The Cellular Environment: Fluids and Electrolytes, Acids and Bases

1
The Cellular Environment Fluids and
Electrolytes, Acids and Bases

• Chapter 3

2
Distribution of Body Fluids

• Total body water (TBW) 60 of total body weight
• Intracellular fluid inside the cells
• Extracellular fluid not encased in cells
• Interstitial fluid found in between cells and
  tissues
• Intravascular fluid- plasma found in circulatory
  system
• Lymph, synovial, intestinal, biliary, hepatic,
  pancreatic, CSF, sweat, urine, pleural,
  peritoneal, pericardial, and intraocular fluids
  are extracellular

3
Water Movement Between the ICF and ECF

• Osmolality the concentrations of solutes in
  water
• Osmotic forces solutes will influence the
  movement of water across membranes
• Aquaporins- water channel proteins in membranes
• Starling hypothesis
• Net filtration forces favoring filtration
  forces opposing filtration
• As fluid flows through capillary it looses water
  and create greater osmotic return of water as it
  flows toward veinule end of capillary

4
Water Movement Between the ICF and ECF
5
Net Filtration

• Forces favoring filtration
• Capillary hydrostatic pressure (blood pressure)
• Interstitial oncotic pressure (water-pulling)
• Forces favoring reabsorption
• Plasma oncotic pressure (water-pulling)
• Interstitial hydrostatic pressure

6
Osmotic Equilibrium
7
Edema

• Accumulation of fluid within the interstitial
  spaces
• Causes
• Increase in hydrostatic pressure
• Losses or diminished production of plasma albumin
• Increases in capillary permeability
• Lymph obstruction elephantitus, flibitus

8
Edema
9
Water Balance

• Thirst perception
• Osmolality receptors in medula respond to osmotic
  pressue of ECF
• Hyperosmolality and plasma volume depletion
• ADH secretion from posterior pituitary
  conserves water in kidney to maintain water
  balance

10
Sodium and Chloride Balance

• Sodium
• Primary ECF cation
• Regulates osmotic forces
• Roles
• Neuromuscular irritability, acid-base balance,
  and cellular reactions
• Chloride
• Primary ECF anion
• Provides electroneutrality

11
Sodium and Chloride Balance

• Renin-angiotensin system substanced produced in
  both liver and kidney
• Angiotensin produced by liver and coverted by
  enzymes activated by renin from Kidney Juxta
  Glomerular Aparatus to a powerful
  vasoconstrictor.
• Aldosterone hormone from adrenal gland to
  regulate Na and K
• Natriuretic peptides
• Atrial natriuretic peptide - hormone from heart
• Brain natriuretic peptide hormone from brain
• Urodilantin (kidney) Kidney hormone

12
Alterations in Na, Cl, and Water Balance

• Isotonic alterations
• Total body water change with proportional
  electrolyte and water change
• Isotonic volume depletion
• Isotonic volume excess

13
Hypertonic Alterations

• Hypernatremia
• Serum sodium gt147 mEq/L
• Related to sodium gain or water loss
• Water movement from the ICF to the ECF
• Intracellular dehydration
• Manifestations
• Intracellular dehydration, convulsions, pulmonary
  edema, hypotension, tachycardia, etc.

14
Water Deficit

• Dehydration
• Pure water deficits
• Renal free water clearance
• Manifestations
• Tachycardia, weak pulses, and postural
  hypotension
• Elevated hematocrit and serum sodium level

15
Hypochloremia

• Occurs with hypernatremia or a bicarbonate
  deficit
• Usually secondary to pathophysiologic processes
• Managed by treating underlying disorders

16
Hypotonic Alterations

• Decreased osmolality
• Hyponatremia or free water excess
• Hyponatremia decreases the ECF osmotic pressure,
  and water moves into the cell
• Water movement causes symptoms related to
  hypovolemia

17
Hyponatremia

• Serum sodium level lt135 mEq/L
• Sodium deficits cause plasma hypoosmolality and
  cellular swelling
• Pure sodium deficits
• Low intake
• Dilutional hyponatremia
• Hypoosmolar hyponatremia
• Hypertonic hyponatremia

