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COMPLETE HISTOLOGY NOTES

Epithelial Tissue | Connective Tissue | Skeletal & Smooth Muscle | Cartilage & Bone

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PART 1: EPITHELIAL TISSUE

1.1 Definition and General Features

• Cells are closely apposed with minimal ECM between them
• Always located at a free surface (external or internal)
• Avascular - receive nutrients by diffusion from underlying connective tissue
• Rich nerve supply
• Rest on a basement membrane (basal lamina)
• High regenerative capacity

1.2 Functions of Epithelial Tissue

1. Protection - epidermis protects against mechanical, chemical, microbial injury
2. Absorption - intestinal lining absorbs digested nutrients
3. Secretion - glandular cells secrete hormones, enzymes, mucus
4. Filtration - kidney tubule epithelium
5. Sensation - taste buds, olfactory epithelium
6. Contractility - myoepithelial cells (in mammary, sweat, salivary glands)
7. Ion transport - renal tubules, intestine

1.3 Basement Membrane

• Lies at the interface between epithelium and connective tissue
• Composed of: basal lamina (secreted by epithelial cells) + reticular lamina (secreted by fibroblasts)
• Basal lamina components: laminin, type IV collagen, nidogen/entactin, heparan sulfate proteoglycans
• Functions: structural support, filtration, scaffold for regeneration, regulates cell polarity

• Lamina lucida (lamina rara) - electron-lucent, close to cell membrane
• Lamina densa - electron-dense, type IV collagen network

1.4 Cell Junctions

1.5 Apical Surface Specializations

• Finger-like projections of apical membrane
• Core of actin filaments cross-linked by fimbrin and villin
• Increase surface area for absorption
• "Brush border" in intestine and kidney
• ~1 µm long, 0.1 µm wide

• Long, non-motile projections (misnamed - not true cilia)
• Found in epididymis and inner ear hair cells
• Core of actin filaments
• Function: absorption (epididymis), mechanosensation (inner ear)

• Long, motile projections (~10 µm)
• Core = axoneme: 9+2 arrangement of microtubule doublets
• Dynein arms provide motor activity (use ATP)
• Found in trachea (mucociliary clearance), fallopian tube (ovum transport), ependyma
• Kartagener syndrome: immotile cilia due to dynein arm defect → bronchiectasis, situs inversus, infertility

1.6 Classification of Epithelia

Based on Number of Layers:

• Simple - single cell layer, all cells touch basement membrane
• Stratified - multiple layers, only basal layer touches basement membrane
• Pseudostratified - appears stratified but all cells contact basement membrane; nuclei at different levels

Based on Cell Shape:

• Squamous - flat, scale-like
• Cuboidal - cube-shaped, nucleus round/central
• Columnar - taller than wide, nucleus at base, oval

Types and Locations:

1.7 Glands

• Exocrine glands - secrete via ducts to surface (salivary, sweat, sebaceous)
• Endocrine glands - secrete hormones directly into blood (no ducts)

• Merocrine (eccrine) - exocytosis; no cell loss (pancreas, most glands)
• Apocrine - apical cytoplasm buds off with secretion (mammary glands)
• Holocrine - entire cell becomes secretory product (sebaceous glands)

• Simple (unbranched duct) vs Compound (branched duct)
• Tubular, acinar (alveolar), or tubuloalveolar

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PART 2: CONNECTIVE TISSUE

2.1 Definition and General Features

• Abundant extracellular matrix (ground substance + fibers)
• Few cells, widely separated
• Richly vascularized (except cartilage)
• Contains wandering (blood-derived) and fixed (resident) cells

2.2 Classification

1. Embryonic connective tissue
   • Mesenchyme - undifferentiated stellate cells in gelatinous matrix (fetus)
   • Mucous (Wharton's jelly) - umbilical cord
2. Connective tissue proper
   • Loose (areolar) - loosely arranged fibers, many cell types; found under epithelia, around organs
   • Dense irregular - randomly oriented collagen fibers; dermis, organ capsules
   • Dense regular - parallel collagen fibers; tendons, ligaments, cornea
3. Specialized connective tissue
   • Cartilage
   • Bone
   • Adipose tissue
   • Blood/lymph
   • Reticular tissue

