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Renal > physiology of the renal tract > Flashcards

physiology of the renal tract Flashcards

1
Q

what is osmolarity?

A

Concentration of osmotically active particles present in a solution

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2
Q

what are the units of osmolarity?

A

mosmol/l for body fluids as these are weak salt solutions.

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3
Q

what are the two factors that need to be known for osmolarity to be calculated?

A

the molar concentration of the solution, and

2) the number of osmotically active particles present

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4
Q

what measures osmolarity?

A

osmometer

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5
Q

what is the difference between osmolality and osmolarity?

A

Osmolality has units of osmol/kg water
Osmolarity has units of osmol/l
For weak salt solutions (incl. body fluids) these 2 terms are interchangeable

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6
Q

what is the osmolarity of body fluids?

A

~300 mosmol/l

i.e. the same osmolarity as 150mM NaCl and 100mM MgCl2.

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7
Q

what is tonicity?

A

Tonicity is the effect a solution has on cell volume

A solution can be either hypo-, hyper- or iso-tonic

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8
Q

what happens when you put a cell in a hypotonic solution?

A

more water outside, cell lysis

less than 300mosmols/l

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9
Q

what happens when you put a RBC in an isotonic solution?

A

normal RNC appearance

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10
Q

what happens when a cell is placed in a hypertonic solution?

A

greater than 300mosmols/l, decreased in cell volume, cells shrink

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11
Q

what else should be considered related to osmolarity and tonicity?

A

also takes into consideration the ability of a solute to cross the cell membrane.

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12
Q

what is the osmolarity of urea and sucrose?

A

300mM, hence the osmolarity will be the same because they do not dissociate into other particles

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13
Q

sucrose is —-tonic solution?

A

isotonic

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14
Q

urea is ——-tonic solution to cells?

A

hypo, because the red blood cell membrane is very permeable to urea because they have transporters that move urea from the outside to the inside, leaving behind water molecules and setting up a water gradient, causing an increase in water in the cell, meaning it is a hypotonic solution

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15
Q

what is the total body water in males?

A

~60% of body weight

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16
Q

what is the total body weight in females?

A

~50% of body weight

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17
Q

what are the two major compartments of total body water?

A

ICF and ECF which is 67% and 33% respectively

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18
Q

ECF includes?

A

Plasma (~20% of ECF)
Interstitial fluid (~80% of ECF)
Lymph (negligible) + Transcellular fluid (negligible)

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19
Q

how do we measure the volume of these particular fluid compartments?

A

‘Tracers’

Obtain the ‘distribution volume’ of a tracer

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20
Q

what are useful tracers?

A

TBW: 3H2O
ECF: Inulin
Plasma: labelled albumin

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21
Q

what is the equation of TBW?

A

ECF + ICF

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22
Q

to measure the distribution of volume of a tracer?

A

Add a known quantity of tracer X (QX; mol or mg) to the body
Measure the equilibration volume of X in the body ([X])
Distribution volumes (litres) = Qx(mol/{x{(mol/litre)

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23
Q

water balance or homeostasis?

A

inputs - outputs

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24
Q

what are inputs?

A

fluid intake, food intake, metabolism

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25
Q

what are the outputs?

A

insensible loss: no physiological or regulatory control/ unpreventable:

skin, lungs

sensible loss: regulatory mechanisms that can change how much is lost
sweat, faces, urine

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26
Q

what is the greatest loss of water in the body?

A

urine, depending of body hydration status, extremely hydrated = more urine produced

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27
Q

water imbalance is manifested as changes in?

A

body fluid osmolarity, imbalance is treated by changes in distribution of what is inside and outside of the cells and normal osmotic equilibrium is restored

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28
Q

effects of environmental temperature on water loss in adults?

A

lungs lose less volume of water, you sweat more and you produce less urine

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29
Q

effects of prolonged heavy exercise on water loss in adults?

A

lungs produce more water, you sweat much more, and you produce less urine,

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30
Q

why do you still produce urine when you are extremely dehydrated?

A

because some of the products that are excreted in urea can only be excreted in solution, hence no matter what urine must be produced

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31
Q

how is water balance maintained in the body?

A

Water balance is maintained by increased water ingestion. Decreased excretion of water by the kidneys alone is insufficient to maintain water balance

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32
Q

what are the concentrations of individual ions in the ICF?

A

Na+ -10
K+ -140
Cl- 7
HCO3- 10

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33
Q

what are the concentrations of individual ions in the ECF?

A

Na+ 140
K+ 4.5
Cl- 115
HCO3- 28

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34
Q

what causes changes in the concentrations of individual ions?

