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Renal > Function Of The Kidneys - Filtration, Reabsorption And Secretion > Flashcards

Function Of The Kidneys - Filtration, Reabsorption And Secretion Flashcards

1
Q

What are the functions of the kidney?

A 
Excrete waste and toxins
Regulate blood ionic composition
Main blood osmolarity
Regulate blood pH
Regulate blood pressure
Regulate blood glucose
Produce hormones
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2
Q

During glomerular filtration which molecules are filtered and which remain in the blood?

A 
Water and low molecular weight molecules are filtered
Plasma proteins (and non-protein elements which are bound to them) remain in the blood
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3
Q

What is the equation which related excretion to filtration, reabsorption and secretion?

A

Excretion = filtration - reabsorption + secretion

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4
Q

What is the term for the bolume of fluid filtered from the glomeruli into the capsule space per unit time?

A

The glomerular filtration rate

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5
Q

What are the forces influencing the glomerular filtration rate?

A

Glomerular blood hydrostatic pressure promotes filtration

Blood colloid osmotic pressure and capsular hydrostatic pressure oppose filtration

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6
Q

What is paracellular reabsorption?

A

A passive process whereby substances pass around tubule epithelial cells via tight junctions and into the interstitial fluid.

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7
Q

What is transcellular reabsorption and how does it occur?

A

Here reabsorption occurs through tubular cells and into the interstitial fluid. Y active transport, passive diffusion, facilitated transport of cotransport.

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8
Q

What molecules can move by paracellular reabsorption?

A 
Water 
Calcium
Chloride
Magnesium
Potassium
Sodium
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9
Q

Why are some substances removed from the blood by secretion?

A

Because they are in excess
Because they are harmful substances
To maintain a healthy pH

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10
Q

Where does reabsorption and secretion mainly occur?

A

The proximal convoluted tubules

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11
Q

Why is the proximal convoluted tubule so highly permeable to water and ions?

A

Because it has a ‘leaky’ apical membrane on its tubular cells

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12
Q

Approximately how many of the sodium ions in the filtrate are reabsorbed at the proximal convoluted tubule?

A

Two thirds

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13
Q

By what mechanism is sodium reabsorbed in the proximal convoluted tubule?

A

Sodium diffuses into the eputhelial cells and is actively pumped out by Na/K-ATPases on the asolateral membrane into the interstitial fluid.

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14
Q

Why is the transport of sodium in the proximal convoluted tubule particularly important?

A

Because it sets up the electrochemical gradient which drives water reabsorption via osmosis and the reabsorption of other solutes by diffusion

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15
Q

How are nutrients such as glucose, amino acids, lactic acid and water-soluble vitamins reabsorbed in the proximal convoluted tubule?

A

By facilitated transport with sodium ions

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16
Q

How are bicarbonate ions reabsorbed?

A

They combine with hydrogen ions to form carbon dioxide and water which can freely pass through the membranes of the tubular cells. Once in the cells they break down into bicarbonate and hydrogen ions again and the bicarbonate ions are transported into the interstitial fluid by sodium/bicarbonate ion transporters.

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17
Q

Which transporter pumps hydrogen ions back into the lumen of the renal tubules so that they can allow the reabsorption of bicarbonate ions?

A

The hydrogen/sodium ion antiporter

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18
Q

How does the reabsorption of chloride ions help with the reabsorption of other ions?

A

Chloride ions are negative and so their reabsorption increases the negative charge of the interstitial fluid, and so sets up an electrochemical gradient that allows other positive ions to diffuse into the interstitial fluid

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19
Q

How are small proteins present in the filtrate reabsorbed?

A

They undergo endocytosis at the apical membrane of the tubule cells and are digested to amino acids which can then be transported across the basolateral membranes of the tubule cells and into the interstitial fluid

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20
Q

Describe the secretion of ammonium ions from the proximal convoluted tubule?

A

These ions result from the deamination of the amino acid glutamine and then are transported back into the lumen of the tubules bey the hydrogen/sodium ion antiporter which will accept ammonium ions instead of hydrogen ions

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21
Q

Describe the effects of the counter current flows in the loop of Henle.

A

In the ascending limb there is ion reabsorption without water reabsorption but these ions just sit in the interstitial fluid (because the vasa recta forms hairpin loops)making it hyperosmotic. This hyperosmality drives water reabsorption in the descending limb.

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22
Q

Calcium channels sit on the apical membrane of which part of the renal tubule to assist reabsorption?

A

The early DCT

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23
Q

Which ions are secreted by the late DCT and collecting tubules of the kidneys?

A

Potassium ions

Hydrogen ions

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24
Q

Which transport molecule is responsible for the secretion of potassium in the renal tubule?

A

Na/K-ATPase

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25
Q

Which transport molecule is responsible for the secretion of hydrogen molecules in the renal tubule?

A

H/K-ATPase

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26
Q

Which cells in the kidney produce renin?

A

Juxtaglomerular cells

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27
Q

Describe how the secretion of renin leads to the secretion of aldosterone by the adrenal glands.

A

Renin acts of angiotensinogen to produce angiotensin I which is then converted to angiotensin II by angiotensin converting enzymes. Angiotensin II then stimulates the adrenal glands to produce and secrete aldosterone.

