Physiology 2 Renal

Front 1

a urine sample with a specific gravity of 1.008-1.012 is said to be what?

Back 1

isosthenuric

Front 2

what are the 8 major renal functions?

Back 2

1. removal of nitrogenous wastes from body
2. maintenance of body fluid balanace
3. maintenance of electrolyte balance
4. maintenance of serum calcium and skeletal health by role with Vitamin D
5. control of systemic and local blood pressure
6. control of circulating red cell mass
7. control of systemic pH
8. detoxification and excretion of endogenous and exogenous drugs and chemicals

Front 3

what is renal secretion?

Back 3

remove substances from non-glomerular blood and put them in the renal tubule for excretion

Front 4

what is renal excretion?

Back 4

the process of removal of substances from the body via urine

Front 5

where do the PTCN originate?

Back 5

from the efferent arterioles from high- and mid cortical glomeruli

Front 6

where does blood flow to the vasa recta originate?

Back 6

only from juxtamedullary glomeruli

Front 7

comment on the permeablities and blood flow through the PTCN and the vasa recta, accordingly.

Back 7

PTCN - high permeability, high blood flow

vasa recta - high permeability, low blood flow

Front 8

how is the kidney innervated and what does this innervation do?

Back 8

sympathetic branches from splanchnic nerves.

efferent:
- vasoconstriction of the arteries
- increases Na absorption in the tubules and collecting ducts
- causes renin release from the juxtaglomerular cells

afferent:
- specialized baroreceptors and chemoreceptors for blood pressure regulation

Front 9

what are the five basic anatomical segments of the renal tubule?

Back 9

1. urinary capsule (not "renal capsule")
2. proximal convoluted tubule
3. nephric loop
4. distal convoluted tubule
5. collecting duct

Front 10

what is the term that refers to the glomerulus and the urinary capsule?

Back 10

urinary corpuscle

Front 11

what are the two types of cells comprising the collecting duct and what ions are they specific to?

Back 11

1. principal cells: Na and K
2. intercalated cells: H+ and bicarb

Front 12

what are the four major functions of the renal collecting duct?

Back 12

1. conduct fluid
2. respond to ADH
3. regulate K secretion or absorption
4. acid-base balance

Front 13

what is the main basic function of the juxtaglomerular apparatus and what are its three basic components?

Back 13

affects renal and systemic blood pressure

components:
1. macula densa
2. juxtaglomerular cells
3. mesangial cells

Front 14

the macula densa:
1. where is it located?
2. structure
3. function

Back 14

1. part of the distal convoluted tubule; it touches the afferent and efferent arterioles of the glomerulus
2. tall columnar cells
3. senses Na/Cl concentration for the purposes of plasma volume and BP regulation

Front 15

juxtaglomerular cells:
1. location
2. structure
3. function

Back 15

1. (mostly) part of the afferent arteriole; located near the glomerulus and macula densa
2. modified smooth muscle cells
3. secrete renin

Front 16

what is the relative amount of blood received from the glomerular efferent arteries by the PTCN versus the arteriolae rectae respecively?

Back 16

the PTCN receives 98-99% of the blood where the arteriolae rectae only receive 1-2% of the blood

Front 17

what is the basic reason why the vasa recta have such low blood flow rates?

Back 17

maintain medullary concentration gradient while allowing water recovery

Front 18

what are the (non-specific) basic functions of the glomerulus, renal tubule and collecting duct?

Back 18

- glomerulus: delivers blood to the tubule and BEGINS filtration
- tubule: completes filtration and modifies filtrate
- collecting duct: makes critical, fine adjustments and removes fluid from the kidney

Front 19

what performs filtration in the nephron?

Back 19

the urinary corpuscle (both the glomerulus and the urinary capsule)

Front 20

what is the urinary corpuscle comprised of and what is its major function?

Back 20

formed from the glomerulus and the urinary capsule, forms the filtration unit of the nephron

Front 21

what is the urinary capsule?

Back 21

the proximal-most part of the renal tubule

Front 22

in the kidney, where are podocytes located and what is their function?

Back 22

they envelop the glomerular capillaries and perform ultrafiltration with their comb-like projections

Front 23

what is special about the basement membrane of the PCT?

