Tissues

Chapter 3

Histology• Study of tissues (approximately 220

types!)• Tissues: groups of highly specialized

cells performing functions that benefit the organism as a whole– Cells must be similar in structure &

function and come from similar embryonic origin

• Four Primary tissue types– Epithelium (covering)– Connective (support)– Muscle (movement)– Nervous (control)

• Organs contain several tissue types, and arrangement of tissues determines organ’s structure & function

Primary Germ Layers• All tissues & organs of the body

develop from one of three primary germ layers:– Ectoderm (outside)

• Lining, skin, nervous

– Endoderm (inside)• Organs, mucosae & glands, linings of cavitiesand tracts

– Mesoderm (middle)• Connective tissue (i.e. blood, bone) and most muscle tissue

Extracellular Materials• ECF: usually fluid, but can be more

gel-like or calcified (i.e. bone)• ECF provides a medium for:

– Dissolving & mixing solutes– Transporting substances– Carrying out chemical reactions

Epithelial Tissue• a.k.a. epithelium (“epithe” = laid on,

covering)• Lining, covering, and glandular tissue

of the body• Covers all free body surfaces and

contains versatile cells• Nearly all substances that the body

gives off or receives must pass through epithelium

• Functions:– Protection– Filtration– Absorption– Secretion

Characteristics of Epithelium• Cells fit closely together to form continuous

sheets – single or multiple layers (desmosomes & tight junctions); little extracellular materials

• Membranes always have one free (unattached) surface or edge (apical surface) that is exposed to body’s exterior or to the cavity of an internal organ (some have modifications like cilia or microvilli)

• Basal surface (lower) of epithelium rests on a basement membrane – structureless material secreted by both epithelial cells and connective tissue cells that border the epithelium

• Epithelial tissues have no blood supply of their own (avascular) and depend on diffusion from the capillaries in underlying connective tissue for food and oxygen

• Regenerate easily (high mitotic rate)• Have a nerve supply• Derived from all three primary germ layers

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Classification of Epithelium

• Two names: – 1st indicates relative number of cell layers

• Simple (one layer) or stratified (multiple layers) or pseudostratified (looks like multiple layers)

– 2nd indicates the shape of its cells• Squamous (flat)• Cuboidal (cube)• Columnar (shaped like columns)• Transitional (varies)

• Stratified epithelium is named based on cells at the free surface!

• Arrangement reflects location and function

Types of Epithelial Tissue

• Covering & Lining Epithelium– Simple Epithelia

• Simple squamous epithelium• Simple cuboidal epithelium• Simple columnar epithelium• Pseudostratified columnar epithelium

– Stratified Epithelia• Stratified squamous epithelium• Stratified cuboidal epithelium • Stratified columnar epithelium• Transitional epithelium

• Glandular Epithelium

Epithelial Tissue ID Quiz

 Tissues you need to be able to identify:

• Simple squamous

• Simple cuboidal• Simple

columnar• Stratified

squamous• Transitional• Pseudostratified

Tissue/ cell parts you need to know:

• Nucleus• Apical (free)

surface• Basal surface• Basement

membrane• Cilia• Goblet cell• Keratin

Simple Squamous Epithelium• Single layer, flat shape

• All cells attached to basement membrane• Fit closely together• Forms membranes where filtration or

exchange of substances by rapid diffusion occurs (absorption, secretion, filtration)

• Ex: air sacs of lungs (O2 & CO2 exchanged), walls of capillaries (nutrients and gases pass between the tissue cells and blood in capillaries), form serous membranes (serosae) – slick membranes that line ventral body cavity and cover organs in that cavity

• Endothelium – lines blood vessels• Mesothelium – lines body cavities and

mesenteries

Simple Cuboidal Epithelium

• Single layer/cube shape• Common in glands and their ducts• Ex. Salivary glands and pancreas,

walls of kidney tubules, covers surface of ovaries

Tubule lining –

longitudinal cut

Tubule lining – cross-section

Simple Columnar Epithelium• Single layer/column (tall) shape

• Often have goblet cells – produce lubricating mucus

• Ex: lines entire length of digestive tract from stomach to anus

• Mucosae (mucous membranes): epithelial membranes that line body cavities open to the body exterior

Pseudostratified Columnar Epithelium

• Appear to be multi-layered, but are actually one single layer that rest on the basement membrane

• Nuclei appear at different heights and some cells shorter than others

• Mainly functions in absorption and secretion

• Can be ciliated (pseudostratified ciliated columnar epithelium)

• Also can have goblet cells• Ex: respiratory tract – mucus produced

by goblet cells in this epithelium traps dust and other debris, and the cilia propel the mucus upward and away from the lungs

