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CHAPTER 5: TISSUES
Tissues
• Groups of cells similar in structure and function• The four types of tissues
• Epithelial • Connective• Muscle• Nerve
Epithelial Tissue• Cellularity – composed almost entirely of cells• Covers organs, forms the inner lining of body cavities, &
lines hollow organs• Special contacts – form continuous sheets held together
by tight junctions and desmosomes• Polarity – apical (free surface side) and basal (thin, non-
living basement membrane) surfaces
Epithelial Tissue • Supported by connective tissue – reticular and basal
laminae• Avascular but innervated – contains no blood vessels but
supplied by nerve fibers • Get nutrients and excrete wastes via diffusion
• Regenerative – rapidly replaces lost cells by cell division• Ex) skin
Classification of Epithelia
• Simple (one layer) or stratified (2 or more layers)
• Name is based on the apical surface
• Functions• Simple – filtration,
absorption, secretion• Stratified - protection
Classification of Epithelia
• Squamous, cuboidal, or columnar
• Have hexagon shape• Makes it more efficient
Epithelia: Simple Squamous
• Single layer of flattened cells with disc-shaped nuclei & sparse cytoplasm
• Fit tightly together (floor tiles)• Functions
• Diffusion & filtration• Provide a slick, friction-reducing lining in lymphatic and
cardiovascular systems
• Present in kidney glomeruli, lining of heart, blood vessels, lymphatic vessels, & serosae
Epithelia: Simple Squamous• Substances pass pretty easily through it
• Ex) lines the air sacs (alveoli) in lungs where oxygen and carbon dioxide are exchanged
• Since it is so thin and delicate, it is easily damaged
Simple Squamous• Description: single layer of flattened cells with disc-
shaped central nuclei & sparse cytoplasm; the simplest of the epithelia
• Function: allows passage of materials by diffusion & filtration in sites where protection is not important; secretes lubricating substances in serosae
• Location: kidney glomeruli, air sacs of lungs, lining of heart, blood vessels & lymphatic vessels, lining of ventral body cavity (serosae)
Simple Squamous Epithelium
Simple Cuboidal Epithelium• Single layer of cube-shaped cells
• Usually have large, centrally located, spherical nuclei
• Present in ovaries, kidney tubules (filtration), & ducts of certain smaller glands like the salivary, thyroid, pancreas, & liver glands• Tissue secretes glandular products
Simple Cuboidal Epithelium
Simple Columnar Epithelium• Single layer of elongated cells with large, spherical nuclei• Goblet cells are often found in this layer
• Secrete mucus for protection on the apical surface
• Functions: secretes digestive fluids & absorbs nutrients from digested foods
• Found in most organs of the digestive tract (stomach, large & small intestines) and the uterus
Simple Columnar Epithelium• Absorption cells have microvilli on their apical surface
• This increases their surface area so more of the substance can be absorbed
Simple Columnar Epithelium
Pseudostratified Columnar Epithelium
• Single layer of cells with different heights; some do not reach the free surface
• Nuclei are seen at different layers• Nonciliated cells are present in the male sperm-carrying
ducts• Ciliated cells have cilia on the apical surface of the cells
• Constantly moving, goblet cells are present and cilia sweeps the mucus away
• Present in the passages of the respiratory system• Mucus from goblet cells trap dust & microorganisms; the cilia move
the mucus & captured particles up and out of the airways
Pseudostratified Columnar Epithelium
Stratified Squamous Epithelium• This membrane composed of several layers of cells
• Function in protection from underlying areas subjected to abrasion
• Forms the external part of the skin’s epidermis (keratinized cells) and linings of the esophagus, mouth, and vagina (nonkeratinized cells)
• Good at regeneration – lost cells are replaced by ones from below
Stratified Squamous Epithelium• Upper layers may be dead because they do not receive
enough nutrients
• Keratinized cells – contain a protective protein• Cells in the top layer DON’T contain nuclei
• Nonkeratinized cells – do not contain the protective protein • Top layer of cells DO contain nuclei
Stratified Squamous Epithelium
Stratified Cuboidal Epithelium• Two or three layers of cuboidal cells that form the lining of
