animal tissues
DESCRIPTION
Animal TissuesTRANSCRIPT
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• Tissues are:– Collections of specialized cells and cell products
organized to perform a limited number of functions• Histology = study of tissues
• The four tissue types are:– Epithelial– Connective– Muscular– Nervous
Tissues and tissue types
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Epithelial Tissue• Cellularity - Consists almost entirely of cells• Covers body surfaces, lines hollow organs, and forms
glands– Outside surface of the body– Lining of digestive, respiratory, cardiovascular and urogenital
systems - Lining of many body cavities
• Polarity - Has apical, basal, and lateral surfaces• Rests on a basement membrane• Avascular - no blood vessels• Regenerative -Replaces lost cells by cell division
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Special Characteristics of Epithelia
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Functions of Epithelia• Protecting underlying structures; e.g., epithelium
lining the mouth• Acting as barriers; e.g., skin• Permitting the passage of substances; e.g., cells
lining air sacs in lungs and nephrons in kidney• Secreting substances; e.g., pancreatic cells• Absorbing substances; e.g., lining of stomach and
small intestine
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Classification of Epithelium• Number of layers of cells– Simple- one layer of cells. Each extends from basement
membrane to the free surface– Stratified- more than one layer. – Pseudostratified- tissue appears to be stratified, but all
cells contact basement membrane so it is in fact simple• Shape of cells– Squamous- flat, scale-like– Cuboidal- about equal in height and width– Columnar- taller than wide
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Classifications of Epithelia
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Simple Squamous Epithelium
Figure 4.3a
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Simple Cuboidal Epithelium
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Simple Columnar Epithelium
Figure 4.3c
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Pseudostratified Ciliated Columnar Epithelium
Figure 4.3d
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Stratified Epithelia
• Contain two or more layers of cells• Regenerate from below• Major role is protection• Are named according to the shape of cells at
apical layer
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Stratified Squamous Epithelium
• Description– Many layers of cells – squamous in shape– Deeper layers of cells appear cuboidal or columnar – Thickest epithelial tissue – adapted for protection
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Stratified Squamous Epithelium
• Specific types – Keratinized – contain the protective protein
keratin• Surface cells are dead and full of keratin
– Non-keratinized – forms moist lining of body openings
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Stratified Squamous Epithelium
• Function – Protects underlying tissues in areas subject to abrasion
• Location – Keratinized – forms epidermis– Non-keratinized – forms lining of esophagus,
mouth, and vagina
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Stratified Squamous Epithelium
Figure 4.3e
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Transitional Epithelium
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Epithelium: Glandular• A gland is one or more cells that makes and secretes an
aqueous fluid• Two types of glands formed by infolding of epithelium:
– Endocrine: no contact with exterior of body; ductless; produce hormones (pituitary, thyroid, adrenals, pancreas)
– Exocrine: open to exterior of body via ducts (sweat, oil)
• Exocrine glands classified either by structure or by the method of secretion
• Classified by structure– Unicellular: goblet cells– Multicellular: sweat, oil, pituitary, adrenal
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Lateral Surface Features
• Tight junctions• Desmosomes• Gap junctions
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Membrane Junctions: Tight Junction
• Integral proteins of adjacent cells fuse together• Completely encircle the cell and form an adhesion belt.• Form an impermeable junction.• Common near apical region
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Lateral Surface Features – Cell Junctions
• Desmosomes – two disc-like plaques connected across intercellular space– Plaques of adjoining cells are joined by proteins
called cadherins – Proteins interdigitate into extracellular space– Intermediate filaments insert into plaques from
cytoplasmic side
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Membrane Junctions: DesmosomeLinker proteins extend from plaque like teeth of a zipper.Intermediate filaments extend across width of cell.
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Membrane Junctions: Gap Junction
• Connexon proteins are trans- membrane proteins.
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Basal Feature: The Basal Lamina
Noncellular supporting sheet between the epithelium and the connective tissue deep to it
Consists of proteins secreted by the epithelial cells Functions:
Acts as a selective filter, determining which molecules from capillaries enter the epithelium
Basal lamina and reticular layers of the underlying connective tissue deep to it form the basement membrane
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Epithelial Surface Features
• Apical surface features – Microvilli – finger-like extensions of plasma
membrane• Abundant in epithelia of small intestine and kidney• Maximize surface area across which small molecules
enter or leave
– Cilia – whip-like, highly motile extensions of apical surface membranes
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Connective Tissue• Most diverse and abundant tissue• Main classes
– Connective tissue proper– Cartilage– Bone tissue– Blood
• Characteristics– Mesenchyme as their common tissue of origin (mesenchyme
derived from mesoderm)– Varying degrees of vascularity– Nonliving extracellular matrix, consisting of ground substance
and fibers – Cells are not as abundant nor as tightly packed together as in
epithelium
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Connective Tissue: Embryonic Origin
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Functions of Connective Tissue
• Enclose organs as a capsule and separate organs into layers. Areolar
• Connect tissues to one another. Tendons and ligaments.
