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Urinalysis > Renal Function > Flashcards

Renal Function Flashcards

1
Q

Tubular reabsorption

A

Body takes back substances (water, glucose…etc) filtered into the urine and puts it back into the bloodstream

Urine -> Blood

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2
Q

Tubular secretion

A

Body secretes substances from the blood to the urine

Blood -> Urine

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3
Q

4 main components of urinary system

A
  1. Kidneys
  2. Ureters
  3. Bladder
  4. Urethra
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4
Q

Kidney function

A
  • Blood is filtered here to form urine
  • Removal nitrogenous waste products from protein catabolism
  • Acid-base balance
  • Retention of essential nutrients
  • Water, electrolyte balance
  • Hormone production (EPO, renin)
  • Vitamin D production to maintain calcium levels
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5
Q

Ureter function

A

Carry urine to bladder

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6
Q

Bladder function

A

Store urine

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7
Q

Urethra function

A

Delivers urine for excretion outside of body

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8
Q

Glomerulus function and what it is

A
  • Sieve that filters urine
  • Bulb-like structure of small blood capillaries
  • Coil of 8 capillary lobes
  • Located in Bowman’s capsule
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9
Q

Inferior vena cava function

A

Takes blood from kidneys

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10
Q

Aorta function

A

Brings blood to kidneys

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11
Q

Renin

A

Hormone produced in kidneys that helps with ADH and aldosterone release/production, thus leading to water and electrolyte balance

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12
Q

What is the functional unit of the kidney? What does it do?

A
  • Nephron
  • Filters blood from renal aorta to create urine, also involved in reabsorption and secretion
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13
Q

Two types of nephrons

A
  1. Cortical nephrons - 85%, in kidney cortex
  2. Juxtamedullary nephrons - in longer loops of Henle (which concentrate urine)
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14
Q

Describe the process of urine creation

A
  1. Blood from renal arteries enters the afferent arteriole
  2. The glomerulus is the first filtering mechanism
  3. Bowman’s capsule
  4. Renal tubules make urine from plasma filtration (PCT, loop of Henle, DCT)
  5. Collecting duct merges urine to carry through ureters to bladder
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15
Q

Peritubular capillaries

A
  • Formed from efferent arteriole
  • Surround urine tubules
  • Reabsorption and secretion happen here
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16
Q

4 renal functions that are controlled by the nephron

A
  1. Renal blood flow
  2. Glomerular filtration
  3. Tubular reabsorption
  4. Tubular secretion
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17
Q

Renal artery function

A

Supplies blood to kidney

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18
Q

T/F
20-25% of the blood leaving the left ventricle of the heart enters the kidneys via the renal arteries

A

True

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19
Q

Blood passes through the kidneys at what rate?

A

1200 ml/min
Approx same as 600 plasma/min bc 50% of blood is plasma

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20
Q

Explain glomerulus sieve-like function

A
  • Retains RBCs and WBCs but filters out small molecules via hydrostatic pressure
  • Stuff < 70 kDa pass thru
  • Non-selective filter of plasma
  • Very water-permeable
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21
Q

Bowman’s capsule

A

Beginning of the renal tubule

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22
Q

Bowman’s space

A
  • Space between capsule and glomerulus
  • Filtrate of blood pools here
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23
Q

Peritubular capillaries merge to form which structure?

A

Vasa recta

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24
Q

What happens in the proximal convoluted tubule (PCT)?

A

Re-adsorption of essential substances (can also happen in DCT and collecting duct)

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25
Q

What happens in the distal convoluted tubule (DCT)?

A

Final adjustment of the urinary composition (water gets reabsorbed back into bloodstream)

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26
Q

What generally happens in the loop of Henle?

A

Major exchanges of water and salts

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27
Q

What happens in the ascending loop of Henle?

A
  • Majority of salts leave urine to go back to bloodstream (salt reabsorption)
  • No water reabsorption in ascending loop bc it’s impermeable to water
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28
Q

What happens in the descending loop of Henle?

