The seven most important
electrolytes in terms of body
functioning are
- Sodium (Na+)
- Potassium (K+)
- Chloride (Cl-)
- Calcium (Ca2+)
- Phosphate (HPO42-)
- Magnesium (Mg2+)
- Bicarbonate (HCO3-)
Role of Electrolytes in the Body
The body contains many ions (electrolytes) essential for physiological functions.
Some electrolytes assist in transmitting electrical impulses in neurons and muscle cells.
Others help stabilize protein structures, including enzymes.
Certain ions support the release of hormones from endocrine glands.
All plasma electrolytes contribute to osmotic balance, regulating water movement between cells and their environment.
Sodium (Na⁺) and Fluid Balance
Sodium is the main cation of extracellular fluid, contributing to ~50% of the osmotic pressure gradient between cells and their environment.
Freely filtered through the kidney’s glomerular capillaries.
Most sodium is reabsorbed in the proximal convoluted tubule, but some remains in the filtrate.
Therefore, normal amounts of sodium are excreted in urine.
Potassium (K⁺) and Membrane Potential
Potassium is the major intracellular cation.
Crucial for establishing the resting membrane potential.
Helps reset neurons and muscle fibers after depolarization and action potentials.
Potassium and Osmotic Pressure Regulation
Potassium has minimal influence on osmotic pressure.
Blood and CSF contain low K⁺ levels, tightly regulated.
Regulation maintained by the Na⁺/K⁺ ATPase pump in cell membranes.
Prevents large osmotic shifts despite high intracellular potassium concentration.
Chloride in Electrolyte Balance
Chloride is the main extracellular anion.
Major contributor to the osmotic pressure gradient between ICF and ECF.
Helps maintain electrical neutrality by balancing extracellular cations (especially Na⁺).
Renal chloride movement (secretion & reabsorption) typically follows sodium handling in the kidneys.
How are sodium, chloride, and potassium regulated in the renal collecting tubule, and which hormones control this process?
Na⁺ and Cl⁻ are reabsorbed from the renal filtrate in the collecting tubule.
K⁺ is secreted into the filtrate at the same site.
This electrolyte exchange is primarily controlled by aldosterone and angiotensin II.
What are the major roles of calcium in the body, both structurally and functionally?
Body contains ~1 kg of calcium, mostly in bones/teeth for structural hardness.
Acts as a mineral reserve for calcium and its salts.
Also functions as an extracellular cation in blood.
Essential for:
Muscle contraction
Enzyme activity
Blood coagulation
Neurotransmitter release from neurons
Hormone release from endocrine glands
How does a presynaptic neuron release neurotransmitters at the synaptic cleft?
Action potential travels down the axon to the synaptic end bulb.
Voltage-gated Ca²⁺ channels open, allowing calcium to enter the neuron.
Rising intracellular Ca²⁺ triggers synaptic vesicles to undergo exocytosis, releasing neurotransmitters into the synaptic cleft.
How are blood calcium levels regulated by parathyroid hormone, calcitriol, and calcitonin?
Parathyroid Hormone (PTH) is the main regulator of blood calcium:
Increases osteoclast activity → more bone resorption → ↑ blood Ca²⁺
Increases Ca²⁺ reabsorption in the kidneys
Calcitriol (active Vitamin D) increases calcium absorption in the small intestine.
When blood calcium is too high, the thyroid gland releases Calcitonin:
Inhibits osteoclasts
Promotes calcium uptake into bones and teeth.
Where is phosphate found in the body, and what roles does it serve?
~85% of phosphate is stored in bones and teeth as calcium-phosphate salts.
Acts as a weak base, helping to buffer intracellular fluids.
Present in key cellular components:
Phospholipid membranes
ATP (energy molecule)
Nucleotides (DNA/RNA)
Physiological buffers
What are the major functions and locations of magnesium in the body?
Mostly stored in the bone matrix as magnesium salts.
Second most common intracellular cation.
Activates enzymes involved in carbohydrate and protein metabolism.
Required for proper function of the Na⁺/K⁺ pump.
Essential for:
Neuromuscular activity
Neural transmission in the CNS
Myocardial (heart) function
How is bicarbonate produced in the body, and what role does it play in blood chemistry?
Second most abundant anion in the blood.
Maintains acid–base balance (major blood buffer).
Produced when CO₂ + H₂O combine (via carbonic anhydrase) to form carbonic acid (H₂CO₃).
Carbonic acid dissociates into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺).
