UHS 2nd year MBBS past papers for Biochemistry, Physiology and Anatomy subjects.

Correct answer: B. Convert toxic ammonia to excretable urea.

Ammonia (from amino acid deamination, bacterial action) is toxic, especially to CNS. Urea cycle in liver converts 2 NH3 + CO2 → urea (water-soluble, excreted in urine). Defects cause hyperammonemia with vomiting, lethargy, coma, brain damage.

Correct answer: B. Branched-chain α-ketoacid toxicity.

Branched-chain ketoacids (especially from leucine) compete with other amino acids for brain transport, inhibit neurotransmitter synthesis, and impair energy metabolism. Acute management: remove branched-chain amino acids, provide calories to stop catabolism.

Correct answer: C. Red blood cells.

Mature erythrocytes lack mitochondria, relying on glycolysis for ATP (maintains membrane pumps, shape). Lactate is end product. 2,3-BPG regulates O2 affinity. Other glycolytic tissues: renal medulla (low O2), fast-twitch muscle fibers, retina, some tumors.

Correct answer: C. Anaerobic glycolysis with lactate production.

Heart normally uses fatty acids (60-90%), but during ischemia switches to anaerobic glycolysis. However, lactate accumulation causes acidosis, and ATP production is insufficient → contractile dysfunction. Preconditioning upregulates glycolytic enzymes.

Correct answer: B. Muscle glycogen.

High-intensity exercise: muscle glycogen → glycolysis → lactate. Glycogen provides rapid ATP without oxygen. Moderate exercise uses fatty acids. Trained athletes have increased mitochondrial density, using more fatty acids, sparing glycogen.

Correct answer: C. pH = 7.25 in metabolic alkalosis.

Mixed disorders occur when compensation is inadequate or excessive, or when two primary disorders coexist. In metabolic alkalosis (primary ↑HCO3−), compensation should cause hypoventilation (↑PCO2) and pH >7.45. pH 7.25 indicates superimposed acidosis.

Correct answer: B. Increased anion gap metabolic acidosis.

DKA involves accumulation of acetoacetic acid and β-hydroxybutyric acid, increasing unmeasured anions and thus the anion gap. Typically: pH 12. May have superimposed metabolic alkalosis from vomiting.

Correct answer: B. Renal compensation for respiratory disorders (days).

Renal compensation for respiratory disorders takes 3-5 days for full effect because it requires increased synthesis of ammonia, induction of transporters, and increased H+ secretion. Respiratory compensation for metabolic disorders occurs within hours.

Correct answer: B. Excrete bicarbonate in urine.

Normally, kidneys excrete excess HCO3− to correct alkalosis. However, if volume depletion, hypokalemia, or hyperaldosteronism persists, increased proximal HCO3− reabsorption and distal H+ secretion prevent correction ("contraction alkalosis" or "chloride-responsive").

Correct answer: B. Na+ - (Cl− + HCO3−).

AG = Na+ - (Cl− + HCO3−). Normal = 8-12 mEq/L. Represents unmeasured anions (proteins, phosphate, sulfate). Increased AG suggests addition of acid (lactic, ketoacids, toxins). Normal AG (hyperchloremic) acidosis suggests HCO3− loss or impaired acid excretion.

Correct answer: A. Glutamine and ATP.

CTP synthetase aminates UTP at position 4 using glutamine nitrogen. Activated by GTP, inhibited by CTP (feedback). Cytidine or cytosine can be salvaged via uridine-cytidine kinase.

Correct answer: A. Early steps of purine synthesis.

6-MP is converted to thio-IMP, which inhibits: 1) PRPP amidotransferase; 2) IMP dehydrogenase; 3) Adenylosuccinate synthetase. Used as immunosuppressant in transplantation and autoimmune diseases.

Correct answer: A. Carbamoyl phosphate (using glutamine, CO2, 2ATP).

Cytosolic carbamoyl phosphate synthetase II uses glutamine (not ammonia like mitochondrial CPS I in urea cycle). Inhibited by UTP, activated by ATP and PRPP. Different from urea cycle enzyme (CPS I) in location, nitrogen source, and regulation.

Correct answer: B. Increasing renal uric acid excretion.

Probenecid inhibits URAT1 transporter in proximal tubule, reducing uric acid reabsorption. Used in under-excretors (90% of gout patients). Contraindicated in overproducers or renal impairment. May precipitate acute gout initially.

