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Physiology > Physiology of the Kidney > Flashcards

Physiology of the Kidney Flashcards

1
Q

The function of the kidney is to maintain…

A
  • Isovolemia
  • Isoionia
  • Isosmosis
  • Isohydria
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2
Q

How does the kidney control isohydria?

A

By elimination of H+ ions

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3
Q

List the functions of the kidney

A
  • Homeostasis
  • Conservation of essential substances
  • Acid-base balance
  • Cardiovascular regulation
  • Exogenous and endogenous component elimination
  • Hormone production
    • Direct
    • Indirect
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4
Q

List the anatomical features of the bovine kidney

A
  • No renal pelvis
  • Lobular surface
  • Pyramids lead to calyxes
  • Calyx leads directly to the ureter
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5
Q

The adipose tissue around the renal sinus functions as a…

A

Shock-absorber

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6
Q

What is the functional unit of the kidney?

A

The nephron

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7
Q

Give the elements of the nephron

A
  • Malpighi body
  • Tubular system
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8
Q

How many nephrons are found in each kidney?

A

1,000,000

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9
Q

What are the 4 basic functions of the nephron?

A
  • Filtration
  • Reabsorption
  • Secretion
  • Excretion
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10
Q

What % of cardiac output does the kidney receive?

A

20-25%

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11
Q

What % of plasma is filtered into the renal tubules?

A

20%

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12
Q

What is the renal filtration rate? excl. bovine

A
  • 125 ml/min
  • 180 l/day
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13
Q

What is the urinary output rate?

A

1.5 l/day

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14
Q

Why is the renal filtration rate higher than the urinary output rate?

A

Fluid is reabsorbed from the tubules

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15
Q

What isn’t filtered by the kidney?

A

Protein

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16
Q

What is the bovine renal filtration rate?

A

486 l/day

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17
Q

List the sections of the tubulary system

A
  • Proximal tubule
  • Henle loop
  • Distal tubule
  • Collecting tubule
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18
Q

Sections of the proximal tubule

A
  • Proximal convoluted tubule
  • Proximal straight tubule
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19
Q

Sections of the Henle loop

A
  • Descending thin limb
  • Ascending thin limb
  • Thick ascending limb
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20
Q

Sections of the distal tubule

A
  • Distal convoluted tubule
  • Distal connective tubule
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21
Q

Sections of the collecting duct

A
  • Cortical collecting duct
  • Medullary collecting duct
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22
Q
A

Proximal convoluted tubule (PCT)

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23
Q
A

Proximal Straight Tubule (PST)

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24
Q
A

Descending Thin Limb (DTL)

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25
Q
A

Distal connective tubule (CNT)

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26
Q
A

Distal convoluted tubule (DCT)

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27
Q
A

Thick ascending limb (TAL)

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28
Q
A

Ascending thin limb (ATL)

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29
Q
A

Cortical collecting duct (CCD)

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30
Q
A

Medullary collecting duct (MCD)

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31
Q

What % of nephrons are juxtamedullary?

A

15%

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32
Q

What % of nephrons are cortical?

A

85%

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33
Q

Urine is formed as a result of which processes?

A
  • Simple filtration
  • Selective/Passive reabsorption
  • Excretion
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34
Q

The layers of the filtration barrier

A
  • Fenestrated endothelium
  • Glomerular basement membrane (GBM )
  • Slit diaphragms
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35
Q

The filtration barrier selectively restricts passage to molecules of certain…

A
  • Size
  • Shape
  • Charge
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36
Q

What is the relative difference in filtration dependent on the charge

A

negative < neutral < positive

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37
Q

List the molecular components of the GBM

A
  • Collagen
  • Laminin
  • Nidogen
  • Proteoglycans
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38
Q

How are the molecular components of GBM arranged?

A
  • Collagen and Laminin form two independent networks
  • Nidogen links these networks
  • Adhesion of collagen and laminin to podocytes and endothelial cells
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39
Q
A

Collagen

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40
Q
A

Laminin

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41
Q
A

Proteoglycan: Anionic filtration barrier

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42
Q
A

Nidogen

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43
Q
A

Adhesion to podocytes

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44
Q
A

Adhesion to endothelial cells

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45
Q

The GBM acts as a barrier to…

A

Large plasma proteins

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46
Q
A
  • Pedicules of the podocytes
  • Contains slit diaphragm
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47
Q

The slit diaphragm has a … structure

A

Zipper-like

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48
Q

The pores of the slit diaphragm are slightly smaller than…

A

Albumin

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49
Q

Where is the slit diaphragm located?

A

Between the foot processes of the podocytes

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50
Q

What indicates that the slit diaphragm is partially elastic?

A

Slit area can increase with increased intraglomerular pressure

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51
Q

Monoclonal antibodies have been used against

A

Glomerular proteins

(Exclusive to the slit diaphragm)

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52
Q

Glomerular proteins were identified with which model?

