Ch 4: Tissues

1. Ch 4: Tissues

2. Intro to tissues • Tissues – • Groups of cells that are similar in structure and function • 4 primary tissue types - • Epithelial (covering & linings) • Connective (support) • Nervous (control) • Muscular (movement)

3. Epithelial tissue • Epithelium – • Epithe = “laid on, covering” • A sheet of cells that covers a body surface or lines a cavity • Forms boundaries between environments • Functions – • Protection • Absorption (process by which the products of digestion pass through the alimentary tube mucosa into the blood or lymph) • Filtration (passage of a solvent and dissolved substances through a membrane or filter) • Excretion (elimination of waste products from the body) • Secretion (passage of material formed by a cell to its exterior) • Sensory reception • Occurs in the body as... • A covering or lining epithelium • Or as glandular epithelium

4. Special characteristics of epithelium • Cellularity – • Composed of closely packed cells with little extracellular material between • Specialized contacts – • Bound together by specialized contacts (desmosomes & tight junctions) • Forms continuous sheets • Polarity – • Possess an apical & basal surface • Apical – free and exposed – most have microvilli • Cilia – propel substances along their free surface (trachea) • Basal – attached surface • Basal lamina – thin supporting sheets made mostly of glycoproteins – acts as a selective filter for the diffusion of nutrients

5. Specialized characteristics cont. • Support – • All epithelial tissue rest & are supported by connective tissue • Reticular lamina – • Below basal lamina • Contains collagen fibers of the connective tissue • Reticular lamina + basal lamina = basement membrane • Reinforces epithelium (helps resist tearing & stretching) • Avascular but innervated – • Avascular = no blood vessels • Nourished by diffusing nutrients from underlying connective tissue • Innervated = supplied by nerves • Regeneration – • High regeneration capacity

6. Cell shapes

7. Classification of epithelium • Naming – • First name – • Indicates the number of layers present • Simple – one layer • Absorption and filtration • Stratified – more than one • Highly abrasive • Shape differs among cell layers • Named due to the apical layer • Second name - • Describes the shape of the cell • Squamous – • Flat and scale like • Cuboidal – • Box/cube like • Columnar – • Tall and column shaped

8. Epithelium • Simple epithelia are mostly concerned with absorption, secretion, and filtration • Simple squamous – • Single layer of flattened cells • Sparse cytoplasm • Bulging nucleus • Filtration & exchange • Special examples; • Endothelium – • “inner covering” • Slick & friction reducing • Lymphatic vessels, blood vessels, heart, & capillaries • Mesothelium – • “middle covering” • Serous membrane lining ventral body cavities • Covers organs

9. Simple squamous

10. Epithelium cont. • Simple cuboidal – • Single layer of cube-shaped cells • Forming the smallest ducts of glands • Kidney tubules • Secretion & absorption • Spherical nuclei • Simple columnar – • Single layer of column-shaped cells • Line the digestive tract (stomach to rectum) • Dense microvili to increase absorption • Goblet cells – • secrete protective mucus

11. Simple cuboidal

12. Simple columnar

13. Epithelium cont. • Pseudostratified columnar – • Contains cells of varying heights • Gives the false (psuedo) impression that there are many layers • Nuclei are at various heights – gives the false impression • All cells rest on basement membrane • Tallest cells reach the free apical surface • May contain cilia & goblet cells • Line the respiratory tract

14. Pseudostratified

15. Stratified epithelium • Stratified epithelia’s main function is protection. • Consists of two or more cell layers • Regeneration occurs at the basal surface • More durable than simple epithelium • Stratified cuboidal – • Rare • Ducts of large glands

16. Stratified epithelium cont. • Stratified squamous – • Most common • Several cell layers • Cells on free surface are squamous shaped (named for free exposed surface) • Underlying cells are cuboidal or columnar • Protection • Basal cells replace apical cells • Apical cells are squamous shaped because they are not receiving adequate nutrients • Rely on diffusion of nutrients • External part of the skin & extends into every body opening

