1. Tissues “Man is an intelligence in servitude to his organs.” - Aldous Huxley

2. Tissue Level of Organization The cells of the body vary widely in terms of function and design. About 200 different types of cells in the body. Collections of specialized cells that perform certain functions are called tissues.

3. Epithelial Tissue Cells that cover internal or external surfaces form epithelial tissue. Characteristics of epithelial tissue include: ▫Cells are closely bound together. ▫An apical surface that is exposed to the environment or an internal passage. ▫A basement membrane that attaches to underlying tissues. ▫Avascular, meaning an absence of blood vessels. ▫Continuous replacement or regeneration of lost and damaged surface cells.

4. Epithelia protects exposed and internal surfaces from damage by physical abrasion, dehydration, infection, and by chemicals. Any substance that enters or leaves the body must do so through a layer of epithelium. The nerve cells that make up the five senses are located within epithelium.

5. Glands; organs that produce secretions, are made of epithelial cells. ▫Exocrine glands discharge secretions to surfaces exposed to the outside, such as the lining of the digestive tract or skin. ▫Endocrine glands secrete directly into tissue fluid or blood.

6. Types of Epithelium Epithelial cells are classified by shape and whether they form layers. Simple epithelium consists of a thin, single layer of cells covering the basement membrane. Stratified epithelium has several layers of cells above the basement membrane, creating a greater degree of protection. ▫Found in areas commonly exposed to mechanical and chemical stress, such as the mouth.

7. Simple squamous epithelium is found in internal surfaces where absorption takes place, or there is little friction due to surrounding fluid. ▫Examples: Lining of the heart, blood vessels, kidney tubules, air sacs of lungs.

8. Simple cuboidal epithelium occurs in areas where increased amounts of secretion and absorption occur. The cells are larger and provide more room more needed organelles. ▫Examples: Pancreas, salivary glands, urine production areas of kidneys.

9. Simple columnar epithelium provides more protection than cuboidal in areas of absorption and secretion. Held together with tight junctions; waterproof attachments made with membrane proteins. ▫Examples: Stomach lining, intestinal tract.

10. Stratified squamous epithelium is a thick protective lining found in areas of high mechanical stress. ▫Held together by desmosomes, which are cytoskeleton attachments at the cell membrane.  Causes the cells to peel off in sheets instead of individually.. ▫Examples: Lining of the mouth, skin, esophagus, and anus.

11. Pseudostratified ciliated columnar epithelium is a mixture of columnar and cuboidal cells that appears layered, but all cells actually do touch the basement membrane. ▫Cilia are present to move mucus. ▫Examples: Lining of the nasal cavity, trachea, and bronchi.

12. Transitional epithelium can stretch and recoil, so its appearance changes. ▫Examples: Urinary bladder.

13. Connective Tissue Connective tissues are distributed throughout the body, never exposed to the outside environmental and have a diverse set of functions and properties. ▫Support and protect other tissues. ▫Transport materials throughout the body. ▫Storage of energy reserves as fat. ▫Defense against microorganisms. Connective tissue is made of a mixture of different types of cells and protein fibers.

14. Reticular fibers Macrophage Blood Vessel Ground substance Mast cell Elastic fibers Macrophage Collagen fibers Fibroblast

15. Fibroblasts produce the protein fibers and the ground substance that fills the empty spaces in connective tissue. Macrophages will phagocytize or “eat” damaged cells, bacteria, or viruses. Mast cells contain vesicles that release defensive chemicals during an injury or infection. Collagen fibers are long, straight, and flexible. Elastic fibers are branched and wavy, giving them the ability to stretch and return back to their original shape. Reticular fibers are thinner and form a branching, interwoven network.

16. Loose Connective Tissues Loose connective tissues are the “packing materials” of the body, filling in spaces to provide cushioning and support.

17. Areolar tissue is elastic and has an extensive blood supply. ▫Has enough collagen and elastin fibers to be strong, and enough ground substance to move independently. ▫Example: Between the skin and muscle.

18. Adipose tissue is a collection of fat cells, also called adipocytes. ▫Provides padding, shock absorption, and thermal insulation. ▫Example: Breasts, bottom layer of skin.

19. Reticular tissue is a network of protein fibers that holds other cells in place, such as white and red blood cells. ▫Example: Spleen, liver, bone marrow, lymph nodes.

20. Dense Connective Tissues Dense connective tissues consist mostly of collagen fibers, with fewer cells and less ground matter.

21. Dense regular connective tissue contain collagen fibers and fibroblasts that stabilize connections between body structures. ▫Example: Tendons connecting bone and muscle.

22. Cartilage Cartilage is a firm gel containing protein fibers and a type of cell called chondrocytes. ▫Chondrocytes are found within small pockets called lacunae. ▫No blood supply.

23. Hyaline cartilage is the most common, providing stiff and flexible support. ▫Matrix is made of densely packed collagen fiber. ▫Example: Respiratory tract, connecting ribs to sternum, and covering the ends of bones.

24. Elastic cartilage is extremely resilient; able to endure distortions while still maintaining its original shape. ▫Contains many more elastic fibers than hyaline cartilage. ▫Example: External ear.

25. Fibrocartilage has very little ground substance, with densely packed collagen fibers. ▫Tough, durable, and resist compression. ▫Example: Spinal cord, knee joint, between bones of pelvis.

26. Bone has a matrix mostly made of calcium compounds and collagen fibers, making it the strongest tissue. ▫Like cartilage, the cells reside in pits called lacunae. ▫Canals provide a blood supply.

27. Fluid Connective Tissues Blood and lymph are the only two types of fluid connective tissues. ▫Transport oxygen, carbon dioxide, nutrients, and wastes throughout the body.

28. Tissue Membranes At the tissue level, a membrane is a physical barrier made of an epithelium supported by connective tissue.

29. Mucous membranes line tracts that must be kept moist at all times, such as the esophagus, intestines, and trachea. ▫Example: The small intestines has a combination of columnar epithelium and areolar tissue.

30. Serous membranes line internal body cavity divisions. ▫Coated with serous fluid to prevent friction. ▫Example: The lungs are lined by simple squamous epithelium and areolar tissue.

31. Cutaneous membranes are thick, dry, and relatively waterproof. ▫Example: Skin, made of stratified squamous epithelium above areolar and dense connective tissue.

32. Synovial membranes protect the ends of bones at joints. ▫Lined with synovial fluid to prevent friction. ▫Example: The bones of the knee joint are lined by mostly areolar tissue with an incomplete epithelium.

33. Muscle Tissue Muscle tissue is made of arrangements of protein filaments that can contract and generate force.

34. Skeletal muscle tissue is made of large, multinucleated cells that can be up to a foot long. ▫The repeating groups of muscle filaments create a series of bands called striations.

35. Cardiac muscle tissue is smaller than skeletal muscle and the cells only contain a single nucleus. ▫Cells are connected at specialized attachment sites called intercalated discs. ▫Each disc contains a gap junction that allows the movement of small molecules and ions between cells.

36. Smooth muscle tissue is made of cells smaller and more slender than skeletal muscle. ▫Striations are not present. ▫Found in layers around various hollow organs that must contract.

37. Nervous Tissue Nervous tissue is specialized for the conduction of electrical impulses. ▫Combination of supporting cells called neuroglia and long, branched neurons. ▫Mostly found in the brain and spinal cord.