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Ch 4: Tissues
Intro to tissues
• Tissues –– Groups of cells that are similar in structure
and function
• 4 primary tissue types - – Epithelial (covering & linings)– Connective (support)– Nervous (control)– Muscular (movement)
Epithelial tissue
• Epithelium – – Epithe = “laid on, covering”– A sheet of cells that covers a body surface or lines
a cavity – Forms boundaries between environments– Functions –
• Protection• Absorption (process by which the products of digestion pass through the
alimentary tube mucosa into the blood or lymph)
• Filtration (passage of a solvent and dissolved substances through a membrane or filter)
• Excretion (elimination of waste products from the body)• Secretion (passage of material formed by a cell to its exterior)
• Sensory reception – Occurs in the body as...
• A covering or lining epithelium • Or as glandular epithelium
Special characteristics of epithelium • Cellularity –
– Composed of closely packed cells with little extracellular material between
• Specialized contacts –– Bound together by specialized contacts
(desmosomes & tight junctions) – Forms continuous sheets
• Polarity – – Possess an apical & basal surface
• Apical – free and exposed – most have microvilli – Cilia – propel substances along their free surface (trachea)
• Basal – attached surface – Basal lamina – thin supporting sheets made mostly of
glycoproteins – acts as a selective filter for the diffusion of nutrients
Specialized characteristics cont. • Support –
– All epithelial tissue rest & are supported by connective tissue
– Reticular lamina –• Below basal lamina• Contains collagen fibers of the connective tissue
– Reticular lamina + basal lamina = basement membrane
• Reinforces epithelium (helps resist tearing & stretching)
• Avascular but innervated –– Avascular = no blood vessels
• Nourished by diffusing nutrients from underlying connective tissue
– Innervated = supplied by nerves• Regeneration –
– High regeneration capacity
Cell shapes
Classification of epithelium• Naming –
– First name – • Indicates the number of layers present• Simple – one layer
– Absorption and filtration
• Stratified – more than one– Highly abrasive– Shape differs among cell layers – Named due to the apical layer
– Second name - • Describes the shape of the cell• Squamous –
– Flat and scale like
• Cuboidal –– Box/cube like
• Columnar –– Tall and column shaped
Epithelium • Simple epithelia are mostly concerned with
absorption, secretion, and filtration– Simple squamous –
• Single layer of flattened cells • Sparse cytoplasm • Bulging nucleus• Filtration & exchange• Special examples;
– Endothelium – » “inner covering”» Slick & friction reducing » Lymphatic vessels, blood vessels, heart, & capillaries
– Mesothelium –» “middle covering” » Serous membrane lining ventral body cavities » Covers organs
Simple squamous
Epithelium cont. • Simple cuboidal –
– Single layer of cube-shaped cells – Forming the smallest ducts of glands– Kidney tubules– Secretion & absorption – Spherical nuclei
• Simple columnar – – Single layer of column-shaped cells– Line the digestive tract (stomach to rectum)
• Dense microvili to increase absorption
– Goblet cells – • secrete protective mucus
Simple cuboidal
Simple columnar
Epithelium cont.
• Pseudostratified columnar –– Contains cells of varying heights – Gives the false (psuedo) impression that there are
many layers• Nuclei are at various heights – gives the false impression
– All cells rest on basement membrane – Tallest cells reach the free apical surface– May contain cilia & goblet cells – Line the respiratory tract
Pseudostratified
Stratified epithelium
• Stratified epithelia’s main function is protection.