2.3 Cells of Connective Tissue

• Lymphocytes, neutrophils, eosinophils, monocytes - migrate from blood during inflammation

2.4 Extracellular Matrix (ECM)

Fibers:

• Most abundant protein in the body (~30% total protein)
• Made of tropocollagen (3 polypeptide alpha chains in right-handed triple helix)
• Synthesized by fibroblasts, chondroblasts, osteoblasts
• Stain pink with H&E; blue with Masson's trichrome
• Types:

• Made of elastin (core) surrounded by fibrillin microfibrils
• Allow stretch and recoil (up to 150% original length)
• Stained by orcein, Weigert's resorcin-fuchsin
• Abundant in large arteries (aorta), lung, elastic ligaments, skin
• Marfan syndrome: fibrillin-1 gene mutation

• Type III collagen + glycoproteins
• Form delicate meshworks supporting cells of liver, spleen, lymph nodes, bone marrow
• Stained by silver impregnation (argyrophilic) - appear black

Ground Substance:

• Amorphous, hydrated gel filling spaces between cells and fibers
• Contains glycosaminoglycans (GAGs), proteoglycans, glycoproteins

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PART 3: SKELETAL MUSCLE

3.1 General Features

• Voluntary, striated muscle
• Multinucleated cells (syncytium) - nuclei peripherally located (at sarcolemma)
• Derived from myoblasts (mesodermal origin)
• Each fiber surrounded by endomysium (delicate reticular fibers)
• Bundles (fascicles) surrounded by perimysium (dense collagen)
• Whole muscle surrounded by epimysium (dense irregular CT)

3.2 Ultrastructure - The Sarcomere

3.3 Sliding Filament Theory (Cross-Bridge Cycle)

1. Rest - troponin I blocks actin binding sites; tropomyosin covers them
2. Excitation - action potential → T-tubules → sarcoplasmic reticulum releases Ca2+
3. Ca2+ binds troponin C → conformational change → tropomyosin moves → exposes actin binding sites
4. Cross-bridge formation - myosin head (ADP+Pi attached) binds actin
5. Power stroke - Pi released → myosin head pivots → pulls actin toward M line → ADP released
6. ATP binding - ATP binds myosin head → cross-bridge detaches
7. ATP hydrolysis - myosin head returns to "cocked" position (ADP+Pi)
8. Cycle repeats

3.4 Excitation-Contraction (E-C) Coupling

• Action potential travels down motor axon → neuromuscular junction
• Acetylcholine released → binds nicotinic receptors on motor end plate
• Depolarization → action potential along sarcolemma and down T-tubules (transverse tubules)
• T-tubules make contact with terminal cisternae of SR at the triad
• Dihydropyridine (DHP) receptors on T-tubule act as voltage sensors
• Ryanodine receptors (RyR1) on SR open → Ca2+ floods sarcoplasm
• Ca2+ binds troponin C → contraction
• Ca2+ ATPase (SERCA) pumps Ca2+ back into SR → relaxation

3.5 Fiber Types

3.6 Motor Unit

• 1 alpha motor neuron + all muscle fibers it innervates
• Small motor units (eyes, fingers): precise movement
• Large motor units (thigh): powerful, less precise
• Size principle (Henneman): motor units recruited from smallest to largest

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PART 4: SMOOTH MUSCLE

4.1 General Features

• Involuntary, non-striated (no sarcomeres)
• Single, spindle-shaped cells (~200 µm long)
• Centrally located, cigar-shaped nucleus
• Found in: hollow viscera (GI tract, uterus, bladder), blood vessels, airways, iris, piloerector muscles
• Derived from mesoderm (most) or neural crest (vessels of head, iris)

