Metabolic system Flashcards
What is the total body water of an average 60 year old male?
45%
What is the serum K value range of moderate hyperkalaemia?
6.1 to 6.9mmol/L
What is osmosis?
Spontaneous net movement of a solvent from a low concentration through a semi-permeable membrane to a higher solute concentration
What other stimuli besides increased plasma osmolarity can activate RAAS?
Stimulation of the sympathetic nervous system Low blood pressure in the kidneys (decreased glomerular filtration rate)
What are isotonic fluids used for?
To increase extracellular fluid volume
Is diffusion a spontaneous or activated process?
Spontaneous
What are two situations where hypotonic solutions might be used?
Diabetic ketoacidosis Hyperosmolar hyperglycaemia
What is metabolic alkalosis? *Note: physiological change*
Increased bicarbonate (>26mEq/L) and elevated pH (>7.45)
Name three other isotonic fluids
5% dextrose in water (also used as a hypotonic solution but it is considered isotonic) 5% dextrose in 0.225% saline Lactated Ringer’s solution
Neuron function and osmoregulation between cells and ECF are accomplished by what two things?
Na/K-ATPase Na/K channels
What are contributing factors to metabolic alkalosis?
Bicarbonate accumulation from exogenous sources Renal acid loss
Is the respiratory buffer mechanism fast or slow to respond to pH changes?
Fast
Name some examples of hypertonic fluids
3% sodium chloride/saline 5% sodium chloride/saline 10% dextrose in water 5% dexrose in 0.9% saline 5% dextrose in 0.45% saline 5% dextrose in Lactated Ringer’s solution 50% dextrose
What are anions?
Electrolytes that generate a negative charge
What are some examples of insensible fluid loss?
Transepidermal diffusion (sweating) Respiratory evaporative water loss (breathing)
What is the meaning of isotonic fluid?
Isotonic fluids have a concentration (tonicity) of dissolved particules equal to that of intracellular fluid
What is the mechanism of altered breathing to counter pH changes called?
Respiratory buffer mechanism
What is the osmotic pressure of a solution?
The pressure by which water is drawn into it through the semi-permeable membranes
Angiotensin II acts on the ____.
Hypothalamus
What is the serum potassium level of hyperkalaemia (general)?
>5.5mmol/L
How is metabolic alkalosis managed (general)?
Correct depletions Control underlying causes
What are the two roles of the kidneys in maintaining the acid-base balance?
Bicarbonate reabsorption and hydrogen excretion
Describe the presentation of hypokalaemia
“A SIC WALT” - Alkalosis - Shallow respirations - Irritability, decreased intestinal motility - Confusion - Weakness - Arrhythmia - Lethargy - Thready pulse
What usually causes hyperkalaemia?
Reduced renal excretion or the release of potassium from cells
What is the most prevalent metallic ion in ECF?
Sodium
What is anion gap used for?
Estimation of the unaccounted for anions in the blood in cases of metabolic disturbance
What is the most common isotonic fluid?
0.9% sodium chloride (normal saline)
Extracellular fluid contains the…
Ions and nutrients needed by the cells to maintain life
What are some causes of resp acidosis?
Respiratory depression Malignant hyperthermia Sepsis Liver failure Rebreathing expired gas Insufflation
What are some possible causes of resp alkalosis?
Hyperventilation Anxiety Exercise Fever Early sepsis Altitude sickness Pain Pregnancy (normal to a degree) Lung diseases
What do the macula densa cells stimulate?
The juxtaglomerular apparatus (JGA)
High plasma osmolarity is often a sign of what?
Low blood volume
What are the two likely causes of metabolic alkalosis?
Overuse of antacids/some diuretics GIT acid loss
What is the most plentiful chemical buffer in the body?
Protein
What is the thirst mechanism that begins in the renal system called?
Renin-angiotensin system mediated thirst *Note: also called the renin-angiotensin-aldosterone system (RAAS)*
At what serum level is hypokalaemia considered severe?
<2.4mmol/L
What two activities/habits are risk factors for hyponatraemia?
Endurance athletes MDMA (methylenedioxymethamphetamine) users
What is resp alkalosis? *Note: physical event and the physiological change*
Excessive elimination of CO2; alveolar hyperventilation. Decreased PaCO2 with an increased pH (>7.45)
List four functions of water in the body
Medium for metabolic reactions within cells Transporter for nutrients, waste products, and other substances Lubricant One way of regulating and maintaining body temperature
What is the total body water of a premature infant?
