Chapter 27 - Fluid, Electrolytes, and Acid-Base Homeostasis Flashcards
What is Body Fluids?
Between 55-65% of total body mass
2/3 inside cells
1/3 outside cells
1- Intracellular Fluid (ICF):
Cytosol
2- Extracellular Fluid (ECF):
Interstitial Fluid 80%
Blood Plasma 20%
What divides Body Fluids and how do they Interact?
Plasma Membrane:
Separates ICF from Interstitial Fluid
Blood Vessel Walls:
Divide the Interstitial Fluid from Blood Plasma
Capillary Walls:
Thin enough to allow exchange of water and solutes between Blood Plasma and Interstitial Fluid
What allows Continuous Exchange of Water and Solutes among Body Fluid Compartments?
Filtration, Reabsorption, Diffusion, and Osmosis:
Allow continuous exchange of water and solutes among body fluid compartments:
1- Balance of inorganic compounds that dissociate into ions (Electrolytes) is closely related to fluid balance
2- Body gains water by ingestion and metabolic synthesis
3- Body loses water via urination, perspiration, exhalation, and in feces
What determines Volume of Metabolic Water Formed?
Level of Aerobic Respiration determines volume of metabolic water formed:
Amount of water formed is directly proportional to the amount of ATP produced
When water loss is greater than water gain, dehydration occurs, leading to increased thirst
What is the Thirst Response?
1- Increased blood osmolarity:
Stimulates osmoreceptors in Hypothalamus
2- Decrease blood volume:
Decreased activity of Atrial Volume Receptors
3- Decrease BP:
Decreased activity of Baroreceptors in blood vessels
Increase release of Renin from Kidneys -> increased Angiotensin II formed
4- Dry Mouth
5- All of that stimulates Thirst Center in Hypothalamus
6- Increase Thirst
7- Increase water intake
8- Increased water intake:
Decrease blood osmolarity
Increase BP and Blood Volume
Relieves mouth dryness
What is Excess Body Water Elimination?
Elimination of excess body water occurs through urine production
Amount of Urinary salt loss is main factor determining body fluid volume
The 2 Main Solutes in urine:
1- Na+
2- Cl-
Wherever solutes go, water follows
What are the 3 Major Hormones that Control Renal Na+ and Cl-?
1- Angiotensin II
2- Aldosterone
3- Atrial Natriuretic Peptide (ANP)
The major hormone that regulates water loss is ADH
What is Regulation of Water and Solute Loss by ADH?
1- Increased blood osmolarity:
Stimulates osmoreceptors in Hypothalamus
2- Decrease blood volume:
Decreased activity of Atrial Volume Receptors
3- Decrease BP:
Decreased activity of Baroreceptors in blood vessels
4- Other factors such as pain, nausea, and stress
5- All of these increase synthesis of ADH by Neurosecretory Cells in Hypothalamus
6- Increased release of ADH from Posterior Pituitary Gland
7- Late DCT and CD of Kidneys become more permeable to water, which increases water reabsorption
8- The increase of water reabsorption in turn:
Decrease blood osmolarity
Increase BP and Blood Volume
What is Regulation of Water and Solute Loss by Aldosterone?
1- Decrease BP and Na+ deficiency in Plasma
2- Increased release of Renin by Kidneys
3- Increased Aldosterone formation
4- Aldosterone:
Increase Na+ reabsorption in late DCT and CD of Kidneys
Water reabsorption accompanies Na+ reabsorption via Osmosis because ADH is also released when there is decrease in BP
5- Increased Na+ reabsorption relives the Na+ deficiency in Plasma
The accompanying water reabsorption increase BP and Blood Volume
What is Regulation of Water and Solute Loss by ANP?
1- Increased Blood Volume
2- Increased stretch of Atria
3- Release of ANP
4- Increase excretion of Na+ into urine (Natriuresis)
Water excretion into urine also increases due to Osmosis
5- Increase water in excretion causes a decrease in BP and Blood Volume
What is Mechanism and Effect of Thirst Center in Hypothalamus?
1- Mechanism:
Stimulate desire to drink fluids
2- Effect:
Water gained if thirst is quenched
What is Mechanism and Effect of ADH?
