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• There are 4 types of epithelial membranes: 1. Serous Membranes • Line body cavities that do not open to the outside • Reduce friction • Inner lining of thorax and abdomen • Cover organs of thorax Types of and abdomen • Secrete serous fluid Membranes 2. Mucous Membranes • Line tubes and organs that open to outside world • Lining of mouth, nose, throat, etc. • Secrete mucus 3. Cutaneous Membranes • Covers body • Skin 4. Synovial Membranes • Composed entirely of connective tissue • Lines joints -Connective Tissue -Muscle Tissue -Nervous Tissue Most abundant tissue in body Composed of cells, fibers, and extracellular matrices Cells usually divide Connective Tissue (CT) Varying degrees of vascularity Many Functions: Protection, defense and repair Insulation (fat storage) Produce blood cells Transportation Binding, support and packaging Fibroblasts Most common Star-shaped, fixed cell Secretes protein into matrix producing fibers. Connective Tissue Cells Macrophages Wandering cells Act as scavengers (phagocytosis) in injury/infection Mast Cells Fixed cells Release heparin (anticoagulant), and histamine (promotes inflammation). Fibers (produced by fibroblasts) Collagenous Connective Tissue Fibers (Collagenous fibers) Thick pieces of protein (collagen). Inelastic. Hold structures together. High tensile strength. Ligaments, tendons. Lots of collagenous fibers = Dense CT (white fibers) Few collagenous fibers = Loose CT Elastic Fibers Connective Tissue (Elastic fibers) Composed of bundles of elastin (elastic protein). Branching fibers Not a lot of tensile strength but very flexible Appear yellow in color. Found in vocal cords, air passages of respiratory system. Reticular Fibers Connective Tissue (Reticular fibers) •Very thin collagenous fibers that branch to form a supporting network. CT Matrix CT cells not adjacent to each other, but have intercellular material (matrix) between them Matrix is made of cells and consists of gel-like fluids and protein fibers CT The general categories of connective tissue are: CT Proper CT Loose CT Adipose tissue Reticular CT Dense CT Elastic CT Specialized CT Cartilage Bone Blood Loose CT: Mainly fibroblasts Fluid to gel-like matrix Collagenous & elastic fibers Bind skin to structures Beneath most epithelia Blood vessels nourish it Between muscles Collagenous fiber Fibroblast Ground substance Elastic fiber (a) (b) Loose CT (Areolar Tissue) • Not very well organized. • It contains fibroblasts, matrix, some fibers scattered about. • It functions to support underlying structures, and helps keep skin bound to the body. • Loose connective tissue is found in the dermis and subcutaneous layers of the skin as well as surrounding muscles. • Sometimes it is called fascia. Adipose CT – made of cells (adipocytes) that contain triglycerides. The lipid is used to store energy to be used by the body Adipose tissue is also found around some organs and joints and forms a cushion for shock absorption. Adipose tissue also insulates the body. Beneath skin, behind eyeballs, around kidneys and heart Cytsol Fat droplet Cell membrane Nucleus (a) (b) Lipid Nucleus of adipocyte Here is a close up of adipose tissue. You can see the large-filled adipocytes. Adipocytes Here’s another view of adipose tissue. Reticular connective tissue consists of a thin supportive network of reticular fibers. It supports internal organ walls The walls of the liver, spleen, and lymphatic organs. CT: Reticular CT Collagenous fibers White blood cell Fibroblast (a) (b) Reticular connective tissue is web-like and forms a supportive network. Dense (fibrous) CT contains thick collagenous fibers packed together. It is found in ligaments and tendons (which have a high tensile strength). Dermis of the skin. Binds body parts together Dense connective tissue has a poor blood supply It also contains some elastic fibers, few fibroblasts. Fibroblasts Collagenous fibers (a) (b) Dense regular CT Dense irregular CT • Fibers are parallel and dark-staining • Fibers are neither parallel nor dark-staining Elastic connective tissue contains many more elastic fibers than collagenous fibers. Contains fibroblasts It is found in attachments between bones like the vertebrae, and in the walls of some hollow internal organs, heart, airways, large arteries. Collagenous fibers Fibroblast Elastic fibers (a) (b) Elastic CT Osseous tissue (bone) has a solid matrix Functions to support, protect, form blood cells Attachment point for muscles Osteocytes (bone cells) are located in lacunae Osteon Lamella Central canal Osteocyte in lacuna Canaliculi (a) (b) Osteocyte Nucleus Cell process in canaliculus • Bone = most rigid CT; hardness comes from mineral salts such as calcium phosphate and calcium carbonate. • It is highly organized into units called osteons. • The primary cell of bone is the osteocyte. • Canaliculi are the canals between the lacunae (small spaces) • Lamellae is the thin plate of bone matrix (rings) Cartilage is rigid and strong, so it can provide support and protection. It also forms a structural model for developing bones. Specialized CT: Cartilage Cartilage consists of cells called chondrocytes Cartilage has no direct blood supply, so nutrients must enter by diffusion. • Hyaline cartilage • Cartilage • Rigid matrix • Chondrocytes in lacunae • Poor blood supply • Three (3) types: • Hyaline Cartilage • Elastic Cartilage • Fibrocartilage • Most abundant • Ends of bones • Nose, respiratory passages • Embryonic skeleton • Elastic cartilage • Flexible • External ear, larynx • Fibrocartilage • Very tough • Shock absorber • Intervertebral discs • Pads of knee and pelvic girdle Nutrients diffuse into cartilage The tissue needs water to help move these substances in Specialized CT: Cartilage As humans age cartilage tends to “dry up” or become dehydrated which lends to degeneration of the tissue. The cartilage cells or chondrocytes also do not divide very frequently, which contributes to poor healing. Chondrocyte Lacunae • Hyaline cartilage has chondrocytes surrounded by lacunae, as shown above. • It also has a glassy-appearing matrix. • It is found at the ends of bones, the soft part of the nose, larynx and trachea. • Hyaline cartilage serves as a model for bone growth. Another picture of hyaline cartilage. Elastic fibers • Elastic cartilage also has the characteristic chondrocyte in lacuna appearance, along with elastic fibers. • This cartilage is found in the larynx and the ear. • Fibrocartilage is characterized by rows of chondrocytes (in lacunae). • It is a very strong cartilage, and is found in the intervertebral discs. Hyaline cartilage Nucleus Lacuna Chondrocyte Extracellular matrix (a) (b) Elastic cartilage Elastic fibers Nucleus Lacuna Chondrocyte Extracellular matrix (a) (b) Fibrocartilage Lacuna Chondrocyte Nucleus Collagenous fiber Extracellular matrix (a) (b) • Blood is also considered a connective tissue. It consists of cells suspended in a matrix of fluid called plasma. (RBCs, WBCs, platelets) • It transports gases such as oxygen and carbon dioxide, and functions in clotting and immunity. White blood cell Red blood cells Plasma (extracellular matrix of blood) Platelets (a) (b) Muscle Tissue • Skeletal muscle • General characteristics: • Muscle cells also called muscle fibers • Contractile • Three (3) types: • Skeletal muscle • Smooth muscle • Cardiac muscle • Attached to bones • Striated • Voluntary • Smooth muscle • Walls of organs • Skin • Walls of blood vessels • Involuntary • Non-striated • Cardiac muscle • Heart wall • Involuntary • Striated • Intercalated discs • Skeletal muscle is striated (caused by the density of overlapping protein filaments called actin and myosin). • Voluntary – we can control this • It moves the muscles • Located on muscles usually attached to bones • Multinucleate – contain multiple nuclei per cell • Cardiac muscle is also striated, but has a unique structure called an intercalated disc. • The disks are special intercellular junctions that allow electrochemical impulses to be conveyed across the tissue. • Found only in heart, and its main function is to allow the heart to beat. • Involuntary – because we cannot control this • Uninucleate – contain only one nucleus per cell Skeletal Muscle Striations Nuclei Portion of a muscle fiber (a) Cardiac Muscle (b) Striations Nucleus Intercalated disc (a) (b) Cytoplasm Nucleus (a) (b) • Smooth muscle is involuntary – we cannot control this • It is non-striated because the myofilaments are not as dense as in cardiac and skeletal muscle. • Smooth muscle is found in organs such as in the gastrointestinal system and the arteries. • Smooth muscle function is to regulate all internal organs’ movements, like stomach, liver, kidneys. • Uninucleate – contain only one nucleus per cell Nervous tissue consists of nervous system cells called neurons, and supportive cells called glia (they bind & support nervous tissue). Nervous tissue function is sensory reception and conduction of nerve impulses Nervous Tissue Found in brain, spinal cord, peripheral nerves Cellular process Cytoplasm Nucleus Cell membrane Neuroglial cells (a) (b) Neuron Glial cell • Nervous tissue contains neurons and glial cells. • Neuron has a main cell body called a soma • Neuron has dendrites that receive messages and a long axon that sends messages