A

Water leaves urine to go back to bloodstream (water reabsorption)

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29
Q

List the 4 factors that influence glomerular filtration

A
  1. Cellular structure of capillary walls
  2. Hydrostatic pressure (pushing out)
  3. Oncotic/osmotic pressure (proteins pushing on to keep things in capillaries)
  4. Renin-angiotensin-aldosterone system (RAAS)
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30
Q

List the 3 cell layers of the glomerulus

A
  1. Capillary wall membrane
  2. Basement membrane
  3. Visceral epithelium
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31
Q

Capillary wall membrane function

A
  • 1st fenestrated (means it contains pores) capillary membrane
  • Permeable to less than 70 kDa
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32
Q

Describe the visceral epithelium

A
  • Contains podocytes
  • Filtration slit
  • Shield of Negativity (has negative charge)
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33
Q

Podocytes

A

Cells with toe-like projections that surround the capillary to induce a second layer of filtration such that even fewer things filter through

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34
Q

Shield of negativity

A

The visceral epithelium has a negative charge to repel negatively charged substances (e.g., albumin) and lets cations/neutral molecules pass through

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35
Q

Hydrostatic pressure

A

Pressure exerted by blood on capillaries to push stuff out

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36
Q

Oncotic/osmotic pressure

A
  • Pressure exerted by the presence of unfiltered plasma proteins in glomerular capillaries to keep stuff in
  • Osmotic pressure caused by presence of colloids
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37
Q

How does change in systemic blood pressure affect glomerular blood pressure?

A

Change in hydrostatic pressure

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38
Q

Function of juxtaglomerular apparatus

A
  • Maintains glomerular blood pressure at constant rate
  • Made of mesangial cells that constrict/dilate the afferent/efferent arterioles
  • Also made of macula densa
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39
Q

How does the body respond to low blood pressure/toxins accum in blood?

A
  • Dilate afferent arterioles
  • Constrict efferent arterioles
  • This increases kidney BP
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40
Q

How does the body respond to high BP?

A
  • Constrict afferent arteriole
  • Prevents over-filtration
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41
Q

What regulates RAAS?

A

Juxtaglomerular apparatus
- juxtaglomerular cells (afferent arteriole)
- macula densa (convoluted tubule)

42
Q

Function of macula densa lining cells

A

Sense salt concentration and urine volume -> signal juxtaglomerular apparatus to release renin

43
Q

T/F
The DCT and juxtaglomerular apparatus are next to the glomerulus/Bowman’s capsule

A

True (slide 27)

44
Q

How does low sodium decrease BP?

A

Low blood sodium leads to less water retention in the circulatory system, which leads to lower blood volume. Low blood volume = decrease BP, thus messing up kidney’s hydrostatic pressure

45
Q

Low BP and plasma sodium lead to what?

A
  1. Renin secretion in blood
  2. Angiotensinogen converts renin into Angiotensin I
  3. Angiotensin I gets converted to Angiotensin II in lung/kidney
  4. Vasoconstriction, PCT sodium reabsorption, aldosterone release, and ADH release
46
Q

ADH

A
  • Hypothalamus secretes, but is stored in pituitary
  • Functions to increase water retention by increasing water permeability of DCT, constricts vessels to increase BP
  • Prevents from peeing out water
  • Released if low water and BP
46
Q

Aldosterone

A
  • Secreted by adrenal complex
  • Acts on DCT and collecting duct
  • Functions to reabsorb sodium and water, excrete potassium and hydrogen ions, and increase both blood volume and BP
47
Q

What happens to renin production if increased salt and BP?

A

Decreases

48
Q

T/F
Every minute, 125 ml of low MW substances are filtered

A

False
120 ml

49
Q

Difference between filtrate and plasma

A

In filtrate: no plasma protein, no protein-bound substances, no RBC/WBC
Plasma has all the above

50
Q

Specific gravity post-glomerulus

A

1.010 = ultrafiltrate of plasma

51
Q

Why don’t we pee out 120 ml/min?

