Unit 1 Chapter 3 Cellular Environment, Fluids & Electrolytes, Acids & Bases

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What is an Electrolyte?

Electrolytes are minerals in your blood and other body fluids that carry an electric charge.
A substance that dissociates into ions in aqueous solution and conducts electricity.


Common Electrolytes

sodium (Na+), potassium (K+), chloride (Cl-), bicarbonate (HCO3-), magnesium (Mg++), calcium (Ca++) phosphate (PO43-)


Function of Electrolytes

Volume and osmotic regulation (controlling the flow of H2O), regulate muscle and nerve function, (myocardial function) maintain acid-base balance , maintain fluid balance, enzyme cofactors


When any electrolyte is measured, is it the ECF or ICF that is measured?

The ECF (extracellular fluid) is measured. The test would look at the plasma which is also known as the ECF.


Make up of the Body's Water

2/3 is Intracellular fluid [ICF] (inside the cell)
1/3 is extracellular fluid (ECF)


Equivalent Weight

...1 mole is Avogadro's number (6.023 x 10^23) of something (molecules, atoms, ions, donuts)
The term equivalent is only used for compounds, acids, bases and salts
In water these compounds ionize into cations and anions
An equivalent weight of something is the amount of that compound that will liberate one mole of cations or anions
EG 1 mole of HCl = H+ Cl- (2 equivalents)[acid]
1 mole of KOH= K+ OH- (2 equivalents [base]
1 mole of KCl = K+ + Cl- (2 equivalents) [salt because there is no H or OH


Equivalent and Milliequivalent

In the body there are very small amounts (by weight) of ions, so they are listed on mOsm/L or mEq/L
To calculate - simply move the decimal point like you do for liters to milliliters
EG Na+ = 0.14 M =0.14 Moles/l=140 mmmoles/L
= 136-146 mEq/L
K+ = 3.4-5.0 mEq/L (move the decimal place to the RIGHT 3 places = ?????????????????


Osmotic Forces

Water movement between the intracellular fluid compartment and the extracellular compartment is primarily a function of Osmotic Forces.



Concentrations of two fluids separated by a membrane are equal.



The concentration of the ECF is higher than the concentration of the ICF. The net movement of water is from the ICF to the ECF
Cells will loose water and shrivel,
The concentration of solvent (water) outside the cell is higher than the concentration of solvent (water) in the cell



A ______________ solution has a lower osmotic pressure than the solution inside the cell - as a result there is a net flow of water into the cell, causing it to swell

Water moves from the ECF to the ICF causing cell swelling & lysis.


What do capillaries do?

Capillaries are small, microscopic blood vessels that run through the whole body. Oxygen and glucose diffuse from the arterial side into the blood and carbon dioxide an waste diffuses out of the venual.


Precapillary sphincters

Smooth muscle cells, guard entrance into capillary, determines into which capillary blood will flow


How does Blood pass through the capillary?

RBC's must fold to pass through, thus the reason for the biconcave structure of the RBC.


Capillary Exchange

Capillary exchange: the movement of substances into and out of capillaries
Most important means of exchange: diffusion. Lipid soluble cross capillary walls diffusing through plasma membrane. E.g., O2, CO2, steroid hormones, fatty acids.
Water soluble diffuse through intercellular spaces or through fenestrations of capillaries. E.g., glucose, amino acids.
Blood pressure, capillary permeability, and osmosis affect movement of fluid from capillaries.
Fluid moves out of capillaries at arterial end and most but not all returns to capillaries at venous end.
That which remains in tissues is picked up by the lymphatic system then returned to venous circulation.
This means that the capillary delivers nutrients on the arteriole side and picks up wastes on the venule side


Capillary filtration

The forcing of fluid and solutes through the capillary wall pores from the intravascular fluid into the interstitial fluid.


Capillary Reabsorption

Process by which water moves by osmosis from the interstitial fluid into protein-rich plasma at the venous end of a capillary bed.


Starlings Law

ECF & ICF fluid shifts occur related to changes in pressure within the compartments
fluid flows only when there is a difference in pressure
Pressure is 9mmHg.


