6. SPECIALISED CONNECTIVE TISSUE.pptx

Tissues

1. SPECIALISED CONNECTIVE TISSUE H. MWALE

2. OBJECTIVES At the end of lecture ,the student should be able to describe: The General properties of specialised connective tissue (adipose, cartilage and bone) Function and location of the different SCTs Different types of connective tissues Applied anatomy associated with connective tissue

3. ADIPOSE TISSUE Adipose tissue is a specialised Loose connective tissue populated mainly by lipid accumulating adipocytes There are two types of adipose tissue; White Adipose Tissue Brown Adipose Tissue

4. Functions are to; Contribute to thermal insulation – Important for temperature regulation Fill spaces between structures/protects – Between organs – Aids fit of valves in heart – Pads of fat protect heels, palms Acts as the largest repository of energy in the body in the form of Triglycerides

5. White adipose White (20--‐25% of total body weight) Superficial depot (subcutaneous) Visceral fat depots ( peri --‐renal, mesenteric) Bone marrow Breast tissue

6. White adipose tissue is hormone responsive to Insulin Glucocorticoids Growth Hormone Noradrenaline

7. White adipocytes are unilocular cells – they have a large lipid droplet surrounded by thin cytoplasm – Flattened, eccentric nuclei. – Fat stored within the cell as triglycerides and cholesterol ester. – Secrete hormones or adipocytokines e.g leptin

8. BROWN ADIPOSE TISSUE These are multilocular cells Have a Polyglonal shape Contain Considerable cytoplasm Scattered lipid droplets within the cytoplasm Round centrally located nucleus Brown colour from presence of mitochondria Used for heat generation

9. Brown adipose can dissipate energy as heat Constitutes about 25% of birth weight in neonates In adults, brown adipose tissue is lost except in a few areas of the body ie . suprarenal

10. CARTILAGE Connective tissue specialised for support Is predominantly composed of a matrix consisting of ground substance and fibres. In general, the functions of cartilage include: Providing support with both elasticity and firmness. Forming the earliest skeleton in the foetus. Permits the elongation of long bones.

11. General Properties All the three types of cartilage are avascular and get their nutrition by means of diffusion from surrounding connective tissue capillaries or by means of synovial fluid from joint cavities. Cartilage have no lymphatic vessels or nerves. All types of cartilages except articular and fibro cartilage, are covered by a sheath of dense connective tissue the perichondrium .

12. Components of Cartilage Has three components: 1.Cartilage Cell Chondrocyte. b) Chondroblast . 2. Fibers a) Collagen type I and II. b) Elastic (depending upon the type of cartilage). 3. Ground Substance a) Hyaluronic acid. b) Proteoglycan. c) Glycoprotein.

13. Types of Cartilage Variation in the composition of matrix components produce three types of cartilages adapted to local biochemical needs. Hyaline cartilage Elastic cartilage Fibro cartilage

14. Hyaline cartilage Most abundant of the three types of cartilage Has perichondrium - a fibrous strip bordering the cartilage, composed mostly of collagenous fibres. Tends to be more cellular next to the cartilage. The chondroblasts arise from this layer.

15. In young cartilage, the chondrocytes occur singly. They are large, spherical cells. In older tissue, the chondrocytes are clustered in groups of 2, 4 or 8 and appear compressed. The matrix is a product of the chondroblasts , as well as the fibroblasts of the perichondrium.

16. Occurrence  Ventral ends of ribs and the articular ends of long bones. Found in the nose, larynx, trachea and bronchi. Surrounding the opening of the external auditory meatus. Makes up the foetal skeleton

17. Chondrocytes in hyaline They appear in a group of up to eight cells, called isogenous group , originating from mitotic division of single Chondrocyte. The chondrocytes are located in cavities within the matrix called lacunae. The peripheral zone around the groups is called territorial matrix.

18. Matrix Consists of Fiber + ground substance It has primarily type II collagen which is in the form of fibrins. The ground substance contain chondroitin 4 and 6 sulfate , and keratin sulfate in the proteoglycans. The hyaluronic acid binds to these proteoglycan and is responsible for high content of solvation water. Chondronectin is the glycoprotein which adheres chondrocytes to matrix collagen

19. ELASTIC CARTILAGE Fresh elastic cartilage has yellowish color because of the presence of elastin. It is identical to hyaline cartilage but in addition to collagen type II it contains an abundant network of fine elastic fibers making it more flexible. It also posses perichondrium.

20. Occurrence  Found in the external ear (auricle) and in the auditory tube. Epiglottis In the larynx forming the corniculate, cuneiform and arytenoid cartilages.

21. FIBROCARTILAGE It has characteristics intermediate between those of dense connective tissue and hyaline cartilage. Always associated with dense connective tissue and the border area between the two tissues is not clear cut. Chondrocytes appears singly or in isogenous groups arranged in rows. Matrix is acidophilic because it contains large amount of collagen type I. No identifiable perichondrium.

22. Occurrence It occurs where a tough support or great tensile strength is required. Intervertebral discs (annulus fibrosus ). Pubic symphysis Insertions of some tendons and ligaments. It never occurs alone but merges with neighbouring hyaline cartilage or fibrous tissue.

