Chapter 3--Tissues

1. Chapter 3--Tissues Biology 112 Tri-County Technical College Pendleton, SC

2. Definition and Types • Tissue is group of cells that are “similar” in structure and function • There are four primary tissue types in the human body: • Epithelium • Connective • Nervous • Muscle

3. Epithelial Tissue Function • Is the lining, covering, and glandular tissue of the body • Functions include: Protection, absorption, filtration, and secretion • Epithelium has some special characteristics • Cells fit close together to form continuous sheets • Neighboring cells bound together by cell junctions including desmosomes and tight junctions

4. Epithelial Functions, ctd. • Membranes all have ONE free (unattached) surface or edge • This apical surface exposed to body’s exterior or to cavity of internal organs • May be slick/smooth or covered with microvilli or cilia • Lower surface rests on BASEMENT MEMBRANE-structureless material secreted by cells • Epithelial cells have NO blood supply of their own (avascular)-depend on diffusion from capillaries in underlying connective tissue

5. Classifying Epithelium (layering) • Each epithelium is given two names • First indicates relative number of cell layers it has • Second describes the shape of its cells • SIMPLE is composed of only ONE layer of cells • STRATIFIED is composed of MORE than one cell layer • Stratified named for cells at free surface and NOT those resting on basement membrane

6. Epithelium Classification, ctd. • SQUAMOUS epithelium cells are flattened like fish scales • CUBOIDAL epithelium cells are cube-shaped like dice • COLUMNAR epithelium cells are shaped like columns • Terms describing arrangement and shape are combined to describe epithelium fully • Use arrangement name first and shape name second

7. Simple Squamous • Single layer of thin squamous cells resting on basement membrane • Usually forms membranes where filtration or exchange of substances by rapid diffusion occurs • Composes air sacs of lungs, walls of capillaries, and the SEROUS MEMBRANES (serosae), the slick membranes that line ventral body cavities and cover organs in that cavity

8. Simple Cuboidal • ONE layer of cuboidal cells resting on BM • Common in glands and their ducts • Salivary glands and pancreas for examples • Forms wall of kidney tubules and covers surface of the ovaries

9. Simple Columnar • ONE layer of columnar cells resting on BM • Tall cells that fit closely together • Specialized for absorption and secretion • GOBLET CELLS often found in this epithelium type—produce lubricating mucus • Line entire digestive tract from stomach to anus • Epithelial membranes that line body cavities open to body exterior called MUCOSAE or mucous membranes

10. Pseudostratified Columnar • All pseudostratified columnar epithelium cells rest on basement membrane • Some shorter than others and their nuclei appear at different heights above BM • Results in psuedo (false) impression that its stratified • Specialized for absorption and secretion • Ciliated variety lines most of respiratory tract • Mucus produced by GC traps dust/debris and cilia propel mucus upward away from lungs

11. Stratified Squamous • Most common stratified epithelium in body • Cells close to edge are squamous whereas cells close to BM are cuboidal/columnar • Usually consists of several layers of cells • Found in sites that receive abuse or friction • Esophagus, mouth, and outer portion of skin

12. Stratified Cuboidal & Columnar • Stratified Cuboidal usually 2 layers thick • Found along ducts of sweat glands and larger ducts of mammary glands • Stratified Columnar basal cells vary in size and shape • Provides protection along portions of pharynx, epiglottis, urethra, anus, salivary gland ducts, and along few large excretory ducts • Both are fairly rare in the human body

13. Transitional Epithelium • Is highly modified stratified squamous epithelium that forms lining of only few organs • Found in urinary bladder, ureters, and part of urethra • Found where “stretching” is necessary • Basal cells are cuboidal/columnar while those at surface vary in appearance • Ability of cells to “slide past” each other and change shape allows “stretching” • Ureter wall/urethra/urinary bladder…enough said

14. Glandular Epithelium • Gland consists of one or more cells that make/secrete particular product (secretion) • Usually proteins in aqueous fluid • Two major types of glands form from epithelial sheets • ENDOCRINE glands lose connection to surface; called “ductless glands” • Their secretions (hormones) diffuse directly in blood vessels that run through the glands • THYROID, ADRENALS, PITUITARY, ETC.

