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Microbiology Paper - Answer Key (Tejas Pal, BSem-IV 'A')

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Q1. A differential media

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Q2. Endotoxin produced by gram-negative bacteria is present in

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Q3. Rheumatic fever is most commonly caused by

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Q4. Neither of these infections are transmitted person-to-person, EXCEPT

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Q5. Antibodies to which of the following antigens of Bacillus anthracis are protective?

Note: Some sources may argue anthrax toxin (option C) antibodies are protective too. However, the standard examination answer is A - Capsular polypeptide, as anti-capsular antibodies prevent the organism from evading phagocytosis.

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Q6. The first symptom of tetanus is

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Q7. Which of the following is the usual cause of Clostridioides difficile-induced colitis?

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Q8. Light subunit of botulinum toxin cleaves the protein that regulates release of

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Q9. Causative agent of papule that evolves into non-healing ulcer is:

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Q10. Causative agent of Lyme disease is:

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Summary Table

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🫁 Respiratory System - Complete Anatomy (Exam Score: 100%)

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OVERVIEW - Ek Nazar Mein Poora System

---

PART 1 - NOSE & NASAL CAVITY

External Nose

• Dorsum (bridge), Apex (tip), Nares (nostrils)
• Framework: Upper = nasal bones; Lower = lateral & alar cartilages

Nasal Cavity (Andar ka Structure)

• Roof: Cribriform plate of ethmoid (olfactory nerves pass through)
• Floor: Hard palate + soft palate
• Medial wall: Nasal septum (septal cartilage + vomer + ethmoid)
• Lateral wall: 3 conchae (turbinates) - Superior, Middle, Inferior

Conchae & Meatuses (HIGH YIELD!)

Blood Supply

• Anteriorly: Anterior ethmoidal artery (from ophthalmic)
• Posteriorly: Sphenopalatine artery (from maxillary)
• Kiesselbach's plexus = Little's area = anterior septum par all arteries milti hain → most common site of epistaxis (nosebleed)

Nerve Supply

• Smell: CN I (Olfactory nerve) - via cribriform plate
• Sensation: CN V1 (anterior) + CN V2 (posterior)

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PART 2 - PHARYNX

3 Parts of Pharynx (Exam Favourite!)

Muscles (Deglutition ke liye)

• Superior, Middle, Inferior Constrictors - CP angle (Killian's dehiscence) = weak area between thyropharyngeus and cricopharyngeus → Zenker's diverticulum banta hai

Nerve Supply

• Motor: CN X (Vagus) via pharyngeal plexus
• Sensory: CN IX (Glossopharyngeal) - oropharynx; CN X - laryngopharynx

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PART 3 - LARYNX ⭐ (Most Important for Exams!)

Cartilages of Larynx (9 total)

1. Thyroid cartilage - Largest; "Adam's apple" (laryngeal prominence); angle = 90° in male, 120° in female → male voice deeper
2. Cricoid cartilage - Only complete ring; signet ring shape (narrow anterior, wide posterior); at C6
3. Epiglottis - Leaf-shaped, elastic cartilage; prevents aspiration during swallowing

Vocal Folds (VERY HIGH YIELD!)

• True vocal cords (Vocal folds): Lower pair; white, avascular; lined by stratified squamous epithelium
• False vocal cords (Vestibular folds): Upper pair; pink; no phonation function
• Rima glottidis = opening between true vocal cords (narrowest part of larynx in adults)
  • Narrowest part in children = subglottis (cricoid level) → croup/subglottic stenosis

Cavities of Larynx

1. Vestibule - Above false cords (inlet to false cords)
2. Ventricle (Sinus of Morgagni) - Between true and false cords
3. Subglottis - Below true cords to trachea

Nerve Supply (HIGH YIELD!)

Exam Trick: RLN injury → hoarseness (unilateral) or aphonia (bilateral). Left RLN longer → loops around aortic arch (right RLN loops around subclavian artery). Left RLN more at risk in thoracic surgery/aortic aneurysm.

Muscles of Larynx

• Abductor (opens cords): Posterior cricoarytenoid (PCA) = ONLY abductor - "Lone Abductor"
• Adductors (close cords): Lateral cricoarytenoid, transverse arytenoid
• Tensor (lengthens cords, raises pitch): Cricothyroid (external branch of SLN)
• Relaxer (lowers pitch): Thyroarytenoid

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PART 4 - TRACHEA

Key Facts

• Length: 10-12 cm
• Extends from C6 (cricoid cartilage) to T4-T5 (carina/bifurcation)
• Cervical part: C6 to C7 | Thoracic part: T1 to T4
• 16-20 C-shaped hyaline cartilage rings (open posteriorly)
• Posterior wall = Trachealis muscle (smooth muscle; closes the "C")

Wall Layers (3)

1. Mucosa - Pseudostratified ciliated columnar (respiratory) epithelium
2. Fibromuscular-cartilaginous layer
3. Adventitia

Carina

• Ridge at bifurcation (T4-T5) divides airstream
• Sensitive cough reflex area
• Widened/distorted carina → sign of enlarged tracheobronchial nodes (e.g., lymphoma, TB)

Blood Supply

• Tracheal branches of inferior thyroid artery
• Venous drainage: companion veins

Nerve Supply

• Recurrent laryngeal nerve (branch of vagus) - motor to trachealis + sensory

Clinical Note

• Aspirated foreign body → goes to RIGHT main bronchus (wider, shorter, more vertical - only 20° angle vs left 35°)

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PART 5 - BRONCHI & BRONCHIAL TREE ⭐

Main Bronchi Comparison (EXAM FAVOURITE!)

