Clinical sciences Flashcards
What is the relative risk reduction?
Relative risk reduction (RRR) or relative risk increase (RRI) is calculated by dividing the absolute risk change by the control event rate
What is the process by which atherosclerosis occurs?
Endothelial dysfunction is triggered e.g. by smoking, HTN and hyperglycaemia
Results in changes to the endothelium
Fatty infiltration of the sub-endothelial space by low-density lipoproteins (LDL)
Monocytes migrate from the blood and become macrophages. These macrophages then phagocytose the LDL and turn into large ‘foam cells’ (fat laden macrophages). As these macrophages die the result can further propagate the inflammatory process
SM proliferation + migration from the tunica media into the intima results in formation of a fibrous capsule covering the fatty plaque
Result of C3 deficiency?
causes recurrent bacterial infections
Results of C5 deficiency?
predisposes to Leiner disease
recurrent diarrhoea, wasting and seborrhoeic dermatitis
Results of C5-9 deficiency?
encodes the membrane attack complex (MAC)
particularly prone to Neisseria meningitidis infection
The MAC essentially punches holes in the surface of the cell. When the happens enough times, the cell is killed. So without these complement subunits this cannot happen.
Results of C1, C2 and C4 deficiency?
Form part of the classical complement pathway. A deficiency in any of these complements makes patients susceptible to immune complex diseases including SLE
What to give alongside ferrous fumarate in iron deficiency and why?
Ascorbic acid (vit C) - think about being told to drink orange juice
Iron is best absorbed in the small intestine in the ferrous form (Fe2+). Ferric iron (Fe3+), however, is more difficult for the intestinal mucosa to absorb. By the addition of Ascorbic acid (vitamin C) to oral iron therapy, there is increased conversion of Fe3+ to Fe2+ in the gastrointestinal tract. This increases the proportion of Fe2+ iron, which is more readily absorbed, thus improving the response to treatment.
Where is iron absorbed?
upper small intestine especially the duodenum
How is iron transported around the body?
carried in plasma as Fe3+ bound to transferrin
What decreases the absorption of iron?
A more alkaline environment: PPIs, gastric achlorhydria (no gastric acid)
tetracycline
tannin (found in tea)
Which type of renal stones form in acid/alkaline urine?
Acid - uric acid
Alkaline - struvite
Struvite = magnesium ammonium phosphate (ammonia is alkaline)
What is the inheritance pattern and cause go homocystinuria?
Homocystinuria is a rare autosomal recessive disease caused by a deficiency of cystathionine beta synthase
What are the features of patients with homocystinuria?
Everything points downwards, looking at legs
Fine, fair hair - pointing to the floor Arachnodactylyl - hands hanging by sides Learning difficulties - LOW IQ DOWNWARDS dislocation of the lens Increased risk of VTEs (DVT in leg)
Investigations in homocystinuria?
increased homocysteine levels in serum and urine
cyanide-nitroprusside test: also positive in cystinuria
Treatment of homocystinuria?
vitamin B6 (pyridoxine) supplements
(Google image for pictures)
B6 is needed in the conversion of homocysteine -> cysteine. Therefore providing more should clear the body of more homocysteine.
What are the stages of the cell cycle and what regulates it?
Regulated by cyclins
G0: resting phase
G1: cells increase in size, under influence of p53, this stage determines cell cycle length
S: synthesis of DNA, RNA, histone, centrosome duplication
G2: cells continue to increase in size
M: mitosis, cell division (shortest phase)
What is the inheritance pattern of mitochondrial diseases?
none of the children of an affected male will inherit the disease
all of the children of an affected female will inherit the disease
inheritance is only via the maternal line as the sperm contributes no cytoplasm to the zygote
What might you see on a muscle biopsy in mitochondrial diseases?
muscle biopsy classically shows ‘red, ragged fibres’ due to increased number of mitochondria
What foods contain folic acid?
Liver, green vegetables and nuts
Which conditions are associated with collagen type 1, 3, 4 and 5?
1 = Osteogenesis imperfecta 3 = Vascular variant of Ehlers-Danlos syndrome 4 = Goodpastures, alports 5 = Classical variant of Ehler-Danlos syndrome
What are the different sleep stages?
N1 → N2 → N3 → REM
Non-REM stage 1: Light sleep, associated with hypnic jerks
Non-REM stage 1: deeper sleep = 50% of all sleep
Non-REM stage 1: deep sleep - night tremors, bed wetting and sleep walking occur here
REM: dreaming occurs, loss of muscle tone/erections
REM can dysfunction - if the patient is DREAMING - must be REM regardless of whether there is hypotonia or not
On ECG:
Theta (N-REM1) → Sleep spindles/K-complexes (N-REM2) → Delta (N-REM3) → Beta (REM)
The Sleep Doctor’s Brain
What is specificity and how is it calculated?