Correct answer: B. Folate (as methylene-THF).

Thymidylate synthase transfers methylene group from methylene-THF to dUMP, forming dTMP and dihydrofolate. This is the only de novo source of thymine methyl group. Folate deficiency causes megaloblastic anemia due to impaired DNA synthesis.

Correct answer: C. Psychogenic polydipsia.

SIADH: euvolemic hyponatremia, inappropriately concentrated urine (>100 mOsm/kg), normal thyroid/adrenal. Psychogenic polydipsia causes hyponatremia with dilute urine (<100). Causes of SIADH: malignancy (SCLC), CNS disorders, drugs, pulmonary disease.

Correct answer: A. Cardiac myxomas, spotty skin pigmentation, endocrine overactivity.

Autosomal dominant. PRKAR1A mutation. Endocrine: pituitary adenomas, adrenocortical hyperplasia, testicular tumors. Other: psammomatous melanotic schwannomas. Differentiate from MEN syndromes.

Correct answer: A. Hyperparathyroidism.

Hypercalcemia from hyperparathyroidism promotes CPPD crystal formation in joints (especially knees). Other associations: hemochromatosis (iron), hypomagnesemia, hypothyroidism. Treat underlying condition, NSAIDs for acute attacks.

Correct answer: C. High insulin, low C-peptide.

Exogenous insulin causes high insulin but low C-peptide (not co-secreted). Insulinoma: both high. Sulfonylurea ingestion: both high (stimulates endogenous secretion). Critical for diagnosing insulin abuse or insulinoma.

Correct answer: B. Increased TBG, increased total T4 but normal free T4.

Estrogen increases TBG → increased total T4/T3 but free levels normal. hCG has TSH-like activity → slightly decreased TSH in first trimester. Increased demand (placental deiodinase, increased volume) → requires 30-50% more thyroid hormone.

Correct answer: C. Somatostatin.

Somatostatin acts as a paracrine inhibitor of both acinar and ductal cell secretion in the pancreas.

Correct answer: A. Premature activation of proteases within the pancreas.

Autodigestion due to intra-pancreatic activation of trypsinogen is a key event in acute pancreatitis.

Correct answer: B. Enzyme secretion.

Secretin primarily stimulates bicarbonate-rich fluid secretion. Enzyme secretion is primarily stimulated by CCK and vagal input.

Correct answer: B. Enteropeptidase.

Enteropeptidase (enterokinase), a brush border enzyme, cleaves trypsinogen to trypsin, which then activates other proteases.

Correct answer: B. Amylin.

Amylin is co-secreted with insulin and contributes to glucose regulation by suppressing glucagon and slowing gastric emptying.

Correct answer: C. Para-aminohippuric acid (PAH).

PAH clearance ≈ effective renal plasma flow as it's almost completely cleared in one pass.

Correct answer: B. Spastic bladder with small capacity.

UMN lesion (above pons) causes detrusor hyperreflexia with small, spastic bladder.

Correct answer: B. S2-S4.

Bulbocavernosus reflex (S2-S4) tests sacral spinal cord integrity; squeezing glans causes anal sphincter contraction.

Correct answer: B. L1-L2.

Cremasteric reflex (L1-L2) tests genitofemoral nerve; stroking inner thigh elevates ipsilateral testicle.

Correct answer: B. Urethral sphincter.

Stress incontinence involves inadequate urethral closure during increased abdominal pressure.

Correct answer: C. Conscious proprioception.

Basal ganglia modulate movement and cognition; proprioception is sensory and processed elsewhere.

Correct answer: B. Emotion, motivation, and memory.

Includes hippocampus, amygdala, cingulate gyrus, and related structures.

Correct answer: B. Executive functions, decision-making, personality.

It integrates information for planning, judgment, and social behavior.

Correct answer: A. Language comprehension.

Damage to Wernicke's area (superior temporal gyrus) causes receptive aphasia.

Correct answer: B. Speech production.

Damage to Broca's area (inferior frontal gyrus) causes expressive aphasia.

Correct answer: B. Can function independently of CNS input.

The enteric nervous system contains complete reflex circuits that can regulate gastrointestinal function autonomously, though modulated by autonomic input.

Correct answer: B. Sympathetic pathways to the face.

Horner's syndrome (ptosis, miosis, anhidrosis) occurs with disruption of the sympathetic chain supplying the face.