4.2 Structure

• No T-tubules (invaginations called caveolae instead)
• Sarcoplasmic reticulum is sparse and less organized
• Thick (myosin) and thin (actin) filaments present but NOT arranged into sarcomeres
• Dense bodies - equivalent of Z discs; anchor actin filaments; contain alpha-actinin
• Intermediate filaments (desmin, vimentin) connect dense bodies to the cell membrane

4.3 Mechanism of Contraction (Calmodulin-MLCK Pathway)

1. Rise in intracellular Ca2+ (from SR and extracellular sources)
2. Ca2+ binds calmodulin (4 Ca2+ per calmodulin molecule)
3. Ca2+-calmodulin complex activates myosin light chain kinase (MLCK)
4. MLCK phosphorylates myosin light chains → activates myosin ATPase
5. Cross-bridge cycling and contraction occur
6. Myosin light chain phosphatase (MLCP) dephosphorylates myosin → relaxation

• NO troponin system
• Regulated by myosin phosphorylation (not actin-linked troponin)
• Calmodulin instead of troponin C
• Much slower cross-bridge cycling (1/10 to 1/300 of skeletal)
• Much lower energy consumption (1/10 to 1/300 of skeletal)
• Latch mechanism - smooth muscle can maintain force with minimal ATP expenditure
• Maximum force often greater than skeletal muscle (4-6 kg/cm2 vs 3-4 kg/cm2)
• Contraction duration: 1-3 seconds (vs milliseconds in skeletal)

4.4 Control of Smooth Muscle

• Autonomic nervous system - sympathetic and parasympathetic
• Hormones - oxytocin (uterus), angiotensin (vessels)
• Local factors - stretch (myogenic response), CO2, O2, pH
• Gap junctions - allow electrical coupling between smooth muscle cells (unitary smooth muscle)

• Gap junctions connect cells electrically
• Contract in coordinated waves
• Example: GI tract, uterus, ureter

• Each cell independently innervated
• Fine, precise control
• Example: iris, ciliary muscle, large blood vessels

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PART 5: CARTILAGE

5.1 General Features

• Avascular, aneural, alymphatic specialized connective tissue
• Receives nutrients by diffusion through matrix
• Matrix produced by chondrocytes (mature cartilage cells) and chondroblasts (immature)
• Surrounded by perichondrium (except fibrocartilage and articular cartilage)
• Resilient, flexible but firm

5.2 Cells

5.3 Types of Cartilage

Hyaline Cartilage

• Most common type
• Matrix: type II collagen (not visible because fibers match matrix refractive index) + chondroitin sulfate + keratan sulfate + hyaluronic acid
• Perichondrium: present (outer fibrous layer + inner chondrogenic layer)
• Chondrocytes in lacunae, may form isogenous groups (cell nests)
• Territorial matrix (around chondrocytes, basophilic) vs interterritorial matrix (between groups, acidophilic)
• Locations: articular cartilage, tracheal rings, costal cartilage, nasal septum, laryngeal cartilages (except epiglottis and corniculate), fetal skeleton, epiphyseal growth plate
• No perichondrium at articular surfaces

Elastic Cartilage

• Similar to hyaline but with abundant elastic fibers (elastin + fibrillin) in matrix
• More flexible than hyaline
• Has perichondrium
• Locations: epiglottis, auricle (pinna) of ear, external auditory canal, auditory tube, cuneiform cartilage of larynx
• Stained by orcein (elastic fibers appear dark)

Fibrocartilage

• Combination of dense regular connective tissue and cartilage
• Type I collagen predominates (visible fibers)
• NO perichondrium
• Chondrocytes in rows between thick collagen bundles
• Locations: intervertebral discs (anulus fibrosus), pubic symphysis, menisci of knee, insertions of tendons, temporomandibular joint
• Resistant to compression and tensile stress

5.4 Growth of Cartilage

• Interstitial growth - chondrocytes divide within matrix (isogenous groups); occurs in young cartilage
• Appositional growth - chondrogenic cells of perichondrium differentiate into chondroblasts and add matrix at periphery; occurs throughout life