90%
What is an example cause of chronic/secondary resp acidosis?
COPD
Describe the presentation of hyperkalaemia
“MURDER” - Muscle cramps/weakness/twitches/paraesthesia - Urine abnormalities - Respiratory distress - Decreased cardiac contractility (hypotension) - ECG changes, palpitations - Reflex changes (lethargy, confusion)
What is the role of the lungs in the bicarbonate buffer system?
Regulate carbonic acid production
Carbonic acid results from combining what two substances?
Carbon dioxide and water
What are the two types of metabolic alkalosis?
Chloride responsive and non-chloride responsive
What other nutrients does extracellular fluid contain?
Oxygen Glucose Fatty acids Amino acids
Is the respiratory buffer mechanism a sustainable mx for pH changes?
No
What is the role of the bicarbonate buffer system?
Decrease the strength of potentially damaging acids and bases (damaging pH changes)
What are other causes of hyperkalaemia?
“MACHINE” - Medications (ACE inhibitors, NSAIDS) - Acidosis (metabolic, respiratory) - Cellular destruction (burns, trauma) - Hypoaldosteronism, haemolysis - Intake (excessive) - Nephrons, renal failure - Excretion (impaired)
What is the meaning of hypotonic fluids?
Hypotonic fluids have a tonicity less than that of intracellular fluid
What increases the risk of hypernatraemia?
Poorly controlled diabetes
Describe the pathophysiology of acute resp acidosis
CO2 is continuously produced by cellular respiration and rapidly accumulates if not adequately expelled through alveolar ventilation by the lungs, leading to hypercapnia
The RAAS regulates concentration of which electrolyte in the body?
Sodium
Bicarbonate (HCO3) buffers which two body fluids?
Blood ISF
What are cations?
Electrolytes that generate a positive charge
Do cells expand or contract when blood plasma has a higher contraction?
Contract
What is the value and physiological description of hypokalaemia?
Serum potassium <3.5mmol/L K+ depletion or shift into cells
Describe the presentation of acute resp acidosis
Confusion Fatigue Lethargy SOB Sweating Tachycardia Miadriasis
True or false: water passes freely and rapidly between all intracellular and extracellular compartments in response to solute changes
True
Where are osmoreceptors primarily found?
Hypothalamus
RAAS: when the concentration of sodium increases, does the production of renin increase or decrease?
Decrease
Do cells expand or contract when blood plasma is more dilute?
Expand
What does angiotensin II stimulation of the hypothalamus trigger?
Thirst sensation Vasoconstriction Aldosterone release
What is the total body water of a neonate?
80%
What are some examples of sensible fluid loss?
Urine output V+D Haemorrhage
What is the role of the kidneys in the bicarbonate buffer system?
Regulate bicarbonate production
Which are faster to compensate for pH changes, the renal or respiratory buffer system?
Respiratory
Extracellular fluid contains large amounts of which three ions?
Sodium Chloride Bicarbonate
What is the effect of carbon dioxide elimination?
The more CO2 eliminated the less carbonic acid is made - this causes pH to rise
What is the Na/K-ATPase?
An active transporter that pumps ions against the gradient
What is an osmoreceptor?
A sensory receptor that detects changes in osmotic pressure (plasma osmolarity)
What is sensible fluid loss?
Loss of measurable fluid volumes
Describe the osmotic pressure state of isotonic fluid infusion and the effect on cells
Osmotic pressure is the same inside and outside the cells, so they neither shrink nor swell with fluid movement
Extracellular fluid is mixed with blood and tissue fluids by which mechanism?
Diffusion through the capillary walls
Movement of fluid between intracellular and extracellular compartments is in response to what?
Changes in solutes
What are the two types of metabolic acidosis?
Anion gap and non-anion gap
What does aldosterone do (in general terms)?
Increases water reabsorption
Where does phosphate (mainly) exist in the body?
Renal tubules
What is the presentation of hyponatraemia?
Lethargy Seizures Coma
Intracellular fluid dissolves ____ and ____.
Solutes and proteins.
True or false: the more concentrated the solution, the weaker the osmotic pressure
False
Breathing faster or deeper eliminates what from the lungs?
Carbon dioxide
Intracellular fluid contains large amounts of which three ions?
Potassium, magnesium, and phosphate
What is the total body water of an obese adult?
40-50%
Which is the major homeostatic control point for maintaining a stable pH balance?
Renal excretion
What is the definition of homeostasis?