A

Congenital Nephrotic Syndrome (NPHS1) model

Leading to heavy proteinuria

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53
Q

Symptoms of massive proteinuria

A
  • Persistent oedema
  • Recurrent infections
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54
Q

By in situ hybridisation, NPHS1 gene product (protein) was shown in the kidney to be expressed specifically in…

A

Podocytes

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55
Q

NPHS1 gene codes to produce which protein?

A

Nephrin

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56
Q

Nephrin is a variety of…

A

Immunoglobulin

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57
Q

List the extracellular structural features of nephrin

A
  • 8 x Ig-like modules (C2)
  • 1 x Fibronectin (type-3-like) module
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58
Q

The type C2 Ig-like modules are usually found in proteins participating in…

A

Cell-cell interactions

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59
Q

Which significant feature(s) can be found in the intracellular region of nephrin?

A

9 x tyrosine residues

Used for ligand binding

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60
Q

Location of the C- and N-terminus of nephrin

A

C-terminus: Intracellularly

N-terminus: Extracellularly

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61
Q

Capillaries which are under high pressure for filtering

A

Non-real capillaries

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62
Q

Capillaries found around the tubule at low pressure

A

Real capillaries

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63
Q
A

Glomerulus

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64
Q
A

Peritubular capillary

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65
Q
A

Cortical nephron

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66
Q
A

Juxta Medullary Nephron

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67
Q
A

Peritubular capillary

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68
Q
A

Vas aferent

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69
Q
A

Vas efferent

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70
Q
A

Venules, v. renalis

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71
Q
A

Vasa Recta

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72
Q

The function of Vasa Recta

A
  • Enters renal medulla
  • Henle’s loop
    • Countercurrent exchange
    • Concentration of urine
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73
Q

Length of Vasa Recta

A

40mm

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74
Q

Sympathetic innervation of the kidney

A
  • Runs to α-adrenergic receptors (on v. afferent)
    • Leads to vasoconstriction of the afferent arteriole
    • GFR reduced
  • Rest: minimum AP
  • Physical activity: Intensive AP
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75
Q

Parasympathetic innervation of the kidney

A

Cholinergic-mediated reaction

(Function not understood)

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76
Q

The function of pain-sensing fibres in the capsule

A

Sense of capsule stretching

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77
Q

The oldest examination method of renal function

A

Analysis of urine and plasma

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78
Q

List the methods of kidney examination

A
  • Tubule puncture
  • Clearance technique
  • X-ray
  • Scinthgraphy
  • Ultrasound
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79
Q

Tubule puncture

A

Examination of the fluid composition

(Kidney structure is too fine to examine histologically)

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80
Q

Steps of the micropuncture method

A
  • Using a fine glass capillary
  • Retrieval of samples from different sections of the tubules
  • Examination of samples under a microscope
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81
Q

Steps of Scintigraphy

A
  • Labelled substance (isotope) administered intravenously
  • Isotope appears in the kidney, reaching a maximum conc.
  • This is detected with a detector on the body surface
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82
Q

Ultrasound examination of the kidney can be used to show

A
  • Anatomical details
  • Blood supply
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83
Q

Steps of the clearance method for kidney function

A
  • Measures volume of plasma which all test substances have been removed from
  • Shows the ability of the kidney to remove substances from the blood plasma
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84
Q

The equation to calculate clearance

A

(U x V)/P = Clearance ml/min

  • U= Conc. in urine*
  • P= Conc. in plasma*
  • V= Produced urine (per minute)*
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85
Q

What are the varieties of renal clearances?

A
  • Glucose
  • Inulin
  • PAH
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86
Q

If 250 ml plasma passes into the kidney, and the flow rate is 125 ml/min…

A

125ml/min couldn’t be filtered

Therefore: Clearance = 125 ml/min

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87
Q

Clearance is independent to…

A

Plasma concentration

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88
Q

Unit for substances excreted by the clearance method

A

ml/min

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89
Q

As well as the clearance value, clearance of substances can be used to determine…

A
  • Functional standards of the kidney
  • Quantitative values of functional disorders
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90
Q

Clearance of certain selected substances which are not reabsorbed nor secreted is equal to…

A

Glomerular filtration rate (GFR)

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91
Q

Clearance of certain selected substances which are entirely secreted is equal to…

A

Renal plasma flow (RPF)

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92
Q

If (a substance’s clearance value) Cx > Cinulin

A

Secretion

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93
Q

If (a substance’s clearance value) Cx < Cinulin

A

Reabsorption

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94
Q

What is the clearance value of glucose?

A

0 ml/min

(Totally reabsorbed)

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95
Q

Clearance of para-amino-hippuric acid (PAH) is….