A

different tissues and animals will have different concentrations of ions

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35
Q

what enables cells to maintain internal environments that differ in composition compared to their surroundings?

A

The cell membrane and membrane transport mechanisms enable cells to maintain internal environments that differ in composition compared to their surroundings

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36
Q

what are the main ions in the ECF?

A

Na+, Cl-, HCO3-

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37
Q

what are the main ions in the ICF?

A

: K+, Mg2+, -vely charged proteins

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38
Q

cell membranes are?

A

selectively permeable

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39
Q

despite the selective permeability of the cell membranes what is true about the osmotic concentrations?

A

ECF and ICF are identical (~300 mosmol/l)

Because changes in solute concentrations lead to immediate changes in water distribution, the regulation of fluid balance and electrolyte balance are tightly intertwined.

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40
Q

what is fluid shift?

A

Movement of water between the ICF and ECF in response to an osmotic gradient.

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41
Q

what happens to the ECF and ICF volume if the osmotic concentration of the ECF increases?

A

ECF becomes hypotonic and ICF volume increases, because of the water gradient, hence ECF decreases

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42
Q

what happens to the ECF and ICF volume if the osmotic concentration of the ECF decreases?

A

ECF becomes hypertonic and ICF volume decreases because of the water gradient, hence ECF volume increases

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43
Q

gain or loss of water?

A

= change in fluid osmolarity

Similar changes in ICF & ECF volumes (both increase or decrease)

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44
Q

gain or loss of NaCl?

A

change in fluid osmolarity

a) Na+ “excluded” from ICF (recall ion distributions
(b) Osmotic water movements

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45
Q

what are the two factors that combine to produce opposite effects in ICF and ECF?

A

These two factors combine to produce opposite changes in ICF and ECF volumes:
ECF NaCl gain: ECF ↑ ICF ↓
ECF NaCl loss: ECF ↓ ICF ↑

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46
Q

gain or loss of isotonic fluid?

A

(e.g. 0.9% NaCl solution) = no change in fluid osmolarity

Change in ECF volume only

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47
Q

kidneys do what to the composition and volume of ECF?

A

Kidney alters composition & volume of ECF

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48
Q

why is regulation of ECF volume vital?

A

for long term regulation of blood pressure

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49
Q

electrolyte balance occurs when?

A

rates of gain = rates of loss

50
Q

what are the two important reasons for electrolyte balance?

A

1) Total electrolyte concentrations can directly affect water balance (via changes in osmolarity)
2) The concentrations of individual electrolytes can affect cell function

51
Q

which two ions are particularly important in electrolyte balance?

A

sodium and potassium

52
Q

why is sodium and potassium particularly important in electrolyte balance?

A

They are major contributors to the osmotic concentrations of the ECF and ICF, respectively
b) They directly affect the functioning of all cells

53
Q

sodium balance, why is it vital to regulate sodium?

A

> 90% of the osmotic concentration of the ECF results from the presence of sodium salts

The total amount of sodium in the ECF represents a balance between two factors (input and output).

Na+ is mainly present in the ECF therefore it is a major determinant of ECF volume (rule-of-thumb: “water follows salt”)

54
Q

potassium balance is vital because?

A

Minor fluctuations in plasma [K+] can have detrimental consequences

55
Q

what is the role of potassium?

A

establishing membrane potential

56
Q

small leakages or increased cellular uptake may severely affect the concentration of potassium in plasma leading to?

A

muscle weakness → paralysis
(ii) cardiac irregularities → cardiac arrest
hence
[K+]plasma must be closely monitored and regulated

57
Q

salt balance intake?

A

fluids and food

58
Q

salt balance output?

A

sweat and faces, urine causes the most excretion of salt

59
Q

what is salt imbalance manifested as?

A

ECF volume

60
Q

regulation of ECF volume is important for?

A

long term regulation of blood pressure

61
Q

what are the filtrations barriers?

A

Glomerular Capillary Endothelium (barrier to RBC)

(2) Basement Membrane (basal lamina) (plasma protein barrier) 

(3) Slit processes of podocytes (plasma protein barrier)
	(Glomerular epithelium)
62
Q

what is the difference between the glomerular capillary and the pores in other capillaries in other tissues?

A

they are much bigger, making the walls of the glomerular capillary endothelium quite leaky

63
Q

the basement membrane

A

acellular layer

64
Q

what makes the inner layer of the bowman’s capsule?

A

the podocytes, foot like cells

65
Q

what moves through the lumen of the capillary to the lumen of the bowman’s capsule?

A

things big enough to cross

66
Q

what happens to negatively charged proteins across the basement membrane?