18
Water Excess

• Compulsive water drinking
• Decreased urine formation
• Syndrome of inappropriate ADH (SIADH)
• ADH secretion in the absence of hypovolemia or
  hyperosmolality
• Hyponatremia with hypervolemia
• Manifestations cerebral edema, muscle twitching,
  headache, and weight gain

19
Hypochloremia

• Usually the result of hyponatremia or elevated
  bicarbonate concentration
• Develops due to vomiting and the loss of HCl
• Occurs in cystic fibrosis

20
Potassium

• Major intracellular cation
• Concentration maintained by the Na/K pump
• Regulates intracellular electrical neutrality in
  relation to Na and H
• Essential for transmission and conduction of
  nerve impulses, normal cardiac rhythms, and
  skeletal and smooth muscle contraction

21
Potassium Levels

• Changes in pH affect K balance
• Hydrogen ions accumulate in the ICF during states
  of acidosis. K shifts out to maintain a balance
  of cations across the membrane.
• Aldosterone, insulin, and catecholamines
  influence serum potassium levels

22
Hypokalemia

• Potassium level lt3.5 mEq/L
• Potassium balance is described by changes in
  plasma potassium levels
• Causes can be reduced intake of potassium,
  increased entry of potassium, and increased loss
  of potassium
• Manifestations
• Membrane hyperpolarization causes a decrease in
  neuromuscular excitability, skeletal muscle
  weakness, smooth muscle atony, and cardiac
  dysrhythmias

23
Hyperkalemia

• Potassium level gt5.5 mEq/L
• Hyperkalemia is rare due to efficient renal
  excretion
• Caused by increased intake, shift of K from ICF,
  decreased renal excretion, insulin deficiency, or
  cell trauma

24
Hyperkalemia

• Mild attacks
• Hypopolarized membrane, causing neuromuscular
  irritability
• Tingling of lips and fingers, restlessness,
  intestinal cramping, and diarrhea
• Severe attacks
• The cell is not able to repolarize, resulting in
  muscle weakness, loss or muscle tone, and flaccid
  paralysis

25
Calcium

• Most calcium is located in the bone as
  hydroxyapatite
• Necessary for structure of bones and teeth, blood
  clotting, hormone secretion, and cell receptor
  function

26
Phosphate

• Like calcium, most phosphate (85) is also
  located in the bone
• Necessary for high-energy bonds located in
  creatine phosphate and ATP and acts as an anion
  buffer
• Calcium and phosphate concentrations are rigidly
  controlled
• Ca x HPO4 K (constant)
• If the concentration of one increases, that of
  the other decreases

27
Calcium and Phosphate

• Regulated by three hormones
• Parathyroid hormone (PTH)
• Increases plasma calcium levels
• Vitamin D
• Fat-soluble steroid increases calcium absorption
  from the GI tract
• Calcitonin
• Decreases plasma calcium levels

28
Hypocalcemia and Hypercalcemia

• Hypocalcemia
• Decreases the block of Na into the cell
• Increased neuromuscular excitability (partial
  depolarization)
• Muscle cramps

• Hypercalcemia
• Increases the block of Na into the cell
• Decreased neuromuscular excitability
• Muscle weakness
• Increased bone fractures
• Kidney stones
• Constipation

29
Hypophosphatemia and Hyperphosphatemia

• Hypophosphatemia
• Osteomalacia (soft bones)
• Muscle weakness
• Bleeding disorders (platelet impairment)
• Anemia
• Leukocyte alterations
• Antacids bind phosphate

• Hyperphosphatemia
• See Hypocalcemia
• High phosphate levels are related to the low
  calcium levels

30
Magnesium

• Intracellular cation
• Plasma concentration is 1.8 to 2.4 mEq/L
• Acts as a cofactor in protein and nucleic acid
  synthesis reactions
• Required for ATPase activity
• Decreases acetylcholine release at the
  neuromuscular junction

31
Hypomagnesemia and Hypermagnesemia

• Hypomagnesemia
• Associated with hypocalcemia and hypokalemia
• Neuromuscular irritability
• Tetany
• Convulsions
• Hyperactive reflexes

