Human Phys. Chp. 4

What is tissue classification based on?

* structure of cells
* composition of noncellular extracellular matrix
* cell function

What are the four examples of tissues?

* epithelial
* connective
* muscle
* nervous

What is histology?

microscopic study of tissues

What are embryonic germ layers?

form early in embryonic development and give rise to all tissues of the body

What are the different embryonic germ layers?

* endoderm: inner layer, forms lining of digestive tract and derivatives
* mesoderm: middle layer, forms tissues like muscle, bone, and blood vessels
* ectoderm: outer layer, forms skin and neuroectoderm

What are some characteristics of epithelial tissue?

* mostly composed of cells, very little extracellular matrix
* covers body surfaces and forms glands
* has distinct tissue surfaces
* cells connect to surrounding cells and extracellular matrix
* avascular: materials must move by diffusion from underlying connective tissue
* high regeneration capacity

What is the basement membrane?

* two layers - basal lamina and reticular lamina
* basal lamina: consists of lamina lucida and lamina densa
* made of specialized extracellular material secreted by the epithelial cells

What is the basement membrane’s function?

supports and guides cells migration during tissue repair; porous to allow movement of materials to and from the epithelial cells above

What are the functions of epithelial tissues?

* protect underlying structures
* acts as a barrier
* permits the passage of substances
* secretes substances
* absorbs substances

What are the two ways of classifying epithelial tissues?

* number of cell layers
* cell shape

What are the four types of epithelial tissues based on number of cell layers?

* simple
* stratified
* pseudostratified columnar
* transitional

What is simple epithelial tissue?

one layer, each extends from basement membrane to free surface

What is stratified epithelial tissue?

more than one layer, shape of cells of the apical layer used to name the tissue

What is pseudostratified columnar epithelial tissue?

tissue appears to be stratified, but all cells contact basement membrane so it is simple not stratified

What is transitional epithelial tissue?

special type of stratified epithelium where the cell shape changes from cuboidal/columnar to squamous-like when stretched

What are the two types of epithelial tissue based on cell shape?

* squamous
* cuboidal
* columnar

What is squamous epithelial tissue?

flat, scale-like

What is cuboidal epithelial tissue?

about equal in height and width

What is columnar epithelial tissue?

taller than wide

How does simple squamous epithelial tissue present?

single layer of flat, often hexagonal cells

What is the function of simple squamous epithelium?

diffusion, filtration, some secretion, and some protection against friction

Where can simple squamous epithelium be found?

* lining of blood vessels and the heart
* lymphatic vessels
* alveoli of the lungs
* portions of the kidney tubules
* lining of serous membranes of body cavities (pleural, pericardial, peritoneal)

What is the structure of simple cuboidal epithelium?

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

What is the function of simple cuboidal epithelium?

* secretion and absorption by cells of the kidney-tubules
* secretion by cells of glands and choroid plexuses
* movement of particles embedded in mucus out of the terminal bronchioles by ciliated cells

Where can simple cuboidal epithelium be found?

kidney tubules, glands and their ducts, choroid plexuses of the brain, lining of terminal bronchioles of the lungs, and surfaces of the ovaries

What is the structure of simple columnar epithelium?

single layer of tall, narrow cells; some cells have cilia or microvilli

What is the function of simple columnar epithelium?

* movement of particles out of the bronchioles of the lungs by ciliated cells
* partially responsible for the movement of oocytes through the uterine tubes by ciliated cells
* secretion by cells of the glands, the stomach, and the intestines
* absorption by cells of the intestines

Where can simple columnar epithelium be found?

glands and some ducts, bronchioles of the lungs, auditory tubes, uterus, uterine tubes, stomach, intestines, gallbladder, bile ducts, and ventricles of the brain

What is the structure of pseudostratified columnar epithelium?

* single layer of cells
* some cells are tall and thin and reach the free surface, and others do not
* the nuclei of these cells are at different levels and appear stratified
* cells are almost always ciliated and are associated with goblet cells that secrete mucus onto the free surface

What is the function of pseudostratified columnar epithelium?

synthesize and secrete mucus onto the free surface and move mucus (or fluid) that contains foreign particles over the surface of the free surface and from passages

Where can pseudostratified columnar epithelium be found?

lining of the nasal cavity, nasal sinuses, auditory tubes, pharynx, trachea, and bronchi of the lungs

What is the structure of stratified squamous epithelium?