Back 23

it is highly convoluted so that PCT cells have a very high surface area; these projections of PCT membrane contain many mitochondria

Front 24

what are the three basic functions of the PCT?

Back 24

1. completion of filtration by the urinary capsule (the proximal aspect of the PCT)
2. absorption - prodigious recovery of filtrate and water
3. secretion - removes substances from the blood that were not filtered and puts them into the tubular lumen

Front 25

what are the three basic functions of the DCT?

Back 25

1. fine tuning of tubular fluid solutes
2. continued dilution of tubular fluid
3. blood pressure regulation by the macula densa (which are part of the DCT)

Front 26

where does the macula densa reside?

Back 26

always between the afferent and efferent arterioles

Front 27

which cells of the JGA secrete renin?

Back 27

juxtaglomerular cells of the afferent arteriole

Front 28

what sub-gross structures lie in the renal cortex?

Back 28

- renal corpuscles
- PCT
- DCT
- PTCN
- JGA

Front 29

what sub-gross structures lie in the renal medulla?

Back 29

- nephric loop
- collecting duct
- vasa recta

Front 30

what are the four major functions of the renal cortex with regards to filtration and regulation?

Back 30

1. urinary corpuscles (glomeruli and urinary capsules) make filtrate
2. PCT and DCT modify the filtrate
3. PTCN delivers and recovers materials to and from the tubules
4. JGA autoregulates renal and systemic blood flow

Front 31

what are five major functions of the renal medulla with regards to filtration and regulation?

Back 31

1. dilution of tubular fluid
2. concentrate medullary salts
3. final control over whether urine is concentrated or dilute
4. acid-base balance
5. K+ homeostasis

Front 32

what are the two basic functions of the nephric loop?

Back 32

1. dilute tubular fluid
2. deposit salts into the medulla

Front 33

what are the two major functions of the vasa recta?

Back 33

1. provide water or salt to the medulla as needed
2. prevent salt washout of the medulla

Front 34

what four hormones are produced by the kidney, where are they produced, and what is their basic function?

Back 34

1. renin - pruduced by the juxtaglomerular cells, blood pressure regulation
2. 1,25-dihydroxycholecalciferol - produced by the proximal tubule, Vitamin D metabolism to increase plasma Ca concentration
3. Erythropoietin: increases RBC production in the bone marrow
4. Prostaglandins: intracellular mediators of renin release and vasoactive on the golumerulus

Front 35

What four major hormones produced outside the kidney act on the kidney and what do they do?

Back 35

1. ADH - upregulates aquaporin production in the late distal tubule and inner medullary collecting duct to concentrate urine.
2. Aldosterone - raises systemic blood pressure by stimulating increased recovery of Na and water
3. atrial natriuretic peptide - causes lower systemic blood pressure by excreting sodium and water into the tubular lumen
4. PTH - acts with 1,25-dihydroxycholecalcferol to regulate plasma Ca levels

Front 36

what is the affect of ADH on the kidney?

Back 36

causes the late distal tubule and inner medullary collecting duct to recover water from the tubular lumen and concentrate the urine by upregulating the expression of aquaporins

Front 37

what three structures form the renal filtration barrier?

Back 37

1. fenestrated capillaries of the glomerulus
2. fused glomerular and renal capsular membranes
3. spaces between the primary and secondary foot processes of the podocytes

Front 38

what is the capillary filtration coefficient and how is it calculated?

Back 38

Kf = (capillary permeability) X (filtration surface area)

Front 39

What are the three major properties of a solute and its ability to be filtered by the renal corpuscle?

Back 39

1. size (primary)
2. electrical charge (+ more soluble than -)
3. deformity of the solute (e.g. globular protein < linear protein)

Front 40

what is the primary property of a solute in its ability to be filtered?

Back 40

size. This predominates over all other features.

Front 41

what are the four fluid pressures affecting corpuscular filtration and in which direction will they alter fluid flow?

Back 41

1. capillary hydrostatic pressure: blood --> urinary space
2. oncotic pressure in the urinary space: blood --> urinary space (normally near zero)
3. oncotic pressure in the glomerular capillaries: urinary space --> blood
4. hydrostatic pressure in the urinary space: urinary space --> blood

Front 42

what is the main fluid force that drives corpuscular filtration?

