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Gut, metabolism and hormones > Reabsorption and micturition- Renal 2 > Flashcards

Reabsorption and micturition- Renal 2 Flashcards

1
Q

-Reabsorption
- Secretion
- Countercurrent
multiplication
- Micturition
(urination)

A
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2
Q

Learning Objectives:
– Describe the routes and mechanisms of tubular
reabsorption and secretion.
– Explain how specific segments of the renal tubule
and collecting duct reabsorb water and solutes.
– Discuss how specific segments of the renal tubule
and collecting duct secrete solutes into the urine.
(considered again).
– Understand the control of the micturition reflex

A
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3
Q

Tubular reabsorption - is it selective? is it variable?
What is the amount of each substance reabsorbed?

A

Tubular reabsorption is tremendous, highly selective, and variable.
The amount of each substance reabsorbed = the quantity required to maintain proper internal fluid environment composition and volume

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4
Q

Tubular reabsorption involves:

A

the transfer of substances from tubular lumen
into peritubular capillaries

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5
Q

Reabsorbed substances must cross how many barrier?

A

5

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6
Q

Most of tubular reabsorption occurs?

A

At proximal convoluted tubule

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7
Q

From the tubules to Peritubular capillaries:
Of 125ml filtered per min, how much is reabsorbed?

A

124mL

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8
Q

How is most water reabsorbed and what % and explain the breakdown of this?

A

Mostly absorbed by osmosis - 99%
99% H2O – Occurs passively by osmosis
- Obligatory (~80%) - follows solutes that get
reabsorbed in proximal tubule and descending
loop of Henle, passive, antidiuretic hormone
(ADH) independent
- Facultative (~20%) - occurs in the distal and
collecting tubules, regulated by ADH (increase
aquaporin insertion)
Does not require ADH

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9
Q

How much sodium, glucose, amino acids and urea is reabsorbed?

A

99.5% Na+
100% glucose, amino acids
50% urea - it is the only metabolic waste that is
reabsorbed

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10
Q

What transport does tubular reabsorption involve?
In selective reabsorption what is reabsorbed from filtrate bak into the blood?

A

Transepithelial transport
Sodium, amino acids, glucose

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11
Q

Passive reabsorption where does this occur and what is it?

A

No energy is required for the substance’s net movement
Occurs down electrochemical or osmotic gradients

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12
Q

Active reabsorption what is it and how does it occur?

A

Occurs if any one of the steps in transepithelial transport of a substance requires energy
Movement occurs against electrochemical gradient

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13
Q

See diagram on slide 7
1. Does H20 generally go across the cell membrane?
2. Do aquaporfins use energy - if not what?
3. What substances can move across membrane?
4. What requires active transport?

A
  1. H20 generally doesn’t across cell membrane as its polar so doesn’t go across phospholipid tails which are hydrophobic
  2. Aquaporfins don’t use energy but they allow channels to get H2O across but still passive as energy is not used
  3. n2+O2 non polar susbances, lipid soluble can across membrane and certain drugs can cross across the membrane
  4. Ions require active transport
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14
Q

Secondary active transport - how do they generate a gradient?
What mechanisms does this occur by?

A
  1. Generate a gradient using energy such as sodium
  2. Occurs by 2 mechanisms called Antiport - exchange diffusion they move in opposite directions e.g. Cl and Bicarbonate ions in opposite directions
    and Symport - cotransport e.g. moving in same direction like glucose, amino acids and sodium
    All dependent on carrier proteins - proteins bound by cargo and exposed to other side of the membrane where they can release the proteins
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15
Q

How is Na reasborbed?
1. What is essential for it?
2. How much energy is used for it by the kidneys?
3. What follows Na^+ reasborption?

A

Concentrated in basolateral membrane of tubular cell

An active Na+/ K+ ATPase pump in basolateral membrane is essential for Na+ reabsorption
* Of total energy spent by kidneys, 80% is used for Na+ transport
* Water follows reabsorbed sodium by osmosis which has a main effect on blood volume and blood pressure

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16
Q

What is sodium ion?
How it it controlled?

A

Major extracellular cation - typically has a strong difference of concentration across the membrane
Tightly controlled
Basically all sodium is reabsorbed
Most reabsorption tajes place in proximal tubule: 67%

Na/K pump is critical for nervous system

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17
Q

How much Na^+ is reabsorbed in proximal tubule and what is the role here?

A

67%
Plays role in reabsorbing glucose, amino acids, H2O, Cl- and urea

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18
Q

LOT OF ALL REABSORPTION OCCURS WHERE?
See diagrams on slide 11,12,13

A

IN PROXIMAL TUBULE

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19
Q

How much Na^+ is reabsorbed in ascending limb of the loop of Henle and what is the role here?

A

25% - Plays critical role in kidneys’ ability to produce urine of varying concentrations

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20
Q

Glucose

A

2nd trasnporters - Sglut2: symporter which enables glucsoe to bemoved from lumen into cytosol with1. sodium moecuels down its ocnentartion gardeint and this is repsonieblf ro 80-90% of its reabsorption
sglut 1- requires 2 allows ratio of 4900:1 to be generated in terms fo how how much glucsoe is in cytsoosl relative to the lumen

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21
Q

How much Na^+ is reabsorbed in distal and collecting tubules and what is the role here?