Correct answer: B. T6.

Lesions above T6 allow unopposed sympathetic discharge from isolated spinal cord segments in response to noxious stimuli below the lesion.

Correct answer: B. Modified sympathetic ganglion.

Chromaffin cells of the adrenal medulla are developmentally similar to postganglionic sympathetic neurons and secrete epinephrine directly into blood.

Correct answer: B. Acetylcholine.

All postganglionic parasympathetic neurons release acetylcholine that acts on muscarinic receptors on target organs.

Correct answer: B. High LH, low/normal FSH.

PCOS features an elevated LH:FSH ratio, insulin resistance, and hyperandrogenism.

Correct answer: C. Androgens.

21-hydroxylase deficiency shunts precursors to androgen pathway, causing virilization.

Correct answer: C. Testosterone.

Testosterone from fetal testes stimulates Wolfian duct development.

Correct answer: C. Inhibin.

Inhibin from granulosa cells selectively suppresses FSH.

Correct answer: B. Progesterone.

Progesterone peaks in the luteal phase to prepare the endometrium.

Correct answer: C. Vestibular function.

Warm or cold water irrigation of the ear canal induces convection currents in the semicircular canals, triggering nystagmus and assessing vestibular integrity.

Correct answer: A. Slow and fast eye movements.

Nystagmus consists of a slow drift followed by a fast corrective saccade, often due to vestibular imbalance.

Correct answer: B. Vestibular system.

Asymmetric vestibular input creates the illusion of movement (vertigo).

Correct answer: A. Stabilize gaze during head movement.

VOR generates compensatory eye movements opposite to head rotation, maintaining visual fixation.

Correct answer: A. Vertical acceleration.

The saccular macula is vertically oriented and senses linear acceleration in the vertical plane.

Correct answer: A. Cystic duct, common hepatic duct, and liver edge.

Surgical triangle for identifying cystic artery during cholecystectomy: cystic duct below, common hepatic duct medially, liver edge above.

Correct answer: B. Spleen.

Spleen lies beneath left 9th-11th ribs, making it vulnerable in lower left rib fractures (common in trauma).

Correct answer: B. Colic flexure lies deep to enlarged spleen.

In splenomegaly, enlarged spleen displaces splenic flexure of colon downward and medially, with colon lying superficial/anterior.

Correct answer: A. It is resonant on percussion.

Spleen is dull to percussion due to solid parenchyma. Resonance suggests pneumothorax or bowel interposition.

Correct answer: A. Splenic artery supplies entire pancreas.

Pancreas has dual supply: head from pancreaticoduodenal arteries (celiac/SMA), body/tail from splenic artery branches.

Correct answer: B. Internal iliac nodes.

Lymphatic drainage of the rectum follows a dual pattern: - Upper rectum: Drains along the superior rectal artery to the inferior mesenteric nodes AND laterally along the middle rectal vessels to the internal iliac nodes. - Lower rectum/anal canal above the pectinate line: Drains to the internal iliac nodes. - Anal canal below the pectinate line and perianal skin: Drains to the superficial inguinal nodes. This pattern dictates the spread of rectal carcinomas.

Correct answer: D. Urethra.

In females, the urethra is very short and pierces the perineal membrane to open externally. Its entire length is essentially superior to the perineal membrane and is thus not located within the superficial perineal pouch. The superficial pouch in females contains the clitoris, bulbs of the vestibule, greater vestibular glands, and the superficial perineal muscles (ischiocavernosus, bulbospongiosus, superficial transverse perineal).

Correct answer: D. Prostate gland.

The prostate gland is situated superior to the perineal membrane (urogenital diaphragm) and is therefore not contained within the deep perineal pouch. The deep perineal pouch is the space between the perineal membrane and the superior fascia of the urogenital diaphragm. In males, it contains the membranous urethra, bulbourethral glands, deep transverse perineal muscles, and the external urethral sphincter.

Correct answer: C. It lies lateral to the transverse processes of the lumbar vertebrae.

This statement is incorrect. The ureter descends on the anterior surface of the psoas major muscle, which places it medial or directly anterior to the tips of the transverse processes of the lumbar vertebrae (L2-L5). It then crosses the bifurcation of the common iliac artery at the pelvic brim. Knowing its precise retroperitoneal course is essential to avoid injury during abdominal surgeries.

Correct answer: B. Membranous urethra.

