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A tissue is a group of cells
Common embryonic origin
Function together to carry out specialized activities
Hard (bone), semisolid (fat), or liquid (blood) Histology is the science that deals with the
study of tissues. Pathologist specialized in laboratory studies
of cells and tissue for diagnoses
Epithelial
▪ Covers body surfaces and lines hollow organs, body cavities, duct, and forms glands
Connective
▪ Protects, supports, and binds organs.
▪ Stores energy as fat, provides immunity
Muscular
▪ Generates the physical force needed to make body structures move and generate body heat
Nervous
▪ Detect changes in body and responds by generating nerve impulses
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Contact points between the plasma membranes of tissue cells
5 most common types:
▪ Tight junctions
▪ Adherens junctions
▪ Desmosomes
▪ Hemidesmosomes
▪ Gap junctions
Web-like strands of transmembrane proteins
Fuse cells together
Seal off passageways between adjacent cells
▪ Common in epithelial tissues of the stomach, intestines, and urinary bladder
▪ Help to retard the passage of substances between cells and leaking into the blood or surrounding tissues
Dense layer of proteins called plaque
Resist separation of cells during contractile activities
Located inside of the plasma membrane attached to both membrane proteins and microfilaments of the cytoskeleton
Transmembrane glycoproteins called cadherins insert into the plaque and join cells
In epithelial cells, adhesion belts encircle the cell
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Contain plaque and cadherins that extends into the intercellular space to attach adjacent cells together Desmosome plaque attaches
to intermediate filaments that contain protein keratin
Prevent epidermal cells from separating under tension and cardiac muscles cells from pulling apart during contraction
Resemble half of a desmosome Do not link adjacent cells
but anchor cells to the basement membrane
Contains transmembrane glycoprotein integrin
Integrins attach to intermediate filaments and the protein laminin present in the basement membrane
Connect neighboring cells via tiny fluid-filled tunnels called connexons Contain membrane proteins
called connexins Plasma membranes of gap
junctions are separated by a very narrow intercellular gap (space) ▪ Communication of cells
within a tissue ▪ Ions, nutrients, waste,
chemical and electrical signals travel through the connexons from one cell to another
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Epithelial tissue consists of cells arranged in continuous sheets, in either single or multiple layers Closely packed and held tightly together
Covering and lining of the body
Free surface
3 major functions: Selective barrier that regulates the movement of materials in
and out of the body
Secretory surfaces that release products onto the free surface
Protective surfaces against the environment
Surfaces of epithelial cells differ in structure and have specialized functions
Apical (free) surface
▪ Faces the body surface, body cavity, lumen, or duct
Lateral surfaces
▪ Faces adjacent cells
Basal surface
▪ Opposite of apical layer and adhere to extracellular materials
Basement membrane
Thin double extracellular layer that serves as the point of attachment and support for overlying epithelial tissue
Basal lamina
▪ Closer to and secreted by the epithelial cells
▪ Contains laminin, collagen, glycoproteins, and proteoglycans
Reticular lamina
▪ Closer to the underlying connective tissue
▪ Contains collagen secreted by the connective tissue cells
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Own nerve supply
Avascular or lacks its own blood supply
Blood vessels in the connective tissue bring in nutrients and eliminate waste
High rate of cell division for renew and repair
Numerous roles in the body (i.e. protection and filtration)
Covering and lining epithelium ▪ Outer covering of skin and some internal organs
Glandular epithelium ▪ Secreting portion of glands (thyroid, adrenal, and sweat
glands)
Normally classified according to: Arrangement of cells into layers
Shapes of cells
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Arrangement of cells in layers Consist of one or more layers depending on function
Simple epithelium
▪ Single layer of cells that function in diffusion, osmosis, filtration, secretion, or absorption
Pseudostratified epithelium
▪ Appear to have multiple layers because cell nuclei at different levels
▪ All cells do not reach the apical surface
Stratified epithelium
▪ Two or more layers of cells that protect underlying tissues in areas of wear and tear
Cells vary in shape depending on their function
Squamous
▪ Thin cells, arranged like floor tiles
▪ Allows for rapid passage of substances
Cuboidal