A

8% - Variable and subject to hormonal control; plays role in regulating ECF volume, BP, K+ secretion

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22
Q

Amino acid uptake is dependent on?
There is what?

A

largely dependent on Na movement down concentration gradient
different carrier proteins some involve symporters with sodium some have hydrogen ions with it

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23
Q

Plasma concentration of K^+ outside and inside cell - what can affect this?

A

Plasma concentration of K^+ are generally lower outside of cell compared to inside the cell but even a small disturbance in this really affects functions in nerves, etc by affecting resting membrane potential of cells

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24
Q
A

Important for controlling pH via hydrogen ions

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25
Where does K^+ secretion occur and what does it rely upon?
Cortical collecting tubule and relies upon active transport of K^+ across basolateral membrane (ROMK-renal outer medullary potassium channels) and passive exit across apical membrane into tubular fluid Achieved by principal cells - mainly for Na^+ but has other roles with K^+
26
Criteria for diagnosing acute kidney injury (acute renal failure):
* Rise in creatinine >26 μmol/L in 48hrs * Rise in creatinine >1.5*baseline within 7 days * Urine output <0.5mL/kg/h for >6 consecutive hours.
27
What is osmosis?
Osmosis is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane in the direction that tends to equalise the solute concentrations on the two sides.
28
What is another important thing reabsorbed by tubular secretion? What is it? How is it removed? Reabsorption? Plasma levels?
Creatine Creatinine is a breakdown product of creatine phosphate in muscle, produced at a steady rate by the body. Creatinine is removed from the blood mainly by glomerular filtration, but also by proximal tubular secretion. Tubular reabsorption of creatinine is minimal. Creatinine plasma level is 70 - 150 μmol/L
29
Acute Kidney Injury Risk factors:10 See diagram 18
1. Chronic kidney disease 2. History of urinary symptoms 3. Diabetes 4. Drugs especially newly started 5. Poor fluid intake/increased losses 6. Chronic liver disease 7. Over the age of 75 8. Cardiac failure 9. Peripheral vascular disease 10. Sepsis
30
Common causes of acute kidney injury?
Ischaemia, sepsis, nephrotoxins although protsaic disease causes up to 25% in some studies and has the best prognosis
31
What does controlling ECF osmolarity prevent?
Changes in ICF volume
32
Above 300mOsm? 300 mOsm? Lower than 300 mOsm?
Hypertonic: increased solute concentration outside cell Isotonic: equal and ideal Hypotonic: Increased solute concentration inside cell causing cells to burst/lyse
33
Depending on the body's state of hydrate the kidney's secrete?
Urine of varying concentrations
34
Urine volume ans osmotic concentration are regulated by?
Controlling water reabsorption
35
Too much H20 in ECF? Water deficit in ECF?
Hypotonic ECF Hypertonic ECF
36
Examples of Micturition reflex problems:
1. Sphincter muscles lose tone: – leading to incontinence 2. Control of micturition can be lost due to: – a stroke – Alzheimer’s disease – CNS problems affecting cerebral cortex or hypothalamus 3. In males, urinary retention may develop if enlarged prostate gland compresses the urethra and restricts urine flow
37
Mechanism of altered urine production depends on what 2 mechanisms?
Countercurrent multiplier Countercurrent exchange
38
Loop of Henle helps control?
Amount of H20 reabsorbed
39
Countercurrent multiplier?
A countercurrent multiplication loop is a system where fluid flows in a loop so that the entrance and exit are at similar low concentration of a dissolved substance but at the far end of the loop there is a high concentration of that substance. Nephron
40
Countercurrent exchange?
A countercurrent exchange system is a system in which two fluids of different properties flow parallel and against each other in semipermeable tubes, which allow compensation for these differences Vasa recta
41
Ascending and descending loops of Henle are different how?
Ascending loop of henle: ions ACTIVELY pumped into the interstitial space. Creates a really salty environment Descending loop of henle is permeable to water water will flow into the high concentration of salt in the interstitial space
42
What does countercurrent multiplier lead to?
A large, vertical osmotic gradient is established in the interstitial fluid of the medulla (from 100 to 1200-1400 mOsm). => The medullary vertical osmotic gradient is established by countercurrent multiplication
43
There is countercurrent flow made by?
Close proximity of 2 limbs
44
COUNTERCUREENT MULTIPLICATION
fluid is moving trough loop at all time and this is how vertical is made Ascending: trasnporters pump ions out so we have reduction in amount of solutes and increase in concentaryion of solutes in interstial fluids so it flows out then there's a Higher solute concentraion in descending limb moves to bottom of limb => pumping ions out of ascending limb and dragging more water out of descending limb Repeat cycles 4-6: get a salty extracellular environment and you get this gradient Flow is very important to drive reasborption of ions and water an cmaintin this concetration gradient => Generates vertical osmotic gradient
45
Countercurrent exchange? What happens as the vasa recata descends? What happens as vessel ascends?
