ch 3 tissue histology

Cuboidal epithelial cell

Location:

Simple squamous epithelia

Stratified squamous epithelia

Description:

Flat, irregularly shaped cell

Function:

Varies depending on location: diffusion, filtration, secretion ( serous membrane), protection

Simple cuboidal epithelium

Location:

Follicle of thyroid gland

Kidney tubules

Ducts of many glands

Surface of ovary

Description:

Single layer of cells that are approximately as tall as wide

Central , spherical nucleus

Function:

Absorption and secretion

Simple squamous epithelium

Location:

Lining of alveoli in the lungs

Endothelium ( lumen of blood and lymphatic vessels and heart chambers)

Mesothelium ( serous membrane lining body cavities)

Description:

single layer of flat, irregularly shaped cells

Central, flattened nucleus

Function:

Diffusion

Filtration

Secretion ( serous membrane)

Comment: mesothelium is epithelium of pleural, peritoneal, and pericardial membranes

Squamous cell

Location:

Simple squamous epithelia

Stratified squamous epithelia

Description:

Flat, irregularly shaped cell

Function:

Varies depending on location: diffusion, filtration, secretion ( serous membrane), protection

Cuboidal epithelial cell

Location:

• Simple cuboidal epithelia

• Stratified cuboidal epithelia

• Stratified columnar epithelia (deep layers)

• Stratified squamous epithelia (deep layers)

Description:

• Cuboidal cell (i.e., approximately as tall as wide)

• Central, spherical nucleus

• Apical surface may have microvilli

Function:

• Varies, depending on location: absorption, secretion, and protection

Lumen of collecting ducts

Location:

• Collecting duct in kidney

Description:

• Central opening lined by simple cuboidal epithelium

Function:

• Receives tubular fluid from multiple nephrons

Simple cuboidal epithelium

Location:

• Follicle of thyroid gland

• Kidney tubules

• Ducts of many glands

• Surface of ovary

Description:

• Single layer of cells that are approximately as tall as wide

• Central, spherical nucleus

Function:

• Absorption and secretion

Cilia on simple columnar epithelium

Location:

• Apical surface of simple columnar epithelium (uterine tube, uterus, efferent ductules of testis, and small bronchi)

Description:

• Motile cell projections

• Anchored to apical (luminal) portion of cell cytoplasm

• Individual cell may have up to 300 cilia

Function:

• Oscillations (bending to-and-fro) of cilia move substances (e.g., cells, mucus, and debris) over cell surface

Comment:

• Cilia in uterine tube beat in wave-like fashion toward uterus, thereby aiding movement of ovum and embryo (peristaltic contraction of wall of uterine tube may also aid in movement of ovum). The binding of sperm to the tips of cilia may facilitate the transport of sperm in the uterine tube toward the ampulla.

Simple columnar epithelium (ciliated)

Location:

• Lining of uterine tubes

• Lining of larger bronchioles of respiratory tract

Description:

• Single layer of tall, ciliated cells

• Basal, ovoid nucleus

• Nonciliated secretory cells (Peg cells) also present; these may have microvilli

• Goblet cells may be present

Function:

• Secretion of mucin

• Cilia move mucus in respiratory tract (pseudostratified epithelium) and oocyte and sperm in uterine tube (simple columnar epithelium)

Comment:

• Estrogen increases rate of ciliary beating on cells in uterine tube

• Cilia not present on stratified epithelia

Columnar epithelial cell (ciliated)

Location:

• Simple columnar epithelia

• Stratified columnar epithelia

Description:

• Columnar cell (i.e., taller than wide)

• Basal, ovoid nucleus

• Cilia present on apical surface

Function:

• Varies depending on location: absorption, secretion (e.g., mucin), protection, and movement of mucus.