15. Glandular Epithelium, ctd. • EXOCRINE glands retain their ducts and their secretions empty through ducts to epithelial surface • Glands located both internally/externally • Sweat and oil glands • Liver and pancreas (be careful with pancreas, it also has endocrine function)

16. Connective Tissue Overview • Connects body parts and is most abundant and widely distributed of tissue types • Connective tissue has some common characteristics • Most are well vascularized (good blood supply) but there are exceptions • Tendons and ligaments have poor blood supply • Cartilages are avascular • As result, these structures heal very slowly (if at all) when injured

17. CT Overview, ctd. • Connective tissues composed of many different cell types plus varying amounts of nonliving substances found outside cells called EXTRACELLULAR MATRIX • Is what makes connective tissue so different • Matrix produced by CT cells and secreted to exterior • May be liquid, semisolid/gel-like, or very hard • Because of EC matrix, CT able to stand stretching and other abuses (abrasion) that no other tissue could endure • As always, there are exceptions

18. CT Overview, ctd. • Fat tissue (adipose) mostly cells with soft EC matrix • Bone and cartilage tissue has very few cells and large amounts of hard EC matrix which makes them very strong • Various types/amounts of fibers deposited in and form part of EC matrix • Collagen (white) fibers, Elastic (yellow) fibers, and Reticular (fine collagen) fibers • Made by CT cells and secreted to outside

19. CT Overview, ctd. • Connective tissue performs many functions: Protecting, Supporting, & Binding together other body tissues • All CT consist of living cells surround by a matrix • Their major differences reflecdt fiber type and number of fibers in their matrix • From the overview to the specific-let us discuss the Connective Tissue

20. Bone Tissue • Often called “osseous tissue” • Composed of bone cells in cavities called LUCUNAE • Surrounded by layers of very hard matrix containing calcium salts and large numbers of collagen fibers • Because of this hardness, bone has exceptional ability to protect/support other body organs

21. Hyaline Cartilage • Less hard and more flexible than bone • Hyaline cartilage is most widespread • Has abundant collagen fibers hidden by rubbery matrix with blue-white appearance • Forms supporting structures of larynx (voice box), attaches ribs to breastbone, and covers ends of bones where they form joints • **skeleton of fetus made of hyaline cartilage

22. More Cartilage…Yeah!! • ELASTIC cartilage found where structure with elasticity desired • Supports external ear • FIBROCARTILAGE highly compressable • Forms cushionlike disks between vertebrae of spinal column

23. Dense Fibrous Tissue • Also known as Dense Connective Tissue • Has collagen fibers as main matrix • Crowded between collagen fibers are rows of FIBROBLASTS (fiber-forming cells) • Forms strong, ropelike structures such as tendons and ligaments • TENDONS attach skeletal muscles to bone • Ligaments connect bone to bone at joints • More stretchy/contains more elastic fibers • Makes up lower layers of skin (arranged in sheets)

24. Areolar Tissue • Also known as Loose Connective tissue & is most widely distributed CT variety • Soft & pliable tissue that cushions/protects body organs it wraps • Functions as universal packing tissue and “glue” because it helps hold internal organs together and in their proper positions • Soft layer of areolar tissue (LAMINA PROPRIA) underlies all mucous membranes

25. Areolar Tissue, ctd. • Fluid matrix contains all types of fibers in loose network • Provides reservoir of water and salts for surrounding tissues • **Essentially all body cells obtain their nutrients from and release their wastes into this “tissue fluid” • When body region inflamed, areolar tissues in area soak up excess fluid like sponge and area swells and becomes puffy • This condition is called EDEMA

26. Adipose Tissue • Is an areolar tissue in which fat cells predominate • Glistening drop of fat occupies most of cell’s volume • Often called “signet ring cells” • Forms subcutaneous tissue beneath skin • Insulates body • Protects some organs individually • Kidneys surrounded by capsule of fat; cushions eyeballs in sockets • Fat “depots” in body (hips/breasts) store fat (fuel)

