what are the three funcitons of the urinary system?
excretion elimination and homeostatic regulation
how does the urinary system help regulate blood volume and blood pressure?
by adjusting the volume of water lost in the urine and releasing erythropoietin and renin
how does the urinary system help regulate plasma ion concentration?
by controlling quantities of sodium potassium and chloride ions lost in urine and by controlling calcium levels through syntesis of calcitriol
how does the urinary system help stabilize blood pH?
by controlling loss of hydrogen ions and bicarbonate ions in urine
how does the urinary system conserve valuable nutrients?
by preventing excretion while excreting organic waste products
what does the urinary system assist the liver with?
detoxifying poisons
what is the renal cortex? what color and texture is it?
the superficial portion of kidneys in contact with renal capsule; reddish brown and granular
what are renal pyramids?
6 to 8 distinct conical or triangular structures in renal medulla
where are the base and tip found
base is abuts the cortex and the tip (renal papilla) project into renal sinus.
how much of the total cardiac output does the kidneys recieve?
20%-25%
what are the two types of nephrons?
cortical and juxtamedullary
which type of nephron make up 85% of all nephrons?
cortical
where are the cortical nephrons located?
within the superficial cortex of kidneys
compare the nephron loop (loop of henle) of the cortical to the one of the juxtamedullary
the cortical nephron is relatively short while the one of the juxtamedullary extends deep into the medulla
what does the efferent arteriole of the cortical nephron do?
delivers blood to a short network of peritubular capillaries
what do the peritubular capillaries of the juxtamedullary nephron do?
connect to vasa recta
what does a large loop mean?
more concentrated urine
what are the two segments of the renal tubule and where are they located?
proximal convoluted tubule and distal convoluted tubule; cortex
what are the segments of the renal tubule seperated by?
nephron loop
what is the nephron loop?
a u-shaped tube that extends partially into the medulla
is filtration at the renal corpuscle active or passive?
passive; no atp is necessary
what kind of solutes enter capsular space during filtration?
metabolic waste and excess ions like glucose, free fatty acids, amino acids, and vitamins
what is reabsorption and where does it occur
when useful materials that are recaptured before filtrate leaves kidneys and it occurs in proximal convoluted tubule
what is the first segment of the renal tubule and where is the entrance to this segment?
proximal convoluted tubule; opposite to the point of connection of afferent and efferent arterioles with glumerulus
describe the epithelial lining of PCT. what does it do?
simple cuboidal with microvilli on apical surfaces. the fuunction is reabsorption and it secretes substances into lumen
what is the nephron loop
renal tubule that turns toward renal medulla
what are the two limbs of the nephron loop? what does each contain?
descending and ascending; thick and thin segement
what does the thick descending limb do? what is its function similar to?
pump sodium and chloride ions out of tubular fluid; PCT
where is the ascending limb? what does it do?
juxtamedullary nephron in the medulla; it creates high solute concentrations in peritubular fluid
what are the thin segments permeable to? what dos the movement of this help?
water only,not solute; helps concentrate tubular fluid
where does the thick ascending limb end?
at a sharp angle near the renal corpuscle where DCT begins
what arethe three organic waste produces?
urea, creatine and uric acid
where are organic waste dissolved, when are they eliminated, and what does their removal include?
dissolved in bloodstream, eliminated only while dissolved in urine and removal is accompanied by water loss
what are the three components of the membrane involved in glomerular filtration
capillary endothelium, dense layer, and filtration silts
what type of capillary are glomerular capillaries? what do their pores do?
fenstrated; prevent passage of blood cells and allow diffusion of solutes including plasma protiens
what is glomerular filtration governed by?
the balance between hydrostatic pressure and colloid osmotic pressure on either side of capillary walls
what is glomerular hydrostatic pressure? what does it tend to do?
blood pressure in glomerular capillaries; push water and solute molecules out of plasma into filtrate
why is the hydrostatic pressure significantly higher than capillary pressure in systemic circuit.
arrangement of vessels at gloerulus
where does blood leaving glomerular capillaries do? how does the diameter of this arteriole compare to the other
flow into an efferent arteriole with a diameter smaller than afferent arteriole
what does the efferent arteriole produce? what does this require?
