1. Tissues Dr. Bruce Forciea

2. Welcome to the fascinating world of tissues. The body is packed with different kinds of tissues. Some are highly organized and some are not. When studying tissues it helps to think about the relationship between the structure of a tissue and its function.

3. First of all, the study of tissues is known as Histology. People who study histology spend a lot of time looking in microscopes at the various body tissues.

4. Let’s look at how tissues are categorized. There are 4 main categories of tissues in the human body: Epithelium Connective Muscle Nervous

5. Epithelium is a tissue that covers other structures. Therefore one side is always exposed to the outside (which could still be inside the body). You will see epithelial tissue covering the inside of body cavities and organs. The outer or superficial portion of your skin is an epithelial tissue.

6. Epithelial tissue does not have a blood supply. Therefore nutrients must enter the tissue by diffusion. Remember diffusion?

7. Epithelial tissue is also anchored to other structures via a basement membrane.

8. Here is an example of an epithelial tissue. Note that one side of the tissue is exposed to the outside and the tissue is connected by a basement membrane. Epithelial tissue Basement membrane

9. Epithelial tissue is categorized according to the shape of the cells and number of layers. With just a couple of exceptions…

10. Epithelial cells come in 3 basic shapes: Squamous Cuboidal Columnar

11. Squamous cells are flat. From the side they look something like a fried egg.

12. Cuboidal epithelium cells are shaped like their name implies. Like little cubes. Cuboidal epithelium

13. Columnar epithelium cells are rectangular in shape. Columnar epithelium

14. Remember, epithelium is also categorized according to number of layers. A single layer of epithelium is called “simple.” If there is more than one layer it is called “stratified.”

15. Here is an example of simple squamous epithelium. Look for a thin layer of flat (squamous) cells. Simple squamous epithelium is a common site for filtration. It is commonly found in the lungs, walls of capillaries and inside of blood and lymphatic vessels.

16. This is stratified squamous epithelium. One characteristic is as the cells reach the surface they flatten out. This is a slide of the most superficial layer of the skin known as the epidermis. Here we see the cells becoming so flattened that they eventually come off. Stratified squamous is also found in the oral cavity, anal canal and vagina.

17. Here’s our picture of cuboidal epithelium. Since there is only one layer, we can call this “simple cuboidal epithelium.” Simple cuboidal epithelium is commonly found in ovaries, kidney tubules, ducts.

18. Stratified cuboidal epithelium also lines ducts. It can be found in the ducts of mammary glands, sweat glands, salivary glands, pancreas

19. Here is a nice single layer of columnar cells. We can call this “simple columnar epithelium.” Simple columnar epithelium can be ciliated or non-ciliated. Ciliated is found in the female reproductive tract. Non-ciliated is found in the uterus and digestive tract.

20. Columnar epithelium can also be stratified. This tissue is found in the vas deferens and pharynx. It provides a thicker lining for some tubular structures in the body.

21. A special type of cell known as a goblet cell is usually associated with columnar epithelium. The goblet cell secretes mucous.

22. Cilia are also seen on columnar cells. The cilia and goblet cells work together to move substances along the cells. An example of this is in the respiratory system. Cilia

23. There are some special cases of epithelium. We’ll take a look at these now.

24. The first special case is called pseudostratified columnar epithelium. It is called pseudostratified because it looks like it’s stratified (more than one layer) but it’s not. It looks stratified because the nuclei of the cells are at various levels. But in reality there is only one layer.

25. This is an example of pseudostratified columnar epithelium. Note that the nuclei are at different levels.

26. Here is pseudostratified next to simple columnar epithelium. Nuclei don’t line up— pseudostratified. Nuclei all line up nicely in one row— simple.

27. The other special case of epithelium is called transitional. Transitional epithelium looks somewhat like stratified squamous, but there is a difference.

28. In transitional epithelium the cells are rounded both at the base of the tissue and the section exposed to the outside.

29. Transitional epithelium is found in the urinary bladder. The multiple layers allow for the bladder to distend and contract. The epithelium also forms a barrier to help protect the bladder from infection.

30. To finish up our discussion about epithelium, we will look at glandular epithelium. Glandular epithelium can secrete substances into the bloodstream (endocrine glands) or into ducts (exocrine glands).

31. Exocrine Glands Can be classified by method of secretion. –Merocrine—release substance via exocytosis –Apocrine—lose small portion of cell body. –Holocrine—release entire cell.

32. Next we will learn about another of the general categories of tissues known as connective tissue.

33. Connective tissue is the most abundant tissue in the body. It consists of special cells called fibroblasts surrounded by a matrix of intercellular material. The matrix can contain fibers such as collagen, elastic, and reticular fibers. Other cells can exist in connective tissue such as macrophages and mast cells (both are types of white blood cells).

34. Connective Tissue Cells Fibroblasts –Star-shaped cell –Secretes protein into matrix producing fibers. Macrophages –Act as scavengers (phagocytosis) Mast Cells –Release heparin (an anticoagulant), histamine (promotes inflammatory reactions).

