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Sodium, Potassium, Chloride Flashcards

1
Q

What are the bodies fluid compartments?

A

intracellular fluid (ICF) and extracellular fluid (ECF)
* ICF: 65% in cells
* intravascular fluid part of ECF: 5-8% in blood vessels
* interstitial fluid part of ECF: 25% between cells
* transcellular fluid part of ECF: 1-2% in epithilial lined spaces

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2
Q

What is the primary function of Na+, K+, Cl-?

A

maintain electrochemical charge or gradients (electrolytic & osmotic control) and exist primarly as free ions and only bind weakly to other molecules

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3
Q

relative concentrations of Na+, K+ and Cl- inside vs. outside the cell?

A
  • Na+ Outside Cell = 135-148 mmol/L
  • Na+ Inside Cell = 12 mmol/L
  • Cl- Outside Cell = 98-108 mmol/L
  • Cl- Inside Cell = 2 mmol/L
  • K+ Outside Cell = 3.8-5.5 mmol/L
  • K+ Inside Cell = 150 mmol/L
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4
Q

Why is the charge of a cell so negative?

A

due to the presence of ANIONIC molecules (nucleic acids, proteins)
* must maintain osmotic balance by pumping IN cations (K+)

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5
Q

How is lectrolyte distribution and balance in the body controlled?

A
  • movement of ions
  • selective permeability of membrane
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6
Q

What is the most ubiquitous pump for electrolyte balance?

A

Na+-K+-ATPase pump which is responsible for 20-40% of BMR
* 3Na+ out, 2K+ in
* Pump creates electrochemical gradient across cell membranes

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7
Q

Describe the electrical and chemical gradients of the Na+/K+ ATPase

A
  • Electrical: Outflow of more Na+ than inflow of K+ so cytoplasm stays more negatively charged and is used to create AP
  • chemical: ↑ extracellular [Na+] vs cytoplasm lets Na+ flow down the gradient into the cytoplasm via transmembrane proteins (ie. SGLT-1, SMVT) which drives many transport processes
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8
Q

What is the Na/K ATPase important for?

A
  • maintains ionic homeostasis
  • regulates cell volume
  • forms basis for water soluble absorption
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9
Q

Describe the Na/K pump

A

transmembrane protein and functional units is heterodimer with two 𝝰- and β- subunits, but different isoforms exist so relative proportion of each varies among tissues.
* molecular basis is Mg2+ dependant
* Characterized by the transient phosphorylation of ATPase protein during the transport cycle

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10
Q

Descrive the process of how Na/K ATPase works

A
  1. transporter picks up 3Na+ inside cell
  2. ATP binds phosphorylating 𝝰-subunit and changing conformation to release Na+ outside of cell
  3. transporter picks up 2 K+ outside of cell
  4. phosphate group on 𝝰-subunit is hydrolyzed triggering release of K+ inside cell
  5. Cycle repeats
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11
Q

What does active absorption of Na+ act as a co-transporter?

A

primary mechanism for passively absorbing Cl-, amino acids, glucose, water through co-transport
* allow for active transport of molecules against the concentration gradient, they build up in the cell & then asymmetric channels on the basolateral side enable passive diffusion & ABSORPTION into circulation

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12
Q

Describe the benefit of the asymmetric distribution of channels and pumps on elongated cells?

A

Asymmetric distribution of channels/PUMPS (basolateral vs luminal membrane) causes Na+ to be pumped OUT of the cell & K+ IN, Na+ actively pumped OUT into interstitial space (into plasma), generates gradient from luminal side intracellularly

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13
Q

Intestine absorption of Na+, Cl-, K+ and water

A
  • Na+: 95-100% absorbed from luminal side via diffusion by ion channels or facilitated diffusion which is assisted by the Na/K pump on basolateral.
  • Cl-: co-transported with Na+ or enters via paracellular space
  • K+: 85-90% absorbed via passive diffusion in colon or H/K pump
  • water: absorption is passive along osmotic gradient by nutrient absorption
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14
Q

How might Na+ facilitate transport of AAs into the cell?

A

The Na+ binding to the AA transporter increases its affinity for the AA (Na+ going down its gradient) which then binds and the complex causes a conformation change that brings both molecules in and the Na+ is pumped back out by Na/K ATPase

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15
Q

What are the main sources of K+?

A

> 90% ICF and ~2% ECF, K+ can usually look after itself
* intestinal absorption from dietary K+
* Loss from muscle with activity
* renal reabsorption

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16
Q

What influences transcellular distribution of K+?

