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Question 1Basic Medical Sciences: Anatomy

The axillary nerve is most closely related to which surgical neck structure of the humerus, making it vulnerable in fractures at this site?

  1. Anatomical neck of the humerus
  2. Surgical neck of the humerus Correct answer.
  3. Greater tubercle
  4. Medial epicondyle

Explanation

The axillary nerve winds around the surgical neck of the humerus together with the posterior circumflex humeral artery. Fractures at the surgical neck therefore risk injuring this nerve, producing deltoid weakness and sensory loss over the lateral shoulder. The anatomical neck is a separate, more proximal landmark.

Question 2Basic Medical Sciences: Anatomy

Which muscle of the rotator cuff is primarily responsible for initiating abduction of the arm during the first 15 degrees?

  1. Infraspinatus
  2. Teres minor
  3. Supraspinatus Correct answer.
  4. Subscapularis

Explanation

Supraspinatus initiates abduction of the shoulder for roughly the first 15 degrees, after which the deltoid becomes the dominant abductor. The other cuff muscles mainly rotate the humerus. Infraspinatus and teres minor are lateral rotators, and subscapularis is a medial rotator.

Question 3Basic Medical Sciences: Anatomy

The femoral triangle is bounded laterally by which structure?

  1. Medial border of adductor longus
  2. Inguinal ligament
  3. Medial border of sartorius Correct answer.
  4. Pectineal line

Explanation

The femoral triangle has the inguinal ligament as its base, the medial border of sartorius laterally, and the medial border of adductor longus medially. Its floor is formed by iliopsoas and pectineus. The femoral vessels and nerve lie within this triangle.

Question 4Basic Medical Sciences: Anatomy

Which cranial nerve provides motor innervation to the muscles of mastication?

  1. Hypoglossal nerve
  2. Maxillary division of the trigeminal nerve
  3. Facial nerve
  4. Mandibular division of the trigeminal nerve Correct answer.

Explanation

The mandibular division (V3) of the trigeminal nerve supplies the muscles of mastication, including masseter, temporalis, and the pterygoids. The maxillary division is sensory only. The facial nerve supplies muscles of facial expression, and the hypoglossal nerve supplies the tongue.

Question 5Basic Medical Sciences: Anatomy

The diaphragm receives its principal motor innervation from which nerve?

  1. Intercostal nerves
  2. Phrenic nerve Correct answer.
  3. Sympathetic trunk
  4. Vagus nerve

Explanation

The phrenic nerve, arising from cervical segments C3 to C5, provides the principal motor supply to the diaphragm. Intercostal nerves supply the intercostal muscles. The vagus and sympathetic trunk provide autonomic supply but not somatic motor control of the diaphragm.

Question 6Basic Medical Sciences: Anatomy

Which structure passes through the foramen ovale of the sphenoid bone?

  1. Optic nerve
  2. Mandibular division of the trigeminal nerve Correct answer.
  3. Facial nerve
  4. Maxillary division of the trigeminal nerve

Explanation

The foramen ovale transmits the mandibular division of the trigeminal nerve along with the lesser petrosal nerve and accessory meningeal artery. The maxillary division passes through the foramen rotundum. The optic nerve passes through the optic canal, and the facial nerve exits through the stylomastoid foramen.

Question 7Basic Medical Sciences: Anatomy

The spleen is normally located in which abdominal region?

  1. Epigastrium
  2. Right hypochondrium
  3. Left hypochondrium Correct answer.
  4. Left iliac fossa

Explanation

The spleen lies in the left hypochondrium, related to the left ninth to eleventh ribs and the stomach. The right hypochondrium contains the liver. The epigastrium contains the stomach and pancreas, and the left iliac fossa contains the descending and sigmoid colon.

Question 8Basic Medical Sciences: Anatomy

Which type of cartilage forms the epiphyseal growth plate of a growing long bone?