1- Mechanism:
Promotes insertion of Aquaporin-2 into Apical membranes of Principal Cells in CD of Kidneys
As a result, water permeability of these cells increase and more water is reabsorbed
2- Effect:
Reduce water loss in urine
What is Mechanism and Effect of Aldosterone?
1- Mechanism:
By promoting urinary reabsorption of Na+ increases water reabsorption via Osmosis
2- Effect:
Reduce water loss in urine
What is Mechanism and Effect of ANP?
1- Mechanism:
Promotes Natriuresis
Elevated urinary excretion of Na+
Accompanied by water
2- Effect:
Increase water loss in urine
What is Water Movement Between Body Fluid Compartments?
When the ECF is Isotonic to the cells of body, they do not shrink or swell
However, changes in osmolarity of ECF (as with dehydration or over-hydration) can cause the cells of body to shrink or swell
What is Water Intoxication?
Water Intoxication:
Occurs when excess body water causes cells to swell dangerously
This may occur when a person consumes water faster than the Kidneys can excrete it
1- Excessive blood loss, sweating, vomiting, or diarrhea coupled with intake of plain water
2- Decrease Na+ concentration (Hyponatremia) of ECF
3- Decreased osmolarity of ECF
4- Osmosis of water from ECF into ICF
5- Water Intoxication (Cells swell)
6- Mental confusion, seizures, coma, and possible death
What is Electrolytes in Body Fluids?
Ions formed when Electrolytes dissociate and dissolve:
1- Control osmosis of water between fluid compartments
2- Help maintain the acid-base balance
3- Carry electrical current
4- Serve as Cofactors
Blood Plasma, Interstitial Fluids, and ICF have different concentrations of Electrolytes and protein ions
Blood Plasma contains more protein ions
Interstitial Fluid contains only a few
What is Na+?
Most abundant Cation (+) in ECF
Used for:
Impulse transmission
Muscle contraction
Fluid and Electrolyte balance
Its level controlled by:
Aldosterone
ADH
ANP
What is Cl-?
Major ECF Anion (-)
Helps regulate osmotic pressure between compartments
Forms HCL in Stomach
Regulated by:
Aldosterone
What is K+?
Most abundant Cation (+) in ICF
Involved in:
Fluid volume
Impulse conduction
Muscle contraction
Regulating pH
Regulated by:
Mineralocorticoids (mainly Aldosterone)
What is HCO3- (Bicarbonate)?
Important Plasma ion
Major member of Plasma’s acid-base buffer system
Kidneys reabsorb or secrete it for final acid-base balance
What is Ca2+?
Most abundant mineral in body
Structural component of Bones and Teeth
Used for:
Blood coagulation
NT release
Muscle tone
Excitability of nerves and muscles
Regulated by:
PTH
What is Ca3(PO4)2?
Phosphate occurs as Calcium Phosphate Salt
Used in:
Buffer system
Regulated by:
PTH
Calcitriol
What is Mg2+?
ICF Cation (+)
Activates enzymes involved in carb and protein metabolism
Used in:
Myocardial function
Transmission in CNS
Operation of Na+ Pump
What is Hyponatremia?
Na+ deficiency
1- Cause:
Low Na+ intake
Increased Na+ loss through vomiting, diarrhea, Aldosterone deficiency, or taking certain Diuretics
Excessive water intake
2- Signs/Symptoms:
Muscular weakness
Dizziness
Headache
Hypotension
Tachycardia
Shock
Mental confusion
Stupor
Coma
What is Hypernatremia?
Na+ Excess
1- Cause:
Dehydration, water deprivation
Excessive Na+ in diet or IV fluids
Causes Hypertonicity of ECF which pulls water out of cells to ECF causing cellular dehydration
2- Signs/Symptoms:
Intense thirst
Hypertension
Edema
Agitation
Convulsions
What is Hypochloremia?
Cl- Deficiency
1- Cause:
Excessive vomiting
Overhydration
Aldosterone deficiency
CHF
Therapy with certain Diuretics like Furosemide (Lasix)
2- Signs/Symptoms:
Muscle spasms
Metabolic Alkalosis
Shallow respirations
Hypotension
Tetany
What is Hyperchloremia?
Cl- Excess
1- Cause:
Dehydration from water loss or water deprivation
Excessive Cl- intake
Severe Renal failure
Hyperaldosteronism
2- Signs/Symptoms:
Lethargy
Weakness
Metabolic Acidosis
Rapid deep breathing
What is Hypokalemia?