28
Q

Increased renin leads to increased aldosterone levels. What affect does this have on sodium and potassium reabsorption and secretion?

A

Increased aldosterone levels, increases sodium reabsorption and increases potassium secretion

29
Q

What factors can lead to the increase secretion of renin and what are these factors sensed by?

A

Decrease in arterial pressure sensed by juxtaglomerular cells which act as intarrenal baroreceptors.
Salt depletion sensed by the macula densa

30
Q

What affect does ANP have an sodium reabsorption and how does it achieve this effect?

A

It inhibits sodium reabsorption by increasing glomerular filtration rate and inhibiting aldosterone secretion

31
Q

Which hormone will increase calcium ion reabsorption whilst simultaneously decreasing phosphate reabsorption?

A

Parathyroid hormone

32
Q

What is the typical water intake for an adult at 23 degrees C undertaking ‘normal daily activities’ and where does this intake come from

A

1200ml from water
1000ml from food
300ml from metabolic processes

33
Q

What is the typical water output for an adult at 23 degrees C undertaking ‘normal daily activities’ and where does this intake come from

A

1500ml from urine
100ml from sweat
200ml from faeces
700ml from insensible loss

34
Q

What is insensible loss?

A

The loss of water through things such as respiratory water loss and leakage of water through the skin

35
Q

What is the value of renal blood flow?

A

Around 650 ml/min

36
Q

What is the renal filtration rate?

A

90-140 ml/min

37
Q

How much of the resting cardiac output do the kidneys receive?

A

25%

38
Q

What is the main cation presence in the extracellular fluid?

A

Sodium

39
Q

What is the main cation present in the intracellular fluid?

A

Potassium

40
Q

What is the main anion presence in the extracellular fluid?

A

Chloride

41
Q

What is the main anion presence in the intracellular fluid?

A

Bicarbonate

42
Q

What are the components of the glomerular filtration barrier?

A

Glomerular endothelium
Collagen-based glomerular basement membrane
Podocyte foot processes forming the filtration slit membrane

43
Q

What is the normal glomerular filtration rate?

A

100ml/min

44
Q

Describe the absorptive process in the ascending loop of Henle which is driven by the sodium/potassium/2 chloride transporter?

A

The Na/K-ATPase sets up a concentration gradient which allows the transport of sodium, potassium and two chloride molecules through a single transporter into the tubular cell. Potassium is then secreted back into the lumen which creates a positive charge in the lumen which drives the transcellular absorption of magnesium and calcium

45
Q

Describe the action of the ENaC channel in the DCT?

A

The action of the channel is driven by Na/K-ATPase and the channel transports sodium into the cell which creates a negative change in the lumen of the tubule which drives the secretion of potassium ions into the lumen

46
Q

Which chemical will be released by the macula densa to cause arteriolar constriction when increased tubular flow is sensed?

A

Adenosine

47
Q

What is the role of ANP and BNP in kidney function?

A

These directly inhibit sodium reabsorption in the DCT and also inhibit renin and ADH secretion

48
Q

Normally, how much fluid is there in the intracellular environment?

A

25L

49
Q

Normally how much fluid is there in the interstitium?

A

12L

50
Q

Normally how much fluid is there in the plasma?

A

3L

51
Q

What is the normal cytoplasmic concentration of potassium?

A

100-120mmol/l

52
Q

What percentage of total body potassium exists in the extracellular fluid?

A

1-2%

53
Q

What is the average UK intake of potassium per day?

A

80mmol / day

3g

54
Q

The body can cope with a daily intake of how much potassium if renal function is normal?

A

20-500mmol/day

55
Q

What percentage of the glomerular filtrate is reabsorbed by the kidney?

A

99%

56
Q

What is the difference between osmolarity and osmolality?

A

Osmolarity - osmole conc per unit volume

osmolality - osmole conc per unit mass

57
Q

What is the concentration of solutes in the plasma?

A

285-295mosm/kg

58
Q

How long is the PCT?

A

14mm

59
Q

What is the only hormone involved in the control of reabsorption in the PCT?

A

Angiotensin II

60
Q

Which hormone, in addition to increasing water reabsorption and causing vasoconstriction, creates the sensation of thirst?

A

ADH

61
Q

What factor, other than angiotensin II, can induce aldosterone release from the bona glomerulosa of the adrenal cortex?

A

High potassium

62
Q

What channel does aldosterone work on in the DCT and collecting ducts to cause sodium reabsorption and potassium secretion?

A

ENaC

63
Q

A dysfunction in the Na/K/2Cl channel in the loop of Henle will lead to which hereditary condition?

A

Bartter’s

64
Q

A dysfunction in the ENaC channel in the DCT and collecting ducts will lead to which hereditary condition?

A

Liddle’s

65
Q

A dysfunction in the transporter channels in the PCT will lead to which hereditary condition?

A

Fanconi’s syndrome

66
Q

Measurement of which electrolyte in the urine can differentiate between Barterr’s and Gitelman’s?

A

Calcium

67
Q

What are the minimum and maximum rate of daily urine output?

A

0.4 litres /day

12 litres / day

Renal (11 decks)

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