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AIIMS RAJKOT - 1ST MBBS ANATOMY PAPER II - COMPLETE ANSWERS

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SECTION A (38 Marks)

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QUESTION 1 (10 Marks) - Gastric Ulcer Perforating into Lesser Sac

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(a) Region where leaking fluid from lesser sac drains through epiploic foramen (1 mark)

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(b) Boundaries of the lesser sac (3 marks)

• Anteriorly: free edge of lesser omentum (hepatoduodenal ligament) containing portal vein, hepatic artery, bile duct
• Posteriorly: IVC (covered by peritoneum)
• Superiorly: caudate lobe of liver
• Inferiorly: first part of duodenum

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(c) Contents of lesser omentum (3 marks)

1. Hepatogastric ligament (thin, translucent - between liver and stomach)
2. Hepatoduodenal ligament (thickened free right edge - between liver and duodenum)

• Portal vein - posterior, between the artery and bile duct
• Hepatic artery proper - left side (of the ligament)
• Common bile duct (CBD) - right side
• Lymph vessels and lymph nodes
• Sympathetic and parasympathetic nerve fibers

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(d) Lymphatic drainage of stomach (3 marks - diagram + description)

• Left gastric lymph nodes (along left gastric artery) - drain fundus and upper body of stomach (both surfaces)

• Right gastroomental nodes (along right gastroepiploic artery) - drain lower right part of stomach

• Right gastric nodes (along right gastric artery) - drain pyloric region

• Left gastroomental + short gastric nodes - drain fundus and upper left stomach

DIAGRAM: Lymphatic Drainage of Stomach

        ←—Left gastric nodes—→
        (along lesser curvature)
              |
FUNDUS ←—Pancreaticosplenic—→ LEFT GASTROEPIPLOIC
              |                        |
         COELIAC NODES ←——————————————
              |
         RIGHT GASTROEPIPLOIC
              |
         Pyloric nodes (right gastric)
         (along greater curvature)

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QUESTION 2 (4 x 5 marks = 20 marks)

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(a) Autosomal Recessive Inheritance (5 marks)

• Gene locus on an autosome (not sex chromosomes)
• Disease appears only in homozygous recessive (aa) individuals
• Heterozygotes (Aa) are carriers - phenotypically normal
• Both sexes equally affected
• Often appears to "skip" generations

     Aa (carrier father) x Aa (carrier mother)
     
           A        a
      ┌─────────────────┐
    A │  AA (normal)  Aa│ (carrier)
      │─────────────────│
    a │  Aa (carrier) aa│ (AFFECTED)
      └─────────────────┘

Ratio: 1 AA : 2 Aa : 1 aa
Probability of disease: 25% (1 in 4)
Probability of carrier: 50% (1 in 2 among normal-appearing children = 2 in 3)

• Horizontal pattern - siblings affected, not parents typically
• Consanguinity increases risk (particularly common in India - cousin marriages)
• Both sexes equally affected

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(b) Microanatomical Anatomy of Kidney + PCT vs DCT comparison (5 marks)

Glomerulus (Bowman's capsule)
       ↓
Proximal Convoluted Tubule (PCT)
       ↓
Loop of Henle
 ┌─────────────────────┐
 Thick descending limb
 Thin descending limb
 Thin ascending limb
 Thick ascending limb
 └─────────────────────┘
       ↓
Distal Convoluted Tubule (DCT)
       ↓
Collecting Duct → Renal Pelvis

• Renal corpuscles (Malpighian corpuscles) = Glomerulus + Bowman's capsule
• Glomerular capillaries lined by fenestrated endothelium
• Podocytes (visceral layer of Bowman's capsule) with foot processes (pedicles) - form filtration slits
• Parietal layer = simple squamous epithelium

• Juxtaglomerular apparatus (JGA): formed by macula densa (DCT cells adjacent to afferent arteriole) + juxtaglomerular cells (modified smooth muscle of afferent arteriole producing renin) + extraglomerular mesangial cells (Lacis cells)
• Peritubular capillaries surround cortical tubules
• Vasa recta - straight capillaries in medulla running parallel to loop of Henle (countercurrent exchange)

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(c) Medial Longitudinal Arch of Foot and Applied Anatomy (5 marks)

