Chapter 3: Fundamental Cells and Tissues

1. Chapter 3: Fundamental Cells and Tissues

2. Cells In the late 1600’s British born Robert Hooke coined the term "cell" to describe the basic unit of life. • Where did the term cell come from? • In 1665 Robert Hooke inspected thin slices of cork and found that they consisted of millions of small, “irregular units” • He used the term cell because the small, bare spaces reminded him of cells in a prison

3. Cell Basics • Cells are the building blocks of all plants and animals • All cells come from the division of preexisting cells • Cells are the smallest units that perform all vital physiological functions • Each cell maintains homeostasis at the cellular level

4. Cell Basics continued Living cells are about 60 % H20 All body cells are constantly bathed in a dilute saltwater solution called interstitial fluid (18 pints). All exchanges between cells and blood are made through this fluid

5. Cell Facts • The human body contains trillions of cells (200 types of cells) • The average cells is just 0.02mm across • The largest cell in the body is an egg cell (0.15mm) • The longest cells are the nerve cells supplying your legs (some measure as much as 4ft in length) • Five million of your body cells die every second

6. Tissues Tissues - Groups of cells similar in structure and function • The four types of tissues: • Epithelial • Connective • Muscle • Nerve (Neural)

7. Epithelial Tissue Epithelium – A sheet of cells that covers a body surface or lines a body cavity. Occurs in the body in two ways: 1. Epithelia – covering and lining epithelium - Forms the outer layer of the skin - Lines the open cavities of the cardiovascular, digestive, urinary and respiratory systems and covers the walls and organs 2.Glandular Epithelium - Forms the glands of the body

8. Special Characteristics of Epithelium • Cells fit closely together to form continuous sheets (single/multiple layers) • Membranes always have one free surface or edge (exposed to body cavity, exterior of the body or lining an internal organ) • Lowest surface (basal surface) of epithelium rests on a basement membrane • Epithelial tissues have no blood supply (avascular) of their own; comes from nearby tissues by way of diffusion • If well nourished, epithelial cells regenerate themselves (high rate of mitosis)

9. Epithelial Tissue Epithelial Functions include: • Protection – against injury, invasion by bacteria, loss of water and heat • Permeability – selective absorption • Sensation – provide information about the external and internal environments (example - sense smell) • Secretion – releases a substance (example – mucus)

10. Classification of Epithelial Tissue Cell Shape: • Squamous = flat (attach like tiles) • Cuboidal = thicker, cube shaped • Columnar = tall, cylindrical • Transitional = change shape from columnar/cuboidal to flat due to stretching

11. Classification of Epithelia Squamous(skwa’mus) Flattened and scalelike Cubodial (ku-boi’dahl) Boxlike, as tall as they are wide. Columnar Tall and column shaped. Figure 4.1b

12. Classification of Epithelial Tissue Number of cell layers: • Simple = one layer (squamous, cuboidal, columnar) • Stratified = Multilayered (squamous, cuboidal, columnar, transitional) • Pseudostratified Columnar= one layer but appears multilayered (not all cells reach the surface)

13. Classification of Epithelial Tissue Each epithelium is given two names. • The first name indicates the number of cell layers present • The second name describes the shape of its cells • Followed by epithelium or epithelial tissue Example : • Simple (1 layer) • Squamous (Flat cell shape) • Epithelium

14. Epithelia: Simple Squamous Figure 4.2a

15. Epithelia: Simple Cuboidal • Single layer of cubelike cells with large, spherical central nuclei • Function in secretion and absorption • Present in kidney tubules, ducts and secretory portions of small glands, and ovary surface Figure 4.2b

16. Epithelia: Simple Columnar Figure 4.2c

17. Epithelia: Pseudostratified Columnar • Single layer of cells with different heights; some do not reach the free surface • Nuclei are seen at different layers • Function in secretion and propulsion of mucus • Present in the male sperm-carrying ducts (nonciliated) and trachea (ciliated) Figure 4.2d

18. Epithelia: Stratified Squamous – Most Common • Thick membrane composed of several layers of cells • Function in protection of underlying areas subjected to abrasion • Forms the external part of the skin’s epidermis (keratinized cells), and linings of the esophagus, mouth, and vagina (nonkeratinized cells) Figure 4.2e

19. Epithelia: Stratified Cuboidal and Columnar Stratified cuboidal • Quite rare in the body • Found in some sweat and mammary glands • Typically two cell layers thick Stratified columnar • Limited distribution in the body • Found in the pharynx, male urethra, and lining of some glandular ducts • Also occurs at transition areas between two other types of epithelia

20. Epithelia: Transitional • Several cell layers, basal cells are cuboidal, surface cells are dome shaped • Stretches to permit the distension of the urinary bladder • Lines the urinary bladder, ureters, and part of the urethra Figure 4.2f

21. Epithelia: Glandular Gland - One or more cells that makes and secretes a particular product (secretion). Classified by: • Site of product release endocrine (internally secreting) exocrine (externally secreting) • Relative number of cells forming the gland unicellular (one-celled) multicellular (many-celled)

22. Endocrine Glands • Ductless glands that produce hormones • Hormones are regulatory chemicals that enter the blood or lymphatic fluid and travel to organs • Each hormone prompts its target organ to respond in some characteristic way

23. Exocrine Glands • More numerous than endocrine glands • Secrete their products onto body surfaces (skin) or into body cavities • Examples include mucus, sweat, oil, salivary glands, the liver (secretes bile), the pancreas (synthesizes digestive enzymes) • Unicellular & Multicellular

24. Mitosis • Equal division of material in the nucleus, followed by division of the cell body (nuclear cell division) • Epithelial cells have a high rate of mitosis to allow for frequent repair