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