Stratified Squamous Epithelium

• Multiple layers, flat shape• Most common stratified epithelium in

body• Cells at free edge are squamous, and

those close to basement membrane can be cuboidal or columnar

• Found in sites that receive a good deal of abuse or friction

• Keratin – protein coating on apical surface (i.e. skin)– Can be keratinized or non-keratinized

• Ex. Esophagus, mouth, outer portion of skin

Non-keratinized

Keratinized

Stratified Cuboidal Epithelium• Two cell layers with (at least) the surface

cells being cuboidal in shape• Fairly rare in body; distribution

extremely limited• Mainly in ducts of large glands (larger

ducts of mammary glands, sweat and salivary glands, pancreas)

Stratified Columnar Epithelium• Multiple layers/Columnar cells

• Basal cells vary in size and shape, see multiple nuclei

• Even less common in body; distribution extremely limited

• Mainly in ducts of large glands• Ex. Urethra, pharynx

Transitional Epithelium

• Variable shapes• Highly modified, sratified squamous

epithelium that forms the lining of only a few organs– Urinary bladder, ureters, and part of the

urethra• Subject to considerable stretching• Cells of basal layer cuboidal or

columnar & cells at free surface vary in appearance

• Not stretched: superficial cells rounded and domelike

• Distended: epithelium thins and surface cells flatten and become squamouslike

Distended

Glandular Epithelium• Gland: one or more cells that make

and secrete a particular product• Secretion: typically contains protein

molecules in an aqueous fluid• Endocrine glands: ductless glands;

secretions (hormones) diffuse directly into the blood vessels that weave through the glands (i.e. thyroid, adrenals, pituitary)

• Exocrine glands: ducts; secretions empty through ducts to epithelial surface (i.e. sweat & oil glands, liver, pancreas)

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Connective Tissue• Connects body parts• Found everywhere in body• Most abundant and widely distributed

tissue• Primary functions:

– Protecting– Supporting– Binding together body

tissues

Connective Tissue Characteristics• Three basic elements: cells, ground

substance, fibers– Extracellular matrix: ground substance +

fibers• Fibers made of protein (collagen is most

abundant protein in body – 25%)

• No free surface (connects!)• Has nerve supply (except cartilage)• Highly vascular

– except cartilage (avascular) & tendon (poorly vascularized)

• Matrix may be fluid, semifluid, gelatinous, fibrous, or calcified (depends on ground substance)– Secreted by connective tissue cells &

adjacent cells– ground substance: structureless; water plus

some adhesion proteins & large, charged, polysaccharide molecules

– Determines tissue’s qualities

Embryonic Origin • Mesenchyme: undifferentiated

connective tissue cells in embryo• All Connective tissue is derived from

mesoderm!!– How is this different from Epithelial

tissue?

Embryonic Connective Tissue• Embryo (0-2 months); Fetus (2 mos.-birth)

• Mesenchyme: almost exclusively in embryo; tissue from which all connective tissue will eventually arise

• Mucous (Wharton’s Jelly): umbilical cord of fetus – gives support

Connective Tissue Cells• Mesenchymal cells become blast cells (immature)

• Blast cells undergo mitosis and secrete the matrix• Mature cells do not divide & make matrix – just

maintain what is there

Connective Tissue Fibers• Type of fiber depends on type of tissue

• Fibers made of proteins• Types of fibers:

– Collagen fibers – tough & resistant to stretching/pulling forces; bone, cartilage, tendons, ligaments

– Elastic fibers – strength & stretching; skin, blood vessels, lungs (smaller than collagen fibers)

– Reticular fibers – collagen + glycoprotein; support in blood vessel walls & form strong supporting network around fat cells, nerve fibers, skeletal/smooth muscle fibers; form basement membrane and framework of soft organs

Types of Connective Tissue

• All CT consist of living cells surrounded by a matrix

• Differences: special cell types, fiber types, # of fibers

• Types:• Bone (Osseous)• Cartilage

• Hyaline cartilage

• Fibrocartilage• Elastic cartilage

• Dense Connective• Dense regular• Dense irregular• Dense elastic

• Loose Connective• Loose areolar• Adipose

• Loose reticular• Blood

Connective Tissue ID QuizTissue types:

• Loose areolar• Adipose• Dense connective• Cartilage• Bone• Blood

Parts:

• Fibroblast• Fibers• Nucleus• Adipocyte• Lipids (fats)• Chondrocyte• Lacuna(e)• Osteocyte• Canaliculi• Haversian system

(osteon)• Red blood cell

(erythrocyte)• White blood cell

(leukocyte)• Platelet (thrombocyte)