  1. Elastic cartilage
  2. Fibrocartilage
  3. Calcified cartilage
  4. Hyaline cartilage Correct answer.

Explanation

The epiphyseal plate is composed of hyaline cartilage, which undergoes endochondral ossification to lengthen the bone. Fibrocartilage forms the intervertebral discs and pubic symphysis. Elastic cartilage occurs in the auricle and epiglottis, and calcified cartilage is a later stage of the ossification process.

Question 9Basic Medical Sciences: Anatomy

A patient sustains a midshaft fracture of the humerus and presents with wrist drop. Which nerve is most likely injured?

  1. Ulnar nerve
  2. Median nerve
  3. Radial nerve Correct answer.
  4. Musculocutaneous nerve

Explanation

The radial nerve runs in the spiral groove against the humeral shaft and is injured in midshaft fractures. Loss of wrist extension produces wrist drop because the extensor muscles of the forearm are paralysed. The median and ulnar nerves supply flexors of the forearm and hand.

Question 10Basic Medical Sciences: Anatomy

During a surgical approach to the posterior triangle of the neck, which nerve lies on the anterior surface of the anterior scalene muscle and is at risk?

  1. Accessory nerve
  2. Transverse cervical nerve
  3. Phrenic nerve Correct answer.
  4. Great auricular nerve

Explanation

The phrenic nerve descends on the anterior surface of the anterior scalene muscle in the neck. Injury here paralyses the corresponding hemidiaphragm. The accessory nerve crosses the posterior triangle more superficially, and the great auricular and transverse cervical nerves are branches of the cervical plexus.

Question 11Basic Medical Sciences: Anatomy

A lesion of the common fibular nerve at the neck of the fibula would most directly impair which movement?

  1. Inversion of the foot
  2. Plantar flexion of the foot
  3. Dorsiflexion of the foot Correct answer.
  4. Flexion of the knee

Explanation

The common fibular nerve winds around the fibular neck and divides into deep and superficial branches. Its deep branch supplies the dorsiflexors, so injury causes foot drop. Plantar flexion is served by the tibial nerve. Inversion is mainly tibialis posterior, and knee flexion is mainly hamstrings.

Question 12Basic Medical Sciences: Anatomy

The blood supply to the head of the femur in adults is most dependent on which artery?

  1. Superior gluteal artery
  2. Obturator artery
  3. Medial circumflex femoral artery Correct answer.
  4. Inferior epigastric artery

Explanation

The medial circumflex femoral artery, via its retinacular branches, provides the main blood supply to the femoral head in adults. Disruption of this supply in femoral neck fractures can lead to avascular necrosis. The obturator artery supplies the acetabular fossa only minimally.

Question 13Basic Medical Sciences: Anatomy

Which structure lies immediately anterior to the trachea in the lower neck?

  1. Longus colli muscle
  2. Oesophagus
  3. Isthmus of the thyroid gland Correct answer.
  4. Recurrent laryngeal nerve

Explanation

The isthmus of the thyroid gland crosses anterior to the second to fourth tracheal rings. The oesophagus lies posterior to the trachea. The recurrent laryngeal nerves run in the tracheo-oesophageal groove, and longus colli lies posteriorly on the vertebral column.

Question 14Basic Medical Sciences: Anatomy

In the inguinal canal, the inferior epigastric vessels are used to distinguish which two types of hernia?

  1. Femoral and obturator hernias
  2. Inguinal and umbilical hernias
  3. Hiatal and paraoesophageal hernias
  4. Direct and indirect inguinal hernias Correct answer.

Explanation

Indirect inguinal hernias pass lateral to the inferior epigastric vessels through the deep ring. Direct inguinal hernias emerge medial to these vessels through the posterior wall. Femoral hernias occur below the inguinal ligament and are unrelated to these vessels.

Question 15Basic Medical Sciences: Anatomy

The middle meningeal artery is a branch of which artery and enters the skull through which foramen?

  1. Vertebral artery through the foramen magnum
  2. Facial artery through the stylomastoid foramen
  3. Internal carotid artery through the foramen lacerum
  4. Maxillary artery through the foramen spinosum Correct answer.

