Urinary system

what does tubular reabsorption do?

moves substances from the filtrate to the blood

what is reclaimed to the blood during tubular reabsorption?

glucose, amino acids, and 99% of water (almost all organic nutrients)

what regulates water and ion reabsorption?

hormones

how many routes of tubular reabsorption are there? and what are they called?

two. transcellular and paracellular

transcellular route

enters apical membrane, travels through cytosol, exits basolateral membrane, enters blood through endothelium of peritubular capillaries

paracellular route

between tubule cells, limited by gap junctions (leaky in proximal nephron), periodic table elements travel in PCT via this route

where are transport proteins found?

within luminal and basolateral membranes

what do transport proteins do?

control transport of various substances

what do peritubular capillaries do?

facilitate reabsorption through bulk flow

what pressure do peritubular capillaries have?

low hydrostatic and high oncotic

what structure aids most reabsorption in PCT by increasing surface area?

microvili

transport maximum

max rate of substance that can be absorbed/secreted across tubule epithelium per certain time

what does maximum transport depend on?

number of transport proteins in membrane

what happens when carriers for a solute are saturated?

excess is excreted in urine

true or false: transcellular transport systems are specific and limited and exist for almost every reabsorbed substance.

true

what is renal threshold?

the maximum amount of a substance that can be transported in the blood without appearing in the urine

if the transport maximum is exceeded, what happens?

substance is excreted in the urine

what is a classic symptom of diabetes?

glucose in the urine, thirst, and urination frequently

are nutrients normally reabsorbed completely in a healthy individual?

yes

what does each nutrient have?

own specific transport protein

why is protein not freely filtered?

due to size and charge

protein moves across luminal membrane through what?

pinocytosis and receptor mediated endocytosis

what are proteins digested by?

lysosomes and peptidases

how do amino acids move back into blood?

facilitated diffusion

how much Na+ is reabsorbed from tubular fluid?

98-100%

where does the Na+ get reabsorbed from majorly? where in general?

PCT. along entire nephron tubule

inside of the tubule cell, what is the Na+ concentration like?

relatively low

inside of the tubule lumen and interstitial fluid, what is the Na+ concentration like?

relatively high

how does Na+ move into tubular cell?

down gradient, across luminal membrane and into tubular cell

what is embedded in the basolateral membrane?

Na+/K+ pumps

what do sodium-potassium pumps require?

substantial energy

near the end of the tubule, what regulates reabsorption?

hormones (Ex. aldosterone and atrial natriuretic peptide

what is aldosterone?

steroid hormone produced by adrenal cortex

what does aldosterone do?

stimulates protein synthesis of Na+ channels and sodium-potassium pumps, increase Na+ reabsorption, and cause water intake

where is aldosterone found?

in plasma membrane of principal cells

what does atrial natriuretic peptide do?

inhibits reabsorption of Na+ in PCT and collecting tubules, inhibits release of aldosterone, more Na+ and water excreted in urine, increases GFR

what provides energy to reabsorb almost every other substance?

Na+ reabsorption by primary active transport

what gives the push needed for transport of other solutes?

secondary active transport

organic nutrients reabsorbed by secondary active transport are cotransported with what?

Na+

examples of organic nutrients cotransported with Na+

glucose, amino acids, ions, vitamins

what is water reabsorbed by?

paracellular transport between cells and transcellular transport through water proteins, aquaporins

how much water is absorbed in PCT?

65%

what is obligatory water reabsorption?

water follows Na+ by osmosis

aquaporins are always present in PCT

how much water is reabsorbed in the nephron loop?

10%

what is passive tubular reabsorption of water?

water is reabsorbed by osmosis, aided by aquaporins

what creates osmotic gradient for water?

movement of Na+ and other solutes

facultative water reabsorption

aquaporins ate inserted in collecting ducts only if ADH is present

what does ADH do?

increases water reabsorption, results in concentrated urine production

how much potassium is reabsorbed in tubular fluid?

60-80%

how much potassium in reabsorbed in thick segment of nephron loop?