Hydrostatic Pressure

The pressure exerted on the wall of a vessel that helps capillary diffusion.
(like water pressure in pipes)


Interstitial Fluid Osmotic Pressure

If plasma proteins pathologically leak into the interstitial fluid, the leaked proteins exert an osmotic effect that tends to promote movement of fluid OUT of the capillaries into the interstitial fluid.
[the force of water trying to dilute out higher concentration of solutes in blood]



Swelling of tissues, sometimes caused by inflammation letting into many white blood cells (decreasing oncotic pressure at the end of the capillaries & not letting as much water back into capillaries & staying in tissues).
More fluid going into the ICF than normal.



Exceeds the ability of venules to reabsorb the fluid causing edema. The fluid has no where to go but to stay in the ECF.


Decreased Plasma Protein

Protein in the capillary is decreased and means less flow of water from the ICF to the capillary.
Fluid enters the interstitial space leading to edema.
Net filtration +26 mmHg Net filtration pressure -8mmHg


Increased Vascular Permeability

Capillaries become more permeable causing exudate to leak into the tissue resulting in edema/swelling, endothelial cells retract(from histamine/prostaglandins) creating larger spaces.
Pressure does not change but vessel permeability increases causing capillaries to become leaky.
Fluid enters the interstitial space leading to edema.
EG Burns


Thirst Center

The regulation of daily water gain.
-Thirst center is located in the hypothalamus
-The hypothalamus detects increases in the blood osmolarity
-blood osmolarity is the concentration of blood which means that we don't have enough H2O , located within the hypothalamus, it is controlled by intracellular dehydration & decreased blood volume.



A condition in which fluid loss exceeds fluid intake and disrupts the body's normal electrolyte balance
Water losses exceeds gains
Decrease in blood pressure
Increases blood osmolarity - which means an increase in blood solutes


Receptors for Dehydration

Hypothalamus, kidneys, baroreceptors [pressure receptors] in the arteries, neurons in the mouth that detect dryness



Enzyme that is produced by the kidney; important for blood pressure and volume regulation; catalyzes the conversion of circulating angiotensinogen to angiotensin I.



Renin is released by kidneys in response to decreased blood volume; causes angiotensinogen to split & produce angiotensin I; lungs convert angiotensin I to angiotensin II; angiotensin II stimulates adrenal gland to release aldosterone & causes an increase in peripheral vasoconstriction



1. JGA senses blood pressure
2. JGA signals kidney to release renin
3. Renin activates angiotensins I and II
4. Angiotensin 2 constricts arterioles, raising bp, and tells the adrenal cortex to release aldosterone


ACE Inhibitors

(-pril) drugs) means Angiotensin Converting Enzyme
-Action: decreases levels of angiotensin II and increases bradykinin by blocking ACE. Vasodilation, reduces blood volume, prevents or reverses pathologic changes in heart and vessels


What are the three characteristics that affect the movement of water through body compartments?

Hydrostatic pressure - the force generated by water. Hydrostatic pressure pushes water OUT of a compartment
Osmotic pressure - the force exerted by solutes. Osmotic pressure draws water into a compartment. This force is dependent only on the concentration of particles (osmolality) in a solute.
Membrane Characteristics - the ability of water and solutes to move between compartments.


Starlings Law of the Capillary

Net hydrostatic pressure and net osmotic pressure determine the movement of water between compartments


Hydrostatic Pressure

Pushes water out of a compartment


Osmotic Pressure

Draws water into a compartment


Net hydrostatic pressure

The capillary hydrostatic pressure minus the interstitial hydrostatic pressure


Net Osmotic Pressure

The capillary osmotic pressure minus the interstitial osmotic pressure.


Starlings Law

Is the mathematical representation of the movement of water between compartments


Positive Net Filtration Pressure

If net filtration pressure is positive, water moves from the capillary into the interstitium


Negative Net Filtration Pressure

If net filtration pressure is negative, water moves from the interstitium into the capillary


Equation for Starling's Law

Contains two forces: hydrostatic pressure and osmotic pressure


Consequences of increased venous hydrostatic pressure

Peripheral edema
Pulmonary edema
ascites [The accumulation of fluid in the peritoneal cavity, causing abdominal swelling.]


Does an increased arterial BP cause capillary hydrostatic pressure?

No - An increased arterial blood pressure does NOT cause an increase in capillary hydrostatic pressure


What does increased venous hydrostatic pressure cause?

Increased venous hydrostatic pressure causes an increase in NET filtration pressure.


