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Y2 - Renal > Physiology > Flashcards

Physiology Flashcards

(93 cards)

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1
Q

What is osmolarity?

A

The concentration of osmotically active particles present in a solution

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2
Q

What factors need to be known for calculation of osmolarity?

A

Molar concentration of a solution

Number of osmotically active particles in a solution

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3
Q

What is the difference between osmolarity and osmolality?

A

Units used
OsmolaRity: osmol/l (but mosmol/lused for body fluids)
OsmolaLity: osmol/kg water
Interchangeable for weak salt solutions including body fluids

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4
Q

What is tonicity?

A

The effect a solution has on cell volume

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5
Q

What are the three categories of tonicity?

A

Isotonic
Hypotonic
Hypertonic

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6
Q

What is an isotonic solution?

A

One that causes no change to cell volume

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7
Q

What is a hypotonic solution?

A

One that contains less water, a concentrated salt solution

Causes decrease in cell volume

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8
Q

What is a hypertonic solution?

A

One that contains more water, a dilute solution

Causes increase in cell volume and eventually cell bursts

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9
Q

What is the approx. total body water percentage?

A

Males: 60%
Females: 50%

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10
Q

What are the 2 major compartments of total body water?

A 
Intracellular fluid (ICF) - 67%
Extracellular fluid (ECF) - 33%
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11
Q

What is included in the ECF?

A

Plasma - 20%
Interstitial fluid - 80%
Lymph, transcellular fluid - negligible

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12
Q

What are tracers?

A

Things that can be used to measure the sizes of fluid compartments

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13
Q

What are examples of useful tracers?

A

Total body water - 3H2O
ECF (and therefore ICF) - inulin
Plasma - labelled albumin

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14
Q

What factors are responsible for input of water?

A

Fluid intake
Food intake
Metabolism

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15
Q

What factors are responsible for output of water?

A

Insensible: skin, lungs
Sensible: sweat, faeces, urine

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16
Q

What are sensible and insensible factors?

A

Insensible are ones that can’t be changed

Sensible can be changed

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17
Q

How does water imbalance manifest?

A

Changes in body fluid osmolarity

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18
Q

Wha are the balances of Na, Cl, HCO3 and K+ in ICF and ECF?

A

Much more Na, Cl and HCO3 in ECF

Much more K+ in ICF

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19
Q

What is fluid shift?

A

The movement of water between the ICF and ECF in response to an osmotic gradient

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20
Q

What are the challenges to fluid homeostasis?

A

Gain or loss of water
Gain or loss of NaCl
Gain or loss of isotonic fluid

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21
Q

Why is regulating K+ balance important?

A

Plays key role in establishing membrane potential

Small leakages or uptake may lead to muscle weakness and paralysis, or cardiac irregularities and arrest

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22
Q

What are the functions of the kidneys?

A

Water balance
Salt balance
Maintenance of plasma volume
Maintenance of plasma osmolarity
Acid-base balance
Excretion of metabolic waste products
Excretion of exogenous foreign compounds
Secretion of renin (control of arterial blood pressure)
Secretion of erythropoietin (EPO; RBC production)
Conversion of vitamin D into active form (Calcitriol: Ca2+ absorption in GI tract)

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23
Q

What is the primary function of the kidney?

A

Regulate the volume, composition and osmolarity of the body fluids and controlled excretion these substances

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24
Q

What is the functional unit of the kidney?