1. Calcaneum (posterior pillar / keystone at inferior end)
2. Talus (summit / apex of the arch - highest point)
3. Navicular bone
4. Three cuneiforms (medial, intermediate, lateral)
5. First, second, third metatarsal heads (anterior pillar)

• Shape and interlocking of bones (wedge shape of talus)

• Spring ligament (plantar calcaneonavicular ligament) - MOST IMPORTANT passive support; runs from sustentaculum tali to navicular; supports head of talus
• Long plantar ligament
• Short plantar ligament (plantar calcaneocuboid)
• Plantar fascia (plantar aponeurosis) - acts as tie beam

• Tibialis posterior (chief active support) - inserts into navicular
• Flexor digitorum longus
• Flexor hallucis longus - acts as tie for medial arch
• Intrinsic foot muscles (abductor hallucis, flexor digitorum brevis)
• Tibialis anterior (from above)

• Weight on talus compresses the arch down
• Plantar fascia prevents spreading of the two pillars like a tie-beam of a roof

1. Flat foot (Pes planus):
   • Medial longitudinal arch is lower than normal or absent
   • Most common in childhood (physiological up to 4-5 years)
   • In adults: rupture of spring ligament, tibialis posterior tendon dysfunction
   • Results in: pain, fatigue, abnormal gait
   • Treatment: arch supports, physiotherapy; surgery in severe cases
2. Pes cavus (High arch):
   • Exaggerated medial longitudinal arch
   • Associated with neurological conditions (Charcot-Marie-Tooth disease)
   • Results in clawing of toes, metatarsalgia
3. Plantar fasciitis:
   • Inflammation at origin of plantar fascia at calcaneal tuberosity
   • Pain on first steps in the morning ("first step pain")
4. March fracture:
   • Stress fracture of 2nd metatarsal neck due to overuse
   • Disruption of dynamic arch support

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(d) Ischio-anal Fossa - Boundaries, Contents + Horseshoe Abscess (5 marks)

1. Pudendal canal (Alcock's canal) - on lateral wall within obturator fascia, contains:
   • Internal pudendal artery and vein
   • Pudendal nerve (S2, 3, 4)
   • Nerve to obturator internus
2. Inferior rectal (anal) vessels and nerves - cross the fossa medially to supply anal canal
3. Perianal branch of S4
4. Fat (ischioanal fat pad) - fills the space and permits expansion of rectum and anal canal
5. Scrotal/labial nerves (perineal branch of pudendal)

• The two ischio-anal fossae communicate behind the anal canal through the deep post-anal space (space of Courtney)
• Infection in one fossa can therefore spread to the other side through this post-anal communication
• This results in a horseshoe abscess - a semicircular abscess surrounding the posterior aspect of the anal canal involving both ischio-anal fossae

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QUESTION 3 (4 x 2 marks = 8 marks)

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(a) Components of Tetralogy of Fallot

1. Pulmonary stenosis (stenosis of pulmonary outflow tract / right ventricular outflow obstruction) - MOST IMPORTANT component
2. Ventricular septal defect (VSD) - large, membranous type
3. Overriding (dextroposition) of aorta - aorta straddles the VSD, receiving blood from both ventricles
4. Right ventricular hypertrophy (RVH) - consequence of pulmonary outflow obstruction

• Source: The Developing Human (Moore), p. 253

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(b) Embryological Basis of Annular Pancreas

• Dorsal pancreatic bud - arises from dorsal wall of duodenum; forms body, tail, and superior part of head of pancreas
• Ventral pancreatic bud - arises from hepatic diverticulum (near bile duct); forms inferior part of head and uncinate process

• The ventral bud splits into two parts OR fails to rotate properly
• Parts of the ventral pancreatic bud encircle the second part of duodenum on both sides before fusing with the dorsal bud
• This forms a ring (annulus) of pancreatic tissue completely surrounding the second part of duodenum
• Results in duodenal obstruction (stenosis or atresia of duodenum)
• Presents in neonates as bilious vomiting, "double bubble sign" on X-ray
• Associated with Down syndrome (Trisomy 21) in 20-30% of cases
• Treatment: duodenojejunostomy or duodenoduodenostomy (NOT removal of pancreas - risk of pancreatitis and bile leak)

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(c) Anatomical Basis of Positive Trendelenburg Sign