Explanation

The middle meningeal artery arises from the maxillary artery and enters the cranial cavity through the foramen spinosum. Its anterior branch runs under the pterion and is torn in extradural haemorrhage. The internal carotid and vertebral arteries supply the brain itself.

Question 16Basic Medical Sciences: Anatomy

Which bronchopulmonary segment is most commonly involved in aspiration in a supine patient?

  1. Lingula of the left upper lobe
  2. Apical segment of the right upper lobe
  3. Superior segment of the right lower lobe Correct answer.
  4. Medial segment of the left lower lobe

Explanation

In a supine patient, aspirated material tends to enter the superior segment of the right lower lobe because of the vertical orientation of the right main bronchus. The right main bronchus is wider and more vertical than the left. The apical segment of the upper lobe is favoured in the erect posture.

Question 17Basic Medical Sciences: Anatomy

Which layer of the scalp is responsible for the free mobility of the scalp and contains the emissary veins?

  1. Dense connective tissue
  2. Epicranial aponeurosis
  3. Loose areolar layer Correct answer.
  4. Skin

Explanation

The loose areolar layer lies between the epicranial aponeurosis and the pericranium and allows the scalp to move freely. It contains emissary veins that connect the scalp veins with the intracranial dural sinuses, so infection can spread intracranially. The skin, dense connective tissue, and aponeurosis are more firmly bound.

Question 18Basic Medical Sciences: Anatomy

A patient presents with loss of sensation over the tip of the little finger. Which nerve root is most likely affected?

  1. C8 Correct answer.
  2. T1
  3. C7
  4. C6

Explanation

The little finger is supplied by the ulnar nerve, whose sensory fibres derive mainly from the C8 root. The C6 root supplies the thumb and lateral forearm. The C7 root supplies the middle finger, and T1 supplies the medial forearm.

Question 19Basic Medical Sciences: Anatomy

The portal vein is formed by the union of which two veins?

  1. Left and right gastric veins
  2. Hepatic and splenic veins
  3. Superior mesenteric and splenic veins Correct answer.
  4. Inferior mesenteric and splenic veins

Explanation

The portal vein is formed behind the neck of the pancreas by the union of the superior mesenteric and splenic veins. The inferior mesenteric vein usually drains into the splenic vein. The hepatic veins drain the liver into the inferior vena cava.

Question 20Basic Medical Sciences: Anatomy

Which part of the male urethra is most commonly injured in a straddle injury?

  1. Prostatic urethra
  2. Penile urethra
  3. Membranous urethra
  4. Bulbous urethra Correct answer.

Explanation

The bulbous urethra is crushed against the inferior surface of the pubic symphysis in straddle injuries. The membranous urethra is injured in pelvic fractures. The prostatic urethra is protected within the prostate, and the penile urethra is mobile.

Question 21Basic Medical Sciences: Anatomy

Which structure forms the medial boundary of the posterior triangle of the neck?

  1. Mandible
  2. Clavicle
  3. Posterior border of sternocleidomastoid Correct answer.
  4. Trapezius

Explanation

The posterior triangle is bounded anteriorly by the posterior border of sternocleidomastoid and posteriorly by the anterior border of trapezius. Its base is the middle third of the clavicle. The mandible forms the upper boundary of the anterior triangle.

Question 22Basic Medical Sciences: Anatomy

In a lesion of the median nerve at the wrist, which muscle remains functional because its nerve supply arises proximal to the carpal tunnel?

  1. Lumbricals one and two
  2. Abductor pollicis brevis
  3. Opponens pollicis
  4. Flexor pollicis longus Correct answer.

Explanation

Flexor pollicis longus is supplied by the anterior interosseous branch of the median nerve in the forearm, proximal to the carpal tunnel. Abductor pollicis brevis, opponens pollicis, and the first two lumbricals are supplied by the recurrent thenar branch or palmar digital branches beyond the wrist and are paralysed in carpal tunnel syndrome.

Question 23Basic Medical Sciences: Anatomy

Occlusion of the artery of Adamkiewicz would most likely produce ischaemia of which spinal cord region?