A

The nephron

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25
What are the functional mechanisms of the nephron?
Filtration Reabsorption Secretion
26
Describe the blood supply to the glomerulus.
Afferent arteriole supplies glomerulus Drained by efferent arteriole This divides into network of peri-tubular capillaries These drain into venues then vein
27
What is the journey of tubular fluid?
``` Formed at Bowman's capsule Drains into proximal tubule Drains into Loop of Henle Enters distal tubule Drains into collecting duct Passes through calyxes into renal pelvis ```
28
What is the juxtaglomerular apparatus?
Where part of the distal tubule passes between afferent and efferent arterioles Contains specialised cells important for function
29
What are the 2 types of nephron?
Juxtamedullary (20%) | Cortical (80%)
30
What are juxtamedullary nephrons?
Have a longer loop of Henle Blood supply has no peri-tubular capillaries - just the vasa recta which is a single capillary loop which follows the loop of Henle Responsible for producing concentrated urine
31
What are cortical nephrons?
Those that have peri-tubular capillaries and a shorter loop of Henle
32
Why is the juxtaglomerular apparatus important?
Granular cells in afferent arteriole produce and secrete renin Macula densa in distal tubule detect the amount of salt present in tubular fluid and sends signal to smooth muscle of the afferent arteriole to contract or relax, regulating the volume of blood passing into the glomerulus
33
How much of the plasma that enters the glomerulus is filtered?
About 20%
34
What equation represents the rate of excretion for any substance handled by the kidney?
Rate of excretion = rate of filtration + rate of secretion - rate of reabsorption
35
What equation represents rate of filtration of a substance?
Rate of filtration = plasma concentration of substance x GFR
36
What equation represents rate of excretion of a substance?
Rate of excretion = concentration of a substance x urine production rate
37
What equation represents rate of reabsorption of a substance?
Rate of reabsorption = rate of filtration - rate of secretion
38
If rate of filtration > rate of excretion, what net effect has happened?
Net reabsorption
39
What equation represents rate of secretion of a substance?
Rate of secretion = rate of excretion - rate of filtration
40
If rate of filtration < rate of excretion, what net effect has happened?
Net secretion
41
What are the barriers to glomerular filtration?
``` Glomerular capillary endothelium (barrier to RBC) Basement membrane (basal lamina) (plasma protein barrier) Slit processes of podocytes (plasma protein barrier) ```
42
What forces comprise net filtration pressure?
Glomerular capillary blood pressure Capillary oncotic pressire Bowman's capsule hydrostatic pressure Bowman's capsule oncotic pressure
43
What are the approximate pressures for each of the filtration forces?
Glomerular capillary blood pressure - 55 mmHg Capillary oncotic pressire - 30 mmHg Bowman's capsule hydrostatic pressure - 15 mmHg Bowman's capsule oncotic pressure - 0 mmHg
44
What is the approximate net filtration pressure?
10 mmHg
45
What is glomerular filtration rate?
Rate at which protein-free plasma is filtered from the glomeruli into Bowman's capsule per unit of time
46
What equation represents GFR?
GFR = Kf (filtration co-efficient) x net filtration pressure
47
What is the major determinant of GFR?
Glomerular capillary fluid blood pressure
48
What factors are responsible for regulation of renal blood flow rate and GFR?
Extrinsic regulation - sympathetic control via baroreceptor reflex Autoregulation - myogenic mechanism, tubule-glomerular feedback mechanism
49
How does arterial blood pressure affect GFR?
Increase in arterial blood pressure increases blood flow into the glomerulus This increases glomerular capillary blood pressure Net filtration pressure increases GFR increases (and vice versa)
50
How do vasoconstriction and vasodilation affect GFR?
Vasoconstriction - decreases GFR (decreased blood flow) | Vasodilation - increases GFR (increased blood flow)
51
How a fall in blood volume and arterial blood pressure affect GFR?
Decrease in arterial BP detected by aortic and coritid-sinus baroreceptors. Increase sympathetic activity Generalised arteriolar vasoconstriction Constriction of afferent arterioles Decrease glomerular capillary BP, decrease GFR Decrease in urine volume, helps compensate for fall in blood volume
52
What factor prevents short term changes in systemic arterial pressure affecting GFR?
Autoregulation
53
What are the auto regulatory mechanisms?
Myogenic | Tubuloglomerular feedback
54
What is myogenic autoregulation?
If vascular smooth muscle is stretched (e.g. increase in pressure) it contracts, this constricting the arteriole
55
What is tubuloglomerular feedback autoregulation?
Uses juxtoglomerular apparatus (unclear how) | If GFR rises, more NaCl flows through the tubule, leading to constriction of afferent arterioles by negative feedback