Congestive Heart Failure (CHF)

The inability of the heart to maintain adequate tissue perfusion. Blood accumulates in the pulmonary venous circulation which increases the hydrostatic pressure in the pulmonary capillaries


Hypertension [Pathology]

Exceeds the ability of venules to reabsorb the fluid causing edema. Fluid has no where to go but to stay in the ECF.


Decreased Plasma Protein

Protein in the capillary is decreased meaning less flow of water from the ICF to the capillary.


Increased Vascular Permeability

Capillaries become more permeable causing exudate to leak into the tissue resulting in edema/swelling, endothelial cells retract(from histamine/prostaglandins) creating larger spaces


Anti-diuretic Hormone

Target: Renal Collecting Ducts
Action: Water reabsorbed into blood, decreased plasma osmolality, less urine.

A hormone secreted by the pituitary gland that increases the permeability of cells membranes, so they absorb more water, especially from urine, that results in small amounts of concentrated urine.

The secretion of ADH is initiated by an increase in plasma osmolality or a decrease in circulating blood volume and a lowered blood pressure.


Atrial Natriuretic Peptide

Target: Renal proximal tubule.
Action: Inhibits Na+ reabsorption into blood causing more urine to be excreted.

A peptide hormone secreted by cardiac atrial cells in response to atrial distension (increased blood flow); causes increased renal sodium excretion and as such lowers blood pressure (antagonizing aldosterone).

Lowers blood volume and pressure by promoting Na+ and water loss.


Excessive Water Consumption

A decrease in plasma and interstitial osmolarity causes water to move into the intracellular environment, resulting in cellular swelling. AKA - water intoxication


Hypernatremia (Na+)

Altered fluid and electrolyte balance
s/s edema, hypertension, confusion, seizures
(>146 mEq/L)
-cellular shrinking
-Oliguria and Anuria (fluids moving out of the cell



Patient has Na+ <135 mEq/L

Caused by:
1. Na+ Loss (absolute); diuresis, burns and sweating, GI losses (vomiting, diarrhea)
2. H2O Excess (dilutes concentration of Na+)
~Hypotonic IVs or inadequate replacement after exercise (Taking in or administering "free" water)
3. Fluid Shifts: renal failure, hyperglycemia
~Other solutes cause a shift of H2O into the plasma
~Returns to normal when underlying cause is corrected

Water moves into the cells -> cells swell
1. Muscle cramps
2. Fatigue
3. Lapse into coma
4. Nauseated
5. Edema
6. Hypotension


Where is the body's sodium concentration maintained?

In the kidneys through the (1) glomerular filtration system (2) renin-angiotensin-aldosterone system


What are Natriuretic Peptides?

Hormones produced by the heart, brain and kidneys that influence sodium reabsorption/excretion and that cause the release of Na in the urine. Include atrial natriuretic peptides (ANP), brain natriuretic peptides (BNP) and urodilantin--kidney (rare).



Patient has K+ <3.5 mEq/L (critical if <2.5 mEq/L)

Caused by:
1. "Obligatory Ion" - moves out w/ fluid
2. Insufficient/Decreased Intake (diet, surgery)
3. Excessive losses (diarrhea, diuretics, laxatives)
4. Transcellular Shift
excessive insulin/epinephrine (diabetics who get too much insulin)
metabolic alkalosis (LOW H+, so K+ enters cells so H+ can come out and regain electroneutrality)

Manifestations: due to LESS excitability of the cell membrane (Sluggish cells and action potential)
1. Nausea/Vomiting, abdominal distention, LOW or NO bowel sounds, Anorexia (DECREASED SMOOTH MUSCLE CONTRACTION)
2. Muscle weakness, fatigue, cramps (DECREASED SKELETAL MUSCLE)
3. Irregular Pulse, Postural Hypotension (LOW BP when standing UPRIGHT)
4. DECREASED deposit of glucose and glycogen
5. Inability to concentrate Urine -> DFV; chronic LOW K+ -> renal cell damage



Patient has K+ > 5.5 mEq/L (critical if > 6.5 mEq/L)

Caused by
1. Renal Failure
2. Aldosterone deficiency (LOSE sodium and HOLD on to potassium)
3. Excessive administration of potassium
4. Tissue trauma, burns, crushing injuries, extensive surgeries (tissues lyse and open up and release K+)
5. Hemolysis of blood sample (red blood cells that lyse when blood is drawn; perhaps from tiny needle)
6. Transcellular Shift
Insulin Deficiency (K+ level builds in ECF)
Metabolic Acidosis
7. Hypoxia - LOW oxygen; can't run Na+/K+ pump and K+ leaks out of cell
8. Altered conductivity in the heart
9. Cell membrane is depolarized (more + than normal)