  1. Sacral segments only
  2. Cervical enlargement
  3. Lower thoracic and lumbar segments Correct answer.
  4. Upper thoracic segments

Explanation

The artery of Adamkiewicz is the major radiculomedullary artery supplying the lower thoracic and lumbar enlargement of the spinal cord. Its occlusion can cause anterior spinal artery syndrome with paraplegia. The cervical enlargement is supplied by radicular arteries from the vertebral system.

Question 24Basic Medical Sciences: Anatomy

A tumour at the cerebellopontine angle would most likely compress which cranial nerve first?

  1. Optic nerve
  2. Hypoglossal nerve
  3. Vestibulocochlear nerve Correct answer.
  4. Olfactory nerve

Explanation

The vestibulocochlear nerve emerges at the cerebellopontine angle, where acoustic neuromas typically arise, causing hearing loss and vertigo. The optic nerve is in the orbit and optic canal. The hypoglossal nerve exits through the hypoglossal canal, and the olfactory nerve lies in the anterior cranial fossa.

Question 25Basic Medical Sciences: Anatomy

During a thyroidectomy, injury to the external branch of the superior laryngeal nerve would most likely impair which function?

  1. Closure of the glottis during swallowing
  2. Sensation of the larynx above the vocal cords
  3. Raising the pitch of the voice Correct answer.
  4. Abduction of the vocal cords

Explanation

The external branch of the superior laryngeal nerve supplies cricothyroid, which tenses the vocal cords and raises voice pitch. Abduction of the vocal cords is mediated by the recurrent laryngeal nerve through posterior cricoarytenoid. Sensation above the vocal cords is carried by the internal branch of the superior laryngeal nerve.

Question 26Basic Medical Sciences: Anatomy

Which type of joint is the temporomandibular joint, and what movement does its articular disc allow?

  1. A synovial saddle joint allowing opposition
  2. A synovial condylar joint with an articular disc permitting both rotation and gliding Correct answer.
  3. A fibrous joint permitting no movement
  4. A synovial hinge joint allowing only flexion and extension

Explanation

The temporomandibular joint is a synovial condylar (bicondylar) joint divided into two compartments by a fibrocartilaginous articular disc. The lower compartment permits hinge-like rotation while the upper compartment permits gliding translation of the disc and condyle. This dual arrangement allows both depression and protrusion of the mandible.

Question 27Basic Medical Sciences: Anatomy

A patient sustains a laceration at the wrist that divides the ulnar artery in the distal forearm. Which arterial channel most reliably maintains perfusion of the superficial palmar arch?

  1. The superficial palmar branch of the radial artery through the palmar arches Correct answer.
  2. The anterior interosseous artery directly
  3. The posterior interosseous artery via the dorsal carpal network
  4. The princeps pollicis artery alone

Explanation

The superficial palmar arch is formed predominantly by the ulnar artery and completed by the superficial palmar branch of the radial artery. When the ulnar artery is divided, the radial contribution through this anastomosis usually preserves flow to the arch. The interosseous and dorsal carpal vessels are smaller contributors and do not reliably supply the arch directly.

Question 28Basic Medical Sciences: Anatomy

A patient has a lesion compressing the axillary nerve within the quadrangular space. Which combination of findings is most consistent with this lesion?

  1. Wasting of the infraspinatus with sensory loss over the medial arm
  2. Wasting of the triceps with sensory loss over the posterior forearm
  3. Wasting of the deltoid with sensory loss over the lateral shoulder Correct answer.
  4. Wasting of the thenar eminence with sensory loss over the index finger

Explanation

The axillary nerve passes through the quadrangular space with the posterior circumflex humeral artery and supplies the deltoid and teres minor. Its terminal branch, the upper lateral cutaneous nerve of the arm, carries sensation from the skin over the lateral shoulder. A lesion there therefore produces deltoid wasting with lateral shoulder numbness.