What is a buffer, and how does it help maintain pH stability in body fluids?
A buffer prevents large or sudden changes in fluid pH.
Works by dampening changes in H⁺ concentration when excess acid or base is present.
Most buffers can act as:
Weak acids → take up OH⁻
Weak bases → take up H⁺
Helps maintain acid–base homeostasis in the body.
How do the body’s buffer systems regulate pH, and how quickly does each system respond?
3 systems
Chemical buffers in the blood act within seconds to stabilize pH.
Respiratory system adjusts pH within minutes by exhaling CO₂.
Renal system regulates pH by excreting H⁺ and conserving bicarbonate, but requires hours to days for full effect.
Which buffer systems help maintain blood pH within the 7.35–7.45 range?
Phosphate buffer system
Protein buffer system
Bicarbonate–carbonic acid buffer system
How does the phosphate buffer system function, and where is it most effective in the body?
Most effective in intracellular fluid (cytosol) and kidney filtrate (urine).
Composed of two ions:
HPO₄²⁻ (monohydrogen phosphate) → acts as a weak base.
H₂PO₄⁻ (dihydrogen phosphate) → acts as a weak acid.
Together they buffer changes in H⁺ to maintain pH stability.
How does the protein buffer system help regulate acid–base balance in the body?
Most abundant buffer system in body cells and plasma.
Proteins act as both weak acids and weak bases.
Carboxyl groups (–COOH) act as weak acids → counter rising pH by releasing H⁺.
Amino groups (–NH₂) act as weak bases → counter falling pH by binding H⁺.
Provides rapid and versatile pH stabilization in cells and plasma.
How does hemoglobin function as the most important protein buffer in acid–base balance?
CO₂ from tissues diffuses into erythrocytes and combines with water → forms carbonic acid.
Carbonic acid dissociates into bicarbonate (HCO₃⁻) and H⁺.
Bicarbonate leaves the RBC and is replaced by chloride ions (chloride shift).
H⁺ is buffered by hemoglobin, preventing major pH changes.
Hemoglobin binding H⁺ facilitates the Bohr effect → promotes O₂ release at tissues.
What is the most important buffer system for maintaining acid–base balance in the blood, and how does it function?
The bicarbonate–carbonic acid buffer system is the primary blood pH regulator.
Bicarbonate (HCO₃⁻) acts as a weak base, binding excess H⁺.
Carbonic acid (H₂CO₃) acts as a weak acid, donating H⁺ when needed.
Together, they stabilize blood pH within the 7.35–7.45 range.
Question: Why is the bicarbonate–carbonic acid buffer system most effective in resisting blood acidification?
Bicarbonate (HCO₃⁻) and carbonic acid (H₂CO₃) exist in a 20:1 ratio in normal blood pH.
Having 20× more bicarbonate makes the system highly effective at buffering added acids.
This is essential because most metabolic wastes produced by the body are acidic.
ow does the respiratory system regulate blood pH through control of carbonic acid levels?
CO₂ in the blood reacts with water to form carbonic acid, and both remain in equilibrium.
When CO₂ rises (e.g., holding breath), more carbonic acid forms → pH decreases (more acidic).
Increasing breathing rate or depth removes more CO₂ → reduces carbonic acid → pH increases (more alkaline).
ow does changing breathing rate at rest affect CO₂ levels and blood pH?
Increased breathing rate → ↓ CO₂ → ↓ H⁺ → temporary increase in blood pH (more alkaline).
Decreased breathing rate → ↑ CO₂ → ↑ H⁺ → temporary decrease in blood pH (more acidic).
Hemoglobin’s oxygen affinity shifts with pH and CO₂:
High pH / Low CO₂ → ↑ hemoglobin–O₂ affinity.
Low pH / High CO₂ → ↓ hemoglobin–O₂ affinity (Bohr effect).
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homeostasis 124
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METABOLISM37
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metabolism28
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endocrine34
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endocrine system 219
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energy delivery and eeg25
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respiratory35
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respitory 253
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respitory 327
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blood 131
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blood 239
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blood vescels53
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cardiovascular31
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cardiovascular 221
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cardiovascular 319
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things i need to know37
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blood pressure 120
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blood pressure 223
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urine 12
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urinary 236
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urine 3 and fliud balance29
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muscle pysiology 122
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muscle physiology 222
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acid and base41
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diving response 115
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control of breathing27
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autonomic control14
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diving response 213
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high altitude 127
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high altitude 221
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space physiology13
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things to know26