17. Stratified squamous

18. Stratified epithelium cont. • Stratified columnar – • Limited distribution • Small amounts in pharynx, male urethra, & some glandular ducts • Transitional – • Forms the hollow organs of the urinary system • Allows for stretch • Basal cells = cuboidal or columnar • Apical cells vary in appearance depending on the level of stretch • Not stretched – multilayered membrane • Stretched (distension) – membrane becomes squamous like

19. Transitional

20. Glandular epithelia • Gland – • Cells that make or secrete (export) a product • Secretion = Active Process • Secretion – aqueous fluid containing proteins • 2 types – • Endocrine • Internally secreting • Ductless (they loose their ducts) • Secrete hormones by exocytosis • Directly into lymph or blood systems • Or directly into the extracellular space • Exocrine • Externally secreting • Have ducts • More numerous in the body • Secrete onto a surface or into body cavities • Sweat, oil, salivary glands

21. Connective tissue • Found everywhere in the body • Consist of living cells surrounded by a matrix • Differences = cell type & fiber type & the amount of the two • Main classes – • Connective tissue proper – fat and fibrous tissue • Cartilage • Bone • Blood • Major functions – • Binding & support • Protection • Insulation • Transportation

22. Connective tissue cont. • Common characteristics – • Common origin – • All connective tissues arises from embryonic tissue called mesenchyme • Degrees of vascularity – • Connective tissue ranges from avascular to highly vascularized • Cartilage – avascular • Dense connective tissue – poor vascularization • All other connective tissue – rich blood supply • Extracellular matrix – • Connective tissue is composed mainly of nonliving extracellular matrix • Separates the cells of the tissue • Allows connective tissue to – • Bear weight • Withstand tension • Endure physical trauma

23. Connective tissue cont. • Ground substance – • Unrestricted material that fills the space between the cells and contains fibers • Mechanism through which nutrients and other dissolved substances can diffuse • Composed of: • Interstitial fluid • Cell adhesion proteins • Proteoglycans – helps determine the stiffness of the ground substance • Fibers – makes the fluid less pliable

24. Connective tissue cont. • Fibers – • Provide support • Collagen fibers – • Strong • Provide large amounts of tensile strength (ability to resist longitudinal strain) • Composed of fiberous protein: collagen • Has a glistening appearance; also called white fibers • Elastic fibers – • Elastin proteins • Allows fibers to stretch & recoil • Skin, lungs, & blood vessels • Reticular fibers – • Reticul – “network” • Fine collagenous fibers that form networks • Extensive branching network • Surrounds blood vessels, supports soft tissue organs, & around basement membranes

25. Connective tissue cont. • Fundamental cell types – • All connective tissues have an immature and mature cell form • “blast” – actively forming cells – secrete ground substance & fibers characteristic of the matrix • 4 primary blast cells - • Osteoblast – bone cells • Fibroblast – connective tissue proper • Chondroblast – cartilage • Hematopoietic stem cell – blood • “cyte” – inactive mature cells • Osteocyte – mature bone cells • Chondrocyte – mature cartilage cells

26. Types of connective tissue • Connective tissue proper – • Loose connective • Areolar, adipose, & reticular • Dense connective • Dense regular, dense irregular

27. Loose connective tissue • Areolar – • “areola” – a small open space • Binds body parts together while allowing them to move freely over one another • Wraps small blood vessels & nerves • Surrounds glands • Forms subcutaneous tissue • Most widely distributed connective tissue • Contains fibroblasts –actively mitotic fiber cells • Loose arrangement of tissue – provides a reservoir of water and salt

28. Areolar

29. Loose connective tissue • Adipose – • Fat tissue • Contain a pure fat droplet, displaces nucleus • Highly vascularized – high metabolic activity • Closely packed cells – little matrix • Adipocytes – • Fat cells • Mature cells are some of the largest cells in the body • Mature cells can’t divide • Develops where areolar tissue is plentiful • Insulation, stores nutrients, & shock absorber • Brown fat – • Consumes its stored nutrients to generate heat to warm the body • Occurs in babies who lack the ability to produce their own heat through shivering

