Musculoskeletal System Histology Flashcards
General CT Structure
Comprises a diverse group of cells within a tissue specific extracellular matrix
Consists of cells and an ECM
Different types of CT have different functions
Classified based on CT composition and organization of cellular and extracellular components and on function
Embryonic CT
Mesenchyme and mucous CT
Embryonic mesenchyme gives rise to various CT of the body
Mesoderm
Found in embryo and within umbilical cord
Wharton’s Jelly
CT Proper
Loose CT tissue
Regular/Irregular dense CT
Specialized CT
Cartilage Bone Adipose Tissue Blood hemopoietic tissue Lymphatic tissue
Mesoderm
From embryonic CT
Primitive CT able to form mesenchyme or ectomesenchyme
2 Types CT proper
Loose CT
Dense CT
Loose CT
Characterized by loosely arranged fibers and abundant cells of various tissue types
Dense CT
irregular CT characterized by abundant fibers and few cells
Dense Regular CT
ordered and densely packed arrays of fibers and cells
3 Types of CT Fibers
Collagen
Reticular
Elastic
Collagen Basic Structure
Abundant in CT fibers
68 nm banding pattern
Molecule is triple helix of 3 intertwined polypeptide chains
Collagen Triple Helix
Chains Every 3rd AA is glycine Hydroxyproline or hydroxylysine will usually proceed glycine Glycoprotein Homotrimeric Heterotrimeric
Classes of collagen
Fibrillar collagens Fibril-associated collagens with interrupted triple helixes Hexagonal network forming collagens Transmembrane collagens Multiplexins Basement membrane forming collagens
Osteogenesis Imperfecta
Type I collagen defect Repeated fractures after mild trauma Brittle bones Abnormal teeth Think skin Weak tendons Blue sclera Progressive hearing loss
Kniest dysplasia/Achondrogenesis
Type II collagen issue Short stature Restricted joint mobility Ocular changes leading to blindness Wide metaphyses Joint abnormality seen in radiographs
Multiple Epiphyseal Dysplasia
MED
Type IX collagen issue
Deformation resulting from impaired endochondral ossification and dysplasia (MED)
Premature degenerative joint disease
Schmidt Metaphysal Chondrodysplasia
Collagen type X issue
Skeletal deformations characterized by modifications of the vertebral bodies and chrondrodysplasia metaphyses of long bone
Weissenbacher-Zweymuller Syndrome
Type XI collagen issue Similar clinical features to type II collagenopatheies in addition to craniofacial and skeletal deformations Severe myopia Retinal detachment Progressive hearing loss
Reticular Fibers
Supporting framework for cellular constituents of various tissues and organs Composed of type II collagen Mesh like pattern or network Boundary of CT and epithelium sites Produce collagen of reticular fibers
Elastic Fibers
Allow tissues to respond to stretch and distension
Elastic property of elastin molecule is related to unusual polypeptide backbone and causes random coiling
Synthesized by fibroblasts and vascular smooth muscle cells
Elastin Polypeptide Backbone
Central core of elastin and a surrounding network of fibrillan microfibrils
Desmosine and Isodesmosine
Fibrillin-1-fibrillin microfibrils play major role in organizing elastin fibers
Major extracellular substance in vertebral ligaments, larynx and elastic arteries
Fibroblast
Principal cell of ct
Responsible for synthesis of collagen, elastic and reticular fibers
Complex carbs of ground substance
Myofibroblast
Elongated, spindly CT consisting of bundles of actin filaments w/associated actin motor proteins
Non-muscular myosin
Basis of mechanotransduction system generated by contraction of intracellular actin bundles transmitted to ECM
Lack basal lamina, different from smooth muscle cells and are located in loose CT
Involved in regulating the shape and emptying of the glands and wound contraction and closure
Macrophages
Phagocytic cells derived from monocytes
True histiocytes
Large golgi and RER/SER, mitochondria, secretory vesicles/lysosomes
Irregular shape, rounded nucleus
Antigen-presenting cells using MHC II molecules to present antigens for CD4 lymphocytes
Can form Langerhans cells (foreign body giant cells) by fusion
Mast Cells
Not present in CT
Surround small blood vessels in brain/SC (meninges)
Develop in bone marrow/differentiation in CT
