Connective Tissue Flashcards
Connective tissue origin, function and main components
Embryonic mesenchyme, a tissue developing mainly form mesoderm
Support, binds tissues together, and protects tissues and organs of the body
Cells
Protein fibers
An amorphous ground substance (proteoglycans, glycosaminoglycans (GAGs), glycoproteins).
Together the fibers and ground substance make up the extracellular matrix. Water within the ground substance allows the exchange of nutrients and metabolic wastes between cells and the blood.
Classification types of connective tissue
Circled is connective tissue proper
Connective tissue proper
LOOSE (Areolar) CONNECTIVE TISSUE-
- forms a layer beneath the epithelial lining of many organs and fills the spaces between fibers of muscle and nerve to provide support
- highly cellular with a random arrangement of collagen fibers (and some elastic & reticular fibers)
- the most numerous cells are fibroblasts
- highly vascularised.
DENSE CONNECTIVE TISSUE -
- more collagen fibers with little ground substance and fewer cells (mostly fibroblasts)
- greater resistance to stretching
- poorly vascularised.
- 1. Dense regular connective tissue- Mainly type 1 collagen fibers oriented in the parallel direction. Found in tendons and ligaments.
- 2. Dense irregular connective tissue- Collagen fibers woven in multiple directions (not organized) and resist tensile forces from many directions. Found in dermis of skin.
Collagen fibres
- Most are type I collagen.
- Provide tensile strength - resistance to stretching.
- Thickest
Elastic fibres
- Contain elastin and fibrillin.
- Provide elasticity - can be stretched and return to its original length.
- Found in ear, alveoli and arteries.
- Thin.
- Don’t take up h and e stain, black
Reticular fibres
- Contain type III collagen.
- Provides Support - network of thin fibers.
- Found in lymphoid organs.
- Reticular fibres cannot be seen in H&E sections but can be stained by silver impregnation methods (argyrophilic).
Fixed vs transient cells
- Fixed (resident) cells remain mostly stationary within the connective tissue; they perform their functions wherever they are formed. Example, fibroblasts, adipose cells.
- Transient cells (free, migratory or wandering cells) originate mainly in the bone marrow and circulate in the bloodstream, which they leave to enter the connective tissue spaces to perform their specific functions. Example, leukocytes (white blood cells) which include neutrophils, eosinophils, basophils, lymphocytes, and monocytes.
Active and inactive fibroblasts
Most abundant cell type in the CT that secretes ECM comp., such as collagen/ elastin.
Active fibroblasts often reside in close association with type I collagen bundles, lying parallel to the long axis of the fibers. They are elongated, fusiform cells possessing pale-staining cytoplasm, difficult to distinguish from collagen when stained with H&E. The most obvious portion of the cell is the darker-stained, large, granular, ovoid nucleus with a well-defined nucleolus.
Inactive fibroblasts (AKA fibrocytes) are smaller and more ovoid. Their nuclei are smaller, elongated, and more deeply stained. These do not manufacture ECM.
Loose connective tissue
Dense regular connective tissue
Regular vs irregular connective tissue
White adipose tissue
Brown adipose tissue
Connective tissue membranes
Cartilage
- Avascular (nutrition by diffusion), no nerve supply, no lymphatic drainage.
- Surrounded by perichondrium except articular cartilage and fibrocartilage.
- Consists of cells and extracellular matrix (fibers + ground substance).
- The cells of cartilage are chondrogenic cells, chondroblasts and chondrocytes.
- Cartilage exhibits tensile strength, provides firm structural support for soft tissues, allows flexibility without distortion, and is resilient to compression.
- Functions as a shock absorber, its smooth surface permits friction-free movement of the joints.
- Cartilage grows by appositional and interstitial growth.
Hyaline cartilage
- Perichondrium: Provides protection, nutrition and repair. Not present on articulatory surfaces
- Most abundant and contains Type II collagen fibers.
- Hyaline cartilage degenerates when the chondrocytes hypertrophy and die and the matrix begins to calcify. This process is a normal and integral part of endochondral bone formation. However, it is also a natural process of aging, often resulting in less mobility and pain in the joints.
- Present at trachea, tip of nose and between 2 bones
Elastic cartilage
- Elastic cartilage has a matrix containing elastin and collagen and is able to recoil after being deformed.
- The outer fibrous layer of the perichondrium is rich in elastic fibers.
- The matrix of elastic cartilage possesses abundant fine-to-coarse branching elastic fibers interspersed with type II collagen fiber bundles, giving it much more flexibility.
