Case-control studies are suitable when investigating a rare disease or in cases where little is known about the disease and the proposed aetiological factor, as a preliminary study. They have the ability to look at multiple risk-factors (exposures) but can only look at a single outcome.

In a case-control study, two groups of patients, one with the disease and one without, are compared on the basis of a proposed causative factor that occurred in the past. They are therefore a retrospective study and useful in hypothesis generation.

Cohort studies are better at identifying rare exposures. One group with an exposure is compared to a control group without that exposure.

Case-control studies are usually less expensive to run and also shorter in duration compared with prospective cohort studies.

​Primary hyperparathyroidism the commonest cause of hypercalcaemia. It is commonest in women aged 50 to 60.
The commonest cause of primary hyperparathyroidism is a solitary adenoma of the parathyroid gland (approximately 85% of cases).

Primary hyperparathyroidism may present with features of hypercalcaemia such as polyuria, polydipsia, renal stones, bone and joint pain, constipation, and psychiatric disorders.

In primary Hyperparathyroidism:
PTH is elevated
Calcium is elevated
Phosphate is lowered

In secondary Hyperparathyroidism:
PTH is elevated
Calcium is low or low-normal
Phosphate is raised in CRF

In tertiary Hyperparathyroidism:
PTH is elevated
Calcium is elevated
Phosphate is lowered in CRF

Digoxin does not cause hypokalaemia, but hypokalaemia does potentiate digoxin toxicity. The adverse effects of digoxin are frequently due to its narrow therapeutic window and include:
Cardiac adverse effects – Sinoatrial and atrioventricular block, Premature ventricular contractions, PR prolongation and ST-segment depression
Nausea, vomiting and diarrhoea
Blurred or yellow vision
CNS effects – weakness, dizziness, confusion, apathy, malaise, headache, depression, psychosis
Thrombocytopenia and agranulocytosis (rare)
Gynaecomastia in men in prolonged administration

Juxtapulmonary or ‘J’ receptors are located on alveolar and bronchial walls close to the capillaries. Their afferents are small unmyelinated C-fibres or myelinated nerves in the vagus nerve. Activation causes depression of somatic and visceral activity by producing apnoea or rapid shallow breathing, a fall in heart rate and blood pressure, laryngeal constriction and relaxation of skeletal muscles via spinal neurones. J receptors are stimulated by increased alveolar wall fluid, pulmonary congestion and oedema, microembolism and inflammatory mediators. J receptors are thought to be involved in the sensation of dyspnoea in lung disease.

There is a lifelong susceptibility to increased risk of infection from a variety of organisms in patients with hyposplenism, especially in children under 5 years and those with sickle cell anaemia. Patients are most susceptible is to the encapsulated bacteria Streptococcus pneumoniae, Haemophilus influenzae type B and Neisseria meningitidis. Streptococcus pneumoniae is particular concerning as it can cause rapid and fulminant disease, which can be fatal. Malaria and animal bites that become infected also tend to be more severe.

Mycobacterium tuberculosis are part of the Mycobacteriaceae family. They are described to have the characteristics of a Gram-positive cell wall but they are not easily stained with Gram stain. This is because their cell wall contains a high lipid content, and this lipid allows the Mycobacteria to bind to alkaline stains with the application and help of heat. Once stained, they are able to resist decolorization even with the use of acid alcohol as the decolourizer, making them very difficult to decolorize, that is why they are known to be acid-fast.

The Ghon complex is a non-pathognomonic radiographic finding on a chest x-ray that is significant for pulmonary infection of tuberculosis. The location of the Ghon’s focus is usually subpleural and predominantly in the upper part of the lower lobe and lower part of the middle or upper lobe.

Skeletal tuberculosis of the spine is referred to as Pott disease.

The risk of reactivation TB is about 3.3% during the first year after a positive PPD skin test and a total of 5% to 15% thereafter in the person’s lifetime. Progression from infection to active disease varies with age and the intensity and duration of exposure. Reactivation TB occurs when there is an alteration or suppression of the cellular immune system in the infected host that favours
replication of the bacilli and progression to disease.

Parathyroid hormone (PTH) is a peptide hormone synthesised by the chief cells of the parathyroid glands, located immediately behind the thyroid gland. PTH is primarily released in response to decreasing plasma [Ca2+] concentration. PTH acts to increase plasma calcium levels and decrease plasma phosphate levels.
Parathyroid hormone (PTH) acts to increase calcium reabsorption in the distal tubule of the nephron (by activating Ca2+entry channels in the apical membrane and the Ca2+ATPase pump in the basolateral membrane) and increase phosphate excretion by inhibiting reabsorption in the proximal tubule of the nephron.

