Unit one: tissue level of organization

1. Tissues Level of Organization
CONTD…………

2. CONNECTIVE TISSUE
 Connective tissue is one of the most abundant and widely distributed
tissues in the body. In its various forms, connective tissue has a variety of
functions.
 It binds together, supports, and strengthens other body tissues; protects and
insulates internal organs; compartmentalizes structures such as skeletal
muscles; serves as the major transport system within the body (blood, a fluid
connective tissue); is the primary location of stored energy reserves (adipose,
or fat, tissue); and is the main source of immune responses.

3. General Features of Connective Tissue
 Connective tissue consists of two basic elements:
Extracellular matrix and cells.
 extracellular matrix is the material located between its widely spaced cells.
The extracellular matrix consists of protein fibers and ground substance, the
material between the cells and the fibers.
 The extracellular matrix is usually secreted by the connective tissue cells and
determines the tissue’s qualities. For instance, in cartilage, the extracellular
matrix is firm but pliable. The extracellular matrix of bone, by contrast, is hard
and inflexible.

4. Contd…………
 In contrast to epithelia, connective tissues do not usually occur on body
surfaces. Also unlike epithelia, connective tissues usually are highly vascular;
that is, they have a rich blood supply.
 Exceptions include cartilage, which is a vascular, and tendons, with a scanty
blood supply. Except for cartilage, connective tissues, like epithelia, are
supplied with nerves.

5. Connective Tissue Cells
 Mesodermal embryonic cells called mesenchymal cells give rise to the cells of
connective tissue.
 Each major type of connective tissue contains an immature class of cells with
a name ending in -blast, which means “to bud or sprout.” These immature
cells are called fibroblasts in loose and dense connective tissue,
chondroblasts in cartilage, and osteoblasts in bone.
 Blast cells retain the capacity for cell division and secrete the extracellular
matrix that is characteristic of the tissue.

6.  In cartilage and bone, once the extracellular matrix is produced, the immature
cells differentiate into mature cells with names ending in -cyte, namely
chondrocytes and osteocytes.
 Mature cells have reduced capacities for cell division and extracellular matrix
formation and are mostly involved in maintaining the matrix.

7. Types of connective tissue
 Fibroblasts are large, flat cells with branching processes. They are present in several
connective tissues, and usually are the most numerous.
 Fibroblasts migrate through the connective tissue, secreting the fibers and certain components
of the ground substance of the extracellular matrix.
 Adipocytes, also called fat cells or adipose cells, are connective tissue cells that store
triglycerides (fats). They are found deep to the skin and around organs such as the heart and
kidneys.

8.  Mast cells are abundant alongside the blood vessels that supply connective tissue.
 They produce histamine, a chemical that dilates small blood vessels as part of the inflammatory
response, the body’s reaction to injury or infection.
 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.
 For example, neutrophils gather at sites of infection, and eosinophils migrate to sites of parasitic
invasions and allergic responses.

9. Contd…
 Macrophages develop from monocytes, a type of white blood cell.
 Macrophages 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; examples include alveolar macrophages in the lungs or splenic
macrophages in the spleen.
 Wandering macrophages have the ability to move throughout the tissue and gather at sites of
infection or inflammation to carry on phagocytosis.

10. Contd….
 Plasma cells are small cells that develop from a type of white blood cell called a B
lymphocyte. Plasma cells secrete antibodies, proteins that attack or neutralize foreign
substances in the body.
 Plasma cells are an important part of the body’s immune response. Although they are found in
many places in the body, most plasma cells reside in connective tissues, especially in the
gastrointestinal and respiratory tracts.
 They are also abundant in the salivary glands, lymph nodes, spleen, and red bone marrow.

11. Connective Tissue Extracellular Matrix
 Each type of connective tissue has unique properties, based on the specific extracellular
materials between the cells. The extracellular matrix consists of two major components: (1)
ground substance and (2) fibers.
 Ground Substance: the ground substance is the component of a connective tissue
between the cells and fibers. The ground substance may be fluid, semifluid, gelatinous, or
calcified.
 The ground substance supports cells, binds them together, stores water, and provides a
medium through which substances are exchanged between the blood and cells.
 It plays an active role in how tissues develop, migrate, proliferate, and change shape, and in
how they carry out their metabolic functions.

12.  Ground substance contains water and an assortment of large organic molecules, many of which are
complex combinations of polysaccharides and proteins. The polysaccharides include hyaluronic acid,
chondroitin sulfate, dermatan sulfate, and keratan sulfate.
 Collectively, they are referred to as Glycosaminoglycans or GAGs. One of the most important
properties of GAGs is that they trap water, making the ground substance more jellylike.
 Hyaluronic acid is a viscous, slippery substance that binds cells together, lubricates joints, and
help to maintain the shape of the eye balls.

13.  Chondroithin sulphate provides support and adhesiveness in cartilage, bone, skin, and blood vessels.
The skin, tendons, blood vessels, and heart valves contain dermatan sulfate; bone, cartilage, and the
cornea of the eye contain keratan sulfate.

14. Fibers
 Collagen fibers
 Elastic fibers
 Reticular fibers.

15. Collagen fibers
 Collagen fibers (colla glue) are very strong and resist pulling forces, but they are not stiff, which allows
tissue flexibility.
 The properties of different types of collagen fibers vary from tissue to tissue. For example, the collagen
fibers found in cartilage attract more water molecules than those in bone, which gives cartilage a more
cushioning effect.
 Collagen fibers often occur in parallel bundles. The bundle arrangement adds great strength to the tissue.
 Chemically, collagen fibers consist of the protein collagen, which is the most abundant protein in your body,
representing about 25% of the total.
 Collagen fibers are found in most types of connective tissues, especially bone, cartilage, tendons, and
ligaments.

16. Elastic fibers
 Elastic fibers, which are smaller in diameter than collagen fibers, branch and join together
to form a network within a tissue.
 An elastic fiber consists of molecules of the protein elastin surrounded by a glycoprotein
named fibrillin, which adds strength and stability. Because of their unique molecular structure,
elastic fibers are strong but can be stretched up to 150% of their relaxed length without
breaking.
 Equally important, elastic fibers have the ability to return to their original shape after being
stretched, a property called elasticity. Elastic fibers are plentiful in skin, blood vessel walls, and
lung tissue.

17. Reticular fibers
 Reticular fibers consisting of collagen arranged in fine bundles with a coating of
glycoprotein, provide support in the walls of blood vessels and form a network around the cells
in some tissues, such as areolar connective tissue, adipose tissue, and smooth muscle tissue.
 Produced by fibroblasts, reticular fibers are much thinner than collagen fibers and form
branching networks. Like collagen fibers, reticular fibers provide support and strength.
 Reticular fibers are plentiful in reticular connective tissue, which forms the stroma (bed or
covering) or supporting framework of many soft organs, such as the spleen and lymph nodes.
These fibers also help form the basement membrane.

18. Classification of Connective Tissues
Embryonic connective
tissue
Mucous connective
tissue
Mesenchyme

19. Mature connective tissue
Areolar
Adipose tissue
Reticular
Dense irregular
Dense regular
Elastic
Loose Dense
Hyaline
Fibro
Elastic
Liquid
connective
Blood
Lymph
Cartilage Bone tissue