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Groups of cells that have specialized structural and functional roles
Four major types
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Epithelial
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Connective
Muscle
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Nervous

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Covers organs
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Forms the inner lining of body cavities
Lines hollow organs
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Always has a free surface, one that is exposed to the outside or to an open space internally
Basement Membrane: nonliving layer of connective tissue that anchors the tissue

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Lack blood vessels
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Nutrients diffuse from underlying connective tissues
Cell readily divide
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Injuries heal rapidly
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Skin cells, stomach and intestine lining are continually damaged and replaced
Tightly Packed with little intercellular material
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Effective barriers: skin and mouth
Secretion, absorption, excretion, and sensory reception

 Simple Squamous Epithelium
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Single thin layer of flattened cells
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Nuclei are broad and thin
Common site of diffusion and filtration
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Line air sacs, capillaries, blood and lymph vessels
Easily damaged

 Simple Cuboidal Epithelium
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Single layer of cubed shaped cells
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Centrally located spherical nuclei
Cover the ovaries and lines most kidney tubules
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Kidney functions in secretion and absorption
Glands of certain ducts: thyroid, pancreas, and liver
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Secretes glandular products

 Simple Columnar Epithelium
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Elongated
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Think tissue  protects underlying tissue
Single layer of cells
Nuclei located near the basement membrane
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Line the uterus and most digestive organs
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Stomach and small intestines
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Secrete digestive fluids and absorb nutrients
Microvilli: cylindrical projections from cell membrane
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Increase surface area  for increased absorption

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Appear stratified or layered, but are not
Possess cilia, which move constantly
Goblet cells scattered throughout secrete mucus
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Cilia sweeps away
Line passage of respiratory system
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Mucus cover linings trap dust and microorganisms
Cilia move the mucus and its captured particles upward and out

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Layered cells  thick tissue
Cells divide in deep layers and newer cells push older one outward, where they flatten
Outer skin layer, epidermis
As they age, accumulate the protein keratin, then harden and die
 tough, hard, waterproof covering
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Blocks foreign invaders
Line the mouth, throat, vagina, and anal canal
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Not keratinized

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Two to three layers of cuboidal cells that form lining of lumen
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More protection than single layer
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Lines the larger ducts of mammary glands, sweat glands, salivary glands, and pancreas
Lining of developing ovary follicles and seminiferous tubules
 female and male respectively

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Several layers of cells
Superficial cells are elongated
Basal layer are cubed shaped
Male urethra
Parts of the pharynx

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Specialized to change in response to tension
Inner lining of urinary bladder
Lines the ureters and part of the urethra
Provides an expandable lining

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Specialized to produce and secrete substances into ducts or into body fluids
Found in glands
Exocrine glands: glands that secrete their products into ducts that open onto some internal or external surface
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Merocrine Glands: watery, protein rich fluid
Apocrine Glands: lose small portions of their glandular cell bodies during secretion
Holocrine Glands: the entire cell lyses during secretion
Endocrine: secrete products into tissue fluid or blood

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Binds structures
Provides support and protection
Serves as a framework
Fills spaces
Store fat
Produce blood cells
Protect against infection
Help repair tissue damage

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Farther apart than epithelial
Have an abundance of intercellular material between them, matrix
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Fibers and ground substance
Can usually divide
Varying degrees of vascularity
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Especially bone and cartilage
Some are flexible
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Adipose

 Fixed: present in stable numbers
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Fibroblasts: most common type
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Large star shaped
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Produce fibers by secreting proteins into the matrix
Mast cells: large widely distributed
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Near blood vessels
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Release heparin, prevent blood clotting
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Release histamine: promotes some reaction of inflammation and allergies

 Wandering: temporarily appear in tissue
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Macrophages: originate as white blood cells
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Specialized for phagocytosis
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Function as scavengers and defensive cells that clears tissues of foreign particles

Produced by fibroblasts
 Collagenous Fibers: thick threads of protein collagen
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Grouped in long, parallel bundles
Slightly elastic and flexible
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Great tensile strength
Components of:
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Ligaments: bone to bone
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Tendons: muscle to bone
White Fibers