• Gluteus medius and gluteus minimus (primary hip abductors)
• Nerve supply: Superior gluteal nerve (L4, L5, S1)
• Origin: gluteal surface of ilium (between anterior and posterior gluteal lines)
• Insertion: greater trochanter of femur

• Patient stands on the affected limb
• Due to weakness/paralysis of gluteus medius and minimus, the pelvis droops/sags on the opposite (unaffected) side
• The pelvis tilts inferiorly toward the swing limb

1. Superior gluteal nerve palsy (most common)
2. Fracture of greater trochanter (disrupts abductor attachment)
3. Coxa vara (reduced neck-shaft angle, shortening abductor lever arm)
4. Congenital dislocation of hip (CDH/DDH)
5. Weakness from polio, neurological disease
6. Space-occupying lesion compressing superior gluteal nerve in greater sciatic foramen
7. Hip surgery with damage to gluteus medius tendon

• Source: Gray's Anatomy for Students, p. 680

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(d) Anatomical Basis of Caput Medusae

• In portal hypertension (due to cirrhosis, hepatic fibrosis, portal vein obstruction), blood cannot flow normally through the liver
• Porto-systemic anastomoses open up to carry blood from the portal system to the systemic venous circulation
• One such anastomosis is at the umbilicus via the paraumbilical veins
• Paraumbilical veins run in the free edge of the falciform ligament, connecting the left portal vein (via a recanalized umbilical vein / ligamentum teres) to the superficial epigastric veins of the anterior abdominal wall
• In portal hypertension, the umbilical vein recanalizes and paraumbilical veins dilate
• Blood flows: Portal vein → paraumbilical veins → umbilicus → superficial epigastric veins (both superior and inferior) → SVC/IVC
• The radiating superficial veins around the umbilicus resemble the snakes radiating from Medusa's head in Greek mythology

• Esophageal varices (left gastric → azygos veins)
• Anorectal varices (superior rectal ↔ middle and inferior rectal)
• Retroperitoneal veins (veins of Retzius)
• Source: Gray's Anatomy for Students, p. 333

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SECTION B (37 Marks)

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QUESTION 4 (1+2+4+2 = 9 marks) - Myocardial Infarction

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(a) Anatomical basis of myocardial infarction (1 mark)

• The left anterior descending (LAD) artery (anterior interventricular branch of left coronary artery) is occluded in ~40-50% of MIs - most common - causes anterior MI
• The right coronary artery (RCA) occlusion causes inferior/posterior MI
• The left circumflex artery occlusion causes lateral MI

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(b) Cardiac dominance and clinical significance (2 marks)

1. In right-dominant circulation (most common), RCA occlusion causes inferior MI + AV node ischemia → heart block, bradycardia
2. In left-dominant circulation, occlusion of the left circumflex is more serious as it supplies more territory
3. Determines which artery to bypass or stent in revascularization procedures
4. In right dominance, sinoatrial (SA) nodal artery is from RCA in 60%; left circumflex in 40%

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(c) Left coronary artery - description and distribution (4 marks)

• Descends in the anterior interventricular sulcus
• Reaches the apex of the heart, may turn around to anastomose with posterior interventricular artery
• Branches:
  • Diagonal branches (1-3) - supply anterior LV wall
  • Septal perforating branches (3-5) - supply anterior 2/3 of interventricular septum
  • Right ventricular branches (small)
• Supply: Anterior wall of left ventricle, anterior 2/3 of interventricular septum, apex of heart, anterior papillary muscle, right bundle branch, left anterior fascicle
• Called the "artery of sudden death" - its occlusion causes massive anterior MI

• Passes in the left atrioventricular (coronary) sulcus toward the left and posteriorly
• Gives off obtuse marginal branches (most important branches)
• Supply: Left atrium, lateral wall of left ventricle, posterior LV (in left dominant), posterior papillary muscle (sometimes)
• In 40% of people: gives SA nodal artery
• In 10-15%: gives AV nodal artery (left dominant)

• Entire left ventricle (except inferior diaphragmatic surface in right dominance)
• Anterior 2/3 of interventricular septum
• Left atrium
• Bundle of His and its branches (left bundle branch and right bundle branch)
• Bundle branches responsible for ventricular conduction

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(d) Why coronary disease in old age is less fatal than in young/middle age? (2 marks)

