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Human Physiology Y3 > Tubular Function > Flashcards

Tubular Function Flashcards

1
Q

Define reabsorption

A

Taken back up into the blood from renal tubule

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2
Q

What is reabsorbed 100%?

A

Glucose

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3
Q

What is reabsorbed 99%?

A

Sodium

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4
Q

What is reabsorbed 50%?

A

Urea

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5
Q

What is reabsorbed 0%?

A

Creatinine

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6
Q

What are the mechanisms of tubular reabsorption?

A

Passive diffusion, facilitated diffusion, active transport and osmosis

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7
Q

What are the two cellular pathways?

A

Transcellular and paracellular

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8
Q

Define transport maximum

A

Maximum rate a substance can be transported across a membrane = STATURATION KINETICS OF CARRIER-MEDIATED TRANSPORT

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9
Q

Difference between secretion and filtration?

A

Filtration refers to the passive process by which fluid and solutes are forced out of the glomerular capillaries and into Bowman’s capsule to form the initial filtrate.

Secretion refers to the active process by which substances are transported from the bloodstream into the renal tubules, primarily in the proximal tubules, distal tubules, and collecting ducts

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10
Q

Define renal threshold

A

Plasma concentration of substance = where it starts to be excreted in urine

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11
Q

What is the ideal vs actual renal threshold of glucose?

A

300 mg/dL = ideal but actually is 180 mg/dL

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12
Q

What happens because the renal threshold of glucose is lower than the Tm?

A

Glucose appears in the urine before the Tm is reached, which is not expected

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13
Q

Do all nephron have the same Tm for glucose?

A

No, some nephrons will begin to excrete glucose before other have reached their Tm

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14
Q

What is reabsorbed in the PCT?

A

More than 65% of filtered water and electrolytes 100% of amino acids and glucose are reabsorbed into blood

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15
Q

What is secreted in the PCT?

A

H+

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16
Q

How is the fluid described in the PCT?

A

Isotonic

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17
Q

What happens in the thin-descending loop of Henle?

A

20% of filtered water is reabsorbed = permeable to water and solutes

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18
Q

Describe thin-descending segment CELLS

A

Cells are thin = not very metbolically active

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19
Q

What are impermeable to water?

A

Thin and thick ascending segments of LOOP OF HENLE

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20
Q

What happens in the thick-ascending loop of Henle?

A

High levels of NaCl reabsorption occurs = hypo-osmotic

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21
Q

Describe the cells in the thick-ascening loop of Henle

A

Thick epithelial cells = high metabolic activity

22
Q

What transporter is found in the thick-ascending limb of the loop of Henle?

A

NKCC co-transporter into cell ATPase = maintains low intracellular Na+ conc

23
Q

What happens in the early distal tubule?

A

Reabsorption of most ions = Na+ , Cl-, Ca2+ and Mg2+ IMPERMEABLE to water

24
Q

What is the early distal tubule referred to?

A

Diluting segment = because impermeable to water

25
What transporters are found in the early distal tubule?
NCC = pumps then into the cell and ATPase removes Na+
26
What controls water reabsorption in collecting duct?
Antidiuretic hormone
27
What are the two cell types found in collecting duct?
Principal cells Type A intercalated cells
28
What transporters are found in principal cells?
BK (big K channel) ROMK (renal outer medullary K channel) EnaC Na/K ATPase
29
What transporters are found in Type A intercalated cells?
H+ ATPase H+/K+ ATPase HCO3-/Cl-
30
What is the role of the principal cell?
K+ secretion into tubular lumen to be excreted Aldosterone controls Na+ reabsorption This can regulate blood pressure
31
What is the role Type A intercalated cells?
Maintain acid-base balance Lower blood pH by secreting H+ into tubular lumen to be excreted K+ reabsorption
32
What happens in the Medullary collecting duct?
Reabsorbs less than 5% of filtered water and Na+
33
What is the role of the medullary collecting duct?
Critical role in determining the urine output and concentration Permeability to water is controlled by ADH
34
What are the factors regulating tubular reabsorption?
Hormonal factors Aldosterone, Angiotensin II, ADH, ANP
35
Define the glomerulotubular balance
Ability of the renal tubules to adjust their reabsorption of sodium ions in response to changes in the rate of glomerular filtration Particularly in proximal tubules
36
What do glomerulotubular balance and tubuloglomerular feedback do together?
Buffer the effects of spontaneous changes in GFR on urine output
37
What is the reabsorption of Na+ coupled with?
H+, glucose, amino acid and phosphate = either by co-transport or exchange
38
What transporters reabsorb glucose?
Glucose and Na+ bind SGLT-2 in apical membrane Glucose enters cell as Na+ moves along electrochemical gradient Na+ is pumped out of the cell Glucose exits by facilitated diffusion via GLUT2
39
How are amino acids reabsorbed and where?
Proximal convoluted tubule Transported by Na+/amino acid co-transporters Amino acid leaves basolateral membrane via diffusion
40
How is potassium regulated?
Principal cells secrete K+ into tubular lumen to be excreted Type A intercalated cells = reabsorb K+ via K+/H+ ATPase
41
What can hyperkalemia and hypokalemia cause?
Hyper = fatal cardiac arrhythmias Hypo = cardiac arrhythmias and muscle weakness which can be life threatening
42
How is low potassium regulated?
Increase activity of Type A intercalated cell Increase H+ secretion (alkalosis) and K+ reabsorption
43
How is high potassium regulated?
Increase aldosterone = increased EnaC (apical) and Na+/K+ ATPase (basolateral) Aldosterone = increases incorporation of K+ secreting channels into luminal membrane
44
What regulates calcium?
Parathyroid hormone
45
Where is calcium reabsorbed?
65% of filtered calcium reabsorbed in PCT Reabsorbed at thick ascending limb and DCT under influence of PTH
46
What forms the countercurrent system?
Vasa recta and loop of Henle
47
What are the roles of vasa recta and loop of Henle in countercurrent mechanism?
Countercurrent multiplier = loop of Henle Countercurrent exchanger = vasa recta
48
What is the role of the countercurrent mechanism?
Maintaining the osmotic gradient
49
What happens if the medulla of the kidney is not hypertonic?
Cannot reabsorb water, even with aquaporins in place
50
What two things flow in opposite directions in the countercurrent system, and why is this important?
Blood and solutes move in opposite direction = causing water to move in the correct direction

Human Physiology Y3 (14 decks)

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