Question 29Basic Medical Sciences: Anatomy

During development, the right umbilical vein and the left umbilical vein follow different fates. Which statement best describes the postnatal remnants derived from the fetal umbilical venous system?

  1. The umbilical veins become the medial umbilical ligaments, while the urachus becomes the ligamentum teres
  2. The left umbilical vein becomes the ligamentum teres, while the ductus venosus becomes the ligamentum venosum Correct answer.
  3. Both umbilical veins persist as the median umbilical ligament
  4. The right umbilical vein persists as the ligamentum teres and the left becomes the ligamentum venosum

Explanation

The right umbilical vein normally regresses early in development, leaving the left umbilical vein as the sole channel carrying oxygenated blood to the fetus. After birth, the intra-abdominal portion of the left umbilical vein fibroses to form the ligamentum teres (round ligament of the liver). The ductus venosus, which shunts blood from that vein into the inferior vena cava, becomes the ligamentum venosum.

Question 30Basic Medical Sciences: Anatomy

A 45-year-old man is unable to abduct his right shoulder beyond about 15 degrees after a fracture of the surgical neck of the humerus. Sensation over the lateral aspect of the proximal arm is reduced. Which nerve has most likely been injured?

  1. Long thoracic nerve
  2. Musculocutaneous nerve
  3. Suprascapular nerve
  4. Axillary nerve Correct answer.

Explanation

The axillary nerve runs with the posterior circumflex humeral vessels through the quadrangular space, immediately related to the surgical neck of the humerus, so fractures at this site commonly injure it. It supplies deltores and teres minor and carries the upper lateral cutaneous nerve of the arm, giving weakness of abduction with sensory loss over the lateral shoulder. The other nerves listed lie away from the surgical neck or supply different muscles and skin territories.

Question 31Basic Medical Sciences: Physiology

The resting membrane potential of a typical mammalian neuron is closest to which value?

  1. +40 mV
  2. −70 mV Correct answer.
  3. −20 mV
  4. 0 mV

Explanation

Resting membrane potential in neurons is normally between −60 and −80 mV, with −70 mV the standard reference value. It is set mainly by the high resting permeability to potassium and the activity of the Na+/K+-ATPase.

Question 32Basic Medical Sciences: Physiology

Which phase of the cardiac cycle corresponds to the first heart sound?

  1. Closure of the atrioventricular valves Correct answer.
  2. Opening of the atrioventricular valves
  3. Rapid ventricular filling
  4. Closure of the semilunar valves

Explanation

The first heart sound is produced by closure of the mitral and tricuspid valves at the start of ventricular systole. The second sound results from semilunar valve closure at the end of systole.

Question 33Basic Medical Sciences: Physiology

The main site of reabsorption of filtered glucose in the nephron is which segment?

  1. Distal convoluted tubule
  2. Descending limb of the loop of Henle
  3. Collecting duct
  4. Proximal convoluted tubule Correct answer.

Explanation

Almost all filtered glucose is reabsorbed in the proximal convoluted tubule via SGLT sodium-glucose cotransporters. Reabsorption is essentially complete below the renal threshold.

Question 34Basic Medical Sciences: Physiology

Which lung volume cannot be measured directly by simple spirometry?

  1. Residual volume Correct answer.
  2. Inspiratory reserve volume
  3. Expiratory reserve volume
  4. Tidal volume

Explanation

Residual volume remains in the lungs after maximal expiration and therefore cannot be exhaled into a spirometer. It is determined indirectly, for example by helium dilution or body plethysmography.

Question 35Basic Medical Sciences: Physiology

Which hormone is released from the posterior pituitary?

  1. Adrenocorticotrophic hormone
  2. Prolactin
  3. Antidiuretic hormone Correct answer.
  4. Growth hormone

Explanation

Antidiuretic hormone (vasopressin) is synthesised in hypothalamic neurons and released from axon terminals in the posterior pituitary. The other listed hormones are anterior pituitary products.

Question 36Basic Medical Sciences: Physiology

The normal resting cardiac output of a healthy adult is approximately which value?

