Connective Tissue

1. Connective Tissue Tissue Lecture 3

2. Connective Tissue • One of the most abundant and distributed tissues of the body. • In its various forms it functions for • strengthening other body tissues, • protects and insulates internal organs, compartmentalizes structures such as skeletal muscle, • serves as the major transport system within the body, • is the primary location of stored energy reserves, and • is the main source of immune responses.

3. General Features • Consists of two basic elements: cells and extracellular matrix. • Extracellular matrix is the material located between the widely spaced cells. • It consists of protein fibers and ground substance, the material between the cells and fibers. • It is secreted by connective tissue cells and determines the tissue qualities: soft and flexible (cartilage) versus hard and inflexible (bone).

4. Do not usually occur on body surfaces. • Most have a blood supply (is vascular), except for cartilage and tendons (very little blood). • Except for cartilage, connective tissues are supplied with nerves.

5. Connective Tissue Cells • Fibroblasts: large, flat cells with branching processes. • They are present in most connective tissues and are the most numerous. • They migrate through the connective tissue secreting the fibers and ground substance of the extracellular matrix.

6. Macrophages: develop from monocytes, a type of white blood cell. • They have an irregular shape with short branching projections and are capable of engulfing bacteria and cellular debris by phagocytosis. • Fixed macrophages reside in a particular tissue: lungs or spleen. • Wandering macrophages have the ability to move throughout the tissue and gather at the sites of infection or inflammation to carry out phagocytosis.

7. Plasma cells: small cells that develop from the B lymphocytes (white blood cells). • Secrete antibodies that attach or neutralize foreign substances in the body. • Most plasma cells are found in the gastrointestinal and respiratory tracts and are also abundant in the salivary glands, lymph nodes, spleen, and red bone marrow. • Mast cells: abundant alongside the blood vessels that supply connective tissue. • They produce histamine that dilate blood vessels in response to bodily injury or infection. • They can also bind to, ingest, and kill bacteria.

8. Adipocytes: are fat cells or adipose cells. • They store triglycerides and are found deep to the skin and around organs such as the heart and kidneys. • White blood cells: are not found in significant numbers in normal connective tissue. • However, in response to certain conditions, they migrate from blood into connective tissues where different white blood cells have different functions.

9. Extracellular Matrix • The extracellular matrix consists of two major components: ground substance and fibers. • Ground substance: the component of a connective tissue between the cells and fibers. • It may be fluid, semifluid, gelatinous, or calcified. • It supports cells, binds them together, stores water, and provides a medium through which substances are exchanged between the blood and the cells. • It plays an active role in how tissues develop, migrate, reproduce, and change shape, and how they carry out their metabolic functions.

10. Ground Substance Molecules • Ground substance contains water and a complex assortment of proteins and polysaccharides. • Hyaluronic acid: a polysaccharide that is viscous, slippery substance that acts to bind cells together, lubricate joints, and helps to maintain the shape of the eyeballs. • Chondroitin sulfate: a polysaccharide that provides support and adhesiveness in cartilage, bone, skin, and blood vessels.

11. Dermatan sulfate: a polysaccharide found in skin, tendons, blood vessels, and heart valves. • Keratan sulfate: a polysaccharide found in bone, cartilage, and the cornea of the eye. • Fibronectin: the main adhesion protein that binds to both collage fibers and ground substance, linking them together. It also attaches cells to the ground substance

12. Fibers • Three types of fibers are embedded in the extracellular matrix between the cells – • Collagen fibers: very strong and resistant to pulling forces. • They are not stiff, which allows tissue flexibility. • They often occur in parallel bundles adding strength to the tissue. • They are found in most types of connective tissue, especially bone, cartilage, tendons, and ligaments.

13. Elastic fibers: smaller than collagen fibers, they branch and join together to form a network within a tissue. • They are strong but can stretch up to 150% of their relaxed length without breaking and can then return to their relaxed state. • Elastic fibers are plentiful in skin, blood vessel walls, and lung tissue.

14. Reticular fibers: consist of collagen arranged in fine bundles with a coating of glycoprotein. • They are much thinner than collagen fibers and form branching networks. • They provide support in the walls of blood vessels and form a network around the cells of areolar connective tissue, adipose tissue, and smooth muscle tissue. • They are plentiful in reticular connective tissue, which forms the stoma or supporting framework of many soft organs, such as the spleen and lymph nodes. • These fibers also help form the basement membrane.

15. Classification • Embryonic connective tissue • Present primarily in the embryo or fetus • Is derived from mesenchyme along with all other connective tissues • Mucous connective tissue (Wharton’s jelly) is found in the umbilical cord

16. Mature connective tissue types • Loose connective tissue • Consists of all three fiber types, several cell types, and semifluid ground substance • Areolar connective tissue: subcutaneous • Adipose tissue: adipocytes • Found with areolar connective tissue • Reticular connective tissue: reticular fibers and cells • Helps bind smooth muscle cells together

17. Dense connective tissue • Contains more numerous, thicker, and dense fibers, but considerably fewer cells than loose connective tissue • Regular connective tissue • Consists of bundles of collagen fibers in a regular, orderly, and parallel arrangement that confers great strength

18. Irregular connective tissue • Contains collagen fibers that are irregularly arranged • Found in the skin, heart valves, perichondrium, periosteum, and tissue surrounding cartilage • Elastic connective tissue • Consists of elastic fibers and fibroblasts • Found in lung tissue and elastic cartilage

19. Cartilage • Dense network of collagen fibers and elastic fibers embedded in chondroitin sulfate • Strength is due to collagen fibers • Resilience is due to chondroitin sulfate • Chondrocytes occur within spaces called lacunae in the matrix • Cartilage is surrounded by a dense irregular connective tissue membrane called the perichondrium • Cartilage has no blood vessels or nerves (except in the perichondrium)

20. Cartilage growth is accomplished by interstitial growth (expansion from within) and appositional growth (from without)

21. Types of cartilage • Hyaline cartilage • Most abundant • Weakest • Fine collagen fibers embedded in a gel-type matrix • Affords flexibility and support • Reduces friction and absorbs shock at the joints

22. Fibrocartilage • Contains bundles of collagen fibers in its matrix • No perichondrium • Strongest type • Combines strength and rigidity • Elastic cartilage • Contains threadlike network of elastic fibers in its matrix • Provides strength and elasticity • Maintains the shape of certain organs

23. Bone • Consists of a matrix containing mineral salts and collagenous fibers and cells called osteocytes • Classified as either compact or spongy, depending on how the matrix and cells are organized • Compact bone is comprised of the osteon or Haversian system • Lamella are concentric rings of matrix that consist of mineral salts that give bone its hardness and collagen fibers that give bone its strength

24. Lacunae are small spaces between lamellae that contain osteocytes • Canaliculiare minute canals containing processes of osteocytes that provide routes for nutrient and waste transport • Central haversian canal contains blood vessels and nerves • Spongy bone has trabeculaeinstead of osteons • Bone supports, protects, helps provide movement, stores minerals, and houses blood-forming tissue

25. Blood • Consists of plasma (liquid matrix) and formed elements (cells) • Erythrocytes function in transporting respiratory gasses • Leukocytes are involved in phagocytosis, immunity, and allergic reactions • Thrombocytes function in blood clotting • Lymph is interstitial fluid flowing in lymph vessels