• Consists of two or more cell layers • Regeneration occurs at the basal
surface • More durable than simple epithelium • Stratified cuboidal –
– Rare– Ducts of large glands
Stratified epithelium cont.• Stratified squamous –
– Most common – Several cell layers – Cells on free surface are squamous shaped (named
for free exposed surface)– Underlying cells are cuboidal or columnar – Protection– Basal cells replace apical cells – Apical cells are squamous shaped because they are
not receiving adequate nutrients• Rely on diffusion of nutrients
– External part of the skin & extends into every body opening
Stratified squamous
Stratified epithelium cont. • Stratified columnar –
– Limited distribution– Small amounts in pharynx, male urethra, & some
glandular ducts• Transitional –
– Forms the hollow organs of the urinary system– Allows for stretch – Basal cells = cuboidal or columnar– Apical cells vary in appearance depending on the
level of stretch – Not stretched – multilayered membrane– Stretched (distension) – membrane becomes
squamous like
Transitional
Glandular epithelia • Gland –
– Cells that make or secrete (export) a product• Secretion = Active Process
– Secretion – aqueous fluid containing proteins– 2 types –
• Endocrine– Internally secreting– Ductless (they loose their ducts)– Secrete hormones by exocytosis
» Directly into lymph or blood systems » Or directly into the extracellular space
• Exocrine – Externally secreting– Have ducts– More numerous in the body– Secrete onto a surface or into body cavities– Sweat, oil, salivary glands
Connective tissue • Found everywhere in the body• Consist of living cells surrounded by a matrix• Differences = cell type & fiber type & the
amount of the two • Main classes –
– Connective tissue proper – fat and fibrous tissue – Cartilage– Bone – Blood
• Major functions –– Binding & support– Protection– Insulation– Transportation
Connective tissue cont. • Common characteristics –
– Common origin –• All connective tissues arises from embryonic tissue
called mesenchyme
– Degrees of vascularity –• Connective tissue ranges from avascular to highly
vascularized • Cartilage – avascular • Dense connective tissue – poor vascularization• All other connective tissue – rich blood supply
– Extracellular matrix –• Connective tissue is composed mainly of nonliving
extracellular matrix• Separates the cells of the tissue• Allows connective tissue to –
– Bear weight– Withstand tension– Endure physical trauma
Connective tissue cont.
• Ground substance – – Unrestricted material that fills the space between
the cells and contains fibers– Mechanism through which nutrients and other
dissolved substances can diffuse – Composed of:
• Interstitial fluid • Cell adhesion proteins• Proteoglycans – helps determine the stiffness of the
ground substance• Fibers – makes the fluid less pliable
Connective tissue cont.• Fibers –
– Provide support – Collagen fibers –
• Strong • Provide large amounts of tensile strength (ability to resist
longitudinal strain) • Composed of fiberous protein: collagen• Has a glistening appearance; also called white fibers
– Elastic fibers –• Elastin proteins • Allows fibers to stretch & recoil • Skin, lungs, & blood vessels
– Reticular fibers – • Reticul – “network” • Fine collagenous fibers that form networks • Extensive branching network • Surrounds blood vessels, supports soft tissue organs, & around
basement membranes
Connective tissue cont. • Fundamental cell types –
– All connective tissues have an immature and mature cell form
– “blast” – actively forming cells – secrete ground substance & fibers characteristic of the matrix
• 4 primary blast cells -– Osteoblast – bone cells– Fibroblast – connective tissue proper– Chondroblast – cartilage– Hematopoietic stem cell – blood
– “cyte” – inactive mature cells • Osteocyte – mature bone cells• Chondrocyte – mature cartilage cells
Types of connective tissue
• Connective tissue proper – – Loose connective
• Areolar, adipose, & reticular
– Dense connective• Dense regular, dense irregular
Loose connective tissue• Areolar –
– “areola” – a small open space – Binds body parts together while allowing them to
move freely over one another– Wraps small blood vessels & nerves– Surrounds glands– Forms subcutaneous tissue – Most widely distributed connective tissue – Contains fibroblasts –actively mitotic fiber cells– Loose arrangement of tissue – provides a
reservoir of water and salt
Areolar
Loose connective tissue• Adipose –
– Fat tissue– Contain a pure fat droplet, displaces nucleus – Highly vascularized – high metabolic activity– Closely packed cells – little matrix– Adipocytes –
• Fat cells • Mature cells are some of the largest cells in the body • Mature cells can’t divide
– Develops where areolar tissue is plentiful – Insulation, stores nutrients, & shock absorber – Brown fat –
• Consumes its stored nutrients to generate heat to warm the body
• Occurs in babies who lack the ability to produce their own heat through shivering
Adipose
Loose connective tissue
• Reticular connective tissue – – Resembles areolar tissue – Contains only reticular fibers– Forms stroma -
• Internal framework • Supports blood cells • Lymph system, spleen, & bone marrow
– Limited within the body even though reticular fibers are numerous
Reticular
Dense connective tissue
• Dense regular – – Contains closely packed bundles of collagen fibers
running in the same direction – Run parallel to the direction of pull – Makes up tendons (attach muscle to bone) and
ligaments (attach bone to other joints) – Great resistance to tension – exerted in a single
direction – Poorly vascularized – slow regeneration
Dense regular
Dense connective tissue
• Dense irregular tissue – – Contains thick bundles of collagen fibers– Arranged in an irregular (more than one
plane) fashion– Found in:
• Dermis • Joint capsules
Dense irregular
Cartilage • Lacks nerve fibers (not innervated) • Avascular • Withstands tension & compression• Tough but flexible • Ground substance –
– Collagen fibers– Elastic fibers– Water (80%)
• Allows cartilage to rebound after being compressed • Nourishes the cartilage cells
• Chondroblasts – produces new matrix• Chondrocytes – found in small groups w/in cavities
(lacunae)
Cartilage cont. • Hyaline –
– Hyalin = glass – Collagen fibers are not apparent within the matrix
– gives it a glass like appearance – Gristle – Most abundant cartilage – Providing firm support with some pliability – Covers the ends of long bones– Absorbs compression– Supports the tip of the nose & connects ribs to
sternum– Epiphyseal plates – actively growing regions near
the end of long bones – continued growth in length
Hyaline
Cartilage cont.
