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