35. Connective Tissue Fibers (produced by fibroblasts) – Collagenous Thick pieces of protein (collagen). Not very elastic. Hold structures together. High tensile strength. Ligaments, tendons. Lots of collagenous fibers = dense CT (white fibers) Few collagenous fibers = Loose CT.

36. Connective Tissue (elastic fibers) – Elastic Composed of bundles of elastin (elastic protein). Not a lot of tensile strength but very flexible Appear yellow in color. Found in vocal cords, air passages of respiratory system.

37. Connective Tissue (reticular fibers) – Reticular Thin collagenous fibers that form a supporting network.

38. There is also a special category of connective tissue that contains: Blood Cartilage Bone

39. The general categories of connective tissue are: Loose Dense Adipose Reticular Elastic

40. Here is a picture of loose connective tissue. This is also in the skin located deep to the epidermis.

41. Loose connective tissue (aka areolar tissue) is not very well organized. It contains fibroblasts, matrix, and some fibers scattered about.

42. Loose connective tissue is found in the dermis and subcutaneous layers of the skin as well as surrounding muscles. Sometimes it is called fascia.

43. Adipose connective tissue consists of cells containing lipid (fat) called adipocytes. The lipid is used to store energy to be used by the body if needed. Adipose tissue is also found around some organs and joints. It forms a cushion for shock absorption. Adipose tissue also insulates the body.

44. Here is a close up of adipose tissue. You can see the large lipid containing adipocytes. Lipid Nucleus of adipocyte

45. Here’s another view of adipose tissue. Adipocytes

46. Reticular connective tissue consists of a thin supportive network of collagen fibers. It is found supporting the walls of the liver, spleen and lymphatic system.

47. Reticular connective tissue is web-like and forms a supportive network.

48. Dense connective tissue contains thick collagenous fibers. It is found in ligaments and tendons which have a high tensile strength. Dense connective tissue has a poor blood supply which is why tendons and ligaments do not heal well. There are also some elastic fibers and fibroblasts.

49. Elastic connective tissue contains more elastic fibers than collagen fibers. Elastic connective tissue is found in attachments between vertebrae and in walls of some hollow internal organs.

50. Next we will look at some of the tissues in the category of specialized connective tissue. Remember this contains blood, bone and cartilage.

51. We’ll start with cartilage. Cartilage is rigid and strong so it can provide support and protection. It also forms a structural model for developing bones. Cartilage consists of cells called chondrocytes, a chondromucoprotein matrix and collagenous and elastic fibers. Cartilage has no direct blood supply so nutrients must enter by diffusion.

52. Since the nutrients for cartilage diffuse into the tissue, the tissue needs water to help move these substances in. As humans age cartilage tends to “dry up” or become dehydrated which lends to degeneration of the tissue. The cartilage cells or chondrocytes also do not divide very frequently which also contributes to poor healing.

53. There are 3 types of cartilage: Hyaline cartilage Fibrocartilage Elastic cartilage

54. Hyaline cartilage has the characteristic chondrocyte in lacunae arrangement along with a “ground glass” appearance to the matrix. It is found at the ends of bones, soft part of the nose, larynx and trachea. Hyaline cartilage serves as a model for bone growth. Chondrocyte Lacunae

55. Another picture of hyaline cartilage. Nice “ground glass” matrix!

56. Elastic cartilage also has the characteristic chondrocyte in lacunae along with elastic fibers. This cartilage is found in the larynx and the ear. Elastic fibers

57. Fibrocartilage is characterized by rows of chondrocytes (in lacunae). It is a very strong cartilage and is found in the intervertebral discs.

58. Bone is the most rigid of connective tissues. Its hardness comes from mineral salts such as calcium phosphate and calcium carbonate. It is highly organized into units called Haversian systems. The primary cell of bone is the osteocyte.

59. Blood is also considered a connective tissue. It basically consists of cells suspended in a matrix of fluid called plasma. It transports gasses such as oxygen and carbon dioxide and functions in clotting and immunity.

60. Next we will investigate muscle tissue. There are 3 types of muscles tissue: Skeletal Cardiac Smooth

61. Skeletal muscle is striated. The striations are caused by the density of overlapping protein filaments called actin and myosin.

62. Cardiac muscle is also striated but has a unique structure called an intercalated disk. The disks are special intercellular junctions that allow electrochemical impulses to be conveyed across the tissue. Intercalated disk

63. Smooth muscle is not striated because the myofilaments are not as dense as in cardiac and skeletal muscle. Smooth muscle is found in organs such as in the gastrointestinal system and the arteries.

64. The last tissue we will investigate is nervous tissue. Nervous tissue consists of nervous system cells called neurons and supportive cells called glia.

65. Nervous tissue contains neurons and glial cells. Neuron Glial cell

66. Practice tissue identification at: http://www.wisc-online.com/objects/index.asp?objID=AP1402

67. Review the following tables in your text: 5.4 p 156 5.6 p 162 5.7 p 175

68. This concludes the unit on tissues. Feel free to review this presentation as often as needed.