K+ Deficiency
1- Cause:
Excessive vomiting/diarrhea
Decreased K+ intake
Hyperaldosteronism
Kidney disease
Therapy with some Diuretics
2- Signs/Symptoms:
Muscle fatigue
Flaccid paralysis
Mental confusion
Increased urine output
Shallow respirations
Changes in EKG including Flattening of T Wave
What is Hyerkalemia?
K+ Excess
1- Cause:
Excessive K+ intake
Renal failure
Aldosterone deficiency
Crushing injuries to body tissues
Transfusion of hemolyzed blood
2- Signs/Symptoms:
Irritability
Nausea
Vomiting
Diarrhea
Muscular weakness
Can cause death by inducing V-Fib
What is Hypocalcemia?
Ca2+ Deficiency
1- Cause:
Increased Ca2+ loss
Reduced Ca2+ intake
Elevated Phosphate levels
Hyperparathyroidism
2- Signs/Symptoms:
Numbness and tingling of fingers
Hyperactive reflexes
Muscle cramps, Tetany, and Convulsion
Bone fractures
Spasms of Laryngeal muscles that can cause death by Asphyxiation
What is Hypercalcemia?
Ca2+ Excess
1- Cause:
Hyperparathyroidism
Some cancers
Excessive intake of Vitamin D
Paget’s Disease of Bone
2- Signs/Symptoms:
Lethargy
Weakness
Anorexia
Nausea
Vomiting
Polyuria
Itching
Bone pain
Depression
Confusion
Paresthesia
Stupor
Coma
What is Hypophosphatemia?
Phosphate Deficiency
1- Cause:
Increase urinary loss
Increased Intestinal absorption
Increased utilization
2- Signs/Symptoms:
Confusion
Seizures
Coma
Chest and muscle pain
Numbness and tingling of fingers
Decreased coordination
Memory loss
Lethargy
What is Hyperphosphatemia?
Phosphate Excess
1- Cause:
Kidneys fail to excrete Phosphate (Renal failure)
Increased intake of Phosphate
Destruction of body cells which releases phosphate into blood
2- Signs/Symptoms:
Anorexia
Nausea
Vomiting
Muscular weakness
Hyperactive reflexes
Tetany
Tachycardia
What is Hypomagnesemia?
Mg2+ Deficiency
1- Cause:
Inadequate intake or excessive loss in urine and feces
Alcoholism
Malnutrition
Diabetes Mellitus
Diuretic therapy
2- Signs/Symptoms:
Weakness
Irritability
Tetany
Delirium
Convulsions
Confusion
Anorexia
Nausea
Vomiting
Paresthesia
Cardiac Arrhythmias
What is Hypermagnesemia?
Mg2+ Excess
1- Cause:
Renal failure
Increased Mg2+ intake (like Mg2+ antiacids)
Aldosterone deficiency
Hyperthyroidism
2- Signs/Symptoms:
Hypotension
Muscular weakness or paralysis
Nausea
Vomiting
Altered mental functioning
What is Acid-Base Balance?
pH of Arterial Blood ranges from 7.35-7.45
Mechanisms that maintain this range:
1- Buffer Systems
2- Exhalation of CO2
3- Kidney excretion of H+
What is a Buffer System?
Most consist of a Weak Acid, and its salt, which function as a Weak Base
Prevent drastic changes in body fluid pH
What is Protein Buffer System?
Protein Buffer System:
Most abundant in ICF and Blood Plasma
1- When pH rises:
COOH group dissociates to act like an Acid
COOH —–> COO- + H+
2- When pH falls:
The free amino group dissociates to act like a Base
NH2 + H+ —–> NH3+
What is Hemoglobin in RBC as Buffer?
Hg in RBC acts as a Buffer:
H2O + CO2 —–> H2CO3 (carbonic acid)
H2CO3 (carbonic acid) —–> H+ + HCO3- (bicarbonate)
Hb-O2 (oxyhemoglobin) + H+ —–> Hb-H (reduced Hg) + O2
What is Carbonic Acid-Bicarbonate Buffer System?