A
  • insulin
  • pH
  • catecholamines
  • osmolarity
  • K+ concentration
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17
Q

When does muscle take up excess K+ from ECF?

A
  • after a meal driven by insulin
  • during exercise driven by catacholamines
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18
Q

What is the resting membrane potential of the cell and how is it maintained?

A

the resting potential is generally -70Mv but may very on tissue with the different Na/K pump isoforms
1. High K+ in cell so chemical forces act on it to leave
2. K+ more permeable to get OUT than Na+ to get IN so overall -ve charge occurs
3. -ve charge inside slows K+ leaving and greater force for Na+ to get IN
4. steady state with -ve charge occurs for passive movement assisted by Na/K-ATPase

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19
Q

What are the steps of an action potential?

A
  1. stimulus occurs
  2. depolarization: incoming propagating current (-50mV) opens all voltage gated Na+ channels from outside so Na+ rushes IN against concentration gradient (-ve inside) & PD drops
  3. repolarization: Only milli secs later voltage gated K+ channel on inside open to let K+ out (slower) (against now +ve PD), meanwhile Na+ ions cease influx & outside channels close again.
  4. re-establish steady state: K+ voltage gated channels close again after delay
    (over shoot), Na,K-PUMP takes over.
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20
Q

What maintains the membrane potential?

A

Na/K-ATPase pump
* critical for nerve impulse transmission, muscle contraction & cardiac function

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21
Q

What major biological functions require the AP process?

A

Muscle, nerve & endocrine cells have “excitable” membranes
* Tension, transmission, secretory functions result from the ability to generate & propagate action potentials; dependent on [K+] gradients

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22
Q

Why do excitable membranes depend on [K+] gradients?

A

Modulations in [K+] can cause electro-physical disturbances & cells cannot maintain normal resting membrane potential
* hyperkalemia
* hypokalemia

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23
Q

Describe hyperkalemia

A

membrane depolarizes (5mmol/L) and cannot repolarize
* Resting membrane potential is closer to the action potential threshold so cells become more excitable
* extracellular K+ higher than normal and K+ does not leak out as fast as it normally would by diffusion (diffusion out slows) & more K+ is retained inside the cell than normal so resting membrane potential is shifted up (closer to threshold) & cell will reach action potentials with smaller graded potentials (over-responsive to smaller signals)

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24
Q

Describe hypokalemia

A

membrane hyperpolarizes
* Resting membrane potential is farther from the action potential threshold so cells get less excitable
* As extracellular K+ decreases, the concentration gradient increases so greater diffusion pressure & so more K+ diffuses out than normal and intracellular becomes more negative than normal so normal signal would not reach threshold & AP not reached (less responsive to signal)

