Chapter 15- Fluid and Acid-base balance Flashcards
What is balance concept?
Input must equal output to maintain a stable balance in ECF
When does a positive balance exist?
When input exceeds output
When does a negative balance exist?
When output exceeds input
What is an example of input?
Ingestion
Metabolic consumption
What is an example of output?
Excretion
metabolic consumption
Why is input poorly controlled?
Eating habits are variable
Where do compensatory adjustments occur?
usually on output side by urinary excretion
What is the most abundant substance in the body?
Water
-Amount varies in different tissues
-Content remains fairly constant
What percent of body fluid is extracellular?
33%
what percent of body fluid is intracellular?
67%
What is extracellular fluid made from?
interstitial fluid- 75%
Plasma- 25%
What are the 2 major fluid compartments?
2/3 within the cells = ICF
1/3 in fluid surrounding the cells= ECF
What are the minor components of ECF?
Lymph and transcellular fluid
What is the barrier separating the ECF and ICF?
Cellular plasma membranes
What does the ICF contain that can’t leave the cells?
Proteins
-cant permeate cell membrane
Difference between ECF and ICF?
Unequal distribution of Na and K
What does the ECF serve as?
Intermediary between the cells and external environment?
What does kidney function do to ECF?
Regulates volume and osmolarity
Why is ECF volume regulated?
maintains blood pressure
What is important in long term regulation of ECF volume?
mainting salt NaCl balance
Why is ECF osmolarity regulated?
Prevent swelling or shrinking of cells
What is important in maiting ECF osmolarity?
Water balance
How does salt input occur?
through ingestion
How is salt balance maintained?
Outputs in urine
+lost in sweating and feces
How do the kidneys adjust the amount of salt excreted?
By controlling Glomerular filtration rate and Tubular reabsorption of sodium
What do deviations in ECF volume trigger?
Trigger renal compensatory responses that bring salt balance back into line
What is osmolarity?
Measure of the concentration of individual solute particles dissolved in a fluid
What do ECF and ICF have the same despite large chemical differences?
Same osmolarity
-no net movement of water
If fluid outside cell has same osmolarity?
isotonic
If fluid outside cell has higher osmolarity?
Hypertonic
If fluid outside cell has lower osmolarity?
Hypotonic
What accounts for the majority of the ECF’s osmotic activity?
Sodium and its attendant anions
What accounts for the majority of ICF’s osmotic activity?
Potassium and accompanying intracellular anions
What leads to changes in ECF osmolarity?
Circumstances that result in a loss or gain of free H2O
Examples of circumstances that alter ECF osmolarity?
- Deficit of free water in ECF
- Excess of free water in ECF
What is the osmolarity of when there is a water deficit?
Hypertonic
-too concentrated
-Dehydration
What is the osmolarity when there is a water excess?
Hypotonic
-too dilute
-overhydration
What happens to cells when they experience hypertonicity?
Cells shrink (ECF is too concentrated: water leaves cells)
What causes hypertonicity?
Insufficient water intake
Excessive water loss
Diabetes insipidus
What are the symptoms and effects of hypertonicity?
âš«Shrinking of brain neurons
-Confusion, irritability, delirium, convulsions, coma
âš« Circulatory disturbances
-Reduction in plasma volume, lowering of blood pressure, circulatory shock
âš« Dry skin, sunken eyeballs, dry tongue
What happens to cells that experience hypotonicity?
Cells swell
-excess water usually excreted in urine
What causes Hypotonicity?
Causes
âš« Patients with renal failure who cannot excrete a dilute urine become hypotonic when they consume more water than solutes
⚫ Can occur in healthy people when water is rapidly ingested and kidney’s do not respond quickly enough
âš« When excess water is retained in body due to inappropriate secretion of vasopressin
Hypotinicity symtoms and effects?
âš« Swelling of brain cells
-Confusion, irritability, lethargy, headache, dizziness,
vomiting, drowsiness, convulsions, coma, death
âš« Weakness (due to swelling of muscle cells)
âš« Circulatory disturbances (hypertension and edema)
âš« Excess free water = Water intoxication
How do you maintain stable water balance?
Water input must equal water output
What are the two types of output loss?
Insensible loss
Sensible loss
What is insensible loss?
Lungs, non-sweating skin
What is sensible loss?
Sweating, feces, urine excretion
-controlled to keep balance
Where is water excretion controlled in the kidney?
Collecting ducts and tubules of nephron
What controls water excretion?
Vasopressin
-restores ECF osmolarity
Where is vasopressin produced?
Hypothalamus
Where is vasopressin released?
Posterior pituitary gland
What is the hypothalamus the location of?
Thirst centre
What are hypothalamic osmoreceptors?
Sense changes in osmolarity
Where are hypothalamic osmoreceptors located?
Near vasopressin-secreting cells and thirst centre
If osmolarity increases what occurs via hypothalamic osmoreceptors?