a lumen
• Layering of cells provides more protection than a single layer
• Lines the larger ducts of the mammary glands, sweat glands, salivary glands, and pancreas
• Pretty rare in the body
Stratified Cuboidal Epithelium
Stratified Columnar Epithelium• Limited distribution in the body
• Found in the pharynx, male urethra, and lining some glandular ducts
• *also occurs at transition areas between two other types of epithelia
Stratified Columnar Epithelium
Transitional Epithelium• Specialized to change in response to increased tension• Has several cell layers, basal cells are cuboidal, surface
cells are dome shaped• Stretches to permit the distension of the urinary bladder• Forms a barrier that helps prevent the contents of the
urinary tract from diffusing back into body• Lines the urinary bladder, ureters, and part of the urethra
(only found in organs of the urinary system)
Transitional Epithelium
Glandular Epithelium• A gland is one or more cells that makes and secretes an
aqueous fluid• Usually found within columnar and cuboidal epithelia• Contain a lot of rough ER• Secretory vesicles fuse w/ membrane & secrete fluid
• Secrete lipids, proteins, steroids
• Classified by:• Site of product release – endocrine or exocrine• Relative number of cells forming the gland – unicellular (goblet) or
multicellular
Endocrine Glands• Ductless glands that produce hormones
• Secretions include amino acids, proteins, glycoproteins & steroids
• Release secretions to surrounding systems & the hormones are transported by blood or lymphatic fluid to organs• Ex) estrogen & testosterone
Exocrine Glands• More numerous than endocrine glands
• Secrete their products onto body surfaces (skin) or into body cavities• Ex) mucous, sweat, oil & salivary glands
• The only important unicellular gland is the goblet cell
• Multicellular exocrine glands are composed of a duct and secretory unit
Connective Tissue• Found throughout the body; most abundant and widely
distributed of the primary tissues
• Types of connective tissue:• Loose connective tissue• Adipose tissue• Dense connective tissue• Cartilage• Bone• Blood
Functions of Connective Tissue• Binding & support of surrounding tissues• Protection• Insulation (adipose)• Transportation
• Materials are able to go through the extracellular matrix
Characteristics of Connective Tissue• Connective tissues have:
• Mesenchyme as their common tissue of origin• Varying degrees of vascularity• Nonliving extracellular matrix consisting of ground substances and
fibers fills spaces between cells• Collagen fibers• Elastic fibers• Reticular fibers
Structural Elements of Connective Tissue
• Ground substance – unstructured material that fills the space between cells
• Fibers – collagen, elastic, or reticular• Cells – fibroblasts, chondroblasts, osteoblasts, and
hematopoietic stem cells
Ground Substance• Interstitial (tissue) fluid• Adhesion proteins – fibronectin and laminin• Proteoglycans – glycosaminoglycans (GAGs)• Functions as a molecular sieve through which nutrients
diffuse between blood capillaries and cells
Fibers• Collagen – tough; provides high tensile strength (thickest)• Elastic – long, thin fibers that allow for stretch (medium)• Reticular – branched collagenous fibers that form delicate
networks (thinnest)
Cells• Fibroblasts – connective tissue proper• Chondroblasts – cartilage• Osteoblasts – bone• Hematopoietic stem cells – blood• White blood cells, plasma cells, macrophages, and mast
cells
Loose Connective Tissue • Also know as areolar tissue• Forms delicate, thin membranes throughout the body;
widely distributed• The cells of this tissue are mainly fibroblasts; they are
separated by a gel-like matrix that contains many collagenous and elastic fibers
• Binds the skin to the underlying organs and fills spaces between muscles
• Wraps and cushions organs
Loose Connective Tissue
Adipose Tissue• Fat• Develops when certain cells store fat in droplets within
their cytoplasm and enlarge• When these cells are so numerous that they crowd other
cells types they form adipose tissue• Lies beneath the skin, spaces between muscles, around
the kidneys, behind the eyeballs, in abdomen, on the surface of the heart, and around certain joints
• Cushions joints and the kidneys, insulates the body, stores energy in fat molecules
Adipose Tissue