A

Constant at low plasma concentration

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96
Q

At high concentrations of PAH…

A

The secretory capacity of renal tubules decreases

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97
Q

The point where excretion doesn’t grow with secretion

A

Transport maximum

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98
Q

Name a substance which is only filtered

(Not reabsorbed/secreted)

A

Inulin

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99
Q

The conc. of inulin in the plasma doesn’t influence…

A

Inulin’s clearance

Even under extremely high values

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100
Q

Describe the path of urea in the kidney

A
  • Freely filtered
  • Passively moves along tubules
  • A portion remains in the interstitium
  • Clearance of urea is always smaller than that of inulin
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101
Q

Transport of urea during tubular cell diseases

A
  • Urea recirculation damaged
  • Urea conc. increases in blood
  • Uraemia
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102
Q

Describe the path of glucose in the kidney

A
  • Filtered freely
  • Doesn’t reach descending limb of Henle’s loop
  • Entirely reabsorbed in the proximal tubule
  • Normally: clearance of glucose is 0
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103
Q

Describe the effect of diabetes on the kidney

A
  • Glucose plasma so high
  • Tubular cells unable to reabsorb it
  • Transfer maximum (Tmgluclose) is therefore reached
  • Glucose appears in the urine
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104
Q
A

TmPAH

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105
Q
A

Cinulin

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106
Q
A

Curea

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107
Q
A

Cglucose

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108
Q
A

Tmglucose

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109
Q

Which processes are occurring?

A

Filtration + Resorption

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110
Q

Which processes are occurring?

A

Filtration + Redfiffusion

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111
Q

Which processes are occurring?

A

Filtration only

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112
Q
A

Filtration + Secretion

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113
Q

The formula to calculate extraction

A

E = (Pa - Pv)/Pa

  • Pa = arterial conc. of substance*
  • Pv = venous concrentration of substance*
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114
Q

Extraction

A

​The ability of the kidney to eliminate a substance from the organism

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115
Q

In extraction, the value of ‘E’ is where no substance reaches the venous side

A

E=1

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116
Q

In extraction, the value of ‘E’ is where no substance reaches the urine

A

E=0

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117
Q

Clearance/Extraction=

A

RPF

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118
Q

What can be used to determine the RPF

A

Clearance of a substance that is:

  • Filtered
  • Excreted

So that none remains in the outgoing renal vein

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119
Q

A substance which is filtered and secreted…

A

PAH

Completely cleared (E=1)

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120
Q

Clearance of PAH =

A

RPF

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121
Q

Give the distributions of blood flow in the tissue layers of the kidney

A
  • Cortex = 90%
  • Outer medulla = 8-9%
  • Inner medulla = 1-2%
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122
Q

GFR

A

Glomerular filtration rate

Amount of filtrate produced per unit time

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123
Q

Constant GFR is maintained at an arterial pressure of…

A

under 80-250mmHg

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124
Q

GFR can be measured by…

A

Inulin and Creatine

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125
Q

Average GFR value

A

120 ml/min

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126
Q

Filtered load/Filtered capacity

A

Mass of substance that is ultrafiltered per unit time

mg/min

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127
Q

If a non-reabsorbing, non-secreting substance is used, it’s GFR value =

A

Clearance value

GFR = (UxV)/P

Substance such as Inulin

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128
Q

Cinulin values amongst the species

A
  • Human = 120
  • Cow = 75
  • Pig = 70
  • Horse = 60
  • Dog = 50
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129
Q

Creatinine

A

Physiological by-product of muscle metabolism

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130
Q

If Cinulin = Ccreatinine

GFR = …

A

Ccreatinine

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131
Q

Which is normally higher:

  • Cinulin
  • Ccreat.
A

Ccreat.

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132
Q

Effect on GFR by: Changes in RBF

A

No substantial influence

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133
Q

Effect on GFR by: Glomerular pressure (GP)

A

Change in GFR similar to GP change

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134
Q

Effect on GFR by: Capsular pressure (CP) increase

A

Reduce GFR

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135
Q

Effect on GFR by: Increase of Glomerular colloid osmotic pressure (GCP)

A

Decrease of GFR

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136
Q

Effect on GFR by: Glomerular membrane permeability

A

Decrease GFR

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137
Q

Effect on GFR by: Reduced total filtration surface (nephrectomy)

A

Decreased GFR

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138
Q
A

Capillary wall

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139
Q
A

Capillary fenestrations

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140
Q
A

Basement membrane

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141
Q
142
Q
A

Glomerular filtrate

143
Q
A

Outer wall of Bowman’s capsule

144
Q

Free filtration occurs at…

145
Q
A

Glomerular (Bowman’s) capsule

146
Q
A

Glomerular ultrafiltrate

147
Q
148
Q
149
Q
150
Q

Value of glomerular blood pressure

A

55-60 mmHg

151
Q

GCP value

152
Q

Capsular pressure value

A

15-20 mmHg

153
Q

Filtration fraction =

154
Q

Ultrafiltration is maintained by…

A

Filtration pressures

155
Q

Transfer maximum (Tm)

A

The upper limit of reabsorption

156
Q

Tmglucose=

A

350 mg/min

157
Q

Glucosuria

A

If the filtered load/Tmglucose is > 350mg/min

158
Q

Tmax

A

Maximum transport

159
Q
A

Normal filtered load range

160
Q
162
Q
A

Glucose loss: Excretion

163
Q
A

Reabsorption

164
Q

Which medical cases can glucose appear in urine?