Back 42

capillary hydrostatic pressure

Front 43

what explains the high oncotic pressure in the golumerular capillaries?

Back 43

high protein concentration

Front 44

why is urinary capsule oncotic pressure normally zero?

Back 44

because the ultrafiltrate in the urinary capsule is the same concentration as the capillary blood.

Front 45

what is the net filtration pressure?

Back 45

pressures favoring filtration - pressures opposing filtration

Front 46

what is the most likely protein found in the urine and why?

Back 46

albumin, because its size makes it just barely able to squeeze through the filtration barrier. It is often the first protein to be seen in the urine in renal disease.

Front 47

what is the cutoff molecular weight of the renal filtration barrier?

Back 47

<70 kDa

Front 48

how do you calculate glomerular filtration rate?

Back 48

(net filtration pressure) X (Kf)
(Kf = permeability X surface area)

Front 49

what does measurement of the GFR tell you about the kidney?

Back 49

how well the kidney can filter the blood

Front 50

what is renal clearance?

Back 50

the ability of the kidney to remove substances from the plasma and excrete them in the urine

Front 51

what three major things can be determined be measuring the renal clearance?

Back 51

1. renal blood flow (RBF)
2. renal plasma flow (RPF)
3. GFR

Front 52

what three conditions must be met for a substance to be used to determine renal clearance and what two basic measurements are taken to determine this value?

Back 52

1. freely filtered
2. not reabsorbed
3. not secreted

- to measure, we need the initial blood concentration of the analyte and the concentration of the analyte in the urine over time

Front 53

what are two common substances used to measure renal clearance?

Back 53

inulin (injected)
creatinine (produced by muscle at a constant rate)

Front 54

what are the "three bloods" in the kidney?

Back 54

1. glomeruli
2. PTCN
3. vasa recta

Front 55

what is the definition of renal filtrate?

Back 55

filtered plasma in the urinary capsular (Bowman's) space BEFORE it enters the tubule

Front 56

what is the definition of renal tubular fluid?

Back 56

fluid that resides in the lumen of the tubule after leaving the capsular space and before it enters the renal pelvis (or equivalent)

Front 57

what is the definition of renal tubular flow and what determines the rate of flow?

Back 57

flow of renal tubular fluid through the tubule. Rate depends entirely on pressure because it is entirely passive (e.g. no muscle contraction)

Front 58

what is the definition of renal tubular transport?

Back 58

transport of materials across or past tubular cells, either into our out of the tubular lumen/blood

Front 59

what is the definition of renal absorption and where does it mainly occur?

Back 59

removal of a substance from the renal tubular fluid and depositing it in the blood. This mainly occurs in the PTCN

Front 60

what is the definition of renal secretion and where does it predominately occur?

Back 60

removal of a substance from the non-glomerular blood and depositing it into the tubular fluid for excretion. Predominately occurs via the PTCN

Front 61

what is the definition of renal excretion?

Back 61

removal of a substance from the body by removing it from the blood by filtration or secretion, depositing it in the renal tubular fluid, and holding it there to eventually depart the body via the urine.

Front 62

what determines when renal excretion can be defined as urine?

Back 62

not until it leaves the tubule and is collected by the renal pelvis or analogous renal structures

Front 63

what is the definition of fractional excretion?

Back 63

the precentage of a filtered substance that is ultimately excreted. This is dependent on how much of this substance is reabsorbed.

Front 64

what is the definition of fractional reabsorption?

Back 64

the percentage of a filtered substance that is reabsorbed (therefore not excreted) by the renal tubule

Front 65

by what forces do substances move into and out of the non-glomerular capillaries?

Back 65

Always passive forces, e.g. concentration gradients. No pumps are present in the capillaries.

Front 66

what are the two major differences between the wall of a capillary in the glomerulus versus that in the PTCN/vasa recta?

Back 66

- not so many pores
- the pores have diaphragms

Front 67

what is a diaphragm in a capillary and in which type of capillary do they exist?

Back 67

they are fibrils of protein spanning the pores of fenestrated capillaries to prevent loss of large blood solutes and blood cells.

Front 68

in what ways does the nature of the interstitium versus the PTCN affect the flow of solutes and fluid that are not secreted by the tubules?