JVP Waveform in Cardiac Cycle Physiology: a wave Right atrial contraction causes atrial systole (end diastole). the c wave During right isovolumetric ventricular contraction, the tricuspid valve bulges into the right atrium, resulting in isovolumetric contraction (early systole). descent by x Rapid ventricular ejection (mid systole) is caused by a combination of right atrial relaxation, tricuspid valve downward movement during right ventricular contraction, and blood ejection from both ventricles. the v-wave Ventricular ejection and isovolumetric relaxation (late systole) occur as a result of venous return filling the right atrium. y lineage Ventricular filling occurs when the tricuspid valve opens, allowing blood to flow rapidly from the right atrium to the right ventricle.

Propofol is a short-acting anaesthetic that is thought to work by potentiating GABA and glycine. It induces anterograde amnesia and anaesthetic effects and is used to induce anaesthesia, outpatient surgeries and preoperative sedation. The dose for induction of anaesthesia is 1.5-2.5mg/kg. The dose for maintenance of anaesthesia is 4-12 mg/kg/hour. Following intravenous injection, propofol acts within 30 seconds and its duration of action is 5-10 minutes.

Propofol produces a 15-25% decrease in blood pressure and systemic vascular resistance without a compensatory increase in heart rate. It is negatively inotropic and decreases cardiac output by approximately 20%.

The main side effects of propofol are:
Pain on injection (in up to 30%)
Hypotension
Transient apnoea
Hyperventilation
Coughing and hiccough
Headache
Thrombosis and phlebitis

Anaemia of chronic disease is one of the most common causes of normocytic anaemia. The anaemia is usually mild (Hb > 90 g/L) and non-progressive. Anaemia of chronic disease is usually associated with low serum iron, low transferrin saturation, and a low total iron binding capacity (TIBC) with normal or raised ferritin which differentiates it from iron deficiency anaemia.

Short vessels called arteriovenous anastomoses (AVAs) link tiny arteries and veins. They have a large lumen diameter. The strong and muscular walls allow AVAs to completely clog the vascular lumen, preventing blood flow from artery to vein (acting like a sphincter). When the AVAs open, they create a low-resistance connection between arteries and veins, allowing blood to flow into the limbs’ superficial venous plexuses. There is no diffusion of solutes or fluid into the interstitium due to their strong muscle walls.

AVAs are densely innervated by adrenergic fibres from the hypothalamic temperature-regulation centre. High sympathetic output occurs at normal core temperatures, inducing vasoconstriction of the AVAs and blood flow through the capillary networks and deep plexuses. When the temperature rises, sympathetic output decreases, producing AVA vasodilation and blood shunting from the artery to the superficial venous plexus. Heat is lost to the environment as hot blood rushes near to the skin’s surface.
AVAs are a specialized anatomical adaptation that can only be found in large quantities in the fingers, palms, soles, lips, and pinna of the ear.

When there are excessive levels of aldosterone independent of the renin-angiotensin aldosterone axis, primary hyperaldosteronism occurs. Secondary hyperaldosteronism occurs due to high renin levels.

Causes of primary hyperaldosteronism include:
Conn’s syndrome
Adrenal hyperplasia
Adrenal cancer
Familial aldosteronism

Causes of secondary hyperaldosteronism include:
Renal vasoconstriction
Oedematous disorders
Drugs – diuretics
Obstructive renal artery disease

Although patients are usually asymptomatic, when clinical features are present, classically hyperaldosteronism presents with:
Hypokalaemia
Sodium levels can be normal or slightly raised
Hypertension
Metabolic alkalosis
Less common, clinical features are:
Lethargy
Headaches
Intermittent paraesthesia
Polyuria and polydipsia
Muscle weakness (from persistent hypokalaemia)
Tetany and paralysis (rare)

The primary functions of the Broca area are both language production and comprehension. While the exact role in the production is still unclear, many believe that it directly impacts the motor movements to allow for speech. Although originally thought to only aid in speech production, lesions in the area can rarely be related to impairments in the comprehension of language. Different regions of the Broca area specialize in various aspects of comprehension. The anterior portion helps with semantics, or word meaning, while the posterior is associated with phonology, or how words sound. The Broca area is also necessary for language repetition, gesture production, sentence grammar and fluidity, and the interpretation of others’ actions.

Broca’s aphasia is a non-fluent aphasia in which the output of spontaneous speech is markedly diminished and there is a loss of normal grammatical structure. Specifically, small linking words, conjunctions, such as and, or, and but, and the use of prepositions are lost. Patients may exhibit interjectional speech where there is a long latency, and the words that are expressed are produced as if under pressure. The ability to repeat phrases is also impaired in patients with Broca’s aphasia. Despite these impairments, the words that are produced are often intelligible and contextually correct. In pure Broca’s aphasia, comprehension is intact.