▪ As tall as they are wide, shaped like cubes or hexagons
▪ May have microvilli
▪ Function in secretion or absorption
Columnar
▪ Much taller than they are wide, like columns
▪ May have cilia or microvilli
▪ Specialized function for secretion and absorption
Transitional
▪ Cells change shape, transition for flat to cuboidal
▪ Organs such as urinary bladder stretch to larger size and collapse to a smaller size
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Simple squamous epithelium
Simple cuboidal epithelium
Simple columnar epithelium (nonciliated and ciliated)
Pseudostratified columnar epithelium (nonciliated and cilated)
Single layer of cells that resembles a tiled floor on the surface
▪ Nucleus is centrally located and appears flattened oval or sphere
Found at sites for filtration or diffusion
Endothelium
The type of simple squamous that lines the heart, blood vessels, and lymphatic vessels
Mesothelium
The type of epithelial layer of serous membranes such as the pericardium, pleura, or peritoneum
Unlike other epithelial tissue, Both are derived from embryonic mesoderm
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Cuboidal shaped cells
Cell nuclei round and centrally located
Found in thyroid gland and kidneys
Functions in secretion and absorption
Column
shaped cells Oval nuclei at
near base Nonciliated
and ciliated
Contains columnar
cells with microvilli at their apical surface and goblet cells
▪ Secreted mucus serves as lubricant for the lining of digestive, respiratory, reproductive and urinary tracts
▪ Also prevents the destruction of the stomach lining by acidic gastric juices
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Columnar epithelial cells with cilia at the apical surface ▪ In respiratory tract,
goblet cells are interspersed among ciliated columnar epithelia
▪ Secreted mucus on the surface traps inhaled foreign particles. Beating cilia moves particles to the throat for removal by coughing, swallowing, or sneezing
▪ Cilia also moves oocytes to the uterine tubes
Pseudostratified columnar epithelium Appears to have
several layers due to nuclei are various depths
All cells are attached to the basement membrane in a single layer but some do not extend to the apical surface
Ciliated cells secrete mucus and bear cilia
Nonciliated cells lack cilia and goblet cells
Two or more layers of cells Specific kind of stratified epithelium depends
on the shape of cells in the apical layer
Stratified squamous epithelium
Stratified cuboidal epithelium
Stratified columunar epithelium
Transitional epithelium
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Several layers of cells that are flat in the apical layer ▪ New cells are pushed up toward apical layer
▪ As cells move further from the blood supply they dehydrate, harden, and die
Keratinized form contain the fibrous protein keratin ▪ Found in superficial layers of the skin
Nonkeratinized form does not contain keratin ▪ Found in mouth and esophagus
Fairly rare type of epithelium
Apical layers are cuboidal
Functions in protection
Also very uncommon
Columnar cells in apical layer only
Basal layers has shorten, irregular shaped cells
Functions in protection and secretion
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Found only in the urinary system
Variable appearance
In relaxed state, cells appear cuboidal
Upon stretching, cells become flattened and appear squamous
Ideal for hollow structure subjected to expansion
Secretions, called hormones, diffuse directly into the bloodstream
Function in maintaining homeostasis
Secrete products into ducts that empty onto the surfaces of epithelium
Skin surface or lumen of a hollow organ
Secretions of the exocrine gland include mucus, sweat, oil, earwax, saliva, and digestive enzymes
Examples of glands include sudoriferous (sweat) glands
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Most abundant and widely distributed tissues in the body
Numerous functions
Binds tissues together
Supports and strengthen tissue
Protects and insulates internal organs
Compartmentalize and transport
Energy reserves and immune responses
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Extracellular matrix is the material located between the cells
Consist of protein fibers and ground substance
Connective tissue is highly vascular Supplied with nerves
Exception is cartilage and tendon. Both have little or no blood supply and no nerves
Fibroblasts
Secrete fibers and components of ground substance Adipocytes (fat cells)
Store triglycerides (fat) Mast cells
Produce histamine White blood cells
Immune response
Neutrophil and Eosinophils Macrophages
Engulf bacteria and cellular debris by phagocytosis Plasma cells
Secrete antibodies
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Ground substance Between cells and fibers
▪ Fluid, semifluid, gelatinous, or calcified