A test’s specificity is the proportion of people without the disease who will have a negative result.
Specificity = True Negatives / (True Negatives + False Positives)
What is the p value?
A measure of the probability that an observed difference could have occurred just by random chance, assuming that the null hypothesis is true
Therefore = to a T1 error
Or, equal to the chance that the value of our study or one at least as extreme as it, could have occurred by chance if the null hypothesis is true
What is the difference between a T1 and T2 error?
T1 = the null hypothesis is rejected when it is true T2 = the null hypothesis is accepted when it is false
What is the ‘power’ and how is it calculated?
the probability of (correctly) rejecting the null hypothesis when it is false
power = 1 - the probability of a type II error
power can be increased by increasing the sample size
What type of vitamin deficiency is pyridoxine and what symptoms?
vitamin B6
This may cause some similar symptoms to pellagra, but classically also peripheral neuropathy
What type of vitamin deficiency produces pellagra?
Vitamin B3 (niacin)
How to calculate the left ventricular ejection volume?
Left ventricular ejection fraction = (stroke volume / end diastolic LV volume ) * 100%
Stroke volume = end diastolic LV volume - end systolic LV volume
How to calculate cardiac output?
Cardiac output = stroke volume x heart rate
What is the p53 gene, what Chr is it located on and when is it commonly seen?
p53 is a TUMOUR SUPPRESSOR GENE located on chromosome 17p. It is the most commonly mutated gene in breast, colon and lung cancer
What is p53s role in the cell cycle?
If it detects damaged DNA, it pauses the process to allow for the DNA to be repaired or destroyed. Therefore if there is a mutation here, the cell cycle won’t be halted and it will result in a short G1 and proliferation of the damaged cell
What is Li-Fraumeni syndrome?
A rare AD disorder characterised by the early onset of a variety of cancers such as sarcoma, breast cancer and leukaemias. It is caused by mutation in the p53 gene.
What is the pre-test probability?
Just the prevalence of the disease in the population
What is the post-test probability?
The proportion of patients with that particular test result who have the target disorder
Post-test probability = post test odds / (1 + post-test odds)
What are the pre-test odds?
The odds that the patient has the target disorder before the test is carried out
Pre-test odds = pre-test probability / (1 - pre-test probability)
What are the post-test odds?
The odds that the patient has the target disorder after the test is carried out
Post-test odds = pre-test odds x likelihood ratio
where the likelihood ratio for a positive test result = sensitivity / (1 - specificity)
What is the inheritance and deficiency in Fabry’s disease?
X-linked recessive
deficiency of alpha-galactosidase A
Symptoms of Fabry’s disease?
burning pain/paraesthesia in childhood angiokeratomas lens opacities proteinuria early cardiovascular disease
F - foggy lens A - angiokeratomas B - burning pain R - renal: proteinurea Y do I have cardiac problems too
What are the three possible intended outcomes of trials? What sample sizes are needed?
superiority: large sample size needed to show a significant benefit over an existing treatment
equivalence: confidence interval of the difference between the two drugs lies within the equivalence margin then the drugs may be assumed to have a similar effect
non-inferiority: similar to equivalence trials, but only the lower confidence interval needs to lie within the equivalence margin (i.e. -delta). Small sample sizes are needed for these trials. Once a drug has been shown to be non-inferior large studies may be performed to show superiority
What electrolyte movement occurs during: Rapid depolarisation Early repolarisation Plateau Final repolarisation Restoration of ionic concentrations
Rapid depolarisation - rapid Na influx Early repolarisation - K efflux Plateau - slow Ca influx Final repolarisation - K efflux Restoration of ionic concentrations - resting potential is restored by Na+/K+ ATPase
Speed of conduction along atrial fibres? AV node conduction? ventricular conduction?
atrial fibres - 1m/sec
AV node conduction - 0.05m/sec
Purkinje fibres - 2-4m/sec -> fastest in the heart
In which foods would you find riboflavin (vit B2)?
Widely found in plant and animal food
eggs, green vegetables and milk
What is the importance of vitamin A and what can a deficiency in it lead to?
