[U3] Intro to Histology

Tissues

Collections of specialized cells and cell products that perform specific functions

Histology

Study of the structure of tissues

Epithelial Tissue

Basic Type of Tissue

Covers exposed external surfaces, lines internal passageways, and forms glands

Connective Tissue

Basic Type of Tissue

Diverse primary tissue, makes up part of every organ of the body

Fills internal spaces, supports other tissues, transports material, stores energy, etc.

Muscle Tissue

Basic Type of Tissue

Tissue, contracts or shortens - makes movement possible

Nervous Tissue

Basic Type of Tissue

Responsbile for coordinating and controlling many body activities, carries electrical signals from one part of the body to another

Epithelia

Epithelial Tissue

Layer of cells covering internal or external surfaces

External - covering; Internal - lining

Glands

Epithelial Tissue

Structures that produce fluid secretions, composed of epithelial tissue

• Physical protection (Internal and External)

• Permeability

• Sensation

• Substance secretion (Glands)

• Substance absorption

What are the functions of epithelial tissue?

Apical Surface

Characteristic of Epithelial Tissue

Exposed surface of epithelial tissue

Basal Surface

Characteristic of Epithelial Tissue

Bottom side of epithelial tissues, attaches with the basement membrane

Avascularity

Characteristic of Epithelial Tissue

Without blood vessels, no blood supply

Simple Epithelium

Classification of Epithelial Tissue (by Number of layers)

Epithelium composed of a single layer of cells, each cell extending from the basement membrane to the free surface

Stratified Epithelium

Classification of Epithelial Tissue (by Number of layers)

Epithelium consisting of more than one layer of cells, only basal layer attaches to the basement membrane

Pseudostratified Epithelium

Classification of Epithelial Tissue (by Number of layers)

Special type of simple (columnar) epithelium, appears falsely stratified

Transitional Epithelium

Classification of Epithelial Tissue (by Number of layers)

Epithelium that is found in organs that contract, appear cuboidal when not stretched and squamous when stretched

Squamous Epithelium

Classification of Epithelial Tissue (by Cell shape)

Flat or scalelike epithelium

Cuboidal Epithelium

Classification of Epithelial Tissue (by Cell shape)

Cube-shaped cells (about as wide as they are tall)

Columnar Epithelium

Classification of Epithelial Tissue (by Cell shape)

Cells tend to be taller than they are wide

• Composed of cells with very little extracellular material

• Covers exterior surfaces

• Covers interior surfaces (linings)

• Has an exposed apical surface

• Attaches at the basal surface with the basement membrane

• Has specialized cell connections and matrix attachments

• Avascular (w/o blood vessles or blood supply)

• Capable of regeneration

What are key characteristics of epithelial tissue?

Basement Membrane

Characteristic of Epithelial Tissue

Where the basal surface of epithelium attaches to

Simple Squamous Epithelium

Classification of Epithelial Tissue

Single layer of flat, often hexagonal cells

• Diffusion

• Filtration

• Secretion (some)

• Protection (some, against friction)

What are the functions of simple squamous epithelium?

• Lining of blood vessels and the heart

• Lymphatic vessels

• Alveoli of the lungs

• Portions of the kidney tubules

• Lining of serous membranes (body cavities)

Where are the locations of simple squamous epithelium?

Mesothelium

Simple squamous epithelium that lines the body cavities

Endothelium

Simple squamous epithelium that lines the heart and blood vessels

Simple Cuboidal Epithelium

Classification of Epithelial Tissue

Single layer of cube-shaped cells, some have microvilli or cilia

• Active Transport

• Facilitated Diffusion

• Secretion

  • Secretion and absorption (by cells of kidney tubules)

  • Secretion (by cells of glands and choroid plexuses)

• Movement of particles (embedded in mucus out of the terminal bronchioles by ciliated cells)

What are the functions of simple cuboidal epithelium?

• Kidney tubules

• Glands and their ducts

• Choroid plexuses of the brain (site for cerebrospinal fluid production)

• Lining of the terminal bronchioles of the lungs

• Surface of the ovaries

Where are the locations of simple cuboidal epithelium?

Simple Columnar Epithelium

Classification of Epithelial Tissue

Single layer of tall, narrow cells, some have microvilli or cilia

• Movement of particles (out of bronchioles of the lungs) (by ciliated cells)

• Movement of oocytes (through uterine tubes) (partial responsibility) (by ciliated cells

• Secretion (by glands, cells of the stomach, cells of the intestines)

• Absorption (cells of the intestines)

What are the functions of simple columnar epithelium?

• Glands and some ducts

• Bronchioles of the lungs

• Auditory tubes

• Uterus and Uterine Tubes

• Stomach

• Intestines

• Gallbladder

• Bile Ducts

• Ventricles of the brain

Where are the locations of simple columnar epithelium?