Bone (Osseous Tissue)• composed of osteocytes (bone cells) sitting in

lacunae (pits)• Surrounded by layers of very hard matrix of

calcium salts & collagen fibers• Exceptional ability to protect & support other

body organs– Great strength & some flexibility

• Movement, storing minerals, houses blood-forming tissue, stores lipids (yellow marrow)

• Parts: – haversian system (osteon) – basic unit– canaliculi – small canals that supply nutrients– central canal – contains blood vessels and nerves– Periosteum surrounds central canal – made of dense

irregular CT– Lamellae – rings of matrix (mineral salts & collagen)

p. 139 – Bone chapter

Cartilage• Less hard and more flexible than bone• Chondrocyte: cartilage cells• Hyaline cartilage (most widespread)

– Abundant collagen fibers hidden by a rubbery matrix with a glassy, blue-white appearance

– Supporting structures of larynx (voice box), attaches ribs to the breastbone, and covers the ends of many bones where they form joints

– Makes up the fetal skeleton– Epiphyseal (growth) plates in long bones during

youth• Fibrocartilage

– Highly compressible, forms the cushionlike disks between the vertebrae of the spinal column

• Elastic Cartilage– Found in structures with elasticity– Supports external ear

Hyaline Cartilage• No blood vessels (except perichondrium)

Fibrocartilage• Bundles of collagen in matrix• Pubic symphysis, intervertebral discs, meniscus

of knee• Support & fusion• No perichondrium• Strongest type: strength & rigidity

Elastic Cartilage• Threadlike fibers in gel matrix• Support & maintains shape• Has perichondrium• Similar to hyaline, but more elastic fibers

– Strength & exceptional stretchability

• Epiglottis (“lid” on larynx), auditory tubes

Dense Connective Tissue• Also called dense fibrous tissue

• Collagen fibers are main matrix element• Fibroblasts (fiber-forming cells) manufacture

the building blocks of the fibers• Forms long, ropelike structures

– Tendons: attach skeletal muscles to bones– Ligaments: connect bones to bones at joints

(contain more elastic fibers than tendons)• Also makes up lower layers of skin (dermis)• Types:

– Dense Regular– Dense Irregular– Dense Elastic

Dense Regular Connective Tissue• Closely packed bundles of collagen fibers

running in same direction – fibers regular and parallel

• Great resistance to tension• Crowded between collagen fibers are

fibroblasts that make fibers & ground substance

• Found in tendons, ligaments, aponeuroses, and fascia

Dense Irregular Connective Tissue• Randomly arranged collagen fibers & few

fibroblasts• Fascia, dermis of skin, periosteum,

perichondrium, joint capsules, membrane capsules around organs, heart valves

• Provides strength• Places where pulling in various directions

occurs (found in sheets)• Same structural elements as dense regular, just

arranged irregularly and with thicker fibers

Dense Elastic Connective Tissue• Elastic fibers & fibroblasts

• Allows stretching of various organs and elasticity (returns to original shape)

• Lungs, walls of trachea, arteries, bronchial tubes, true vocal cords, and some ligaments

Loose Connective Tissue• Softer, more cells and fewer fibers than any

other connective tissue type (*except blood)• Types:

– Areolar Tissue– Adipose Tissue– Reticular Connective Tissue

Loose Areolar Connective Tissue• All three types of fibers, semi-fluid ground

substance, several cells• Most widely distributed connective tissue• Soft, pliable – cushions and protects body

organs• Universal packing tissue and connective tissue

“glue”– Holds organs together and in proper positions

• Reservoir of water and salts for surrounding tissues – All cells obtain nutrients from & release wastes into

this “tissue fluid”

• Edema: areolar tissue in area soaks up excess fluid when area is inflamed – area swells and becomes puffy

• Phagocytes scavenge for bacteria and debris and dead cells in this tissue to destroy

Adipose Tissue• Commonly called fat• Adipocytes: specialized to store triglycerides• Droplet of oil occupies most of fat cell &

compresses nucleus• Subcutaneous tissue beneath skin – insulates

body and protects from bumps and extremes of heat & cold

• Cushions individual organs and stores fat for fuel if needed

• Newborns – brown fat (rich blood supply & more mitochondria)– Helps them maintain body temperature

Loose Reticular Connective Tissue• Made of reticular cells (resemble fibroblasts) &

reticular fibers• Limited to certain sites – forms “stroma”

– internal framework that supports free blood cells (lymphocytes) in lymphoid organs (i.e. lymph nodes, liver, spleen, bone marrow)

• Binds together smooth muscle

Blood (Vascular Tissue)• Plasma + formed elements (erythrocytes,

leukocytes, thrombocytes)• Blood plasma = nonliving, fluid matrix

– “fibers” – soluble protein molecules that are visible only during blood clotting