Weakness, Paresthesia (numbess and tingling), Bradycardia (irregular Heart Rate), Cardiac Arrest



(8.6 -10.5 mg/dl) is necessary in many metabolic processes
-Main cation in bones and teeth
-Cofactor in the clotting pathways
-Key: calcium blocks sodium channels



(2.5-4.5 mg/dl) is found throughout the body.
-Bone (calcium phosphate = hydroxyapatite)
-Creatine phosphate (brain and muscle energy source
-ATP (energy currency)


Calcium & Phosphate

The concentrations of calcium and phosphate are inversely related -
If one increases, the other decreases


What system in the body maintains calcium and phosphate?

The renal system


Why is Vitamin D important to the body?

-Important for intestinal absorption of Ca++
-In the absence of vitamin D, blood Ca++ drops and bones become soft and flexible (bones are mostly collagen because mineral portion is lacking)
-In children - known as Rickets



childhood disease caused by deficiency of vitamin D and sunlight associated with impaired metabolism of calcium and phosphorus



calcium >12.5 mg/dL
phosphate < 2.0 mg/dl
- most often occurs when calcium is mobilized from the bony skeleton, due to malignancy or prolonged immobilizatoin
-Decreased neuromuscular excitability (hyperpolarization)
-Increased bone fractures
-Kidney stones



calcium <8.5 mg/dl
phosphate >4.5 mg/dl
-increased neuromuscular excitability (partial depolarization)
-Muscle cramps



-Intracellular cation
-Plasma concentration 1.8 - 2.4 mEq/L
-Acts as a cofactor in cellular reactions
--important for protein and nucleic acid synthesis
-Required for ATPase activity
-KEY: decreased acetylcholine release at the neuromuscular junction (NMJ)
EG - Given in pre-eclampsia



Magnesium > 2.5 mEq/L
- skeletal muscle depression
- Bradycardia
- Muscle weakness



Magnesium < 1.5 mEq/L
- occurs more frequently than hypermagnesemia -
- may aggravate manifestations of alcohol withdrawal, such as delirium tremors (DT)
- chronic alcoholism is the most common cause
-Neuromuscular irritability
-Hyperactive reflexes



The pH scale measures the acidity or the opposite (alkalinity) of a substance. 7 is the neutral midpoint of the scale, values below which represent increasing acidity, and above which represent increasing alkalinity.


What is a pH of 7?

Neutral (equal amounts of H+ and OH- ions


What is a pH of > 7?

Alkaline/base (more OH- ions than H+ ions)


What is a pH of <7?

Acidic (more H+ ions than OH- ions)


What are Buffers?

Solutions that moderate pH changes
Act as a H+ and/or OH- "sponge" so that pH is kept relatively constant


What is the most important buffer system in the human body?

Carbonic acid-bicarbonate buffer system


Carbonic-acid/bicarbonate buffer system

A key buffer system in the body.

Carbonic acid (H2CO3) can act as a weak acid and the bicarbonate ion (HCO3-) can act as a weak base. Hence, this buffer system can compensate for either an excess or a shortage of H+.

EG. If there is an excess of H+, HCO3- can function as a weak base and remove the excess H+, becoming H2CO3.


What two organ systems in the body regulate acid/base balances?

Lungs (respiratory system) retain or excrete CO2
Kidneys (metabolic system) retain or excrete HCO3-


Acidosis & Alkalosis in the Body

The respiratory system and renal system must work together to maintain the body's appropriate pH.
-The respiratory system affects pH by changing the pCO2 level
-The kidneys affect pH by retaining HCO3-



Target: Renal distal tubule
Action: Na+ and Chloride are reabsorbed into the blood. K+ is excreted into urine usually resulting in more urine.


ECF Compartments

Interstitial space (fluids/lymph)
Intravascular space (plasma and blood vessel compartments)
Other ECF compartments include:-
**transcellular fluids such as the synovial, intestinal, biliary, hepatic, pancreatic & cerebrospinal fluids; sweat, urine and pleural, synovial, peritoneal, pericardial, and intraocular fluids.