  1. 25 L/min
  2. 1 L/min
  3. 15 L/min
  4. 5 L/min Correct answer.

Explanation

Cardiac output equals heart rate multiplied by stroke volume, roughly 70 beats/min × 70 mL, giving about 5 L/min at rest. This matches total body oxygen delivery needs at rest.

Question 37Basic Medical Sciences: Physiology

Which blood cell type is primarily responsible for oxygen transport?

  1. Platelet
  2. Lymphocyte
  3. Neutrophil
  4. Erythrocyte Correct answer.

Explanation

Erythrocytes contain haemoglobin, which binds oxygen in the lungs and releases it in the tissues. Their biconcave shape and lack of nucleus maximise haemoglobin content and deformability.

Question 38Basic Medical Sciences: Physiology

Which neurotransmitter is released at the neuromuscular junction of skeletal muscle?

  1. Gamma-aminobutyric acid
  2. Acetylcholine Correct answer.
  3. Dopamine
  4. Noradrenaline

Explanation

Somatic motor neurons release acetylcholine, which binds nicotinic receptors on the motor end plate to trigger muscle contraction. Acetylcholinesterase then terminates the signal.

Question 39Basic Medical Sciences: Physiology

A patient has a plasma osmolarity of 310 mOsm/L. Which change in antidiuretic hormone secretion is expected, and through which receptor does it act on the collecting duct?

  1. Increased ADH secretion acting on V2 receptors Correct answer.
  2. Decreased ADH secretion acting on V2 receptors
  3. Increased ADH secretion acting on beta-1 receptors
  4. Decreased ADH secretion acting on V1 receptors

Explanation

Raised plasma osmolarity is detected by hypothalamic osmoreceptors, which increase ADH release. ADH acts on V2 receptors of collecting duct principal cells, promoting aquaporin-2 insertion and water reabsorption.

Question 40Basic Medical Sciences: Physiology

During exercise, which combination of changes best explains the rise in venous return to the heart?

  1. Reduced skeletal muscle pump activity and venodilation
  2. Increased skeletal muscle pump activity and venoconstriction Correct answer.
  3. Decreased circulating catecholamines and reduced venous tone
  4. Reduced respiratory pump activity and bradycardia

Explanation

Rhythmic muscle contraction compresses veins and drives blood toward the heart, while sympathetic venoconstriction increases mean systemic filling pressure. Together these raise the pressure gradient for venous return.

Question 41Basic Medical Sciences: Physiology

An increase in arterial PCO2 from 40 to 50 mmHg has which immediate effect on the pulmonary vasculature?

  1. Selective constriction of bronchial arteries only
  2. Pulmonary vasodilation
  3. No change in pulmonary vascular resistance
  4. Pulmonary vasoconstriction Correct answer.

Explanation

Alveolar hypoxia and hypercapnia cause hypoxic pulmonary vasoconstriction, which diverts blood from poorly ventilated regions. This differs from systemic vessels, which dilate in response to hypercapnia.

Question 42Basic Medical Sciences: Physiology

A patient with a lesion of the right optic nerve will show which visual field defect?

  1. Left homonymous hemianopia
  2. Total blindness of the right eye Correct answer.
  3. Total blindness of the left eye
  4. Bitemporal hemianopia

Explanation

The optic nerve carries all fibres from one eye, so a complete lesion causes monocular blindness on that side. Chiasmal and post-chiasmal lesions produce the other patterns.

Question 43Basic Medical Sciences: Physiology

Which change in the oxygen-haemoglobin dissociation curve is produced by a rise in temperature and 2,3-DPG?

  1. A left shift with increased oxygen affinity
  2. A right shift with decreased oxygen affinity Correct answer.
  3. A left shift caused by increased carbon dioxide binding
  4. No shift but reduced haemoglobin concentration

Explanation

Raised temperature and increased 2,3-DPG reduce haemoglobin's affinity for oxygen, shifting the curve to the right. This favours oxygen unloading in metabolically active tissues.

Question 44Basic Medical Sciences: Physiology

Section of the vagus nerves below the diaphragm would have which effect on gastric acid secretion?