Back 68

it favors absorption because:

- high capillary flow rates will always ensure that the solute concentration of the PTCN is at a constant rate, equal to or lower than that of the interstitium for molecules that are actively pumped into the interstitium

- a net negative charge of proteins dissolved in the PTCN allows for migration of cations from the interstitium into the PTCN

- solvent drag sucks solutes into the PTCN

- total oncotic pressure of the PTCN is very high due to dissolved protein, thus drawing water into the PTCN

- the hydrostatic pressure in the PTCN is less than that of the tubule, thus creating a driving force for paracellular transport

- secretion of substances into the tubular lumen creates a concentration gradient and an electrochemical gradient favoring removal of certain substances form the PTCN

Front 69

what is the tubular maximum?

Back 69

the maximum rate at which a substance can be absorbed/secreted by the renal tubule.

Front 70

what is maximal secretion capacity and what happens if this capacity is exceeded for a particular substance?

Back 70

the amount of substance that can be removed from the systemic blood and placed into the PTCN. If this capacity is exceeded, blood concentrations of a particular substance can rise because the kidney can not get rid of it fast enough.

Front 71

what happens if the maximal reabsorption capacity of a particular substance is exceeded?

Back 71

this substance will be excreted in the urine and potentially deplete it from the blood.

Front 72

what is the renal threshold?

Back 72

the concentration of a solute at which the concentration in the blood exceeds the tubular maximum. The solute will be present in the urine.

Front 73

to which absorptive process does solvent drag particularly apply?

Back 73

absorption via the paracellular spaces

Front 74

by what means does the kidney use to transport water?

Back 74

simple diffusion only. Never active transport.

Front 75

what mode of transport responds to electrochemical gradients?

Back 75

facilitated diffusion

Front 76

where are the Na-K ATPase pumps located in the kidney tubules?

Back 76

in the basolateral membrane everywhere in the nephron except for the thin nephric loops

Front 77

in the tubular cells proximal to the PTCN, Na-K ATPase pumps what to where and what happens?

Back 77

- Na into into the interstitium and 2 K into the cell.

- The PTCN carries the Na away and K diffuses out of the cell, along its concentration gradient, through ion channels on the apical membrane.

- this process creates a net negative charge inside the cell, and a concentration gradient thus creating a huge driving force for Na to reenter the tubular cell.

Front 78

what is the major method in which water is reabsorbed?

Back 78

via Na reabsorption

Front 79

what is the most active nephric segment?

Back 79

the proximal tubule

Front 80

what four modes of transport does the proximal tubule utilize in absorption?

Back 80

- (simple and facilitated) diffusion
- solvent drag
- ion channels
- (primary and secondary) active transport

Front 81

under normal circumstances how much of and by what means does the PCT reabsorb glucose?

Back 81

100% of glucose is reabsorbed by secondary active transport.

Front 82

how are proteins reabsorbed by the PCT?

Back 82

small proteins are degraded by proteases on the brush border and absorbed as single amino acids.

larger proteins are reabsorbed by pinocytosis and degraded to amino acids via lysosomes.

Front 83

how much Na is reabsorbed by the PCT and by what means?

Back 83

- about 2/3 of sodium is reabsorbed by the PCT

- most is via the Na-K ATPase pump
- the rest is passive, paracellular transport via chloride early on or by itself later along the tubule

Front 84

how is Cl reabsorbed by the PCT?

Back 84

- only passive transport
- ion channels in cell membranes
- tight junctions are permeable to Cl
- transport of other molecules sets up a chemical gradient for chloride to leave the tubule

Front 85

how is bicarbonate reabsorbed by the PCT?

Back 85

by secondary transport by TWO transporters in the BASAL membrane

Front 86

what ions does the nephric loop absorb? How is this done? What is the purpose?

Back 86

- Na, Cl, K, HCO3, and Ca
- mostly by active transport, without water, via the thick ascending limb
- this effectively dilutes the renal tubular fluid by extracting ions but leaving water.

Front 87

what are the three segments of the nephric loop?

Back 87

- thin descending limb
- thin ascending limb
- thick ascending limb

Front 88

what is transported by the thin descending limb?