A
  • Diabetes mellitus
  • Pregnancy
165
Q

Secretion maximum

A

The point where above a certain plasma conc., secretion becomes constant

(all secreting nephrons reach their maximum)

166
Q

Excretion =

A

Filtration + Secretion

167
Q

3 Phases of excretion

A
  • Linear phase
  • SDL phase
  • Saturation phase
168
Q
169
Q
170
Q
A

Filtration

171
Q
A

Linear phase

172
Q
A

SDL phase

Self-depression limit phase

173
Q
A

Saturation phase

174
Q

Self-depression limit (SDL) phase

A
  • Cells become unable to secrete
  • Secretion capacity is reached
  • Excretion decreases
175
Q

Saturation phase

A
  • Curve is parallel with filtration
  • No more secretion
  • Excretion depends on filtration
176
Q

Neural regulation of renal circulation

A
  • Cortical vessels innervated by sympathetic nerves
  • No sympathetic innervation to the medulla
177
Q

Cortical vessels take part in which processes?

A
  • Pressor reflex
  • Redistribution of blood
178
Q

Pressor reflex of the kidney

A
  1. Decrease of blood pressure
  2. Depressor centre activity decreases
  3. Pressor activity increased
  4. Periperal vasoconstriction
  5. Renal ischemia
179
Q

Redistribution of blood in the kidney

A

Increased sympathetic tonicity

  1. Increased muscular activity/shock/pain
  2. Renal ischaemia
  3. Redistribution of blood
180
Q

Is innervation of renal circulation essential?

181
Q
A

Juxtaglomerular apparatus

(JGA)

182
Q
A

Bowman capsule

183
Q
A
  • Afferent arteriole
  • Glomerulus
  • Efferent arteriole
184
Q
A

Mesangial Cells

185
Q
A

Macula densa cells

186
Q
A

Epithelial cells of the distal tubule

187
Q
A

Juxtaglomerular cells

188
Q

JGA is made up of…

A
  • Macula densa
  • Mesangial cell
  • Swollen smooth muscle
      • myoepithelial of vas. aff/eff
189
Q

Function of JGA

A
  • Renin production
  • A sensor of salt + water metabolism
  • Baroreceptor
  • Hormone production
    • Angiotensin-II
190
Q

Where is renin used?

A

In the renin-angiotensin system

191
Q

The theories of JGA level regulation of renin secretion

A
  • Baroreceptor threory
  • Macula densa theory
192
Q

Baroreceptor theory of renin secretion

A
  • Triggered by EC hypovolemia
  • Vas. aff pressure decrease
  • Transmural pressure decrease
  • Arterial smooth muscle relax
  • JGA-__baro__-R stimulated
  • Renin secretion
193
Q

Macula densa theory of renin secretion

A
  • Triggered by reduced Na-content of distal tubule
  • Stimulation of macula densa cells
  • Stimulation of myoepithelium of juxtaglomerular cells
  • Renin secretion
194
Q

RAS

A

Renin-angiotensin system

195
Q

Effects of RAS on angiotensin II

A
  • Pressor effect
  • Salt retention
    • Direct
    • Indirect
  • Nervous system effect
196
Q

The nervous system effect of RAS on angiotensin II

A
  • Increase arterial pressure
  • Dipsogenic effect
  • Increase catecholamine synthesis
    • Increased intrarenal vasoconstriction
  • ADH stimulation
197
Q

Effect of RAS on angiotensin III

A
  • Pressor effect 50% lower than Angiotensin II
  • Stimulation of aldosterone secretion is equivalent to Angiotensin II
198
Q
199
Q
A

Angiotensinogen

200
Q
A

Angiotensin-I

201
Q
A

Angiotensin-converting enzyme

Found mainly in the lungs

202
Q
A

Angiotensin-II

203
Q
A
  • ADH Stimulation
  • Salt appetite
  • Thirst
  • GFR, RFB decrease
204
Q
A
  • Aldosterone production
  • Vasoconstriction
205
Q
A

Increased salt + water intake

206
Q
A

Increased salt + water conservation

207
Q
A

Hypovolemia counterregulated

208
Q

Effect of Ag-II on salt + water reabsorption

209
Q

Effect of Ag-II on salt + water intake

A

Stimulates intake

210
Q

Title the figure

A

Renin-angiotensin system

211
Q

Pressor effects of angiotensin-II

A

Increase of BP

212
Q

Effects of angiotensin-II on direct salt retention

A
  • Increase of Na+/ H+ exchange
  • Increase HCO3- reabsorption in the proximal tubule
213
Q

Effects of angiotensin-II on indirect salt retention

A
  • Vas efferent constriction
  • GFR + RPF diminishes
  • RPF redistribution to the cortex
  • Urine formation decrease
214
Q

CNS effects of angiotensin-II

A
  • Pressor centre stimulation
  • Dipsogenic effect → Increased water intake
  • Sympathetic stimulation
  • Increased ADH release
215
Q

Prostaglandins

A
  • Synthesised in the kidney
  • Strong vasodilator
    • ​​Effects v. aff + v. eff
216
Q