Bronchial Tree - Order of Division

Trachea
  → Main bronchi (1st order)
    → Lobar bronchi (2nd order)
      → Segmental bronchi (3rd order)
        → Subsegmental bronchi
          → Bronchioles (no cartilage, <1.5mm diameter)
            → Terminal bronchioles
              → Respiratory bronchioles
                → Alveolar ducts
                  → Alveolar sacs
                    → Alveoli (gas exchange!)

Cartilage disappears at bronchiole level - bronchioles stay open via transpulmonary pressure

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PART 6 - LUNGS ⭐⭐ (Maximum Marks Here!)

Basic Facts

• Shape: Half-cone
• Right lung: Heavier, larger, 3 lobes
• Left lung: Smaller, 2 lobes (heart occupies space → cardiac notch)

Surfaces

• Costal surface - ribs se lagti hai
• Mediastinal surface - heart + great vessels; has hilum
• Diaphragmatic surface (base) - concave; sits on diaphragm
• Apex - projects 2-3 cm above clavicle (into root of neck)

Lobes & Fissures

Lingula = tongue-like projection of left superior lobe; corresponds to right middle lobe

Bronchopulmonary Segments (BPS) - HIGH YIELD!

• Right lung: 10 segments
• Left lung: 8-9 segments (1+2 fused as apicoposterior, 7+8 may fuse)

Hilum of Lung - Contents (Anterior → Posterior)

• Pulmonary veins (anterior + inferior)
• Pulmonary artery (middle)
• Bronchus (posterior)

Mnemonic: "VAB" = Veins Anterior, Bronchus Posterior

Right Hilum Special:

• Right superior lobar bronchus = eparterial (above the pulmonary artery) - only bronchus above artery
• All other bronchi = hyparterial

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PART 7 - ALVEOLI & GAS EXCHANGE

Microscopic Anatomy

Surfactant

• Reduces surface tension in alveoli
• Prevents collapse (atelectasis)
• Deficient in premature babies → Respiratory Distress Syndrome (RDS)

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PART 8 - BLOOD SUPPLY & LYMPHATICS

Dual Blood Supply

Lymphatics - 2 Systems

1. Deep/Peribronchial system → follows bronchi → bronchopulmonary nodes → tracheobronchial nodes
2. Superficial/Subpleural system → follows veins → tracheobronchial nodes

Hilar nodes = most important in TB and lung cancer

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PART 9 - PLEURA

Layers

• Visceral pleura - covers lung surface (no pain receptors)
• Parietal pleura - lines thoracic wall, diaphragm, mediastinum (has pain receptors)
• Pleural cavity - potential space; contains ~5 mL serous fluid (lubricant)

Parts of Parietal Pleura

• Costal (lines ribs)
• Diaphragmatic
• Mediastinal
• Cervical pleura (Pleural cupula) - extends into root of neck above 1st rib

Pleural Recesses (Exam Favourite!)

Nerve Supply

• Costal parietal pleura: intercostal nerves (chest pain)
• Central diaphragmatic pleura: phrenic nerve → referred shoulder tip pain

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PART 10 - DIAPHRAGM (Respiratory Muscle)

Openings (HIGH YIELD!)

Mnemonic: I 8 10 eggs At 12 (IVC at T8, Esophagus at T10, Aorta at T12)

Nerve Supply

• Motor: Phrenic nerve (C3, 4, 5) - "C3, 4, 5 keeps the diaphragm alive"
• Sensory (central): Phrenic nerve
• Sensory (peripheral): Intercostal nerves (T7-T12)

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QUICK REVISION TABLE - All High Yield Points

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Sources: Color Atlas of Human Anatomy Vol. 2 (Thieme), Gray's Anatomy for Students, Guyton & Hall Medical Physiology - all textbook-verified.

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🦴 Respiratory Anatomy - PART 2: Thoracic Cage + Mediastinum

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PART A - THORACIC CAGE (Bony Framework)

Overview

• Superior thoracic aperture (inlet): T1, rib 1, manubrium - opens into neck
• Inferior thoracic aperture (outlet): T12, rib 12, xiphoid, costal margin - closed by diaphragm

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Sternum - 3 Parts (HIGH YIELD!)