  1. Selective loss of intestinal phase secretion
  2. Increased basal acid secretion
  3. No effect on acid secretion
  4. Reduced cephalic-phase acid secretion Correct answer.

Explanation

Vagal efferents mediate the cephalic phase of gastric secretion and also potentiate gastrin release. Cutting them below the diaphragm removes this vagal drive and reduces acid output.

Question 45Basic Medical Sciences: Physiology

Which mechanism best explains why the glomerular filtration rate remains nearly constant when arterial pressure varies between 80 and 180 mmHg?

  1. Direct proportional change in efferent arteriolar resistance
  2. Tubuloglomerular feedback and myogenic autoregulation of the afferent arteriole Correct answer.
  3. Passive changes in glomerular capillary surface area
  4. Increased oncotic pressure of Bowman's capsule fluid

Explanation

Renal autoregulation maintains constant renal blood flow and GFR over this pressure range. The myogenic response and tubuloglomerular feedback adjust afferent arteriolar tone to stabilise glomerular capillary pressure.

Question 46Basic Medical Sciences: Physiology

A drug that blocks beta-1 adrenergic receptors would be expected to produce which set of effects?

  1. Bronchodilation and mydriasis
  2. Increased sweating and piloerection
  3. Tachycardia and increased renin release
  4. Bradycardia and reduced renin release Correct answer.

Explanation

Beta-1 receptors mediate sympathetic stimulation of heart rate and renin release from juxtaglomerular cells. Blockade therefore slows the heart and lowers renin and thus angiotensin II formation.

Question 47Basic Medical Sciences: Physiology

Which statement correctly describes the countercurrent multiplier function of the loop of Henle?

  1. Both limbs are freely water-permeable, so no osmotic gradient develops
  2. The descending limb actively transports sodium chloride out of the tubule
  3. The ascending limb is water-permeable and secretes sodium into the interstitium
  4. The ascending limb actively reabsorbs solute while being relatively water-impermeable, creating a hypertonic medullary interstitium Correct answer.

Explanation

The thick ascending limb pumps NaCl into the interstitium while remaining relatively impermeable to water, so the interstitium becomes hypertonic. The descending limb, which is water-permeable and solute-impermeable, then equilibrates with this gradient.

Question 48Basic Medical Sciences: Physiology

A patient with a lesion of the ventromedial hypothalamus would be expected to develop which change in feeding behaviour?

  1. Severe anorexia and weight loss
  2. Hyperphagia and obesity Correct answer.
  3. Loss of thirst only, with normal feeding
  4. Normal feeding but absent circadian rhythm

Explanation

The ventromedial hypothalamus is classically described as a satiety centre; lesions cause hyperphagia and obesity. In contrast, lateral hypothalamic lesions produce aphagia and weight loss.

Question 49Basic Medical Sciences: Physiology

Which factor most increases the filtration fraction in the kidney?

  1. Dilation of the afferent arteriole with unchanged efferent tone
  2. Constriction of the efferent arteriole with unchanged afferent tone Correct answer.
  3. A rise in Bowman's capsule hydrostatic pressure
  4. A fall in plasma protein concentration

Explanation

Filtration fraction is GFR divided by renal plasma flow. Efferent arteriolar constriction raises glomerular capillary pressure and GFR while reducing renal plasma flow, so the fraction rises.

Question 50Basic Medical Sciences: Physiology

Which change occurs in the alveolar gas equation when a patient hyperventilates at a constant rate of oxygen consumption?

  1. Alveolar PO2 rises and alveolar PCO2 falls Correct answer.
  2. Both alveolar PO2 and PCO2 remain unchanged
  3. Alveolar PO2 falls and alveolar PCO2 rises
  4. Both alveolar PO2 and PCO2 rise

Explanation

Hyperventilation increases alveolar ventilation, washing out carbon dioxide and lowering alveolar PCO2. Because alveolar PO2 is inversely related to PCO2 at constant oxygen consumption, it rises.