A

the basement membrane is negatively charged, hence the proteins are repelled. The basement membrane acts to retain the proteins. because the RBCs are too big, they should not get through the molecular sieve. if you find blood in urine, then there is something wrong with this mechanism

67
Q

fluid filtered from the glomerulus into the Bowman’s capsule must pass through?

A

the three layers that make up the glomerular membrane

68
Q

what type of process is glomerular filtration?

A

passive, instead this process is driven by the balance of forces acting on the membrane

69
Q

what are th 4 process that drive filtration?

A

glomerular capillary blood pressure, capillary oncotic pressure, bowman’s capsule hydrostatic fluid pressure, bowman’s capsule oncotic pressure, anything that can bypass this pressure will enter the bowman’s capsule

70
Q

what are the 2 fluid pressures?

A

pressure of blood, glomerular capillary blood pressure - 55mmHg, largest of the four pressure, key determinant, sets up the net filtration

Bowman’s capsule hydrostatic (fluid) pressure - this pressure opposes the glomerular capillary blood pressure - 15mmHg

71
Q

the glomerular capillary is special because?

A

the pressure stays the same from start to the end, the diameter of the afferent is bigger than the efferent, building up of the back daming effect, maintaining the pressure of the blood constant

72
Q

what are the 2 oncotic pressures?

A

colloid/osmotic - pressure of plasma proteins

Capillary oncotic pressure and Bowman’s capsule oncotic pressure , you should not have plasma proteins in the Bowman’s capsule oncotic pressure, across this membrane, exerting an osmotic effect, dragging anything small enough to cross the membrane, opposes blood pressure - 30mmHg

73
Q

what is the pressure of the Bowman’s capsule oncotic pressure?

A

it is 0mmHg, because there are no plasma proteins present in the bowman’s capsule

74
Q

to find the net filtration pressure:

A

the difference between the sum of the fluid pressures and the oncotic pressures - giving us a net filtration pressure of 10mmHg, this is the pressure that pushes fluid and anything that can bypass the membrane to form the initial glomerular fluid

75
Q

what are the starling forces?

A

the balance of hydrostatic pressure and osmotic forces

76
Q

what is the composition of tubular fluid

A

same compositions as the start of the tubular fluid as roughly as plasma apart from the large plasma proteins

77
Q

what is GFR?

A

rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s capsule per unit time.
- collective across both kidneys and across all nephrons, this is dependent on how holy or how large the holes are

78
Q

how do you decrease GFR?

A

kidneys are filtering less, so less urine produced

79
Q

what is the major determinant of the GFR?

A

glomerular (blood) pressure is the major determinant of GFR

80
Q

GFR =

A

Kf x net filtration pressure where Kf = filtration coefficient = how “holey” the glomerular membrane is

81
Q

what is the extrinsic regulation of GFR?

A

sympathetic control via baroreceptor reflex

82
Q

what is the autoregulation of GFR instrinic?

A 
Myogenic mechanism
	(b) Tubuloglomerular feedback mechanism
83
Q

what mechanisms keep the GFR constant-ish?

A

extrinsic and intrinsic mechanisms

84
Q

if you have contraction of the muscle in the afferent arteriole?

A

there is less blood flowing though the blood capillary, decreased net filtration pressure, decreased GFR

85
Q

if you have vasodilation in the afferent arteriole?

A

more blood flowing, increase net filtration pressure, increased GFR

86
Q

fall in blood volume (e.g. hemorrhage) (extrinsic control)

A

decreased blood pressure, detected by aortic and carotid sinus baroreceptors, increased sympathetic activity, generalized arteriolar vasoconstriction and constriction of afferent arterioles, decreased BPgc and decreased GFR and decreased urine volume, reducing fluid loss form the body helping to compensate for the initial loss of volume in the body

87
Q

intrinsic control of blood pressure?

A

increase in blood pressure during exercise, so GFR is increased, prevention of losing lots of fluids and salts is constant GFR, allows individual to produce enough urine and this occurs through auto regulation of GFR

88
Q

what is auroregulation?

A

Autoregulation prevents short term changes in systemic arterial pressure affecting GFR

89
Q

what protects changes in MABP?

A

RBF & GFR protected from changes in MABP over wide range of MABP

90
Q

what are the two ways that auto regulation occurs?

A

myogenic and tubuloglomerular feedback

91
Q

what is myogenic auto regulation?

A

If vascular smooth muscle is stretched (i.e. arterial pressure is increased), it contracts thus constricting the arteriole

92
Q

what is the tubuloglomerular feedback auto regulation?

A

Involves the juxtaglomerular apparatus (mechanism remains unclear),
If GFR rises, more NaCl flows through the tubule leading to constriction of afferent arterioles

93
Q

what are the macula dense cells?

