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P1: Ren > Structure And Function Of The Renal Tubule > Flashcards

Structure And Function Of The Renal Tubule Flashcards

1
Q

What happens in the renal tubule?

A

→ Filtered fluid is converted to urine

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2
Q

What is the composition of glomerular filtrate?

A

→Same composition as plasma except that there are no cells and very little protein

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3
Q

When does urine formation begin?

A

→ large amounts of fluid that is free of protein is filtered from the glomerular capillaries into the Bowman’s Capsule.

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4
Q

What is the glomerular filtrate?

A

→ An ultrafiltrate of plasma

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5
Q

What is reabsorption?

A

→moving from the tubular lumen into the peritubular capillary
→ returning wanted substances into the blood

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6
Q

What is secretion?

A

→ moving from the peritubular capillary plasma into the tubular lumen

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7
Q

What is the pathway substances have to take to be reabsorbed?

A

→cross the luminal membrane
→ diffuse through the cytosol
→ across the basolateral membrane
→ into the blood

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8
Q

What is co-transport?

A

→ Movement of one substance down its concentration gradient

→ allows the transport of another substance against its concentration gradient

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9
Q

What is the sodium-glucose transporter called in the kidney?

A

→ SGLT-2

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10
Q

What is the effect of SGLT-2 inhibitors?

A

→ don’t allow glucose to be carried across with sodium into the peritubular capillaries

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11
Q

What are the techniques used to investigate tubular functions in humans?

A

→ Clearance studies

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12
Q

What are the techniques used to investigate tubular functions in animals?

A

→ Micropuncture & isolated perfuse tubule

→ Electrophysiological analysis

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13
Q

How is micropuncturing done?

A

→ isolate the nephron

→ sample tubular fluid in different parts of the nephron

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14
Q

How is the electrical potential measured?

A

→ Micropipettes are inserted into the cell

→PD is measured across the whole cell epithelium

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15
Q

What is patch clamping for?

A

→The current flow through an individual ion channel is measured

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16
Q

What cells is the nephron made from?

A

→ a single layer of epithelial cells resting on a basement membrane

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17
Q

What are the 7 parts of the nephron?

A 
→ PCT
→Thin Descending limb
→ Thin ascending limb
→ Thick ascending limb
→ DCT
→ Collecting duct
→ Medullary collecting duct
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18
Q

What are the two types of nephron?

A

→ Cortical nephron

→Juxta-medullary nephron

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19
Q

What do juxta medullary loops do?

A

→ they have a long loop of Henle

→ They are better at concentrating urine

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20
Q

What percentage of each type of nephron do humans have?

A

→ 85% cortical

→ 15% juxta medullary

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21
Q

What are the efferent arterioles in the juxtamedullary nephrons divided into?

A

→ Specialized capillaries (vasa recta)

→ they extend downward into the medulla and lie side by side with loops of Henle

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22
Q

Where is the PCT?

A

→ Adjacent to the Bowmans capsule

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23
Q

What are the adaptations of the PCT for transport?

A

→ Mitochondria for active transport

→ Brush border on the luminal side which gives a large surface area for rapid exchange

→Enzymatic proteins and carriers

→ the PCT has a high permeability

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24
Q

How much is filtered at the PCT?

A

→ 65-70% of the filtered load

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25
Q

What is Fanconi’s syndrome?

A

→ Proximal tubule reabsorptive mechanisms are defective so glucose, amino acids, Na+, K+ are all found in the urine

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26
Q

What are the 3 functional segments of the loop of Henle?

A

→ Thin descending
→ Thin ascending
→ Thick ascending

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27
Q

What is the structure of the thin ascending & descending loops?

A

→ Thin epithelial cells
→ No brush border
→ few mitochondria
→ low metabolic activity

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28
Q

What is the structure of the thick ascending loop?

A 
→ Thick epithelial cells
→ Extensive intracellular folding
→ Few microvilli
→Many mitochondria
→ High metabolic activity
29
Q

What is the function of the loop of henle?

A

→ role in diluting and concentrating urine

→ adjusts the rate of water secretion/absorption

30
Q

What are the permeabilities of the loop of henle?

A

→ Only the descending limb is permeable to water

→ the other two are impermeable to water

31
Q

What do the loop diuretics do?

A

→ act causing 20% of filtered Na+ to be excreted

32
Q

Describe how the countercurrent multiplier works

A

→on the ascending limb side there are a lot of Na+/K+ pumps
→ They pump Na+ out all the time
→ Salt accumulates in the interstitial space around the loop of Henle
→ It pulls water out of the descending limb via osmosis
→water cannot be reabsorbed by the ascending limb
→ as fluid flows down the osmolality increases
→ all the fluid is more concentrated
→as the fluid moves out it is hypo-osmotic

33
Q

What maintains the medullary osmotic gradient?

A

→the vasa recta forms in a countercurrent to the loop of henle
→water can diffuse into the blood
→ Salts can diffuse into the loop of henle

34
Q

What is the first part of the DCT and what is it linked to?

A

→ Macula densa

→ Juxtaglomerular complex

35
Q

What does the macula densa do?

A

→ provides feedback control of the GFR

36
Q

What are the functions of the DCT?

A

→ Solute reabsorption without H2O absorption
→ high Na+/K+ ATPase activity in the basolateral membrane
→ dilution of tubular fluid
→ Role in acid base balance via the secretion of NH3

37
Q

How can you make the DCT permeable to water?

A

→ using ADH

38
Q

What are the collecting ducts formed from?

A

→ joining collecting tubules

39
Q

What are the 2 types of cells in the collecting ducts?

A

→ intercalated cells

→ principal cells

40
Q

What kind of epithelium is in the collecting duct?

A

→ cuboidal epithelia

41
Q

What is the collecting duct permeable to?

A

→ urea

→ made permeable to H2O by ADH

42
Q

What do intercalated cells do?

A

→ Involved in acidification of urine and acid-base balance

43
Q

What do principal cells do?

A

→ Play a role in Na balance and ECF volume regulation

44
Q

Where is ADH made and stored?

A

→ In the hypothalamus

→ In the pituitary gland

45
Q

How does ADH concentrate urine?

A

→ triggering the kidney tubules to reabsorb water back into bloodstream

46
Q

What is the most important effect of ADH?

A

→ conserve body water by reducing the loss of water in the urine

47
Q

What is the most important variable in regulating ADH secretion?

A

→ Plasma osmolality

48
Q

What are changes in osmolality sensed by?

A

→ osmoreceptors in hypothalamus

49
Q

What happens when an osmoreceptor detects changes in osmolality?

A

→triggers ADH secretion from the posterior pituitary
→ taken to the kidneys
→ make the collecting duct permeable to water

50
Q

How does ADH/ vasopressin cause the collecting duct to be more permeable to water?

A

1) ADH binds to its V2 receptors on the peritubular capillary wall
2) it leads to the insertion of aquaporins into the luminal membrane near the collecting duct
3) water is removed from the urine
4) it stimulates the synthesis of new aquaporins

51
Q

How does urea enter the glomerular filtrate?

A

→ It filters freely through the glomerulus and passes down the tubule

52
Q

How is urea reabsorbed from the collecting duct?

A

→ as water is reabsorbed from the CD
→ Urea is concentrated so that it moves out
→ absorbed into the surrounding capillaries and into the interstitial of the medulla
→ contributes to the osmotic gradient around the loop of Henle

53
Q

What do increasing urea levels in the kidney indicate and why?

A

→ pre-renal failure

→ reabsorption is enhances

54
Q

How are urea levels in the kidney monitored?

A

→ Blood urea nitrogen test

55
Q

What happens to the collecting duct during water deprivation?

A

→ ADH acts
→ Aquaporins are inserted into the luminal membrane
→ small urine volume - less dilute
→Water reabsorption increases the CD urea concentration and ADH increases the duct permeability to urea and therefore its reabsorption is increased
→ osmolarity is greater than hypoosmotic fluid

56
Q

What happens to the collecting duct during water excess?

A

→ no ADH acts
→ water remains in the CD
→ large urine volume - more dilute
→osmolarity is lower than hypoosmotic fluid that entered the duct

57
Q

What kind of fluid enters the collecting duct?

A

→ Hypo-osmotic fluid

58
Q

What are the 4 factors that allow the medullary osmotic gradient to be maintained?

A

→ Active transport of Na+ and co-transport of K+ and Cl- out of the thick ascending limb into the medullary interstitium
→ Active transport of ions from collecting duct into the interstitium
→ Facilitated diffusion of urea from collecting ducts into the medullary interstitium
→ Little diffusion of water from ascending limbs of tubules into medullary interstitium

59
Q

What is polycystic kidney disease?

A

→ genetic disorder characterized by growth of numerous cysts in the kidney

60
Q

What are diseases of the glomerulus called?

A

→ glomerulonephritis

61
Q

What happens in diseases of the glomerulus?

A

→ inflammation of glomeruli or some or all of the nephrons

→ can be primary or secondary to things like diabetes

62
Q

What are the two diseases of the tubules?

A

→ Obstruction

→Impairment of transport functions

63
Q

How can hypertension lead to kidney damage?

A

→ Kidneys regulate ECF and influence BP

→ compensatory mechanisms in response to high BP leads to chronic kidney damage

64
Q

How can congestive cardiac failure lead to kidney damage?

A

→ Fall in cardiac output
→ renal hypoperfusion
→ registered as hypovolaemia
→ compensation results in pulmonary oedema

65
Q

How does diabetic nephropathy lead to kidneys being damaged?

A

→ Filtering system of the kidneys get destroyed over time

66
Q

What does lithium treatment result in?

A

→acquired nephrogenic diabetes insipidus

→ reduced aquaporin 2 expression

67
Q

What is the role of the vasa recta?

A

→ The vasa recta is permeable to both H2O and salts and could disrupt the salt gradient established by the loop of Henle.
→ To avoid this, the vasa recta acts as a counter-current multiplier system as well.
→ As the vasa recta descends into the renal medulla, water diffuses out into the surrounding fluids, and salts diffuse in.
→ When the vasa recta ascends, the reverse occurs.
the concentration of salts in the vasa recta is always about the same, and the salt gradient established by the loop of Henle remains in place.
→ Water is removed by VR, so doesn’t dilute longitudinal osmotic gradient.

68
Q

Why is it important that the medullary blood flow in vasa recta is slow?

A

sufficient to supply the metabolic needs of the tissue, but minimize solute loss from the medullary interstitium.

P1: Ren (13 decks)

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