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25
What is the result of hyperkalemia?
* muscle weakness * arrhythmias * 8 mmol/L can cause complete cardiac arrest
26
What is the result of hypokalemia?
* muscle weakness * decreased smooth muscle contractility * severe cases <3.5 mmol/L paralysis, alkalosis
27
What factors contribute to water/fluid balance?
water input (2.5L/day) and output (2.5L/day) * input: absoroption across GI & production by cellular metabolism * output: excretion in urine and feces &loss through sweat and respiration
28
What controls osmotic homeostasis and fluid balance?
Na+ and kidneys * ion transport effects fluid balance effects osmotic homeostasis
29
What is normal osmotic pressure?
300 mOsm in & out of cells (intracellular, interstitial, plasma) * cells remain same volume (osmotic equilibrium)
30
What happens with drinking large amounts of pure water?
↓ [solutes] ↓ ([osmotic]) if uncorrected, water will flow into cells where the osmotic concentration is higher so kidneys quickly excrete water to compensate which increases urine volume of low osmolarity.
31
What happens with consuming large quantity of salt nuts and no water?
↑ plasma [osmotic] If uncorrected, cell volume may shrink so kidneys respond by quickly modifying [urine] to excrete more solutes in a decreased volume of urine
32
How does the kidney compensate for changes in fluid?
By controlling the rate of water excretion via changes in the rate of water reabsorption
33
What are the main compartments of the kidney?
* cortex: composed of glomerulus, Bowmans capsule, juxtaglomarular apparatus, convoluted tubules * medulla: composed of collecting ducts and loops of henle
34
Function of the kidney renal tubules
passive water re-absorption, couples to active re- absorption of solutes (including Na+, K+ & Cl-).
35
How does solute transport vary depending on the segment of kidney tubules?
* Proximal & Distal tubules have Na,K-ATPase PUMPS that drive an osmotic gradient to re-absorb water. * Descending limb of Henle is impermeable to ions (no pumps) & draws out water only. * Ascending limb of Henle has Na,K PUMPS, & draws solute (re-absorbs) out from the tubular fluid.
36
What is the system of the loop of henle?
Countercurrent Multiplier System Generates differential osmotic gradient from the anatomical arrangement of loop of henle, which is in turn used along the length of the collecting duct to control the rate of water re-absorption from urine and allows for efficient disposal of excess solutes and water * Allows kidneys to dilute urine to 1/6 the osmolarity of plasma or concentrate it up to 4x that of plasma so excrete urine of highly variable osmolarity (50-1200 mOsm/L)
37
What is osmolarity?
the concentration of a solution expressed as the total number of solute particles per liter.
38
Where is osmolarity typically high and low in the kidney tubules?
* the bottom of the loop of henle is typically ↑ osmolarity, being salty concentrated in NaCl+urea since water drawn out * distal tubule is often ↓ osmolarity with solutes being reabsorbed
39
What is the functional unit of the kidney?
the nephron Each kidney is made up of about a million nephron filtering units which include a filter, called the glomerulus, and a tubule.
40
What is the two step
1. the glomerulus filters your blood 2. the tubule returns needed substances to your blood and removes wastes.
41
What is filtered into the glomerulus?
*100% filtered Includes *water, *salts, *bicarbonate, *glucose, *amino acids, creatinine, urea | *are reabsorbed in the proximal tubule
42
How does the filtrate move through the nephron?
* 100% filtered into glomerulus * up to 65% solutes can be reabsorbed in proximal tubule * water is drawn out in the descending limb * solutes reabsorbed in the ascending limb * about 10% of filtrate left in the distal tubule * more reabsorption of solutes occurs in the collecting duct * 0.5-5% of filtrate remains
43
What are some major hormones involved in osmotic homeostasis?
* Aldosterone (from adrenal cortex) * anit-diuretic hormone (ADH) (from posterior pituitary gland) * Angiotensin II (Ang II) * Atrial natriuretic peptide (ANP) * Vitamin D3 (calcitriol) * parathyroid hormone (PTH)
44
What is the role of aldosterone and ADH?
Both act on distal convoluted tubule and collecting ducts * **aldosterone**: conserves water via reabsorption of Na+ (water follows salt) using Na/K exchange channels (K+ excreted, Na+ retained) * **ADH**: controls rate/amount of water renal reabsorption via aquaporin-2
45
What stimulates the release of aldosterone and ADH?
↓BP or severely dehydrated * Body limits urine output to conserve/retain water releasing aldosterone (adrenal cortex) & ADH (posterior pituitary gland).
46
What system is aldosterone a part of?
renin-angiotensin system (vasoconstriction causes ⇧BP) * plays a crucial role in the regulation of renal, cardiac, and vascular physiology, and its activation is central to many common pathologic conditions including hypertension, heart failure, and renal disease
47
How does ADH stimulate re-absorption of water?