1. Progressive narrowing in old age is slow: Atherosclerosis in elderly patients accumulates over decades. This slow, gradual narrowing stimulates angiogenesis and collateral vessel formation from adjacent coronary branches. These collaterals can maintain myocardial perfusion even when the main vessel is severely stenosed or occluded.
2. Ischemic preconditioning: Repeated minor ischemic episodes "precondition" the myocardium, making it more resistant to irreversible injury from a major occlusion.
3. In young/middle age: Acute plaque rupture (thrombosis) on a previously non-obstructive plaque causes sudden, complete occlusion with NO TIME for collateral development. The myocardium has no alternate supply and infarcts rapidly. This is why sudden cardiac death is more common in relatively young males.
4. Collateral network: In the elderly, the ischemic territory may receive retrograde flow through anastomoses between LAD-RCA (around the apex), circumflex-RCA (posterior), and perforating septal vessels - limiting infarct size.

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QUESTION 5 (4 x 5 marks = 20 marks)

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(a) Microanatomical structure of testis + functions of various cells (5 marks)

• Testis is covered by three coats: tunica vaginalis (outer, derived from peritoneum), tunica albuginea (fibrous, forms septa), tunica vasculosa (inner vascular)
• Septa divide testis into ~250-300 lobules, each containing 1-4 seminiferous tubules

• The functional units of testis
• 150-300 per testis, each ~70 cm long
• Lined by germinal (seminiferous) epithelium - a complex stratified epithelium containing:

• Tall columnar cells resting on basement membrane
• Large pale nucleus with prominent nucleolus
• Function:
  • Support, nourish, and protect developing spermatocytes (blood-testis barrier)
  • Form the blood-testis barrier (tight junctions between adjacent Sertoli cells) - protects developing sperm from immune attack
  • Phagocytose residual bodies of developing spermatids
  • Secrete androgen-binding protein (ABP) - concentrates testosterone in tubule lumen (FSH-stimulated)
  • Secrete inhibin - feedback inhibition of FSH from pituitary
  • Secrete Müllerian inhibitory factor (MIF/AMH) in fetal testis - causes regression of Müllerian (paramesonephric) ducts in male fetus
  • Secrete estradiol (via aromatase)
  • Provide structural framework for spermatogenesis

• Spermatogonia (type A dark, type A pale, type B) - stem cells at base
• Primary spermatocytes - largest cells, in meiosis I
• Secondary spermatocytes - short-lived, in meiosis II
• Spermatids - haploid, undergo spermiogenesis
• Spermatozoa - released into lumen

• Located in the interstitial tissue between seminiferous tubules
• Large polygonal cells with eosinophilic granular cytoplasm
• Contain Reinke crystalloids (rod-shaped protein crystals, pathognomonic)
• Occur in clusters near blood vessels
• Function:
  • Produce testosterone (and other androgens) in response to LH from pituitary
  • Testosterone required for: spermatogenesis, development of male secondary sexual characteristics, maintenance of male reproductive tract, anabolic effects, libido

Cross-section of Seminiferous Tubule:

LUMEN
  ↑
Spermatozoa
Spermatids (spermiogenesis)
Secondary spermatocytes
Primary spermatocytes (meiosis I)
Spermatogonia (stem cells)
Basement membrane
  ↓
Interstitium → LEYDIG CELLS (testosterone)
              + Blood vessels
              + Lymphatics

[Sertoli cells span from basement membrane to lumen]

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(b) Implantation (5 marks)

• Hatching of blastocyst from zona pellucida (day 4-5)
• Uterine endometrium must be in secretory phase (days 15-28 of cycle) - prepared by progesterone from corpus luteum
• "Window of implantation" - days 20-24 of a 28-day cycle

• Blastocyst loosely attaches to endometrium with its embryoblast pole (inner cell mass / embryonic pole) directed toward the endometrium

• Firm attachment via cell surface adhesion molecules (integrins, L-selectin)
• Trophoblast and endometrial epithelium make tight contact

• Syncytiotrophoblast (outer layer) proliferates and erodes endometrial epithelium
• Syncytiotrophoblast is invasive - has no cell boundaries, secretes enzymes (matrix metalloproteinases) that digest endometrial stroma
• By day 8: blastocyst is half-embedded; by day 9-10: completely embedded (interstitial implantation)

