Connective tissue Flashcards
Functions of connective tissue
Mechanical support Metabolic Transport Storage Defense and protection
Classification of connective tissue
Connective tissue proper: loose, dense (regular, irregular)
Specialized: Adipose, elastic, reticular
Skeletal CT: cartilage, bone
Blood
General composition of connective tissue
Cells: fibroblasts, chondroblasts, osteoblasts…
ECM:
- fibers
- Ground substance (GAG, PG, GP)
Cells of connective tissue proper
Fixed cell Population: fibroblasts, reticular cells, adipocytes, pericytes, macrophages
Wandering cell Population: White blood cells, Plasma cells
Fibroblasts
- Fusiform (spindelförmig)
- Many cytoplasmic processes when activated
- Large ovoid nucleus
- Basophilic cytoplasm with rER, Golgi apparatus, mitochondira
synthesize and secrete ECM and growth factors - Major role in active growth and wound healing
Mature fibroblasts
= fibrocytes smallerheterochromatic nuclei Acidophiic cytoplasm do not divide not active
Myofibroblasts
growth factor –> fibroblasts turn into myofibroblasts
properties of both fibroblasts and myoblasts
actin Filaments transverses cytoplasm
–> wound closure after injury and then apoptosis
–> synthesize ECM
Reticular cells
Star shaped with Long cytoplasmic processes
synthesize type III Collagen
Found in stroma of hemopoietic and immune organs
Adipocytes
throughout loose CT
Pericytes
also called: adventitial cells or perivascular cells
Around capillaries and postcapilarry venules
Have characterisitcs of smooth muscles cells
Are a type of mesenchymal stem cells
contract
Undifferentiated mesenchymal (stem) cells
adult stem cells reside in niches
niches are found in bone marrow and loose CT
Macrophages
- derived from monocytes
- irregularly shaped with kidney shaped nucleus
- when activated: pseudopodia
- have ingested material in their cytoplasm (lysosomes, vesicles, Golgi apparatus, rER)
- belong to the Mononulcuear Phagocyte System
Function: Phagocytosis as defense or clean up Antigen presentation (Antigen presenting cells APC)
Dendritic cells
- Antigen presenting cells
- Long, branched cytoplasmic processes
- In tissues in contact with external Environment –> Spleen and lymph nodes
- Dendritic cells of Skin and oral mucosa: langerhans
Mast cells
- develop in bone marrow
- differentiate in CT
- large ovoid cell
- spherical nucleus
- cytoplasm with basophilic granules
- granules contain histamine, Heparin
- for Inflammation and hypersensitivity –> increasing the permeability of blood vessels and increasing of mucous production; smooth muscle contraction in bronchial tree
Leukocytes in CT
Neutrophils, eosinophils, basophils, monocytes and lymphocytes are wandering cells in CT
Plasma cells
- large
- from B lymphocytes
- large, eccentric nucleus
- Basophilic cytoplasm because rER and Golgi
–> synthesize and secrete antibodies
CT fibers
- Collagen fibers
- Reticular fibers
- Elastic fibers
Fibroblasts can synthesize all fibers, but not all fibers are synthesized by fibroblasts:
- Cartilage: Chrondroblasts –> Collagen and elastic fib.