Effect of the kallikrein-kinin system

A
  • Stimulates hepatic kininogen
  • Causing bradykinin production (Vasodilator)
217
Q

Constancy of RPF and GFR are maintained by…

A

Adaptive contraction of the afferent arteriole

218
Q

In canines, increase and decrease of GFR plays a role in the increase/decrease of…

A

Sodium excretion

219
Q

Autoregulation to BP rise of RPF and GFR

A

Bayliss-effect

220
Q

Autoregulation to BP fall of RPF and GFR

A
  • Afferent arteriole: Vasodilation
  • Efferent arteriole: Vasoconstriction
221
Q

Tubuloglomerular feedback

A
  • Macula densa of juxtaglomerular apparatus senses volume change
  • Secretes signals to adjust GFR
222
Q

Title the figure

A

GFR autoregulation

223
Q

Steps of: V.afferent vasodilator feedback

Tubuloglomerular feedback

A
  1. GFR Decrease
  2. Fluid flow Decrease
  3. Na/Cl reabsorption Increase
  4. Macula Densa Activated
  5. V. afferent dilation
  6. RBF Increase
  7. GP Increase
  8. GFR returns to normal
224
Q

Steps of: V. efferent vasoconstrictor feedback

Tubuloglomerular feedback

A
  1. GFR Decrease
  2. Na/Cl reabsorption Increase
  3. Tubular Na+ Decrease
  4. Macula densa Activated
  5. RAS activated
  6. Angiotensin II produced
  7. V. efferent constrictor release
  8. GP Increase
  9. GFR returns to normal
225
Q

Supplementary mechanism

Autoregulation at increased blood pressure

A
  • BP increase
  • Kidney vessel resistance Increase
  • Vasoconstriction
  • No change in RBF

Bayliss-effect

226
Q

Which vessels does kidney autoregulation not protect?

A

Medullary vessels

227
Q

Title the figure

A

Autoregulation of renal circulation

228
Q
A

Adaption range

229
Q

What % of the filtered material is reabsorbed into the proximal tubule?

230
Q

Describe Na+ transport at the proximal tubule

A
  • Na+/K+ ATPase pump
  • Cell → interstitium
  • The decrease of Na+ draws more Na + into the cell
  • Excess IC K+ leaves the K+ channel
231
Q

Describe Na+-related transport of H+ at the proximal tubule

A
  • Na+ entry into the cell via Secondary active transport
  • H+ secretion
  • Ensures the removal of metabolic hydrogen
232
Q

Describe HCO3- transport at the proximal tubule, in the lumen

A
  • Cell is impermeable to HCO3 -
  • HCO3 - + H+ forms carbonic acid
  • H2CO3 → H2O + CO2
  • Catalysed by carbonic anhydrase
  • CO2 can diffuse through the cell membrane
233
Q

Describe HCO3- transport at the proximal tubule, in the tubulary cells

A
  • CO2 → H+ + HCO3-
  • Catalysed by carbonic anhydrase
  • H+ reaches lumen via secondary active transport
  • HCO3- + Na+ ion → Interstitium
  • Via Na/3HCO3- cotransporter
  • (Indirect HCO3- transport)
234
Q

Effect of HCO3- reabsorption inhibition

A

High loss of Na+ and water

(Diuresis = Increased urine formation)

235
Q

Describe Cl- transport at the proximal tubule

A
  • Prerequisite: pHlumen < pHcell
  • Cl--acidic anion antiporter:
    • Cl- → Cell
    • Acid ion → Lumen
  • Acidic ion binds H+ → Free acid
  • Free acid → Cell: Dissociation
  • Transport from cell to interstitium:
    • Cl- channel
    • K+/Cl- cotransporter
    • HCO3- reabsorption increased Cl- gradient
236
Q

Describe the H2O transport at the proximal tubule

A
  • Movement by increased peritubular oncotic pressure
  • From Lumen → Interstitium
  • Water transport by: Aquaporin-1 (AQP-1)
237
Q

Which 3 compounds are 100% withdrawn from the proximal tubule

A
  • Glucose
  • Amino acids
  • Na+
238
Q

How much urea is passively reabsorbed through the cell and paracellular pathways

A

Approximately half

239
Q

The permeability of the descending limb of Henle’s loop

A

High permeability

240
Q

% of substance reabsorbed in the ascending thick limb of Henle’s loop (TAL)

241
Q

Describe transport processes in the thick ascending limb of the Henle’s loop (TAL)

A
  • Furosemide sensitive Na+/K+/2Cl- synporter
  • Na+/K+/2Cl- → Cell
  • Utilises energy from basolateral Na+/K+-ATPase pump
  • Electroneutral transport
  • TAL is impermeable for H2O + Urea
  • K+ + Cl- passively leaves cell → Interstitium
  • Na+ eliminated by ATPase pump
242
Q

Describe transport processes in the distal convoluted tubule

A
  • Na+/Cl- symport protein reabsorb additional 5% of filtrate at luminal side
  • Na+/K+ ATPase pump:
    • Reabsorbed Na+ → Interstitium
  • K+/Cl- cotransporter:
    • Cl- → Interstitium
  • Ca2+ transport begins
243
Q

