1. © 2013 Pearson Education, Inc. Connective Tissue Most abundant and widely distributed of primary tissues Four main classes –Connective tissue proper –Cartilage –Bone –Blood

2. © 2013 Pearson Education, Inc. Major Functions of Connective Tissue Binding and support Protecting Insulating Storing reserve fuel Transporting substances (blood)

3. © 2013 Pearson Education, Inc. Characteristics of Connective Tissue Three characteristics make connective tissues different from other primary tissues –Have mesenchyme (an embryonic tissue) as their common tissue of origin –Have varying degrees of vascularity (blood vessels) –Have extracellular matrix Connective tissue not composed mainly of cells Largely nonliving extracellular matrix separates cells –So can bear weight, withstand tension, endure abuse

4. © 2013 Pearson Education, Inc. Structural Elements of Connective Tissue Three elements –Ground substance –Fibers –Cells Composition and arrangement varies in different connective tissues

5. © 2013 Pearson Education, Inc. Ground Substance Unstructured material that fills space between cells –Medium through which solutes diffuse between blood capillaries and cells Components –Interstitial fluid –Cell adhesion proteins ("glue" for attachment) –Proteoglycans Protein core + large polysaccharides (chrondroitin sulfate and hyaluronic acid) Trap water in varying amounts, affecting viscosity of ground substance

6. © 2013 Pearson Education, Inc. Connective Tissue Fibers Three types of fibers provide support –Collagen Strongest and most abundant type Tough; provides high tensile strength –Elastic fibers Networks of long, thin, elastin fibers that allow for stretch and recoil –Reticular Short, fine, highly branched collagenous fibers (different chemistry and form than collagen fibers) Branch, forming networks that offer more "give"

7. © 2013 Pearson Education, Inc. Cells "Blast" cells –Immature form; mitotically active; secrete ground substance and fibers –Fibroblasts in connective tissue proper –Chondroblasts in cartilage –Osteoblasts in bone –Hematopoietic stem cells in bone marrow "Cyte" cells –Mature form; maintain matrix –Chondrocytes in cartilage –Osteocytes in bone

8. © 2013 Pearson Education, Inc. Other Cell Types in Connective Tissues Fat cells –Store nutrients White blood cells –Neutrophils, eosinophils, lymphocytes –Tissue response to injury Mast cells –Initiate local inflammatory response against foreign microorganisms they detect Macrophages –Phagocytic cells that "eat" dead cells, microorganisms; function in immune system

9. © 2013 Pearson Education, Inc. Types of Connective Tissues: Connective Tissue Proper All connective tissues except bone, cartilage and blood Two subclasses –Loose connective tissues Areolar Adipose Reticular –Dense connective tissues (also called fibrous connective tissues) Dense regular Dense irregular Elastic

10. © 2013 Pearson Education, Inc. Areolar Connective Tissue Support and bind other tissues –Universal packing material between other tissues Most widely distributed Provide reservoir of water and salts Defend against infection Store nutrients as fat Fibroblasts Loose arrangement of fibers Ground substance When inflamed soaks up fluid  edema

11. © 2013 Pearson Education, Inc. Adipose Tissue White fat –Similar to areolar but greater nutrient storage –Cell is adipocyte Stores nutrients –Scanty matrix –Richly vascularized –Shock absorption, insulation, energy storage Brown fat –Use lipid fuels to heat bloodstream not to produce ATP

12. © 2013 Pearson Education, Inc. Reticular Connective Tissue Resembles areolar but fibers are reticular fibers Fibroblasts called reticular cells Supports free blood cells in lymph nodes, the spleen, and bone marrow

13. © 2013 Pearson Education, Inc. Dense Regular Connective Tissue Closely packed bundles of collagen fibers running parallel to direction of pull –White structures with great resistance to pulling –Fibers slightly wavy so stretch a little Fibroblasts manufacture fibers and ground substance Few cells Poorly vascularized

14. © 2013 Pearson Education, Inc. Dense Irregular Connective Tissue Same elements but bundles of collagen thicker and irregularly arranged Resists tension from many directions –Dermis –Fibrous joint capsules –Fibrous coverings of some organs

15. © 2013 Pearson Education, Inc. Connective tissue proper: dense connective tissue, elastic Description: Dense regular connective tissue containing a high proportion of elastic fibers. Function: Allows tissue to recoil after stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration. Location: Walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes. Photomicrograph: Elastic connective tissue in the wall of the aorta (250x). Aorta Heart Elastic fibers Figure 4.8f Connective tissues.