- Aorta: smooth muscle cells –> elastic fibers
- Lymph nodes: reticular cells –> reticular fibers
- BM: epithelial cells –> Collagen fibers
Collagen fibers
- composed of Collagen protein
- felxible, unbranched, high tensile strength
- bones, cartilage, tendons, ligaments, Skin, Cornea…
Structure: either in different directtions or highly organized
–> each bundle appears as a bundle of fine subunits: COLLAGEN FIBRILS
Collagen fibrils
made of Collagen molecules
Collagen (tropocollagen)
three Alpha polypeptide chains –> triple Helix (Collagen fibril)
Many Collagen fibrils –> Collagen bundle (Collagen Fiber)
Collagen types (Fibril forming)
I –> Skin, tendons, ligaments
II –> cartilage, vitreous of eye
III –> Skin, muscle, blood vessels, immune organs
Collagen types (Basement membrane forming)
IV; VI; VII –> link epithelial tissue to b.m. and ECM
Collagen synthesis
- transcription of Collagen genes
- 3 Alpha chains into triple Helix in rER
- Through Golgi apparatus –> Oligosaccharides are added
- secretory vesicles
- procollagen/triple helix is secreted from cell
Foramtion Collagen fibrils
- PROCOLLAGEN PEPTIDASE: cleaves uncoiled Ends of procollagen
- Collagen molecules into Collagen fibrils
- Collagen fibrils into Collagen fibers
Reticular fibers
- composed of type III Collagen –> reticulin
- DO NOT FORM BUNDLES
- form supporting Framework of hemopoietic and immune Organs (here they are secreted by reticular cells)
- fibroblasts also make reticular fibers –> support epithelia, blood vessels, nerves, muscles
Elastic fibers
- can occur either in loose branching Networks, in bundles, or as fenestrated Sheets
- synthesized by fibroblasts and smooth muscle cells
- two structural components: central core of leastin and surrounding microfibrils
Structure of elastic fibers
CENTRAL CORE
- synthesized and secreted by fibroblasts as TROPOELASTIN
- in ECM: Elastin
SURROUNDING NETWORK OF MICROFIBRILS
- made of fibrillin
Components of Ground substance
- Glycosaminoglycans (GAG)
- Proteoglycans (PG)
- Glycoproteins (GP)
GAG
- Long, unbranched Polysaccharide
- very hydrophilic
- are usually Bound to protein core as part of prpteoglycan
PG
- protein core to which GAGs are covalently bonded
- for binding cells, fibers….
Hyaluronan
Long, rigid GAG
- Major component of ECM of umbilical cord, Skin, articular cartilage, synovial fluid
GP
- small multiadhesive proteins
- numerous binding sites to cells, signaling molecules, …
- imortant in stabilizing the ECM and linking it to cell surfaces
Functions of Ground substance
1- Resistance to compressive Forces
2- Diffusion of gases, nutrients
3- Stabilizing the ECM
Two subtypes of embryonic CT
Mucous Connective tissue
Mesenchyme
Mesenchyme
- from Mesoderm
- in head Region: also derived from neural crest cells
- fills spaces between prgan primordia and differentiate
Composition:
- Mesenchymal cells: undifferentiated, star shaped, contact by processes
- ECM with Ground substance and loose Aggregate of Collagen fibrils
Mucous CT
in Umbilical cord
Cells: fibroblasts
ECM: Ground substance (wharton’s jelly) with hyaluronic Acid and Collagen fibers
–> protection of umbilical vessels
Loose connective tissue
- cells of various types and ECM with loosely arranged fibers
- flexible, not very resistant to stress
- site of inflammatory reactions
- beneath Epithelium, supporting stroma of inner Organs, space between Organs, surrounds blood vessels
–> Diffusion of Oxygen and nutrients, Diffusion on CO2 and metabolic wastes
Dense irregular CT
- fibers are densely packed and oriented in various directions
- Little Ground substance
- resists in Tension –> mechanical support
- dermin, fasciae, organ capsules
Dense regular CT
- parallel packed Arrays of fibers and few cells
- Little Ground substance
- resists in Tension in linear direction
- tendons, ligaments, aponeuroses
Tendon
- between parallel Collagen fibesr are mature fibroblasts
- tendon is subdivided into bundles by loose CT
bundles of tendons
Collagen Fiber = Primary bundle
Secondary bundle surrounded by ENDOTENDINEUM
tertiary bundle surrounded by PERITENDIDNEUM
Tendon surrounded by capusle –> EPITENDIDUEM
LOOK AT DRAWING IN NOTES
Myotendineus junction
- muscle fibers split in their Ends
- Collagen fibers penetrate muscle to form interdigitations
- endtendideum connects with endomysium, perten…..usw
Osteotendineus junction
- Collagen fibers form the tendon intermix with the Collagen fibers of periosteum
- some fibers penetrate into the bone: Sharpey’s fibers
Elastic (yellow) ligaments
White ligaments (join bone to bone)
- thick elastic fibers arranged in parallel
- each elastic Fiber surrounded by Collagen fibers (loose CT)
- less regularly arranged than tendons because elastic fibers branch
Aponeuroses
- fibers are arranged in multiple layers
- dense and regular Collagen fibers in one layer tend to be arranged at a 90° angle to those in the neighboring layers
- Fibroblasts arranged in parallel between fibers and Little Ground substance
Adipose tissue types
White: mature, in adults, predominant type –> especially in hypodermis
Brown: during fetal life, diminishes during first decade
White adipocyte (unilocular)
- Lipid droplet surrounded by thin layer of cytoplasm and flattened nucleus
- are surrounded by blood vessels and reticular fibers
Functions of White adipose tissue
- Energy homeostasis
- Body shape
- insulation
- cushion
- secreting endocrine substances (Hormones, grwoth factors, …)
Brown adipose tissue
- in newborns: in back, neck, Thorax, abdominal Region
- disappears from most sites except from around kidneys, adrenal Glands, Aorta and mediastinum
Brown adipocyte (multilocular)
- smaller than White
- many Lipid droplets!
