Cell function, synaptic and junctional transmission Flashcards
Regarding body fluid composition, which of the following accounts for approximately 40% of bodyweight?
A Total body water (TBW)
B Intra cellular fluid (ICF)
C Plasma
D Extra cellular fluid (ECF)
Explanation
TBW=60%
ICF=40%
ECF=20% (interstitial fluid 15%, plasma=5%)
Which of the following penetrates cerebro-spinal fluid (CSF) most easily?
A N2O
B H2O, CO2, O2
C HCO3
D Na, K, Cl
B
Explanation
H and HCO3 penetrate slowly as compared to CO2, which has physiologic significance in the regulation of respiration. Lipid soluble free forms of steroid hormones also penetrate easily, whereas proteins do not.
The main buffer in interstitial fluid is?
A Ammonia
B Haemoglobin
C Bicarbonate
D Phosphate
C
Explanation
Blood- Bicarbonate, protein and HB.
Interstitial fluid- Bicarbonate. Intracellular fluid- Proteins, phosphate.
CSF and urine- Bicarbonate and phosphate
Which of the following accounts for 20% of total body weight?
A Total body water (TBW)
B Extracellular fluid (ECF)
C Blood volume
D Intracellular fluid (ICF)
B
Explanation
TBW=60%
ICF=40%
ECF=20% (interstitial fluid 15%, plasma=5%)
The intracellular component of the body water accounts for about 40% of body weight and the extracellular component for about 20%. Plasma is 5% of body weight, and total blood volume is about 8% of body weight.
Regarding intracellular fluid (ICF), which of the following is incorrect?
A Mg2+ of 20 mmol/l
B Na+ of 135 mmol/l
C PO4- of 103 mmol/l
D K+ of 140 mmol/l
B
Explanation
Intracellular:
Na 15mmol/L
K 150mmol/L
Cl 9mmol/L
Mg 13mmol/L
Phosphate 100mmol/L
Extracellular
Na 150mmol/L
K = 5.5mmol/L
Cl 125mmol/L
Mg 1mmol/L
Phosphate 1mmol/L
Values may vary a bit
Looking at the contents of a litre bag of 0.9% Sodium Chloride solution, Which of the following is incorrect?
A pH range 4.0-7.0
B There is 9g of sodium chloride/1000ml
C The osmolality is approximately 270 mOsm
D Approximatly 150mmol/L of sodium
C
Explanation
A litre bag of 0.9%NACL
Each 1000ml contains NACL 9grams
Approximately 150mmols of Na and Cl per 1000ml
pH range 4.0-7.0
Approximate osmolality 300mOsm (taken from the product information)
Extra: “to be specific”-
In a 1L bag of N/S: Na+ = 154mEq Cl- = 154mEq Therefore, theoretical osmolality = 308mOsm/L But: Na in plasma = 140mEq, and Cl in plasma = 110mEq ∴ the respective concentrations of both ions are actually very different to that of plasma, AND the osmolality of normal saline is actually hypertonic with respect to plasma (308mOsm/L vs. 285) However when NaCl is dissolved in water, only 92.6% is actually dissolved (the remainder is NaCl in water), i.e. the “osmotic coefficient” = 0.926 Therefore the real osmolality of normal saline = 308 x 0.926 = 285, which is isotonic with plasma
1 litre of 5% dextrose given intravenously would distribute predominantly to?
A Extracellular compartment
B Intracellular compartment
C Intravascular compartment
D Interstitial compartment
B
Explanation
A 5% dextrose solution is similar to the infusion of pure water, and water distributes itself evenly throughout the body spaces. Therefore, most will go to the intracellular fluid (ICF) due to its percentage. Some goes interstitial and some stays intravascular.
or…
5% Dextrose (Sugar 50g/1litre H20) is hypotonic, it has a lower osmotic pressure than plasma. It has a lower osmolality than plasma. After infusion intravenously it rapidly equilibrates with the intracellular fluid and is therefore useless for resuscitation.
or… Latest edition
A 5% glucose infusion is isotonic when initially infused intravenously, but glucose is metabolised, so the net effect is that of infusing a hypotonic solution.