Vit A - needed to produce rhodopsin, a light-absorbing molecule used for low light and colour vision
Deficiency = can cause blindness
Other than Wernicke’s, what can thiamine (B1) deficiency cause?
dry beriberi: peripheral neuropathy
wet beriberi: dilated cardiomyopathy
What can vitamin B3 produce?
Pellagra
Which nerve roots supply the musculocutaneous nerve and what are the common injuries?
C5-C7
Elbow flexion
Sensory to lateral part of the forearm
Rarely independent injury
Which nerve roots supply the axillary nerve and what are the common injuries?
C5-C6
Shoulder abduction
Sensory to inferior region of the deltoid muscle
May be caused by a humeral neck fracture/dislocation
Which nerve roots supply the radial nerve and what are the common injuries?
C5-C8
Extension (forearm, wrist, fingers, thumb)
Defect causes WRIST DROP
Sensory to small area between the dorsal aspect of the 1st and 2nd metacarpals
May be caused by a humeral midshaft fracture
Which nerve roots supply the medial nerve and what are the common injuries?
Motor to LOAF muscles
Sensory to latter 3.5 fingers
Caused by carpel tunnel
LOAF = Lateral two lumbricals Opponens pollis Abductor pollis brevis Flexor pollis brevis
Which nerve roots supply the ulnar nerve and what are the common injuries?
C8 -T1
Motor: Intrinsic hand muscles except LOAF
Sensory: Medial 1½ fingers
May be caused by medial epicondyle fracture
Which nerve roots supply the long thoracic nerve and what are the common injuries?
C5-C7
Damage results in a winged scapula
Often during sport, can be following mastectomy
What is Erb-Duchenne palsy and what causes it?
(‘waiter’s tip’)
due to damage of the upper trunk of the brachial plexus (C5,C6)
may be secondary to shoulder dystocia during birth
the arm hangs by the side and is internally rotated, elbow extended
What is Klumpke injury?
due to damage of the lower trunk of the brachial plexus (C8, T1)
May be secondary to shoulder dystocia during birth. Also may be caused by a sudden upward jerk of the hand
associated with Horner’s syndrome
What is the mechanism of PCR?
Add to the cauldron:
- DNA section, 2x DNA primers, free nucleotides (A,T,C,G) and the Taq polymerase enzyme
Heat up sample - bonds between DNA will break
Cool it down - primers will bond to section of the DNA
Heat up again a bit - Taq enzyme with fill in the gaps with nucleotides
Overall the amount of DNA doubles with each cycle -> DNA amplification
What is the chi-squared test?
used to compare proportions or percentages e.g. compares the percentage of patients who improved following two different interventions
What is the odds and odds ratio?
Odds are a ratio of the number of people who incur a particular outcome to the number of people who do not incur the outcome. The odds ratio may be defined as the ratio of the odds of a particular outcome with experimental treatment and that of control.
See pass med for example
Which kidney lies higher than the other?
Left - approximately 1.5cm higher
think about your liver being in the way
Which 3 structures are in direct contact with the R and L kidney?
R: Right suprarenal gland
Duodenum
Colon
L: Left suprarenal gland
Pancreas
Colon
What is the mechanism of NO?
NO is produced in endothelial cells and travels to SM cells
Here it is involved in the formation of cGMP which is involved in the relaxation of vessel walls causing vasodilation
What is prevalence/incidence bias (Neyman bias)?
When a study is investigating a condition that is characterised by early fatalities or silent cases. It results from missed cases being omitted from calculations
What is admission bias (Berkson’s bias)?
Cases and controls in a hospital case control study are systematically different from one another because the combination of exposure to risk and occurrence of disease increases the likelihood of being admitted to the hospital
What is recall bias?
Difference in the accuracy of the recollections retrieved by study participants, possibly due to whether they have disorder or not
What is publication bias?
Failure to publish results from valid studies, often as they showed a negative or uninteresting result. Important in meta-analyses where studies showing negative results may be excluded
What is work-up bias?
In studies which compare new diagnostic tests with gold standard tests, work-up bias can be an issue. Sometimes clinicians may be reluctant to order the gold standard test unless the new test is positive, as the gold standard test may be invasive (e.g. tissue biopsy). This approach can seriously distort the results of a study, and alter values such as specificity and sensitivity. Sometimes work-up bias cannot be avoided, in these cases it must be adjusted for by the researchers.
What is expectation bias?
Only a problem in non-blinded trials. Observers may subconsciously measure or report data in a way that favours the expected study outcome.
What is the Hawthorne effect?
Describes a group changing it’s behaviour due to the knowledge that it is being studied
Studied efficiency in The Hawthorne Works, people worked a lot harder during observation