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MBBS 1st Professional Anatomy - Internal Assessment Answers

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Q.1 - Describe the Knee Joint (20 Marks)

Type of Joint

1. Femorotibial joint - between femoral condyles and tibial condyles (weight-bearing)
2. Femoropatellar joint - between patella and patellar surface of femur

Articular Surfaces

• Two femoral condyles (medial and lateral) - covered by hyaline cartilage
• Superior tibial condyles (tibial plateau)
• Posterior aspect of the patella and the V-shaped trench on anterior distal femur
• All enclosed in a single articular cavity

Menisci

• Two C-shaped fibrocartilaginous discs: medial and lateral menisci
• Both attached at each end to the intercondylar area of the tibial plateau
• Medial meniscus: attached to the joint capsule and tibial collateral ligament (less mobile, more prone to injury)
• Lateral meniscus: not attached to fibular collateral ligament (more mobile)
• Function: deepen articular surface, distribute load, act as shock absorbers

Synovial Membrane

• Attaches to margins of articular surfaces and outer margins of menisci
• Two cruciate ligaments lie outside the articular cavity but inside the fibrous capsule
• Forms the large suprapatellar bursa superiorly between the femur and quadriceps tendon

Ligaments

a) Extra-capsular Ligaments:

b) Intra-capsular (Cruciate) Ligaments:

• Anterior cruciate ligament (ACL): From anterior intercondylar area of tibia - ascends posteriorly to lateral wall of intercondylar fossa of femur. Prevents anterior displacement of tibia on femur.
• Posterior cruciate ligament (PCL): From posterior intercondylar area of tibia - ascends anteriorly to medial wall of intercondylar fossa of femur. Prevents posterior displacement of tibia on femur.

Intra-articular Structure

• Ligament of Wrisberg (posterior meniscofemoral ligament) - connects posterior horn of lateral meniscus to medial condyle of femur
• Transverse ligament - connects anterior horns of both menisci

Movements

Locking and Unlocking Mechanism

• In full extension, the femur medially rotates on the fixed tibia (when standing), which "screws home" the joint. The cruciate ligaments become taut, menisci become compressed - this is the locked position requiring minimal muscle energy.
• Unlocking: The popliteus muscle medially rotates the tibia (or laterally rotates the femur), releasing the screw-home mechanism to allow flexion to begin.

Intra-articular Structure - Bursae (clinically important)

• Suprapatellar bursa (communicates with joint cavity)
• Prepatellar bursa (housemaid's knee when inflamed)
• Infrapatellar bursa (clergyman's knee)

Applied Anatomy

• Unhappy triad (O'Donoghue): ACL + medial meniscus + tibial collateral ligament - injured by valgus + rotational force
• Drawer sign: Anterior drawer test (ACL), Posterior drawer test (PCL)
• McMurray's test: Meniscal tears
• Genu valgum (knock knee) / Genu varum (bow leg): Abnormal angulation at knee

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Q.2 - Describe Lungs Under the Following Headings (20 Marks)

a) External Features

• Larger and heavier (~620 g)
• Has 3 lobes (upper, middle, lower) separated by horizontal and oblique fissures
• Shorter and wider due to the liver on the right
• Horizontal fissure separates upper from middle lobe
• Oblique fissure separates middle and lower lobes

• Smaller (~560 g)
• Has 2 lobes (upper and lower) separated by oblique fissure only
• Longer and narrower due to the heart being more to the left
• Has a cardiac notch on the anterior border
• Has the lingula (tongue-like projection of upper lobe)

• Apex: projects 2.5 cm above the clavicle into the root of the neck
• Base: rests on the diaphragm (concave)
• Costal surface: convex, relates to ribs
• Mediastinal surface: contains the hilum
• Anterior, posterior, and inferior borders

b) Well-labeled Diagram of Mediastinal Surface of Both Lungs

Structures at the hilum (from anterior to posterior):
- Pulmonary vein (anterior and inferior)
- Pulmonary artery (middle)
- Main bronchus (posterior and superior)
 → "VABP" or "VAB" arrangement

• Cardiac impression (right atrium and right ventricle)
• SVC groove (anterosuperiorly)
• Azygos vein arch (superior to hilum)
• Esophageal groove (posterior to hilum)
• Subclavian artery groove (apex)
• IVC groove (inferoposterior)

• Large cardiac impression (left ventricle - deeper than right)
• Arch of aorta groove (above hilum)
• Descending thoracic aorta groove (posterior to hilum)
• Subclavian artery groove (apex)
• Esophageal groove (narrow - not as prominent as right)
• Groove for left brachiocephalic vein (anterosuperior)

c) Bronchopulmonary Segments of Both Lungs

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Q.3 - Brief Answer Questions (5x6 = 30 Marks)

a) Right Atrium

1. Superior vena cava (upper posterior portion)
2. Inferior vena cava (lower posterior portion)
3. Coronary sinus (between IVC and tricuspid valve)