Cilia on pseudostratified columnar epithelium

Location:

• Apical surface of pseudostratified columnar epithelium

• Lining of most of respiratory tract, epididymis, parts of urinary tract, and large excretory ducts of glands

Description:

• Motile cell projections

• Anchored to apical (luminal) portion of cell cytoplasm

• Individual cell may have up to 300 cilia

Function:

• Oscillations (bending to-and-fro) of cilia move substances (e.g., cells, mucus, and debris) over cell surface

Columnar epithelial cell (ciliated)

Location:

• Simple columnar epithelia

• Stratified columnar epithelia

Description:

• Columnar cell (i.e., taller than wide)

• Basal, ovoid nucleus

• Cilia present on apical surface

Function:

• Varies depending on location: absorption, secretion (e.g., mucin), protection, and movement of mucus

Columnar epithelial cell (ciliated)

Location:

• Ciliated pseudostratified columnar epithelium of respiratory tract (nasal cavity, pharynx, larynx, trachea, and bronchi)

Description:

• Specialized secretory cell

• Constitutes 30% of cells of respiratory epithelium

Function:

• Produces mucin and releases it into lumen

Pseudostratified columnar epithelium (ciliated)

Location:

• Lining of most of respiratory tract (nasal cavity, nasopharynx, larynx, trachea, and bronchi)

• Lining of epididymis

• Lining of parts of urinary tract (parts of female urethra, and membranous and spongy urethra in male)

• Lining of large excretory ducts of glands

Description:

• Single layer of cells, all of which contact basal lamina but only some reach the apical surface

• Nuclei at different levels, which gives "impression" of a stratified epithelium

• Usually ciliated

Function:

• Protection

• Secretion (mucin) and movement of mucus, cells, and particles

• Mucus secreted by goblet cells

Comment:

• Pseudostratified epithelium also known as respiratory epithelium

• Cilia not present on stratified epithelia

Dermis

Location:

• Skin (between epidermis and hypodermis)

Description:

• Two layers: papillary (superficial), composed of areolar connective tissue; and reticular (deep), composed of dense irregular connective tissue

• Contains appendages of skin: hair follicles and glands (sweat and sebaceous)

• Contains sensory nerve endings and dense network of blood and lymphatic vessels

• Includes part of hair follicle (which develops as invagination from epidermis)

Function:

• Supports epidermis

• Dense concentration of collagen and elastin gives skin strength

• Receives general sensory stimuli (pain, touch, and temperature) via nerve endings and specialized receptors

• Regulates body temperature

Comment:

• Muscles of facial expression insert on dermis

epidermis

Location:

• Skin (superficial to dermis)

Description:

• Keratinized stratified squamous epithelium of variable thickness

• Avascular

• Major cell type is keratinocyte

• Thick skin has five layers (superficial to deep): stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale

• Thin skin has four layers (stratum lucidum is missing)

• Cells of stratum lucidum and stratum corneum lack nuclei

Function:

• Physical barrier

• Protection of underlying structures

Comment:

• Also contains stem cells, melanocytes, Merkel cells, and dendritic cells

• Depends on underlying dermis for nutrients (i.e., vascular supply)

Squamous cell (without nucleus)

Location:

• Apical layer of stratified squamous epithelia (keratinized)

Description:

• Flat, irregularly shaped cell

Function:

• Variable, depending on location: diffusion, filtration, secretion (serous membranes), protection

Stratified squamous epithelium (keratinized)

Location:

• Epidermis of skin

Description:

• Multiple layers of cells

• Apical cells are squamous; basal cells are typically cuboidal or polyhedral

• Apical cells lack nuclei; these are dead cells that contain large amounts of the protein keratin

Function:

• Protection of underlying tissue

Comment:

• As cells reach apical surface, they accumulate the cytoskeletal (intermediate filament) protein keratin. These cells lose their nuclei and other cell organelles die and are sloughed off (shed).

Stratum basale

Location:

• Skin

• Deepest layer of epidermis

Description:

• Single layer of columnar or high cuboidal cells resting on basement membrane

• Keratinocyte is predominant cell

• Also contains melanocytes, Merkel cells (touch receptors), and stem cells

Function:

• Keratinocytes undergo mitosis, producing stem cells and cells that migrate into stratum spinosum

Also known as:

• Basal layer or stratum germinativum

Comment:

• Cells in stratum basale and stratum spinosum responsible for turnover of epidermal keratinocytes

• Melanocytes of this layer produce melanin, a natural sunscreen

Stratum corneum

Location:

• Skin

• Outermost layer of epidermis

Description:

• Up to 30 layers of cornified, dead cells

• Dead cells contain keratin

Function:

• Creates barrier to fluids

Also known as:

• Keratin layer

Comment:

• Cells sloughed (shed) from surface and continually replaced from deeper layers

• Sloughed cells form major component of household "dust"

• Latin: cornu = horn

Stratum granulosum

Location:

• Skin

• Epidermis, between stratum spinosum and stratum lucidum

Description:

• Three to five layers of flattened keratinocytes

• Keratinocytes contain dark staining keratohyalin granules (precursor of keratin)

• Nuclei of keratinocytes in various stages of degeneration

Function:

• Protection for deeper layers

Also known as:

• Granular layer

Comment:

• Not a distinct layer in thin skin

Stratum spinosum

Location:

• Skin

• Epidermis, between stratum basale and stratum granulosum

Description:

• Many layers of keratinocytes

• Deepest cells can divide

• Cells firmly attached to each other by desmosomes (cell junctions)

• Also contains dendritic (Langerhans) cells

Function:

• Helps maintain physical strength of epidermis

• Helps maintain barrier to infectious agents and harmful substances

Also known as:

• Prickle cell layer

Comment:

• Cells in stratum basale and stratum spinosum responsible for turnover of epidermal keratinocytes

Squamous cell (with nucleus)

Location:

• Simple squamous epithelia

• Stratified squamous epithelia

Description:

• Flat, irregularly shaped cell

Function:

• Variable, depending on location: diffusion, filtration, secretion (serous membranes), protection

Stratified squamous epithelium (nonkeratinized)

Location:

• Oral cavity and oropharynx, esophagus, and anus

• Uterine cervix, vagina, distal female urethra, and spongy urethra (male)

Description:

• Multiple layers of cells

• Apical cells are squamous; basal cells are typically cuboidal or polyhedral

• Apical cells have nuclei; these are living cells

Function:

• Protection of underlying tissue

Comment:

• Nonkeratinized stratified squamous epithelia are moist due to glandular secretions

Transitional epithelium

Location:

• Lining of urinary system (ureters, urinary bladder, and prostatic urethra)

• Lining of alantoic duct

Description:

• Multiple layers of cells

• Appearance varies depending on whether tissue is distended or relaxed

• In relaxed state, apical cells have characteristic dome shape; these flatten with distension

Function:

• Accomodates distension and relaxation with changes in urinary volume

Also known as:

• Urothelium

Comment:

• Different parts of male urethra lined by different epithelia: prostatic urethra - transitional; membranous and spongy urethra - stratified and pseudostratified columnar; navicular fossa in terminal part of spongy urethra - stratified squamous nonkeratinized

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Collagen fiber in areolar connective tissue

Location:

• Extracellular matrix (ECM)

Description:

• Type I collagen

• Ribbon-like bundles

Function:

• Tensile strength provides support for connective tissue

Comment:

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

Elastic fiber in areolar connective tissue

Location:

• Extracellular matrix (ECM) in areolar connective tissue

Description:

• Network of branching, interwoven fibers

• Typically small than collagen fibers

Function:

• Limit distensibility and overstretching of tissues

Comment:

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

• Areolar connective tissue is a type of loose connective tissue

Ground substance of areolar connective tissue

Location:

• Extracellular matrix (ECM)

Description:

• Non-cellular component of connective tissue ECM

• Abundant, viscous gel-like substance

• Composed primarily of water; stabilized by glycosaminoglycans, proteoglycans, and glycoproteins

Function:

• Substance of connective tissue that supports and binds cells and fibers

• Facilitates diffusion of gases, electrolytes, nutrients, and cellular waste products between cells and vasculature

• Barrier to macromolecules

Comment:

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

• Areolar connective tissue is a subtype of loose connective tissue

Mast cell and granules

Location:

• In connective tissue

• Along and/or near blood vessels in most tissues

Description:

• Large, round or ovoid cell (20-30 µm in diameter)

• Has abundant granules that contain heparin and histamine

Function:

• Releases granules (degranulates) as part of immune response; heparin inhibits blood clotting, histamine dilates blood vessels and increases blood flow

• Initiates immediate hypersensitivity response (anaphylaxis)

• Mediates allergic response

Comment:

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Nucleus of fibroblast

Location:

• Central in fibroblast

Description:

• Largest organelle (size depends on activity of fibroblast)

• Elongated, ovoid structure

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA and nucleolus

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Adipocyte

Location:

• Adipose connective tissue

Description:

• Spherical cell (up to 120 µm in diameter)

• Contains lipid inclusion (droplet)

• Has thin rim of cytoplasm and peripherally-located nucleus (large lipid inclusion pushes cytoplasm and nucleus to periphery of cell, resulting in classic "signet ring" in histological preparations)