Describe transport processes in the:

  • Distal connective tubule
  • Collecting tubule
A
  • Permeability depends on hormonal effects
  • Hormonally regulated urine formed here
  • CNT + CCT → Mineralocorticoid dependent Na+ reabsorption
  • CCT → ADH-dependent water reabsorption
  • MCT →
    • ADH-dependent water reabsorption
    • ANP dependent Na+ excretion
  • Intercalar cells:
    • Regulation of acid/base K+ balance
244
Q

Aldosterone controls…

A
  • In distal + collecting tubules
    • K+ excretion + reabsorption
    • Na+ reaborption
245
Q

Principal and intercalar cells are found in…

A
  • Distal connective tubule
  • Collecting tubule
246
Q

Role of principal cells

A
  • Secretion of K+
    • Regulated by mineralocorticoids
  • Regulate water reabsorption
    • By expressing AQP-2
      • As a result of ADH
247
Q

Role of intercalar cells

A
  • Maintenance of acid/base balance
    • Secreting H+
    • Forwarding of HCO3-
248
Q

How does HCO3- in the kidney relate to acidosis?

A
  • HCO3- changes place with Cl- (via antiporter)
    • HCO3- forwarded onto the blood
    • Acidic component forwarded onto the lumen
  • Works as an effective defence against acidosis
  • The reverse is observed in alkalosis
249
Q

H+ of cell water is forwarded to the lumen via…

A

Electrogenic luminal H+ pump (ATPase)

250
Q

Water transport on the CNT and CCT or MCT sections is regulated by…

251
Q

AQP-2 is bound to…

A

Microsomes inside the principal cells

252
Q

Distal connected tubule + collecting duct:

  • In the presence of ADH, AQP-2 migrate…
A

To the luminal pole

Facilitates water movement according to osmotic conditions

253
Q

Name the process

A

ADH-mediated H2O transport

254
Q

Intercalar cell function during alkalosis

A
  • HCO3- release into the lumen
  • H+ release into the interstitium
255
Q

Describe ammonia transport relating to acid/base balance in the proximal tubule

A
  • Goal: R_emove metabolically formed hydrogen ions_
  • NH3 binds to H+ → NH4+
  • Excreted as salt:
    • Ammonium phosphate
    • Ammonium sulphate
  • pH of urine doesn’t fall to an extremely low value
256
Q

Describe the cycle of ammonia/ammonium

A
  • In thick ascending limb (TAL)
  • NH4+ taken up by cells by K+/NH4+ exchange
  • NH4+ cannot leave on the luminal side (impermeable)
  • NH4+ → interstitium → descending limb (countercurrent multiplier)
  • Medullary NH4+ increase
  • Active uptake of NH4+ by collecting tubule cells
257
Q

ADH is secreted by the…

A

Neurohypophysis

258
Q

List the triggers increasing ADH secretion

A
  • Hyperosmosis of plasma → Osmoreceptors
  • Stress
  • Pain
259
Q

List the triggers decreasing ADH secretion

A
  • Baroreceptors → BP increase
  • Stress, volume receptors
  • ANP production → Central + atrial
260
Q

Effects of ADH secretion

A
  • AQP-2 expression →​ Water retention
    • Extrarenal
    • Renal
      • DCT
      • Collecting duct
  • Vessel contraction (If bleeding)
  • Corticoid production increase
261
Q

ANP

A

Atrial natriuretic peptide

262
Q

List the triggers increasing ANP secretion

A
  • Atrial stretch → pre-pro-ANP
  • Salt load
  • Fluid load
263
Q

Give the effect of ANP secretion

A
  • Na+ excretion increase
    • cGMP production increase
    • Na+/H+ exchange decrease
264
Q

Stimuli of aldosterone

A
  • Hyperkalemia (Plasma [K+] increase)
  • BP fall
  • Hypophysis: ACTH
265
Q

Describe aldosterone secretion stimulated by hyperkalaemia

A
  • Triggered by K+ increase in the blood
  • Measured by z. glomerulosa cells
  • Aldosterone considered to be the single regulator of K+ excretion
266
Q

Hormones affecting the kidney

A
  • Parathormone
  • Calcitonin
  • Glucocorticoids
267
Q

Hormones produced in the kidney

A
  • 1,25-OH-D3 hormone
  • Erythropoietin
  • Prostaglandin
268
Q

Sources of water intake

A
  • Fluid consumption
  • Intermediary metabolism
  • Food
269
Q

Fluid intake by direct fluid consumption

270
Q

Fluid intake by the intermediary metabolism

271
Q

Sources of water output

A
  • Sweat
  • Lungs
  • Urine
  • Faeces
  • Milk/saliva
272
Q

Fluid output by sweat

A

0.35 l/day

273
Q

Fluid output by lungs

A

0.35 l/day

274
Q

Fluid output by urine

275
Q

Fluid output by faeces

276
Q

Osmotic load results in…

A
  • Blocking of tubular H2O reabsorption
  • Leads to osmotic diuresis
277
Q

Hydropenia leads to…

A

Low volume production of hyperosmotic urine

278
Q

Hydration leads to…

A

High volume production of hypoosmotic urine

279
Q

Fast restoration of isosmotic conditions is usually carried out at the expense of…