Pseudostratified Columnar Epithelium

Classification of Epithelial Tissue

Single layer of cells, some cells are tall and thin and reach the free surface, and others do not; nuclei of cells are at different levels and appear stratified; cells are almost always ciliated, associated with goblet cells

Goblet Cells

Specialized epithelial cells, found in the respiratory and digestive tracts, that produce and secrete mucin, a key component of mucus

• Synthesize and secret mucus (onto free surface)

• Move mucus (or fluid) containing foreign particles over the surface of free surface and from passages

What are the functions of pseudostratified columnar epithelium?

• Lining of nasal cavity

• Nasal sinuses

• Auditory tubes

• Pharynx

• Trachea

• Bronchi of lungs

Where are the locations of pseudostratified columnar epithelium?

Stratified Squamous Epithelium

Classification of Epithelial Tissue

Several layers of cells, cuboidal in the basal layer and progressively flattened toward the surface; can be nonkeratinized or keratinized

Nonkeratinized Stratified Squamous Epithelium

Classification of Epithelial Tissue

Moist stratified squamous epithelium, surface cells retain a nucleus and cytoplasm

Keratinized Stratified Squamous Epithelium

Dry, “waterproof” stratified squamous epithelium, cytoplasm of cells at the surface is replaced by keratin, and the cells are dead

• Protects against abrasion

• Barrier against infection

• Reduces loss of water from body

What are the functions of stratified squamous epithelium?

• Keratinized: outer layer of skin

• Nonkeratinized:

  • Mouth

  • Throat

  • Larynx

  • Esophagus

  • Anus

  • Vagina

  • Inferior Urethra

  • Corneas

Where are the locations of stratified squamous epithelium?

Stratified Cuboidal Epithelium

Classification of Epithelial Tissue

Relatively rare; Multiple layers of cells, somewhat cube-shaped

• Protection

• Secretion

• Absorption

What are the functions of stratified cuboidal epithelium?

• Sweat gland ducts

• Ovarian follicular cells

• Salivary gland ducts

Where are the locations of stratified cuboidal epithelium?

Stratified Columnar Epithelium

Classification of Epithelial Tissue

Relatively rare; Multiple layers of cells with tall, thin cells resting on layers of more cube-shaped cells; ciliated (in the larynx)

• Protection

• Secretion

What are the functions of stratified columnar epithelium?

• Mammary gland ducts

• Larynx

• Male Urethra (portion only)

Where are the locations of stratified cuboidal epithelium?

Transitional Epithelium

Classification of Epithelial Tissue

Stratified cells, appear cuboidal when not streched and squamous when stretched (by fluid)

• Accommodates fluctuations in the volume of fluid in an organ or a tube

• Protects against caustic effects of urine

What are the functions of transitional epithelium?

• Lining of urinary bladder

• Ureters

• Superior urethra

Where are the locations of transitional epithelium?

Microvilli

Free surface modifications

Free surface extensions found in cells that absorb or secrete

Endothelium

Free surface modifications

Smooth surfaces in the lining of blood vessels that reduce friction

Folded Surfaces

Free surface modifications

Orientation of surfaces that increase surface area e.g. in the lining of the small intestines

Cilia

Free surface modifications

Moves mucus along the tissue surface (simple columnar and pseudostratified columnar epithelia)

• Mechanically bind cells together

• Aid in formation of permeability barrier

• Provide mechanism for intercellular communication

What are the functions of cell connections?

Desmosomes

Cell Connections

Rivet structure, “spot-welds"; Mechanical links that bind cells together

Hemidesmosomes

Cell Connections

Half desmosomes that anchor cells to the basement membrane

Tight Junctions

Cell Connections

Cells fused (zipped) together; that form barriers and anchor cells to each other

Adhesion Belts

Cell Connections

Structures below tight junctions; help tight junctions anchor epithelial cells to each other

Prevents the passage of materials between epithelial cells (they completely surround the cell)

Gap Junctions

Cell Connections

Small channels that allow small molecules and ions to pass from one epithelial cell to an adjacent one

Intercellular communication (coordination of cell activities)

Endocrine Glands

Glands without ducts, secret products (hormones) into the bloodstream

Exocrine Glands

Glands with ducts, prdocuts are made and secreted (saliva, sweat, digestive secretions)

Duct

Part of gland; tube that transports the secreted material to the free surface of the epithelium

Unicellular Gland

Type of Exocrine Gland

“Goblet cells” Composed of only a single epithelial cell, produces mucus onto the surface of the tissue