Large rounded cell, spherical nucleus/basophil granules
Anaphylactic reactions, binds antiboides to mast cells
Release contents once bound (histamine SRS-A–>Vasodilation/edema)
Mast Cell Granule contents
Heparan sulphate
Heparin-blocks coagulation, responsible for basophilia
Histamine
Eosinophil chemotactic factor ECF and Neutrophil chemotactic factor attracts these cells
Leukotrientes, tryptase, chymase, TNF-a, IL 3, 4, 5, 6, 8, 16 and PGF2) inflammatory response
Cartilage
Form of CT composed of cells called chondrocytes and highly specialized EC matrix
Avascular tissue 95% consists of ECM
Areas of weight bearing and movement
Firm matrix, lot’s of GAGs and hyaluronic acid
3 subtypes
Hyaline Cartilage
Type II collagen fibers GAGs Proteoglycans Multi-adhesive proteins Fetal skeletal tissue, epiphyseal plates Resists compression, foundation for skeleton Perichondrium Calcification Chondroblasts and chondrocytes Limited growth and repair
Elastic Cartilage
Elastic fibers and elastic lamellae in addition to matrix material of hyaline cartilage (brown) Ex. pinna of ear Provide support Perichondrium No calcification Chondroblasts and chondrocytes present Type II collagen Interstitial and appositional growth
Fibrous Cartilage
Type I collagen/ Type II Collagen Matrix material of hyaline cartilage (pink) IV discs Resists deformation under stress No perichondrium Calcification occurs Chondrocytes and fibroblasts Interstitial and appositional growth, limited repair ability
Chondrocyte
Large rounded chondrocyte cell produce matrix
Light cytoplasm and a small nucleus
Were chondroblasts
Now completely surrounded by matrix
Chondroblasts
Chondroblasts-found in growing cartilage
Do not aggregate into clumps and secrete matrix
Secrete cartilage matrix
Turn into chondrocytes and get completely surrounded by matrix
Cartilage Growth
Arises from mesenchyme during chondrogenesis
Mesenchymal cell aggregation, induced by chondroblasts
Appositional Growth
chondroblasts formed in inner layer of perichondrium (produce type I collagen) Produce matrix (type II collagen) Turn to chondrocytes (new cartilage AT surface of existing cartilage)
Interstitial Growth
Division of chondrocytes within lacunae
Isogenous groups form new cartilage within cartilage mass
Limited Repair
Avascular tissue dependent on perichondrium
Hyaline cartilage often calcifies (replaced by bone)
Bone ECM
Hydroxyapatite crystals form mineral of bone
Collagen type I
Glycoproteins (osteocalcin, osteonectin, osteopontin)
Bone Cells
Osteocyte (in lacunae)
Osteoblasts
Osteoprogenitor cells
Osteocytes
Bone Function
Support
Protection
Storage site for Ca2+/Phosphate
Compact Bone
Shaft and spongy bone
Epiphysis forming trabeculae
Haversion Lamellae
Concentrical lamellae surround haversion canal forming cylindrical units called osteon/Habversion systems
Contains vessels and nerves-connected by Volkman’s canal
Lacunae between lamellae with osteocytes
Canaliculi penetrate lamellae with osteocytic processes
Interstitial Lamellae
Between osteon space and filled with old haversion systems
Outer circumferential Lamellae
Lining outer surface of bone under peristeum
Inner circumferential lamellae
lining under surface of bone under endosteum
Volkmann’s Channels
Provide major route of entry for vessels to pass through compact bone
Immature Bone
skeleton of fetus
Adult alveolar sockets/tendon attachments
Non-lamellar woven bone w/interlacing collagen fibers
More cell rich than mature bone
Randomly arranged cells
Matrix less mineralized and more ground substance than mature bone staining more basophilic
Osteoprogenitor Cells
Derived from mesenchymal stem cells and flattened cells
Look like fibroblasts
Resting cell can differentiate into osteoblast and secrete bone matrix
Basophilic cytoplasm
Inner layer of peristeum, endosteum, line of haversion/Volkmann’s canals
Capable to divide/differentiate osteoblasts
Appositional bone formation
Osteoblast
Secretory cells, division capable Type I collagen Ground substances Form unmineralized bone Surrounded by osteoid Basophilic cytoplasm Single cuboidal cell layer on surface of growing bone Calcification process initiators Contain alkaline phosphatase
Osteocytes