• Transport vehicle for cardivoascular system– Carries nutrients, wastes & respiratory gases;

immunity; clotting

Muscle Tissue• Highly specialized to contract and produce

movement• Types of muscle tissue:

– Skeletal Muscle– Cardiac Muscle– Smooth Muscle

Muscle & Nervous Tissue ID Quiz

Tissue types:• Skeletal muscle• Cardiac muscle• Smooth muscle• Nervous tissue

Parts:• Nucleus• Striations

(bands)• Intercalated disc• Neuron• Cell body• Dendrite• Axon• Neuroglia

Skeletal Muscle Tissue• Packaged by connective tissue sheets into organs• Attached to bones• Controlled movements/voluntary movements• Muscular System• Cells are long, cylindrical, multinucleate, have

striations (stripes)• Cells called “muscle fibers” because they are

elongated• Fibers run parallel to each other• Function: Motion, maintenance of posture, heat

production (maintaining temperature)

Cardiac Muscle Tissue• Only in heart wall• Function: pump and propel blood• Involuntary• Striations, uninucleate• relatively short, branching cells that fit tightly

together at intercalated discs (attach cells end to end)

• Contain gap junctions that allow ions to pass freely from cell to cell resulting in rapid conduction of electrical impulse across the heart

Smooth Muscle Tissue• no striations visible• Involuntary muscle • Single nucleus, spindle-shaped (pointed at each

end)• Stomach, uterus, blood vessels, airways, walls of

hollow organs (viscera) i.e. urinary & gall bladder– Contracts: cavity becomes smaller (constriction)– Relaxes: cavity dilates and enlarges (dilation)

• Peristalsis – wavelike motion keeps food moving through small intestine

• Contracts more slowly than other types

Nervous Tissue• Internal communication• Found in brain, spinal cord, and nerves• Two types of cells:

– Neurons: receive and conduct electrochemical impulses from one part of the body to another

– Neuroglia: supporting cells that insulate, support, and protect delicate neurons within the structures of the nervous system

Neurons• Receive & conduct electrochemical impulses• Two functional characteristics:

– Irritability– Conductivity

• Cytoplasm drawn out into long processes• Parts:

– Cell body – nucleus & organelles– Dendrites – processes that receive impulse– Axons – process(es) that send impulse

Neuroglia• Supporting cells of the nervous tissue• Don’t generate nerve impulse• Often sites of tumors because they can divide• Insulate, support, protect neurons

Tissue Repair (Wound Healing)• Tissue injury stimulates the body’s

inflammatory and immune responses and healing begins almost immediately

• Returning to homeostasis• Tissue repair/wound healing occurs in two

ways:– Regeneration – replacement of destroyed tissue

by the same kind of cells (parenchyma cells – functioning cells of organ)

– Fibrosis – repair by dense (fibrous) connective tissue (scar tissue) – (stroma – supporting cells of organ – connective tissue)

– Which type depends on:• Type of tissue damaged• Severity of injury

• Different tissue types have different capacities for renewal of parenchyma cells– During embryonic development, muscle & nervous

become highly differentiated and lose capacity for mitosis; epithelial and connective tissues general have a capacity for renewal

Tissue Repair (Wound Healing)1. Inflammation

– Nonspecific body response that tries to prevent further injury

– Inflammatory chemicals are released and make capillaries permeable

– Fluid with clotting proteins seep into injured area from blood

– Clot is constructed to stop loss of blood and hold wound together

– Scab forms where clot is exposed to air

Tissue Repair (Wound Healing)2. Granulation Tissue

– Delicate pink tissue composed largely of new capillaries

– Grow into damaged area from undamaged blood vessels nearby

– Fragile & bleed freely (i.e. when scab picked)– Contains phagocytes that dispose of blood clot– Contains connective tissue cells (fibroblasts) that

produce the building blocks of collagen fibers (scar tissue) to permanently bridge the gap

Tissue Repair (Wound Healing)3. Regeneration & Fibrosis

– Surface epithelium regenerates across the granulation tissue below the scab

– Scab detaches when surface epithelium has covered wound

– Fibrosis (scar) usually underneath regenerated epithelium

• Scar Tissue: strong, lacks flexibility, in ability to perform normal tissue functions

• Adhesions can resultfrom fibrosis and cause abnormal joining of adjacent tissue (recentsurgery sites) – can causeobstructions (abdomen)

Tissue Repair (Wound Healing)• Tissue repair can be affected by:

– Nutrition– Blood circulation

• Transport of oxygen, nutrients, antibodies, etc.• Removal of tissue fluids, bacteria, and debris

– Age• Young are better nutritionally• Better blood supply• Cells have higher metabolic rate• Cells & extracellular components change with age• Collagen/elastic fibers change with age