• Uterine tube (most common - ~95%, especially ampullary part)
• Ovary
• Abdominal cavity
• Internal os of cervix (placenta previa)

• Endometrial stromal cells transform into decidual cells under progesterone influence
• Provides nutrition and immunological tolerance

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(c) Locking and Unlocking of Knee Joint (5 marks)

• When the knee approaches full extension, rotation occurs between femur and tibia
• As the last few degrees of extension are reached, the femoral condyles (medial is larger/longer than lateral) undergo lateral rotation on the tibial plateau relative to the tibia (or medial rotation of the tibia on a fixed femur)
• This is the "screw-home mechanism" (coronary ligament tightening, ACL and PCL tightening, menisci jamming)
• Specifically: the tibia medially rotates on the femur (or the femur laterally rotates on a fixed tibia) through approximately 5° during the terminal phase of extension
• This tightens the cruciate and collateral ligaments, causes medial displacement of menisci, and jams the femoral condyles firmly into the tibial plateau
• Result: knee is mechanically locked, held in extension without muscle effort (seen in normal standing)

• The final rotation is produced by the pull of the quadriceps femoris on the tibial tuberosity via patellar ligament (tibial rotation component)

• To flex the locked knee, it must first be unlocked
• Popliteus muscle (the "key" to unlock the knee) unlocks the joint
• Popliteus rotates the femur laterally on a fixed tibia (or rotates the tibia medially on a fixed femur)
• This reverses the screw-home mechanism and "unscrews" the locked knee, slackening the ligaments and allowing flexion to proceed

• Origin: lateral surface of lateral femoral condyle (and lateral meniscus via popliteofibular fascicle)
• Insertion: posterior surface of upper tibia above soleal line
• Nerve supply: tibial nerve (L4, L5, S1)
• Function: unlocks knee, prevents forward displacement of femur in squatting

• Damage to popliteus tendon (e.g., posterolateral corner injury): difficulty unlocking knee, rotatory instability
• The popliteus also pulls the lateral meniscus posteriorly during flexion, preventing meniscal entrapment
• "Locked knee" clinically often refers to bucket-handle meniscal tear causing inability to fully extend - must be distinguished from anatomical locking

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(d) Supports of Uterus and Applied Anatomy (5 marks)

• Levator ani muscle (pubococcygeus, iliococcygeus, puborectalis) forms the pelvic diaphragm
• Provides the most important support for all pelvic viscera
• Levator ani contraction closes the urogenital hiatus

• Most important ligamentous support
• Passes from cervix and upper vagina to lateral pelvic walls
• Prevents uterine prolapse and displacement

• Runs from cervix anteriorly to pubic symphysis
• Prevents retroversion and holds bladder neck

• Runs from cervix posterolaterally to sacrum (S2-S4)
• Keeps cervix pulled posteriorly, maintaining anteversion
• Contains autonomic nerve fibers (presacral nerve)

• From uterine horn → inguinal canal → labium majus
• Maintains anteversion of uterus
• Has NO role in supporting the weight of uterus
• Contains artery of Sampson

• Double fold of peritoneum - NOT a true ligament
• Provides minimal support, mainly carries vessels and tubes

• Urogenital diaphragm (perineal membrane)
• Perineal body

• Descent of uterus into or through the vagina
• Causes: weakness of levator ani (childbirth injury, aging, obesity, chronic cough)
• Types: 1st degree (cervix in vagina), 2nd degree (cervix at introitus), 3rd degree/procidentia (complete - uterus outside)
• Management: pelvic floor exercises (Kegel), pessary, surgical repair (colporrhaphy, hysteropexy)

• Round ligament is landmark for identifying uterovesical fold of peritoneum
• Cardinal and uterosacral ligaments must be avoided while ligating uterine artery

• Cardinal ligament must be clamped to reduce bleeding (uterine artery runs within it)
• Ureter runs ~2 cm lateral to cervix, close to uterine artery ("water under the bridge") - must be identified and protected

• Uterosacral ligaments are common sites for endometriotic nodules - painful

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QUESTION 6 (4 x 2 marks = 8 marks)

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(a) Branches of Abdominal Aorta