Function:

• Stores fat (energy source)

Also known as:

• Fat cell

Comment:

• Adipocytes that contain single lipid inclusion (called unilocular) form white adipose tissue (fat)

• Adipocytes that contain multiple lipid inclusions (called multilocular) form brown adipose tissue (fat)

• Groups of adipocytes in H&E stained sections have "chicken wire" appearance

• When differentiated, cannot divide

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Nucleus of adipocyte

Location:

• Peripheral in mature adipocyte

Description:

• Largest organelle (5-10 µm in diameter)

• "Flattened" structure

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA and nucleolus

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Adipocyte also known as fat cell

• Lipid inclusion in mature adipocyte enlarges to push nucleus and cytopasm to periphery of cell, resulting in classic "signet ring" appearance in histological preparations

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Leukocyte

Location:

• Lymphatic and other organs

• Connective tissue (including blood)

Description:

• Nucleated cell

• 1.5-3 times larger in diameter than erythrocytes (red blood cells)

• Two classes: granulocytes and agranulocytes

• Granulocytes (which have abundant granules) include neutrophils, eosinophils, and basophils

• Agranulocytes (which lack abundant granules) include lymphocytes and monocytes

Function:

• Initiate and participate in immune response

Also known as:

• White blood cell

Comment:

• Relative abundance in blood: neutrophils (60-70%) > lymphocytes (20-25%) > monocytes (3-8%) > eosinophils (2-4%) > basophils (0.5-1.0%)

Macrophage

Location:

• Lymphatic organs

• Loose connective tissue under surface membranes

• Alveoli of lung (alveolar macrophages)

• Liver (phagocytic Kupffer cells)

• Central nervous system (microglia)

• Skin (Langerhans cells)

Description:

• Morphology variable, depending on location and function (approximately 12 µm in diameter)

• In connective tissue: numerous lysosomes and phagosomes, and irregular-shaped nucleus

Function:

• Phagocytosis

• Cytokine secretion (e.g., interleukin-1) when stimulated by T lymphocytes

• Antigen presentation upon antigen uptake

Also known as:

• Histiocyte

Comment:

• Derived from monocyte

• Phagocytosis (also called endocytosis) is process by which cells ingest particles and form endosomes (usually >250 nm in diameter)

• Antigen presenting cells include: macrophages, dendritic cells, reticular cells, and B lymphocytes

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter; nanometer (nm) is 1/1,000,000th of a millimeter

Reticular fiber

Location:

• Extracellular matrix (ECM)

• Stroma of lymph nodes, spleen, thymus, bone marrow

Description:

• Branched network of thin fibers

• Composed of type III collagen

Function:

• Tensile strength increases support role for connective tissue

Comment:

• Reticular fibers produced by fibroblasts

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

Collagen fiber in dense regular connective tissue

Location:

• Extracellular matrix (ECM)

Description:

• Type I collagen

• Compact fiber bundles arranged in parallel

• Little ground substance between bundles

Function:

• Tensile strength provides support for connective tissue

Comment:

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

Ground substance of dense regular connective tissue

Location:

• Extracellular matrix (ECM)

Description:

• Non-cellular component of connective tissue ECM

• Composed primarily of water; stabilized by glycosaminoglycans, proteoglycans, and glycoproteins

• Limited ground substance compared to loose connective tissue

Function:

• Substance of connective tissue that supports and binds cells and fibers

• Facilitates diffusion of gases, electrolytes, nutrients, and cellular waste products between cells and vasculature

• Barrier to macromolecules

Comment:

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

Nucleus of fibroblast

Location:

• Central in fibroblast

Description:

• Largest organelle (size depends on activity of fibroblast)

• Elongated, ovoid structure

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA and nucleolus

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Collagen fiber in dense irregular connective tissue

Location:

• Extracellular matrix (ECM)

Description:

• Type I collagen

• Compact fiber bundles (less regular arrangement than in dense regular connective tissue)

• More ground substance between bundles than in dense regular connective tissue

Function:

• Tensile strength provides support for connective tissue

Comment:

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

Ground substance of dense irregular connective tissue

Location:

• Extracellular matrix (ECM)

Description:

• Non-cellular component of connective tissue ECM

• Composed primarily of water; stabilized by glycosaminoglycans, proteoglycans, and glycoproteins