- nucleus is round, eccentric Position
- cytoplasm contains mitochondria
- rich supply of capillaries
Function of BAT
Thermoregulation: generates hear
Elastic tissue
- consists mainly of elastic fibers
- in walls of arteries, yellow ligaments
Reticular tissue
- composed of: reticular cells and reticular fibers
- in supporting stroma of hemopoietic and immune Organs, endocrine Glands, liver
Characteristics of cartilage
- Avascular
- Aneural
- Receives nutrive substnace by Diffusion brom blood vessel in Perichondrium and CT
- growths by Interstitial and appositional growth
- support, flexibility and resilience
found in: respiratory tract, outer ear, articular surfaces, fetal Skeleton, growing bones
cartilage cells
Chondrogenic cells
Chondroblasts
Chondrocytes
look at drawing in notes!!!!
Embryonic development of cartilage
Mesenchyme –> chrondrogenic –> Chondroblast (produce ECM) –> chonrdocytes (surrounded by ECM)
Chondroblasts
- elliptical cells
- rER, large Golgi
- produce ECM with Collagen or elastic fibers
- occuply spaces called LACUNAE
- can divide
- Group of daughter cells –> isogenous group
Chondrocytes
- do not divide
- smaller Golgi
- Lipid droplets
- less active: synthesize and replace Matrix
Cartilage fibers
- Type II Collagen (in all types of cartilage)
+Elastic fibers (in elastic cartilage)
+ Type I Collagen fibers (in fibrocartilage)
Perichondrium
- surrounds only hylaine cartilage and elastic cartilage
- Two layers
1. Outer fibrous layer (dense irregular CT with vessels)
2. inner cellular layer (flat chondrogenic cells for appositional grwoth) –> only in Young cartilage!
is not found in articulat surfaces!!!!
Appositional growth
- Formation of new cartilage at the Surface of an existing cartilage
- Chondrogenic cells in Perichondrium differentiate into chondroblasts that produce ECM
Interstitial growth
- Chondroblasts within cartilaginous mass undergo mitosis in lacunae
- each daughter within growing isogenous Group prosuces ECM -> cartilage expands
Hyaline cartilage
- type II Collagen and big amount of Ground substance
- most common
- on articular surfaces, nose and respiratory tract, ribs, fetal Skeleton
- precursos of bones that develop by endochondral ossification
- surrounded by Perichondrium except epiphyseal plate and articular cartilage
- undergoes calcification with age!!!
