Tissues

Organized groups of cells that are similar in structure and function

Tissues

• Tissues are organized into organs.• Organs can contain more than one type• Four main types:– Epithelial Tissue– Connective Tissue– Muscle Tissue– Nervous Tissue

Epithelial Tissue• Also called epithelium

(epithe = covering)• Lining, covering, and

glandular tissue of body• Functions include

protection, absorption, filtration, and secretion

• Special Properties:– Avascular– Reproduce rapidly – Packed together tightly

Epithelial Tissues

• Each epithelium has two names:– One signifies the number of cell layers : • simple epithelium (one layer of cells) • stratified epithelium (more than one layer)

– The second name describes the shape of its cells• Squamous cells (flattened like fish scales) • Cuboidal cells (cube-shaped like dice)• Columnar cells (shaped like columns)

Simple squamous epithelium

• Single layer• Thin squamous

cells resting on basement membrane

• Forms serous membranes that line the body cavity

• In air sacs of lungs

Simple cuboidal epithelium

• Single layer• Cuboidal cells

resting on basement membrane

• Common in glands and ducts

• Forms walls of kidney tubules

Simple columnar epithelium

• Single layer• Columnar cells• Goblet cells that

secrete mucus are in this layer

• Lines digestive tract

• Mucous membranes that line body cavities

Pseudostratified Columnar Epithelium

• Vary in height so false impression that stratified

• Functions in secretion and absorption

• Lines respiratory tract

Stratified squamous epithelium

• Most common stratified epithelium

• Found in areas that receive friction, like esophagus, mouth, and skin

Transitional Epithelium• Highly modified

stratified squamous epithelium

• Forms lining of urinary bladder, ureter, and urethra

• Basal layer = columnar / cuboidal

• When organ is distended (stretched) with urine, the cells flatten and become squamous-like

• Allows ureter wall to stretch with greater volumes of urine

Glandular Epithelium• Gland – one or more cells that make and

secrete a product• Secretion – product of gland that contains

proteins in aqueous solution• Endocrine gland – ductless, diffuse secretion

(hormones) directly into the blood (ex: thyroid, adrenal, pituitary glands)

• Exocrine gland – retain ducts, secretions empty through ducts to epithelial surface (ex: sweat glands, liver, pancreas)

Connective Tissue

• Connects body parts• Most abundant and widely distributed tissue• Functions include protecting, supporting, and

binding together other tissues• Well vascularized (exceptions tendons,

ligaments; cartilage is avascular)• Connective tissues includes cells plus

extracellular matrix – nonliving substance outside cells

Extracellular Matrix• Produced by connective tissue and

secreted to exterior• Ground substance composed largely

of water and proteins• Cell adhesion proteins allow

connective tissue cells to attach to matrix fibers

• The following types of connective tissue are discussed in order of most rigid to softest

Bone

• Bone – osseus tissue, composed of bone cells in cavities called lacunae, surrounded by hard matrix of calcium salts and collagen fibers

• Protects and supports body organs

Cartilage

• Less hard and more flexible than bone• Chondrocyte – mature cartilage cell• Hyaline cartilage – most widespread– Abundant collagen fibers in a matrix with glassy

appearance (hyalin = glass)– Forms larynx, connects ribs to sternum, covers

bones to form joints– Fetus skeleton made of hyaline cartilage

Hyaline Cartilage

Fibrocartilage

• Highly compressible

• Forms disks between vertebrae

Elastic Cartilage

• Found in a structure with elasticity

• Supports external ear

Dense Connective Tissue

• Also called dense fibrous tissue• Collagen fibers as main matrix element• Fibroblasts – fiber forming cells between

collagen fibers• Two types:– Tendons – connect skeletal muscles to bones– Ligaments – connect bones to bones at joints

• Ligaments more stretchy (more elastic fibers) than tendons

Dense Fibrous Tissue

Loose Connective Tissue

• Softer, fewer fibers and more cells than other connective tissues except blood

• Areolar tissue – most widely distributed connective tissue– Soft, pliable, “cobweb”-like tissue– Cushions and protects body organs it wraps– Provides reservoir of water and salts for

surrounding tissue– site where nutrients are obtained and wastes

released

Areolar Tissue

Loose Connective Tissue• Adipose Tissue – commonly called fat– Areolar tissue in which fat cells predominate– Insulates body and protects it from extreme T– Stored in body and cushions some organs

Adipose Tissue

• Oil occupies most of a fat cell’s volume and compresses the nucleus, displacing it to one side

Blood

• Blood – vascular tissue; consists of blood cells surrounded by a matrix called blood plasma

• Atypical connective tissue• Transport vehicle for cardiovascular system

Muscle Tissue

• Muscle tissues are highly specialized to contract or shorten to produce movement

Skeletal Muscle

• Skeletal muscle tissue – skeletal muscle organs connected to the skeleton.

• Controlled voluntarily• Form flesh of the body – muscular system• Contraction leads to pulling on bone or skin• Result is movement or changes in expression• Cells are long, cylindrical, multinucleate, and

have obvious striations

Skeletal Muscle

• Long• Cylindrical• Multinucleate• Striations• Called “muscle

fibers”

Cardiac Muscle

• Found only in the heart• Contractions lead to propelling of blood

through the blood vessels• Cardiac muscle cells are uninucleate, short,

branching with striations and fit tightly together at intercalated disks– Gap junctions with ion flow

• Involuntarily controlled

Cardiac Muscle

• Cells short• Striated• Branching• Uninucleate• Intercalated

Discs

Smooth Muscle

• Smooth muscle (Visceral Muscle) – found in walls of hollow organs (stomach, uterus, blood vessels, etc.)

• Contractions lead to the organ constricting or dilating so substances are propelled

• No striations, uninucleate, spindle-shaped

Smooth Muscle

• No striations• Uninucleate• Pointed ends

(spindle shaped)

Nervous Tissue

• Nervous Tissue – made of cells called neurons• Neurons receive and conduct electrochemical

impulses from one part of body to another• Neurons and supporting cells (insulate and

protect neurons) make up the nervous system: the brain, spinal chord, and nerves

• Cytoplasm drawn out in extensions allows neurons to conduct impulses long distances

Neuron

• Neurons in human hippocampus