Chapter 4 - Histology: Tissue Types and Functions

Tissue

Group of structurally and functionally related cells and their external environment that together perform common functions.

Extracellular matrix (ECM)

Substance surrounding the cell in a tissue that consists of extracellular fluid, ground substance, and protein fibers.

Functions of ECM

Providing the tissue with the strength to resist tensile (stretching) and compressive forces, directing cells to their proper places within a tissue, regulating the development, mitotic activity, and survival of cells, and holding cells in their proper positions.

Epithelial tissue

A tissue type composed of epithelial cells in a thin basal layer of extracellular matrix that functions to cover and line all body surfaces and hollow organs.

Connective tissue

Tissue type characterized by extensive ECM, functions in support, protection, and transport.

Muscular tissue

Tissue type specialized for contraction.

Nervous tissue

Tissue type involved in the transmission of electrical signals.

Ground substance

Shapeless, gel-like component of ECM that contains ECF with water + ions + nutrients + other solutes, glycosaminoglycans, proteoglycans, and glycoproteins.

Protein fibers

Large, long structures embedded within ground substances; composed of multi fibrous protein subunits that entwine to form long rope-like structures.

Collagen fibers

Multiple subunits of protein fibers in the ECM of a tissue that are composed of the protein collagen and give a tissue tensile strength.

Elastic fibers

Protein fibers in the ECM of a tissue that are composed of elastin surrounded by glycoproteins and give a distensibility (stretching to 1 ½ times resting length with no breakage) and elasticity.

Reticular fibers

Thin protein fibers in ECM of a tissue that form nets which organs such as spleen and lymph nodes and form supportive networks around blood vessels and nerves.

Glycosaminoglycans (GAGs)

Long, straight polysaccharide chains such as small chondroitin sulfate and large hyaluronic acid.

Proteoglycans

Consists of GAGs bound to a protein core (looks like a bottle brush) and makes ECM firmer and resist compression.

Cell-adhesion molecules (CAMs)

Type of glycoproteins that glue cells to each other and to ECM, binding to cell surface proteins, protein fibers, and proteoglycans.

Tight junctions (occluding junctions)

Intercellular junctions that hold cells tightly together in a tissue, making the space between them relatively impermeable and preventing macromolecules from passing between adjacent cells.

• Composed of integral proteins in plasma membrane of adjacent cells

• Found in between cells of blood vessels to prevent substance from leaving the blood

• Acts like a zipper

Desmosomes

Intercellular junctions that hold cells together in a tissue to increase the tissue's resistance to mechanical stresses.

• Composed of integral proteins that band two cells (desm- → band or bond)

• Acts like a button

Gap junctions

Intercellular junctions that connect the cytosol of neighboring cells and allow water and solutes to pass between them.

Epithelial cells

Cells joined by tight junctions and desmosomes.

Structure of epithelial tissue

Lacks blood vessels.

ECM

Extracellular matrix located beneath the basement membrane, anchors underlying blood vessels in place and provides a barrier between the epithelial tissue and underlying tissue.

Basement membrane

Composed of two components: basal lamina and underlying reticular lamina.

Basal lamina

Synthesized by epithelial cells, consists mostly of collagen fibers and ground substance.

Underlying reticular lamina

Synthesized by connective tissue deep to the epithelial tissue, consists of reticular fibers and ground substance.

Apical surface

Free edge of epithelial cell or tissue, exposed to external environment or some internal body space, bound to basal surface to thin basement membrane.

Basal surface

Edge attached to deeper cells or basal lamina.

Functions of epithelium tissue

Covers body/organs surfaces, lines body and organ cavities, forms some glands.

Protection

Epithelial tissues provide a continuous surface that shields underlying tissues from mechanical or thermal injury.

Immune defenses

Epithelial tissues provide a barrier against invading microorganisms.

Secretion

Epithelial cells form glands that produce oil or hormones that secrete through ducts or into the bloodstream.

Transport into other tissues

Certain substances cross by passive or active transport and enter other tissues, critical for nutrient absorption.

Sensation

Epithelia are rich in nerves that detect changes in internal and external environments.

Neuroepithelium

Specialized epithelium responsible for senses of light, taste, smell, hearing, and equilibrium.

Simple epithelia

A type of epithelial tissue composed of a single layer of epithelial cells.

Stratified epithelia

A type of epithelial tissue composed of two or more layers of epithelial cells.

Squamous

Epithelial cell shape that is flattened.

Cuboidal

Epithelial cell shape that is square.

Columnar

Epithelial cell shape that is tall.

Simple squamous epithelium

A single layer of squamous epithelial cells

Simple cuboidal epithelium

A single layer of roughly cubed shaped epithelial cells

Simple columnar epithelium

A single layer of tall and rectangular epithelial cells

Pseudostratified columnar epithelium

A single layer of columnar epithelial cells with uneven nuclei, giving the appearance of being stratified

Stratified squamous epithelium

several layers of squamous (flat) epithelial cells + underlying basal lamina

Location of stratified squamous epithelium

Located in the oral cavity, esophagus, anus, and vagina

Types of stratified squamous epithelium

2 types of stratified squamous epithelium: keratinized and nonkeratinized

Stratified cuboidal epithelium

2 layers of cuboidal epithelial cells + underlying basal lamina

Location of stratified cuboidal epithelium

Lines the ducts of certain exocrine glands (ex: sweat glands)

Stratified columnar epithelium

a few layers of columnar epithelial cells (in apical layer) and cuboidal epithelial cells (in basal layers) + underlying basal lamina

