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Anatomy Exam 3 > Lecture 3 : Role of the Tubules in Urine Formation > Flashcards

Lecture 3 : Role of the Tubules in Urine Formation Flashcards

1
Q

Glomerular filtration

A

dumps cell-free and protein-free blood filtrate into the container (glomerular capsule or Bowman’s capsule)

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2
Q

The kidneys will process ____ of filtrate a day

A

180 L (47 gallons)

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3
Q

Tubular reabsorption

A

reclaims what the body needs to keep (from tubule to blood) – which is ALMOST everything

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4
Q

Tubular secretion

A

selectively adds to the waste container (from blood to tubule)

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5
Q

Anything remaining in kidney tubule at the end is EXCRETED as ____

A

urine

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6
Q

The ____ and the _____ are low pressure capillary beds adjacent to the renal tubule

A

peritubular capillaries

vasa recta

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7
Q

Peritubular Capillaries:

A

Efferent arteriole gives rise to peritubular capillary bed

Surround PCT and DCT in cortex - will reclaim (reabsorb) most of the solutes and water from the filtrate

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8
Q

Vasa recta:

A

Efferent arteriole gives rise to vasa recta – long straight capillaries

Follow nephron loop deep into medulla – maintain osmotic gradient that makes it possible to concentrate urine

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9
Q

Processes we need to understand in the renal tubule:

A

Filtrate to blood
Blood to filtrate

Countercurrent mechanisms

Role of blood flow in vasa recta of medulla

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10
Q

In PCT:

A

most reabsorption occurs here and is unregulated

maintains osmotic equilibrium

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11
Q

Nephron loop:

A

only water leaves in descending limb

only salt leaves in ascending limb

(Exceptions to what you think about osmosis)

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12
Q

In DCT and collecting duct:

A

hormones control reabsorption

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13
Q

Aldosterone:

A

Na+ reabsorption

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14
Q

ADH:

A

water reabsorption

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15
Q

The renal tubule has a single layer of ___
but each region has a unique histology

A

epithelium

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16
Q

The filtrate is modified through the processes of ___ and ____ which occur by transport mechanisms in the epithelial cells of the renal tubule.

A

reabsorption
secretion

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17
Q

Proximal tubule histology:

A

simple cuboidal epithelium with microvilli

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18
Q

Descending limb of nephron loop histology:

A

simple squamous epithelium

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19
Q

Distal tubule histology:

A

simple cuboidal epithelium with few microvilli

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20
Q

Thick ascending limb of nephron loop histology:

A

simple cuboidal epithelium with no microvilli

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21
Q

Proximal Tubule Cells are Specialized for ___

A

Transport

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22
Q

Microvilli

A

Increase surface area for absorption

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23
Q

Mitochondrion

A

Provide the energy needed for the active transport processes

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24
Q

The proximal convoluted tubule is the primary site for tubular reabsorption:

A

nearly ALL glucose, amino acids, and most electrolytes are reabsorbed in PCT, and about 65-70% of Na+ and water.

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25
Q

Mechanisms of Tubular Reabsorption:

A

Transcellular Route and Paracellular Route

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26
Q

Transcellular Route:

A

1) transport across the apical membrane

2) diffusion through the cytosol

3) transport across the basolateral membrane

4) movement through the interstitial fluid and into the capillary

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27
Q

Paracellular Route:

A

1) movement through leaky tight junctions, particularly in the proximal convoluted tubule

2) movement through the interstitial fluid and into the capillary

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28
Q

Transcellular transport mechanisms :
review of passive transport processes

A

1) simple diffusion = fat-soluble molecules directly through phospholipid bilayer

2) osmosis = solvent like water through a specific channel protein or lipid bilayer

3) carrier-mediated facilitated diffusion = via a protein carrier (they are specific for a chemical)

29
Q

Transcellular transport mechanisms :
Primary and secondary active transport

A

primary active transport = ATP-driven Na+K- pump stores energy by creating a steep concentration gradient for a Na+ entry into the cell

secondary active transport = as Na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient into the cell

30
Q

The Na-K ATPase pump moves _____ out of the cell and ____ into the cell for each ATP molecule that is hydrolyzed; this establishes a concentration gradient for Na+.

A

3 Na+ ions
2 K+ ions

31
Q

Other substances are co-transported with Na+ in secondary active transport :

A

glucose, amino acids, some ions, vitamins

32
Q

Sodium Potassium Pumps are on the ____

A

basal surface of the cuboidal cells of the PCT

33
Q

Secondary Active Transport Proteins are on the ____

A

apical surface of the cuboidal cells of the PCT

34
Q

The sodium gradient provides a driving force to move other substances

A

Sodium and glucose cotransport

Sodium and amino acid cotransport

Sodium and hydrogen ion antiport

35
Q

The majority of tubular reabsorption occurs in the _______

A

Proximal Convoluted Tubule (PCT)

sodium, glucose, amino acids, ions, urea

36
Q

“Water follows solutes” =

A

“obligatory” water reabsorption by osmosis because aquaporins are always present in PCT cells

37
Q

_______ are specific and limited

A

Transport proteins

38
Q

Transport maximum

A

is # of transport proteins available in tubule cell membrane

39
Q

If the amount of a substance in the filtrate exceeds the number of transport proteins that are available, the transporters are _____

A

saturated

40
Q

When all the transport proteins are saturated for a given substance (ex. glucose), some of the substance _____

A

stays in the urine.

41
Q

Diabetes mellitus = ______ if transport maximum exceeded, glucose is excreted in the urine; water stays with glucose so increased urine volume = _____

A

high blood glucose

diuresis

42
Q

Proximal Convoluted Tubule is always in osmotic equilibrium (isosmotic) with surrounding interstitial fluid and blood in ____

A

peritubular capillaries

43
Q

PCT CANNOT SEPARATELY ADJUST ___ AND WATER!

A

SALT

44
Q

Osmolarity at the end of the Proximal Convoluted Tubule

A

Osmolarity of blood entering kidney = 300

Filtrate is isosmotic with plasma at end of PCT : solutes and water have moved together

Lost water on the way down so filtrate becomes more concentrated

45
Q

Osmolarity of the filtrate changes as it moves through the ____

A

nephron loop

46
Q

The kidneys have an osmotic gradient extending from the cortex through the depths of the _____

A

medulla

47
Q

The Renal cortex is ____ with arterial blood (~300 mOsm)

A

isosmotic

48
Q

An increasing osmotic gradient extends through the whole renal medulla creating the ______

A

medullary osmotic gradient

49
Q

The nephron loop dips into a ___ environment

A

salty

the deeper it extends into the medulla, the saltier the interstitial space around the tubule

50
Q

The thick and thin limbs of the ______ function differently

A

nephron loop

51
Q

Simple squamous cells
of thin descending limb:

A

no significant active transport

52
Q

Simple cuboidal cells
of thick ascending limb:

A

active transport

53
Q

The Nephron Loop separates salt movement from _____

A

water movement

54
Q

Cells in the thin _____ have aquaporins that allow water to leave tubule by osmosis

A

descending limb

55
Q

Cells in the thick ______ have no aquaporins and are impermeable to water; they actively transport salts out of tubule into interstitial space

A

ascending limb

56
Q

In PCT-

A

most reabsorption occurs here and is unregulated

57
Q

Nephron loop -

A

only water leaves in descending limb

only salt leaves in ascending limb

58
Q

______ creates an osmotic gradient through interactions of the two limbs of the nephron loop

A

COUNTERCURRENT MULTIPLIER

59
Q

The nephron loop acts as a _____

A

countercurrent multiplier

60
Q

Filtrate flows in the opposite direction in the two limbs of the nephron loop,
= ______

A

countercurrent

61
Q

Tubule cells that line the descending limb of the nephron loop are (passively) permeable to water, but NOT to ____

A

salts

62
Q

Tubule cells that line the ascending limb of the nephron loop actively pump salts out of the tubule lumen into the interstitium, but:

A

WATER CANNOT LEAVE the ascending limb because these cells have no aquaporins

63
Q

The countercurrent multiplier depends on three properties of the nephron loop to establish the osmotic gradient:

A

1) filtrate flows in the opposite direction (countercurrent) through parallel sections of nephron loop

2) the descending limb is permeable to water, but not salt

3) the ascending limb is impermeable to water, but pumps out salts

64
Q

The countercurrent exchanger ensure the medullary gradient doesn’t get ______

A

washed away

65
Q

Vasa recta are very permeable to water and solutes:

A

So, blood within vasa recta remains nearly isosmotic with surrounding fluid, absorbing water and solutes without undoing osmotic gradient.

66
Q

Osmolarity at the start of the distal convoluted tubule :

A

At start of DCT,
~20% of filtered water ~10% of filtered Na+
remains in filtrate

If we do no further adjustments to filtrate, we will make a finished urine that is more dilute than blood, and that carries wastes and some ions away

67
Q

The remainder of the tubule is where we ___ absorption and secretion to “fine tune” filtrate to the needs of the body

A

regulate

68
Q

At the DCT and Collecting Duct:

A

Make urine more dilute or more concentrated than blood

Change ion concentrations further

Adjust pH

Anatomy Exam 3 (11 decks)

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