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Functions of urinary system Flashcards

week 6

1
Q

What % and V of CO do they kidneys recieve?

A

25% = 1.25L/min

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2
Q

What are the 2 structures that make up the double capillary network (DCN)?

A

Glomerulus and Peritubular Capillaries

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3
Q

What is the pressure and net fluid movement of the Glomerulus at the DCN?

A

High HPcap 60mmHg

filtration

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4
Q

What is the pressure and net fluid movement of the Pertubular Capilaries at the DCN?

A

low HPcap 20mmHg

reabsorption

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5
Q

what are the special features of the renal circulation?

A

Receives 25% of Cardiac Output

DCN = high –> low BP

Low and slow renal medullary blood flow

Autoregulation

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6
Q

Compare Corticol vs JM nephrons

A

Glomeruli
C= outer 2/3s cortex
JM= inner cortex

LoH
C= short
JM= long, deep into medulla

Arteriole
C= efferent –> Peritubular Cap
JM= efferent - vasa recta

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7
Q

What are the functions of intraglomerular Mesangial cells?

A

Regulate GFR via vasoconstriction/dilation

Structural support

Phagocytise ICs and macromolecules

Secrete prostaglandins and proinflammatory cytokines

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8
Q

Structural features of Glomerulus

A

Visceral epithelium (podocytes and pedicles)

Filtration sites (gaps between adjacent pedicels).

Fenestrated capillaries (permeable to water, Na, urea and glucose)

Intraglomerular mesangial cells

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9
Q

What are the structures forming the JGA

A

Extraglomerular mesangial cells

Macula densa (late TAL/ early DCT)

Granular cells (afferent arteriole)

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9
Q

What is the site of inflammation in glomerular disease?

A

Intraglomerular mesangial cells

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10
Q

What are the components of the GFB and how are they selective?

A

Endothelial cells (fenestrated, size/charge selection)

Glomerular basement membrane (mesangial cells, size/charge)

Podocytes (charge selection)

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11
Q

What factors determine filtration through GFB?

A

Size (<4nm freely filtered, >8nm excluded)

Electrical charge (neg repelled)

Binding to plasma proteins (bound not filtered)

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12
Q

What are Filtration slits?

A

Foot process of podocytes that interlock to cover basement membrane and separated by a gap.

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13
Q

What is a filtration slit diaphragm?

A

Each slit bridged by a diaphragm that is formed from proteins (Nephrin, podocin, cadherin, a-actin-4)

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14
Q

What happens if there are mutations in genes that encode slit diaphragm proteins?

A

Proteinuria and renal failure

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15
Q

Physiology of proteinuria

A

Loss of neg charge of the GFB allows plasma proteins to enter

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16
Q

What is the normal GFR?

A

125ml/min = 180L/day

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17
Q

what occurs if the GFR is too high?

A

Rapid fluid movement through tubules –> Insufficient time for reabsorption –> decreased reabsorption

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18
Q

What factors affect the GFR?

A

Size of capillary bed

capillary permeability

pressure gradients across the capillary wall

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19
Q

what would be the GFR that indicates

a) renal disease
b) renal failure

A

a) <60ml/min
b) <15ml/min

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20
Q

What are the 4 pressures that favour/oppose filtration across the GVM and their values?

A

Glomerular capillary hydrostatic (60mmHg)

Bowmans Capsule hydrostatic (18mmHg)

Glomerular Capillary oncotic (32mmHg)

Bowman’s capsule oncotic (ommHg

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21
Q

What are the three mechanisms of regulation for GFR and RBF?

A

Renal autoregulation (myogenic mechanism/ tuboglomerular feedback)

Neural control (SNS)

Hormonal control (RAAS)

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22
Q

How does myogenic mechanisms autoregulate GFR and RBF?

A

arterial smooth muscle rapidly responds to changes in BP

e.g
Increased afferent BP –> stretch receptors –> SMC contraction –> vasoconstriction –> decrease in GFR

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23
Q

Outline a tuboglomerular feedback mechansim in response to increased GFR.

