Renal Lecture 2

Front 1

when proximal tubule cells transport solutes out of lumen and water follows by osmosis, what do you have?

Back 1

reabsorption

Front 2

primary function of proximal tubule?

Back 2

bulk reabsorption of isosmotic fluid

Front 3

as fluid flows through proximal tubule, 70% gets reabsorbed leaving:

Back 3

54L in lumen

Front 4

filtrate passes through loop, more solute reabsorbed than water and becomes more hyposmotic to plasma

Back 4

true

Front 5

when fluid proceeds to loop of henle what is created:

Back 5

dilute urine

Front 6

secretion:

Back 6

moved from plasma to tubule lumen

Front 7

excretion:

Back 7

removal from body

Front 8

amount filtered=

Back 8

amount filtered- amount reabsorbed + amount secreted

Front 9

amount of substance excreted in urine reflects:

Back 9

how that substrate was handled during its passage through the nephron

Front 10

if reabsorption decreases to half the normal rate, what happens?

Back 10

the body would run out of plasma in under an hour

Front 11

filtration fraction=

Back 11

20% of plasma passing thru glomerulus (into nephron)

Front 12

what percent goes into efferent arteriole?

Back 12

80% ( peritubular capillaries)

Front 13

what percent of fluid is reabsorbed?

Back 13

19%

Front 14

what is the total percent of plasma that entered the kidney that returns to systemic circulation

Back 14

99%

1% excreted to outside environment

Front 15

where are mesangial cells?

Back 15

they lie between and around the glomerular cap

Front 16

renal corpuscle contains filtration barriers (3 layers)

Back 16

1. glomerular capillary endothelium
2. basal lamina
3. Bowman's capsule epithelium

Front 17

how do mesangial cells alter blood flow?

Back 17

with actin-like contractile filaments

Front 18

what to mesangial cells secrete?

Back 18

cytokines

Front 19

how do fenestrated capillaries form filtration barrier?

Back 19

no blood cells pass, (-) charged plasma proteins partially repelled by (-) charged protein on pore membrane

Front 20

what is the basal lamina

Back 20

acellular layer of extracellular matrix that separated capillary endothelium from epithelial lining of Bowman's capsule

Front 21

how does the basal lamina act as a filtration barrier?

Back 21

it acts like a sieve that excludes plasma proteins from fluid

Front 22

what are podocytes found in Bowman's capsule?

Back 22

extended foot processes that wrap around capillaries.

Front 23

what are foot processes in the kidney

Back 23

cytoplasmic extensions from podocytes that wrap around glomerular capillary and interlace with one another to form narrow filtration slits

Front 24

what are important proteins in podocyte filtration slit membranes

Back 24

nephrin and podocin

Front 25

what happens if nephrin and podocin are abnormal or absent

Back 25

proteins will leak across glomerular filtration barrier into urine

Front 26

what are filtration slits

Back 26

narrow- closed by semi-porous membrane

Front 27

what do filtered substances pass through?

Back 27

endothelial pores and filtration slits

Front 28

what is nephrin?

Back 28

zipper-like protein that forms a slit diaphragm

Front 29

what is CD2AP

Back 29

protein of the podocyte cytoskeleton

Front 30

what is the hydrostatic pressure of blood flowing through the glomerular capillaries that forces fluid thru leaky endothelium?

Back 30

55mmHg

Front 31

what happens to the pressure along the capillary resulting in filtration taking place throughout the capillary?

Back 31

it declines

Front 32

colloid osmotic pressure inside the glomerular capillary is greater than that of fluid in Bowman's capsule due to what?

Back 32

proteins in plasma

Front 33

what is the pressure gradient for colloid osmotic (pie) that favors fluid movement into the capillary

Back 33

30mmHg

Front 34

Bowman's capsule is an enclosed space, so fluid in capsule creates hydrostatic fluid (Pfluid) that :

Back 34

opposes fluid into the capsule

Front 35

what is the pressure gradient for hydrostatic fluid?

Back 35

15 mmHg

Front 36

what is the net driving force considering Ph- pie - Pfluid?

Back 36

10mmHg

Front 37

when you combine the net driving force with leaky fenestrated capillaries what do you get?

Back 37

rapid fluid filtration into tubules

Front 38

diabetic nephropathy disease progression:

Back 38

increased glomerular filtration
proteinuria
later stages: filt rate decreases, thickening of basal lamina, changes in podocytes and mesangial cells
mesangial cell proliferation increases and impedes blood flow
dialysis required or even a transplant

Front 39

GFR

Back 39

volume of fluid that filters into Bowman's capsule per unit time.