• Sulcus terminalis: External groove corresponding to crista terminalis
• Fossa ovalis: Oval depression in interatrial septum - remnant of foramen ovale
• Limbus fossae ovalis: Raised margin around fossa ovalis
• Valve of inferior vena cava (Eustachian valve): Directs blood to foramen ovale in fetal life
• Valve of coronary sinus (Thebesian valve): Small valve at coronary sinus opening
• Tricuspid valve guards the right atrioventricular orifice

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b) Azygos System of Veins

1. Azygos vein (right side)
2. Hemiazygos vein (left, lower)
3. Accessory hemiazygos vein (left, upper)

• Origin: Junction of right ascending lumbar vein + right subcostal vein (at L1-L2)
• Enters thorax through aortic hiatus of diaphragm
• Ascends in posterior mediastinum to the right of thoracic duct
• At T4 level: arches anteriorly over root of right lung to drain into SVC
• Tributaries: Right superior intercostal vein (2nd-4th), 5th-11th right posterior intercostal veins, hemiazygos, accessory hemiazygos, esophageal, mediastinal, pericardial, and right bronchial veins

• Origin: Junction of left ascending lumbar + left subcostal vein (at L8-L9)
• Receives lower 4-5 left posterior intercostal veins
• Crosses midline at T9 to drain into azygos vein

• Drains 4th-8th left posterior intercostal veins
• Crosses midline at T7-T8 to drain into azygos vein

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c) Fertilization and Its Effects

1. Capacitation: Sperm undergoes changes in female genital tract (hyperactivation, removal of surface coat)
2. Acrosome reaction: Acrosomal enzymes (hyaluronidase, acrosin) released to penetrate zona pellucida
3. Sperm penetrates zona pellucida via ZP3 receptor binding
4. Cortical reaction: Cortical granules released - blocks polyspermy (zona reaction)
5. Completion of meiosis II: Secondary oocyte completes second meiotic division to form the ovum + second polar body
6. Pronuclei formation: Male and female pronuclei form
7. Syngamy: Pronuclei fuse - diploid zygote formed (46 chromosomes)

1. Restores the diploid number (46 chromosomes)
2. Determines the sex of the individual (XX = female, XY = male)
3. Initiates cleavage (mitotic divisions)
4. Prevents polyspermy (cortical reaction)
5. Completes meiosis II of secondary oocyte
6. Determines genetic variation through chromosome recombination

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d) Popliteal Fossa

• Tibial nerve (most superficial and medial)
• Popliteal vein (middle)
• Popliteal artery (deepest, most medial) - continuation of femoral artery
• Common fibular (peroneal) nerve - along medial border of biceps femoris
• Small saphenous vein (pierces popliteal fascia to join popliteal vein)
• Popliteal lymph nodes

• Popliteal aneurysm: Most common peripheral artery aneurysm
• Baker's cyst (popliteal cyst): Distension of semimembranosus bursa; communicates with joint cavity
• Common fibular nerve injury: Most commonly damaged nerve at knee - causes foot drop

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e) Types and Histology of Cartilages

1. Hyaline Cartilage

• Most abundant type
• Gross appearance: Bluish-white, glassy, semi-transparent
• Matrix: Type II collagen fibers embedded in ground substance (chondroitin sulfate + keratan sulfate + hyaluronic acid); fibers not visible with routine staining
• Chondrocytes: In lacunae; form isogenous groups (cell nests)
• Perichondrium: Present (except articular cartilage and epiphyseal plates)
• Locations: Articular surfaces, costal cartilages, tracheal rings, laryngeal cartilages, nasal septum, fetal skeleton
• Calcification: Occurs with aging

2. Fibrocartilage (White Fibrocartilage)

• No perichondrium
• Matrix: Abundant type I collagen fibers in parallel bundles (visible on H&E stain); less ground substance
• Chondrocytes: In lacunae, often in rows between collagen bundles
• Strongest type - resists compression and tension
• Locations: Intervertebral discs (annulus fibrosus), pubic symphysis, menisci of knee, articular discs (TMJ, sternoclavicular joint), insertions of tendons

3. Elastic Cartilage

• Perichondrium: Present
• Matrix: Dense network of elastic fibers + type II collagen; stains with elastic stains (orcein, Verhoeff)
• Chondrocytes: In lacunae; more numerous than hyaline
• Most flexible - springs back to shape
• Locations: Pinna (auricle), eustachian tube, epiglottis, cuneiform and corniculate laryngeal cartilages