The membranous urethra is the shortest (1-2 cm long), narrowest, and least distensible segment. It passes through the urogenital diaphragm (perineal membrane and deep perineal pouch), surrounded by the external urethral sphincter. Its fixed position makes it susceptible to injury in pelvic fractures (leading to urethral strictures) and iatrogenic damage during catheterization or surgery.

Correct answer: C. Basilar artery.

The labyrinthine artery (or internal auditory artery) typically arises from the anterior inferior cerebellar artery (AICA), which is itself a branch of the basilar artery. Less commonly, it may arise directly from the basilar artery. It enters the internal acoustic meatus along with CN VII and VIII to supply the membranous labyrinth of the inner ear.

Correct answer: D. Epithelial cells of the choroid plexus.

The epithelial cells of the choroid plexus are a key component of the blood-CSF barrier, not the blood-brain barrier. The BBB proper consists of: 1) capillary endothelial cells with tight junctions, 2) a thick basement membrane, and 3) astrocytic end-feet surrounding the capillaries. The choroid plexus epithelium has its own tight junctions and separates fenestrated capillaries from the CSF in the ventricles.

Correct answer: D. Cerebral aqueduct (of Sylvius).

The cerebral aqueduct is a narrow, tubular channel connecting the third and fourth ventricles. Its walls are lined by simple ependyma, but it does not contain choroid plexus tissue. The choroid plexus is found in the lateral ventricles (body and inferior horn), the roof of the third ventricle, and the roof of the fourth ventricle.

Correct answer: C. The arachnoid villi (granulations).

While CSF is produced by the choroid plexus, it is absorbed back into the venous system primarily via arachnoid villi (granulations). These specialized structures project into the dural venous sinuses. CSF pressure forces fluid through the endothelial cells of the villi into the sinus blood. The foramen of Magendie is an exit from the ventricular system, not an absorption site.

Correct answer: B. Facial, vestibular, hypoglossal.

The floor of the fourth ventricle, particularly at the medullary (caudal) level, contains important motor and sensory nuclei close to the midline. These include the hypoglossal nucleus (CN XII) and the dorsal motor nucleus of vagus (CN X) medially, and the vestibular nuclei more laterally. The facial nucleus is in the caudal pons, but its internal genu contributes to the facial colliculus in the pontine part of the floor.

Correct answer: B. Lingual nerve only.

The anterior 2/3 of tongue has dual innervation: 1. General sensation: lingual nerve (branch of V3) 2. Taste: chorda tympani (branch of CN VII) If taste is preserved but general sensation is lost, only the lingual nerve is damaged. If both are lost, both nerves are affected. This demonstrates the principle of separate pathways for different sensory modalities within the same anatomical region.

Correct answer: A. Retropharyngeal space.

The retropharyngeal space is a potential space between the buccopharyngeal fascia (covering pharynx/esophagus) and prevertebral fascia. It extends: - Superiorly: to base of skull - Inferiorly: into posterior mediastinum (to T4 level) - Laterally: continuous with lateral pharyngeal space This provides a direct pathway for spread of infection from the neck to the mediastinum—a life-threatening condition called descending necrotizing mediastinitis.

Correct answer: B. Axillary nodes.

Approximately 75% of breast lymphatic drainage, especially from the lateral quadrants, goes to the axillary lymph nodes (arranged in five groups: pectoral, subscapular, humeral, central, and apical). The parasternal nodes drain mainly the medial quadrants. Understanding this pattern is crucial for staging breast cancer and planning surgical management (sentinel lymph node biopsy, axillary dissection).

Correct answer: A. Vagus nerve.

The vagus nerve (CN X) runs within the carotid sheath (along with common/internal carotid artery and internal jugular vein). Within the neck, it gives off the superior laryngeal nerve, and its recurrent laryngeal branch (which loops around subclavian artery on right or aortic arch on left) ascends to innervate all intrinsic laryngeal muscles except cricothyroid. Damage causes hoarseness and impaired vocal cord abduction.

Correct answer: C. Fourth and sixth arches.

Laryngeal muscles develop from fourth and sixth pharyngeal arches: - Fourth arch: derivatives include cricothyroid, innervated by superior laryngeal nerve (branch of vagus) - Sixth arch: derivatives include all other intrinsic laryngeal muscles, innervated by recurrent laryngeal nerve (branch of vagus) This embryological origin explains the dual vagal innervation pattern of laryngeal muscles.

