Chapter 3: Fundamental Cells and Tissues

1. Chapter 3: Fundamental Cells and Tissues

2. Objectives – Lesson 1 • TSWBAT to define histology. • TSWBAT to identify the four basic tissue types. • TSWBAT to identify five important characteristics of epithelial tissue. • TSWBAT to identify four essential functions of epithelial tissue.

3. 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

4. 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

5. 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

6. 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

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

8. 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 – layers of cells that cover internal or external surfaces - Forms the outer layer of the skin - Lines the open cavities of the reproductive, cardiovascular, nervous, digestive, urinary and respiratory systems and covers the walls and organs (line all passageways that communicate with the outside world) 2.Glandular Epithelium - Forms the glands of the body (provide fluid secretions)

9. Epithelial Tissue Functions • Protection – protect exposed and internal surfaces from abrasion, dehydration, and destruction by foreign agents • Permeability – any substance that enters or leaves your body must cross an epithelium (provides selective absorption) • Sensation – provide information about the external and internal environments (example - sense smell) • Secretion – gland cells releases a substance (example – mucus)

10. 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 (lack blood vessels); must obtain nutrients by diffusion or absorption from nearby tissues • If well nourished, epithelial cells regenerate themselves (high rate of mitosis)

11. Check point • Define histology. • Identify the four major types of tissues in the body.

12. Classification of Epithelia • There are many different specialized types of epithelia • Organized into categories based on: • Cell shape • The number of cell layers between the basement membrane and the exposed surface of the epithelium

13. Classification of Epithelial Tissue Cell Shape: • Squamous = flat (attach like tiles) • Cuboidal = thicker, cube shaped • Columnar = tall, cylindrical

14. 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

15. Classification of Epithelial Tissue Number of cell layers: Simple = one layer of cells covers the basement membrane • Thin/Fragile • Located in protected areas in the body (ventral body cavities, heart chambers and blood vessels). Why? • Regions in which secretion or absorption occurs (lining of the intestines, lungs) • Stratified = Multilayered (several layers cover basement membrane) • Located in areas that are exposed to stresses (mouth, skin)

16. 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

17. Epithelia: Simple Squamous Figure 4.2a

18. 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

19. Epithelia: Simple Columnar Figure 4.2c

20. Pseudostratified Columnar • Includes several types of cells with varying shapes and functions • The distances between the cell nuclei and the exposed surface vary, so the epithelium appears to be layered (stratified) • It is not truly stratified because every epithelial cell contacts the basement membrane • Typically possess cilia (slender organelle that extends above the free surface of an epithelial cell and undergoes movement)

21. 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

22. 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

23. 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

24. Transitional Epithelium • Unusual stratified epithelium because it tolerates repeated cycles of stretching and recoiling without damage • It is called transitional because the appearance of the epithelium changes as stretching occurs

25. 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

26. 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)

27. 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

28. 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

29. 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