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11. Urinary > 3. Filtration by the Glomerulus > Flashcards

3. Filtration by the Glomerulus Flashcards

1
Q

What are the divisions of the renal artery?

A

Renal artery -> segmental arteries -> interlobar ateries -> arcuate arteries -> interlobular arteries -> afferent arterioles.

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2
Q

How is the pressure of blood inside the glomerulus increased?

A

The diameter of each afferent arteriole is slightly greater than the diameter of the associated efferent arteriole.

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3
Q

What percentage of blood delivered to the kidneys is filtered?

A

20%. The other 80% exits via the efferent arteriole.

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4
Q

What is the size limit for filtration in the kidneys?

A

Molecular weight 5200 or an effective molecular radius of 1.48nm.

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5
Q

What repels protein movement in the kidneys?

A

Podocytes glycocalyx have negatively charged glycoproteins.

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6
Q

What is the glomerula filtrate/ ultrafiltrate?

A

The water and solutes that have been forced out of the glomerular capillaries and pass into Bowman’s space.

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7
Q

What are the three layers for filtrate to pass through?

A

The capillary endothelium, basement membrane, and podocyte layer.

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8
Q

How does filtrate pass throguh the capillary endothelium?

A

It moves between cells.

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9
Q

What is the basement membrane?

A

Acellular gelatinous layer of collagen/glycoproteins.

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10
Q

What is the basement membrane permeable to?

A

Small proteins.

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11
Q

What forms filtration slits in the podocyte layer?

A

Interdigitating pseudopodia.

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12
Q

What three forces cause plasma filtration?

A

Hydrostatic pressure in the capillary, hydrostatic pressure in the Bowman’s capsule, and the osmotic pressure difference between the capillary and tubular lumen.

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13
Q

How does the charge off filtrate affect filtration?

A

If no charge, the bigger the molecule it is, the less likely it is to pass through. The negative charge of anions repels so it’s harder for molecules to get through. The positive charge of cations allow for slightly bigger ions to get through.

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14
Q

In relation to charge, what can cause proteinuria?

A

The negative charge on the filtration barrier can be lost in many diseases. This means more proteins are readily filtered and end up in the urine.

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15
Q

What is tubular reabsorption?

A

The 99% of filtrate that doesn’t leave the body and is instead reabsorbed into the blood and passes through the renal tubules.

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16
Q

What are the three mechanisms of tubular reabsorption?

A

Osmosis, diffusion, and active transport.

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17
Q

What is reabsorption in the PCT driven by?

A

Sodium uptake. Other ions accompany sodium to maintain electro-neutrality.

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18
Q

What are the two routes of reabsorption?

A

Transcellular or paracellular.

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19
Q

How is Na+ reabsorbed in the tubules?

A

It is pumped out of tubular cells across the basolateral membrane by 3Na+-2K+-ATPase. Na+ moves across the apical membrane down the concentration gradient. Water moves down the osmotic gradient created.

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20
Q

How can solutes enter the tubular fluid?

A

By glomerula filtration or secretion.

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21
Q

What substances are secreted into the tubular fluid?

A

Protons, potassium, ammonium ions, creatinine, urea, some hormones and some drugs.

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22
Q

What is the model for organic cation secretion in the PCT?

A

Entry by passive carrier using the gradient set up by the 3Na-2K-ATPase pump, and then secretion into the lumen using the K+-OC+ exchanger driven by H+ gradient created by Na+-H+-antiporter.

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23
Q

How can Na+ act as a driving force for reabsorption?

A

Using the concentration gradient set up by 3Na+-2K+-ATPase.

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24
Q

What are the Na+ transporters in the proximal tubule?

A

Na-H-antiporter and Na-glucose-symporter.

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25
Q

What is the Na+ transporter in the loop of Henle?

A

Na-K-2Cl symporter.

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26
Q

What is the Na+ transporter in the early distal tubule?

A

Na-Cl symporter.

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27
Q

What is the Na+ transporter in the late distal tubule and collecting duct?

A

ENaC.

28
Q

How does the body reabsorb glucose, amino acids, vitamins, and other organic substances?

A

Using symporters driven by the Na+ concentration gradient set up by the Na-K-ATPase.

29
Q

Which transporter does glucose use for reabsorption in the PCT?

A

Na-glucose symporter, SGLUT.

30
Q

How does SGLUT transport glucose?

A

It move glucose against its concentration gradient into the tubule cels. Glucose then moves out of the tubule cell on the basolateral side by facilitated diffusion.