- found at ear and epiglottis
Fibrocartilage
- Chondrocytes arranged in parallel rows.
- No perichondrium.
- Provides resistance to mechanical forces.
- Fibrocartilage possesses dense, coarse type I collagen fibers in its matrix, which aids it in withstanding tensile forces.
- Found at intervertebral disc and pubic symphysis
Types of cartilage summary
Histology image hyaline cartilage
Histology image elastic cartilage
Histology image hyaline and fibrocartilage
Types of cartilage table
Interstitial cartilage growth
Interstitial growth produces longer bones as the cartilage lengthens and is replaced by bone tissue
- Individual mesenchymal cells retract their processes and congregate in cell clusters to form chondrification centers.
- Due to kartogenin, cells in the chondrification centers differentiate into chondroblasts and secrete cartilage matrix, entrapping themselves within small individual compartments called lacunae. Once surrounded by this matrix, these cells are known as chondrocyte.
- As the cells of an isogenous group manufacture matrix, they are pushed away from each other, forming separate lacunae and, thus, enlarging the cartilage from within.
Appositional cartilage growth
appositional growth occurs when new bone tissue is deposited on the surface of the bone, resulting in bone thickening.
Bone
- Highly vascular, consists of cells, fibres , and extracellular material with mineral deposits.
- Important for haemopoiesis and acts as reservoir for calcium and minerals.
- Covered by periosteum except at articular surfaces.
- Bone protects many organs and provides firm attachments for muscles.
- Microscopically categorized into primary (woven) and secondary (lamellar/mature).
- Primary bone has abundant osteocytes and irregular bundles of collagen, which are later replaced and organized as secondary bone.
- Secondary is further categorized into Compact (cortical) and Spongy (cancellous/trabecular).
Eat- epiphysis
My- metaphysis
Dust- diaphysis
Bone diagram
Osteon
Volkmanns canal
Bone histology
Intramembranous ossification
Osteoblast is directly coming from mesenchymal stem cell. First osteoblasts create ECM which is osteoid (unmineralized portion). Osteoblasts incorporate into osteoid to become osteocytes.
Endochondral ossification
(a) Chondroblasts develop in primitive mesenchyme and form an early perichondrium and cartilage model.
(b) The developing cartilage model assumes the shape of the bone to be formed, and a surrounding perichondrium becomes identifiable.
(c) At the midshaft of the diaphysis, the perichondrium becomes a periosteum through the development of osteoprogenitor cells and osteoblasts, the osteoblasts producing a collar of bone by intramembranous ossification. Calcium salts are deposited in the enlarging cartilage model.
(d) Blood vessels grow through the periosteum and bone collar, carrying osteoprogenitor cells within them. These establish a primary (or diaphyseal) ossification centre in the centre of the diaphysis.
(e) Bony trabeculae spread out from the primary ossification centre to occupy the entire diaphysis, linking up with the previously formed bone collar, which now forms the cortical bone of the diaphysis.
(f) At about term, secondary or epiphyseal ossification centres are established in the centre of each epiphysis by the ingrowth, along with blood vessels of mesenchymal cells which become osteoprogenitor cells and osteoblasts.
Postnatal development of bone
(a)The initial enlargement of the secondary (epiphyseal) ossification centre within the epiphyseal cartilage, leaving an epiphyseal plate of cartilage and a surround of cartilage which will ultimately become the articular cartilage.
(b) The fine detail of the epiphyseal plate between the secondary epiphyseal ossification centre on one side and the developing diaphyseal trabecular bone on the other. Chondrocytes in the epiphyseal plate proliferate in columns towards the diaphysis, becoming hypertrophied as they deposit cartilage matrix. The matrix becomes progressively mineralized before osteoblasts deposit osteoid on the calcified matrix model.
(c) Epiphyseal plate cartilage (E), the proliferative zone (PZ), the hypertrophic zone (HZ), the calcified cartilage zone (CCZ) and the beginning of the ossification zone (OZ) can be seen. At this stage, there is haemopoietic marrow in the spaces between the ossifying plates of cartilage (OC). Secondary ossification centres develop in the epiphyseal cartilage at a later stage of development. The two ossification centers do not merge until the epiphyseal plate disappears.
Primary and secondary centre of ossification
Secondary center of ossification occurs in each epiphysis; ossification follows a similar pattern as that at the primary center except:
1. No periosteal band is formed.
2. Ossification occurs in a radial manner from the original center of the secondary center of ossification.
3. Bone resorption does not occur; thus, spongy bone permanently fills the epiphyses.
4. Ossification does not replace articular cartilage.
Special connective tissue summary