Found in the respiratory and digestive tracts

Simple Glands

Type of Exocrine Gland

Multicellular glands, have a single, nonbranched duct

Simple Tubular Gland

Type of Simple Gland

Forms a straight tube with no branching of the secretory portion; found in the stomach and colon

Simple Branched Tubular

Type of Simple Gland

Gland with several tubular secretory portions branching from the single duct; found in the stomach

Simple Acinar Gland

Type of Simple Gland

Glands with a single sac-like secretory portion; e.g. sebaceous glands

Simple Branched Acinar

Type of Simple Gland

Glands with several acinar secretory portions branching from the single duct; e.g. sebaceous glands

Compound Gland

Type of Exocrine Gland

Multicellular glands with several branched ducts

Compound Tubular Gland

Type of Compound Gland

Glands with multiple ducts, each with a narrow tubular secretory portion; e.g. mucous glands of the duodenum

Compound Acinar Gland

Type of Compound Gland

Glands with multiple ducts; each with several sac-like secretory portions; e.g. mammary glands

Compound Tubuloacinar Glands

Type of Compound Gland

Glands with multiple ducts; each with several tubular and acinar secretory portions; e.g. pancreatic glands

Merocrine Secretion

Glands - Mode of Secretion

Involves the release of secretory products by exocytosis without cell damage; most common type of secretion

Apocrine Secretion

Glands - Mode of Secretion

Involves the release of secretory products as pinched-off fragments of the gland cells; e.g. mammary glands (fatty portion)

Holocrine Secretion

Glands - Mode of Secretion

Involves the shedding of entire cells; e.g. sebaceous glands

• Cells

• Protein Fibers

• Extracellular Matrix

What comprises connective tissue?

• Diverse (makes up part of every organ of the body)

  • Enclose and separate other tissue

  • Connect tissues to one another

  • Support moving parts of the body

  • Store compounds

  • Cushion and insulation

  • Transportation

  • Protection

What are the functions of connective tissue?

Extracellular Matrix

Extracellular components of connective tissue that make up most of the tissue volume (protein fibers, ground substance)

Mesenchyme

Origin of connective tissue, gives rise to all other connective tissue

Osteoblasts

Cells in Connective Tissue

Cells that form new bone and grow and heal existing bones

Osteocytes

Cells in Connective Tissue

Cells that maintain bone, formed when an osteoblast becomes embedded in the matrix it has secreted.

Osteoclasts

Cells in Connective Tissue

Cells that break down bone that is old or damaged, to make space for new bone tissue.

Fibroblasts

Cells in Connective Tissue

Cells that form fibrous connective tissue; most abundant fixed cells of connective tissue proper

Fibrocytes

Cells in Connective Tissue

Cells that maintain fibrous connective tissue fibers

Chondroblasts

Cells in Connective Tissue

Cells that form cartilage

Chondrocytes

Cells in Connective Tissue

Cells that maintain cartilage

Macrophages

Cells in Connective Tissue

Phagocytotic immune system cells; large cells that are capable of moving about and ingesting foreign substances, including microorganisms in the connective tissue

Mast Cells

Cells in Connective Tissue

Nonmotile cells that release chemicals such as histamine to promote inflammation

• Protein Fibers

• Ground Substance

• Fluid

What comprises the extracellular matrix of connective tissue?

Ground Substance

Component of Extracellular Matrix

Consists of non-fibrous protein and other molecules

Matrix Protein Fibers

Protein fibers that help form most connective tissues

Collagen Fibers

Matrix Protein Fibers

Most common fibers in connective tissue proper, microscopic ropes, very flexible but resist stretching

Reticular Fibers

Matrix Protein Fibers

Very fine, short collagen fibers that branch to form a supporting network

Elastic Fibers

Matrix Protein Fibers

Fibers with the ability to return to their original shape after stretch or compression

Proteoglycans

Material that makes up the matrix ground substance of connective tissue; large molecules that consist of a protein core attached to many long polysaccharides

Trap large quantities of water between polysaccharides, allows them to return to their original shape when compressed or deformed

Embryonic Connective Tissue

Type of Connective Tissue (Age)

Type of connective tissue found in a developing embryo; consists primarily of mesenchyme and mucoid connective tissue

Adult Connective Tissue

Type of Connective Tissue (Age)

Connective tissue in adults; by 8 weeks of embryonic development, most embryonic connective tissue has become specialized to form the types of connective tissue seen in adults

Loose Connective Tissue

Connective Tissue Proper

Consists of relatively few protein fibers that form a lacy network, with numerous spaces filled with ground substance and fluid

Areolar Connective Tissue

Loose Connective Tissue

Fine network of fibers (mostly collagen fibers, few elastic fibers) with spaces between them; cushions most organs

Consists of collagen, reticular, and elastic fibers