• Limited ground substance compared to loose connective tissue

Function:

• Substance of connective tissue that supports and binds cells and fibers

• Facilitates diffusion of gases, electrolytes, nutrients, and cellular waste products between cells and vasculature

• Barrier to macromolecules

Comment:

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

Nucleus of fibroblast

Location:

• Central in fibroblast

Description:

• Largest organelle (size depends on activity of fibroblast)

• Elongated, ovoid structure

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA and nucleolus

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Chondrocyte (in lacuna) in hyaline cartilage

Location:

• Cartilage matrix (gel-like extracellular matrix)

Description:

• Chondrocyte is mature cartilage cell

• One, two, or sometimes four chondrocytes can reside in a single lacuna; chondrocytes, particularly in developing cartilage, divide and daughter cells remain in same lacuna (this represents an isogenous group; Greek: isos = same + genos = family)

Function:

• Secretes cartilage matrix

Comment:

• Lacuna (plural, lacunae) is a small cavity

• Living chondrocyte fills lacuna; apparent space around chondrocyte in lacuna due to shrinkage during tissue processing for light microscopy

• Hyaline cartilage present in articular surfaces, larynx, tracheal rings, and nasal septum

Extracellular matrix of hyaline cartilage

Location:

• Cartilage extracellular matrix (ECM)

Description:

• Composed primarily of type II collagen; also includes proteoglycans, glycoproteins, and extracellular fluid

• Collagen does not form thick bundles

• Does not contain blood or lymphatic vessels, or nerves

Function:

• Resists mechanical stresses (e.g., compression, stretching, torsion)

Also known as:

• Extracellular matrix also known as extracellular space, extracellular fluid (ECF), tissue fluid, or interstitial fluid

Comment:

• Collagen in hyaline and elastic cartilage is predominantly type II; fibrocartilage contains type I collagen

• ECM of bone is calcified; ECM of cartilage is not calcified

• Hyaline cartilage present in articular surfaces, larynx, tracheal rings, and nasal septum

Lacuna (with chondrocyte) in hyaline cartilage

Location:

• Cartilage extracellular matrix (ECM)

Description:

• Small cavity

• Contains one, or more, chondrocytes

• Living chondrocyte fills lacuna; apparent space around chondrocyte in lacuna due to shrinkage during processing for light microscopy

Comment:

• Plural is lacunae

• One, two, or sometimes four chondrocytes can reside in a single lacuna; chondrocytes, particularly in developing cartilage, divide and daughter cells remain in same lacuna (this represents an isogenous group; Greek: isos = same + genos = family)

• Chondroblasts (immature cartilage cells), which give rise to chondrocytes, also found within lacunae

• Hyaline cartilage present in articular surfaces, larynx, tracheal rings, and nasal septum

Nucleus of chondrocyte

Location:

• Central in chondrocyte

Description:

• Largest organelle (5-10 µm in diameter)

• Spherical structure

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA

• Nucleolus prominent

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Chondrocyte (in lacuna) in elastic cartilage

Location:

• Cartilage matrix (gel-like extracellular matrix)

Description:

• Chondrocyte is mature cartilage cell

• One, two, or sometimes four chondrocytes can reside in a single lacuna; chondrocytes, particularly in developing cartilage, divide and daughter cells remain in same lacuna (this represents an isogenous group; Greek: isos = same + genos = family)

Function:

• Secretes cartilage matrix

Comment:

• Lacuna (plural, lacunae) is a small cavity

• Living chondrocyte fills lacuna; apparent space around chondrocyte in lacuna due to shrinkage during tissue processing for light microscopy

• Elastic cartilage present in larynx, epiglottis, auditory (Eustachian) tube, external auditory acoustic meatus, and external ear

Elastic fiber in elastic cartilage

Location:

• Extracellular matrix (ECM) in elastic cartilage

Description:

• Network of branching fibers

Function:

• Makes elastic cartilage more flexible than hyaline cartilage

Comment:

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

• Elastic cartilage present in larynx, epiglottis, auditory (Eustachian) tube, external acoustic meatus, and external ear

Ground substance of elastic cartilage

Location:

• Extracellular matrix (ECM)

Description:

• Non-cellular component of connective tissue ECM

• Solid, gel-like matrix

• Composed primarily of water; stabilized by glycosaminoglycans, proteoglycans, and glycoproteins