Ground substance of hyaline cartilage
- most important PG is AGGRECAN
- each hyaluran molecule is bounded with large number of aggrecan molecules –> form large PG Aggregates
- Aggrecan molecules have large negative charge ith Affinity for water
- -> hyline cartilage provides resilience and Diffusion of small metabolites
Regions in isogenous Groups in cartilage
- Capsular Matrix : immediately surrounding the lacunam basophilic staining
- Territorial Matrix: surrounding isogenous Group, contains Network of type II collagen
- Interterritorial Matrix: outside territoral Matrix, occupies space between Groups of chondrocytes
Articular cartilage
= hyaline cartilage without Perichondrium
FOUR ZONES
1. Superficial (tangential) Zone: pressure resistant, flattened chondrocytes, type II Collagen
2, Middle (transitional) Zone: contains round chondrocytes randomly distributed
3. Deep (radial) Zone: round chondrocytes, arragned in columns, Collagen fibers between the columns
4. Calcified Zone: contacts the bone, calcified matriy and small chondrocytes
Elastic cartilage
- External ear, Eustachian tube, Epiglottis
- has Perichondrium
- DOES NOT CALCIFY
- structure is similar to hyaline cartilage
- elastic fibers in addiction to Collagen fibers
- more flexibility than hyline cartilage
Fibrocartilage
- in intervertebral Disc, articular Disc, meniscs, pubic Symphysis, insertions of tendons and ligaments
- resistance to both compression and shearing Forces
- NO PERICHONDRIUM
- grows by Interstitial growth only
- few or no isogenous Groups
- fibroblasts
- fibers are arranged in bundles and made both of Collagen type I and II
Repair of cartilage
- Cartilage has limited ability to repair due to avascularity, immobility of chondrocytes and limited ability of chondrocytes to proliferate
- repair can only happen when defect involves Perichondrium
- In adults: new blood vessels develop at site of healing that stimulates calcification and grwoth of bone rather than actual cartilage repair
bones
- support and protection
- attachment for muscles
- Calcium and Phosphate Reservoir
mineralized ECM!!
35% organic substances
65% inorganic substances
ECM in bones is called…
osteoid
Cells of bone tissue
Osteogenic/ osteoprogenitor
Osteoblasts
Osteocytes
osteoclasts
Osteoprogenitor cells
- from embryonic mesenchymal cells or mesenchymal stem cells
- flat, small amount of rER, poorly developed Golgi
- periosteum, endosteum, Haversian and Volksmann’s canals
Osteoblasts
- Spindle shaped
- cytoplasm is basophilic due to well developed golgi, rER and mitochondria
- on Surface of forming bone
- produce bone Matrix
- mediate the calcification of the osteoid
Bone Matrix
- Collagen fibers (type I)
- Ca Carbonate, Ca Fluoride, Citrate, Mg, Na
Caclification process
- Osteoblasts secrete vesicles
- Vesicles are rich in alkaline phosphatase
- Increases concentration of Ions and iniates the Formation of Crystals
- Crystals are embedded within Collagen fibers and in Ground substance
Osteocytes
= Osteoblast surrounded by ECM
- not active
- narrow spindle shaped, branched, decrease in number of organelles
- processes into canaliculi where they form gap junctions
- Canaliculi link the lacunae
- synthesize Little amount of new Matrix
- synthesize Enzymes –> osteocytic osetolysis is regulated to maintain Calcium homeostasis
Osteoclasts
- multinucleated!
- Acidophilic cytoplasm
- at sites where bone is being removed
- rest directly on bone tissue –> in Hawship’s lacuna
- many lysosomes, vesicles, well developed Golgi
- secrete acids, collagenase, and other Enzymes
- derived from MPS
three regions of osteoclasts
- Ruffled border: direct contact with bone, Deep microvilli for exocytosis of Enzymes and endocytosis of Degradation products
- Clear Zone: ring- like, cytoplase, abundant actin Filaments, lacks other organelles!
- Basolateral Zone: exocytosis of digested material, contains rER, golgi, lysosomes
Osteoclastic osteolysis
- Degradation of bone by osetocalsts
- bone remodeling
- Ca homeostasis
Woven (immature) bone tissue
- produced rapidly
- mechanically weak, because:
1- more Ground substance
2- irregular organization of Collagen
3- not heavily mineralized
in: all fetal bones, after fractures, in pathologies
Lamellar (mature) bone
- slow production
- mechanichally strong
- Collagen fibers are regularly arranged and form lamellae
Gross structure of mature bone (7)
- Compact bone (outside of the bone)
- Spongy bone: interior of the bone
- Marrow or medullary cavity: cavity with Yellow marrow in diaphysis
- Red bone marrow: in spaces in spongy bone of epiphyses
- Endosteum: lines inner space of bone
- Periosteum: covers bone
- Hyaline cartilage: covers articular surfaces
Lamellar compact bone
- in outer layers of bone
- in structural-functional Units called OSTEONS or HAVERSIAN SYSTEM
- osteons: columns alinged in the same direction along lines of stress
osteon
- 5-15 concentric lamellae surrounding a central canal –> Haversian canal
- canal contains: blood vessels, nerves, loose CT containing osteoprogenitor cells
- Perforating /Volkmann’s canals: channels that connect osteonal canals to each other
Other lamellae of compact bone
- Interstitial lamellae: between osteons
- outer circumferential lamellae: lie next and parallel to periosteum
- inner circumferential lamellae: lie nect and parallel to endosteum
Lamellar spongy bone
- in Ends of Long bone and inside flat bones
- arranged in trabeculae or spicules
- Trabeculae are composed of parallel lamellae and osetocytes along with them
- have no true osteons
- covered with thin endosteum
- spaces in between filld with red bone marrow!