Correct answer: B. Upper half from paramesonephric ducts, lower half from urogenital sinus.

The upper vagina forms from fused paramesonephric ducts, while the lower vagina develops from the urogenital sinus via the vaginal plate.

Correct answer: B. Urethral folds.

Urethral folds do not fuse in females and develop into the labia minora. Labioscrotal swellings become labia majora.

Correct answer: B. Vaginal plate.

Sinovaginal bulbs are endodermal outgrowths from the urogenital sinus that proliferate to form the solid vaginal plate, which later canalizes.

Correct answer: C. Labioscrotal swellings.

Labioscrotal swellings fuse in the midline in males to form the scrotum; they remain separate in females as labia majora.

Correct answer: A. Urogenital sinus and urethral folds.

The penile urethra forms from endodermal lining of the urogenital sinus that extends into the genital tubercle, covered by ectodermal urethral folds that fuse.

Correct answer: B. Basilar membrane.

The sensory organ for hearing, the organ of Corti, sits on the flexible basilar membrane within the cochlear duct. Hair cells are anchored here, with their stereocilia embedded in the overlying tectorial membrane.

Correct answer: C. Deep cerebellar nuclei (e.g., dentate nucleus).

Purkinje cell axons are the sole output of the cerebellar cortex. They are inhibitory (GABAergic) and project to and synapse on neurons in the deep cerebellar nuclei (and vestibular nuclei).

Correct answer: B. Primary motor cortex.

Betz cells are giant pyramidal neurons located specifically in layer V of the primary motor cortex (area 4). Their large axons form part of the corticospinal tract for voluntary motor control.

Correct answer: C. Internal granular layer IV.

The Outer Band of Baillarger is a distinct horizontal stripe of fibers (mainly thalamocortical afferents) in layer IV of the neocortex. It is most prominent in primary sensory areas like the visual cortex.

Correct answer: B. Deep cerebellar nuclei (e.g., dentate, fastigial).

The axons of Purkinje cells are the sole output of the cerebellar cortex. They are GABAergic and project to and inhibit the neurons in the deep cerebellar nuclei (and to a lesser extent, the vestibular nuclei).

Correct answer: A. Parafollicular C cells of thyroid.

The ultimobranchial bodies (from the ventral portions of the fourth pouches, or sometimes considered a fifth pouch) fuse with the thyroid gland. They give rise to the parafollicular C cells, which are neural crest-derived and secrete calcitonin.

Correct answer: B. 3rd and 4th pouches.

The superior parathyroid glands (parathyroids IV) develop from the dorsal wings of the fourth pharyngeal pouches. The inferior parathyroid glands (parathyroids III) develop from the dorsal wings of the third pharyngeal pouches.

Correct answer: C. Thyroid diverticulum at foramen cecum.

The functional follicular cells of the thyroid gland originate from a median endodermal thickening in the floor of the primitive pharynx, which evaginates to form the thyroid diverticulum at the site of the future foramen cecum.

Correct answer: B. Near hyoid bone.

The thyroglossal duct has an intimate embryological relationship with the developing hyoid bone, often passing through it or immediately anterior. Consequently, cysts most frequently present adjacent to the hyoid bone.

Correct answer: C. Median plane of neck.

A thyroglossal duct cyst is a remnant of the epithelial tract of the thyroid gland's descent from the foramen cecum at the base of the tongue to its final position in the neck. It therefore always presents in the midline or just off midline.

Correct answer: C. Mesoderm.

The adrenal cortex develops from mesodermal cells of the coelomic epithelium (intermediate mesoderm) that proliferate and surround the medulla.

Correct answer: C. Neural crest cells.

The adrenal medulla is derived from neural crest cells that migrate into the developing adrenal gland and differentiate into chromaffin cells.

Correct answer: B. Infundibulum.

The posterior pituitary (neurohypophysis) originates from the infundibulum, a downward projection of neuroectoderm from the floor of the diencephalon.

Correct answer: B. Rathke's pouch.

The anterior pituitary (adenohypophysis) originates from Rathke's pouch, an upward evagination of oral ectoderm from the roof of the stomodeum.

Correct answer: A. Brain growth and molding during birth.

Fontanelles are unossified membranous areas between the flat bones of the neonatal skull. They permit the bones to overlap (molding) during vaginal delivery and allow for rapid postnatal expansion of the brain.