A

sense NaCl content tubular fluid, in response to increase in salt, the macula dense release chemicals that causes the contraction of the afferent arteriole, decreasing blood flow down the glomerular capillary, decreasing net filtration pressure, in a negative feedback fashion

94
Q

kidney stones

A

buildup of fluid due to a kidney stone - increasing the bowman’s capsule fluid pressure causing a decrease in GFR, due to decrease in net filtration pressure

95
Q

diarrhea?

A

plasma proteins are still present within the capillary, and will exert a greater pressure, dehydrated, so increase in capillary oncotic pressure leading to a decreased in GFR

96
Q

severely burned patients?

A

loss of plasma proteins, causing a loss of capillary oncotic pressure leading to an increase in GFR

97
Q

decrease in filtration coefficient?

A

change in surface area available for filtration - reducing GFR, because is affects the rate at which urine Is produced and excreted

98
Q

what is renal plasma clearance?

A

A measure of how effectively the kidneys can ‘clean’ the blood of a substance
Equals the volume of plasma completely cleared of a particular substance per minute
Each substance that is handled by the kidney will have it’s own specific plasma clearance value

99
Q

what are the units of clearance?

A

ml/min - clearance of substance X

100
Q

inulin

A

not produced by the body, is found in garlic and onions etc. it is not metabolized by the kidney, not toxic and it is easily measured in urine and blood and it is freely filtered at the glomerulus and is neither absorbed not secreted

101
Q

inulin clearance?

A

is GFR because the substance is not reabsorbed at any point, 125ml/min, there is 125ml of inulin-free plasma returned to the plasma

102
Q

rate of filtration?

A

inulin plasma x GFR = conc. urine x Vurine

103
Q

what can be used instead of inulin/

A

creatinine, giving us a close approximation, this is because inulin has to administered and has to be measured multiple times

104
Q

glucose

A

normally filtered, passes through the sieve, normally all the glucose filtered is reabsorbed by the proximal convoluted tubule, normally not secreted - clearance is therefore 0

105
Q

urea

A

metabolic waste products excreted in urine, partly reabsorbed and not secreted, clearance < GFR, only a portion of the plasma is cleared

106
Q

hydrogen ions

A

secreted but not reabsorbed, therefore clearance > GFR, all of the filtered plasma is cleared of a substance, and the peritubular plasma from which the substance is secreted, is also cleared

107
Q

tubular reabsorption or secretion?

A

if clearance is GFR then substance is secreted into tubule

108
Q

if all the PAD in the plasma that escapes filtration>

A

it is secreted from the peritubular capillaries

109
Q

what is PAH?

A

Para-amino hippuric acid (PAH) = exogenous organic anion

Used clinically to measure renal plasma flow (= 650 ml/min)

110
Q

why use pAH?

A

PAH is 1) freely filtered at glomerulus,
2) secreted into the tubule (not reabsorbed) & 3) completely cleared from the plasma

used to clinically measure renal plasma flow

111
Q

creatinine

A

(Creatinine is a muscle metabolite produced at a near constant rate. It is freely filtered and not reabsorbed but is slightly secreted,  gives a close approximation of GFR and is easier to measure than inulin clearance)

112
Q

what is an ideal marker to find a GFR marker?

A

Non-toxic

(2) Inert (i.e. not metabolised) 
(3) Easy to measure

(a) A GFR marker should be filtered freely; NOT secreted or reabsorbed

113
Q

what is the an idea RPF marker?

A

should be filtered and completely secreted.
Non-toxic
(2) Inert (i.e. not metabolised)
(3) Easy to measure

114
Q

what is the filtration fraction?

A

Filtration fraction is the fraction of plasma flowing through the glomeruli that is filtered into the tubules
i.e. ~20% of the plasma that enters the glomeruli is filtered.
The remaining 80% moves on to efferent arterioles and then the peritubular capillaries.

115
Q

how do you calculate filtration fracture?

A

GFR/RPF = 0.19 = 20% in a healthy person

116
Q

what is GFR in a healthy person?

A

125 ml/min (calculated from inulin clearance)

= 180 litres/day !! (= 60x plasma volume!!)

117
Q

what is RPF in a healthy person?

A

650ml/min calculated from PAH clearance

118
Q

what is RBF in a healthy person?

A

RPF x 1/1-HCT = ~1200ml/min

119
Q

how much of CO does the kidney receive?

A

~24% of CO when CO =5litres/min at rest

120
Q

RPF

A

collectively through both kidneys and individual nephrons, how much plasma is flowing through them

Renal (15 decks)

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