 Elastic Fibers: elastin protein
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Branch, forming complex networks
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Weaker than collagenous fibers
Stretch easier and resume original shape
Common In: Vocal Cords
Yellow Fibers
 Reticular Fibers
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Very thin collagenous fibers
Highly branched and form delicate supporting networks

 Areolar Tissues: forms delicate, thin membranes
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Cells located some distance apart and separated by a gel-like matrix containing collagenous and elastic fibers
Binds the skin to the underlying organs and fills space between muscles
Beneath most epithelium

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Fat
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Specialized form of connective tissue that develops when certain cells store fat in droplets within the cytoplasm and enlarge
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Cushions joints and some organs
Insulates for heat
Stores energy
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 beneath the skin around kidneys abdominal membrane around certain joints between muscles behind eyeballs surface of the heart

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Many closely packed, thick, collagenous fibers
Fine network of elastic fibers
Relatively few cells, mostly fibroblasts
Very strong
Poor blood supply  slow repair
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Part of tendons and ligaments
Protective white layer of eyeball
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Deeper skin layers

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Chondrocytes: cartilage cells
Perichondrium: protective tissue enclosing cartilaginous structures
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Supplies nutrients
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Lack of direct blood supply  slow healing
Rigid connective tissue
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Support, framework and attachments
Protects underlying tissues
Structural models for developing bones

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Hyaline Cartilage: most common
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Very fine collagenous fibers in a matrix
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White glass
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Ends of bones in joints, soft part of nose, supporting rings of respiratory passage

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Elastic Cartilage: dense network of elastic fibers
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More elastic and flexible
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Ears & larynx
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Fibrocartilage
 very tough tissue, many collagenous fibers
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Shock absorber: knees and pelvic girdle
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Pads of intervertebral disks between vertebrae

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Most rigid connective tissue
Hardness: mineral salts between cells
 calcium phosphate and calcium carbonate
Great amount of collagen
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Supports body structures
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Protects cranial and thoracic cavities
Attachment for muscle
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Contain red marrow
 forms WBC
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Stores and releases inorganic chemicals,
Ca and P

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Osteocytes: bone cells
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Located in the lacuanae
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Forms concentric circles
Osteon: layers of osteocytes around the osteonic canal
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Contains blood vessels
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Material can move rapidly between blood vessels and bone cells
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Heals faster than cartilage

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Transports materials between interior body cells and the external environment
Helps maintain homeostasis
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Composed of formed elements suspended in a fluid matrix
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Fluid Matrix: blood plasma
Formed Elements: RBC, WBC, platelets
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Forms in red marrow in long bones

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Contractile
Muscle Fibers: elongated cells that can shorten
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Move body parts
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As they contract, fibers pull at their attached ends
3 Types
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Skeletal Muscle Tissue
Smooth Muscle Tissue
Cardiac Muscle Tissue

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Muscle is attached to bone
Voluntary: consciously controlled
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Contract when stimulated by nervous impulse then relax
Moves head, trunk, and limbs
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Facial Expressions, write, talk, sing, chew, swallow, and breathe

 Appearance
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Long thread like fibers
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Striations: alternating light and dark cross-markings
Each cell has many nuclei just beneath the cell membrane

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Smooth  cells lack striations
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Shorter than skeletal cells
Spindle-shaped
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Single, centrally located nucleus
Comprises the walls of hollow internal organs
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Stomach, intestines, urinary bladder, uterus, and blood vessels

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Involuntary: cannot be consciously stimulated
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Moves food through digestive tract
Constricts blood vessels
Empties urinary bladder

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Only in the heart
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Bulk of the heart
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Pumps blood through the heart chambers into blood vessels
Cells: striated and joined end to end
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Muscle fibers are branched
Connected in complex networks
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Single nuclei
Intercalated disk: where it touches another cell
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Specialized intercellular junction
Controlled involuntarily

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Brain, spinal cord, and peripheral nerves
Neurons: basic cells
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Send nerve impulses along cytoplasmic extensions, or nerve fibers
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Single to: neutrons, muscles, or glands
Coordinated, regulate, and integrate many body functions

 Neuroglial Cells
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Support and bind the components of nervous tissue
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Carry on phagocytosis
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Supply nutrients to neurons  connecting with blood vessels