Front 40

what is the GFR

Back 40

125mL/min (180L/day)

Front 41

what is GFR influenced by?

Back 41

filtration pressure and filtration coefficient

Front 42

what are the components of filtration pressure?

Back 42

renal blood flow and blood pressure

Front 43

what are the components of filtration coefficient?

Back 43

capillary surface area available for filtration and permeability of interface between capillary and Bowman's capsule

Front 44

GFR is constant over a wide range of BP

Back 44

true

Front 45

what drives the hydrostatic pressure that drives glomerular filtration.

Back 45

BP

Front 46

what is GFR controlled by?

Back 46

regulation of blood flow through renal arteries

Front 47

what happens when there is increased renal artery pressure and decreased renal blood flow?

Back 47

blood diverted to other organs

Front 48

what happens when there is increase resistance in afferent arterioles?

Back 48

decreased GFR and RBF

Front 49

what happens when there is increase resistance in efferent arterioles?

Back 49

increase GFR and decreased RBF

Front 50

if there is an increased GFR what will happen to glomerular pressure

Back 50

increase

Front 51

why is it important to maintain constant GFR even when blood pressure varies?

Back 51

because hi GFR could damage filtration barriers

Front 52

how does it maintain constant GFR?

Back 52

myogenic response: vascular smooth muscle in afferent arteriole's response to pressure changes

tubuloglomerular feedback

Front 53

how does the myogenic response work?

Back 53

Hi BP-- stretch activated ion channels open--voltage gated Ca channels open--vSM contracts-- flow decreases--GFR decreases
** but <80mmHg GFR also decreases

Front 54

what is tubuloglomerular feedback?

Back 54

paracrine signalling where changes in fluid flow influence GFR
(juxtaglomerular apparatus)

Front 55

what happens in the juxtaglomerular apparatus that controls GFR?

Back 55

GFR increase-- flow thru tubule increase- flow past macula densa increase- paracrine from macula densa to afferent arteriole--afferent arteriole constricts-- resistance in afferent arteriole increases-- hydrostatic pressure in glomerulus decreases-- GFR decreases

Front 56

what is renin?

Back 56

enzyme in salt and water balance

Front 57

how do sympathetic neurons work with GFR?

Back 57

via alpha receptors (vSM): there is a sharp BP drop - sympathetically induced vasocontriction decreases GFR to conserve fluid volume

Front 58

how do hormones work with GFR?

Back 58

Angiotensin II: potent vasoconstrictor
Prostoglandins: vasodilators
Appear to act on: podocytes (change slit size), and megangial cells (contraction changes capillary surface area for filtration)

Front 59

filtrate flowing out of Bowman's capsule into proximal tubule has:

Back 59

same solute concentration as ECF.

Front 60

To move solute out of lumen, tubule cells must:

Back 60

use active transport and water follows solute

Front 61

sodium is reabsorbed by:

Back 61

active transport

Front 62

electrochemical gradient drives:

Back 62

anion reabsorption

Front 63

water moves by :

Back 63

osmosis, following solute reabsorption

Front 64

concentration of other solutes increase as fluid volume in lumen decreases. Permeable solutes are reabsorbed by:

Back 64

diffusion
(K, Ca++, urea)

Front 65

solutes moving down the gradient use:

Back 65

open leak channels or facilitated diffusion carrier

**Na involved

Front 66

molecules that go against their gradient need :

Back 66

primary or secondary active transport


**Na involved

Front 67

sodium linked secondary transport in the nephron is responsible for abs of many substances:

Back 67

glucose, AA, ions, and various organics

Front 68

steps in secondary transport: symport w/sodium

Back 68

1. Na moving down its electrochemical gradient using the SGLT protein pulls glucose into the cell against its concentration gradient.
2. glucose diffuses out the basolateral side of the cell using the GLUT protein
3. Na is pumped out by Na-K-ATPase
(glucose and Na reabsorbed)

Front 69

what is urea

Back 69

a nitrogenous waste product

Front 70

passive resorption of urea w/concentration gradient can move by diffusion

Back 70

true

Front 71

how does the passive resorption of urea work?

Back 71

initially equal--active transport of Na and other solutes in p.tubule creates a urea concentration gradient-- when Na and other solutes reab in p.t. transfer of osmotically active particles makes ECF more concentrated than filtrate remaining in lumen-- in response to osmotic gradient water moves across epithelium-- urea hasn't move yet=no gradient-- when water leaves, filtrate conc of urea increases-- urea moves b/c of gradient

Front 72

excretion=

Back 72

filtration - reabsorption
(inc) (constant)

Front 73

glucose is not secreted so:

Back 73

glucose excreated

Front 74

Tm

Back 74

transport saturation

Front 75

see slides of graph on pg 8

Back 75

??