Functions to support and bind cells, store water, and allow exchange between blood and cells
Complex combination of proteins and polysaccharides
Fibers Collagen fibers
Elastic fibers
Reticular fibers
Embryonic connective tissue Mesenchyme and mucous connective tissue
Mature connective tissue Loose connective tissue
▪ Areolar, adipose, and reticular
Dense connective tissue ▪ Dense regular, dense irregular, and elastic
Cartilage ▪ Hyaline, fibrocartilage, and elastic cartilage
Bone tissue
Liquid connective tissue ▪ Blood and lymph
Mesenchyme
▪ Gives rise to all other connective tissues
Mucous (Wharton’s Jelly)
▪ Found in umbilical cord of the fetus
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Most widely distributed in the body
Contains several types of cells and all three fibers
Contains adipocytes
Good for insulation and energy reserves
White (common) and brown adipose tissue
Fine interlacing reticular fibers and cells
Forms the stroma of liver, spleen, and lymph nodes
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Dense connective tissue
Contains numerous, thicker, and denser fibers
Packed closely with fewer cells than loose connective tissue
Dense regular connective tissue
Bundles of collagen fibers are regularly arranged in parallel patterns for strength
Tendons and most ligaments
Collagen fibers are usually irregularly arranged
Found where pulling forces are exerted in many directions
Dermis of skin and heart
Contain branching elastic fibers
Strong and can recoil to original shape after stretching
Lung tissue and arteries
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Cartilage is a dense network of collagen fibers and elastic fibers firmly embedded in chondroitin sulfate Chrondrocytes ▪ Cartilage cells found in the spaces called lucunae
Pericondrium ▪ Covering of dense irregular connective tissue that
surrounds the cartilage ▪ Two layers: outer fibrous layer and inner cellular layer
No blood vessels or nerves, except pericondrium
Most abundant cartilage in the body
Surrounding by perichondrium (some exceptions like articular cartilage)
Provide flexibility and support. Reduces friction
Chondrocytes are scattered among bundles of collagen fibers within the extracellular matrix
Lack a perichondrium
Strongest type of cartilage
Found in intervertebral disc (between vertebrae)
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Chondrocytes are located within a threadlike network of elastic fibers
Perichondrium is present
Provides strength and elasticity
Cartilage grows slowly When injured or inflamed, repairs is slow due
to its avascular nature. Two patterns of cartilage growth:
Interstitial growth
▪ Growth from within the tissue
Appositional growth
▪ Growth at the outer surface of the tissue
Bones are organs composed of several different connective tissues: bone (osseous) tissue, periosteum, and endosteum.
Compact or spongy Osteon or haversian system
Spongy bone lacks osteons. They have columns called trabeculae
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Blood tissue
Connective tissue with liquid extracellular matrix called blood plasma
Lymph
Mucous membranes Lines a body cavity that
opens directly to the exterior
Epithelial layer is important for the body’s defense against pathogens
Connective tissue layer is areolar connective tissue and is called lamina propria
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Serous membranes or serosa
Lines a body cavity that does not open directly to the exterior. Also covers the organs that lie within the cavity
Consist of areolar connective tissue covered by mesothelium (simple squamous epithelium) that secrete a serous fluid for lubrication
Synovial membranes
Lines joints and contains connective tissue but not epithelium
Consists of elongated cells called muscle fibers or myocytes
Cells use ATP to generate force
Several functions of muscle tissue
Classified into 3 types: skeletal, cardiac, and smooth muscular tissue
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Attached to bones of the skeleton
Have striations
Voluntary movement or contractions by conscious control
Vary in length (up to 40 cm) and are roughly cylindrical in shape
Cardiac muscle tissue Have striations
Involuntary movement or contraction is not consciously controlled
Intercalated disc unique to cardiac muscle tissue
Walls of hollow internal structures
▪ Blood vessels, airways of lungs, stomach, and intestines
Nonstriated
Usually involuntary control
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Consists of two principle types of cells
Neurons or nerve cells
Neuroglia
Neurons and muscle fibers Exhibit electrical excitability
The ability to respond to certain stimuli by producing electrical signals such as action potentials
Actions potentials propagate along a nerve or muscle plasma membrane to cause a response
▪ Release of neurotransmitters
▪ Muscle contraction