5.5 Calcification

• Mature hyaline cartilage may calcify (hydroxyapatite crystals deposited)
• Calcified cartilage is then eroded and replaced by bone during ossification
• Exceptions: tracheal cartilage (partial calcification), articular cartilage (resists calcification)

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PART 6: BONE

6.1 General Features

• Hardest connective tissue (due to mineralization)
• Matrix: 70% inorganic (hydroxyapatite: Ca10(PO4)6(OH)2), 30% organic (osteoid: type I collagen + proteoglycans + glycoproteins)
• Functions: support, protection, locomotion, calcium/phosphate homeostasis, hematopoiesis (red bone marrow)
• Highly vascular and constantly remodeling

6.2 Cells

• Seals to bone surface via integrins (sealing zone)
• Ruffled border secretes HCl (carbonic anhydrase II) → dissolves mineral
• Lysosomal enzymes (cathepsin K, MMP) degrade organic matrix
• Forms Howship's lacunae (resorption pits)

6.3 Bone Matrix

6.4 Types of Bone (Microscopic)

Woven (Immature) Bone:

• Randomly oriented collagen fibers
• Many osteocytes, irregular arrangement
• First bone formed (during development, fracture repair)
• Weaker; replaced by lamellar bone

Lamellar (Mature) Bone:

• Parallel, organized collagen lamellae
• Lamellae alternate fiber directions (like plywood) - maximizes strength
• Osteocytes in lacunae between lamellae; connected by canaliculi

6.5 Types of Bone (Macroscopic)

• Dense outer shell
• Organized into osteons (Haversian systems)
• Osteon = concentric lamellae around central Haversian canal (blood vessels + nerves)
• Volkmann's (perforating) canals - horizontal, connect Haversian canals
• Interstitial lamellae - remnants of old osteons
• Circumferential lamellae - inner and outer surfaces of bone

• Interconnecting trabeculae (bars/plates)
• Spaces filled with bone marrow
• No Haversian systems; osteocytes fed by diffusion
• Found at epiphyses of long bones, vertebral bodies, diploe of flat bones

6.6 Periosteum and Endosteum

6.7 Ossification (Bone Formation)

Intramembranous Ossification:

• Bone forms directly from mesenchyme (no cartilage model)
• Sequence: mesenchymal condensation → osteoblasts secrete osteoid → mineralization → woven bone → lamellar bone
• Forms: flat bones of skull, mandible, clavicle, part of maxilla

Endochondral Ossification:

• Bone replaces hyaline cartilage model
• Forms: long bones, short bones, vertebrae, ribs (most of skeleton)
• Sequence:
  1. Cartilage model forms
  2. Periosteal bone collar forms around diaphysis
  3. Primary ossification center appears in diaphysis - chondrocytes hypertrophy, matrix calcifies, blood vessels invade with osteoblasts
  4. Secondary ossification centers in epiphyses
  5. Epiphyseal growth plate (physis) persists until adulthood

Epiphyseal Growth Plate Zones (from epiphysis to diaphysis):

6.8 Bone Remodeling

• Continuous process throughout life
• Coupling: osteoblast activity is linked to osteoclast activity
• RANK-RANKL-OPG axis:
  • RANKL (on osteoblasts) binds RANK (on osteoclast precursors) → osteoclast activation
  • OPG (osteoprotegerin) - decoy receptor produced by osteoblasts, blocks RANKL → inhibits osteoclasts
• Parathyroid hormone (PTH): stimulates osteoclast activity (via osteoblasts → RANKL upregulation) → bone resorption, raises serum Ca2+
• Calcitonin: inhibits osteoclasts → bone deposition, lowers serum Ca2+
• Vitamin D: increases intestinal Ca2+ absorption; deficiency → rickets (children) or osteomalacia (adults)

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MCQ SECTION: 105 Questions with Answers

EPITHELIAL TISSUE MCQs (Q1-25)

• A) Avascular
• B) Cells closely packed with minimal ECM
• C) Rests on basement membrane
• D) Derived from mesoderm exclusively