A

Bc we reabsorb most of the filtrate

52
Q

Describe active transport processes in tubular reabsorption

A
  • PCT: glucose, aa, salts
  • Ascending loop of Henle: chloride ion
  • DCT: sodium ion
53
Q

Describe passive transport processes in tubular reabsorption

A
  • H2O: reabsorbed everywhere except ascending loop of Henle
  • Urea: convoluted tubule and ascending loop of Henle
  • Sodium ion: passively transported during active transport of chloride ion
54
Q

Maximal reabsorptive capacity (Tm)

A
  • Tm = transport max (mg/min or ml/min
  • Maximum ability of renal tubules to reabsorb solute in filtrate
55
Q

Renal threshold

A

Plasma conc at which active transport stops

56
Q

T/F
Active transport is not influenced by conc of substance being transported

A

False
Active transport can be influenced by conc of substance being transported

57
Q

Renal thresholds of glucose and phosphate

A
  • Glucose = high (160-180 mg/dl)
  • Phosphate = low (appears in urine at plasma levels only slightly above normal)
58
Q

How can renal threshold and plasma concentrations be clinically useful?

A

Help to distinguish btwn excess solute filtration vs renal tubular damage

59
Q

Where does renal concentration start and end?

A
  • Starts in loop of Henle driven by osmotic gradients and countercurrent mechanism
  • Ends at DCT and collecting duct. Aldosterone in DCT and ADH in collecting duct
60
Q

Describe process of tubular concentration

A
  1. Renal conc starts in loop of Henle
  2. Water removed via osmosis in descending loop of Henle
  3. Sodium and chloride reabsorbed in ascending loop of Henle
  4. Aldosterone in DCT promotes sodium reabsorption
  5. ADH in collecting duct promotes water reabsorption
61
Q

Countercurrent mechanism

A
  • Functions to allow salt and water reabsorption
  • Salt pumped out of ascending limb by active transport, which increases osmolality of interstitial fluid
  • Then, water leaves descending limb by passive transport, thus increasing the osmolality of filtrate into descending limb
62
Q

Effect of dehydration in tubular reabsorption

A
  • Increased ADH secretion, which increases the permeability of the tubule/collecting duct
  • Water reabsorption increases and decreases urine volume
  • Urine more conc, thus higher specific gravity (amount solute in solvent)
63
Q

Effect of being well hydrated on tubular reabsorption

A
  • Decreased ADH secretion, which reduces the permeability of the tubule/collecting duct
  • Water reabsorption decreases and thus increases urine volume
  • More dilute urine, thus lower specific gravity
64
Q

List 2 reasons for tubular secretion

A
  1. Elimination of waste not filtered by glomerulus and medications/foreign substances
  2. Regulate acid-base balance via secretion of hydrogen ions
65
Q

Medications/foreign substances in tubular secretion

A
  • Bound to carrier plasma proteins
  • Not removed by glomerular filtration
  • High affinity for cells in PCT
  • Transported across into filtrate (show up in urine)
66
Q

Normal blood pH

A

7.35-7.45

67
Q

Is HCO3- filtered by the glomerulus?

A

Yes and must return to blood via active transport to maintain pH

68
Q

List 3 major mechanisms of acid-base balance in kidney

A
  1. Excrete hydrogen ions to reabsorb bicarb (happens in PCT)
  2. Excrete hydrogen ions combined with phosphate (HPO4-) to make H2PO4
  3. Excretion of hydrogen ions bound to ammonia to produce ammonium ion

All above mechanisms increase pH

69
Q

Urine pH range

A

4.6-8.0
avg 6.0

70
Q

Why is there no abnormal urine pH range?

A

Urine can vary from acid to alkaline and diet can influence urine pH

71
Q

Why do we reject urine samples with pH >9?

A

Bacteria likely breaking down urea into ammonia

72
Q

List glomerular filtration tests

A
  • Inulin clearance
  • Creatinine clearance
  • Calculated glomerular filtration
73
Q

List tubular reabsorption tests

A
  • Osmolarity
  • Free water clearance
74
Q

What are the two most common renal function tests?

