Connective tissues are found throughout the body. They are characterized by widely spaced cells (with one exception), and a large amount of non-living, intercellular material called the matrix. The basic function of connective tissues is to connect things together. There are eleven connective tissues. Three of these: blood, compact bone, and cancellous bone are more thoroughly discussed in the chapters on blood and skeletal tissue respectively.
The other connective tissues can be determined by the answers to two questions: 1. Are the cells in lacunae? 2. What kind of fibers are in the tissue? Before you can answer the questions, you must have a thorough understanding of lacunae and fibers!
Lacunae (sing. - lacuna) are holes within the matrix of the tissue. The cells of the tissue live inside these holes like hermits in a cave.
There are three kinds of fibers found in connective tissues. These are collagenous, elastic, and reticular. Collagenous fibers (also called dense, white, and regular) are composed of the protein collagen. They are white, long, unbranched, tightly packed, and often assume a wavy appearance. Elastic fibers are composed of the protein elastin and are elastic, that is they return to their original shape when they are stretched and released. Elastic fibers are branched. Reticular (reticulum = L. net) fibers are also branched. The branching pattern of reticular fibers is such that they form a net-like arrangement.
To identify connective tissues under the microscope ask and answer two questions: 1. Are the cells in lacunae? If so, you are looking at either osseous or cartilaginous material, and 2. What kinds of fibers are present? There may be none, one, or three kinds of fibers visible.
la. Cells in lacunae.
There are two kinds of osseous tissue, compact and cancellous (spongy). The matrix of compact bone is organized into columns of concentric rings (osteons). The matrix of cancellous bone has a sponge-like appearance. Osseous tissue is easily identified if you have seen it once. These two tissues are covered in more detail in chapter seven.
Cartilaginous material can be divided into three groups. Hyaline cartilage or gristle has no visible fibers, though they are present. Elastic cartilage has many elastic fibers and fibrocartilage contains bundles of collagenous fibers. Cartilages do not contain blood vessels. The cells of cartilages are called chondrocytes (chondros = Gr. cartilage; cytos = Gr. cell).
lb. Cells not in lacunae.
Connective tissues which do not have lacunae are called "connective tissues proper". There are five types determined by the kinds of fibers which are present.
Areolar tissue has an airy, "cotton-candy" appearance. All three types of fibers, collagenous, elastic, and reticular, can be found in areolar tissue. Reticular connective tissue contains reticular fibers, elastic connective tissue has elastic fibers, while dense connective tissue has collagenous (dense) fibers. Dense connective tissue is also called collagenous. Adipose or fat tissue has no visible fibers. Adipose tissue is an exception among connective tissues in that the cells are packed together and there is no large amount of matrix.
A final, special connective tissue is vascular or blood tissue. This connective tissue is the only liquid tissue in the body. Blood will be covered in more detail in chapter twenty-six.
Write the correct name of each connective tissue into the blanks of Figure 5.2.
Figure 5.2 Connective Tissues
Adipocyte Adipose Areolar Chondrocyte Collagen (fiber) Collagenous (tissue) (dense, white) Elastic (X2) Elastic fiber Fibrocartilage Hyaline Lacuna Nucleus (of cell) Reticular Reticular fiber
Fill in the chart below with the appropriate terms. Connective Tissues
(cartilage, cells in lacunae) 1. _
(cells not in lacunae)
fibers (none visible)
(osseous; cells in lacunae, blood vessels present) 1. _
(special connective tissue) 1. _ (liquid)
Examine and sketch the following tissues as seen with a microscope: adipose, areolar; blood, cancellous bone, compact bone, dense (collagenous) connective, elastic cartilage, reticular connective, fibrocartilage, and hyaline cartilage.
As you examine the tissues, ask yourself these questions:
1. Are the cells in lacunae?
2. Which types of fibers are visible?
Be able to identify each of these tissues from a drawing, a description, and microscopically.
1. How can you tell the difference between simple and stratified epithelial tissues?
2. Why isn't pseudostratified tissue considered to be a truly stratified tissue?
3. What is the purpose of a goblet cell?
4. Which epithelial tissue lines the urinary bladder?
5. What are the three basic functions of epithelial tissues?
6. Name three anatomical characteristics of all epithelial tissues.
7. What are microvilli and where are they found?
8. Which type of epithelial cells may have cilia?
9. What is the one liquid tissue in the body?
10. Besides being connective tissues, how are adipose and hyaline cartilage alike? How are they different?
11. Which three connective tissues contain elastic fibers? How can you tell these three apart?
12. How are cartilage and bone different?
13. Give two characteristics of all connective tissues (except adipose).
14. How are cartilage and bone different from the connective tissues proper?
15. List and describe the three types of fibers found in connective tissues.
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