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• A) Basal lamina only (secreted by epithelial cells)
• B) Reticular lamina only (secreted by fibroblasts)
• C) Basal lamina + reticular lamina
• D) Type I collagen + fibronectin only

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• A) Type I
• B) Type II
• C) Type III
• D) Type IV

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• A) Provide mechanical strength
• B) Allow intercellular communication
• C) Seal paracellular spaces and control permeability
• D) Anchor cells to the basement membrane

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• A) Connexins
• B) Desmoglein and desmocollin (cadherins)
• C) Claudins and occludins
• D) Integrins

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• A) 9+2 (9 peripheral doublets + 2 central singlets)
• B) 9+0 (9 peripheral doublets, no central pair) - primary cilia
• C) 8+1
• D) 7+2

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• A) Absent cilia
• B) Defective dynein arms of cilia
• C) Absent microvilli
• D) Defective desmosomes

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• A) Esophagus
• B) Trachea
• C) Urinary bladder and ureter
• D) Cornea

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• A) Simple columnar
• B) Simple cuboidal
• C) Simple squamous
• D) Pseudostratified columnar

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• A) Urinary bladder
• B) Trachea and bronchi
• C) Small intestine
• D) Vagina

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• A) Merocrine
• B) Apocrine
• C) Holocrine
• D) Endocrine

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• A) True motile cilia
• B) Long non-motile microvilli (actin core)
• C) Flagella
• D) Kinocilia

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• A) Claudins
• B) Cadherins
• C) Connexins
• D) Integrins

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• A) Replacement of stratified squamous epithelium by columnar epithelium
• B) Replacement of columnar/pseudostratified epithelium by stratified squamous epithelium (squamous metaplasia)
• C) Loss of tight junctions
• D) Failure of ciliary beat

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• A) Simple squamous
• B) Simple cuboidal
• C) Simple columnar
• D) Stratified cuboidal

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• A) Simple squamous
• B) Simple cuboidal
• C) Pseudostratified
• D) Stratified squamous

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• A) Gut epithelium
• B) Salivary glands, mammary glands, sweat glands
• C) Kidney tubules
• D) Trachea

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• A) Dense connective tissue
• B) Basement membrane
• C) Cartilage matrix
• D) Bone matrix

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• A) Keratinized stratified squamous
• B) Non-keratinized stratified squamous
• C) Simple columnar
• D) Pseudostratified

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• A) Cilia on surface cells
• B) Abundant microvilli
• C) Umbrella cells with fusiform vesicles and unique membrane plaques
• D) Goblet cells

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• A) Two adjacent epithelial cells
• B) Epithelial cell to basement membrane
• C) Epithelial cell to extracellular fluid
• D) Fibroblasts in dermis

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• A) Basal cells are post-mitotic
• B) Surface cells are nucleated
• C) Basal cells are mitotically active and anchor to basement membrane
• D) Found in esophagus

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• A) Holocrine
• B) Apocrine
• C) Merocrine (eccrine)
• D) Endocrine

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• A) 9+2
• B) 9+0
• C) 9+1
• D) 7+2

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• A) Unbranched
• B) Branched
• C) Absent
• D) Present only in endocrine glands

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CONNECTIVE TISSUE MCQs (Q26-50)

• A) Fibronectin
• B) Elastin
• C) Collagen
• D) Laminin

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• A) Tendons
• B) Basement membrane
• C) Liver, spleen, lymph nodes, bone marrow stroma
• D) Cartilage

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• A) H&E
• B) Masson's trichrome
• C) Silver impregnation (argyrophilic staining)
• D) Orcein stain

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• A) Histamine
• B) Heparin
• C) Tryptase
• D) Plasminogen activator

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• A) Phagocytosis
• B) Antibody production
• C) Synthesis of ECM components (collagen, elastic fibers, ground substance)
• D) Histamine release

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• A) T lymphocytes
• B) B lymphocytes
• C) Monocytes
• D) Mast cells

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• A) Type I collagen gene (COL1A1)
• B) Fibrillin-1 gene (FBN1)
• C) Elastin gene (ELN)
• D) Lysyl oxidase gene