With regard to total body water (TBW), which of the following statements is correct?
A Is typically 63% of body weight
B Increases with age
C Is greater in men than women
D Is typically 45% of bodyweight
C
Explanation
Total body fluid decreases with age, is typically around 60% of body weight and is composed largely of intracellular fluid.
Old question: in current textbook the percentage of TBW is 60%. Therefore 63% and 45% are wrong. TBW is greater in men than women is more correct.I
Extra:
Intracellular component 40%
Extracellular component 20%.
Of the extracellular component, approximately 25% is in the vascular system (plasma=5% of body weight)and 75% outside the blood vessels (interstitial fluid=15%of body weight). The total blood volume is about 8% of body weight
Regarding the composition of extracellular fluid (ECF) compared to that of intracellular fluid (ICF), which of the following statements is correct?
A ECF has an increased potassium concentration
B ECF has a decreased magnesium concentration
C ECF has a decreased sodium concentration
D ECF has an increased phosphate concentration
B
Explanation
Intracellular fluid has the highest concentration of phosphate. 99% of magnesium is intracellular or in bone. Approximately 98 percent of the body’s potassium stores are found within the cells
Which of the following is correct regarding the composition of extracellular fluid (ECF) when compared to that of intracellular fluid (ICF)?
A ECF has a decreased phosphate concentration
B ECF has a decreased sodium concentration
C ECF has an increased potassium concentration
D ECF has an increased magnesium concentration
A
Explanation
Intracellular fluid has the highest concentration of phosphate. 99% of magnesium is intracellular or in bone
The ratio of HCO3- ions to carbonic acid at a pH of 7.1 is?
A 10
B 100
C 1
D 0.1
A
Explanation
pH=pKa + log (HCO3/H2CO3)
pKa=6.1 and the H2CO3 is in equilibrium with CO2
Therefore
pH=6.1 + log {[HCO3]/0.0301PCO2}
Extra
The ratio at pH-This is taken directly out of the current textbook. In the primary exam you cannot use calculators, so the formula:
pH = pka + log HCO3/H2CO3 ;
7.4 = 6.1 + log HCO3/H2CO3;
1.3 = log HCO3/H2CO3 turns out log 20 = 1.3 so ratio is 20 cannot be used.
I think that the values just needed to be learnt. I have left this question as is, as it may come up again
7.4 = 20
7.3=16
7.1=10
6.0=0.9
What is the hydrogen ion concentration at a pH of 7.4?
A. 0.0003 meq/L
B. 0.00001meq/L
C. 0.00002 meq/L
D. 0.00004 meq/L
D
Explanation
pH=H ion concentration -meq/L
4.5 = 0.03
7.0 = 0.0001
7.4 = 0.00004
7.7 = 0.00002
8.0 = 0.00001
The definition of pH:
pH = -log [H+]
7.4 = -log [H+] [H+]
= 10^-7.4 (10 to the power of -7.4) [H+]
= 0.00000004 mol/L
= 0.00004 mmol/L
= 0.00004 mEq/L
Regarding basic physiological measures, all of the following are true except?
A. One equivalent of Na+ is 23g
B. Osmolality is affected by the volume of various solutes in the solution and temperature
C. pH is defined as the logarithm to the base 10 of the reciprocal of the H+ concentration
D. Carbon has a molecular mass of 12 dalton
B
Explanation
Osmolarity is the number of osmoles per liter of solution.
Osmolality is the number of osmoles per kilogram of solvent.
The osmolal concentration of a substance in a fluid is measured by the degree to which it depresses the freezing point by 1.86 degrees Celsius. Therefore, osmolarity is affected by the volume of various solutes in the solution and temperature, while the osmolality is not.
