Ch. 24 - Urinary System

Question 1

Functions of urinary system

Answer 1

eliminate metabolic waste, regulate ion levels, regulate bp, eliminate biologically active molecules (drugs, hormones)

Question 2

Functions of kidney

Answer 2

form calcitriol, produce and release erythropoietin, gluconeogenesis

Question 3

erythropoietin

Answer 3

secreted by kidney in response to low blood oxygen and stimulates red bone marrow to increase erythrocyte production.

Question 4

filtrate

Answer 4

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

Question 5

tubular fluid

Answer 5

new name for filtrate when it enters PCT

Question 6

pathway of tubular fluid movement

Answer 6

PCT, Nephron loop, DCT, collecting tubules, collecting ducts. Once it reaches collecting ducts it is called urine.

Question 7

Urine

Answer 7

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.

Question 8

Glomerular filtration

Answer 8

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

Question 9

Tubular reabsorption

Answer 9

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.

Question 10

Tubular secretion

Answer 10

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.

Question 11

filtration membrane

Answer 11

porous, thin, negatively charged structure formed by glomerulus and visceral layer of glomerular capsule. Has 3 layer.

1. endothelium of glomerulus (innermost): fenestrated, allows plasma and dissolved substances to pass while restricting passage of larger objects (erythrocytes)
2. basement membrane of glomerulus: glycoprotein and proteoglycan molecules restricts passage of large plasma proteins
3. 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.

Question 12

podocytes

Answer 12

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.

Question 13

mesangial cells

Answer 13

specialized cells positioned between glomerular capillary loops. They have phagocytic, contractile, and signaling properties. Phagocytizes any trapped filtered material within basement membrane of glomerulus.

Question 14

freely filtered substances

Answer 14

small substances like water, glucose, amino acids, and ions that pass easily through filtration membrane

Question 15

not filtered substances

Answer 15

formed elements and large proteins that cannot pass through filtration membrane

Question 16

limited filtration substances

Answer 16

proteins of intermediate size are usually blocked from filtration due to negative charge or size.

Question 17

glomerular hydrostatic (blood) pressure HPg

Answer 17

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.

Question 18

blood colloid osmotic pressure OPg

Answer 18

osmotic pressure exerted by dissolved solutes that opposes filtration and draws fluid back into glomerulus.

Question 19

capsular hydrostatic pressure HPc

Answer 19

pressure in glomerular capsule due to filtrate; impedes movement of additional fluid.

Question 20

determining net filtration pressure

Answer 20

if pressures promoting filtration are greater than pressures opposing the difference is net filtration pressure (NFP)
HPg - (OPg + HPc) = NFP

Question 21

glomerular filtration rate

Answer 21

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

Question 22

regulation of glomerular filtration rate

Answer 22

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)

Question 23

Renal autoregulation (intrinsic)

Answer 23

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.

Question 24

Myogenic response

Answer 24

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.

Question 25

tubuloglomerular feedback mechanism (juxtaglomerular apparatus)

Answer 25

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.

Question 26

limitations to maintaining GFR

Answer 26

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.

Question 27

neural and hormonal GFR control (extrinsic)

Answer 27

involve physiologic processes to change GFR in contrast to renal autoregulation which attempts to maintain GFR

Question 28

Decreasing GFR through sympathetic stimulation

Answer 28

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.

Question 29

Increasing GFR through atrial natriuretic peptide

Answer 29

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.

Question 30

paracellular transport

Answer 30

movement of substances between epithelial cells

Question 31

transcellular transport

Answer 31

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.

Question 32

peritubular capillaries

Answer 32

low hydrostatic pressure and high oncotic pressure. Facilitate reabsorption of substances through bulk flow; most reabsorption in PCT aided by microvilli increasing surface area.

Question 33

Transport Maximum Tm

Answer 33

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.

Question 34

glucosuria

Answer 34

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.

Question 35

Nutrient reabsorption

Answer 35

normally reabsorbed completely; each nutrient has its own transport protein

Question 36

Glucose transport

Answer 36

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.

Question 37

Transport of protein

Answer 37

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.

Question 38

sodium reabsorption

Answer 38

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.