* several layers of cells that are cuboidal in the basal layer and progressively flattened toward the surface
* the epithelium can be non-keratinized (moist) or keratinized

Describe non-keratinized stratified squamous epithelium

surface cells retain a nucleus and cytoplasm

Describe keratinized stratified squamous epithelium

the cytoplasm of cells at the surface is replaced by a protein called keratin, and the cells are dead

What is the function of stratified squamous epithelium?

* protects against abrasion
* forms a barrier against infection
* reduces loss of water from the body

Where can stratified squamous epithelium be found?

keratinized: outer layer of the skin

non-keratinized: mouth, throat, larynx, esophagus, anus, vagina, inferior urethra, and corneas

What is the structure of stratified cuboidal epithelium?

multiple layers of somewhat cube-shaped cells

What is the function of stratified cuboidal epithelium?

secretion, absorption, protection against infection

Where can stratified cuboidal epithelium be found?

sweat gland ducts, ovarian follicular cells, salivary gland ducts

What is the structure of stratified columnar epithelium?

multiple layers of cells with tall, thin cells resting on layers of more cube-shaped cells; the cells are ciliated in the larynx

What is the function of stratified columnar epithelium?

protection, secretion

Where can stratified columnar epithelium be found?

mammary gland ducts, larynx, a portion of the male urethra

What is the structure of transitional epithelium?

stratified cells that appear cuboidal when the organ or tube is not stretched and squamous when the organ or tube is stretched by fluid

What is the functional of transitional epithelium?

accommodates fluctuations in the volume of fluid in an organ or a tube; protects against the caustic effects of urine

Where can transitional epithelium be found?

lining of urinary bladder, ureters, and superior urethra

What is the function of smooth epithelium, and what is it also called?

reduce friction; endothelium

What is the function of folds in epithelium?

help change shape, useful in transitional epithelium

What is the function of microvilli in epithelium?

increases surface area for absorption or secretion, specialized microvilli modified as sensory receptors

What is the function of cilia on epithelium?

Move mucus across the surface of cells

Where are cell connections found?

On the lateral and basal surfaces of cells

What are the functions of cell connections?

* form permeability layer
* Bind cells together
* Provide mechanism for intercellular communication

What are the types of cell connections?

* desmosomes and hemidesmosomes
* Tight junctions
* Adhesion belt
* Gap junctions

What are desmosomes?

* disk-shaped regions of cell membrane
* often found in areas subjected to stress
* consists of an especially adhesive material between the cells and intermediate protein filaments that extend into cytoplasm of cells
* stratified squamous epithelium of the skin

What are hemidesmosomes?

* half of a desmosome
* attach epithelial cells to basement membrane preventing tissue movement

What are tight junctions?

hold cells together, form permeability barrier

What are adhesion belts?

found just below tight junctions that help anchor epithelial cells to each other to prevent passage of materials between cells; provides additional strength to tight junctions

What are gap junctions/what do they do?

* protein channels aid intercellular communication
* allows ions and small molecules to pass through
* function in epithelium unclear
* coordinate function of cardiac and smooth muscle
* may help coordinate movement of cilia in ciliated types of epithelium

How do gap junctions coordinate function of cardiac and smooth muscle?

by allowing electrical signals to pass from cell to cell

What are glands?

specialized secretory organs of epithelium with supporting network of C.T.

What are the two types of glands?

* endocrine: no open contact with exterior, no ducts, have an extensive network of blood vessels, produce hormones
* exocrine: open contact maintained with exterior by way of ducts that open onto the free surface of the epithelium

How are exocrine glands classified?

by structure of the duct, structure of the secretory portion, and by the method of secretion

What are unicellular glands?

single cell (ex: goblet cells that secrete mucus)

What are simple glands?

* multicellular glands with single, nonbranched duct
* secretory portion can be tubular or acinar (sac-like)

What are compound glands?