1. ADH binds to receptor 2. G-coupled protein receptor activated and PKA stimualtes Aquaporin-2 expression on apical membrane 3. water floods into cell via channels 4. water rapidly exits cell via aquaporin-3 channels in basolateral membrane 5. water flows into blood
48
Where is ADH high/low?
* left: no water being reabsorbed so low * right: lots of water being reabsorbed so high
49
How does aldosterone conserve water?
Via reabsorption of Na+ * Aldosterone secretion results in extra Na+ channels in apical membrane & Na/K pumps in basolateral membrane so influx of Na into cells + active pumping of Na into plasma (Cl- follows) retains both salt & water * Also stimulates thirst & ADH release & a potent vasoconstrictor
50
Physiological response of with a salt deficit
Na+ imbalance - Increased salt appetite and thirst * ↑ aldosterone: more Na+ reabsorbed (less excreted) * ↑ADH: more water reabsorbed (less excreted)
51
Physiological response with excess water loss
fluid imbalance * ↑ADH: more water reabsorbed (less excreted)
52
What are pressure receptors? | DRAW!
Special pressure sensors called baroreceptors (or venoatrial stretch receptors) located in the right atrium of the heart detect increases in the volume and pressure of blood returned to the heart. These receptors transmit information along the vagus nerve to the CNS.
53
What do low pressure receptors do?
In the atria and pulmonary vein (associated with ↑ renal sympathetic activity) detect/ correct for hypovolemia (body loses fluid) and restore circulating volume and BP (low to high)
54
What do high pressure receptors do?
In the aortic arch & carotid sinus (associated with ↓ renal sympathetic activity) detect/ correct for hypervolemia (fluid overload) and restores circulating volume and BP (high to low)
55
Main kidney functions
* sodium balance * potassium excretion * acid excretion * calcium/ phospate balance * erythropoesis
56
What is the kidneys responce to chronic kidney disease (CKD) and how can it be treated?
57
What are cases with excessive retention of Na+ and Cl-?
* Large amounts of sea water and/or fast infusion of saline * Hypersecretion of Aldosterone * congestive heart failure * renal failure * Hypernatremia (serum [Na+] >145 mmol/L)
58
What does large amounts of sea water/ saline cause?
excessive retention of Na+ and Cl- * body compensates and symptoms include hypernatremia → secretion of ANPs more Na+ excretion, hypervolemia, acute hypertension
59
Result of hypersecretion of aldosterone on electrolyte balance
excessive retention of Na+ and Cl- * i.e. Cushing’s syndrome, ↓K+, ↑blood pH, ↑BP
60
Result of congestive heart failure on electrolyte balance
excessive retention of Na+ and Cl- * ↓BP causes baroreceptors to think body needs volum so ↑Na+ * often includes renal failure to control Na+ reabsorption
61
Hypernatremia on electrolyte balance
Excessive retention of Na+ and Cl- A hyperosmolar condition due to a ↓ in total body water relative to Na+ * usually due to water deficiency so osmotic shift of water out of cells resulting in ↓ in intracellular water & brain volume
62
Cases with deficiency of Na+ and Cl-
* hyponatremia * underlying medical conditions * drinking too much water in endurance sports * ↑ renal loss/↓ reabsorption of Na+ * non-renal losses via GI
63
Result of hyponatremia on electrolyte balance
excess of water relative to solute (relative ratio)
64
Result of drinking to much water during endurance sport on electrolyte balance
deficiency in Na+ and Cl- via dilution * Body water levels rise, cells begin to swell * Neurologic problems due to osmotic shift of water into brain cells
65
What causes ↑ renal loss/↓ reabsorption of Na+?
* diuretics * diabetes (glucose = presence of excess osmotic solutes) * renal disease * ↓ aldosterone secretion/activity
66
What are non-renal losses of Na+ and Cl-?
losses via GI such as vomiting and diarrhea
67
Fill the table
68
Symptoms associated with fluid volume
affects BP & CNS function
69
Serum [K+] in hypokalemia
< 3.5 mmol/L
70
hypokalemia causes and symptoms
* causes: most commonly due to ↑ K+ excretion, but also inadequate intake or extra- to intracellular shift or combination * symptoms: usually related to muscular or cardiac function (membranes hyperpolarize)
71
Serum [K+] in hypokalemia
greater than 5.5 mmol/L
72
Causes and symptons of hyperkalemia
* causes: usually a combination of excessive intake, ↓ excretion or shift from intracellular to extracellular (i.e. low GFR +↑ intake of K+ foods) * symptoms: usually related to muscular or cardiac function – weakness/fatigue most common, but can lead to sudden death from cardiac arrhythmias (membranes hypopolarize)
73
Describe excessive dietary intake causing hyperkalemia
* Eating disorders or unusual diets (↑K+ foods, i.e. bananas, oranges, dried fruits, fruit juices, nuts, vegetables with ↓Na+) * heart healthy diets (↓Na+/↑K+) * ↑K+ in herbal supplements, sports drinks, salt substitutes or drugs
74
Describe why decreased excretion of K+ in hyperkalemia might occur
* Renal insufficiency or failure * Drugs (i.e. K+ sparing diuretics, NSAIDs, ACE inhibitors, trimethoprim – antibiotic that antagonizes Na+ channels in distal tubules)
75
Describe what causes the intracellular to extracellular shift in hyperkalemia