resistance; relatively high pressure to force blood into it
what is capsular hydrostatic pressure? what does it do? what does it result from?
capsular hydrostatic pressure that opposes glomerular hydrostatic pressure; pushes water and solutes out of filtrate into plasma; resistance to flow along nephron and conducting system (avg is 15 mm Hg)
what is the net hydrostatic pressure?
difference between glomerular hydrostatic pressure and capsular hydrostatic pressure
what is colloid osmotic pressure?
osmotic pressure resulting from the presence and capsular hydrostatic pressure
what does blood colloid osmotic pressure tend to do?
draw water out of filtrate into plasma. opposes filtration (avg is 25 mm Hg)
what is net filtration pressure?
average pressure forcing water and dissolved materials out of glomerular capillaries into capsular spaces
what is there a difference between at the glomerulus?
hydrostatic pressure and BCOP accross glomerular capillaries
what is the creatinine clearance test used for?
to estimate GFR
how much flitrate is generated in glomeruli each day? where is 99% of it reabsorbed?
180 liters; renal tubules
wht three interacting levels control the GFR
autoregulation, hormonal regulation, and autonomic regulation
what are the hormonal regulations of the GFR?
renin-angiotensin system and natiutic peptides (ANP and BNP)
what three stimuli causes the juxtagloumerular complex to relesase renin?
1. decline in blood pressure at glomerulus due to decrease in blood volume fall in systemic pressures, or blockage in renal artery or tributaries
2. stimulation of juxtaglomerular cells by sympathetic innervation
3. decline in osmotic concentration of tubular fluid at macula densa
what does angiotensin II activation do?
constricts efferent arterioles of nephron elevating glomerular pressure, stimulates reabsorption of sodium ions and water at PCT, stimulates secretion of aldosterone by adrenal cortex, stimulates thirst, and triggers release of ADH which stimulates reabsorption of water in distal portion of DCT and collecting system
what does angiotension II do?
increases sympathetic motor tone, causes a brief powerful vasconstriction, and elevates arterial pressures throughout the body
was do the increase of sympathetic motor tone by angiotensin II cause to happen?
mobilizes the venous reserve, increases cardiac output and stimulates peripheral vasoconstriction
what does aldosterone do?
accelerates sodium reabsortion in DCT and cortical portion of collecting system
what are natriuretic peptides? what do they do?
hormones that regulate GFR; trigger dilation of afferent arterioles and constriction of efferent arterioles and elevate glomerular pressure and increase GFR
where are natriuretic peptides released and when?
by the heart in response to stretching walls due to increased blood volume or pressure
what are the two types of natriuretic hormones and where are they released?
atrial natriuretic peptide (ANP) released by the atria and Brain natriuretic peptide (BNP) released by ventricles
what does reabsorption do?
recover useful materials from filtrate
what does secretion do?
ejects waste products, toxins, and other undesirable solutes
where does reabsorption and secretion occur? what changes from segment to segment with these two things?
in every segment of nephron except renal corpuscle; relative importance
how much of the filtrate produced in the renl corpuscle does the PCT cells usually reabsorb? where does this reabsorbed material go?
60-70%; it enters the peritubular fluid and diffuse into peritubular capillaries
what are the five functions of the PCT?
reabsorption of organic nutrients, active reabsorption of ions, reabsorption of water, passive reabsorption of ions, secretion
what is important in every pct process?
sodium ion reabsorption
how do sodium ions enter tubular cells?
diffusion through leak channels; sodium lined cotransport organic solutes, and countertransport for hydrogen ions
how does the nephron loop reabsorb around half the water and 2/3 of the sodium an chloride ions remaining in tubular fluid
by the process of countercurrent exchange
what is countercurrent multiplication?
the exchange that occurs between the two parallel segments of loop of henle- the thin descending limb and the thick ascending limb
what does countercurrent refer to?
the exchange between tubular fluids moing in opposite directions ( fluid n descending limb flows toward renal pelvis and fluid in ascending limb flows toward cortex)
what does multiplication refer to?
the effect of exchange hat increases as movement of fluid continues
what are the parallel segments of the nephron loop separated by? how do their characteristics compare?