A

The shift of isovolaemia

280
Q

Hyperosmosis can be created artificially or physiologically by…

A
  • A substance that cannot be reabsorbed
    • Mannit
    • Glucose
  • A substance that can be reabsorbed after filtration
    • Sodium
281
Q

What occurs after hyperosmosis

A
  • Hypothalamic osmoreceptors (_nucl_.* *supraopticus**) stimulated
  • ADH release → Water retention
282
Q

Non-reabsorbing substances cause…

A

Osmotic diuresis

Osmotically active substance → removes water from the body

Compensated for by water uptake (e.g diabetes)

283
Q

Because animals take up water periodically…

A
  • Volume + urine osmolality change in a wide range
  • 2-5ml/kg bwt/kg - 200-229ml/kg bwt/kg
  • 1400 mosmol/l - 50 mosmol/l
284
Q

Osmotic layering

A
  • Rapid changing of the quantity + osmolarity of the urine
  • Low energy requirement
  • High capacity
285
Q

Which mechanisms are responsible for the creation and maintenance of osmotic layering?

A
  • Countercurrent multiplier mechanism
  • Countercurrent exchanger mechanism
286
Q

The osmotic concentration of the interstitium is…

287
Q

Why don’t deep medullary cells shrink?

A
  • The IC space is full of ‘inert’ osmoliths
  • No metabolysis
288
Q

Calculate osmotic clearance

A

Cosm = Uosm x V/Posm

289
Q

What are these characteristic of:

  • Uosm = Posm
  • CH2=0
A

Isosmotic urine

290
Q

What are these characteristic of:

  • Uosm > Posm
  • CH2 = Negative
A

Hyperosmotic urine

291
Q

What are these characteristic of:

  • Uosm < Posm
  • CH2 = Positive
A

Hyposmotic urine

292
Q

Osmotic plateau =

293
Q

Osmotic plateau values for:

  • Human
  • Dog
  • Desert animals
A
  • Human = 4
  • Dog = 5-6
  • Desert animals = 20
294
Q

Concentrating capacity is proportional to…

A

The number of Juxtamedullary glomeruli

295
Q

Interstitial hyperosmosis is maintained by…

296
Q

Urinary hyperosmosis is maintained by

297
Q

Creation and maintenance of increasing osmolality is driven by…

A
  • Na-pump
  • Repetitive reabsorption of Na+ of the TAL
  • Recirculation of urea
298
Q

Increasing osmolality results in…

A

Interstitial hyperosmosis

(creates a suction force)

299
Q

Describe the process of the countercurrent multiplier

A
  • Na+ pump increases interstitial osmolality
  • H2O: descending limb → interstitium
  • Urea/Na+ cannot follow the same path
300
Q

What is responsible for the maintenance of osmotic layering?

A

Countercurrent exchanger

301
Q

What is the function of a countercurrent mechanism?

A
  • Maintains the status quo
  • Doesn’t create temperature differences between
302
Q

The countercurrent exchanger in the kidney

A

Vasa recta

303
Q

Roles of Vasa recta

A
  • Slow blood flow
  • Fluid + solute exchange between 2 arms
  • Diffusion equilibrium between interstitium + blood
  • Isoosmotic blood leaves interstitium
304
Q

The osmotic gradient of the interstitium affects…

A
  • Lumen osmolality
  • Quantity of urine
  • Composition of urine
305
Q

Which changes may occur when osmotic conc. of interstitium is different to the tubular liquid?

A
  • Salt leaves the tubule
  • Salt enters the tubule
  • Water leaves the tubule
  • Water enters the tubule
  • Combination of the above
306
Q

The maximum deviation from isosmosis can only be…

307
Q

Role of ADH

A

Maintain Isosmosis

308
Q

Damage to hypothalamus ADH secreting locus results in…

A

Hyposmotic urine (Diabetes)

309
Q

Increased diuresis following extra H2O load can be blocked by…

310
Q

Hydropenia results in…

A

Blood ADH increase

311
Q

ADH level of action

A

Connecting part of Distal tubule + Collecting duct

312
Q

Summarise ADH mechanism of action

A
  • ADH receptor → cAMP release
  • AP-2 → H2O
  • AP-1 → H2O reabsorbed
313
Q

Mechanism of dehydration on ADH release

A
  • Dehydration → [Salt] in blood increases
  • Osmotic pressure increase
  • Receptors in hypothalamus detect this
  • ADH release
  • Thirst centre in hypothalamus also responds
314
Q

Describe Verney’s experiment

A
  • Dog drinking → diuresis occurs
  • ADH/NaCl applied → diuresis stops
  • The electrical stimulus of n**ucl. supraopticus → diuresis stops
315
Q