27. Reticular Connective Tissue • Consists of delicate network of interwoven reticular fibers associated with RETICULAR CELLS which resemble fibroblasts • Limited to certain sites • Forms STROMA (bed/mattress) which is internal supporting framework • Stroma can support many free blood cells (mostly lumphocytes) in lymph organs such as lymph nodes, spleen, and bone marrow

28. Blood Connective Tissue • Blood (vascular tissue) composed of blood cells surrounded by nonliving matrix (blood plasma) • Fibers are soluble protein molecules that become visible only during blood clotting • Transport vehicle for cardiovascular system • Carries nutrients, wastes, respiratory gases, and many other substances throughout body

29. Nervous Tissue • Functional unit is the NEURON • Neurons receive and conduct electrochemical impulses from one part of body to another • IRRITABILITY and CONDUCTIVITY are two major functions of nervous tissue • Neurons may be quite long (up to 3 feet) because cytoplasm may be drawn out into extensions • Neurons along with supporting cells (called glial or neuroglial cells that insulate, support, and protect neurons) make up structures of nervous system • Brain, spinal cord, and nerves

30. Muscle Tissue Overview • Highly specialized to contract (shorten) • Muscle cells elongated to provide long axis for contraction • Called muscle “fibers” • Three types of muscle tissue • SKELETAL, CARDIAC, and SMOOTH

31. Skeletal Muscle, and more… • Packaged by connective tissue sheets into organs called skeletal muscles which are attached to skeleton • Can be controlled voluntarily and form flesh of body (word of caution here) • When contract, they pull on bones or skin • Result is body movement of change in facial expressions • Cells are long, cylindrical, and multinucleate • Have obvious striations (stripes)

32. That’s the beat of a heart… • Cardiac muscle found only in the heart • Has striations, uninucleate, branching cells that fit tightly together at junctions called INTERCALATED DISKS • Contain gap junctions that allow ions to free pass from cell to cell • Results in rapid conduction of exciting electrical impulse across heart • Involuntary/not under conscious control

33. Smooth Muscle Tissue • Also called VISCERAL muscle because NO striations are visible • Spindle shaped cells with single nucleus • Found in walls of hollow organs (stomach, bladder, uterus, and blood vessels) • When contracts, cavity of organ constricts or dilates so that substances are propelled through organ along specific pathway • Contracts much more slowly than skeletal/cardiac • PERISTALSIS is wavelike motion that keeps food moving through small intestine (typical of smooth muscle tissue)

34. Tissue Repair • Tissue injury stimulates body’s inflammatory and immune responses and healing process begins almost immediately • Tissue repair (wound healing) occurs in 2 major ways • REGENERATION is replaced of destroyed tissue by the same kind of cell • FIBROSIS involves repair by dense (fibrous) CT; i.e., formation of SCAR tissue • Which of these occurs depends on TYPE of tissue damaged and SEVERITY of injury

35. Tissue Repair, ctd. • Clean cuts (incisions) heal more successfully that ragged tears (lacerations) • Tissue injury triggers series of events • CAPILLAIRES become very permeable allowing fluids rich in clotting proteins to seep into injured area • Leaked clotting proteins form clot, stopping blood loss, holds edges of wound together, and seals off damaged area • Prevents bacteria (other harmful stuff) from spreading to surrounding tissues

36. Tissue Repair, ctd. • Clot exposed to air, dries and hardens to form scab • GRANULATION tissue next phase • Delicate, pink tissue composed largely of capillaries that grow into damaged area • Capillaries are delicate and bleed freely • Also contains phagocytes and connective tissue cells (fibroblasts) that synthesize collagen fibers (scar tissue) to permanently bridge the gap

37. Tissue Repair, ctd. • Surface epithelium begins to regenerate and cover granulation tissue beneath scab • Final result is fully regenerated surface epithelium that covers area of fibrous scar • Scar is either invisible or visible as white line depending on severity of wound • Epithelial tissues such as skin epidermins, mucous membranes, and fibrous connective tissue regenerate beautifully

38. Tissue Repair, ctd. • Skeletal muscle regenerates poorly, if at all • Cardiac and nervous tissue replaced only by SCAR tissue • Scar tissue is strong but lacks flexibility of more normal tissues • Is unable to perform normal functioning of tissue it replaces • May hamper functioning of an organ (bladder, heart, etc.)