31
Q

What causes glucose to spill over into the urine?

A

If the system of glucose reabsorption reaches capacity - transport maximum and the concentration of glucose exceeds that.

32
Q

How can high blood glucose cause polyuria?

A

Too much glucose means it enters the urine and water follows by osmosis so the volume of urine is increased.

33
Q

What is the renal threshold for glucose?

A

200mg/100ml.

34
Q

What is clearance?

A

The volume of plasma from which a substance can be completely cleared to the urine per unit time.

35
Q

What is the input to the kidney?

A

The renal artery.

36
Q

What is the output to the kidney?

A

Renal vein and the ureter.

37
Q

How can clearance be calculated?

A

Clearance = (amount in urine x urine flow rate)/(arterial plasma concentration).

38
Q

If substance X is present in the urine at concentration of 100mg/ml and the urine flow rate is 1ml/min, what is the excretion rate of substance X?

A

100mg/ml x 1ml/min = 100mg/min.

39
Q

If substance X is present in the urine at concentration of 100mg/ml, the urine flow rate is 1ml/min, and the plasma concentration is 1mg/ml, what is the clearance of substance X?

A

(100x1)/1 = 100ml per min. So 100ml of plasma would be completely cleared of substance X per minute.

40
Q

What is the glomerula filtration rate?

A

The volume of plasma from which any substance (X) is completely removed by the kidney in a given amount of time (usually one minute).

41
Q

What does GFR measure?

A

The kidney’s ability to filter a substance, thus its overall function.

42
Q

When measuring the GFR, what must the substance measured be able to do?

A

Freely filtered across the glomerulus. Not be reabsorbed, secreted or metabolised by the cells of the nephron. Pass directly into the urine.

43
Q

What substances can be used to calculate GFR?

A

Creatinine and insulin.

44
Q

How can GFR be calculated?

A

(Amount in urine x urine flow rate)/ arterial plasma concentration.

45
Q

What is the normal GFR range for males?

A

115-125ml/min.

46
Q

What is the normal GFR range for females?

A

90-100ml/min.

47
Q

How much blood does the kidney receive?

A

1.1 litres per minutes.

48
Q

What is the breakdown of RBCs and plasma in blood that reaches the kidneys?

A

45% RBCs and 55% plasma.

49
Q

What is renal plasma flow?

A

The amount of plasma that reaches the kidneys, blood is 55% plasma and 45% RBCs.

50
Q

How can renal plasma flow be calculated?

A

Total blood reaching the kidneys x 55% = 1.1l/min x 55% = 605ml/min.

51
Q

What is the filtration fraction?

A

The proportion of a substance that is actually filtered.

52
Q

What percentage of plasma is filtered?

A

20%.

53
Q

How is filtration fraction calculated?

A

Filtration fraction = glomerular filtration rate/ renal plasma flow.

54
Q

How is renal blood flow and GFR regulated?

A

By autoregulation, myogenic response, tubular glomerular feedback.

55
Q

What is the myogenic response of the kidneys to reduced arterial BP?

A

Afferent arterioles constrict.

56
Q

What is the myogenic response of the kidneys to increased arterial BP?

A

Afferent arterioles dilate.

57
Q

Which cells respond to changes in tubular flow rate from changes in GFR and amount of NaCl reaching the distal tubule?

A

Macula densa.

58
Q

If NaCl increases, what is the tubular glomerular feedback response?

A

GFR needs to decrease so adenosine is released to cause vasoconstriction of afferent arterioles.

59
Q

If NaCl decreases, what is the tubular glomerular feedback response?

A

GFR needs to increase so prostaglandins are released to cause vasodilation of afferent arteriole.

60
Q

What is general overflow aminoaciduria?

A

All amino acids are present in the urine.

61
Q

What can cause general overflow aminoaciduria?

A

Inadequate deamination in the liver, or an increased GFR. Often seen in early pregnancy.

62
Q

What is specific overflow aminoaciduria?

A

Where only a specific amino acid is present in the urine.

63
Q

What can cause specific overflow aminoaciduria?

A

Genetic inability to break down one amino acid, e.g. phenlyalanine in phenylalanine ketonuria.

64
Q

What can cysteinuria be associated with?

A

Stone formation.

65
Q

Why is cysteinuria associated with stone formation?

A

It is an abnormally insoluble amino acid, especially in acidic urine, so forms stones.

11. Urinary (12 decks)

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