Fluid, Electrolyte and Acid-Base Balance- slides

percentage of body fluid

human body 45-75%, depends on age and amount of adipose and skeletal tissue

fluid %….

decreases with age, infants (highest %), elderly (lowest%)

fluid %…

decreases with increased body fat , Adipose (20% water) , Skeletal (75% water)

water fluid % (most to least)

• Infant (75%)

• Children (65%)

• Adult male (60%)

• Adult female (55%)

Fluid in our body

Intracellular (ICF) and Extracellular (ECF)

• ICF- 2/3 of total body fluid

• ECF- 1/3 of total body fluid (interstitial fluid (2/3), blood plasma (1/3))

Do male or Female have more fluid %?

Males have more skeletal muscle, which retains 75% water

Females have more adipose tissue, which retains 20% water

total body fluids include…

• intracellular fluid

• interstitial fluid

• plasma

• gastric juices

• CSF

• lymph

• serous fluid

Hypertonic solution

Occurs when excess extracellular fluids are lost → cells dehydrate by osmosis

(cells shrink due to the movement of water from the cell to the extracellular fluid as water moves with salt)

Hypertonic solution

Occurs when excess water is added the extracellular fluid compartment → cells gain water by osmosis (cells swell due to water moving into cell from the extracellular fluid to the cell)

Order of hypertonic solution

1. Water is lost from extracellular fluid compartment

2. Solute concentration increases in extracellular fluid compartment

3. Water leaves the cells by osmosis

4. Cell shrinks (shrivels)

Order of hypotonic solution

1. Excess water is added to extracellular fluid compartment

2. Solute concentration of extracellular fluid compartment decreases

3. Water enters cells by osmosis

4. Cell swells

To remain properly hydrated

fluid intake= fluid output

Fluid intake is about…

2500ml/day

• Pre-formed H2O (2300ml/day)

• Metabolic H2O (200ml/day)- cellular respiration by product

Fluid output is about…

2500 ml/day

• sensible(feces/urine) and insensible(expired air /sweat/evaporation/perspiration)

• facultative(urine-controlled) and obligatory(through lungs/skin)

Another factor of maintaining water gain and loss

• Increases in plasma osmolarity(concentration) triggers thirst and release of ADH(conserves water)

Fluid imbalance

Occurs if fluid intake doesn’t = fluid output

Osmolarity- constant (isotonic fluid is lost or gained)

• volume depletion

• volume excess

Osmolarity changes- water gained or lost

• dehydration (losing only water-sweating)

• hypotonic hydration (drinking a lot of water, dilutes other solutes- blood)

And

• fluid sequestration (excess fluid accumulation in a particular location

Water intoxication (hypotonic hydration)

Drinking water faster than the kidneys can excrete it (can lead to convulsions, coma and death)

• Hyponatremia: low Na+(sodium) in blood → decreases osmolarity

• Excessive blood loss, sweating, vomiting or diarrhea couple with intake of plain water → decreased sodium concentration of interstitial fluid and plasma (hyponatremia) → decreased osmolarity of interstitial fluid and plasma (hypotonic) → osmosis of water from interstitial fluid into intracellular fluid → Water intoxication (cells swell) → convulsions, coma, and death

Edema

• fluid sequestration(body fluid distributed abnormally)

• caused by:

abnormal changes in the cardiovascular system

abnormal blood composition

changes to lymph vessels (chemotherapy or lymph blockages)

Means of regulating fluid balance

• monitor blood volume

• blood pressure

• blood plasma osmolarity

How does fluid intake increase blood volume?

• more blood in blood circulation → increased BP

• increased BP

• decreased osmolarity( if water gain exceeds solute gain)

Fluid intake increases blood volume by adding water to the bloodstream, which raises the overall volume of plasma. This can lead to increased blood pressure and improved supply of nutrients and oxygen to tissues.

How does fluid output decrease blood volume?

• decreased BP

• increased osmolarity (if more water is lost then solutes)

fluid loss through urine, sweat, or respiration reduces blood circulation volume, leading to lower blood pressure and increased osmolarity. This occurs when output exceeds intake.

Main hormones in fluid regulation and solute output..

Decrease urine output(reabsorb water, increased BP), increase blood volume and pressure

• ADH

• Aldosterone

• Angiotensin II

Increased urine output, decreased blood volume and pressure ( sodium is excreted and water follows sodium → more urine)

• ANP(atrial natriuretic peptide)

These hormones include ADH, Aldosterone, and Angiotensin II, which work to increase blood volume and pressure by reducing urine output, while ANP promotes increased urine output, decreasing blood volume and pressure.

H2O follows…

• salt

• Na+ excreted → water follows → decrease blood volume

• Natriuresis: excessive loss of sodium in urine

• H2O follows Na+ excretion in urine, leading to a decrease in blood volume.

What main factor determines body fluid volume?

• extent of urinary SALT loss

What main factor determines body fluid osmolarity?

• extent of URINARY water loss

Role of ADH in regulation of water output

• produced by hypothalamus

• stored in posterior pituitary

• constrict arterioles

- increase BP in SA

- reduce blood loss

- conserve water

• increased absorption of water in kidneys

Binding of ADH to cell receptors of collecting tubes …

• stimulates aquaporin channels to increase water reabsorption

• aquaporins being inserted into plasma membrane → increased flow of water out of tubule and into blood stream

Aldosterone

• produced by adrenal gland

• reabsorbs sodium into blood stream → releasing (increased excretion) potassium

• facilitates reabsorption of sodium → reabsorption of water

Aldosterone job in maintaining Na+ and K+ levels

• increased blood K+ levels and decreased blood Na+ levels → Aldosterone released from adrenal cortex → aldosterone targets kidneys → decreased K+ excretion and increases Na+ reabsorption by kidneys → blood Na+/K+ levels normalize

Angiotensin II

• kidney releases renin into blood and liver releases angiotensin into blood(inactive II) → angiotensin II is formed from angiotensin I by the action of the enzyme ACE → angiotensin II stimulates aldosterone secretion by adrenal cortex → aldosterone stimulates Na+ and H2O reabsorption in the nephrons

a hormone that increases blood pressure by promoting aldosterone release, stimulating sodium reabsorption in kidneys and vasoconstriction.

