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Flashcards in physiology Deck (68)
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Average input and output in a day?

- 2500 in and 2500 ml out
metabolism 10%
foods 30%
beverages 60%

feces 4%
sweat 8%
insensible losses via skin and lungs 28%
urine 60%


What is hydrostatic pressure?
Osmotic pressure?

HP: pressure due to fluid pushing against vessels wall - pushing fluid out of the capillary (in capillary 35 mm Hg at arterial end and 17 mm at venous end)

OP: pressure due to presence of nondiffusable solutes (plasma proteins)
- in capillary: pulling fluid in


What leads to an increase in Na+ concentration in the body? (hypernatremia)

- water loss
- Na+ excess
(normal plasma Na+ = 140-145 mmol/L)


What leads to a decrease in Na+ in the body? (hyponatremia)

- water excess
- Na+ loss


Consequences of hyponatremia and hypernatremia?

- water moves in or out of cells: cells will shrink or swell, this has profound effects on the brain
- neuro function is altered:
rapid shrinking can tear vessels and cause hemorrhage
rapid swelling can cause herniation because skull is origin, brain can't increase volume more than 10% w/o herniation


Difference b/t hypertonic and hypotonic solution and effect on cells?

- in hypotonic - cell swells because solution isn't as concentrated, water moves into the cell
- in hypertonic: cell shrinks because solution is so overly concentrated - water moves out of the cell


What does extracellular hypertonicity increase? clinical significance?

- expression of gene encoding proteins that increase intracellular osmoles:
membrane transporters: Na+-H+ exchanger
enzymes: aldose reductase that synthesize intracellular solutes (sorbital)

clinical significance: rapid changes in ECF tonicity alter cell volume and cause neuro complications, while slow changes have much less effect on cell volume and much less clinical effect


Largest percentage of body fluid?

- intracellular fluid: 28 L


Describe how body stays in equilibrium with fluids?

- fluid loss= fluid intake
- electrolyte loss = electrolyte intake

- fluid intake: reg by thirst mech, habits
- elect intake: dietary habity
- fluid output: reg mainly by kidneys
- elect output: reg mainly by kidneys


Function of the glomerulus?

- filtration of blood
- network of capillaries involved in 1st step of urine formation
- receives blood from afferent arteriole and leaves glomerulus by efferent arteriole.
- plasma filtrate flows from glomerulus into bowmans capsule
(glomerulus + bowman's capsule = renal corpuscle - fxn production of filtrate)


Function of Bowman's capsule?

- Beginning of nephron, receives filtrate from glomerulus
- plasma filtrate passes through 3 layers:
1) capillary endothelium
2) basement membrane (neg charged) - almost any molecule smaller than 3 nm can pass freely into capsular space.
3) podocytes of Bowman's capsule
- molecules that can be filtered out: water, salt ions, electrolytes, glucose, AAs, and urea, lipids
- larger molecules: proteins, RBCs don't normally get filtered out (unless kidney infection or trauma - let proteins and RBCs pass through)


Where does most of the active secretion occur?

- distal convoluted tubule: uric acid, K+, H+, drugs, foreign substances, creatine, bile salts


Where does most of the reabsorption occur? difference b/t active and passive transport?

proximal tubule
- active transport: require ATP - Na/K pump, symporter (Na with glucose or AAs), antiproton (Na+ and H+)
- passive transport: Na symporter (glucose, aas), ion channels, osmosis of water (medulla)


What factors affects reabsorption?

- high concentration of solute can exceed the threshold of the kidney's ability to reabsorb it. (ex: glucose - 180 mg/dl - renal threshold). If above threshold - then it will spill in the urine

- rate of flow: increased rate of flow decreases reabsorption


What is the function of the proximal convoluted tubule?

