Chapter 4: Tissues

Tissue

a group of specialized cells and the extracellular substances (matrix) surrounding them

Histology

microscopic study of tissue structure

Pathology

study of diseased tissues

Biopsy

removal of tissue from any part of the body

Autopsy

examination of organs of a dead body to know the cause of death or to study changes caused by a disease

Four basic tissue types

• Epithelial
• Connective
• Muscular
• Nervous

Embryonic Tissue

endoderm
mesoderm
ectoderm

endoderm

the inner layer, forms the lining of the digestive tract and its derivatives

mesoderm

the middle layer, forms tissues such as muscle, bone, and blood vessels

ectoderm

ectoderm

neuroectoderm

portion of the ectoderm that becomes the nervous system

neural crest cells

groups of cells that break away from the neuroectoderm during development; give rise to parts of the peripheral nerves, skin pigment, medulla of adrenal gland, many tissues of face

EPITHELIAL TISSUE (Epithelium)

‑ covers and protects surfaces, both outside and inside the body
‑ protects by covering body structures or lining body spaces (internal and external)

Free or apical surface

where cells are exposed and not attached to other cells

Lateral surface

where cells are attached to other epithelial cells

Basal surface

attached to a basement membrane

Basement membrane

filter and barrier to cell movements; secreted by epithelial and connective tissue cells; helps attached the epithelial cells to the underlying tissues; supports and guide cell migration during tissue repair

Simple epithelium

single layer of cells, with each cell extending from basement membrane to free surface

Stratified epithelium

more than one layer of cells, but only the basal layer attaches the deepest layer to the basement membrane

Pseudostratified columnar epithelium

-appears to be stratified but consists of one layer of cells

pseudo

means false

Squamous

flat or scale like

Cuboidal

cube-shaped; wide as they are tall

Columnar

tall and thin; taller than they are wide

Transitional

- modification
of stratified epithelium
- Roughly cuboidal to columnar
when not stretched
squamous-like when stretched

Simple Squamous Epithelium

- single layer of thin, flat cells often hexagonal cells; the nuclei appear as bumps when viewed in cross section
- diffusion, filtration, some secretion, and some protection against friction

Simple cuboidal epithelium

- single layer of cube-shaped cells; some cells have microvilli (kidney tubules) or cilia (terminal bronchioles of the lungs)

• secretion, excretion, absorption
• carry out active transport, facilitated diffusion, or secretion
• secretion and absorption by cells of the kidney tubules, glands, and choroid plexuses
• movement of particles embedded in mucus out of the terminal bronchioles by ciliated cells

cilia

move mucus

microvilli

increase the surface area for secretion and absorption

Simple Columnar Epithelium

-single layer of tall, narrow cells; some cells have cilia (bronchioles of lungs, auditory tubes, uterine tubes, uterus) or microvilli (intestines)

• produces and secretes mucus and digestive enzymes
(small intestine)
• movement of particles out of bronchioles by ciliated cells
• movement of oocytes through uterine tubes secretion by
ciliated cells
• secretion by cells of the glands, the stomach, and the
intestines
• absorption by cells of the intestines

Mucus

a clear, thick fluid that protects the lining of the intestine

Pseudostratified Columnar Epithelium

- single layer of cells; some cells are tall and thin and reach the free surface, and others do not; nuclei are at different levels and appear stratified; almost always ciliated and associated with goblet cells
- synthesize and secrete mucus onto the free surface and move mucus that contains foreign particles

goblet cells

secrete mucus onto the free surface

Stratified Epithelium

- several layers of cells that are cuboidal in the basal layer and progressively flattened toward the surface
- protects against abrasion, forms a barrier against infection, and reduce loss of water from the body

nonkeratinized (moist)

surface cells retain a nucleus and cytoplasm

keratinized

surface is replaced by keratin and the cells are dead

Stratified Cuboidal Epithelium

- more than one layer of cuboidal epithelial cells
- absorption, secretion, and protection

Stratified Columnar Epithelium

- more than one layer of epithelial cells, but only the surface cells are columnar; deeper layers are irregular or cuboidal in shape
- secretion, protection, some absorption

Transitional Epithelium

- stratified cells that appear cuboidal when the organ or tube is not stretched and squamous when stretched
- accommodates fluctuations in the volume of fluid in an organ/tube; protects against the caustic effects of urine

function is diffusion

Cells are normally flat and thin

major function is secretion or absorption

Cells are usually cuboidal or columnar.