peritubular fluid; they are very different
describe the permeability to the thin descending limb
permeable to water and relatively impermeable to solutes
describe the permeability of the thick ascending limb. what does it contain?
relatively impermeable to water and solutes. it contains an active transpor mechanism that pumps Na+ and Cl- from tubular fluid into peritubular fluid of medulla
what do sodium and chloride pumps do?
elevate osmotic concentration in peritubular fluid around thin descending limb and causes osmotic flow of water out of thin descending limb and into peritubular fluid which increases solute concentration in thin descending limb
where does the concentrated solution arrive and what does it cause?
thick ascending limb and accelerates Na+ and Cl- transport into peritubular fluid of medulla
what does solute pumping at ascending limb cause?
and increase solute concentration in descending limb which accelerates solute pumping in ascending limb
where does contercurrent multiplication occur? what does it move and where does it move it?
apical surface; Na+, K+, and Cl- out of tubular fluid
what is the carrier protein used in contercurrent multiplication
Na+-K+/2Cl-
describe the route for potassium ions.
pumped into peritubular fluid by cotransport carriers, removed from peritubular fluid by sodium- potassium exchange pump,and diffuse back into lumen of tubule through potassium leak channels
describe the route for sodium and chloride ions.
removed from tubular fluid in ascending limb which elevates osmotic concentration of peritubular fluid around thin descending limb
what happens as tubular fluid flows along thin descending limb?
osmosis moves water into peritubular fluid, leaving solutes behind. osmotic concentration of tubular fluid increases
where are 2/3 of Na+ and Cl- in tubular fluid pumped out before reaching DCT causing the solute concentration to decline and why?
thick ascending limb because of the highly effectie pumping mechanism
what is the osmotic concentration of tubular fluid at the DCT?
100 mOsm/L
what is the rate of ion transport across thick ascending limb proportional to?
ion's concentration in tubular fluid
where are more Na+ and Cl- pumped into medulla?
at the start of thick ascending limb near cortex
what does the regional difference in the ion transport rate cause?
concentration gradient within medulla
what is the maximum solute concentration of peritubular fluid near the turn of the nephron loop? how much of this is from Na+ and Cl- pumped out of ascending limb? what is the remainder?
1200 mOsm/L; 2/3; from urea
what locations are impermeable to urea?
thic ascending limb, DCT, and collecting ducts
what happens to the concentration of urea as water is reabsorbed?
the concentration rises
how many mOsm/L of urea are found in tubular fluid reaching papillary ducts?
450
what is permeable to urea?
papillary ducts
what are two benefits of contercurrent multiplication?
efficiently reabsorbs solutes and water before tubular fluid reaches DCT and collecting system and it establishes a concentration gradient that premits passive reabsorption of water form tubular fluid in collecting system.
what is aldosterone and what all does it do?
a hormone produced by the adrenal cortex that controls ion pump and channels, stimulates synthesis and incorporation of Na+ pumps and channels in plasma membranes along DCT and collecting ducts and reduces Na+ lost in urine
what is produced by prolonged aldosterone stimulation and dangerously reduces plasma concentration?
hypokalemia
what opposes secretion of aldosterone and its actions on DCT and collecting system?
natriuretic peptides (ANP and BNP)
what regulates calcium ion reabsorption at he DCT?
parathyroid hormone and calcitriol
what is contained in blood entering peritubular capillaries?
undesirable substances that did not cross filtration membrane at glomerulus
what causes the rate of K+ and H+ secretions to rise or fall and how?
the concentrations in peritubular fluid. higher concentration and higher rate of secretion
how do potassium ions diffuse into lumen?
through potassium leak channels
what do tubular cells exchange?
Na+ in tubular fluid for excess K+ in body fluids
what generates hydrogen ion secretions?
dissociation of carbonic acid by the enzyme carbonic anhydrase
what does hydrogen ion secretion do? what causes it to accelerate?
acidifies tubular fluid,elevates blood pH, and accelerates when blood pH falls
what is acidosis and when does it develop?
lactic acidosis and develops after exhaustive muscle activity
what causes ketoacidosis to develop?
starvation or diabetes mellitus
what controls blood pH? what are these important to?
H+ removal and bicarbonate production at kidneys; homeostasis
what is alkalosis? what can cause it?
abnormally high blood pH; prolonged aldosterone stimulation which stimulates secretion
what are the responses to acidosis?
PCT and DCT deaminate amino acids, ammonium ions are pumped into tubular fluid and bicarbonate ions enter bloodstream through peritubular fluid
what do PCT and DCT deaminate amino acids do?
ties up H+ and yields ammonuium ions (NH4+) and bicarbonate ions (HCO3-)
what are some benefits of tubular deamination?
provides carbon chains for catabolism and generates bicarbonate ions to buffer plasma
describe reabsorption and secretion at collecting ducts?
receives tubular fluid from nephron and carries it toward renal sinus
how is water and solute loss regulated in the collecting system?
by aldosterone and ADH
what does aldosterone control? what is it opposed by?
sodium ion pumps and actions are opposed by natiuretic peptides
what does ADH control and what is it suppressed by?
permeability to water; natriuretic peptides
what is reabsorbed in the collecting system?
sodium ions, bicarbonate, and urea
what is secreted in the collecting system and why?
hydrogen or bicarbonate ions. it controls body fluid pH
what happens when there is a low pH in peritubular fluid.
carrier protiens pump H+ into tubular fluid and reabsorbs bicarbonate ions
what happens when there is a high pH in peritubular fluid.
collecting system secretes bicarbonate ions and pumps H+ into peritubular fluid
how is urine volume and osmotic concentration controlled?
through control of water reabsorption
how is water reabsorbed?
through osmosis in proximal convoluted tubule and descending limb of nephron loop
what does ADH cause to appear in apical cell membranes and why?
water channels (aquaporins) to increase the rate of osmotic water movement
what does higher levels of ADH increase?
number of water channels and water permeability of DCT and collecting ststem
what happens if there is no ADH?
water is not reabsorbed and all fluid reaching DCT is lost in urine producing large amounts of dilute urine
what causes DCT and collecting systems to always be permeable to water?
the hypothalamus is continuously secreting ADH
how much urine does a healthy aduly produce per day?
1200 mL with osmotic concentration o 800-1000 mOsm/L
what is diuresis? what does it typically indicate?
the elimination of urine typically indicating production of large volumes of urine
what is diuretics?
drugs that promote water loss in urine
what does diuretic therapy reduce?
blood volume, blood pressure and extracellular fluid volume
what is the function of the vasa recta?
to return solutes and water reabsorbed in medulla to general circulation without disrupting the concentration gradient
what is the osmotic concentration of blood entering the vasa recta?
300 mOsm/L
when does the osmotic concentration of blood to increase? what does it involve?
as the blood descends into the medulla. it involves solute absorption and water loss
what does blood flowing toward the cortex do? what does it involve?
gradually decreases with solute concentration of peritubular fluid. it involves solute diffusion and osmosis
what does the vasa recta carry out of the medulla and why?
water and solute; balances solute reabsorption and osmosis in medulla
what are the seven steps of renal function
1. glomerulus
2. proximal convoluted tubule
3. PCT and descending limb
4. thick ascending limb
5. DCT and collecting ducts
6. DCT and collecting ducts
7. vasa recta
what has the same composition as blood plasma?
filtrate produced at renal corpuscle
what happens during step two of renal function?
active removal of ions and organic substrates (produces osmotic water flow out of tubular fluid that reduces volume of filtrate and keeps solutions inside and outside tubule isotonic
what happens during step three of renal function?what is there a reduction in and why?
water moves into peritubular fluids, leaving highly concentrated tubular fluid. a reduction in volume occurs by obligatory water reabsorption
what happens during step four of renal function? what accounts for a higher proportion of total osmotic concentration?
tubular cells actively transport sodium and chloride out of tubule. urea account for higher proportion of total osmotic concentration.
what happens during step five of renal function? what is adjusted and how?
final adjustments in composition of tubular fluid; osmotic concentration through active transport
what happens during step six of renal function? what is exposed here and what does it determine?
final adjustments in volume and osmotic concentration of tubular fluid; ADH, final urine concentration
what happens during step seven of renal function? what does it maintain?
absorbed solutes and water reabsorbed by nephron loop and the ducts; concentration gradient of medulla