Specialised CT.pdf

Specialised Connective Tissue: Cartilage and Bone, Histology ANAT2241: Histology JOYCE EL-HADDAD [email protected] @orientatewithjoyce Lecture Outline • Overview of connective tissue classification • Cartilage histology • Bone histology Learning Outcomes: LO1. To recognise the histologica...

Specialised Connective Tissue: Cartilage and Bone, Histology ANAT2241: Histology JOYCE EL-HADDAD [email protected] @orientatewithjoyce Lecture Outline • Overview of connective tissue classification • Cartilage histology • Bone histology Learning Outcomes: LO1. To recognise the histological appearance of the different types of cartilage: hyaline, elastic and fibrocartilage LO2. To understand the role of the perichondrium in the formation of cartilage and the mechanisms of appositional and interstitial growth. LO3. To know the architecture of compact and spongy (cancellous) bone, the structure of osteons (Haversian systems), the importance and position of Haversian and Volkmann’s canals LO4. To differentiate between osteoblasts, osteocytes and osteoclasts and understand their roles in bone formation. LO5. To identify and describe the processes of intramembranous and endochondral bone formation. Cartilage o Plays a critical role in providing structural support for soft tissues and a sliding area for joints o Avascular o Firm consistency (plastic-like) o Allows for the bone to grow in length o Highly hydrated (70-75%) water, collagen (15-20%) and proteoglycans (210%) – hence glossy appearance o Cells: Chondroblasts > Chondrocytes (in matrix cavities – lacunae; synthesise and secrete e. m.) and an extensive extracellular matrix. o Types (matrix composition): – Hyaline, – Fibrocartilage, – Elastic. LO1. To recognise the histological appearance of the different types of cartilage: hyaline, elastic and fibrocartilage Junqueira LC & Carneiro J, 2003, Basic Histology, 10th ed. Chondrocytes 1 µm EM of a chondrocyte in hyaline cartilage of the trachea. The eccentrically placed nucleus (Nu) has euchromatin and patches of heterochromatin and is surrounded by a well-defined nuclear envelope. The cytoplasm is replete with organelles involved in synthesis and secretion. RER and a well-developed Golgi complex (GC) are prominent. The RER consists of parallel arrays of narrow cisternae studded with ribosomes. Mitochondria (Mi) lie scattered among elements of the RER. The surrounding matrix contains a meshwork of type II collagen fibrils. 35,000×. (Courtesy of Dr. B. J. Crawford) Matrix Nu RER Mi GC 1µm LO1. To recognise the histological appearance of the different types of cartilage: hyaline, elastic and fibrocartilage 6.7 ULTRASTRUCTURE OF CHONDROCYTES somes and well-developed rough endoplasmic reticulum (RER) Ultrastructural features of chondrocytes reflect function: synthesis with dilated cisternae. The prominent juxtanuclear Golgi complex Hyaline cartilage LO1. To recognise the histological appearance of the different types of cartilage: hyaline, elastic and fibrocartilage Hyaline cartilage • Bluish white, glossy. • Location: at ends of long bones, anterior ends of ribs, nose, parts of larynx, trachea and bronchi and fetal skeleton. • Function: cushioning, smooth low friction surface for joints, flexibility and support in respiratory system, frame for ossification (epiphyseal plate). • Growth and repair very limited in adults. LO1. To recognise the histological appearance of the different types of cartilage: hyaline, elastic and fibrocartilage Osteoarthritis LO1. To recognise the histological appearance of the different types of cartilage: hyaline, elastic and fibrocartilage consisting of collagen and hydrated PGs and an outer annulus fibrosis of fibrocartilage composed of concentric lamellae of collagen fibers. Fibrocartilage • LM of fibrocartilage of the annulus fibrosis of an intervertebral disc. Between the chondrocytes (C) in the matrix (M) are coarse bundles of dense, intensely eosinophilic collagen fibers (arrows), which are all oriented in the same direction. The elongated chondrocytes, found in short rows, are surrounded by a narrow zone of basophilic ground substance. Fibrocartilage lacks a perichondrium. Part of the nucleus pulposus (NP), seen in the upper right, has an amorphous appearance. 380×. H&E. Combination of dense regular connective tissue and cartilage • Chondrocytes and fibroblasts embedded in bundles of collagen fibers and proteoglycans. • Collagen fibres lie parallel to lines of stress Location: pubic symphysis, intervertebral discs, menisci of knee. • C • Function: support and fusion, resists deformation under stress. • Limited ability to repair6.5in HISTOLOGY OF FIBROCARTILAGE Fibrocartilage is found in the symphysis pubis, the annulus fibroadults. sis of intervertebral discs, and at points of attachment of tendons LO1. To recognise the fibrocartilage NP M to bone. It is a mixture between dense regular connective tissue (similar in many respects to tendon or ligament) and hyaline cartilage. It combines the tensile strength, firmness, and durability of tendon with resistance to compression of cartilage. In contrast to other types of