Central regulation of ADH secretion

A

Via CNS

  • AV3V of the third ventricle stimulated
  • ADH secretion
  • Thirst
316
Q

Summarise the reaction to hyperosmosis

A
  • EC + IC balance → Hyperosmotic isovolemia
  • Hypothalamus: Osmoreceptor activity increase
  • ADH in blood increase
  • Distal tubule: AP-2 expression increase
  • Free water clearance decrease, water retention
  • Isosmotic hypervolemia
317
Q

Summarise the reaction to hyposmosis

A
  1. ADH inhibition
  2. No H2O retention
  3. Hypovolemic isosmosis
318
Q

The thirst centre is composed of…

A
  • Anteroventral wall of the 3rd ventricle
  • Anterolateral part of the preoptic hypothalamus
  • AV3V region of 3rd Ventricle
319
Q

Excitation of the thirst centre is triggered by…

A

Extreme water intake

320
Q

Basic stimuli for exciting thirst

A
  • IC-dehydration
  • Losing blood
  • Food intake
  • Angiotensin-II
321
Q

Temporary relief of thirst

A
  • Stops unnecessary drinking
  • Water → Oesophagus/stomach
    • Relieves thirst for 30 mins
322
Q

Body process with excess salt intake

A
  • 1-2 days
  • Verney-mechanism activated
  • Extra salt and water stay in the EC space
  • EC space is extended → hypervolemia
323
Q

Body process with excess water intake

A
  • Volume increase → BP increase
  • Baroreceptors stimulated → Peripheral vasodilation + oncotic pressure decrease
  • Fluid leaves circulation → Interstitium
324
Q

ANP secreted from

A

Cardiac Atrium

325
Q

The function of ANP release

A

Increase Na+​ excretion

by inhibiting Na+ reabsorption

326
Q

Volume receptors

A
  • Stretch receptors
  • Centre of volume regulation
  • Around diencephalon
327
Q

Pressure diuresis

A
  • BP increase → Diuresis increase
328
Q

Summarise the reaction to hypovolemia

A
  • RAS inhibition
  • ANP stimulation
    • Na+ excretion
    • RAS + ADH inhibition
  • Isovolemia
329
Q

Smooth muscles of the bladder

A
  • Exhibit reflex relaxation
  • Plasticity → Allows uptake of large volumes
  • Filling → Sympathetic differentiation of bladder
    • Bladder loosened, sphincter contracted
  • Urination → Parasympathetic dominance
    • Bladder contracted, sphincter dilates
330
Q

What forwards urine to the renal pelvis?

A

Contraction of the calix

331
Q

Lower urinary tract components

A
  • Urinary bladder
  • Urethra
332
Q

How is urination induced?

A

Filling of bladder → Increase of mechanoreceptor activity

333
Q
A

Maximal stretch and mechanoreceptor activity

334
Q
A

Stimulus of urination

335
Q
A

Reflex-relaxation

336
Q
337
Q

Which motor systems control urination?

A
  • Lumbar → Sympathetic
  • Sacral → Parasympathetic
  • Somatic → M. abd., perineum, outer sphincter
338
Q

Describe bladder filling

A
  • Parasympathetic activity inhibited by sympathetic activity
  • Sympathetic Tone
    • → M. detrusor relaxes
    • → Contracts smooth muscle of bladder neck
  • Outer urethral muscles contract (n. pudendus**)
339
Q

Sympathetic Tone contracts the smooth muscles of the bladder neck via the…

A

Alpha1 receptors

340
Q

Describe urination

A
  • Increased mechanoreceptor activity → Pons
  • Increased parasympathetic activation
    • Inhibits somatic and sympathetic activity
  • Bladder wall contracts, sphincters relax
341
Q

Because the pons is connected to the cortex and hypothalamus…

A

Animals can be trained to retain urine

342
Q

Average urine production (l/day/bodyweight) for:

  • Cattle
  • Horse
  • Swine
  • Dog
  • Cat
A
  • Cattle: 9
  • Horse: 5.5
  • Swine: 2.5
  • Dog: 1.2
  • Cat: 0.1
343
Q

The average speed of urine formation (ml/min/100kg) for:

  • Cattle
  • Horse
  • Swine
  • Dog
  • Cat
A
  • Cattle: 1 - 3
  • Horse: 0.2 - 1.3
  • Swine: 0.5 - 2.2
  • Dog: 0.4 - 1.2
  • Cat: 0.7 - 1.4
344
Q

Maximum urinary osmolarity of birds

A

500-600 mosmol/l

345
Q

Why is avian osmolarity so low?

A

Urea is almost absent in the medullary interstitium

346
Q

Some avian nephrons lack…

A

Henle’s loop

(reptilian-type nephron)

347
Q

Birds have a urinary bladder: true or false?

348
Q

Salt and water content of avian urine is adjusted by…

A

Cloaca and Large intestine

349
Q

Apart from urination, salt can be excreted by…

A
  • Salt glands
  • Secreted nasaly
350
Q

Secreted fluid from seagull salt glands can reach an osmolarity of…

A
  • 800-1000 mosmol/l

Physiology (18 decks)

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