16. © 2013 Pearson Education, Inc. Cartilage Chondroblasts and chondrocytes Tough yet flexible Lacks nerve fibers Up to 80% water - can rebound after compression Avascular –Receives nutrients from membrane surrounding it Perichondrium Three types of cartilage: –Hyaline cartilage –Elastic cartilage –Fibrocartilage

17. © 2013 Pearson Education, Inc. Bone Also called osseous tissue Supports and protects body structures Stores fat and synthesizes blood cells in cavities More collagen than cartilage Has inorganic calcium salts Osteoblasts produce matrix Osteocytes maintain the matrix Osteons – structural units Richly vascularized

18. © 2013 Pearson Education, Inc. Blood Most atypical connective tissue – is a fluid Red blood cells most common cell type Also contains white blood cells and platelets Fibers are soluble proteins that precipitate during blood clotting Functions in transport

19. © 2013 Pearson Education, Inc. Muscle Tissue Highly vascularized Responsible for most types of movement Three types –Skeletal muscle tissue Found in skeletal muscle Voluntary –Cardiac muscle tissue Found in walls of heart Involuntary –Smooth muscle tissue Mainly in walls of hollow organs other than heart Involuntary

20. © 2013 Pearson Education, Inc. Nervous Tissue Main component of nervous system –Brain, spinal cord, nerves –Regulates and controls body functions Neurons –Specialized nerve cells that generate and conduct nerve impulses Neuroglia –Supporting cells that support, insulate, and protect neurons

21. © 2013 Pearson Education, Inc. Covering and Lining Membranes Composed of at least two primary tissue types –An epithelium bound to underlying connective tissue proper –Are simple organs Three types –Cutaneous membranes –Mucous membranes –Serous membranes

22. © 2013 Pearson Education, Inc. Cutaneous Membranes Skin Keratinized stratified squamous epithelium (epidermis) attached to a thick layer of connective tissue (dermis) Dry membrane

23. © 2013 Pearson Education, Inc. Mucous Membranes Mucosa indicates location not cell composition All called mucosae –Line body cavities open to the exterior (e.g., Digestive, respiratory, urogenital tracts) Moist membranes bathed by secretions (or urine) Epithelial sheet lies over layer of connective tissue called lamina propria May secrete mucus

24. © 2013 Pearson Education, Inc. Serous Membranes Serosae—found in closed ventral body cavity Simple squamous epithelium (mesothelium) resting on thin areolar connective tissue Parietal serosae line internal body cavity walls Visceral serosae cover internal organs Serous fluid between layers Moist membranes Pleurae, pericardium, peritoneum

25. © 2013 Pearson Education, Inc. Tissue Repair Necessary when barriers are penetrated Cells must divide and migrate Occurs in two major ways –Regeneration Same kind of tissue replaces destroyed tissue Original function restored –Fibrosis Connective tissue replaces destroyed tissue Original function lost

26. © 2013 Pearson Education, Inc. Steps in Tissue Repair: Step 1 Inflammation sets stage –Release of inflammatory chemicals –Dilation of blood vessels –Increase in vessel permeability –Clotting occurs

27. © 2013 Pearson Education, Inc. Steps in Tissue Repair: Step 2 Organization restores blood supply –The blood clot is replaced with granulation tissue –Epithelium begins to regenerate –Fibroblasts produce collagen fibers to bridge the gap –Debris is phagocytized

28. © 2013 Pearson Education, Inc. Steps in Tissue Repair: Step 3 Regeneration and fibrosis –The scab detaches –Fibrous tissue matures; epithelium thickens and begins to resemble adjacent tissue –Results in a fully regenerated epithelium with underlying scar tissue

29. © 2013 Pearson Education, Inc. Regenerative Capacity in Different Tissues Regenerate extremely well –Epithelial tissues, bone, areolar connective tissue, dense irregular connective tissue, blood-forming tissue Moderate regenerating capacity –Smooth muscle and dense regular connective tissue Virtually no functional regenerative capacity –Cardiac muscle and nervous tissue of brain and spinal cord –New research shows cell division does occur Efforts underway to coax them to regenerate better

30. © 2013 Pearson Education, Inc. Developmental Aspects Primary germ layers –Superficial to deep: ectoderm, mesoderm, and endoderm –Formed early in embryonic development –Specialize to form the four primary tissues Nerve tissue arises from ectoderm Muscle and connective tissues arise from mesoderm Epithelial tissues arise from all three germ layers

31. © 2013 Pearson Education, Inc. Aging Tissues Normally function well through youth and middle age if adequate diet, circulation, and infrequent wounds and infections Epithelia thin with increasing age so more easily breached Tissue repair less efficient Bone, muscle and nervous tissues begin to atrophy DNA mutations possible  increased cancer risk