cartilage, fibrocartilage lacks a distinct perichondrium, which blends imperceptibly with surrounding connective tissue or hyaline cartilage. Its matrix is intensely eosinophilic because numerous collagen fibers are present. Arranged in parallel bundles, often in line with the direction of pull or stress applied, histological ofappearance the different types of they give aappearance characteristic fibrous to the matrix, which is readily seen in routine histologic preparations. The matrix contains a minimal amount of amorphous ground substance, which is usually seen at boundaries of lacunae, where it is slightly basophilic or stains positively for periodic acid-Schiff (PAS). Chondrocytes are thinly dispersed in the matrix and are arranged in short, parallel rows between collagen fiber bundles. In contrast to hyaline cartilage, with type II collagen in its matrix, fibrocartilage is composed of type I collagen. Fibrocartilage initially forms from dense connective tissue that is rich in fibroblasts, some of which differentiate into chondrocytes. Thus, a mixture of chondrocytes and fibroblasts is characteristic of mature fibrocartilage. At any location, damaged hyaline or elastic cartilage is repaired via forcartilage: hyaline, elastic and mation of fibrocartilage. Elastic cartilage • • • Normal components of hyaline cartilage with addition of an abundant network of elastic fibres Support with flexibility. Location; external ear, external auditory canal, epiglottis. C Pe M Netter’s Histology, 3rd edition LO1. To recognise the histological appearance of the different types of cartilage: hyaline, elastic and fibrocartilage L child carti sma arran shrin chon cons beca Resor The mad stain matr whic CARTILAGE GROWTH Cartilage growth occurs in two ways: 1) appositional (width): chondroblast cells secrete matrix against the external face of existing cartilage 2) interstitial (length): chondrocytes divide and secrete new matrix expanding cartilage from within LO2. To understand the role of the perichondrium in the formation of cartilage and the mechanisms of appositional and interstitial growth BONE Function of Bone 1. 2. 3. 4. 5. 6. Mechanical Support Protection Movement Storage (fatty acid reserve and minerals) Acid Base Balance Blood Formation (hemopoiesis) What is bone tissue composed of? Cells: • Osteogenic • Osteoblasts • Osteocytes • Osteoclasts Extracellular Matrix (mineralised): • Major organic component: 90% collagen fibers; type I; other organic components - type V collagen, proteoglycans and glycoproteins • Difference to other connective tissue: mineral deposition in matrix leading to calcification (hydroxyapatite Ca10 (PO4)6(OH)2) Cells Function Osteogenic - Unspecialised stem cell developed from mesenchyme (undergo cell division); prominent role in growth and remodelling. - Give rise to osteoblasts - Located in the inner portion of the periosteum, endosteum and in the canals that contain blood vessels. Osteoblast - Responsible for synthesis of the organic component of matrix and influence deposition of inorganic components. - Present only on the surface: cells cuboidal/columnar or flat. - When completely surrounded by matrix osteoblasts become osteocytes. Osteocyte - Osteocytes maintain bone matrix. - Can respond to mechanical forces and lay down new matrix or remove matrix. - Located within lacunae - Communicate with neighbouring osteocytes via canaliculi Osteoclast - Arise by the fusion of monocytes or macrophages. - Multinucleated, branched, motile, phagocytic; bone resorption. - Use lysosomes to break down the matrix - resorption. Osteoclasts are hormonally influenced. Bone formation Formed by either intramembranous or endochondral ossification Intramembranous: occurs in areas of ordinary mesenchyme where osteoblasts/bone forming cells differentiate directly within richly vascularized mesenchymal tissue (flat bones of skull, mandible, and clavicles) Endochondral ossification: occurs in preexisting hyaline cartilage models. Here mesenchymal cells differentiate into osteoblasts and the fetal skeleton acts like a cartilage template is modified to facilitate mineralization, vascular invasion and replacement by bone Intramembranous Ossification • Occurs in areas of ordinary mesenchyme where osteoblasts/bone forming cells differentiate directly within richly vascularized mesenchymal tissue • Location: flat bones of skull, mandible, and clavicles. • Intramembranous bone formation begins during gestation when mesenchymal cells aggregate at sites of richly vascularized connective tissue and differentiate into osteoblasts. • The osteoblasts secrete osteoid, which is an organic matrix of proteoglycans and type I collagen fibres. • Osteoblasts also secrete alkaline phosphatase, which induces mineralization of osteoid via precipitation of inorganic calcium phosphate salts. LO5. To identify and describe the processes of intramembranous and endochondral bone formation. Intramembranous Ossification LO5. To identify and describe the processes of intramembranous and endochondral bone formation. Endochondral Ossification • Bone forming from cartilage of the fetal