Simple epithelium

is involved with diffusion, secretion, or absorption

Stratified epithelium

serves a protective role

Squamous cells

function in diffusion or filtration

Cuboidal or columnar cells

which contain more organelles, secrete or absorb

Free surfaces

can be smooth or lined with microvilli or cilia

Smooth free surface

reduces friction as material moves across it

endothelium

lining of blood vessels that is a specialized type of simple squamous; reduces friction as blood flows through the vessels

Microvilli

cylindrical extensions of the cell membrane that increase the free surface area

Cilia

propel materials along the free surface of cells; moves mucus

Desmosomes

‑ mechanical links that bind cells together
‑ contain plaque and have transmembrane glycoprotein (cadherins) that extend into the intracellular space between adjacent cells membranes and attach to one another

Hemidesmosomes

‑ modified desmosomes; anchor cells to the basement membrane
‑ resemble desmosome but do not link adjacent cells
‑ “half-desmosomes”
‑ transmembrane proteins: integrins

Tight junctions

‑ bind adjacent cells together and form permeability barriers
‑ prevent the passage of material between epithelial cells

Adhesion belt

‑ found just below the tight junction
‑ not as strong as desmosomes, they act as a weak glue that holds cells together

Gap junctions

- small channels that allow small molecules and ions to pass from epithelial cell to adjacent
‑ allow intercellular communicatio

connexin

proteins which form tiny fluid filled tunnels

connexons

connect neighboring cells

Glands

‑ secretory organs
‑ composed primarily of epithelium, with a supporting network of connective tissue

Exocrine glands

glands with ducts; ex: sweat or oil glands

Simple

no branches; ex: intestinal glands

Compound

many branches; ex: mucous gland of oral cavity

Tubular

end of duct; shaped as tubules (small tubes)

Alveolar/Acinar

sac-like structure

Tubuloacinar/Tubuloalveolar

combination of the tubular and alveolar

Merocrine Secretion

‑ produce vesicles that contain secretory products
‑ release through exocytosis
‑ used by water-producing sweat glands and exocrine portion of pancreas

Apocrine Secretion

‑ release of secretory products as pinched-off fragments of the gland cells
‑ milk-producing mammary gland (combination of apocrine and merocrine)

Holocrine Secretion

‑ secretory products are stored in the cells of gland
‑ involves the shedding of entire cells
‑ used by sebaceous (oil) glands of the skin

Endocrine glands

‑ no ducts (directly into bloodstream)
‑ have extensive blood vessels
‑ cellular products are called hormones (secreted into the bloodstream and carried throughout the body)
‑ ex: thyroid, thymus, pituitary glands, etc.

CONNECTIVE TISSUE

‑ a diverse primary tissue type that makes up part of every organ in the body
‑ cells far apart
‑ contain large amounts of extracellular matrix

Tendons

connect bone to muscle

Ligaments

connect bone to bone

-blast

cells build; create the matrix

-clast

cells that breakdown, remodel

-cyte

cells for maintenance

Macrophages

large white blood cells capable of moving and ingesting foreign substances

Mast cells

nonmotile cells that release chemicals, such as histamine, that promote inflammation

Adipocytes (adipose cells)

contain large amounts of lipid

WBC (leukocytes)

increases dramatically in response to injury or infection

Platelets

fragments of hemopoietic cells that function in the clotting process to reduce bleeding from a wound

Undifferentiated mesenchymal cells

-a type of adult stem cell that persist in connective tissue; have the potential to form multiple cell types

Three major components of Extracellular Matrix

(1) ground substance
(2) protein fibers
(3) fluid (blood)

Collagen fibers

most abundant; look like ropes and are flexible but resist stretching

Type I collagen

most abundant; found in tendons, ligaments, skin, and bone

Type II collagen

found in cartilage

Type III collagen

found in reticular fibers

Reticular fibers

very fine, short collagen fibers; support network that fills spaces between organs and tissues

Elastic fibers

have the ability to recoil after being stretched or compressed

Ground substance

‑ non fibrous proteins and sugars (proteoglycans)
‑ shapeless background against which the collagen fibers are seen through microscope

Hyaluronic acid

long, unbranched polysaccharide chain composed of repeating disaccharide units

Proteoglycans

large molecules that consists of a protein core attached to many long polysaccharides called glycosaminoglycans

Chondroitin sulfate

common glycosaminoglycan

Proteoglycan aggregate

trap large quantities of water allowing them to return to original shape when compressed or deformed

Adhesive molecules

hold the proteoglycan aggregates together and attach them to cells of tissue

Chondronectin

in ground substance of cartilage

Osteonectin

in ground substance of bone

Fibronectin

in ground substance of fibrous connective tissue

Mesenchyme

- mesenchymal cells are irregularly shaped; the extracellular matrix is abundant and contains scattered reticular fibers
- mesenchyme is the embryonic tissue from which connective tissues, as well as other tissues, arise

Mucous Connective Tissue

- mesenchymal tissue that remains unspecialized; the cells are irregularly shaped; the extracellular matrix is abundant and contains scattered reticular fibers
- Umbilical cord of newborn

Loose Connective Tissue

‑ Few protein fibers that form a lacy network, with
numerous spaces filled with ground substance and fluid
‑ Function: support and protect
‑ Location: between organs, muscles, glands, skin