A

Increased GFR –> increased [NaCl] and uptake –> increased ATP and adenosine –> vasoconstriction –> decreased GFR

24
Where is the autoregulatory range?
80-180mmHg
25
Constriction of which arteriole has the greatest effect on GFR?
Efferent Arteriole decreased RBF --> increased HpCap --> increased GFR due to smaller dianeter in basal state
26
What is the impact of a haemorrhage on RBF and GFR?
Decreased BV --> decreased BP --> SNS activation --> vasoconstriction --> decreased RBF and GFR
27
What is the impact of SNS activity on GFR and RBF?
Vasoconstriction of afferent (decreased GFR) and efferent (increased GFR) Arterioles Increased renin = increased Na absorption
28
What hormones impact regulation of GFR and RBF?
Epine and NE Endothelin ANG2 Adenosine Prostaglandins ANP/BNP
29
What are the 2 tramnsport pathways for renal reabsorption and secretion?
Transcellular (through cells) Paracellular (between cells) - passive
29
What is bulk flow?
Water and solutes from interstitial fluid --> peritubular capillaries
30
What is/are the primary and secondary transporters
pri Na/K ATPase Sec Na/Glucose symporter Na/AA symporter NaCl cotransporter Na/H+ exchnage (NHE)
30
How is water reabsorbed?
1. osmosis (passive reabsorption) 2. moves paracellularly through tight junctions towards higher solute concentration
31
What allows PCT to have a high reabsorption capacity?
Brush border (high SA) Carrier proteins Large number of mitochondria (Na/K/ATPase pump maintainence)
32
What features make the thin ascending/ descending limbs different?
poorly developed apical/ basolateral surfaces and few mitochondria
33
Why do all nephrotic cells contain single nomotile primary cilium?
they: Contain mechanosensory (V) and chemosensory ([solute]) Initiates Ca dependent signalling pathways
33
What substances does the PCT reabsorb?
Na+, K+, Cl-, Bicarbonate, Glucose, AAs, proteins Urea and water
34
What substances does the PCT secrete?
H+, K+, Ammonia Creatine, oxalate, uric acid Bile salts, diuretics PAH
35
Permeability of Thin Descending LoH
Highly permeable to Water Moderate for Na and urea
36
Permeability of Thin Ascending LoH
Impermeable to water Small amounts of NaCl in JM nephrons
37
Permeability of Thick Ascending LoH
impermeable to water Active RA of Na-2Cl H+ secretion
38
Permeability of CD and Distal Tubule
Early distal = same as TAL (impermeable to water) Late Distal and CD = ADH-dependant permeability Ca and Na reabsorption
39
Permeability of Collecting Duct
Na+ and bicarbonate Medullary part= urea Secretes H+
40
What is the function of the Glomerulotubular balance
Ensure constant fraction of filtered load is reabsorbed.
40
what hormones regulate tubular reabsorption?
Aldosterone ANG2 ADH ANP PTH
41
Aldosterone action
Increases Na reabsorption and K+ secretion Increases H+ secretion
42
Actions of ANG2
Acts on PCT, TAL and DT Increases Na reabs and H+ sec
43
Actions of ADH
increases Na reabs in TAL Increased water reabs in DCT and CD Increased urea reabs in medullary CD
44
Actions of ANP
Acts on entire nephron Decreases reabs of Na and increases Na sec
45
Actions of PTH
Acts on PCT, TAL and DCT Decreased PO4 and increased Ca reabs
46
What other factors help regulate tubular reabsorption
peritubular physical forces SNS (increases Na reabsorption) arterial pressure (pressure natriuresis) osmotic factors
47
what is the RBF and normal value?
Renal Blood Flow amount of blood through kidneys 1250mL/min
48
What is the RPF and normal value?
Renal plasma flow amount of plasma through kidnets 700mL/min
49
What factors govern GFR?
size of capillary bed permeability of cap hydrostatic and osmotic pressure gradients
50
what is the formula for determining GFR?
GFR= Kf x Net Filtration Rate
51
what is the effect of constriction on: a) afferent arterioles b) efferent arterioles
a) decreases PGC due to less arterial pressure = reduced GFR b) elevates pGC and increases GFR
52
what is the effect of dilation on: a) afferent arterioles b) efferent arterioles
a) increased PGC due to more arterial pressure = increased GFR b) decreased PGC = decreased GFR
53
Outline the Tubuloglomerular Feedback system.
increase in GFR --> elevates NaCl --> uptake of NaCl across macula densa cells --> increase in ATP and Adenosine --> ATP and Adenosine bind to smoothmuscle of afferent arteriole --> increase in intra Ca --> vasoconstriction --> retruns GFR to normal

HRM (9 decks)

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