• Support and movement. Bones.• Storage. Fat.• Insulation. Fat.• Transport. Blood.• Protection. Bone, cells of the immune system.
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Structural Elements of Connective Tissue
• Ground substance – material that fills the space between cells
• Fibers – collagen, elastic, or reticular• Cells – fibroblasts, chondroblasts,
osteoblasts, hematopoietic stem cells, and others
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Connective Tissue Cells• Fibroblasts - secrete the proteins needed for fiber synthesis
and components of the extracellular matrix• Adipose or fat cells (adipocytes). Common in some tissues
(dermis of skin); rare in some (cartilage)• Mast cells. Common beneath membranes; along small blood
vessels. Can release heparin, histamine, and proteolytic enzymes in response to injury.
• Leukocytes (WBC’s). Respond to injury or infection• Macrophages. Derived from monocytes (a WBC). Phagocytic;
provide protection• Chondroblasts - form cartilage• Osteoblasts - form bone• Hematopoietic stem cells - form blood cells• Undifferentiated mesenchyme (stem cells). Have potential to
differentiate into adult cell types.
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Extracellular Matrix - ECM• ECM has 3 major components
1. Protein fibers 2. Ground substance 3. Fluid• Protein fibers– Collagen fibers. Composed of the protein collagen. Strong,
flexible, inelastic; great tensile strength (i.e. resist stretch). Perfect for tendons, ligaments
– Elastic fibers. Contain molecules of protein elastin that resemble coiled springs. Returns to its original shape after stretching or compression. Perfect for lungs, large blood vessels
– Reticular fibers. Formed from fine collagenous fibers; form branching networks (stroma). Fill spaces between tissues in organs.
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Ground Substance• Interstitial (tissue) fluid within which are one or more of the
molecules listed below:– Hyaluronic acid: a polysaccharide. Very slippery; serves as
a good lubricant for joints. Common in most connective tissues.
– Proteoglycans: protein and polysaccharide complex. Polysaccharides called glyocosaminoglycans (chondroitin sulfate, keratin sulfate). Protein part attaches to hyaluronic acid. Able to trap large amounts of water.
– Adhesive molecules: hold proteoglycan aggregates together. Chondronectin in cartilage, osteonectin in bone, fibronectin in fibrous connective tissue.
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Areolar Connective Tissue
Figure 4.12b
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Adipose Tissue
Figure 4.12c
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Reticular Connective Tissue
Figure 4.12d
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Dense Irregular Connective Tissue
Figure 4.12e
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Dense Regular Connective Tissue
Figure 4.12f
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Elastic Connective Tissue
• Bundles and sheets of collagenous and elastic fibers oriented in multiple directions
• In walls of elastic arteries (aorta), lungs, vocal ligaments• Strong, yet elastic; allows for recoil of tissue after being
stretched
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Connective Tissue: Cartilage• Composed of chondrocytes (cells) located in matrix-surrounded
spaces called lacunae. • Type of cartilage determined by components of the matrix. • Firm consistency. • Ground substance: Proteoglycans and hyaluronic acid
complexed together trap large amounts of water (microscopic sponges). Allows tissue to spring back after being compressed.
• Avascular and no nerve supply. Heals slowly.• Perichondrium. Dense irregular connective tissue that
surrounds cartilage. Fibroblasts of perichondrium can differentiate into chondroblasts (cartilage-forming cells)
• Types of cartilage– Hyaline– Fibrocartilage– Elastic
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Hyaline Cartilage
Figure 4.12g
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Elastic Cartilage
Figure 4.12h
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Fibrocartilage
Figure 4.12i
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Bone Tissue
Figure 4.12j
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Blood Tissue
Figure 4.12k
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Muscle Tissue• Characteristics– Cells are referred to as fibers– Contracts or shortens with force when stimulated– Moves entire body and pumps blood
• Types– Skeletal:attached to bones– Cardiac: muscle of the heart. – Smooth: muscle associated with tubular
structures and with the skin. Nonstriated and involuntary.
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Skeletal Muscle Tissue
Figure 4.14a
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Cardiac Muscle Tissue
Figure 4.14b
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Smooth Muscle Tissue
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Nervous Tissue