Perisoteum
two layers
- Outer fibrous layer of dense irregular CT
- Inner cellular layer with osteoprogenitor cells
Endosteum
- lines trabeculae of spongy bone and compact bone Surface facing the marrow cavity
- fine loose CT with osetoprogenitor cells
- covers central canals
Shapey’s fibers
Collagen fibers of the fibrous layer of periosteum that extend into the bone
- -> helps anchor the periosteum to the bone
- -> also used to attach tendons and ligaments to the bone
Endochondral ossification - steps
- cartilage model: Mesenchyme - chondroprogenitor - Chondroblast –> hyaline cartilage covered by Perichondrium
- Formation of bone collar (periosteum): Perichondrium - periosteum around diaphysis
- Primary Center of ossification:
Center of cartilage –> chondrocytes degenerate –> large cavity –> mesenchymal –>osetoprogenitor –> Osteoblast –> woven bone composed of mixed spicules - Secondary Center of ossification
Osteoprogenitors into epiphysis
Mixed spicules
Intramembranous ossification
- Center of ossification:
Mesenchyme - osteoprogentitor - Osteoblast - Deposition of osteoid and ist mineralization
Osetoblasts - osteocytes
Primary bone spicules - Woven spongy bone
Appositional growth of Primary bone spicules - Lamellar bone
Osteoclastic Resorption and osteoblastic Deposition
Mesenchyme - bone marrow
Primary bone spicule
composed of woven bone tissue
osteocytes: inside spicule
Osteoblasts: Surface of spicule
Osteoclasts: Surface of spicule
Sutures and fontanelles
- at birth: bones of skull are separated by sutures and fontanelles with osteoprogenitor cells- for repid streching of Cranium in fetal life and childhood
- new bone tissue forms in sutures and old bone tissue remodels
Mixed spicule
- composed of calcified cartilage with woven bone on Surface of cartilage
- osteocytes in the spicule
- Osteoblasts and osteoclasts on Surface
- persist for short time before cartilage is replaced by bone
- bone component grows by appositional growth
Epiphyseal growth plate
transverse plate oh hyaline cartilage in the metaphysis at each end of a grwoing Long bone
function: growth in length
Zones of epiphyseal plate
von außen nach innen
- Zone of reserve cartilage: no cellular roliferation or matric production
- Zone of Proliferation: cells are larger, active and produce Matrix, division and organization into columns
- Zone of Hypertrophic cartilate: enlarged cells, metabolically active and in columns
- Zone of Caclification: cartilage becomes calcified, as a scaffold for new bone, hypertrophied cells degenerate, blood vessels invade the Region
amount of cartilage produced = amount resorbed
Bone remodeling
during growth
during aging
bones respond to changes in weight, posture, mechanical stress or changes in their internal Architecture
bones must be resorbed and reformed
Internal remodeling of bone
New osteons are formed during the aging
osteoclasts bore a tunnel through compact bone
new blood vessels and CT with osteoblasts
Factors that affect bone growth and remodeling
- nutritional factors
2. Endocrine factors
Endocrine effects on bone
Parathyroid Hormone: stimulates osteocytic osteolysis –> induces osteocalst activity and increases CA Levels
Calcitonin: stimulates Calcium salt deposit in bone, inhibits bone Resorption and lowers CA levels
Nutrinional effects on bone
Vitamin D: needed so that Calcium and phosphorus can be absorbed in intestines
Vitamin C: needed for Collagen and bone Matrix production
Vitamin A: maintains the rate of grwoth ob bone