The physiological process by which the internal systems of the body are maintained at equilibrium despite variations in external conditions
Names some examples of hypotonic fluids
0.45% saline 0.225% saline 0.33% saline
What are the osmoreceptors in the walls of the ascending loop of Henle of the nephron called?
The macula densa cells
Is cellular energy expended in the process of diffusion?
No
What is metabolic acidosis? *Note: physical event and the physiological change*
Increased acid within the body due to excessive production or ineffective elimination of acids Reduced bicarbonate (<22mEq/l) and low pH (<7.35)
At what serum K level is hyperkalaemia classified as ‘severe’?
>7.0mmol/L
What is the overall chemical effect of breathing slower/shallower?
pH reduction (becomes more acidic)
How do proteins act as a buffer?
Binding with and neutralising acids
The mechanism of aldosterone’s effect is similar to what hormone?
Anti-diuretic hormone (ADH)
What is respiratory acidosis? *Note: physical event and the physiological change*
Hypoventilation of the alveoli; CO2 retention. Increased PaCO2 with a decreased pH (<7.35)
Describe the osmotic pressure state of hypertonic fluid infusion and the effect on cells
Osmotic pressure is greater outside the cells so water is drawn out of them, making them shrink
What does the JGA do when the macula densa detects high plasma osmolarity?
Releases renin into the bloodstream
Water will always follow which solute?
Sodium
Describe the osmotic pressure state of hypotonic fluid infusion and the effect on cells
Osmotic pressure is greater inside the cells so water is drawn into them, making them swell which can cause them to burst or lyse.
What is angiotensin I converted into?
Angiotensin II
What is insensible fluid loss?
Loss of immeasurable fluid volumes
Hypotonic fluids should never be given to patients with any of what three conditions?
ICP Extensive burns Trauma (already hypovolaemic)
What is diffusion?
The tendency of molecules to spread out in order to occupy available space
What is hypernatraemia and how does it effect cells?
High serum sodium (>150mmol/L) Causes cellular shrinkage, which can cause tearing
What is the meaning of hypertonic fluids?
Hypertonic fluids have a tonicity greater than that of intracellular fluid
Hypokalaemia commonly results from what two causes?
Excessive GIT or renal loss
What does renin do in the bloodstream?
Cleaves angiotensinogen into angiotensinogen I
What is hyponatraemia and how does it effect cells?
Low serum sodium (<130mmol/L) or excess of body water Expands intracellular volume
Carbonic acid rapidly dissociates to form what ion?
Bicarbonate
What converts angiotensin I to angiotensin II and where in the body does this occur?
Angiotensin-converting enzyme (ACE) in the lungs
What is the meaning of a higher anion gap measurement?
An increase in the percentage of one or more unmeasured anions in the bloodstream
What is the term for high serum sodium levels?
Hypernatraemia
What are the three components of homeostasic maintenance?
Receptor, control centre, and effector
What is the overall chemical effect of breathing faster/deeper?
pH elevation (becomes more alkaline)
What occurs when osmoreceptors detect high plasma osmolarity, and what is this mechanism called?
They send signals to the hypothalamus which creates the biological sensation of thirst Hypothalamus-mediated thirst
True or false: RBCs with H+ acts a buffer
True
Describe the presentation of resp alkalosis
Lip/extremity paraesthesia Carpal/pedal spasm Muscle cramps Dizziness/light-headedness Syncope
Molecules in liquid have a tendency to diffuse from a (more/less) concentrated environment to a (more/less) concentrated environment
More Less
What is a solute?
A substance that dissolves (salts is one example)
Non-anion gap metabolic acidosis is likely to have one of which three sources?
Iatrogenic Renal Gastrointestinal
What are the two most important mechanisms sodium is involved in?
Neuron function Osmoregulation between cells and extracellular fluid
Chemical buffers are present in ____, ____, and ____.
Blood ICF ISF
True or false: resp acidosis can be chronic or acute
True
What is the presentation of hypernatraemia?
“FRIED SALT” - Flushed - Restless, confused - Increased BP and fluid retention - Edema (oedema *Note: stupid American mnemonics…*) - Decreased urine, dry - Skin (flushed) - Agitation - Low fever - Thirst
What is the total body water of an average female?
50%
True or false: the anions responsible for anion gap metabolic acidosis depend on the cause
True
What is the total body water of an average male?
60%
What is the definition of osmotic pressure?
The pressure required to maintain an equilibrium, with no net movement of solvent.
What is the term for low serum sodium levels?
Hyponatraemia
What causes renal tubular acidosis?
Impaired ability to secrete H+ or absorb HCO3
