Cartilage Histology

Cartilage is a resilient and smooth elastic connective tissue, a rubber-like padding that covers and protects the ends of long bones at the joints, and is a structural component of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many other body components.

Histology

Junqueira’s Basic Histology Text and Atlas, 15th Ed

1. Cartilage "Mohmmadrjab" S. Seder Faculty of Medicine Histology

2. Table of contents Introduction Types of cartilages Hyaline cartilage Elastic cartilage Fibrocartilage Cartilage formation, growth, and prepair

3. Introduction Cartilage is a resilient and smooth elastic connective tissue , a rubber-like padding that covers and protects the ends of long bones at the joints, and is a structural component of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many other body components.

4. Cartilage is found in many areas of the body including: Joints between bones e.g. the elbows, knees and ankles Ends of the ribs Between the vertebrae in the spine Ears and nose Bronchial tubes or airways

5. Cartilage: Important for: Support to softer tissues Formation and growth of long bones Consists of: Extracellular matrix containing mainly, Collagen and/or elastin fibers Proteoglycans Water

6. Cartilage is characterized by: An (ECM) with high concentrations of GAGs and proteoglycans , interacting with collagen and elastic fibers . Structural features of its matrix make cartilage ideal for a variety of mechanical and protective roles within the adult skeleton and elsewhere. Cartilage is mainly (~80%) water. Cartilage is made up of specialized cells called chondrocytes.

7. Extracellular matrix components of cartilage including proteoglycan aggregates, collagen, integrins and fibronectin

8. Unlike connective tissue proper, cartilage contains only chondrocyte and no other cell types. These chondrocytes produce large amounts of extracellular matrix composed of collagen fibres, proteoglycan, and elastin fibers.

9. The cartilage cells or chondrocytes are contained in cavities in the matrix, called cartilage lacunae.

10. All types of cartilage lack vascular supplies; and chondrocytes receive nutrients by diffusion from capillaries in surrounding connective tissue.

11. Cartilage also lacks nerves.

12. The perichondrium is a sheath of dense CT that surrounds cartilage in most places (except articular cartilage of joints), forming an interface between the cartilage and the tissues supported by the cartilage. Perichondrium contains blood supply, nerves, lymphatics. Perichondrium contains collagen fibers, fibroblasts, chondroblasts.

13. Types of cartilages Variations in the composition of the matrix characterize three main types of cartilage: Hyaline cartilage Elastic cartilage Fibrocartilage

14. Dense connective tissue of perichondrium is shown here with hyaline and elastic cartilage.

15. Important features of the major cartilage types

16. Hyaline Cartilage Fibrocartilage Elastic Cartilage

17. Hyaline cartilage Hyaline (Gr. hyalos , glass) cartilage , the most common of the three types. Is homogeneous and semitransparent in the fresh state.

18. In adults hyaline cartilage is located in: Epiphyseal plate (bone growth plate) ​Articulate cartilage (cartilage of the joints) Costal cartilages (connects ribs to sternum) Respiratory Cartilages (larynx, reinforces air passageways) Nasal Cartilage (supports external structure of the nose)

19. In the embryo , hyaline cartilage forms the temporary skeleton that is gradually replaced by bone.

20. Matrix of Hyaline Cartilage The dry weight of hyaline cartilage is nearly 40% collagen embedded in a firm, hydrated gel of proteoglycans and structural glycoproteins. In routine histology preparations, the proteoglycans make the matrix generally basophilic and the thin collagen fibrils are barely discernible. Most of the collagen in hyaline cartilage is type II , although small amounts of minor collagens are also present.

21. Aggrecan is the most abundant proteoglycan of hyaline cartilage. Another important component of cartilage matrix is the structural multiadhesive glycoprotein chondronectin.

22. Chondrocytes cells in Hyaline cartilage matrix: Chondrocytes cells occupy relatively little of the hyaline cartilage mass. At the periphery of the cartilage, young chondrocytes or chondroblasts have an elliptic shape, with the long axes parallel to the surface. Deeper in the cartilage, they are round and may appear in groups of up to eight cells that originate from mitotic divisions of a single chondroblast and are called isogenous aggregates . As the chondrocytes become more active in secreting collagens and other ECM components, the aggregated cells are pushed apart and occupy separate lacunae.

23. Isogenous Group Are located in the mature cartilage zone. Contains from 4 to 8 mature chondrocytes. Result from successive mitotic division. Are surrounded by cartilage matrix.