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Q.4 - Short Answer Questions (1x10 = 10 Marks Each)

a) Hamstring Muscle

• Three muscles: Biceps femoris, Semitendinosus, Semimembranosus
• Origin: Ischial tuberosity (long head of biceps from ischial tuberosity; short head from linea aspera)
• Nerve supply: Tibial division of sciatic nerve (except short head of biceps - common fibular division)
• Action: Flex knee, extend hip; biceps femoris also laterally rotates the leg
• Applied: "Hamstring strain" - common sports injury

b) Iliotibial Tract

• A thickened band of fascia lata on the lateral aspect of the thigh
• Receives insertions of tensor fascia lata and gluteus maximus
• Inserts into Gerdy's tubercle on the anterolateral aspect of the lateral tibial condyle
• Function: Stabilizes the knee, extends and abducts the hip
• Applied: Iliotibial band syndrome (runner's knee) - common in long-distance runners

c) Popliteus Muscle

• Origin: Lateral surface of lateral condyle of femur (inside knee joint capsule); also from lateral meniscus
• Insertion: Posterior surface of proximal tibia (above soleal line)
• Nerve supply: Tibial nerve (L4, L5, S1)
• Action: Unlocks the knee by medially rotating the tibia on femur (or laterally rotating femur on tibia in non-weight-bearing); also prevents forward displacement of femur on tibia
• Also retracts lateral meniscus during lateral rotation

d) Angle of Louis (Sternal Angle)

• Also called the manubriosternal joint or angle of Louis
• Junction between manubrium and body of sternum
• It is a secondary cartilaginous joint (symphysis)
• Clinically important landmark:
  • Level of 2nd costal cartilage (rib counting starts here)
  • Level of bifurcation of trachea (T4-T5 vertebral level)
  • Level where arch of aorta begins and ends
  • Divides superior and inferior mediastinum
  • Level of azygos vein draining into SVC

e) Typical Intercostal Space

• Located between adjacent ribs
• Contains 3 layers of muscles:
  1. External intercostal muscle (fibers run downward and forward)
  2. Internal intercostal muscle (fibers run downward and backward)
  3. Innermost intercostal muscle
• Neurovascular bundle (VAN - Vein, Artery, Nerve from above downward) runs in the subcostal groove at the inferior border of each rib, between internal and innermost intercostal muscles
• Applied: Pleural tap (thoracocentesis) is done at the upper border of a lower rib to avoid the neurovascular bundle

f) Types and Histology of Cartilages

g) Adductor Canal (Hunter's Canal)

• An aponeurotic tunnel in the middle third of the medial thigh
• Boundaries: Anteriorly - sartorius muscle; Posteromedially - adductor longus and magnus; Laterally - vastus medialis
• Contents: Femoral artery, femoral vein (posterior to artery), saphenous nerve, nerve to vastus medialis
• The femoral artery exits at the adductor hiatus to become the popliteal artery

h) Pott's Fracture

• A fracture-dislocation of the ankle joint (not spine)
• Classic description: Bimalleolar fracture (fractures of both medial and lateral malleoli) with or without posterior malleolus fracture
• Caused by forced eversion of the foot
• Applied: Trimalleolar fracture (all three malleoli) is the most unstable ankle injury

i) Functions of Placenta

1. Nutrition - transfers glucose, amino acids, fatty acids from mother to fetus
2. Respiration - transfers O2 from mother to fetus, CO2 in reverse
3. Excretion - transfers urea, uric acid, bilirubin to maternal circulation
4. Endocrine - secretes hCG (maintains corpus luteum), hPL (human placental lactogen), progesterone, estrogen
5. Immunological - transfers maternal IgG antibodies (passive immunity); forms immune barrier
6. Barrier function - limits passage of some drugs and microorganisms (though incomplete - TORCH organisms cross)

j) Histology of Bone (Secondary / Mature Bone)

• Compact (cortical) bone: Dense outer shell
• Cancellous (trabecular/spongy) bone: Inner spongy framework

• Osteon (Haversian system): Basic structural unit - concentric lamellae of bone matrix around a central Haversian canal (contains blood vessels, nerves)
• Haversian canal: Longitudinal canal with blood vessels
• Volkmann's canals: Transverse canals connecting Haversian canals to each other and to the periosteum
• Lacunae: Spaces in bone matrix containing osteocytes
• Canaliculi: Fine channels connecting lacunae - allow exchange of nutrients
• Interstitial lamellae: Remnants of old osteons between Haversian systems
• Circumferential lamellae: Outer (subperiosteal) and inner (endosteal) lamellae

• Osteoblasts: Bone-forming cells; secrete osteoid (type I collagen + ground substance)
• Osteocytes: Mature bone cells trapped in lacunae
• Osteoclasts: Bone-resorbing cells; multinucleated; associated with Howship's lacunae; contain tartrate-resistant acid phosphatase (TRAP)

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