tissues – cells working together dr. anderson gcit
TRANSCRIPT
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Tissues – Cells Working Together
Dr. Anderson GCIT
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Tissues
• Collections of similar cells that work together in an organ to perform a very specific function in that organ for the organism
• Four basic tissue types– Epithelial– Connective– Movement– Control
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Epithelial Tissue
• Sheets of cells that cover the body or line body cavities– Covering – lining epithelium• Skin• Lines open cavities of digestive, respiratory,
cardiovascular and reproductive systems
– Glandular epithelium • Makes up the various glands (secretory organs) of the
body
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Functions of Epithelia• Protection
– Protects stomach from digesting itself by secreting buffering compounds
• Absorption– Cells can take in substances via endocytosis/diffusion/active
transport• Filtration
– Certain substances are preferentially removed/added to blood• Excretion
– Wastes exit via exocytosis, diffusion• Secretion
– Cells products (proteins) are exported via exocytosis, diffusion• Sensory Perception
– Cells on the surface contain nerve endings that respond to stimulus (heat, pain, pressure, etc.)
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Characteristics of Epithelia• Polarity– All epithelial cells have two distinct “ends”
• Apical Surface – free surface exposed to exterior or lumen of a body cavity
• Basal Surface – bordered by the basal lamina, a non-cellular adhesive sheet to which epithelial cells are attached that acts as a filter between the epithelia and underlying connective tissue
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Polarity of Epithelial Cells
Apical surface
Basal surface
Basal lamina
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Epithelial Connections
• Tight Junctions– Prevent the movement of
materials between cells
• Desmosomes– Provide support and
tensile strength to tissues
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Epithelial Support
• All epithelial cells are supported by a thin layer of connective tissue called the reticular lamina (just deep to the basal lamina)
• The basal lamina and the reticular lamina form the basement membrane
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Communication and Transport
• Epithelial cells are innervated (nerves penetrate into the tissue)
• However, epithelial cells are NOT perfused directly with blood vessels– Materials must be transported to and from blood
in vessels lying under the basement membrane
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Epithelial Regeneration• Cells are frequently lost due to abrasion,
wounds, etc.
• Epithelial cells have the capacity to regenerate the lost tissue via mitosis
• How is this adaptive to the organism?
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Classification of Epithelia
• Morphology– Squamous– Cuboidal– Columnar
• Arrangement– Simple – Stratified
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Epithelial Morphology
• Squamous – flat, much shorter than wide
• Cuboidal – height and width are equidistant
• Columnar – Height much greater than width
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Stratified Epithelium
• Contain two or more cell layers• Major role: Protection• E.G - skin
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Glandular Epithelia• Tissues that secrete substances (usually
proteins) made by the cells in the tissue
• Endocrine glands – no ducts– Produce hormones, proteins, steroids, etc.
• Exocrine Glands – secrete onto body surfaces or into cavities– Mucus, sweat, oil, pancreas, salivary,
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Exocrine Glands• Unicellular – mucus glands and goblet cells
• Multicellular - 3 parts– Duct - for export– Secretory unit – makes product to be secreted– Fibrous capsule – connective tissue, blood vessels
and nerves; may divide the gland into lobes
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Mode of Secretion
• Cells metabolize the chemical to be released
• Cells release this chemical into the duct via exocytosis (or cell lysis)
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Tubular – if secretory cells are present in the duct
Alveolar – if secretory cells are in the pocket of tissue
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Connective Tissue
• Function1. Binding and support (Bone, cartilage, fascia)2. Protection – Osteocytes (Bone)3. Insulation – Adipose Tissue (fat)4. Transportation ( Blood)
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Common Characteristics
• Common embryologic origin (mesenchyme)• Degrees of vascularity• Consists of living cells and an extracellular
matrix– Non-living cell-derived substances– Made of ground substance and fibers
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Ground Substance
• Made of interstitial fluid, cell adhesion proteins, proteoglycans
• Can range from very little to great viscosity– Serves to control diffusion
rates into and out of adjoining cells (between blood vessels and epithelium)
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Fibers
• Collagen – provide tensile strength
• Elastic Fibers - (elastin) can stretch, allowing flexibility
• Reticular Fibers – collagen-based fibers that support small blood vessels and organs
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Cells
• Relative to what organ is being examined, each has a different job
• Osteocytes
• Chondrocyte
• Hemocyte
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Types of Connective Tissue
• Loose Connective Tissue– Areolar– Adipose
• Dense Connective Tissue– Regular– Irregular– Elastic
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Areolar Connective Tissue
• Very loosely arranged fibers in matrix– Provides a reservoir
for water and salts for surrounding tissues
– Very viscous– Damage to this area
or nearby tissues results in water retention – an edema
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Adipose Connective Tissue
• Fat tissue – composed of adipocytes
• Almost the entire volume of the cell is taken up by stored lipids
• Stores energy, but subcutaneous fat (under the skin) acts as a – Shock absorber– Insulator
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Dense Regular Connective Tissue• Contains closely packed collagen
fibers that run parallel to the direction of pull providing great tensile strength– Fibroblasts are interspersed within
this tissue to make new collagen fibers
• Found in:– Tendons – connect muscle to bone– Aponeuroses – connect muscles to
muscles– Fascia – covering that surrounds
individual muscles
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Dense Irregular Connective Tissue
• Also contains bundles of collagen fibers, but are arranged irregularly
• Forms fibrous coverings (capsules) that surround some organs and joints, e.g. kidneys, bones, cartilage, etc.
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Cartilage• Combines flexibility and strength for
support and shock absorption
• Not vascular and not innervated
• Hyline cartilage• Elastic Cartilage• Fibrous Cartilage
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Hyaline Cartilage
• Hyaline (glassy) cartilage
– Provides firm support to the ends of long bones (cushioning)
– Connects bones and provides structure• Bridge of nose• Connects ribs to sternum• Predecessor to bone in
human embryos
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Elastic Cartilage• More flexible and less rigid than hyaline
cartilage• Examples– Ear– Epiglottis
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Fibrocartilage
• Able to resist heavy compressive forces in areas of the body under the most strain– Cartilage between the
femur and tibia/fibula in the knee
– Intervertebral discs
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Bone
• Primarily provides support to the body, but also houses tissues that produce fat and blood cells (marrow)
• Bone is well supplied by blood vessels (bones are living tissue)
• Great diversity of shapes and functions
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Blood
• Blood cells (WBC, RBC, platelets) surrounded by a liquid matrix (plasma)
• Transports materials to all of the cells in the body– O2, CO2, food, wastes,
hormones, etc.• Provides the second line
of defense against pathogens
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Nervous Tissue
• Comprises the brain, spinal cord, and peripheral nerves
• Major cell type– Neurons – respond
to stimuli and transmit impulses
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Muscle Tissue• Responsible for most types
of movement– Internal movement as well
as external
• Three types– Skeletal – under voluntary
control, moves skeleton– Smooth – under
involuntary control, moves substances into, out of, or through the body
– Cardiac – heart muscle, under involuntary control (largely)