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• A) Contains sulfate groups
• B) Is linked to a core protein
• C) Is a non-sulfated GAG not attached to core protein
• D) Is found only in bone

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• A) Type IV collagen mutation
• B) Type I collagen mutation
• C) Fibrillin mutation
• D) Elastin mutation

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• A) Neutrophils
• B) Eosinophils
• C) Fibroblasts
• D) Monocytes

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• A) Dermis
• B) Organ capsules
• C) Tendons and ligaments
• D) Under epithelia (lamina propria)

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• A) Cell adhesion and cell migration
• B) Bone mineralization
• C) Elastic recoil
• D) Muscle contraction

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• A) Hyaluronic acid
• B) Dermatan sulfate
• C) Chondroitin sulfate and keratan sulfate
• D) Heparin

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• A) Fibroblasts
• B) Mast cells
• C) Adipocytes (white fat)
• D) Plasma cells

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• A) Tendons
• B) Dermis
• C) Lamina propria of mucous membranes and subcutaneous tissue
• D) Organ capsules

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• A) Fibrillin
• B) Collagen processing (types I and V)
• C) Elastin
• D) Hyaluronic acid

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• A) They originate from lymphocytes
• B) They are resident histiocytes derived from blood monocytes
• C) They synthesize collagen
• D) They do not participate in antigen presentation

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• A) Fibroblast
• B) Reticular cell (specialized fibroblast)
• C) Macrophage
• D) Mast cell

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• A) It contains no proteins
• B) Proteins are extracted during tissue processing
• C) It is highly acidic
• D) It stains bright red

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• A) Hydroxylation of proline in collagen
• B) Cross-linking of collagen and elastin (oxidizes lysine residues)
• C) Synthesis of hyaluronic acid
• D) Mineralization of bone

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• A) Has fewer mitochondria
• B) Generates heat via uncoupling protein-1 (UCP-1/thermogenin) in mitochondria
• C) Has a single large lipid droplet
• D) Is found mainly in subcutaneous tissue of adults

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• A) Dense regular connective tissue
• B) Mucous connective tissue (embryonic)
• C) Reticular connective tissue
• D) Elastic connective tissue

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• A) Fibroblast
• B) Plasma cell
• C) Mast cell
• D) Eosinophil

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• A) Chondrocytes only
• B) Fibroblasts and smooth muscle cells
• C) Osteoblasts
• D) Mast cells

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• A) Collagen fibers
• B) Elastic fibers
• C) Proteoglycans bound to water in ground substance
• D) Reticular fibers

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SKELETAL MUSCLE MCQs (Q51-70)

• A) Myofibril
• B) Sarcomere (Z disc to Z disc)
• C) Motor unit
• D) Fascicle

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• A) I band
• B) H zone
• C) A band
• D) Z disc distance

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• A) Endomysium
• B) Perimysium
• C) Epimysium
• D) Fascia

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• A) Na+
• B) K+
• C) Ca2+
• D) Mg2+

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• A) Excess Ca2+ activates permanent contraction
• B) Lack of ATP prevents myosin detachment from actin
• C) Excessive K+ efflux
• D) Tetanus of all motor units simultaneously

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• A) High anaerobic capacity, few mitochondria
• B) High aerobic capacity, many mitochondria, fatigue resistant
• C) Large diameter, powerful contractions
• D) Found mainly in fast, explosive movements

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• A) One T-tubule + two terminal cisternae of SR
• B) Three T-tubules
• C) Two T-tubules + one terminal cisterna
• D) T-tubule + mitochondria + ribosome

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• A) Largest motor units are recruited first
• B) All motor units fire simultaneously
• C) Smallest (slowest) motor units are recruited first, followed progressively by larger ones
• D) Fast-twitch units are always recruited before slow-twitch

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• A) Anchor thin filaments at Z disc
• B) Connect myosin to Z disc; acts as molecular spring for passive elasticity
• C) Regulate Ca2+ release
• D) Form the M line exclusively

