterone from adrenal cortex. 4. Stimulate thirst, increasing fluid intake 5. Promotes release of endothelian from endothelium - a potent vasoconstrictor. AKA - INCREASE PERMEABILITY OF COLLECTING DUCT TO Na+, INCREASING ABSORPTION |
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What antagonises ANGII?
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ANP - Atrial Naturetic Peptide
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What does ANP do?
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Promote vasodilation and diuresis.
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Explain BRADYKININ
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Active peptide which is synthesized by cleavage of a kininogen precursor.
Increases vascular permeability and contraction of nonvascular smooth muscle. |
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Explain PROSTACYCLIN (PGI2).
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Produced by endothelial cells and prevents platelet clumping.
It is a vasoidilator. |
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Explain ADH.
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Has weak vasoactive actions. Released from posterior pituitary in response to a drop in BP or decreased blood volume.
Acts on receptors in collecting ducts to increase reabsorption of H2O and promotes vasoconstriction. |
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Explain NO.
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Responsible for vasodilation.
Most pronounced in renal afferent arterioles. Inhibited by ANGII. Maintains normal vascular tone and BP. |