Function:

• Substance of connective tissue that supports and binds cells and fibers

• Facilitates diffusion of gases, electrolytes, nutrients, and cellular waste products between cells and vasculature

• Barrier to macromolecules

Comment:

• ECM of bone is calcified; ECM of cartilage is not calcified

• In connective tissue, extracellular protein fibers (e.g., collagen, elastic) plus ground substance form ECM

• Elastic cartilage present in larynx, epiglottis, auditory (Eustachian) tube, external auditory acoustic meatus, and external ear

Lacuna (with chondrocyte) in elastic cartilage

Location:

• Cartilage extracellular matrix (ECM)

Description:

• Small cavity

• Contains one, or more, chondrocytes

• Living chondrocyte fills lacuna; apparent space around chondrocyte in lacuna due to shrinkage during processing for light microscopy

Comment:

• Plural is lacunae

• One, two, or sometimes four chondrocytes can reside in a single lacuna; chondrocytes, particularly in developing cartilage, divide and daughter cells remain in same lacuna (this represents an isogenous group; Greek: isos = same + genos = family)

• Chondroblasts (immature cartilage cells), which give rise to chondrocytes, also found within lacunae

• Elastic cartilage present in larynx, epiglottis, auditory (Eustachian) tube, external auditory acoustic meatus, and external ear

Nucleus of chondrocyte

Location:

• Central in chondrocyte

Description:

• Largest organelle (5-10 µm in diameter)

• Spherical structure

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA

• Nucleolus prominent

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Central canal of osteon

Location:

• Center of osteon

Description:

• Longitudinal channel at core of concentric lamellae of osteon

• 20-100 µm in diameter

• Contains blood vessels, lymphatics, and nerves

Also known as:

• Haversian canal

Comment:

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Osteocyte in lacuna

Location:

• Calcified bone matrix (extracellular matrix)

Description:

• Osteocyte is mature bone cell

• Stellate (star shaped) cell

Function:

• Secrete substances that maintain bone matrix

• Detect and respond to mechanical stress on bone

Comment:

• Latin: lacus = a lake or hollow

• Plural of lacuna is lacunae

Osteon

Location:

• Compact bone

Description:

• Structural unit of compact bone

• Main components include: concentric lamellae (layers), central canal (Haversian system), osteocytes, and canaliculi

• Concentric lamellae of compact bone surround a central canal that contains blood vessels and nerves

• Osteocytes, which reside in lacunae, have processes that extend into canaliculae (a network of small canals) and contact processes of other osteocytes

Function:

• Functional unit of compact bone

• Structural support of compact bone

Comment:

• Osteon also known as Haversian canal system

• Compact bone also known as dense or cortical bone

• Other structures in compact bone, but not part of osteon, include: perforating (Volkmann) canals, circumferential lamellae, and interstitial lamellae

Erythrocyte

Location:

• Blood vessels of body

• Heart

Description:

• Biconcave disc shape

• Mature cells lack nuclei and organelles

• Make up 99% of the formed elements of blood

Function:

• Transports oxygen and carbon dioxide to and from tissues of body

Also known as:

• Red blood cell (RBC)

Leukocyte

Location:

• Lymphatic and other organs

• Connective tissue (including blood)

Description:

• Nucleated cell

• 1.5-3 times larger in diameter than erythrocytes (red blood cells)

• Two classes: granulocytes and agranulocytes

• Granulocytes (which have abundant granules) include neutrophils, eosinophils, and basophils

• Agranulocytes (which lack abundant granules) include lymphocytes and monocytes

Function:

• Initiate and participate in immune response

Also known as:

• White blood cell

Comment:

• Relative abundance in blood: neutrophils (60-70%) > lymphocytes (20-25%) > monocytes (3-8%) > eosinophils (2-4%) > basophils (0.5-1.0%)

Platelet

Location:

• Circulating blood

Description:

• Small, disc-shaped cell fragment (approximately 2 µm in diameter)

• Lacks nucleus

• Formed by fragmentation of cytoplasm of megakaryocyte (a cell in red bone marrow)

Function:

• Contributes to clot formation

Also known as:

• Thrombocyte (abnormally low number in circulating blood known as thrombocytopenia)

Comment:

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Nucleus of skeletal muscle fiber

Location:

• Periphery of muscle fiber, just inside plasma membrane

Description:

• Each skeletal muscle fiber contains numerous, flattened nuclei

• Largest organelle (5-10 µm in diameter)

• Spherical or ovoid structure

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA and nucleolus

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Position within fiber contrasts with central location in cardiac muscle

• Skeletal muscle fiber also known as skeletal muscle cell

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Branched cardiac muscle fiber

Location:

• Myocardium (muscular walls of heart)

• Walls of pulmonary veins and superior vena cava

Description:

• Short, branched muscle fibers joined end-to-end by intercalated discs

• Striated, involuntary muscle

• Contains one or two centrally placed nuclei

• Perinuclear cytoplasm apparent

Function:

• Involuntary contraction of myocardium

• Contraction may be modulated by autonomic nervous system

Comment:

• Intercalated discs contain numerous desmosomes and gap junctions

• Skeletal muscle fibers do not branch

• Cardiac muscle fiber also known as cardiac muscle cell

Intercalated disc

Location:

• Between cardiac muscle fibers

Description:

• Interdigitating folds of cell membrane that are sites of adhering (mechanical) junctions and gap (electrical) junctions

Function:

• Mechanical connection between adjacent cardiac muscle cells

• Electrical connection between adjacent cardiac muscle cells, providing for spread of polarization impulses throughout myocardium

Comment:

• Adhering junctions also known as desmosomes

• Cardiac muscle fiber also known as cardiac muscle cell or cardiomyocyte

Nucleus of cardiac muscle fiber

Location:

• Centrally located in cardiac muscle fiber

Description:

• Each cardiac muscle fiber contains one or two spherical or ovoid nuclei

• Largest organelle (5-10 µm in diameter)

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA and nucleolus

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Position within fiber contrasts with peripheral location in skeletal muscle

• Cardiac muscle fiber also known as cardiac muscle cell

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Longitudinal smooth muscle fiber

Location:

• Wall of hollow organs (e.g., gastrointestinal tract)

• Within stroma of many organs

Description:

• Spindle-shaped muscle cells with tapered ends

• Each fiber has single, centrally-placed nucleus

• Fibers are tightly packed and organized in longitudinally oriented "sheets"

Also known as:

• Involuntary muscle

Smooth muscle fiber

Location:

• Wall of hollow organs (e.g., vessels, airways, GI tract, bladder, and uterus)

• Within stroma of many organs (e.g., prostate)

Description:

• Spindle-shaped muscle cells with tapered ends

• Each fiber has single, centrally-placed nucleus

• Fibers tightly packed and arranged in staggered arrays

Also known as:

• Involuntary muscle

Axon

Location:

• Neuron

Description:

• Single, cylindrical process, which may be more than a meter long, extending from soma (cell body) of neuron

• Arises from axon hillock (which is devoid of Nissl substance)

• Usually without branches near cell of origin

• Terminates as axon terminal on other neurons or effectors

Function:

• Conveys efferent nerve impulses (i.e., away from soma)

• Conveys information to other neurons or effectors

Also known as:

• Nerve fiber

Comment:

• Axons with diameter greater than 2 µm usually myelinated

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Dendrite

Location:

• Central nervous system

• Ganglia of autonomic nervous system

Description:

• Tapered, highly branched processes extending from soma (cell body) of neuron

Function:

• Convey afferent nerve impulses (i.e., towards soma)

• Receive information from other neurons

Comment:

• Not myelinated

Neuron

Location:

• Central nervous system (CNS)

• Peripheral nervous system (PNS)

Description:

• Variable shape (uni-, bi-, or multipolar)

• Nucleus often has prominent nucleolus

• Abundant ribosomes cluster to form chromatophilic material (Nissl bodies)

• Have speciailzed processes: axon and dendrites

• Axon: single, long, thin process connected to soma at region known as axon hillock

• Multiple dendrites: multiple, relatively short, branched processes

Function:

• Generate, conduct, and receive nerve (electrical) impulses

• Axons direct information away from soma

• Dendrites direct information toward soma

Nucleus of neuron

Location:

• Soma (cell body) of neuron

Description:

• Largest organelle (5-10 µm in diameter)

• Spherical or ovoid structure

• Nuclear envelope comprised of double membrane (i.e., two lipid bilayers)

• Contains cellular DNA and nucleolus

Function:

• DNA replication

• DNA transcription into mRNA

• Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus)

Comment:

• Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly

• Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter