Ch. 24 - Urinary System Flashcards
Functions of urinary system
eliminate metabolic waste, regulate ion levels, regulate bp, eliminate biologically active molecules (drugs, hormones)
Functions of kidney
form calcitriol, produce and release erythropoietin, gluconeogenesis
erythropoietin
secreted by kidney in response to low blood oxygen and stimulates red bone marrow to increase erythrocyte production.
filtrate
180 L produced daily. It is filtered plasma with certain solutes and minimal protein. it is caught within capsular space and funneled into PCT. Materials not filtered remain in blood and exit renal corpuscle through efferent arteriole
tubular fluid
new name for filtrate when it enters PCT
pathway of tubular fluid movement
PCT, Nephron loop, DCT, collecting tubules, collecting ducts. Once it reaches collecting ducts it is called urine.
Urine
enters papillary duct located within renal papilla and flows within renal sinus of kidney from minor calyx, major calyx, to renal pelvis. Renal pelvis connects to urinary bladder that stores urine.
Glomerular filtration
first step in urine formation. Glomerular capillaries separates some water and dissolved solutes from blood plasma and enter capsular space of renal corpuscle due to pressure differences across filtration membrane. The separated fluid is called filtrate
Tubular reabsorption
second step in urine formation. movement of components within tubular fluid by diffusion, osmosis, or active transport. Move from lumen of tubules and collecting ducts across walls and return to blood within peritubular capillaries and vasa recta. Excess solutes, waste, and some water remains in tubular fluid.
Tubular secretion
third step in urine formation. Involves movement of solutes, usually by active transport. Move out of blood within peritubular and vasa recta capillaries and into tubular fluid. Materials are moved selectively into tubules to be excreted.
filtration membrane
porous, thin, negatively charged structure formed by glomerulus and visceral layer of glomerular capsule. Has 3 layer.
- endothelium of glomerulus (innermost): fenestrated, allows plasma and dissolved substances to pass while restricting passage of larger objects (erythrocytes)
- basement membrane of glomerulus: glycoprotein and proteoglycan molecules restricts passage of large plasma proteins
- Visceral layer of glomerular capsule. wraps around glomerular capillaries; composed of specialized cells called podocytes that have long processes called pedicels that support capillary wall and are separated by filtration slits restricting passage of small proteins.
podocytes
cells on visceral layer of glomerular capsule that have long processes called pedicels that support the capillary wall without completely enclosing it. They are separated by thin spaces called filtration slits that restrict passage of small proteins.
mesangial cells
specialized cells positioned between glomerular capillary loops. They have phagocytic, contractile, and signaling properties. Phagocytizes any trapped filtered material within basement membrane of glomerulus.
freely filtered substances
small substances like water, glucose, amino acids, and ions that pass easily through filtration membrane
not filtered substances
formed elements and large proteins that cannot pass through filtration membrane
limited filtration substances
proteins of intermediate size are usually blocked from filtration due to negative charge or size.
glomerular hydrostatic (blood) pressure HPg
blood pressure in glomerulus. It pushes water and some solutes out into capsular space and higher than bp in other systemic capillaries, which is required for filtration to occur. afferent arteriole has larger diameter than efferent.
blood colloid osmotic pressure OPg
osmotic pressure exerted by dissolved solutes that opposes filtration and draws fluid back into glomerulus.
capsular hydrostatic pressure HPc
pressure in glomerular capsule due to filtrate; impedes movement of additional fluid.
determining net filtration pressure
if pressures promoting filtration are greater than pressures opposing the difference is net filtration pressure (NFP)
HPg - (OPg + HPc) = NFP
glomerular filtration rate
rate at which the volume of filtrate is formed. Measured volume per unit of time (usually 1 min). Increased net filtration increases GFR, substances in urine, and amount of solutes and water remaining in tubular fluid. Decreases filtrate reabsorption
regulation of glomerular filtration rate
tightly regulated and helps kidney control urine production based on physiologic needs. GFR influenced by changing luminal diameter of afferent arteriole and altering surface area of filtration membrane. Processes within kidney itself (intrinsic controls) and external to kidney (extrinsic controls)
Renal autoregulation (intrinsic)
intrinsic ability of kidney to maintain constant bp and GFR. Maintains in spite of changes in systemic arterial pressure by 2 mechanisms: myogenic response and tubulogolmerular feedback mechanism.
Myogenic response
contraction or relaxation of smooth muscle of afferent arteriole in response to stretch. Decreased bp causes less stretch so smooth muscle relaxes and vessels dilate to allow more blood into glomerulus and for GFR to remain normal. With increased bp, opposite happens to compensate for greater systemic pressure.
tubuloglomerular feedback mechanism (juxtaglomerular apparatus)
backup to myogenic mechanism in response to high bp. If glomerular bp increases, amount of NaCl in tubular fluid is also increased which is detected by macula densa cells in juxtaglomerular apparatus resulting in further vasoconstriction of afferent arteriole.
limitations to maintaining GFR
renal autoregulation can maintain normal glomerular pressure when mean arterial pressure is within 80-180 mm Hg. If below 80 arterioles are at maximum dilation and glomerular bp and GFR decrease. If it gest too low, waste elimination cannot occur. If above 180, arterioles at maximum constriction and glomerular bp and GFR increase causing more urine formation.
neural and hormonal GFR control (extrinsic)
involve physiologic processes to change GFR in contrast to renal autoregulation which attempts to maintain GFR
Decreasing GFR through sympathetic stimulation
happens during emergency or exercise and results in decrease of GFR through vasoconstriction and granular cell release of renin (causing angiotensin II production and contraction of mesangial cells) Contraction of mesangial cells decreases surface area of glomerulus, decreasing GFR. Body conserves water under stressful conditions.
Increasing GFR through atrial natriuretic peptide
peptide hormone released from cardiac muscle cells in response to stretch from atria in heart and increases GFR through relaxation of afferent arteriole, inhibits release of renin (relaxing mesangial cells to increase surface area) The net increase in GFR with increased urine production decreases blood volume and pressure.
paracellular transport
movement of substances between epithelial cells
transcellular transport
movement of substances across epithelial cells. Must ross luminal membrane in contact with fluid and basolateral membrane on basement membrane. Transport proteins are embedded within these layers to control movement of substances.
peritubular capillaries
low hydrostatic pressure and high oncotic pressure. Facilitate reabsorption of substances through bulk flow; most reabsorption in PCT aided by microvilli increasing surface area.
Transport Maximum Tm
maximum rate of substance that can be reabsorbed or secreted across tubule epithelium per certain time. Depends on number of transport proteins in membrane. If less than 375, glucose in tubule is all reabsorbed, but if greater, excess glucose is secreted in urine.
glucosuria
excretion of glucose in urine where plasma glucose is above 300 mg/dl. Glucose acts as an osmotic diuretic (pulls water into tubular fluid and loss of fluid in urine). Classic symptom of diabetes along with polyuria and polydipsia.
Nutrient reabsorption
normally reabsorbed completely; each nutrient has its own transport protein
Glucose transport
transported into tubule cell by Na/ glucose symporter protein where the energy from Na moving down its gradient is used to move glucose up its gradient by secondary active transport. It is then moved by uniporters out of tubule across basolateral membrane and back to blood in peritubular capillaries. 100% is reabsorbed in healthy individuals.
Transport of protein
most not freely filtered. Some small and medium-sided may appear in filtrate and are transported from tubular fluid in PCT back into blood. It moves across luminal membrane by pinocytosis and receptor-mediated endocytosis and is then digested by lysosomes or peptidases and returned to blood as amino acids by facilitated diffusion.
sodium reabsorption
98-100% reabsorbed from tubular fluid (majority in PCT). Concentration is relatively low inside tubule cells and high within tubule lumen and interstitial fluid, so it moves down gradient across luminal membrane into tubular cells. Na/K pumps in basolateral membrane keep Na low within tubule cell and requires substantial energy. Reabsorption is regulated by hormones near end of tubule such as aldosterone and atrial natriuretic peptide.
aldosterone
steroid hormone produced by adrenal cortex that stimulates protein synthesis of Na channels and Na/K pumps embedded in plasma membranes of principal cells to increase Na reabsorption and water reabsorption.
atrial natriuretic peptide
inhibits reabsorption of Na in PCT and collecting tubules and inhibits release of aldosterone. More Na and water is excreted in urine which increases GFR.
Reabsorption and secretion of potassium
it is both reabsorbed and secreted 60%-89% reabsorbed. it is dependent of movement of Na. As Na is reabsorbed and water follows across luminal membrane, there is an increased concentration of remaining solutes in tubular fluid which creates gradient between tubular and interstitial fluid. K moves down gradient from tubular fluid by paracellular route. This allows passive reabsorption of other solutes. 10-20% reabsorbed in thick segment of nephron loop. Intercalated cells reabsorb K and principal cells secrete K based on aldosterone level (less with more aldosterone)
Calcium and phosphate balance
60% in blood goes to filtrate and remainder is bound to protein and prevented from filtration. 90-95% of this is filtered as blood passes through glomerular capillaries. PTH regulates excretion of Ca and PO4
PTH calcium and phosphate regulation
regulates excretion of Ca and PO4 by inhibiting PO4 reabsorption in PCT and stimulating Ca reabsorption in DCT. This allows for less phosphate available to make calcium phosphate so calcium deposition in bone decreases and Ca 2 blood levels increase.
bicarbonate ions filtration
move freely across filtration membrane. if filtered HCO3 is not reabsorbed, blood becomes too acidic. 80-90% reclaimed from tubular fluid and remainder taken up from thick segment of ascending limb. filtered bicarbonate is replaced, not reabsorbed. If blood is acidic then synthesized HCO3 is reabsorbed into blood and H is secreted within filtrate by type a intercalated cells to increase blood PH and decrease urine pH. If alkaline blood then type b intercalated cells activate and secrete HCO3 and reabsorb H to lower blood pH and increase urine pH.
type a intercalated cells
excretes H within filtrate to increase blood pH and decrease urine pH
type b intercalated cells
secretes HCO3 and reabsorbs H to lower blood pH and increase urine pH.
nitrogenous waste
metabolic waste containing nitrogen. Main ones are urea, uric acid, and creatinine.
urea
molecule produced from protein breakdown that is both reabsorbed and secreted. 50% is excreted in urine and helps establish concentration gradient in the interstitial fluid.
uric acid
produced form nucleic acid breakdown in liver and is both reabsorbed and secreted.
creatinine
produced from creatinine metabolism in muscle and only secreted.
elimination of bioactive substances
most secretion occurs in PCT and includes certain drugs like penicillin and aspirin… urobilin, hormone metabolites and some hormones like human chorionic gonadotropin and epinephrine.
concentration gradient
present in interstitial fluid surrounding nephron and is established by various solutes such as Na and Cl. progressively increase in concentration from cortex into medulla and exerts osmotic pull to move water into interstitial fluid.
countercurrent multiplier
positive feedback mechanism involving nephron loop to help establish gradient. the juxtamedullary nephrons primarily involved. descending limb is permeable to water and not to salts so water moves out and more salt concentration within. The ascending limb is impermeable to water and salts are pumped out to get salt gradient in interstitial fluid
vasa recta
blood in vasa recta travels in opposite direction to tubular fluid of adjacent nephron loop.
countercurrent exchange system
water diffuses out of vasa recta capillaries by osmosis and salt in interstitial fluid enters vasa recta increasing salt concentration. Since vasa recta runs next to descending limb that is impermeable to salts the gradient reverses with salt diffusing out and water in.
urea recycling
help concentration process in interstitial fluid. recycled urea is 1/2 of solutes of interstitial fluid gradient. Urea is removed from tubular fluid in collecting duct by uniporters and diffuses back into tubular fluid in thin segment of ascending limb and remains until reaching collecting duct. Urea is cycled between collecting tubule and nephron loop.
summary of reabsorption and secretion
after filtration a majority of other substances are reabsorbed or secreted. Nephron loop, vasa recta, and urea recycling is responsible for establishing concentration gradient of interstitial fluid necessary for normal function of ADH. The regulation of specific substances are controlled mainly by principal and intercalated cells. Urine is excreted out and composed of water, dissolved substances and waste.
measuring glomerular filtration rate
the rate of filtrate formed per unit of time can be measured by insulin injection because insulin is freely filtered and not reabsorbed or secreted. Urine collected and measured for volume and concentration and plasma concentration of insulin in measured in time intervals.
GFR = UV/P - normal is 125 mL/min
GFR = UV/P
used to measure glomerular filtration rate.
U= concentration of insulin in urine
V= volume of urine produced
P= concentration of insulin in plasma
renal plasma clearance test
another means of assessing kidney function that measures volume of plasma cleared of substance in given time. If substance is neither reabsorbed nor filtered the clearance is equal to GFR, in it is reabsorbed, clearance is lower than GFR and if it is filtered and secreted, clearance is higher than GFR. can help determine GFR or appropriate dosages.
Drug clearance
affects appropriate dosage level
creatinine clearance
only slightly higher than GFR and can be used to approximate GFR.
urine
product of filtered and processed blood plasma. It is sterile unless contaminated with microbes in kidney or urinary tract.
composition of urine
95% water and 5% solutes. Solutes are salts, nitrogenous wastes, some hormones drugs and ketone bodies.
Volume of urine
average 1-2 L per day. variation due to fluid intake, bp, temp, diuretics, diabetes. Minimum of .5 L to eliminate wastes.
pH of urine
normally between 4.5- 8.0. more acidic with more protein or wheat in diet and less acidic with more fruits and vegetables. influenced by metabolism nd infection
specific gravity of urine
density of a substance compared to water. it is slightly higher than water due to solutes.
color of urine
almost clear to dark yellow- dependent of concentration of urobilin. With more urine volume, lighter color.
smell of urine
urinoid, normal smell of fresh urine. may develop ammonia smell if allowed to stand. fruity smell in diabetes.
micturition
expulsion of urine from bladder. associated with storage reflex and micturition reflex regulated by sympathetic and parasympathetic divisions of ANS respectively.
sympathetic axons of bladder
extend from T11 to L2 and cause contraction of internal urethral sphincter and inhibits contraction of detrusor muscle and micturition.
parasympathetic division of bladder.
from micturition center in pons, extends from s2-s4 in pelvic splanchnic nerves. Contraction of detrusor, relaxation of internal urethral sphincter to stimulate micturition.
pudendal nerve of somatic nervous system
innervates external urethral sphincter; contracts to prevent urination
storage reflex
continuous sympathetic stimulation causes relaxation of detrusor to accommodate urine and keeps internal sphincter contracted. pudendal nerve keeps external sphincter closed.
micturition reflex.
volume of urine in bladder reaches 200-300mL. Baroreceptors are activated and stimulate micturition center in pons. Micturition center alters nerve signals down spinal cord through pelvic splanchnic nerves and parasympathetic stimulation causes detrusor muscle to contract and internal sphincter to relax.
conscious control of urination
initiated from cerebral cortex through pudendal nerve to cause relaxation of external sphincter and initiated by contraction of abdominal muscles.
after bladder emptying
detrusor muscle relaxed and neurons of storage reflex are activated instead of micturition reflex. You can empty bladder prior to micturition reflex if you contract abdominal muscles and compress bladder (initiating baroreceptors)
If urination is not activated at time of first reflex…
relaxation of detrusor muscle due to stress relaxation response. micturition reflex is activated again after another 200-300 mL added and urination occurs involuntarily between 500-600 mL.
