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Tissues
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Epithelial Tissue Epithelial tissue: covers internal or external surfaces. Protection, secretion, absorption, excretion, sensory reception Characteristics: Cells close together Apical surface exposed to environment or hollow internal cavity Basement membrane attaches to underlying tissues Absence of blood vessels Continuous regeneration of surface cells
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Types of Epithelium Simple epithelium: thin, single layer of cells covering the basement membrane. Stratified epithelium: several layers of cells above the basement membrane Ex: areas exposed to mechanical and chemical stress, such as the mouth.
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Simple squamous epithelium: found in internal surfaces where absorption takes place, and there is little friction Ex: Lining of the heart, blood vessels, kidney tubules, air sacs of lungs.
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Simple cuboidal epithelium: in areas where increased amounts of secretion and absorption occur
Cells are larger and provide more room for organelles Ex: Pancreas, salivary glands, kidneys
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Simple columnar epithelium: provides more protection in areas of absorption and secretion
Examples: Stomach lining, intestinal tract
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Stratified squamous epithelium: thick protective lining found in areas of high mechanical stress
Ex: Lining of the mouth, esophagus, and anus, and skin
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Pseudostratified ciliated columnar epithelium: mixture of columnar and cuboidal cells that appears layered, but all cells touch the basement membrane Cilia are present to move mucus Ex: Lining of the nasal cavity, trachea, and bronchi
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Transitional epithelium: can stretch and recoil, so its appearance changes
Ex: Urinary bladder
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Glands: organs that produce secretions
Made of epithelial tissues Exocrine glands discharge secretions to the outside Ex: lining of the digestive tract, skin Endocrine glands secrete directly into tissue fluid or blood Ex: thyroid, pituitary, etc.
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Connective Tissue Connective tissues: a mixture of cells and protein fibers, distributed throughout the body, never exposed to the outside environment Have diverse functions: Support and protect other tissues Transport materials Storage of energy reserves as fat Defense against microorganisms
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Major cell types: Fibroblasts: large in size, produce protein fibers
Macrophages: phagocytize or “eat” damaged cells, bacteria, or viruses Mast cells: release defensive chemicals during an injury or infection
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Connective tissue fibers:
Collagen fibers: long, straight, and flexible, add strength Elastic fibers: give stretch and flexibility to connective tissues Reticular fibers: thin, form supportive networks
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Disorder Molecular Defect Signs and Symptoms Chondrodysplasia Collagen fibers are too wide and asymmetric Stunted growth; deformed joints Dystrophic epidermolysis bullosa Breakdown of collagen fibrils that attach skin layers to each other Stretchy, easily scarred skin, lax joints Hereditary osteoarthritis Substituted amino acid in collagen chain alters shape Painful joints Marfan syndrome Too little fibrillin, and elastic connective tissue protein Long limbs, sunken chest, lens dislocation, spindly fingers, weakened aorta Osteogenesis imperfecta type I Too few collagen triple helices Easily broken bones; deafness; blue sclera Stickler syndrome Short collagen chains Joint pain; degeneration of retina and fluid around it
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Loose Connective Tissues
Loose connective tissues: the “packing materials” of the body, filling in spaces to provide cushioning and support
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Areolar tissue: elastic and has an extensive blood supply
Collagen and elastin for strength Ex: Between the skin and muscle
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Adipose tissue: collection of fat cells
Provides padding, shock absorption, and thermal insulation Ex: Breasts, abdomen, beneath skin
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Reticular tissue: network of protein fibers that holds other cells in place, such as white and red blood cells Ex: Spleen, liver, bone marrow, lymph nodes
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Dense connective tissues: consist mostly of collagen fibers, with little blood supply
Found in tendons and ligaments
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Cartilage Cartilage: rigid connective tissue that provides structural framework for various structures Chondrocytes (cartilage cells) are found within small fluid filled pockets called lacunae. No blood supply
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Hyaline cartilage: the most common, providing stiff and flexible support
Matrix is made of densely packed collagen fibers Ex: Respiratory tract, connecting ribs to sternum, and covering the ends of bones
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Elastic cartilage: extremely resilient; able to endure distortions while still maintaining original shape Contains many more elastic fibers than hyaline cartilage Ex: External ear
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Fibrocartilage: has very little ground substance, with densely packed collagen fibers
Tough, durable, and resistant to compression Ex: Spinal cord, knee joint, between bones of pelvis
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Bone: most rigid connective tissue, with mineral salts and collagen within the matrix
Supports the body, protects, forms muscle attachments, blood cell formation
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Fluid Connective Tissues
Blood and lymph are the only two types of fluid connective tissues Transport oxygen, carbon dioxide, nutrients, and wastes throughout the body
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Nervous Tissue Nervous tissue: specialized for the conduction of electrical impulses, found in brain and spinal cord Neurons conduct nervous impulses Neuroglia support and nourish neurons
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Muscle Tissue Muscle tissue: made of arrangements of protein filaments that can contract and generate force
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Skeletal muscle: attached to bone, cells are long and cylindrical and have many nuclei
Controlled voluntarily The repeating groups of muscle filaments create bands called striations
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Cardiac muscle: found only in the heart, consists of branching fibers, cells have a single nucleus
Cells are connected at specialized attachment sites called intercalated discs, and appear striated Involuntary movement
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Smooth muscle: tissue is made of cells smaller and more slender than skeletal muscle, found in the walls of internal organs, blood vessels, and bladder Striations are not present
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Tissue Membranes Mucous membranes: line cavities that open to the outside. Have goblet cells that secrete mucous Ex: oral, nasal cavities, digestive, respiratory, urinary, and reproductive systems
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Cutaneous membranes: are thick, dry, and relatively waterproof.
Serous membranes: line internal body cavities, secrete serous fluid to reduce friction Ex: Lungs Cutaneous membranes: are thick, dry, and relatively waterproof. Ex: Skin
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Synovial membranes: line joints and secrete synovial fluid that reduces friction
Ex: The bones of the knee joint
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