1. Coeliac trunk (T12) - supplies foregut (lower esophagus to 2nd part of duodenum, liver, spleen, pancreas)
2. Superior mesenteric artery (SMA) (L1) - supplies midgut (3rd part of duodenum to left 2/3 of transverse colon)
3. Inferior mesenteric artery (IMA) (L3) - supplies hindgut (left 1/3 of transverse colon to upper rectum)

1. Inferior phrenic arteries - first branches, supply diaphragm (also give superior suprarenal arteries)
2. Middle suprarenal arteries (L1)
3. Renal arteries (L1-L2) - each gives inferior suprarenal artery
4. Gonadal arteries (L2): testicular (men) / ovarian (women)

• 4 pairs of lumbar arteries (L1-L4) - segmental supply to posterior abdominal wall, spinal cord

• Median sacral artery (at L4 bifurcation) - vestigial caudal artery

• Right and left common iliac arteries at L4

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(b) Nerve supply of pleura

• Innervated by autonomic nerve fibers (pulmonary plexus - sympathetic and parasympathetic)
• Insensitive to pain (no somatic innervation)
• Sensitive to stretch

• Pleurisy (inflammation of parietal pleura) causes sharp, stabbing chest pain that worsens with breathing - localized to chest wall (intercostal innervation)
• Central diaphragmatic pleural irritation (e.g., subphrenic abscess, liver abscess, MI) causes shoulder tip pain via phrenic nerve (C3-C4-C5 = also cutaneous supply of shoulder via supraclavicular nerves)
• Pneumothorax: visceral pleural rupture (painless) but parietal pleural irritation causes pain

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(c) Embryological Derivatives of Thoracic Diaphragm

• Arises from C3, C4, C5 (cervical segments)
• Explains why the diaphragm (which forms near the pericardial region of the neck then descends) retains its original cervical segmental nerve supply
• "C3, 4, 5 keeps the diaphragm alive"

• Most common: failure of the pleuroperitoneal membrane to develop/fuse completely on the LEFT side → Bochdalek hernia (posterolateral) - most common CDH
• Bowel herniates into left chest, causing pulmonary hypoplasia
• Morgagni hernia - anterior (parasternal) - failure of sternal and costal portions to meet
• Presents as: respiratory distress at birth, scaphoid abdomen, absent bowel sounds on chest

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(d) Clinical Applications of Karyotyping

1. Diagnosis of chromosomal abnormalities:
   • Trisomy 21 (Down syndrome) - 47,XX/XY,+21
   • Trisomy 18 (Edwards syndrome) - 47,+18
   • Trisomy 13 (Patau syndrome) - 47,+13
   • Monosomy X (Turner syndrome) - 45,X0
   • Klinefelter syndrome - 47,XXY
2. Prenatal diagnosis:
   • Amniocentesis (14-20 weeks) or chorionic villus sampling (CVS, 10-12 weeks)
   • Fetal cells analyzed for chromosomal abnormalities
   • Especially for advanced maternal age (>35 years - increased nondisjunction risk)
3. Diagnosis of ambiguous genitalia / disorders of sexual development (DSD):
   • Determines genetic sex (XX vs XY vs mosaics)
   • Guides treatment decisions
4. Oncology - cancer diagnosis and prognosis:
   • Philadelphia chromosome (t(9;22)) in CML (BCR-ABL fusion)
   • Burkitt lymphoma t(8;14) - c-Myc translocation
   • Retinoblastoma - deletion of 13q14
   • Karyotyping guides targeted therapy (e.g., imatinib for Ph+ CML)
5. Recurrent spontaneous abortions:
   • Balanced translocations in parents identified
   • ~5% of couples with recurrent miscarriage have a chromosomal translocation in one parent
6. Infertility investigation:
   • Klinefelter (XXY), Y chromosome microdeletions (azoospermia factor - AZF region)
   • Turner syndrome (primary amenorrhea)
7. Mosaicism detection: Different cell lines (e.g., 45,X/46,XX mosaicism in Turner syndrome)

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All answers above are written at 1st MBBS level (Anatomy - Paper II) per BCI/NMC curriculum covering gross anatomy, embryology, histology, and neuroanatomy as taught in standard 1st MBBS texts (Gray's Anatomy for Students, Moore's Clinically Oriented Anatomy, The Developing Human, Snell's Clinical Anatomy, and Gray's Atlas).