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• A) Initiates the power stroke
• B) Causes myosin head to detach from actin
• C) Triggers Ca2+ release
• D) Phosphorylates troponin

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• A) Norepinephrine
• B) GABA
• C) Acetylcholine (nicotinic receptor)
• D) Glutamate

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• A) Sarcoplasmic reticulum membrane
• B) T-tubule membrane (voltage sensor)
• C) Sarcolemma
• D) Mitochondrial inner membrane

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• A) Only myosin (thick) filaments
• B) Only actin (thin) filaments, bisected by Z disc
• C) Overlap of actin and myosin
• D) Myosin only in the H zone

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• A) Regulates length of thick filaments
• B) Connects myosin to Z disc
• C) Runs alongside thin filaments, regulates their length
• D) Forms the M-line cross-links

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• A) Endomysium
• B) Perimysium
• C) Epimysium
• D) Tendon

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• A) Voltage-gated Ca2+ channels
• B) Nicotinic acetylcholine receptors (nAChR) at NMJ
• C) Ryanodine receptors
• D) SERCA pumps

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• A) Muscle shortens, external load moves
• B) No change in muscle length; tension develops
• C) Only type I fibers are active
• D) No ATP is consumed

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• A) Anchors actin thin filaments
• B) Cross-links myosin thick filaments in the center of the H zone
• C) Contains troponin
• D) Is the site of titin attachment to thin filaments

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• A) Types of macrophages
• B) Resident stem cells under the basal lamina; responsible for muscle regeneration
• C) Found in cardiac muscle only
• D) Schwann cells

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• A) Direct Ca2+ entry from outside the cell in skeletal muscle (primary mechanism)
• B) Opening of RyR1 (ryanodine receptor) on SR via DHP receptor mechanical coupling → Ca2+ release
• C) Immediate MLCK activation
• D) Phosphorylation of myosin light chains

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SMOOTH MUSCLE MCQs (Q71-85)

• A) Contain actin and myosin
• B) Have a single, centrally placed nucleus
• C) Are striated
• D) Are multinucleated

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• A) Troponin-tropomyosin complex
• B) Ca2+-calmodulin → MLCK pathway (myosin phosphorylation)
• C) DHP receptor-RyR coupling
• D) Na+ influx

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• A) The rapid cycling of cross-bridges
• B) Ability to maintain sustained force with minimal energy expenditure (dephosphorylated myosin remains attached)
• C) Closure of K+ channels
• D) Activation of MLCP

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• A) Has faster cross-bridge cycling
• B) Requires more energy for sustained contraction
• C) Has maximum force often greater than skeletal muscle (4-6 kg/cm2 vs 3-4 kg/cm2)
• D) Has troponin as its Ca2+ sensor

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• A) Has gap junctions between all cells
• B) Each cell is independently innervated; precise control; no gap junctions
• C) Is found in the GI tract
• D) Contracts spontaneously (myogenic)

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• A) Sarcomeres
• B) T-tubules (invaginations that increase membrane surface area and regulate Ca2+ influx)
• C) Dense bodies
• D) Lysosomes

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• A) A band
• B) I band
• C) Z discs (anchor actin filaments; contain alpha-actinin)
• D) M lines

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• A) Iris dilator muscle
• B) Bladder detrusor muscle (urination)
• C) GI tract wall musculature
• D) Arteriole wall

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• A) Increases contraction
• B) Causes relaxation by dephosphorylating myosin LC, reducing cross-bridge activity
• C) Activates calmodulin
• D) Raises intracellular Ca2+

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• A) Blocking Ca2+ channels
• B) Activating guanylyl cyclase → cGMP → PKG → MLCP activation and MLCK inhibition
• C) Opening K+ channels directly
• D) Inhibiting calmodulin

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• A) GI tract
• B) Uterus
• C) Cranial blood vessels and iris
• D) Urinary bladder

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• A) 10-50 msec
• B) 100 msec
• C) 1-3 seconds
• D) 10-30 seconds

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• A) cAMP
• B) cGMP
• C) IP3 (triggers SR Ca2+ release) and DAG
• D) cAMP only