Maintains matrix Death of osteocyte forms bone resorption Elongated cells Multiple processes Inactive-few organelles Formative-RER Resorptive-lysosomes
Bone lining cells
From osteoblasts
Cover bone
Not remodeling
Communicate with gap junctions
Periosteal cells: line external bone surfaces
Endosteal cells: line internal bone surfaces
Maintenance, nutritional support of osteocytes embedded in underlying bone matrix and regulate movement of Ca2+ and phosphate into/out of bone
Osteoclast
Responsible for bone reabsorption
Large multinucleated acidophilic cells do bone resorption
From monocytes
Nuclei on side of cells
Surface contacts bone, forms membrane infoldings
Rests in resorption bay (Howship’s Lacuna)
Decalcifies underlying bone
Releases lysosomal hydrolases that digest organic components
PTH increases osteoclast activity, calcitonin decreases it
Intramembraneous Ossification
Mesenchymal cells aggregate and turn into osteoblasts
Osteoblasts secrete osteoid, mineralizes it, encloses themselves into lacuane and makes osteocytes
Ossification occurs in embryo skull bone, fractures at broken ends
Mandible formation
Appositional growth w/osteoprogenitor cells
Endochondral Ossification
Starts with hyaline cartilage model of bone
Perichondrium forms a bony collar around cartilage model (appositional growth–>periosteum)
Primary ossification center
Chondrocytes in middle of model become hypertrophic
Secrete alkaline phosphatase, surrounding matrix undergoes calcification
Calcified matrix inhibits diffusion of nutrients-death from suicidal cells
Death of chondrocytes-matrix breaks down forms cavity
Osteoblasts build up bone
2ndary ossification centers, capillary loops into epihpysis
Forms epiphyseal plate towards the opposite directions lengthening bone
Layers of Epiphyseal cartilage
- Zone of reserve cartilage
- Zone of proliferation-cartilage cells in rows
- Zone of hypertrophy
- Zone of calcified cartilage
- Zone of resorption (resorption of dead chondrocytes)
Epiphyseal Cartilage Growth
Bone increases in diameter with appositional growth (periosteum)
Osteoclasts continuously remodel the bone
Periosteum
Perichondrial cells that do not give rise to chondrocytes in midregion of cartilage in developing bone
CT tissue that is no longer functionally a perichondrium and has a new role
Contains osteogenic layer of osteoblasts
Perichondrium
Dense CT composed of cells that indistinguishable from fibroblasts
Source of new cartilage cells
Locations for bone remodeling
ECM of bone, cartilage and in dentinum, cementum and enamel of teeth
Matrices of ALL except enamel have collagen fibrils and ground substances
Matrix Vesicel Secretion
Local concentrations of Ca2+ and PO4 ions in matrix must exceed normal threshold level
Osteocalcin
ALP/Alkaline phosphatase increases local concentration of PO4 ions and is stimulated by high levels of Ca2+ which is than able to increase Ca2+ (positive feedback)
Crystallization of CaPO4
Osteoblasts release small matrix vesicles into bony matrix and contain ALP and pyrophosphotase causing cleaving of PO4 ions which then causes crystalization of CaPO4 b/c cleavage of PO4 = increase of local isoelectric point
CaPO4 Crystals
Initiate matrix mineralization by formation/deposition of hydroxyapatite crystals (Ca10(PO4)6(OH)2 into the matrix surrounding the osteoblasts
Metabolic Function of Bone
Reservoir for body Ca2+
PTH hormone
Calcitonin
PTH
Raises low blood Ca2+ levels to normal
Stimulates both osteocytes/osteoclasts to resorb bone allowing release of Ca2+ into the blood
Acts on Kidney to excrete excess phosphate and reduce excretion of calcium
Calcitonin
Secreted by PTH and lowers elevated blood Ca2+ levels to normal
Inhibits bone resorption and inhibits effects of PTH on osteoclasts
Bone Repair
- Fracture
- Neutrophils/Macrophages accumulate
- Fibroblasts/Capillary Proliferation
- Granulation tissue
- Tissue becomes denser w/cartilage
- Dense CT and cartilage grow covering bone at fx site formation
- Osteoprogenitor cells divide
- Osteoblasts that deposit new bone progresses toward fx site
- Deposit new bone in callus
- Bony callus
- Cartilage calcifies
- Endosteal proliferation/differentiation occurs in marrow cavity and medullar bone grows from both ends of fracture towards center
- Spongy bone is formed
