electrolytes Flashcards
What is the primary function of electrolytes in the body?
Electrolytes maintain electrochemical gradients through electrolytic and osmotic control. This is essential for:
Fluid balance
Electrical signal transmission (e.g., nerve impulses, muscle contractions)
Osmotic control across membranes
How are Na⁺, K⁺, and Cl⁻ distributed in the body? Provide normal concentrations inside and outside cells.
Sodium (Na⁺):
Outside Cell (ECF): 135–148 mmol/L
Inside Cell (ICF): 12 mmol/L
Potassium (K⁺):
Outside Cell (ECF): 3.8–5.5 mmol/L
Inside Cell (ICF): 150 mmol/L
Chloride (Cl⁻):
Outside Cell (ECF): 98–108 mmol/L
Inside Cell (ICF): 2 mmol/L
what charge does the cell cytoplasm maintain? why?
the cytoplasm maintains a highly negative charge due to the prescence of anionic molecules
- must maintain the balance by pumping in K+
What mechanisms regulate electrolyte distribution and movement?
Passive Diffusion: Movement along concentration gradients through ion channels
Active Transport: Movement against gradients, requiring ATP
Selective Membrane Permeability: Controls movement of proteins, phosphates, and ions to maintain osmotic balance
Describe the fluid compartments in the body. what do you expect in terms of distribution? what is it comprised of?
Intracellular Fluid (ICF): ~65% of total body water, contained within cells
Extracellular Fluid (ECF): ~35%, includes:
-Intravascular Fluid (Plasma): 5–8%
-Interstitial Fluid (3rd Space): Fluid between cells (~25%)
-Transcellular Fluid: 1–2%, e.g., cerebrospinal fluid
How does the Na⁺/K⁺-ATPase pump work, and what is its significance? what does it drive in the body?
Pumps 3 Na⁺ out and 2 K⁺ in per ATP hydrolyzed.
Maintains:
1) Electrical Gradient: More negative inside the cell.
2)Chemical Gradient: Higher Na⁺ outside, higher K⁺ inside.
Drives:
Action potential propagation (nerve/muscle function).
Transport of nutrients (e.g., glucose, amino acids).
Regulation of cell volume.
What role does the Na⁺/K⁺-ATPase pump play in absorption?
the active absorption of Na+ creates an electrochemical gradient tht drives the passive transport of Cl-, amino acids, glucose and water
What is the significance of asymmetric transporter distribution in epithelial cells?
Asymmetric distribution ensures:
1) Active absorption of nutrients and electrolytes.
2) Efficient passive diffusion of ions and water.
3) Directional movement of substances across epithelial barriers.
Summarize the intestinal absorption efficiency of Na⁺, Cl⁻, and K+
Na⁺: 95–100% absorbed via co-transporters, exchangers, and diffusion
Cl⁻: Absorbed with Na⁺ or via paracellular routes
K⁺: 85–90% absorbed, primarily in the colon (passive or H⁺/K⁺ pump)
How does the Na⁺ gradient drive nutrient transport?
many transport systems rely on co transportation driven by secondary active transport
What is the role of the Na⁺/K⁺-ATPase pump in maintaining potassium (K⁺) homeostasis? how does absorption differ during various states?
tightly regulated
-Maintained through kidney regulation, muscle uptake, and ECF buffering
-Skeletal muscle takes up excess K⁺ from ECF after meals, or during exercise
90% reabsorbed in the kidneys;
100% during K⁺ deprivation or fasting
what do you expect for levels of K+ intake vs excretion?
levels of excretion are similar to intake
What is the resting membrane potential (RMP), and how is it maintained?
RMP = -70 mV, maintained by:
1) high (-) in the cell causes chemical forces to push K+ out of the cell
2) K⁺ Leak Channels: K⁺ leaves the cell passively (asymmetric # of channels)
- overall (-) inside
3) Electrical forces attract K⁺ back into the cell due to (-) inside the cell
4) steady state occurs for PASSIVE movement at -70mv
5) Na⁺/K⁺-ATPase Pump: maintains gradients
6) Cl⁻ movement is passive, following the membrane potential
How does the Na⁺/K⁺-ATPase pump support action potential generation? explain how the cell becomes depolarized and repolarized.
Depolarization:
Voltage-gated Na⁺ channels open, Na⁺ rushes into the cell, reducing the RMP, causing all of the volatge gated channels to open
Repolarization:
Voltage-gated K⁺ channels open more slowly, allowing K⁺ to leave and restore the RMP
Na⁺/K⁺ pump resets ion concentrations post-action potential to maintain excitability
Describe the effects of hyperkalemia and hypokalemia on membrane potential. what causes it? what occurs as a result? what symptoms can be attributed to each? what [ ] do you expect for each moleucle?
Hyperkalemia (↑ECF K⁺):
Depolarization; making cells more excitable.
-Severe cases cause arrhythmias and cardiac arrest (>8 mmol/L).
Hypokalemia (↓ECF K⁺):
Hyperpolarization; making cells less excitable.
-Causes muscle paralysis, and alkalosis if severe (<3.5 mmol/L)
What factors influence K⁺ movement between ECF and ICF?
Hormones (Insulin, Catecholamines): Stimulate K⁺ uptake into cells
pH Changes: Acidosis promotes K⁺ release from cells; alkalosis promotes uptake
Osmolarity: Impacts intracellular and extracellular K⁺ gradients
What are the causes of excess water loss?
1) sweating
2) GIT
-infections, malabsorption
-toxins that increase NaCl secretion into lumen, causing water to flow
3) dehydration
what is the typical osmolarity level? how does the body compensate for changes?
300mOsm
- the kidney controls the rate of water reabsorption to regulate the changes in water excretion
what occurs in the renal tubules of the kidney? what is absorbed in which part of the loop of henle? how is this done?
passive water re-absorption coupled to active solute re-absorption
1) Descending Limb: Impermeable to solutes; only water is reabsorbed.
2) Ascending Limb: Impermeable to water; Na⁺ and Cl⁻ are actively reabsorbed
What is the countercurrent multiplier system?
A mechanism in the Loop of Henle that:
-Creates an osmotic gradient (from cortex to medulla)
-Concentrates or dilutes urine based on the body’s needs
-Maintains plasma osmolarity between 50–1200 mOsm/L depending on hydration
how effective are the kidneys at dilution and concentration of plamsa? provide numbers?
can dilute urine to 1/6 of plasma and concentrate it up to 4x
-urine osmolarity varies greatly
what is included in the filtrate from the glomerulus? what occurs to these solutes after they enter the bowmans capsule?
water, salt, HCO3-, GLU, AA, creatine, urea
-which are reabsorbed in the proximal tubule
how is the [urine] impacted by the loop of henle?
concentrated urine is formed when tubular fluid equibrilates with the hypertonic interstitium while dilute urine is formed when the tubular fluid equibrilates with the hypotonic interstitium
How do ADH and aldosterone regulate water and electrolyte balance? what are they stimulated by? what do they do? what is their effect?
Stimulated by dehydration or decreased BP (aldosterone); both work in distal convoluted tubule and collecting duct
Aldosterone:
-Stimulates Na⁺ reabsorption and K⁺ excretion
-Water follows Na⁺, increasing fluid retention
-part of renin-angiotensin system which causes vasoconstruction to increase BP
ADH (Antidiuretic Hormone):
-regulates water reabsorption through [aquaporins] in the collecting duct.
-Reduces urine volume and by absorbing water