skeleton. This is the hyaline cartilage model • The perichondrium already surrounding the hyaline cartilage, has mesenchymal cells in it. • The mesenchymal cells within the perichondrium differentiate into osteoblasts. • This forms a bony collar – i.e. it ‘chokes’ the hyaline cartilage. • Because the hyaline cartilage is receiving no blood supply at this point, the cells swell up, secrete calcified cartilage and die • Blood vessels make their way to the new formed bone, and come in to the dying zone the osteoblasts and osteoclasts. • Start to build bone all bone except the epiphyseal plate LO5. To identify and describe the processes of intramembranous and endochondral bone formation. Growth and ossification of long bones (humerus, midfrontal section). Endochondral Ossification At 8 weeks At 10 weeks Hyaline cartilage Perichondrium Periosteal bud containing capillaries, mesenchymal cells and osteoprogenitor cells passes through bony collar to invade diaphysis Hypertrophic calcifying cartilage in primary ossification center Periosteum Thin bony collar Secondary ossification centers for head and greater tubercle Bone of proximal epiphysis Calcifying cartilage Articular cartilage Secondary ossification center in epiphysis Proximal epiphyseal growth plate Outer part of periosteal bone beginning to transform into compact bone Epiphyseal growth plates Proximal metaphysis Diaphysis growth in width occurs by periosteal bone formation Sites of growth of long bone Medullary (marrow) cavity Distal epiphyseal growth plate Epiphyseal capillary Distal metaphysis At birth At 5 years Articular cartilage LO5. To identify and describe the processes of intramembranous and endochondral bone formation. At 10 years Growth Plate Zones Structural and functional changes in chondrocytes C Reserve zone Matrix production Proliferative zone Matrix production and mitosis Zone of maturation and hypertrophy Accumulation of lipid, glycogen, alkaline phosphatase; matrix calcification Zone of provisional calcification Cell death hysis Zone of ossification - Primary From spongiosa Saladin (2007) LO5.. Bone growth in length • • • • The growth plate is the cartilaginous portion of long bones where the longitudinal growth of the bone takes place. Its structure comprises chondrocytes suspended in a collagen matrix that go through several stages of maturation until they finally die, and are replaced by osteoblasts, osteoclasts, and lamellar bone. Chondrocytes progress from a resting state to enter the phases of proliferation and hypertrophy. Under the influence of oestrogen, the proliferation of chondrocytes decreases as the resting chondrocytes are consumed During the terminal phase of differentiation, cartilage is replaced by blood vessels and organized bone tissue, and once chondrocytes have died, the longitudinal growth of the bone ceases and the growth plate closes LO5.. Bone Tissue Classification • Primary (immature, woven): temporary, with few exceptions replaced by mature in adults; irregular array of collagen fibres, low mineral content, high proportion of osteocytes. • Secondary (mature, lamellar): collagen fibres arranged in lamellae. Two subtypes: compact and spongy. LO5.. https://www.researchgate.net/publication/224929158_Bone_Structure_Development_and_Bone_Biology_Bone_Pathology/figures?lo=1 Bone structure (compact) Haversian system = osteon, a cylindrical unit with concentric lamellae of bone matrix surrounding a central canal. Long axis of osteon usually parallel to long axis of bone. Haversian canals contain 1 or 2 capillaries, lymph vessels and nerves. Areas between haversian systems called interstitial lamellae; outer- circumferential lamellae. Cementing substance surrounds haversian system (mineralised matrix, few collagen fibres) LO3. To know the architecture of compact and spongy (cancellous) bone, the structure of osteons (Haversian systems), the importance and position of Haversian and Volkmann’s canals Junqueira LC & Carneiro J, 2003, Basic Histology, 10th ed. Bone structure LO3. To know the architecture of compact and spongy (cancellous) bone, the structure of osteons (Haversian systems), the importance and position of Haversian and Volkmann’s canals Junqueira LC & Carneiro J, 2003, Basic Histology, 10th ed. Bone structure Perforating (Volkmann’s) canals run perpendicular to haversian canals; run transversely across bone from periosteum to endosteum, also connecting osteons. LO3 •http://www.lab.anhb.uwa.edu.au/mb140/ Junqueira LC & Carneiro J, 2003, Basic Histology, 10th ed. Bone structure (spongy) No osteons; lamellae arranged in an irregular lattice of thin columns called trabeculae; spaces in btw contain red or yellow bone marrow (numerous blood vessels) Within each trabecula – osteocytes (within lacunae) connected with canaliculi. Blood supply directly from the surrounding blood vessels. LO3 Bone remodelling Stress to periosteum of bony prominences→ osteoblasts activation. Absence of stress loss of bone tissue. Wolff’s law: bone in a healthy person or animal will adapt to the loads it is placed under. http://www.wheelessonline.com/image7/troch1.jpg Thank you!