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• A) Multiunit contraction
• B) Phasic (rhythmic) peristaltic contractions driven by interstitial cells of Cajal (pacemakers)
• C) Sustained tonic contraction only
• D) Direct skeletal-muscle-type cross-bridge cycling

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• A) 10-100x greater
• B) Equal
• C) 1/10 to 1/300 as much
• D) 2x greater

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CARTILAGE MCQs (Q86-95)

• A) Hyaline cartilage
• B) Elastic cartilage
• C) Fibrocartilage
• D) Hyaline in the trachea

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• A) Hyaline cartilage
• B) Elastic cartilage
• C) Fibrocartilage (type I collagen)
• D) Dense regular connective tissue only

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• A) Fibrocartilage
• B) Elastic cartilage
• C) Hyaline cartilage (and elastic)
• D) Calcified cartilage only

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• A) Type I
• B) Type II
• C) Type III
• D) Type IV

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• A) Division of mature chondrocytes within lacunae
• B) Differentiation of perichondrial chondrogenic cells → chondroblasts → new matrix at surface
• C) Ossification of cartilage
• D) Hypertrophy of existing chondrocytes

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• A) Hyaline
• B) Fibrocartilage
• C) Elastic
• D) Calcified hyaline

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• A) Haversian canals
• B) Diffusion through the matrix from surrounding perichondrium or synovial fluid
• C) Capillaries between chondrocytes
• D) Canaliculi

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• A) Type I collagen
• B) Type II collagen in cartilage (and type IX, XI)
• C) Hyaluronic acid
• D) Elastin

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• A) Resting zone
• B) Zone of proliferation
• C) Zone of hypertrophy
• D) Zone of calcification

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• A) Rich in type I collagen; acidophilic
• B) Rich in proteoglycans; basophilic (strongly stained)
• C) Same composition as interterritorial matrix
• D) Acellular and electron-dense

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BONE MCQs (Q96-105)

• A) Type II collagen
• B) Type I collagen (~90% of organic matrix)
• C) Fibronectin
• D) Chondroitin sulfate

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• A) Mesenchymal osteoprogenitor cells
• B) Osteoblasts
• C) Fusion of monocyte/macrophage precursors (hematopoietic origin)
• D) Fibroblasts

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• A) Spongy (cancellous) bone
• B) Compact (cortical) bone
• C) Woven bone
• D) Both compact and spongy bone

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• A) Long bones (femur, tibia)
• B) Vertebrae and ribs
• C) Flat bones of the skull, mandible, and clavicle
• D) Carpal and tarsal bones

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• A) Osteoclast activity
• B) Osteoblast activity
• C) Chondrocyte apoptosis
• D) Bone resorption

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• A) Osteoporosis
• B) Rickets (impaired mineralization → wide growth plates, bowing of long bones)
• C) Scurvy
• D) Osteogenesis imperfecta

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• A) Direct stimulation of osteoclasts via PTH receptors on osteoclasts
• B) Stimulation of osteoblasts to upregulate RANKL → activate osteoclast precursors → bone resorption → raise serum Ca2+
• C) Inhibition of bone remodeling
• D) Increased osteoblast matrix production only

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• A) Adjacent Haversian canals
• B) Lacunae of osteocytes to each other and to Haversian canals (nutrient-waste exchange)
• C) Bone marrow to periosteum
• D) Volkmann's canals to surface

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• A) Failure of bone mineralization
• B) Decreased bone mass (low BMD) with normal mineralization; increased fracture risk
• C) Excess osteoclast function with abnormal bone architecture (Paget's)
• D) Congenital absence of osteoblasts

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• A) Stimulating osteoclast differentiation
• B) Acting as a decoy receptor for RANKL, blocking RANK-RANKL interaction → inhibiting osteoclastogenesis
• C) Activating RANK on osteoclasts
• D) Increasing PTH secretion

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SUMMARY TABLE: Key Staining Techniques

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SUMMARY TABLE: Tissue Origins (Embryology)

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