24. Territorial matrix vs. Interterritorial matrix The territorial matrix is the tissue surrounding chondrocytes (cells which produce cartilage) in cartilage.

25. Staining variations within the matrix reflect local differences in its molecular composition. Immediately surrounding each chondrocyte, the ECM is relatively richer in GAGs than collagen, often causing these areas of territorial matrix to stain differently from the intervening areas of interterritorial matrix

26. Except in the articular cartilage of joints, all hyaline cartilage is covered by a layer of dense connective tissue, the perichondrium , which is essential for the growth and maintenance of cartilage. The outer region of the perichondrium consists largely of collagen type I fibers and fibroblasts, but an inner layer adjoining the cartilage matrix also contains mesenchymal stem cells which provide a source for new chondroblasts that divide and differentiate into chondrocytes.

27. P: Perichondrium C: Chondrocytes & Chondroblasts M: Matrix Hyaline Cartilage

28. Hyaline Cartilages

29. Elastic cartilage Is a type of cartilage that provides both strength and elasticity to certain parts of the body, such as the ears. Within the outer ear, it provides the skeletal basis of the pinna, as well as the lateral region of the external auditory meatus.

30. Elastic cartilage is essentially similar to hyaline cartilage except that it contains an abundant network of elastic fibers in addition to a meshwork of collagen type II fibrils , which give fresh elastic cartilage a yellowish color. With appropriate staining the elastic fibers usually appear as dark bundles distributed unevenly through the matrix.

31. C: Chondrocytes P: Perichondrium M: Matrix

32. Elastic Cartilage is more flexible than hyaline cartilage, elastic cartilage is found in the auricle of the ear, the walls of the external auditory canals, the auditory (Eustachian) tubes, the epiglottis, and the upper respiratory tract.

33. Elastic cartilage function is two-fold: to change cartilage shape in response to tension, compression, and bending before returning to an at-rest state, and to provide a strong but flexible structure.

34. Hyaline vs. Elastic Cartilige Elastic cartilage looks very similar to hyaline cartilage under a microscope, and special stains must be used to show the otherwise invisible elastic fibers that give this particular cartilage type its name. Like hyaline, elastic cartilage also has single or multiple chondrocytes housed within spaces called lacunae. The extracellular matrix of elastic cartilage contains higher levels of type II collagen.

35. Hyaline vs. Elastic Cartilige

36. Fibrocartilage Fibrocartilage is the tough, very strong tissue found predominantly in the intervertebral disks and at the insertions of ligaments and tendons. Fibrocartilage takes various forms in different structures but is essentially a mingling of hyaline cartilage and dense CT.

37. Fibrocartilage Hyaline cartilage

38. Chondrocytes of fibrocartilage occur singly and often in aligned isogenous aggregates, producing type II collagen and other ECM components, although the matrix around these chondrocytes is typically sparse. Areas with chondrocytes and hyaline matrix are separated by other regions with fibroblasts and dense bundles of type I collagen which confer extra tensile strength to this tissue.

39. Fibrocartilage C: Chondrocytes

40. Intervertebral discs of the spinal column are composed primarily of fibrocartilage and act as lubricated cushions and shock absorbers preventing damage to adjacent vertebrae from abrasive forces or impacts.

41. Fibrocartilages

42. Hyaline cartilage / Elastic cartilage / Fibrocartilage

43. Hyaline cartilage / Elastic cartilage / Fibrocartage Hyaline cartilage Elastic cartilage Fibrocartilage

44. Hyaline cartilage / Elastic cartilage / Fibrocartage

45. Hyaline cartilage / Elastic cartilage / Fibrocartage

46. Cartilage formation, growth, and prepair All cartilage forms from embryonic mesenchyme in the process of chondrogenesis . The first indication of cell differentiation is the rounding up of the mesenchymal cells, which retract their extensions, multiply rapidly, and become more densely packed together.

47. Chondrogenesis

48. In general the terms “chondroblasts” and “chondrocytes” respectively refer to the cartilage cells during and after the period of rapid proliferation. At both stages the cells have basophilic cytoplasm rich in RER for collagen synthesis. Chondrocytes in growing cartilage

49. Cartilaginous structures grow by mitosis of existing chondroblasts in lacunae (interstitial growth) or formation of new chondroblasts peripherally from progenitor cells in the perichondrium (appositional growth). Repair or replacement of injured cartilage is very slow and ineffective, due in part to the tissue’s avascularity and low metabolic rate.

50. Growth of epiphyseal plate

51. Epiohyseal plate (interstatial growth)

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