According to a 2018 audit conducted by the Royal College of Emergency Medicine (RCEM), the standard of care for children presenting to EDs with fractured limbs has deteriorated, with most patients waiting longer than ever before for pain relief. More than one-tenth of the children who came in with significant pain from a limb fracture received no pain relief at all.

For all patients, including children, the Agency for Health Care Policy and Research (AHCPR) in the United States recommends using the ABCs of pain management:
A – Ask about pain regularly. Assess pain systematically.
B – Believe the patient and family in their reports of pain and what relieves it.
C – Choose pain control options appropriate for the patient, family, and setting.
D – Deliver interventions in a timely, logical, coordinated fashion.
E – Empower patients and their families. Enable patients to control their course to the greatest extent possible.

The RCEM guidelines recommend assessing a child’s pain within 15 minutes of arrival. This is a fundamental requirement. For the assessment of pain in children, a variety of rating scales are available; which one is used depends on the child’s age and ability to use the scale. These are some of them:
Faces of Wong-Baker Scale for assessing pain
Scale of numerical evaluation
The behavioural scale is a scale that measures how people behave.

The RCEM has provided the following visual guide:
The RCEM has established the following guidelines for when patients in severe pain should receive appropriate analgesia:
100% within 60 minutes of arrival or triage, whichever is earliest
75% within 30 minutes of arrival or triage, whichever is earliest
50% within 20 minutes of arrival or triage, whichever is earliest

E. coli may cause several different gastrointestinal syndromes. Based on virulence factors, clinical manifestation, epidemiology, and different O and H serotypes, there are five major categories of diarrheagenic E. coli, enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), and enteroadherent, which includes diffusely adherent E. coli (DAEC) and enteroaggregative E. coli (EAEC). These five categories are sometimes
collectively referred to as enterovirulent E. coli or diarrheagenic E. coli.

Norwalk virus is part of the Caliciviridae family of viruses which are single-stranded RNA viruses and are the most common cause of infectious gastroenteritis in the US.

Rotaviruses are the most common cause of viral gastroenteritis
in infants and children. With the introduction in 2006 of a human-bovine rotavirus vaccine (RV5; RotaTeq, Merck), a delay in the onset of rotavirus
season was seen. RotaTeq is a series of three oral vaccines beginning at 6 to 12 weeks of age. A second vaccine, Rotarix (RV1; GlaxoSmithKline, Middlesex, England), was approved in June 2008.

Cryptosporidium causes an illness characterized by abdominal cramping, watery diarrhoea, vomiting, fever, and anorexia. This organism is resistant to chlorine, so public swimming pools can be the source of an outbreak.

G. lamblia has a worldwide distribution and has frequently been identified as the causative agent of outbreaks of gastroenteritis and traveller’s diarrhoea.

Juxtaglomerular cells are specialised smooth muscle cells mainly in the walls of the afferent arterioles (and some in the efferent arterioles) which synthesise renin.

A history of stroke and poor nutritional status points towards a nutritional deficiency as the most likely cause of her symptoms. The examination would differentiate between Vitamin B12 and Folic acid deficiency as in the former. The patient has a beefy red tongue and symptoms indicating peripheral nervous system involvement or subacute combined spinal cord degeneration. The patient may also have a lemon-yellow skin colour, loss of proprioception and vibratory sense and oral ulceration.

Investigations in B12 deficiency can reveal the following:
1. Macrocytic anaemia
2. Neutropoenia
3. Thrombocytopaenia
4. Blood film: anisocytosis, poikilocytosis
5. Low serum B12
6. Raised serum bilirubin (haemolysis)
7. Intrinsic factor antibodies
8. Positive Schilling test

Cryptococcus neoformans typically causes a chronic lymphocytic meningitis in immunosuppressed patients or those with intense exposure e.g. pigeon fanciers.

Cortisol is a steroid hormone produced in the zona fasciculata of the adrenal cortex. It is released in response to stress and low blood glucose concentrations.
Cortisol acts to: raise plasma glucose by stimulating glycolysis and gluconeogenesis in the liver and inhibiting peripheral glucose uptake into storage tissues, increase protein breakdown in skeletal muscle, skin and bone to release amino acids, increase lipolysis from adipose tissues to release fatty acidsand at higher levels and mimic the actions of aldosterone on the kidney to retain Na+ and water and lose K+ ionssuppress the action of immune cells

Listeria monocytogenes is a gram-positive bacteria that does not produce spores.

Staphylococcus aureus is a gram-positive bacteria, while Candida albicans is a gram-positive yeast with a single bud.

Among the choices, gram-negative bacteria include only Klebsiella pneumoniae and Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an oxidase-positive bacterium, while Klebsiella pneumoniae is an oxidase-negative bacterium.

P. aeruginosa can cause urinary tract infections (UTIs) and is spread through poor hygiene or contaminated medical equipment or devices, such as catheters that haven’t been fully sterilized.