10-20%

which route does K+ move down? what type of reabsorption does K+ allow?

paracellular. passive reabsorption of other solutes

what reabsorbs K+ continuously?

intercalated cells

what secretes K+ at varying rates?

principal cells

what is the most powerful stimulant for aldosterone?

high K+ levels

as water is reabsorbed, what increases?

solute concentration in filtrate

what follows water in peritubular capillaries down concentration gradient?

fat-soluble substances, ions, urea

how much calcium and phosphate enters filtrate? what happens with the remainder?

60%. remainder is protein bound and prevented from filtration

how much calcium and phosphate passes through glomerular capillaries?

90-95%

what does parathyroid hormone do?

regulates excretion of calcium and phosphate, inhibits phosphate reabsorption in PCT, stimulates calcium reabsorption in DCT, less phosphate available to form calcium phosphate, calcium deposition in bone decreased, calcium blood levels increased

true or false: bicarbonate ions move freely across filtration membrane

true

what happens if filtered bicarbonate is not absorbed?

blood becomes too acidic

how much bicarbonate is reclaimed from tubular fluid?

80-90%

how much bicarbonate is taken up from thick segment of the ascending limb?

10-20%

is filtered bicarbonate replaced or reabsorbed?

replaced

where is pH of urine and blood regulated?

collecting tubules

what happens if blood is acidic?

synthesized bicarbonate is reabsorbed into the blood, hydrogen is excreted within filtrate by type A intercalated cells, increase in blood pH and decreases urine pH

what happens if the blood is too alkaline?

type B intercalated cells active, secrete bicarbonate and reabsorb hydrogen. Lower blood pH and increase urine pH

what is the most active reabsorption section?

PCT

what nutrients are reabsorbed in the PCT?

glucose/amino acids (majority), sodium/water (65%), other electrolytes/ions, urea

where does obligatory water reabsorption via aquaporin happen?

PCT

what is reabsorbed in the descending limb of the loop of Henle?

mostly water

what is reabsorbed in the ascending loop of Henle?

sodium (thin segment), potassium, chlorine, and minerals

what hormone decreases urine output via aquaporin adjustment (aka facultative water absorption)?

ADH

what hormone increases reabsorption of sodium via transporter adjustment?

aldosterone

what is tubular secretion?

movement of substances from peritubular capillaries into renal tubule

where is tubular secretion primarily?

PCT and cortical collecting ducts

what substances are released during tubular secretion?

drugs/drug metabolites, urea, excess potassium, hydrogen/bicarbonate to control blood pH

what is nitrogenous waste?

metabolic waste containing nitrogen

main nitrogenous waste products

urea, uric acid, and creatinine

what is urea?

molecule produced from protein breakdown

is urea absorbed or secreted?

both

what percentage of urea is excreted in urine?

50%

what does urea do?

helps establish concentration gradient in interstitial fluid

what is uric acid?

produced from nucleic acid breakdown in liver

is uric acid absorbed or secreted?

both

what is creatinine?

produced from creatinine metabolism in muscle

is creatinine absorbed or secreted?

only secreted

where does most secretion of drugs and bioactive occur?

PCT

what are some examples of drugs, metabolic wastes, and hormones secreted in PCT?

penicillin, sulfonamides, aspirin, urobilin, hormone metabolites, human chorionic gonadotropin, epinephrine

what is a concentration gradient?

established by various solutes such as sodium and chlorine which progressively increase from cortex to medulla

where is a concentration gradient located?

interstitial fluid surrounding nephron

what does the concentration gradient do?

exerts osmotic pull to move water into interstitial fluid when ADH is present

what is the countercurrent multiplier?

positive feedback mechanism which involves nephron loop and helps establish gradient

which nephron class is primarily involved in the nephron loop?

juxtamedullary nephrons

what is the descending limb of the nephron loop permeable to? what is it impermeable to?

permeable to water and impermeable to salts

true or false: salt moves from tubular fluid to interstitial fluid.

false.

water moves from tubular fluid to interstitial fluid and salts are retained in tubular fluid

what is the ascending limb impermeable to?

impermeable to water and salts are pumped out

true or false: more concentrated the salts, the more is pumped out. The less concentrated the salts, the less is pumped out.

true

how does blood travel in vasa recta?

opposite direction to tubular fluid of adjacent nephron loop

what does the countercurrent exchange do?

maintains concentration gradient