• Elastic –– Found where strength & exceptional
stretch are needed – Contains large amounts of elastin fibers –
• Allows for repeated bending
– External ear – Epiglottis – covering the respiratory system
Elastic
Cartilage cont. • Fibrocartilage –
– Found where strong support & ability to withstand pressure are required
– Rows of chondrocytes alternating with rows of thick collagen fibers
– Compresses and resists tension – Intervertebral disks– Spongy cartilage of the knee joint
Fibrocartilage
Bone• Bone –
– Osseous – Supports & protects the body – Additional collagen fibers & calcium salts found in
extracellular matrix – Provides cavities for fat storage & blood cells– Osteoblasts – produce organic portions of the
matrix – bone salts deposited on & between the fibers
– Osteocytes – reside in the lacunae – Highly vascularized
Bone (osseous tissue)
Blood
• Blood –– Classified as a connective tissue
because...• Developed from mesenchyme • Consists of blood cells & plasma proteins
surrounded by plasma • Fibers – soluble protein molecules that become
visible during clotting• Transport vehicle for the body
Blood
Nervous tissue • Nervous tissue –
– Main component of the nervous system– Regulates & controls body functions – Brain, spinal cord, & nerves – Composed of 2 cell types –
• Neurons –– Specialized cells that generate and conduct electrical
impulses– Branching cells – Cytoplasmic extensions – allows them to transmit
electrical impulses
• Supporting cells –– Nonconductive cells that support, insulate, and
protect the neurons
Nervous tissue
Muscle tissue • Muscle tissue –
– Highly cellular– Well vascularized – Responsible for movement – 3 types –
• Skeletal –– Attaches to the skeleton & produces voluntary body movement – Packaged by connective tissue – Form the flesh of the body – Contain many nuclei & striations (indicates the alignment of myofilaments) – Voluntary muscle
• Cardiac –– Only in the walls of the heart – Responsible for the involuntary movement of the heart – Contain striations – Uninucleated– Branching cells that fit together & the intercalated disc junctions – Involuntary muscle
• Smooth –– No visible striations – One nucleus – Found in the walls of hollow organs (other than the heart) – digestive,
reproductive, & urinary organs – Involuntary muscle
Muscles
Membranes • Cutaneous membrane –
– Cutaneous membrane, or skin, is an organ system consisting of keratinized squamous epithelium (epidermis) firmly attached to a thick layer of dense irregular connective tissue (dermis)
– Dry membrane because its exposed to the air • Mucous membrane –
– Line hollow body cavities (ie. digestive organs)– Open to the exterior– Adapted for absorption or secretion – Bathed in mucus – Contain stratified squamous or simple columnar epithelium
• Serous membrane –– Found in closed cavities– Serous fluid that lubricates the facing surface– Named for their location & organ association (ie. pleura,
pericardium)– Consist of simple squamous epithelium– Rests on a thin layer of areolar (loose connective) tissue
Membranes
Tissue repair • Tissue repair occurs in two ways:
regeneration (replacement of destroyed tissue with the same kind of tissue) & fibrosis (replaces damaged tissue with fibrous connective tissue – scar tisse)
• 3 steps in the repair process –– Inflammation –
• Prepares the area for the repair process • Allows white blood cells & plasma to seep into the
injured area • Forms a clot & holds the wound together
– Organization –• Restores the blood supply• Clot is replaced by delicate pink tissue – granulation
tissue • Restores blood supply
– Regeneration & fibrosis –• Permanent repair • New tissue regenerates under the scab
Embryonic & fetal development • Primary germ layers –
– Ectoderm –• Most superficial layer (external layer) • Nervous tissue
– Mesoderm –• Middle layer • Muscle and connective tissue
– Endoderm –• Deepest layer (internal layer) • Epithelial tissue
Primary Germ layers
Aging
• Increased age – – Epithelia becomes thin– Number of collagen fibers decreases– Bone, muscle, nervous tissue begin to
atrophy
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