56
What is plasma clearance?
A measured how effectively the kidneys can clean the blood of a substance
57
What equation represents plasma clearance?
Clearance = rate of excretion/plasma concentration
58
For which substances does clearance = GFR?
Inulin | Creatinine
59
Why is it useful when a substance's clearance = GFR?
Substance can be used clinically as a measure of GFR
60
What is an example of a substance that is filtered, completely reabsorbed and not secreted?
Glucose
61
What is the clearance for glucose?
0
62
When will clearance be 0?
If substance is filtered, completely reabsorbed and not secreted If a substance is not filtered and not secreted (e.g. large proteins)
63
What is an example of a substance that is filtered, partly reabsorbed and not secreted? And what is the relationship between clearance and GFR for this situation?
Urea | Clearance < GFR
64
What is an example of a substance that is filtered, secreted, but not reabsorbed? And what is the relationship between clearance and GFR for this situation?
H+ | Clearance > GFR
65
What has happened to a substance if clearance < GFR
Substance has been reabsorbed
66
What has happened to a substance if clearance > GFR
Substance has been secreted into tubule
67
What has happened to a substance if clearance = GFR
Substance is neither reabsorbed nor secreted
68
What is PAH (para-amino hipuric acid) used for and why?
Used clinically to measure renal plasma flow | It is freely filtered at the glomerulus, secreted and not absorbed, and completely cleared from the plasma
69
What is filtration fraction?
The fraction of the plasma flowing through the glomeruli that is filtered into the tubules
70
What substances are fully or almost fully reabsorbed?
Fluid (99%) Salt (99%) Glucose (100%) Amino acids (100%)
71
Is reabsorption specific or non-specific?
Specific
72
Is filtration specific or non-specific?
Non-specific
73
What substances are reabsorbed in the proximal tubule?
``` Sugars Amino acids Phosphate Sulphate Lactate ```
74
What substances are secreted in the proximal tubule?
``` H+ Neurotransmitters Bile pigments Uric acid Drugs Toxins ```
75
What is secondary active transport?
The carrier molecule is transported coupled to the concentration gradient of an ion
76
What is facilitated diffusion?
Passive carrier-mediated transported of a substance down its concentration gradient
77
Where are Na+ ions reabsorbed?
All sections apart form descending limb of loop of Henle
78
How is Na+ reabsorbed?
Diffuses through channels from filtrate into tubular cells Also enters tubular cells by facilitated diffusion with glucose, amino acids, H+ Pumped out using Na+/K+ATPase into interstitial fluid Diffuses into peritubular capillary
79
How is water reaborbed?
The osmotic gradient created by transport of sodium drives the paracellular movement of water into the interstitial fluid The blood is concentrated with plasma proteins which adds to the oncotic drag
80
How is glucose reabsorbed?
Enters tubular cells by Na+ glucose co-transporter | Enters interstitial fluid by facilitated diffusion
81
What is transport maximum?
The maximum rate at which a particular substance can be reabsorbed
82
How much of salt and water are reabsorbed in the proximal tubule?
About 67%
83
How is tubular fluid described when it leaves the proximal tubule?
Iso-osmotic
84
What is the function of the loop of Henle?
Generates a portico-medullar solute concentration gradient to enable the formation of hypertonic urine
85
What does counter-current flow describe?
Fluid travels downtime descending limb and up the ascending limb of the loop of Henle
86
Which parts of the loop of Henle are permeable and impermeable to water?
Descending limb is permeable | Ascending limb is impermeable
87
Which parts of the loop of Henle have active NaCl reabsorption?
Descending limb has no active NaCl reabsorption | Ascending limb has active NaCl reabsorption
88
What do the selective permeabilities of the ascending and descending limbs of the loop of Henle create?
Enable an osmotic gradient to be established in the medulla
89
What is the function of potassium in the reabsorption of NaCl?
Is recycled Pumped into interstitial fluid with Cl Pumped back into tubular cell in exchange for Na
90
What 3 substances does the triple co-transporter transport?
Na Cl K
91
What is countercurrent multiplication?
The term for the increase in osmolality as you travel down into the medulla due to countercurrent flow
92
What is the purpose of counter-current multiplication?
To concentrate the medullary interstitial fluid to enable the kidney to produce urine of different volume and concentration according to the amounts of circulating ADH
93
What ensures that the blood flow through the medulla doesn't wash away the NaCl and urea?
Vasa recta capillaries follow hairpin loops Vasa recta capillaries are freely permeable to NaCl and water Blood flow to vasa recta is low

Y2 - Renal (2 decks)

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