Location of stratified columnar epithelium

Lines the ducts of certain exocrine glands (ex: salivary glands, male urethra, conjunctiva→ thin clear membrane lining the anterior surface of eye part + inner eyelid)

Transitional epithelium

several layers of transitional shape between cuboidal (in basal layers) and squamous (in apical layers) epithelial cells + underlying basal lamina

Location of transitional epithelium

Found in organs of urinary system (kidneys, ureters, urinary bladder, urethra/ urothelium)

Shape change in transitional epithelium

Cells can change shape from cuboidal to squamous when stretched

Location of simple squamous epithelium

air sacs in lungs, lining of lumen in blood vessel, and kidneys

Location of simple cuboidal epithelium

kidney tubules, respiratory passages, ducts of exocrine glands, and many endocrine glands (ex: thyroid gland)

Location of simple columnar epithelium

lining of digestive tract and many hollow organs

Location of pseudostratified columnar epithelium

lining of nasal cavity + respiratory passages

Keratinized stratified squamous epithelium

Apical layers of cells lack nuclei, nonliving cells, apical cells filled with protein, keratin→ making it tough and resistant to friction, forms outer layer of our skin

Nonkeratinized stratified squamous epithelium

Apical layers of cell nucleated, living cells, found in organs that require protection from mechanical abrasion that need to retain moist surface

Ciliated simple columnar epithelium

Has cilia that project from apical surface, mucus covers apical surface and moves by cilia, Ex: air passages in lungs and uterine tubes

Nonciliated simple columnar epithelium

No cilia, often has microvilli, lines most of digestive tract (from stomach to anal canal)

Exocrine glands

gland that secretes a product thru a duct to the external surface of the body or into respiratory, gastrointestinal, and/or genitourinary tract (urinary + reproductive system)

Endocrine glands

gland that secretes a hormone(s) directly into the bloodstream to influence functions of distant target cells, lacks ducts

Goblet cells

unicellular exocrine gland that secrete mucus, found in lining of digestive and respiratory tracts

Merocrine secretion

Type of exocrine secretion in which the product is packaged into secretory vesicles for release by exocytosis.

Ex of exocrine gland that use merocrine secretion

Salivary and sweat glands.

Holocrine secretion

Type of exocrine secretion in which secretory cells accumulate a product, and the cell ruptures and dies.

Function of dead cells in holocrine secretion

Dead cells are shed and replaced by cells that undergo mitosis.

Ex of exocrine gland that use holocrine secretion

Sebaceous glands of the skin, which secretes sebum.

Apocrine secretion

Rare type of secretion that produces secretion by pinching off portions of the cytoplasm.

Ex of apocrine secretion

Mammary glands.

Mode of secretion for salivary glands

Merocrine secretion.

Mode of secretion for sweat glands in axillary region

Apocrine secretion.

Mode of secretion for oil producing sweat glands

Holocrine secretion.

Collagen fibers

Unbranched, cable-like long fibers that are strong, flexible, and resistant to stretching; appear white in fresh tissue.

Location of collagen fibers

In tendons and ligaments.

Reticular fibers

Similar to collagen but much thinner; form branching, interwoven framework that is tough but flexible.

Location of reticular fibers

Abundant in stroma of organs such as lymph nodes, spleen, and liver.

Elastic fibers

Contain protein elastin; they branch and rejoin, appearing wavy, and stretch and recoil easily, have yellowish color

Location of elastic fibers

Abundant in skin, arteries, and lungs.

Basic components of connective tissue

Three basic components are cells, fibers, and ground substance.

Four functions of connective tissue

1. Connecting and binding: connects body structures and binds other tissue layers in organs.

2. Support: supports body weight.

3. Protection: protects certain internal organs and provides shock absorption.

4. Transport: moves substances from one place to another.

Fluid connective tissue

Blood, which is the main transport medium in the body.

Four cell types in connective tissue proper

Fibroblasts, phagocytes, adipocytes, and mast cells.

Fibroblast

Cell type within connective tissue proper that produces components of ECM.

Adipocytes

Fat cells; the main cell type in adipose tissue.

Mast cells

Largest cell within connective tissue that secretes inflammatory mediators.

Phagocytes

Cells of immune system that ingest foreign substances, microorganisms, dead/damaged cells by phagocytosis.

Areolar connective tissue

A type of connective tissue proper primarily composed of ground substance

Dense connective tissue

Type of connective tissue proper primarily composed of protein fibers.

Dense irregular connective tissue

A type of dense connective tissue that contains collagen fibers arranged in irregular bundles

Dense regular collagenous connective tissue

A type of dense connective tissue proper that contains thick collagen fibers arranged in regular bundles

Dense regular elastic connective tissue

A type of dense connective tissue proper that contains elastic fibers arranged in regular bundles

Reticular tissue

A type of connective tissue proper that contains numerous, interweaved reticular fibers produced by surrounding fibroblasts

Adipose tissue

A type of connective tissue proper that consists of fat storing adipocytes

Cartilage

specialized connective tissue that is tough/ flexible

Function of Cartilage

absorbs shock & resistant to tension, compression, shearing forces

Hyaline cartilage

most abundant type that consist of large amounts of ground substances w/ fine type of collagen fiber that forms small bundles

Fibrocartilage

type of cartilage with bundles of collagen fibers, fibroblasts, chondroblasts, and chondrocytes

Elastic cartilage

type of cartilage with ECM filled with elastic fibers

Bone (osseous tissue)

specialized connective tissue; hard/dense tissue that forms bone