* multicellular glands with ducts with many branches
* secretory portion may be tubular, acinar, or both

What are the three modes of exocrine gland secretion?

* merocrine: exocytosis (most common)
* apocrine: pinched off fragments of gland cells (mammary glands and ceruminous glands)
* holocrine: shedding of entire cells (sebaceous glands)

What are some functions of connective tissue?

* enclose organs and separate organs into layers
* connect tissues to one another (ex: tendons and ligaments)
* support and movement (ex: bones)
* storage (ex: fat)
* cushion and insulate (ex: fat)
* transport (ex: blood)
* protect (ex: cells of immune system)

What does the suffix -blast indicate?

create matrix

What does the suffix -cyte indicate?

maintain matrix

What does the suffix -clast indicate?

break down matrix for remodeling

What do osteoblasts, osteocytes, and osteoclasts do?

* osteoblasts form bone
* osteocytes maintain bone
* osteoclasts break it down

What do chondroblasts and chondrocytes do?

* chondroblasts form cartilage
* chondrocytes maintain it

What do fibroblasts and fibrocytes do?

* fibroblasts form fibrous connective tissue
* fibrocytes maintain it

What do mast cells do?

* play important role in inflammation
* can release heparin, histamine, and proteolytic enzymes in response to injury

What role do white blood cells play?

respond to injury or infection

What do macrophages do?

phagocytize to provide protection against foreign and injured cells

What are the two types of macrophages?

* fixed: stay in position in C.T.
* wandering: move by amoeboid movement through the C.T.

What are platelets?

fragments of hematopoietic cells involved in clotting

What are undifferentiatied mesenchyme (stem cells)?

have potential to differentiate into adult cell types, not specialized yet

What are the three major components of the extracellular matrix?

* protein fibers
* ground substance
* fluid

What are the three types of protein fibers of the matrix?

* collagen: most common protein in the body; strong, flexible, inelastic
* reticular: fill spaces between tissues and organs; fine, collagenous, form branching networks
* elastic: returns to its original shape after distension or compression; contains molecules of protein elastin that resemble coiled springs; molecules are cross-linked

What are some examples of ground substance in the matrix?

* hyaluronic acid: polysaccharide, good lubricant, vitreous humor of eye
* proteoglycans: protein and long polysaccharides called glycosaminoglycans; protein part attaches to hyaluronic acid; traps large amounts of water
* adhesive molecules

What categories are used to classify embryonic C.T.?

* mesenchyme
* mucous C.T.

What categories are used to classify adult CT?

* connective tissue proper
* loose
* dense
* supporting CT
* cartilage
* bone
* fluid CT
* blood
* hematopoietic - red and yellow bone marrow

What is the structure of areolar CT?

fine network of fibers with spaces between them; fibroblasts, macrophages, and lymphocytes located in the spaces

What function does areolar CT have?

loose packing, support, nourishment for associated structures

What is the difference between yellow and brown adipose tissue?

* yellow: white at birth, turns yellow with age
* gets color from cytochromes and is specialized to generate heat

What is cartilage composed of?

chondrocytes located in matrix-surrounded spaces called lacunae

What are lacunae?

matrix-surrounded spaces in cartilage

What is the perichondrium?

dense irregular CT that surrounds cartilage

What do fibroblasts of perichondrium differentiate into?

chondroblasts

What are the three types of cartilage?

hyaline, fibrocartilage, elastic

What organic substance is bone matrix made of?

collagen fibers

What inorganic substance is bone matrix made of?

hydroxyapatite (calcium and phosphate)

Where are osteocytes located?

lacunae

What are the two types of bone?

spongy and compact

What is the matrix of blood made of?

other tissues, unlike other types of CT

What is hematopoietic fluid CT?

* forms blood cells
* found in bone marrow

What are the two types of bone marrow?

red: hematopoietic tissue surrounded by a framework of reticular fibers, produces red and white blood cells

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yellow: yellow adipose tissue, does NOT produce blood cells

Which type of marrow replaces the other as children grow?

yellow replaces much of red

What are the three types of muscle tissue?

skeletal, cardiac, smooth