INI CET Practice Set 1

Explanation: In adults, the medial circumflex femoral artery (via its retinacular branches) provides the major blood supply to the femoral head. The artery of the ligamentum teres (from the obturator artery) is a minor contributor. This explains why femoral neck fractures can lead to avascular necrosis of the femoral head.

Explanation: The ductus arteriosus connects the pulmonary trunk (left pulmonary artery) to the arch of the aorta, shunting blood away from the non-functioning fetal lungs. After birth, it closes functionally within 24-48 hours and becomes the ligamentum arteriosum. Failure to close results in patent ductus arteriosus (PDA).

Explanation: The plateau phase (phase 2) of the ventricular action potential is maintained by the influx of calcium ions through L-type calcium channels, balanced by outward potassium current. This prolonged plateau distinguishes the cardiac action potential from skeletal muscle and prevents re-excitation (tetany).

Explanation: ADH (vasopressin) acts on the collecting duct by inserting aquaporin-2 (AQP2) water channels into the apical membrane via V2 receptors (Gs-cAMP pathway), thereby increasing water permeability and reabsorption. Deficiency causes diabetes insipidus.

Explanation: The Km is the substrate concentration at which the reaction velocity is half of Vmax. It is a measure of the affinity of the enzyme for its substrate — a low Km indicates high affinity. Km is altered by competitive inhibitors (increased) but not by non-competitive inhibitors.

Explanation: Type III hypersensitivity is mediated by antigen-antibody immune complex deposition in tissues, activating complement and recruiting neutrophils that cause tissue damage. Examples include serum sickness, post-streptococcal glomerulonephritis, SLE nephritis, and the Arthus reaction.

Explanation: Haemangioma (cavernous haemangioma) is the most common benign tumour of the liver. It is usually an incidental finding, typically solitary, and located in the right lobe. Biopsy is contraindicated due to the risk of haemorrhage.

Explanation: The Quellung reaction is a diagnostic test in which the polysaccharide capsule of Streptococcus pneumoniae swells when treated with specific anticapsular antisera. It allows rapid identification and serotyping. Over 90 serotypes have been identified using this method.

Explanation: The Paul-Bunnell test detects heterophile antibodies (IgM against sheep/horse RBCs) that appear in infectious mononucleosis caused by Epstein-Barr virus (EBV). The Monospot test is a rapid latex agglutination variant. Heterophile-negative mono should prompt testing for CMV.

Explanation: In zero-order (saturation) kinetics, a constant AMOUNT of drug is eliminated per unit time regardless of plasma concentration, because the metabolising enzymes are saturated. Examples include ethanol, phenytoin at high doses, and aspirin. The half-life increases with increasing dose.

Explanation: Omeprazole is a proton pump inhibitor (PPI) that irreversibly inhibits the H+/K+ ATPase enzyme (proton pump) on the luminal surface of gastric parietal cells. It is a prodrug activated in the acidic environment of the canaliculus. It is the most potent suppressor of gastric acid secretion.

Explanation: Cadaveric spasm (instantaneous rigor mortis) is the immediate stiffening of muscles at the moment of death, without the usual period of primary relaxation. It is most commonly seen in the hands — grasping an object at the time of death (e.g. a weapon, grass in drowning). It cannot be reproduced after death and thus has strong medico-legal significance.

Explanation: Under India's Universal Immunisation Programme, BCG (Bacille Calmette-Guérin) vaccine is given at birth or as early as possible. It is an intradermal injection of 0.05 mL (for infants <1 month) or 0.1 mL given over the left deltoid region. It provides protection against severe forms of childhood TB (TB meningitis, miliary TB).

Explanation: Myopia (short-sightedness/near-sightedness) is the most common refractive error globally. The eyeball is too long or the cornea too curved, causing parallel rays of light to focus in front of the retina. It is corrected with concave (minus) lenses.

Explanation: Acute angle-closure glaucoma presents with severe eye pain, redness, nausea/vomiting, blurred vision, halos around lights, a mid-dilated fixed pupil, and a stony-hard eyeball. Gradual painless loss of peripheral vision is characteristic of chronic open-angle glaucoma, not angle-closure.

Explanation: A negative Rinne test (BC > AC) indicates conductive hearing loss, where sound transmission through the external and middle ear is impaired (e.g. otitis media, otosclerosis, tympanic perforation). In sensorineural hearing loss, the Rinne test is positive (AC > BC) but both are reduced.