Electrolytes…

• solutes that are dissolved in H2O

• cause electricity

• Kidneys excrete excess water through dilute urine

• Kidneys excrete excess electrolytes through concentrated urine

• Ions form when electrolytes dissolve and dissociate

Functions of electrolytes

• control osmosis between body fluid compartments

• help maintain the acid-base balance

• carry electrical current

• serve as cofactors for enzymes

IMPORTANT electrolytes

Cations

• Sodium (Na+)

• Potassium (K+)

• Calcium (Ca++)

Anions

• Chloride (Cl-)

• Bicarbonate (HCO3-)

• Phosphate (HPO4--)

Most concentrated electrolytes in intracellular fluid (most to least)

• Potassium (K+)

• Phosphate (HPO4--)

• Magnesium (Mg++)

• Sodium (Na+)

• Calcium (Ca2+)

• Chloride (Cl-)

Most concentrated electrolytes in plasma ( most to least) - most abundant in body 2/3

• Sodium (Na+)

• Chloride (Cl-)

• Bicarbonate (HCO3-)

• Protein

• Potassium (K+)

• Calcium (Ca++)

• Phosphate (HPO 2—)

hyponatremia

lower than normal concentration of SODIUM (NA+)

hypernatremia

an abnormal increase in blood SODIUM (NA+)

hypokalemia

an abnormally low POTASSIUM (KA+) blood level

hyperkalemia

an abnormally elevated POTASSIUM (KA+) blood level

hypochloremia

lower than normal CHLORIDE (Cl-) blood levels

hyperchloremia

higher than normal CHLORIDE (Cl-) blood levels

hypocalcemia

abnormally low CALCIUM (Ca2+)blood levels

hypercalcemia

abnormally high CALCIUM (Ca2+) blood levels

Normal Blood pH

7.35-7.45

• if out of range, proteins (enzymes) get denatured/inactive

Mechanisms that maintain proper pH…

Buffer systems

• most consist of weak acid and a base (bicarbonate buffer)

• prevent drastic changes in body fluid pH

Exhalation of carbon dioxide

• increased exhalation of CO2 → blood pH rises( fewer H+) increases pH (alkaline)

• decreased exhalation of CO2 → blood pH falls (more H+) decreases pH (acidic)

Kidney excretion of H+

• slowest mechanism

• renal tubes secrete H+ into urine and reabsorb HCO-3(bicarbonate)

Buffer systems in the body

Protein buffers

• Most abundant buffers in body cells(ICF) and blood(ECF)

• Nearly all proteins can function as buffers (hemoglobin)

Phosphate buffers

• important buffers in intracellular fluid (ICF) and urine.

Bicarbonate-Carbonic acid buffer

• important regulator of blood pH

• most abundant buffers in ECF(blood)

Respiratory regulation of Acid-Base Balance

Exhaling CO2 → rise in pH

Retaining CO2 → drop in pH

CO2+H2O ← → H2CO3 (carbonic acid) ←→ H+(hydrogen ion) + HCO3- (bicarbonate ion)

Respiratory regulation when pH DECREASES

• more H+ in blood → ACIDOSIS → stimulates brain and arterial receptors → increase in respiration rate (get rid of CO2 which is acidic) → blood CO2 decreases → blood H2CO3 decreases → less H+ → increase in pH → homeostasis restored

• When blood pH decreases, the body responds to acidosis by stimulating increased respiration, leading to greater exhalation of carbon dioxide. This decrease in CO2 concentration reduces carbonic acid levels, thereby lowering hydrogen ion concentration and restoring pH balance.

Respiratory regulation when pH INCREASES

• less H+ in blood → ALKALOSIS → stimulates brain and arterial receptors → decrease in respiration rate (retaining CO2 which is acidic) → blood CO2 increases → blood H2CO3 increases → more H+ → decrease in pH → homeostasis restored

• When blood pH increases, the body responds to alkalosis by reducing respiration, leading to CO2 retention. This increase in CO2 raises carbonic acid levels, increasing hydrogen ion concentration and restoring pH balance.

Bicarbonate ions filtration and conservation

• Tubular cells are not permeable to bicarbonate, thus, bicarbonate is conserved rather than reabsorbed

• Bicarbonate ions are freely filtered in the glomerulus, the renal tubules don’t directly reabsorb them Instead, bicarbonate is produced within the tubular cells then utilized in the carbonic acid-bicarbonate buffer system to maintain blood pH

Steps

• 1: sodium ions are reabsorbed from the filtrate in exchange for H+ by an antiport mechanism in the apical membranes of cells lining the renal tubule

• 2: the cells produce bicarbonate ions that can be shunted to peritubular capillaries

Acidosis

blood pH below 7.35

Alkalosis

blood pH above 7.45

Metabolic Acidosis

• more H+

• decreased pH

• decreased bicarbonate levels which lead to decreased carbon dioxide since exhalation increases therefore less H+ are produced

Metabolic Alkalosis

• less H+

• increased pH

• increased bicarbonate levels, which lead to increased carbon dioxide since breathing decreased and more CO2 was retained, which made more H+