* diabetes mellitus * beta-blocker therapy * metabolic acidosis (diabetic ketoacidosis) * catabolic states
76
Describe inadequate dietary intake causing hypokalemia
* eating disorders * starvation * pica * alcoholism * dental/swallowing problems * low K+ TPN
77
Describe why increased excretion of K+ in hypokalemia might occur
* mineralocorticoid excess (i.e. Cushing syndrome, hyperaldosteronism, steroid therapy) * hyperreninism * osmotic diuresis (hyperglycemia) * GI losses (i.e. vomiting & diarrhea causing hypovolemia sp body tries to retain Na+), * hypomagnesemia * drugs (i.e. diuretics, methylxanthines) * genetic & renal disorders
78
Describe what causes the extracellular to intracellular shift in hyperkalemia
* alkalosis (metabolic or respiratory- increasing pH/loss of H ions) * insulin or glucose administration * refeeding * hypothermia
79
Fill in the chart
80
Symptoms associated with muscular function
nerve transmission, muscle contraction
81
What is the result of sweat on electrolyte balance?
losing water & electrolytes * Causes hypovolemia + a loss of sodium + insensible & obligate urine losses * Replacing with water only dilutes the bodies Na+ further causing hypoosmolarity
82
What are the AIs of Na+ and Cl-?
83
Na+ and Cl- AIs for pregnancy and lactation
AI does not change despite tissue building & plasma volume of fetus & added NaCl in milk * Na+: 1.5 g/d * Cl-: 2.3 g/d
84
Salt AIs for adults
3.8 g/day (note that salt is 40% Na) * Na+: 1.5 g/d * Cl-: 2.3 g/d
85
Upper limit of Na+ and Cl-
* Na+ = 2.3 g * Cl- = 3.6 g * = 6 g/day of Salt (NaCl)
86
How much sodium is associated with higher BP?
Na+ intake of 2.3 g/d is associated with higher blood pressure (vs 1.2 g/d)
87
How are Na+ and Cl- typically consumed?
Consumed mainly as NaCl which naturally low in fruits & veggies & higher in meats, but especially prevalent in process foods: * ~10% of intake naturally occurring in food * ~15% added at table * ~75% from food processing
88
What is the daily average intake of NaCl?
Daily average intake is highly variable (estimated by assessing salt intake or urinary excretion) * =2-5 g of Na (US) so 5-13 g NaCl * US median intake of Na from foods (not incl. salt added at table) is 2.3 g/d (women) & 4 g/d (men)
89
What is the recommended minimum intake of Na+ and Cl-?
We are physiologically better able to handle low salt intake * 500 mg Na * 750 mg Cl
90
Aside from NaCl, how else is Na added to food products?
* monosodium glutamate (MSG) * sodium citrate * sodium nitrite * sodium saccharin * baking soda (sodium bicarbonate) * sodium benzoate * hydrolyzed vegetable protein (HVP).
91
How does NaCl differ between 1/2 cup of fresh veggies vs. canned veggies?
* Fresh <0.04 g * Canned >0.2 g
92
sources high in sodium and chloride
93
Where is sodium used in the food industry?
* Color Developer: Promotes development of color in meats & sauerkraut * Fermentation Controller: Keeps organic action in check in cheeses, sauerkraut, baked goods * Binder: Holds meat together as it cooks * Texture Aid: Allows dough to expand & not tear * Preservative: Binds water, makes it unavailable to bacteria
94
What contribute to ↑ Na+ intake?
* convenience foods * ready-to-eat meals * canned foods * eating out frequently
95
How to reduce Na+ intake
* minimize processed foods * choose fresh foods * Read labels to compare foods and select reduced sodium option
96
Difference between salt and sodium
Not interchangeable * 1 g of salt contains 0.4 g Na+
97
Tips to reduce sodium intake
* Use herbs & spices to flavour foods * Avoid adding salt to your food when eating * Limit use of condiments * Buy fresh or frozen vegetables * Rinse canned foods (i.e. beans) to remove excess salt * Choose breakfast cereals that are lower in sodium * Buy low or reduced sodium versions or no salt added
98
What are the AIs for K+?
99
What is associated with >4.7 g/d of K+?
associated with ↓ risk of stroke, hypertension, osteoporosis & kidney stones
100
Why is AI higher for lactation?
Needs higher due to extra K secreted in breast milk * 5.1 g/d
101
How is K+ typically consumed?
K+ widely available in fruits, vegetables but dietary intake varies widely depending on dietary habits
102
What is the average intake of K+?
* Median consumption (NHANES III) = 2.2 g/d (F) & 3.3 g/d (M) * Only 10% of men & < 1% of women meet AI
103
What is the UL for K+?
No UL * may consume as much as 11 g/d without any consequences (kidney very good at excretion) * 18 g may cause problems ... No cases of hypokalemia reported from food but supplemental potassium should only be provided under medical supervision
104
Reccomended minimum intake of K+?
2 g/d
105
Food sources of potassium
High in fresh fruits & vegetables!!! * Particularly leafy green & root veg, vine fruit, also some in beans, peas, tree fruits * Also milk/yogurt, meats
106
How can potassium be used as a salt substitute?
Can ↑ K+ intake, providing 0.4 - 2.8 g K/tsp * 100% KCl * mixtures, 65% NaCl, 25% KCl, 10% MgSO4
107
What does processing do to the sodium and potassium content of foods?
As foods become more processed K+ is lost Na+ is gained

NUTR 302 (20 decks)

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