Front 76

secretion

Back 76

enables the nephron to enhance excretion of a substance.

ECF to nephron lumen

Front 77

if a substance is filtered and not reabsorbed it is:

Back 77

excreted very efficiently

Front 78

if more secreted into tubule from peritubular capillary:

Back 78

excretion more efficient

Front 79

what is secreted that is important for homeostasis?

Back 79

K+ and H+

Front 80

Secretion depends mostly on membrane transport systems. what are most organic compounds carried by?

Back 80

secondary active transport: moving substances against their gradient

Front 81

Penicillin and probenecid

Back 81

when penicillin given it would be 80% excreted in 3 to 4 hrs. when given with probenecid, it would remove it and leave penicillin alone so it would stay in the body longer.

Front 82

excretion

Back 82

removed from the body.

Front 83

excretion=

Back 83

filtration- resorption + secretion

Front 84

excretion depends on:

Back 84

1.filtration rate
2. whether the substance is reabsorbed, secreted or both as it passes thru the tubule.

Front 85

renal processing and GFR is clinically important because:

Back 85

GFR is an indicator of overall kidney function and the FDA needs info on kidney processing of every drug

Front 86

what is clearance?

Back 86

1. a noninvasive way to measure GFR
2. the rate of removal of a solute from the body by excretion or metabolism
3. is the volume of plasma passing thru the kidneys that is totally cleared of the solute in a given time

Front 87

inulin

Back 87

polysaccharide isolated from tuberons roots of a variety of plants

Front 88

inulin clearance =

Back 88

GFR

Front 89

how much inulin that has been filtered into tubule is excreted?

Back 89

100%

Front 90

As filtered inulin and filtered plasma pass along nephron, what happens?

Back 90

all plasma reabsorbed but inulin remains

Front 91

what it is called when plasma has no inulin

Back 91

cleared

Front 92

inulin clearance is:

Back 92

100mL of plasma cleared / min

Front 93

inulin is equal to GFR because?

Back 93

any substance that is freely filtered but neither reabsorbed or secreted, clearance is equal to GFR

Front 94

equation 1

Back 94

filtered load of X = [X]plasma * GFR

Front 95

equation 2

Back 95

filtered load of inulin= excretion of inulin

Front 96

equation 3

Back 96

excretion rate of inulin = [inulin]plasma * GFR

Front 97

equation 4

Back 97

GFR= excretion rate of inulin
-------------------------------------------------
[inulin]plasma

Front 98

equation 5

Back 98

clearance rate of X= excretion rate of X (mg/min)
-------------------------------------------
[X]plasma (mg/ml plasma)

Front 99

equation 6

Back 99

inulin clearance = excretion rate of inulin
-----------------------------------------------
inulin

Front 100

equation 7

see examples pg 10 slides

Back 100

GFR = inulin clearance

Front 101

what is used in the clinical setting to estimate GFR?

Back 101

creatine

Front 102

creatine

Back 102

breakdown product of phosphocreatinine, an energy-storage compound found primarily in muscles

Front 103

are phosphocreatine production rate and breakdown rates relatively constant?

Back 103

yes

Front 104

why is creatine not perfect

Back 104

some secreted in urine

Front 105

renal handling of solutes:
filtration is greater than excretion

Back 105

net reabsorption of X

Front 106

renal handling of solutes:
excretion is greater than filtration

Back 106

net secretion of X

Front 107

renal handling of solutes:
filtration and excretion are the same

Back 107

no net reabsorption or secretion

Front 108

renal handling of solutes:
clearance of X is less than unulin clearance

Back 108

net reabsorption of X

Front 109

renal handling of solutes:
clearance of X is equal to inulin

Back 109

X is neither reabsorbed nor secreted

Front 110

renal handling of solutes:
clearance of X is greater than inulin clearance

Back 110

net secretion of X

Front 111

micturation

Back 111

urine-renal pelvis- ureter (smooth mus)-bladder- (micturation) urethra

Front 112

bladder holds

Back 112

500 mL

Front 113

internal sphincter

Back 113

smooth muscle, continuation of bladder wall
passively controlled

Front 114

external sphincter

Back 114

ring of skeletal muscle, controlled by somatic motor neurons

stays contracted

Front 115

steps in micturation

Back 115

1. stretch receptors fire
2. parasympathetic neurons fire. motor neurons stop firing
3. smooth muscle contracts. internal sphincter passively pulled open. external sphincter releases