- Compact bone
- Bony callus removed by osteoclasts and remodeling to restore original shape
6-12 week process
Skeletal Muscle
Multinucleated syncytium and each muscle cell is called a muscle fiber
Multinucleated skeletal muscle cell
Myoblasts
Individual muscle cells fuse to form muscle fiber
Sarcolemma
Plasma membrane of muscle cell
External laminda and surrounded by reticular lamina
Endomysium
Reticular fibers that immediately surround individual muscle fibers
Perimysium
Thicker CT that surrounds group of fibers
Forms a bundle or fascilcle
Epiysium
Sheath of dense CT surrounding a collection of fascicles
Type I
Slow oxidative fibers
Red with lots of mitochondria and lots of myoglobin
Resist fatigue but generate less tension
Type IIa
Fast oxidative glycolytic fibers
Intermediate fibers
MEdium size
Lots of mitochondria
High myoglobin content and lots of glycogen and can undergo anaerobic glycolysis
Fast twitch, fatigue resistant motor units seen in sprinters
Type IIb Fibers
Fast glycolytic
Large fibers are light pink and have less myoglobin and few mitochondria compared to other types
High anaerobic enzyme activity and are fast twitch
Fatigue prone fibers
High muscle tension
Rapid contraction, prescise fine movements, digits and extraocular
Short distance sprinters and weight lifters
Myofibril
Muscle fiber longitduinally arrayed structural subunits
Bundles of myofilaments
Idividual filamentous polymers composed of myosin II (thick filaments) and actin
Contractile element striated muscle
Surrounded by sER
A Band
Myosin Thick filaments
Z line
Myosin Thin filaments
Extend to A band and edge of H-zone
I-Band
Only filaments run from end of thick filament to next thick filament
Z-Disc
Anchors thin filaments of adjacent sarcomeres
Thin filaments
F-actin
Tropomyosin
Troponin
Troponin
3 globular proteins
Troponin C-Binds Ca2+
Troponin T-tropomyosin and Troponin I binds to actin inhibiting actin/myosin interactions
Titin
Forms elastic lattice that anchors thick filaments in the Z lines and prevents excessive stretching by having spring like elements
A-actinin
Short bipolar rod that bundles thin filaments into parallel arrays and anchors them to Z-line
Nebulin
Elongated
Inelastic protein attached to Z-lines
Runs parallel to thin filaments to help anchor them
Tropomodulin
Small acting binding protein attached to free portion of thin filament
Maintains/regulates length of sarcomere actin filament
Desmin
Intermediate filament that forms a lattice surrounds sarcomere at Z-lines attaching them to one another and to plasma membrane
Myomesin
Myosin-binding protein that holds thick filaments in register @M-line
C Protein
Myosin-binding protein that does same thing as myomesin
Dystrophin
Large protein thought to link laminin which resides in external lamina of muscle cell to actin filaments (anchors muscle fiber)
Sarcomere Contraction
Sarcomere becomes shorter but thicker
Myofilaments remain same length
NMJ
Motor end plate and NT at presynaptic terminal is ACh
Release ACh into synaptic cleft initiates depolarization of PM
Folds and cholinergic receptors only in plasma membrane bordering the cleft @ the top of folds
Bind nicotinic receptors (ligand-gated Na+ channel) on sarcolemma
Motor Unit
Neuron along with specific muscle fibers that it innervates and can innervate several to hundred muscle fibers
What happens when Nerve Supply is Disrupted?
Tissue can atrophy so nerve supply is important to normal muscle shape/strength
Skeletal Muscle Innervation
Encapsulated sensory receptors in muscles/tendons
Proprioreceptors provide info about degree of stretching/tension in muscle
Muscle Spindle
Stretch receptor found in skeletal muscle
Spindle cells/neuron terminals surrounded by internal capsule
Muscle spindle transmits info about degree of stretching in a muscle fiber/length
Sensory 1A
Carry info from muscle spindle to CNS
Gamma Motor Efferent
From brain/SC
Innervates spindle cells and regulates sensitivity of stretch receptor by keeping intrafusal fibers taught in muscle spindle so it can sense stretch
Golgi tendon organs
Tendons of muscle and responds to increased stretch
Sensory afferent Ib nerve fibers
monitors muscle tension/force of contraction w/in optimal range