A

Creatinine clearance and osmolality

75
Q

Clearance test

A
  • Used to measure filtering capacity of glomeruli
  • Measure substance that cannot be reabsorbed or secreted by tubules bc reabsorption causes false decrease and secretion causes false increase
  • Rate that kidneys can remove filterable substance from blood
76
Q

List types of clearance tests

A
  • Urea
  • Inulin
  • Creatinine
  • Beta-macroglobulin
  • Cystatin C
  • Radioisotopes
77
Q

Exogenous substance

A

Infused

78
Q

Endogenous substance

A

Naturally present in body

79
Q

Explain inulin clearance test

A
  • Exogenous
  • Inulin is fructose polymer
  • Test requires continuous infused substance
  • Original ref method
  • Not used anymore bc need to infuse over long time and requires pt to pee many times -> too much hassle
80
Q

Explain creatinine clearance test

A
  • Endogenous
  • Most common
  • Creatinine is waste product of muscle metabolism and relatively constant level in blood
  • Results affected by #functioning nephrons, nephron functional capacity, if you have one kidney
81
Q

What is the creatinine clearance test used for?

A
  • determine extent of nephron damage in known cases of renal disease
  • monitor effectiveness of treatment
  • determine feasability of administering meds
  • Not useful for detecting early renal disease bc 1st problem is tubular reabsorption, not glomerular filtration
82
Q

Disadvantages of the creatinine clearance test

A
  • Some creatinine secreted by tubules
  • Meds can cause falsely low serum levels
  • Bacteria break down urinary creatinine at room temp
  • Heavy meat diet elevated urine creatinine
  • Not reliable if pt has muscle wasting disease bc higher urine creatinine
83
Q

How do you calculate GFR in terms of creatinine clearance?

A

ml plasma cleared = (urine creat)/plasma creat) * (vol urine/min)

C = UV/P

U = urine creat
P = plasma creat
V = vol/min collected over 24 hr

84
Q

Additional glomerular filtration tests

A
  • eGFR using just serum creatinine measurement
  • Cystatin C measurement
  • Beta-2 macroglobulin measurement
85
Q

Cystatin C

A
  • Small protein produced by nucleated cells
  • Not secreted
  • Used in pediatric, diabetes, and elderly pts bc independent of muscle mass
86
Q

Beta-2 macroglobulin

A

Dissociates from HLA
Use immunoassay (not good for immunologic disorders bc HLA in blood)

87
Q

Concentration tests

A
  • Used to determine ability of tubules to reabsorb essential salts/water filtered by glomerulus
  • Urin conc determined by body’s hydration status
  • Kidney reabsorbs only amt needed to preserve adequate supply of body water
  • Monitor fluid intake when measuring conc
88
Q

Solute dissolved in solvent causes changes in which colligative properties?

A
  • Lower freezing point
  • Higher boiling point
  • Increased osmotic pressure
  • Lower vapor pressure
89
Q

1 mol of a non-ionizing substance dissolved in 1 kg of water lower the freezing point by _____

A

1.86°C

90
Q

Osmometry

A
  • Compare freezing point depression of urine sample to known saline solution to calc final result
  • Super cool sample to -27°C, heat then raises temp to freezing point
  • Vibration -> crystallization -> heat
91
Q

Ref range for serum osmolality

A

275-300 mOsm

92
Q

Ref range for urine osmolality

A

50-1400 mOsm

93
Q

Real urine osmolality

A

300-800 mOsm

94
Q

Why is the ratio of urine to serum osmolality clinically useful?

A
  • Normal ratio 1:1 (urine:serum)
  • Ratio reaches 3:1 with controlled decrease in fluid intake as urine becomes more concentrated
95
Q

List clinical significances of osmolality testing

A
  • eval renal conc ability
  • monitor course of renal disease
  • monitor fluid therapy
  • differential diagnosis in sodium levels
  • eval ADH response
96
Q

List 3 types of diabetes mellitus

A
  • gestational
  • Type 1
  • Type 2
97
Q

Diabetes insipidus

A
  • Disease where kidneys can’t conserve water so you pee it all out
  • 2 mechanisms:
    1. Reduced ADH production
    2. Inability of renal tubules to respond to ADH
98
Q

Interpret the following ADH injection result after decreased fluid intake for 24 hr:
urine:serum ratio is not 3:1

A

Renal tubules do not have functional ADH receptors. Collecting duct not functioning

99
Q

Interpret the following ADH injection result after decreased fluid intake for 24 hr:
urine:serum ratio is equal to 3:1

A

Decreased/inadequate ADH production

Urinalysis (1 decks)

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