Back 88

water only. No salts. This effectively concentrates the renal filtrate

Front 89

what is transported by the thin ascending limb?

Back 89

passively permeable to salts but not water. This effectively dilutes the renal filtrate.

Front 90

what is the mechanism for initiating a hypertonic medullary osmolarity?

Back 90

active transport of Na/Cl by the ascending thick limb.

Front 91

how is potassium recovered in the thick ascending limb?

Back 91

by a Na-K-2Cl co-transporter on the apical membrane

Front 92

how is hydrogen ion secreted in the thick ascending limb?

Back 92

by a sodium-proton antiporter on the apical membrane

Front 93

how is calcium recovered in the thick ascending limb?

Back 93

apical ion channels and paracellularly

Front 94

what are the major functions of the DCT?

Back 94

1. reabsorb salts to attain "fine tuning" of the tubular fluid
2. continue diluting tubular fluid (important part of water balance)
3. respond to altered Na concentrations by the macula densa to adjust renal and systemic BP

Front 95

how do the PCT and DCT differ in their response to body signals?

Back 95

The PCT does not respond to body signals; the DCT has receptors for fine-tuning based on body signals.

Front 96

what are the four major mechanisms of DCT reabsorption?

Back 96

1. passively via paracellular or ion channels
2. Na-K ATPase active transport
3. Na-Cl (secondary active) cotransport on the apical membrane
4. Ca ATPase transporter in the basal membrane

Front 97

where does the majority of the pH regulation occur in the kidney?

Back 97

the medullary collecting duct

Front 98

where is the H-ATPase pump located and what is its purpose?

Back 98

in the medullary collecting duct, to secrete protons out of the blood and into the tubular lumen for pH regulation.

Front 99

where is the major site for potassium concentration regulation?

Back 99

the medullary collecting duct. It can absorb or secrete as necessary.

Front 100

what is the function of the principal cells and where are they located?

Back 100

they are located in the collecting duct and reabsorb Na and Cl via a Na-K ATPase primary and secondary active transport.

Front 101

besides the direct H-ATPase pump, by what other mechanism does the collecting duct secrete H+ into the tubular lumen?

Back 101

with an apical H-K ATPase pump

Front 102

what affect does aldosterone have on the kidney?

Back 102

in the late tubule, affects Na reabsorption and K secretion

Front 103

what are the four major effects of the renal filtrate's first cortical pass?

Back 103

1. form filtrate
2. make mass adjustments
3. reduce volume
4. deliver to medulla

Front 104

what is the major function of the renal vasa recta?

Back 104

to recover water and solutes and provide the medulla with blood flow without washing out the salts and disrupting the concentration gradient.

Front 105

what are the three basic components required for osmotic adjustment of urine?

Back 105

1. a "vertical" medullary osmotic gradient
2. a collecting duct variablly permeable to water
3. a means of recovering water from the medulla

Front 106

what six anatomical features are necessary for the establishment and maintenance of high medullary osmolarity?

Back 106

1. hairpin turn of the nephric loop
2. immediate proximity of the ascneding and descending limbs of the nephric loop
3. opposite direction in flow in the two limbs of the nephric loop
4. parallel arrangement of the vasa recta to each other and with the nephric loops
5. immediate proximity of the collecting ducts to the vasa recta
6. minimal thickness of the interstitium

Front 107

what osmotically active particles are in highest proportion in the medulla?

Back 107

urea, Na, Cl

Front 108

comment on the permeability of the thick ascending nephric limb

Back 108

salt-permeable; water impermeable

Front 109

comment on the permeability of the thin descending nephric limb

Back 109

water permeable; salt impermeable

Front 110

comment on the permeability of the thin ascending nephric limb

Back 110

salt-permeable; water impermeable

Front 111

what is the driving force for salt to leave the thin ascending limb of the nephric loop?

Back 111

the tubular fluid is saltier than the interstitium

Front 112

comment on the renal tubule's permeability to urea

Back 112

only permeable in the thin descending limb and the distal medullary collecting duct

Front 113

by what process does the vasa recta supply blood to the medulla without disrupting the concentration gradient?

Back 113

countercurrent exchange

Front 114

if the vasa recta is permeable to everything, then how can it recover water from the medulla?