Sternal angle marks: Level of T4/T5, 2nd costal cartilage / Rib 2, bifurcation of trachea (carina), arch of aorta begins and ends, superior/inferior mediastinum boundary, SVC begins on right side, azygos vein drains into SVC

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Ribs - Classification (EXAM FAVOURITE!)

Typical Rib (3-9) - Parts

• Head - 2 articular facets (articulates with vertebral bodies of its own + one above)
• Neck - connects head to tubercle
• Tubercle - articulates with transverse process of its vertebra
• Shaft/Body - has costal groove on inferior inner surface (VAN lives here!)
• Angle - where shaft bends anteriorly
• Costal cartilage - anterior end connects rib to sternum

Atypical Ribs

• Rib 1: Flat, wide, shortest; no costal groove; has scalene tubercle (scalenus anterior attaches); groove for subclavian vein (anterior) and artery (posterior)
• Rib 2: Flat, twice as long as rib 1; has tuberosity for serratus anterior
• Rib 10: Head has SINGLE articular facet
• Ribs 11 & 12: No neck, no tubercle, no costal cartilage; pointed anteriorly (floating)

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PART B - INTERCOSTAL SPACES ⭐⭐

Structure

3 Intercostal Muscles

External intercostal membrane = anterior continuation of external intercostals (no muscle fibers anteriorly near sternum) Internal intercostal membrane = posterior continuation of internal intercostals (no muscle fibers posteriorly near vertebra)

Neurovascular Bundle (VAN) - HIGH YIELD!

V - Vein (most superior, in groove)
A - Artery (below vein)
N - Nerve (most inferior, often outside groove = most vulnerable!)

Clinical: Needle for thoracocentesis (pleural tap) ALWAYS inserted over the SUPERIOR margin of the LOWER rib to avoid VAN → enter just ABOVE the lower rib!

Intercostal Nerves

• = Anterior rami of T1-T11 spinal nerves
• T12 = subcostal nerve (below rib 12)
• Carry: Somatic motor (to intercostal muscles) + Somatic sensory (skin + parietal pleura) + Sympathetic fibers
• Branches: Posterior (back muscles) → Lateral cutaneous (midaxillary line, divides anterior + posterior) → Anterior cutaneous (parasternal)

• T1: Partly joins brachial plexus
• T2 lateral cutaneous branch = Intercostobrachial nerve → supplies medial arm skin (referred cardiac pain goes to medial arm via this!)
• T7-T11: Continue into abdominal wall

Blood Supply of Intercostal Space

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PART C - MEDIASTINUM ⭐⭐⭐ (Maximum Exam Marks!)

Definition

Divisions - The Key Diagram

MEDIASTINUM
├── SUPERIOR MEDIASTINUM (above sternal angle / T4/T5)
└── INFERIOR MEDIASTINUM (below sternal angle / T4/T5)
    ├── ANTERIOR MEDIASTINUM (sternum → pericardium)
    ├── MIDDLE MEDIASTINUM (contains pericardium + heart)
    └── POSTERIOR MEDIASTINUM (pericardium/diaphragm → vertebrae)

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SUPERIOR MEDIASTINUM (Between manubrium and T1-T4)

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ANTERIOR MEDIASTINUM (Sternum → Pericardium)

• Inferior part of thymus (extension)
• Fat and connective tissue
• Lymph nodes (parasternal)
• Sternopericardial ligaments (sternum → fibrous pericardium)
• Mediastinal branches of internal thoracic vessels

Clinical: Anterior mediastinal masses = "4 Ts" - Thymoma, Teratoma/Germ cell tumor, Terrible lymphoma, Thyroid (retrosternal)

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MIDDLE MEDIASTINUM (The Heart Compartment)

• Pericardium + Heart
• Origins/roots of great vessels (aorta, pulmonary trunk, SVC, IVC, pulmonary veins)
• Phrenic nerves (run on each side of pericardium)
• Pericardiacophrenic vessels

Pericardium - Layers

Fibrous pericardium (outer, tough connective tissue)
  └── Serous pericardium
        ├── Parietal layer (lines fibrous pericardium)
        └── Visceral layer = Epicardium (covers heart)
              └── Between parietal + visceral = Pericardial cavity (small amount of fluid)

• Transverse sinus - behind great arteries, in front of great veins; surgeon's finger goes through here to clamp aorta
• Oblique sinus - behind left atrium; blind recess; fluid collects here in pericardial effusion

• Fibrous + parietal serous pericardium → Phrenic nerve (referred pain to shoulder)
• Visceral pericardium (epicardium) → autonomic (pain-insensitive)

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POSTERIOR MEDIASTINUM (Behind pericardium/diaphragm, in front of T5-T12)

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SUMMARY MASTER TABLE - Mediastinum Contents

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CLINICAL HIGH-YIELD POINTS (Exam Sawal!)

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QUICK REVISION - All New Additions

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