30. Adipose

31. Loose connective tissue • Reticular connective tissue – • Resembles areolar tissue • Contains only reticular fibers • Forms stroma - • Internal framework • Supports blood cells • Lymph system, spleen, & bone marrow • Limited within the body even though reticular fibers are numerous

32. Reticular

33. Dense connective tissue • Dense regular – • Contains closely packed bundles of collagen fibers running in the same direction • Run parallel to the direction of pull • Makes up tendons (attach muscle to bone) and ligaments (attach bone to other joints) • Great resistance to tension – exerted in a single direction • Poorly vascularized – slow regeneration

34. Dense regular

35. Dense connective tissue • Dense irregular tissue – • Contains thick bundles of collagen fibers • Arranged in an irregular (more than one plane) fashion • Found in: • Dermis • Joint capsules

36. Dense irregular

37. Cartilage • Lacks nerve fibers (not innervated) • Avascular • Withstands tension & compression • Tough but flexible • Ground substance – • Collagen fibers • Elastic fibers • Water (80%) • Allows cartilage to rebound after being compressed • Nourishes the cartilage cells • Chondroblasts – produces new matrix • Chondrocytes – found in small groups w/in cavities (lacunae)

38. Cartilage cont. • Hyaline – • Hyalin = glass • Collagen fibers are not apparent within the matrix – gives it a glass like appearance • Gristle • Most abundant cartilage • Providing firm support with some pliability • Covers the ends of long bones • Absorbs compression • Supports the tip of the nose & connects ribs to sternum • Epiphyseal plates – actively growing regions near the end of long bones – continued growth in length

39. Hyaline

40. Cartilage cont. • Elastic – • Found where strength & exceptional stretch are needed • Contains large amounts of elastin fibers – • Allows for repeated bending • External ear • Epiglottis – covering the respiratory system

41. Elastic

42. Cartilage cont. • Fibrocartilage – • Found where strong support & ability to withstand pressure are required • Rows of chondrocytes alternating with rows of thick collagen fibers • Compresses and resists tension • Intervertebral disks • Spongy cartilage of the knee joint

43. Fibrocartilage

44. Bone • Bone – • Osseous • Supports & protects the body • Additional collagen fibers & calcium salts found in extracellular matrix • Provides cavities for fat storage & blood cells • Osteoblasts – produce organic portions of the matrix – bone salts deposited on & between the fibers • Osteocytes – reside in the lacunae • Highly vascularized

45. Bone (osseous tissue)

46. Blood • Blood – • Classified as a connective tissue because... • Developed from mesenchyme • Consists of blood cells & plasma proteins surrounded by plasma • Fibers – soluble protein molecules that become visible during clotting • Transport vehicle for the body

47. Blood

48. Nervous tissue • Nervous tissue – • Main component of the nervous system • Regulates & controls body functions • Brain, spinal cord, & nerves • Composed of 2 cell types – • Neurons – • Specialized cells that generate and conduct electrical impulses • Branching cells • Cytoplasmic extensions – allows them to transmit electrical impulses • Supporting cells – • Nonconductive cells that support, insulate, and protect the neurons

49. Nervous tissue

50. Muscle tissue • Muscle tissue – • Highly cellular • Well vascularized • Responsible for movement • 3 types – • Skeletal – • Attaches to the skeleton & produces voluntary body movement • Packaged by connective tissue • Form the flesh of the body • Contain many nuclei & striations (indicates the alignment of myofilaments) • Voluntary muscle • Cardiac – • Only in the walls of the heart • Responsible for the involuntary movement of the heart • Contain striations • Uninucleated • Branching cells that fit together & the intercalated disc junctions • Involuntary muscle • Smooth – • No visible striations • One nucleus • Found in the walls of hollow organs (other than the heart) – digestive, reproductive, & urinary organs • Involuntary muscle