Explanation: Trousseau sign (carpopedal spasm induced by inflating a BP cuff) is a clinical feature of hypocalcaemia. The increased neuromuscular excitability due to low calcium causes the characteristic flexion of the wrist, metacarpophalangeal joints, and adduction of the thumb (main d'accoucheur). Chvostek sign (facial muscle twitch on tapping) is another sign.

Explanation: Anti-double-stranded DNA (anti-dsDNA) antibodies are highly specific (>95%) for systemic lupus erythematosus (SLE). Their titres correlate with disease activity, particularly lupus nephritis. Anti-Smith (anti-Sm) antibodies are the MOST specific but less sensitive for SLE.

Explanation: The anterior wall of the first part of the duodenum (D1) is the most common site of peptic ulcer perforation. Posterior duodenal ulcers tend to erode into the gastroduodenal artery, causing haemorrhage rather than perforation, because the posterior wall is retroperitoneal.

Explanation: Murphy's sign is positive in acute cholecystitis. The examiner palpates the right subcostal region (at the intersection of the right costal margin and the lateral border of the rectus abdominis) while the patient inspires deeply. Inspiratory arrest due to pain when the inflamed gallbladder descends to meet the palpating hand is a positive sign.

Explanation: The Alvarado score (MANTRELS) is a clinical scoring system for acute appendicitis, using symptoms (Migration of pain, Anorexia, Nausea/vomiting), signs (Tenderness in RIF, Rebound tenderness, Elevated temperature), and lab findings (Leucocytosis, Shift to left). A score >=7 is highly suggestive of appendicitis.

Explanation: A partograph is a graphical record of the progress of labour, plotting cervical dilatation and descent of the fetal head against time. It includes alert and action lines to identify prolonged labour. WHO recommends its use to reduce maternal and neonatal morbidity by enabling early intervention.

Explanation: Uterine atony (failure of the uterus to contract adequately after delivery) is the most common cause of postpartum haemorrhage, accounting for approximately 70-80% of cases. The '4 Ts' mnemonic covers the causes: Tone (atony), Trauma, Tissue (retained products), and Thrombin (coagulopathy).

Explanation: Physiological jaundice appears on day 2-3 of life, peaks by day 3-5 in term neonates (day 5-7 in preterm), and resolves by 2 weeks. It is due to immature hepatic glucuronyl transferase and increased RBC breakdown. Jaundice appearing within the first 24 hours is always pathological (e.g. Rh/ABO incompatibility).

Explanation: Under India's national immunisation schedule, the first dose of measles-containing vaccine (MR - Measles-Rubella) is given at 9 completed months. The second dose (MR-2) is given at 16-24 months. Earlier administration may be ineffective due to interference from maternal antibodies.

Explanation: Colles' fracture is an extra-articular fracture of the distal radius within 2 cm of the wrist joint, with dorsal displacement and dorsal angulation of the distal fragment (producing a 'dinner fork' deformity). It results from a fall on an outstretched hand (FOOSH) with the wrist in dorsiflexion.

Explanation: Loss of response to surgical stimulation (absence of movement, haemodynamic changes, or autonomic responses to incision) is the most reliable clinical indicator of adequate depth of anaesthesia. BIS (Bispectral Index) monitoring provides an objective EEG-based assessment (target 40-60 for adequate anaesthesia).

Explanation: The double bubble sign (two gas-filled spaces — stomach and proximal duodenum — with no distal gas) is pathognomonic of complete duodenal atresia. It occurs because of obstruction at the second part of the duodenum. It is commonly associated with Down syndrome (trisomy 21).

Explanation: Nikolsky sign is positive in pemphigus vulgaris, where the intraepidermal acantholysis (loss of intercellular adhesion due to IgG antibodies against desmoglein 3) allows the epidermis to slide over the dermis. It is negative in bullous pemphigoid (subepidermal separation). It may also be positive in SJS/TEN and staphylococcal scalded skin syndrome.

Explanation: Wernicke encephalopathy is caused by thiamine (vitamin B1) deficiency, most commonly in chronic alcoholics. The classic triad is confusion, ophthalmoplegia (especially lateral rectus palsy / CN VI), and cerebellar ataxia. If untreated, it progresses to Korsakoff psychosis (irreversible amnesia with confabulation).