- very active, infolded plasma membrane - one layer of epithelial cells with long apical microvilli, reabsorbs about 65% of glomerular filtrate
- 75% of Na is reabsorbed here
- TUBULAR REABSORPTION of vital substances is primaray fxn of PCT
- isotonic reabsorption of all organic nutrients (glucose and aas), and most bicarb, Na+ and chloride, and 75-90% of H2O
- generates and secretes ammonia (buffers pH)
- ** angiotensin II acts in proximal tubule to increase Na+ and H2O reabsorption. PTH acts on this to increase phosphate excretion


What drugs work on the PCT?

- acetazolamide and mannitol


2 different categories of nephrons?

- cortical: 85% of nephrons, originate in superficial part of cortex, they have short, thick loops of Henle that penetrate only a short distance into the medulla.
- juxtamedullary nephrons: remaining 15%, originate deeper in corext and have longer and thinner loops of Henle that penetrate the entire lengh of the medulla. These are largely concerned with urine concentration


How many liters of filtration a day do the kidneys produce? O2 consumption?

- 180 L = 47 gallons
178.5 L gets reabsorbed
normal GFR: 120-125 ml/min

- O2 consumption: 20-25% of body's O2


steps of kidney functions?

1: glomerular filration
2: tubular reabsorption removes useful solutes from the filtrate, returns them to the blood
3: tubular secretion removes add wastes from the blood and adds them to the filtrate
4: concentration: removes water from urine, concentrates wastes


Function of the loop of Henle (thin descending limb)

- passively absorbs H2O (perm to H2O) but impermeable to sodium and solutes


Function of thick ascending limb of loop of Henle?

- impermeable to H2O but actively reabsorbs Na+(25%), K+, Cl- via co-transporter
- indirectly aids in reabsorption of Mg+ and Ca+
- TAL helps maintain hyperosmotic medullar gradient needed to produce concentrated urine (in presence of ADH)


What diuretics work on TAL? SE of these diuretics?

- loop diuretics
- unable to concentrate urine - produces very dilute urine

- SEs:
hypocalcemia, hypomagnesemia, and hypokalemia. decreases reabsorbtion of Na+, K+, and Cl- and also indirectly inhibits Mg+ and Ca+ reabsorption.

- hypochloremic metabolic alkalosis: since chloride is lost due to reduced absorption, body reabsorbs bicarb to maintain electro neutrality
- hyponatremia: prevent concentration of urine (more common in thiazide diuretics)


Function of Early DCT?

- reabsorbs Na+ (5%)
- TUBULAR secretion is the main job (organic acids, toxins, drugs, K+, H+)
- dilutes urine by actively reabsorbing Na+ and Cl-
- PTH: to increase Ca+ reabsorption (Ca+/Na+ exchange)


What diuretics work on early DCT?

- thiazide diuretics: impair urinary dilution, may cause hyponatremia if increased water intake


Main function of DCTs?

- dermine final osmolarity of urine (via aldosterone and ADH)
adosterone: increases Na+ reabsorption (1-2% of Na)
- ADH: concentrates urine, reabsorb water, only permeable to water in presence of ADH (increase in ADH during hypovolemia, hyperosmolarity, and increased RAAS act)


What diuretics work on DCTs?

- K+ sparing diuretics (inhibits aldosterone so can't exchange K+ for Na+ reabsorption)
- worried about hyperkalemia and metabolic acidosis


Function of the collecting duct?

- variable reabsorption of water and reabsorption or secretion of Na+, K+, H+, and bicarb ions


What is renal clearance?

- of a substance is the vol of plasma completely cleared of a substance per min by the kidneys


What substances are used to measure GFR?

- substances that are freely filtered and not reabsorbed - inulin, I-iothalamate, and creatinine - renal clearance = GFR


Relationship b/t GFR and serum creatinine concentration?

- normal GFR: 125 ml/min = 0.8-1.3
- if it decreases by half - 60: Cr concentration = 2, not good!! - half kidney function
- drops down to 25 ml/min - Ccr = 8 - probably need dialysis, sx