23. BONE Main constituent of the adult skeleton Supports fleshy structures, protects vital organs and harbours the bone marrow. Bone tissue is highly vascularized and metabolically very active. It serves as a reservoir of calcium, phosphate, and other ions that can be released or stored in a controlled fashion to maintain constant concentrations of these important ions in body fluids

24. Bone is a specialized connective tissue composed of intercellular calcified material, the bone matrix, and three cell types: Osteocytes which are found in cavities ( lacunae ) within the matrix Osteoblasts which synthesize the organic components of the matrix Osteoclasts which are multinucleated giant cells involved in the resorption and remodelling of bone tissue.

25. Osteoblasts Osteoblasts are responsible for the synthesis of the organic components of bone matrix (type I collagen, proteoglycans, and glycoproteins). Osteoblasts are exclusively located at the surfaces of bone tissue, side by side, in a way that resembles simple epithelium. When they are actively engaged in matrix synthesis, osteoblasts have a cuboidal to columnar shape and basophilic cytoplasm. Some osteoblasts are gradually surrounded by newly formed matrix and become osteocytes in a space called a lacuna .

26. Osteocytes Mature bone cells that sit in lacunae Oval shaped cell with condensed nuclear chromatin Gap junctions between osteocytes provide nutrition (15 cells in a row) Maintain bony matrix; death causes resorption of matrix

27. Osteoclasts Derived from monocytes; engulf bony material (phagocytic) Large, multinucleated and branched found in Howship’s lacunae Surface foldings forming ruffled border increasing the active resorptive area. Secrete enzymes ( colleganase etc ) that digest matrix Inhibited by calcitonin; stimulated by PTH

28. Periosteum Consists of outer layer of collagen fibers and fibroblast. The fibers penetrate the bone matrix by Sharpey’s fiber Contain an inner layer of reserve cells which can differentiate into osteoblast cells

29. Endosteum Consists of connective tissue Lines medullary and marrow cavities of bone

30. Types of Bone Microscopically • Primary ( woven) • Secondary (Lamellar) Macroscopically • Compact • Cancellous (Both have lamellar arrangement)

31. Woven Bone Primary bone tissue is usually temporary and is replaced in adults by secondary bone tissue, except in a very few places in the body ( eg , near the sutures of the flat bones of the skull, in tooth sockets, and during bone healing) Characterized by random deposition of fine collagen and increased cellularity. Relatively radiolucent (low mineral contents).

32. Lamellar (Secondary) Bone Characterized by Arrangement of collagen fibers in lamellae organized concentrically around a vascular canal containing blood vessels and nerves. The lamellae and the vascular canal constitute the Haversian system or osteon . Lacunae containing osteocytes are present between the lamellae. Mineralized matrix with few fibers present around each osteon, called the cementing substance .

33. Compact Bone 4 Types of lamellae seen: Haversian system (osteon) Outer circumferential Inner circumferential Interstitial • Volkman’s canal communicate the osteons and, periosteal and endosteal surfaces.

34. Spongy Bone Bony tissue is in the form of trabeculae having lamellar arrangement. Vascular canals are absent as the vessels in marrow cavities provide nutrition by means of diffusion

35. BONE FORMATION Bone can be formed in two ways: by direct mineralization of matrix secreted by osteoblasts ( intramembranous ossification ) or by deposition of bone matrix on a pre-existing cartilage matrix ( endochondral ossification ). In both processes, the bone tissue that appears first is primary or woven.

36. Endochondral Bone Formation Within the model of hyaline cartilage. Appearance of bone collar by intramembranous ossification Degeneration, hypertrophy and calcification of central cartilage Inversion by blood vessels bringing osteoprogenitor cells Osteoblasts cover the bone Primary then secondary ossification centers appear

37. Intramembranous Bone Formation Connective tissue develops embryonically and gives rise to bone. Cells in connective tissue (mesenchyme) differentiate into osteoblasts. Osteoblasts lay down collagen eventually starts to calcify and become osteocytes. Cancellous bone eventually becomes compact bone.

38. Applied Anatomy Fractures – Open and – Closed Healing of these takes place in three stages; - repair by granulation tissue - union by callus - consolidation by mature bone

39. Osteonecrosis/Ischemic bone necrosis is cellular death of bone components due to interruption of the blood supply Osteophytes , commonly referred to as bone spurs are bony projections that form along joint margins Osteoarthritis or osteoarthrosis , is a join disease that results from breakdown of joint cartilage and underlying bone

40. Osteomalacia is the softening of the bones caused by defective bone mineralization secondary to inadequate levels of available phosphate and calcium or because of overactive resorption of calcium from the bone which can be caused by hyperparathyroidism (which causes hypercalcemia) Osteomyelitis is infection and inflammation of bone or bone marrow. Osteogenesis imperfecta also known as brittle bone disease is a congenital bone disorder characterized by brittle bones that are prone to fracture. People with OI are born with defective CT, or without the ability to make it, usually because of a deficiency of type I collagen

41. Osteopetrosis , literally "stone bone" is an extremely rare inherited disorder whereby the bones harden, becoming denser. Osteoporosis is a disease where there is decreased bone density/ strength thereby increasing the risk of a bone fracture. It is the most common reason for a broken bone among old people.

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