• Hypermagnesemia
• Skeletal muscle depression
• Muscle weakness
• Hypotension
• Respiratory depression
• Lethargy, drowsiness
• Bradycardia

32
pH

• Inverse logarithm of the H concentration
• If the H are high in number, the pH is low
  (acidic). If the H are low in number, the pH is
  high (alkaline).
• The pH scale ranges from 0 to 14 0 is very
  acidic, 14 is very alkaline. Each number
  represents a factor of 10. If a solution moves
  from a pH of 6 to a pH of 5, the H have
  increased 10 times.

33
pH

• Acids are formed as end products of protein,
  carbohydrate, and fat metabolism
• To maintain the bodys normal pH (7.35-7.45) the
  H must be neutralized or excreted
• The bones, lungs, and kidneys are the major
  organs involved in the regulation of acid and
  base balance

34
pH

• Body acids exist in two forms
• Volatile
• H2CO3 (can be eliminated as CO2 gas)
• Nonvolatile
• Sulfuric, phosphoric, and other organic acids
• Eliminated by the renal tubules with the
  regulation of HCO3

35
Buffering Systems

• A buffer is a chemical that can bind excessive H
  or OH without a significant change in pH
• A buffering pair consists of a weak acid and its
  conjugate base
• The most important plasma buffering systems are
  the carbonic acidbicarbonate system and
  hemoglobin

36
Carbonic AcidBicarbonate Pair

• Operates in both the lung and the kidney
• The greater the partial pressure of carbon
  dioxide, the more carbonic acid is formed
• At a pH of 7.4, the ratio of bicarbonate to
  carbonic acid is 201
• Bicarbonate and carbonic acid can increase or
  decrease, but the ratio must be maintained

37
Carbonic AcidBicarbonate Pair

• If the amount of bicarbonate decreases, the pH
  decreases, causing a state of acidosis
• The pH can be returned to normal if the amount of
  carbonic acid also decreases
• This type of pH adjustment is referred to as
  compensation
• The respiratory system compensates by increasing
  or decreasing ventilation
• The renal system compensates by producing acidic
  or alkaline urine

38
Carbonic AcidBicarbonate Pair
39
Other Buffering Systems

• Protein buffering
• Proteins have negative charges, so they can serve
  as buffers for H
• Renal buffering
• Secretion of H in the urine and reabsorption of
  HCO3
• Cellular ion exchange
• Exchange of K for H in acidosis and alkalosis

40
Buffering Systems
41
Acid-Base Imbalances

• Normal arterial blood pH
• 7.35 to 7.45
• Obtained by arterial blood gas (ABG) sampling
• Acidosis
• Systemic increase in H concentration
• Alkalosis
• Systemic decrease in H concentration

42
Acidosis and Alkalosis

• Four categories of acid-base imbalances
• Respiratory acidosiselevation of pCO2 due to
  ventilation depression
• Respiratory alkalosisdepression of pCO2 due to
  alveolar hyperventilation
• Metabolic acidosisdepression of HCO3 or an
  increase in non-carbonic acids
• Metabolic alkalosiselevation of HCO3 usually
  due to an excessive loss of metabolic acids

43
Metabolic Acidosis
44
Anion Gap

• Used cautiously to distinguish different types of
  metabolic acidosis
• By rule, the concentration of anions () should
  equal the concentration of cations (). Not all
  normal anions are routinely measured.
• Normal anion gap Na K Cl HCO3 10
  to 12 mEq/L (other misc. anions the ones we
  dont measurephosphates, sulfates, organic
  acids, etc.)

45
Anion Gap

• An abnormal anion gap occurs due to an increased
  level of an abnormal unmeasured anion
• Examples DKAketones, salicylate poisoning,
  lactic acidosisincreased lactic acid, renal
  failure, etc.
• As these abnormal anions accumulate, the measured
  anions have to decrease to maintain
  electroneutrality

46
Metabolic Alkalosis
47
Respiratory Acidosis
48
Respiratory Alkalosis