Back 114

- low hydrostatic pressure
- high oncotic pressure (dissolved proteins)

Front 115

what could be expected to be true for the salt concentration, oncotic pressure, flow rate, and osmolarity of the blood leaving the vasa recta versus the blood entering the vasa recta at the same cross-sectional positions?

Back 115

- salt concentration: the same
- flow rate: higher in the efferent blood
- oncotic pressure: lower in the efferent blood
- osmolarity: the same

Front 116

what two parts of the nephric loop serve to dilute the tubular fluid?

Back 116

- the ascending nephric limb
- the DCT

Front 117

comment on the permeability of the DCT

Back 117

permeable to salt, but not to water. actively transports salt out of the tubular fluid to make it hypotonic

Front 118

*** what is the normal blood pH?

Back 118

7.4

Front 119

what bodily systems are best able to deal with acute fluctuations in pH? chronic?

Back 119

acute: lungs and buffers in the bodily fluids

chronic: kidney via adjusting pH of the urine (excretion of H+)

Front 120

which parts of the nephron are involved in secretion of H+ or bicarb to adjust pH?

Back 120

proximal tubule
collecting duct

Front 121

what are the three basic renal mechanisms of acid-base balance?

Back 121

1. secrete and excrete H+
2. recover filtered bicarb
3. generate new bicarb

Front 122

what are the two main buffers of the tubular fluid?

Back 122

bicarb and phosphate

Front 123

why is phosphate more effective at excreting H+ in the urine than bicarb?

Back 123

because phosphate is still negatively charged when it binds a proton and therefore cannot reenter the cell. bicarb can dissociate into water and CO2. CO2 can freely permeate a cell

Front 124

specifically where are the H-ATPase pumps located?

Back 124

in the intercalated cells of the collecting duct

Front 125

where is ammonium synthesized in the nephron and what is the resulting effect?

Back 125

synthesized in the PCT (from glutamine), the NH4+ is excreted, thus ridding the body of a proton and the metabolite of glutamine produces a molecule of bicarb.

Front 126

what is the pathway of ammonium being produced in the kidney to being excreted?

Back 126

- ammonium produced by the PCT and secreted into the tubular lumen
- in the medulla, converted to ammonia by the thick ascending nephric limb
- passes through the medulla, into the collecting duct, where it is converted back to ammonium
- this bypasses the cortex and avoids being put into the bloodstream in large amounts
- a small amount enters the vasa recta and is converted to urea in the liver

Front 127

what do the two different types of intercalating cells of the collecting duct do?

Back 127

- one type secretes acid and recovers bicarb
- the other type secretes bicarb and recovers acid

Front 128

what is the major enzyme involved in the production of bicarb?

Back 128

carbonic anhydrase (H2O + CO2 --> H+ + HCO3-)

Front 129

*** what is the main goal of local renal blood pressure control?

Back 129

maintain a steady GFR

Front 130

how does ADH cause the kidney to increase systemic blood volume?

Back 130

1. collecting duct increased permeability to urea allows for more water passage from the descending thin nephric limb to the vasa recta

2. increased aquaporins in the collecting duct concentrate the urine by transferring water from the collecting duct to the vasa recta

Front 131

how does the JGA cause the kidney to increase systemic blood volume?

Back 131

secretion of renin activates the renin-angiotensin-aldosterone system. Aldosterone increases sodium reabsorption in the PCT and water goes with it to the PTCN.

Front 132

how does the macula densa increase the GFR?

Back 132

increases the diameter of the afferent arterioles and decreases the diameter of the efferent arterioles

Front 133

how does sympathetic stimulation affect the blood flow to the kidney?

Back 133

- the afferent arterioles are directly innervated by sympathetic fibers
- sympathetic drive causes vasoconstriction of the afferent arteriole
- reduced renal perfusion shunts blood to the muscles and other parts of the body

Front 134

what is the renal myogenic reflex?

Back 134

stretch receptors in the arteriolar wall causes constriction of the vascular smooth muscle of the afferent, thus decreasing blood flow to the glomerulus. The efferent arterioles relax to overcome any tendency for a raise in hydrostatic pressure in the glomerulus. This returns the GFR to normal.

The reverse can also happen when blood pressure drops.