Extra:
Osmolarity is a measure of the number of osmoles per litre of solution (osmolality is the number of osmoles per kilogram) and can be measured using a variety of techniques including - freezing point depression - boiling point elevation - vapour pressure changes - osmotic pressure gradients across semipermeable membranes.(Osmolality is not affected by the volume of the various solutes in solution and temperature). pH is defined as the logarithm to the base 10 of the reciprocal of the H+ concentration. The molecular mass of carbon is 12 dalton. An equivalent is a measure of mass (the amount of substance it takes to combine with 1 mole of hydrogen ions or electrons). The equivalent weight of sodium is 23g (not 23g/L)
Where are steroids synthesised in steroid secreting cells?
A. Mitochondira
B. Rough endoplasmic reticulum
C. Golgi apparatus
D. Smooth endoplasmic reticulum
D
Explanation
The agranular endoplasmic reticulum (smooth ER), is the site of steroid synthesis in steroid secreting cells and is the site of detoxification processes in other cells. The rough (granular) ER is concerned with protein synthesis and the initial folding of polypeptide chains with the formation of disulfide bonds. The SER plays an important role in skeletal and cardiac muscle
See below for a full explanation of steroid synthesis. Be aware, that the mitochondria are also involved. However, I will leave the question and answer as is.
Note: - cholesterol is moved into the mitochondria by steroidogenic acute regulatory protein (StAR) to reach cholesterol demolase, where it is converted to pregnenolone. Prgnenolone is moved to the smooth ER to be dehydrogenated to progesterone by 3 beta-hydroxysteroid dehydrogenase. (note also that 17a-hydroxypregnenolone and 17a-hydroxyprogesterone are formed from pregnenolone and progesterone respectively by the action of 17a-hydroxylase, which is another MITOCHONDRIAL p450 enzyme). Hydroxylation of progesterone and 17a-hydroxyprogesterone to 11-deoxycorticosterone and 17a-deoxycortisol occurs in the smooth ER. These are then moved back into the mitochondria to be 11-hydroxylated to form corticosterone and cortisol. Additionally, is also found in the mitochondria. So the initial and final steps of glucocorticoid and mineralocorticoid synthesis are actually the mitochondria. The only steroids formed in the smooth ER are DHEA and androstenedione
Which of the following mediators in the brain is only excitatory?
A Glutamate
B Acetylcholine
C GABA
D Glycine
A
Explanation
GABA is the main inhibitory mediator in the brain, where it is the transmitter at 20% of CNS synapses.
Glycine and acetylcholine have both excitatory and inhibitory effects in the CNS.
Glutamate is the main excitatory transmitter in the brain and spinal cord, and it has been calculated that it is the transmitter responsible for 75% of the excitatory transmissions in the brian.
Aspartate is an excitatory neurotransmitter as well. It occurs in the pyramidal cells and spiny stellate cells in the visual cortex, but it has not been studied in great detail.
Which nerve fibre is the last to be affected with the use of local anaesthetics?
A. Pain, temperature
B. Proprioception, somatic motor
C. Touch, pressure
D. Motor to muscle spindles
B
Explanation
The order of susceptibility of nerve fibres to conduction block by local anaesthetics are C>B>A
The largest fibre diameter, A alpha-proprioception and somatic motor, are the last to be affected.
Types of A fibres
Largest to smallest diameter
A alpha- proprioception and somatic motor
A beta-touch and pressure
A gamma- motor to muscle spindles
A delta- pain and temp
Hypoxia: B>A>C (most susceptible to least)
Pressure: A>B>C (most susceptible to least)
Extra:
Aα - Proprioception and somatic motor - Large and heavily myelinated Aβ - Touch and pressure - Medium and heavily myelinated Aγ - Motor to muscle spindles - Medium and heavily myelinated Aδ - Fast pain and temp - Small and heavily myelinated B - Preganglionic autonomic nerves - Small and lightly myelinated C - Slow pain, postganglionic autonomic - Small and unmyelinated
The function of nerve fibres with the largest diameter is:
A Pain, temperature
B Proprioception, motor
C Touch, pressure
D Motor to muscle spindles
B
Explanation
Type A nerve fibres include alpha, beta, gamma and delta. Conduction speeds and diameter decrease down the list, with alpha being the largest diameter. The function of alpha fibres is proprioception and motor function.