Dense Connective Tissue• Consists of many closely packed, thick, collagenous fibers
and a fine network of elastic fibers• It has relatively few cells most are fibroblasts• Collagenous fibers of dense connective tissue are very
strong enables the tissue to withstand pulling forces• Often binds body parts together as parts of tendons and
ligaments• Protective white layer of the eyeball & in the deeper skin
layers• Tissue repair is slow because of the poor blood supply to
dense connective tissue
Dense Connective Tissue• Attaches muscles to bone or to other muscles and bone
to bone
• Found in:• Tendons – attaches muscle to bone• Ligaments – attaches bone to bone• Aponeuroses – attaches muscle to muscle
Dense Connective Tissue
Cartilage• Rigid connective tissue• Provides support, frameworks, and attachments, protects
underlying tissues and forms structural models for many developing bones
• Cartilage matrix is abundant and largely composed of collagenous fibers embedded in a gel-like ground substance
• Chondrocytes cartilage cells• Occupy small chambers called lacunae and are completely within
the matrix
Cartilage• Cartilaginous structure is enclosed in a covering of
connective tissue call perichondrium• Perichondrium contains blood vessels that provide
cartilage cells with nutrients by diffusion• Cartilage does not heal quickly and chondrocytes do not
divide frequently because of a lack of a direct blood supply
Cartilage• Three types of cartilage:
• Hyaline cartilage • Elastic cartilage• Fibrocartilage matrix similar to hyaline cartilage but less firm with
thick collagen fibers• Provides tensile strength and absorbs compression shock• Found in the intervertebral discs, the pubic symphysis, and in discs of
the knee joint
Hyaline Cartilage• Amorphous, firm matrix w/ imperceptible network of
collagen fibers
• Supports, reinforces, cushions, and resists compression
• Found in embryonic skeleton, the end of long bones, nose, trachea, and larynx
Elastic Cartilage• Similar to hyaline cartilage but with more elastic fibers
• Maintains shape and structure while allowing flexibility
• Supports external ear (pinna) and the epiglottis
Fibrocartilage• Matrix similar to hyaline cartilage but less firm with thick
collagen fibers
• Provides tensile strength and absorbs compression shock
• Found in the intervertebral discs, the pubic symphysis, and in discs of the knee joint
Bone• Hard, calcified matrix with collagen fibers found in bond• Osteocytes are found in lacunae and are well
vascularized• Supports, protects, and provides levers for muscular
action• Stores calcium, minerals, and fat• Marrow inside bones is the site of hematopoiesis
making of red blood cells
Bone
Blood• Red and white cells in a fluid matrix (plasma)• Contained within blood vessels• Functions in the transport or respiratory gases, nutrients,
and wastes
Nervous Tissue• Branched neurons with long cellular processes and
support cells• Transmits electrical signals from sensory receptors to
effectors• Receptors Brain Effectors
• Found in the brain, spinal cord, and peripheral nerves
Nervous Tissue
Muscle Tissue• Contractile – the elongated cells (muscle fibers) can
shorten
• As muscle tissues contract, the fibers pull at their attached ends• This moves body parts
• Three types:• Skeletal • Smooth• Cardiac
Skeletal Muscle Tissue• Long, cylindrical, multinucleated cells with obvious
striations• Multinucleated because many cells are fused together to make 1
long cell
• Initiates and controls voluntary movement
• Found in skeletal muscles that attach to bones or skin
Skeletal Muscle Tissue
Smooth Muscle Tissue• Sheets of spindle-shaped cells with central nuclei that
have no striations why its called smooth
• Shorter than skeletal muscle• Usually can’t be stimulated to contract by conscious efforts
• Propels substances along internal passageways• Ex) food down the digestive tract, constricts blood vessels, empties
the urinary bladder
• Found in the walls of hollow organs• Stomach, intestines, urinary bladder, uterus, blood vessels
Smooth Muscle Tissue
Cardiac Muscle Tissue• Only found in the walls of the heart
• Cells are striated with a single nucleus
• Where cells connect to one another it is a specialized intercellular junction intercalated disk
• Cardiac muscle is controlled involuntarily
• Pumps blood through the heart chambers and into blood vessels
Cardiac Muscle Tissue