Important regulator of blood pH
Most abundant buffer in ECF
Based on the:
1- Bicarbonate ion (HCO3-) which acts as a Weak Base
2- Carbonic Acid (H2CO3) which acts as a Weak Acid
If pH falls:
HCO3- removes excess H+
H+ + HCO3- —–> H2CO3
If pH rises:
H2CO3 can provide H+
H2CO3 —–> H+ + HCO3-
What is Phosphate Buffer System?
Important buffer in ICF and urine
Acts similarly to Carbonic Acid-Bicarbonate Buffer System:
1- Dihydrogen Phosphate (H2PO4-) acts a Weak Acid
2- Monohydrate Phosphate (HPO42-) acts as Weak Base
OH- (Hydroxide ion) + H2PO4- —–> H2O + HPO42-
H+ + HPO42- —–> H2PO4-
What is Exhalation of CO2 Buffer System?
Exhalation of CO2:
Mixes CO2 with H2O in blood to form Carbonic Acid (H2CO3)
Exhaling CO2 leads to less acid production and a rise in pH
Whereas retaining CO2 leads to more acid production and a drop in pH
CO2 + H2O <—–> H2CO3 <—–> H+ + HCO3-
What is Negative Feedback Loop of Decreased Blood pH?
1- Decrease blood pH (more H+ concentration)
2- Central Chemoreceptors in Medulla Oblongata and Peripheral Chemoreceptors in Aortic and Carotid Bodies send nerve impulses
3- Dorsal Respiratory Group (DRG) in Medulla Oblongata sends nerve impulses
4- Diaphragm contracts more forcefully and frequently, so more CO2 is exhaled
5- As less H2CO3 forms, and fewer H+ are present, Blood pH increases (and H+ concentration decreases)
What is Kidney Excretion of H+?
Excreting H+ in urine removes nonvolatile acids
PCT and CD of Kidneys secrete H+ into Tubular fluid then Urine
Reabsorb HCO3- so it’s not lost in Urine
Some H+ secreted into Tubular Fluid of CD is buffered by HPO42- and NH3
The buffers are excreted in urine
What is Acidosis?
Blood pH < 7.35
What is Alkalosis?
Blood pH > 7.45
What is Respiratory Acidosis?
Blood pH drops due to:
Retention of CO2 which leads to excess H2CO3 (carbonic acid)
(and decrease pH)
1- Causes:
Hypoventilation due to Emphysema
Pulmonary Edema
Trauma to Respiratory Center
Airways obstructions
Dysfunction of muscles of respiration
2- Compensatory Mechanisms:
Renal:
Increase excretion of H+
Increased reabsorption of HCO3-
If complete then pH will be normal but pCO2 high
What is Respiratory Alkalosis?
Blood pH rises due to:
Excessive loss of CO2 as in Hyperventilation
(and increase pH)
1- Causes:
Hyperventilation due to oxygen deficiency
Pulmonary disease
CVA
Severe accident
2- Compensatory Mechanisms:
Renal:
Decreased excretion of H+
Decreased reabsorption of HCO3-
If complete then pH normal but pCO2 low
What is Metabolic Acidosis?
Arterial Blood levels of HCO3- fall
(and decreased pH)
1- Causes:
Loss of HCO3- due to diarrhea
Accumulation of acid (ketosis)
Renal Dysfunction
2- Compensatory Mechanisms:
Respiratory: Hypoventilation slows loss of CO2
If complete pH will be normal but HCO3- high
What is Metabolic Alkalosis?
Arterial Blood levels of HCO3- rise
(and increased pH)
1- Causes:
Loss of acid due to vomiting
Gastric suctioning
Use of certain Diuretics
Excessive intake of Alkaline drugs
2- Compensatory Mechanisms:
Respiratory: Hypoventilation slows CO2 loss
If complete pH will be normal but HCO3- high
How does Aging affect Fluid, Electrolytes, and Acid-Base Balance?
Significant diseases exist between adults and infants with respect to fluid distribution, regulation of fluid and electrolyte balance, and acid-base homeostasis
Factors that influence distribution:
1- Metabolic Rate
2- Functional Development of Kidneys
3- Body surface area
4- Breathing Rate
5- Ion concentrations
Older adults often have impaired ability to maintain balance
Often suffer from dehydration, Hypernatremia, Hypokalemia, and Acidosis