Maintains this vertical osmotic gradient H20 diffuses and solutes in H20 flows back in and solutes out and this maintains the medullary osmotic gradient
46
What does the Vasa Recta do?
Preserve the vertical osmotic gradient by countercurrent exchange
47
Urine transport, strorage and elimination takes place in the?
urinary tract
48
Micturition ?
spinal reflex based on strecth receptors in lining of mucosa in the bladder it can be overriden voluntarily
49
Pelvic nerve - sensory afferents: stretch recepetors in mucosa
Hypogastric nerve -> Sympathetic From L2: NA, B3 receptor- Inhibit detrusor Contracts int. sphincter Pelvic nerve-> parasympathetic From S2-4: ACh, M3 receptor - Activates detrusor & opening of int. sphincter Pudendal nerve -> Motor, voluntary control Activates ext sphincter
50
1. Primary Active Transport occurs by? 2. Which side faces interstitial space and which towards the membrane? 3. Which way does it drive Na and K? 4. Explain symporters?
1. Primary active transport: Na/K pump 2. Side facing into interstitial fluid the basolateral side facing out towards the membrane 3. Can drive sodium against its concentration out into interstitial fluid and drive potassium from interstitial fluid out and into cytosol by using Primary active transport 4. Symporters carry 2 things in same direction: Na down its concentration and simultaneously like glucose, amino acids can move up its concentration gradient
51
Secondary active transport occurs via 2 mechanisms: 1. Antiport which is exchange diffusion 2. Symport which is co transport Explain them and give examples?
1. In antiport, driving ions and transport molecules move in the opposite direction. Most of the ions are exchanged in this way. For example, coupled movement of chloride and bicarbonate ions across the membrane is initiated by this mechanism. 2. In symport, the solute and driving ions move towards the same direction. For example, sugars such as glucose and amino acids are transported across the cell membrane by this mechanism.
52
Tubular secretion involves the transfer of what from where to where? What transport is used?
Transfer of substances from peritubular capillaries into the tubular lumen Involves transepithelial transport
53
Tubular secretion - kidney tubules can selectively do what?
Kidney tubules can selectively add some substances to the substances already filltered
54
Most important ions in secretory systems?
K^+, H^+ ions and organic ions
55
Where is K^+ secreted? What must concentration be to maintain normal membrane excitability in muscles and nerves?
Secreted only in the distal and collecting tubules under control of aldosterone (lecture 3). Keeps plasma K+ concentration at 3.5 - 5 mmol/L to maintain normal membrane excitability in muscles and nerves
56
Where is H^+ ion secreted and what is it important in regulating?
Secreted in proximal, distal, and collecting tubules Important in regulating acid-base balance (lecture 4).
57
Organic ions accomplish what and where are they secreted?
Accomplish more efficient elimination of foreign organic compounds from the body Secreted in the proximal tubule
58
Cortical nephrons which are 85% of all nephrons mainly perform what functions?
Excretory and regulatory functions
59
Juxtamedullary nephrons which are 15% of all nephrons main functions is to?
Concentrate and dilute urine
60
Medullary vertical osmotic gradient is established by?
Countercurrent multiplication
61
Countercurrent flow is made by?
Close proximity of 2 limbs
62
Ascending limb of loop of Henle actively transports? What is it impermeable to and what does this mean? Where does the interstitial fluid face in countercurrent multiplication?
The ascending limb actively transports NaCl out of the tubular lumen into the surrounding interstitial fluid. It is impermeable to water. Therefore, water does not follow the salt by osmosis. This interstitial fluid faces against the flow of fluid (countercurrent) in the descending limb, attracting the water by osmosis for reabsorption
63
Descending Limb of loop is highly permeable to?
Water but impermeable to sodium for reabsorption
64
As the Vasa recta descends? As it ascends? What does this do?
H20 diffuses out and solutes in As vessels ascend H20 flows back in and solutes out The maintains the medullary osmotic gradient
65
If we were so overhydrated we had no ADH what happens?
Decreased osmolarity of extracellular fluids Then decreased ADH release from posterior pituitary Decreased number of aquaporins (H20 channels) in collecting duct Then decreased H20 reabsorption from collecting duct Leading to a large volume of dilute urine being produced and released
66
If we were so dehydrates we had maximal ADH what happens?
Increased osmolarity of extracellular fluids, increased ADH release from posterior pituitary and increased number of aquaporins (H20 channels) in collecting duct and increased H20 reabsorption from collecting duct and thus a small volume of concentrated urine made and released
67
Normally urine is?
Is a clear, sterile solution Yellow colour (due to pigment urobilin) Generated in kidneys from urobilinogens
68
Urinary tract composed of?
Ureters, urinary bladder and urethra
69
Urinary bladder - 1. Structure? 2. Function? 3. Full bladder has? 4. Emptying =?
1. Hollow, muscular organ 2. Functions as temporary reservoir urine storage 3. Full bladder can contain 1 liter of urine 4. Emptying = mictruition
70
Micturition - urination takes place via what kind of reflex? How can it be overriden?
Spinal reflex Can be overriden voluntarily

Gut, metabolism and hormones (22 decks)

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