Increased vasopressin and thirst is stimulated
If osmolarity decreases what occurs via hypothalamic osmoreceptors?
decreased vasopressin and thirst is suppressed
What else stimulates vasopressin secretion and thirst?
left atrial receptor (reduction in arterial pressure)
Angiotensin II (when RAAS is activated to conserve Na)
What does ECF fluid volume control?
Blood pressure
What does ECF fluid osmolarity control?
Cell volume: The shape of the cell
What is Acid-Base balance?
Precise regulation of free/unbound hydrogen concentration in ECF (body fluids)
What are acids?
Group of H containing substances that dissociate in solution to release free H and anions
What kind of acid has a greater tendency to dissociate in a solution?
Strong acids
What is a base?
Substance that can combine with free H and remove it from solution
What is pH?
A scale used to express the concentration of H+
What is acidosis?
When blood pH falls below a 7.35
-Becomes acidic
What is alkalosis?
When blood pH is above a 7.45
-Becomes basic
What are consequences related to fluctuations in pH?
a) changes in excitability of nerve and muscle cells
b) marked decrease of H causes over excitability of nervous
c) influences enzyme activity
d) changes K levels in body (affects cardiac functions)
What are some sources of H+ in the body?
- Carbonic acid formation
- Inorganic acids produced during breakdown of nutrients
- organic acids from intermediary metabolism (fatty acids)
What are the body’s lines of defence for pH changes?
- Chemical buffer system
- Respiratory system
- Kidneys
What is the chemical buffer system?
Fist line of defence with four systems. Minimises changes of pH by binding with or yielding free H+
What are the four systems of the chemical buffer system?
- H2CO3-, HCO3 System
- Protein Buffer system
- Hemoglobin (CO2) system
- Phosphate system
What is theH2CO3-, HCO3 System?
Primary ECF buffer for non carbonic acids
What is carbonic acid?
Reaction of water with CO2
H2CO3
What are inorganic acids?
Acids produced during the breakdown of nutrients
e.g; H2SO4, phosphoric acids found in meats
What are organic acids?
acids resulting from intermediary metabolism
e.g; Fatty acids
What is the protein buffer system?
Primary ICF buffer, it also buffers ECF
What is Hemoglobin (CO2) system?
Primary buffer against carbonic acid changes
What is the phosphate system?
Important urinary buffer, also buffers ICF
What is the respiratory system’s role in the Chemical buffer system?
Second line of defence
Acts at moderate speed, regulates pH by control rate of CO2 removal
What is the kidney’s role in the Chemical Buffer system?
Third line of defence
Takes hours to days to compensate for changes adjusts
a. H+ excretion
b. HCO3- excretion
c. Ammonia secretion
What causes Acid-base imbalances?
Arise from either respiratory dysfunction or metabolic disturbances
What is respiratory acidosis ?
Blood pH falls below a 7.35 because of abnormal CO2 retention arising from hypoventilation
What are some possible causes of Hypoventilation —> respiratory acidosis?
Lung disease
e.g; emphysema, bronchitis, asthma
Depression of respiratory centre by drugs/disease
nerve, muscle disorders reducing respiratory muscle activity
Holding breath
How does the body compensate for respiratory acidosis?
a. Chemical buffers immediately take uo additional H+
b.Kidneys conserve all filtered HCO3- and add new HCO3- to plasma, and excrete more H+
What compensation inmost important during respiratory acidosis?
Kidneys
What is respiratory alkalosis?
Blood pH rises above 7.45 primarily due to excessive loss of CO2 from body as a result of Hyperventilation
-its a loss of H+ and HCO3-
What causes respiratory alkalosis?
Fever
Anxiety/other stressors
Aspirin poisoning
Physiologic mechanisms at high altitudes
How does the body compensate for respiratory alkalosis?
a. Chemical buffer systems liberate H+
b. After a few days if it continues, kidneys conserve H+ and excrete more HCO3-
What is metabolic acidosis?
Blood pH falls below a 7.35 due to any type of acidosis except those caused by excess CO2 in body fluids
Its a reduction in plasma HCO3 or accumulation of non-carbonic acids
What causes metabolic acidosis?
-Severe diarrhoea
-Diabetes mellitus
-Strenuous exercise
-Uremic acidosis
How does the body compensate for metabolic acidosis?
a. Buffers take up extra H+
b.Lungs blow off additional H+ generating CO2
c.Kidneys excrete more H+ and conserve more HCO3
What is metabolic alkalosis?
Blood pH rises above a 7.45 due to a reduction in plasma H+ caused by relative deficiency of non-carbonic acids
What causes metabolic alkalosis?
-Vomiting
-Ingestion of alkaline drugs
How does the body compensate for metabolic alkalosis?
a. Chemical buffers immediately liberate H+
b. Ventilation reduces
c.If condition persists, kidneys conserve H+ and excrete excess HCO3- in urine