Question 39

aldosterone

Answer 39

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.

Question 40

atrial natriuretic peptide

Answer 40

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.

Question 41

Reabsorption and secretion of potassium

Answer 41

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)

Question 42

Calcium and phosphate balance

Answer 42

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

Question 43

PTH calcium and phosphate regulation

Answer 43

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.

Question 44

bicarbonate ions filtration

Answer 44

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.

Question 45

type a intercalated cells

Answer 45

excretes H within filtrate to increase blood pH and decrease urine pH

Question 46

type b intercalated cells

Answer 46

secretes HCO3 and reabsorbs H to lower blood pH and increase urine pH.

Question 47

nitrogenous waste

Answer 47

metabolic waste containing nitrogen. Main ones are urea, uric acid, and creatinine.

Question 48

urea

Answer 48

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.

Question 49

uric acid

Answer 49

produced form nucleic acid breakdown in liver and is both reabsorbed and secreted.

Question 50

creatinine

Answer 50

produced from creatinine metabolism in muscle and only secreted.

Question 51

elimination of bioactive substances

Answer 51

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.

Question 52

concentration gradient

Answer 52

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.

Question 53

countercurrent multiplier

Answer 53

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

Question 54

vasa recta

Answer 54

blood in vasa recta travels in opposite direction to tubular fluid of adjacent nephron loop.

Question 55

countercurrent exchange system

Answer 55

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.

Question 56

urea recycling

Answer 56

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.

Question 57

summary of reabsorption and secretion

Answer 57

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.

Question 58

measuring glomerular filtration rate

Answer 58

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

Question 59

GFR = UV/P

Answer 59

used to measure glomerular filtration rate. U= concentration of insulin in urine V= volume of urine produced P= concentration of insulin in plasma

Question 60

renal plasma clearance test

Answer 60

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.

Question 61

Drug clearance

Answer 61

affects appropriate dosage level

Question 62

creatinine clearance

Answer 62

only slightly higher than GFR and can be used to approximate GFR.

Question 63

urine

Answer 63

product of filtered and processed blood plasma. It is sterile unless contaminated with microbes in kidney or urinary tract.

Question 64

composition of urine

Answer 64

95% water and 5% solutes. Solutes are salts, nitrogenous wastes, some hormones drugs and ketone bodies.

Question 65

Volume of urine

Answer 65

average 1-2 L per day. variation due to fluid intake, bp, temp, diuretics, diabetes. Minimum of .5 L to eliminate wastes.

Question 66

pH of urine

Answer 66

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

Question 67

specific gravity of urine

Answer 67

density of a substance compared to water. it is slightly higher than water due to solutes.

Question 68

color of urine

Answer 68

almost clear to dark yellow- dependent of concentration of urobilin. With more urine volume, lighter color.

Question 69

smell of urine

Answer 69

urinoid, normal smell of fresh urine. may develop ammonia smell if allowed to stand. fruity smell in diabetes.

Question 70

micturition

Answer 70

expulsion of urine from bladder. associated with storage reflex and micturition reflex regulated by sympathetic and parasympathetic divisions of ANS respectively.

Question 71

sympathetic axons of bladder

Answer 71

extend from T11 to L2 and cause contraction of internal urethral sphincter and inhibits contraction of detrusor muscle and micturition.

Question 72

parasympathetic division of bladder.

Answer 72

from micturition center in pons, extends from s2-s4 in pelvic splanchnic nerves. Contraction of detrusor, relaxation of internal urethral sphincter to stimulate micturition.

Question 73

pudendal nerve of somatic nervous system

Answer 73

innervates external urethral sphincter; contracts to prevent urination

Question 74

storage reflex

Answer 74

continuous sympathetic stimulation causes relaxation of detrusor to accommodate urine and keeps internal sphincter contracted. pudendal nerve keeps external sphincter closed.

Question 75

micturition reflex.

Answer 75

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.

Question 76

conscious control of urination

Answer 76

initiated from cerebral cortex through pudendal nerve to cause relaxation of external sphincter and initiated by contraction of abdominal muscles.

Question 77

after bladder emptying

Answer 77

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)

Question 78

If urination is not activated at time of first reflex...

Answer 78

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.