ch 5 tissues (epithelial)

what is a tissue?

a group of cells with specialized structures that perform a specific function

how are cells in certain tissues separated?

they’re separated by fluid spaces or intercellular spaces OR tightly packed by intercellular junctions

tight junction

close space between cells by fusing cell membranes (sheetlike membranes)

tight junction examples

digestive tract, blood vessels in brain

desmosome

bind cells by forming “spot welds” between cell membranes

desmosome examples

skin cells

gap junctions

forms tubular channels between cells that allow exchange of substances between joined cells

gap junctions examples

heart muscle

how do you distinguish tissues?

cell size, cell shape, cell organization, and cell function

how and what forms organs? do organs have specialized functions?

when tissues assemble and interact, they form organs; yes!

what are the major types of tissue?

epithelial, connective, muscle, and nervous

epthelial functions

protect, secrete, absorb, and excrete

connective functions

bind, support, protect, fill spaces, store fat, and produce blood cells

muscle function

movement

nervous function

conducts impulse for coordination, regulation, integration, and sensory reception

epithelial tissue characteristics

covers body surfaces and organs, forms inner lining of body cavities, lines hollow organs, and composes glands; cells are tightly packed to form a barrier

examples of hollow organs

lungs, tubules of the kidneys, chambers of the heart - anywhere that has open space

do epithelial have free space always, sometimes, or never? what’s the free space also known as?

they always has free space, the apical. also exposed to the OUTSIDE or internal OPEN space

what’s the purpose of basement membrane? is it living?

serves as an anchor for the epithelium to the connective tissue BENEATH; it’s a non-living membrane

hows connective tissue formed?

reticular fibers, similar to collagen, but thinner

why is the basement membrane darker than the rest?

due to the nuclei dividing near the base

how does epithelial tissue get nutrients?

from the underlying connective tissue by diffusion

does epithelial readily divide?

yes, for example, skin cells are constantly dividing. due to this, the surface of our skin is actually “dead” due to the lack of blood vessels, while deeper in our epithelial tissue, it’s “alive and younger.”

how is epithelial tissue specifically identified?

by number of layers of cells and cell shape

simple

1 layer of cells

stratified

more than 1 layer of cells

psuedostratified

1 layer of cells that looks stratified

squamous

thin, flattened cells

cuboidal

cubelike cells

columnar

elongated cells

what are the different types of epithelial tissue?

simple squamous epithelium, stratified squamous epithelium, simple columnar, pseudo-stratified columnar, simple cuboidal, and transitional

describe simple squamous; where are they common to find?

• single layer of thin, flat cells

• cells fit together like floor tiles

• common at sites of diffusion

simple squamous examples

lines of air sacs, walls of capillaries

describe stratified squamous

• thick tissue made up of many layers of cells

• cells divide in deep layers, pushing older ones outward, where they flatten

examples of stratified squamous

outer layer of the skin, lines the mouth

what does skin cells produce? when does this occur?

as skin AGES, they produce a protein known as “keratin.” causes cells to harden then die

what does keratin do? what molecule is it?

causes cells to harden then die; a protein

what is keratinization? what’s its purpose?

the production of a covering that is dry, tough, anda a protective barrier. it protects against water loss and blocks harmful substances entering the skin

where is the only place stratified squamous doesn’t harden? where does it line?

oral, stratified squamous doesn’t keratinize; remains soft and apical cells remain alive (retaining the nuclei)

describe simple columnar

• single layer of elongated cells that help to protect underlying tissue

• secretes mucus, digestive fluids, and absorbs nutrients

in simple columnar, where is the nuclei located?

they’re located along the basement membrane

which tissue type contains microvilli? what’s microvilli’s purpose?

simple columnar; microvilli increases the surface area

what are the glandular cells referred as? what is their purpose?

goblet cells; they secrete mucus onto free surfaces

what does mucus do?

it’s a protective fluid that prevents pathogens from entering the body

examples of simple columnar

lines the uterus and digestive tract, stomach and intestines

describe pseudo-stratified columnar

• appears stratified, but they’re not. cells are just one layer thick (every cell is attached to the basement membrane)

• cells nuclei are at two or more levels

what does pseudo-stratified columnar tend to possess? why?

posses cilia on the free surface; sweeps away mucus

what other cells do pseudo-stratified columnar posses? why?

goblet cells; to produce mucus

examples of pseudo-stratified columnar (location and purpose)

respiratory system, protection

describe stratified columnar

• consists of several layers of cells

• superficial cells are elongated and overlay a basal layer of cube-shaped cells

examples of stratified columnar

male urethra, parts of the pharynx, and larger ducts of exocrine glands

describe simple cuboidal

• single layer of cube-shaped cells

• centrallt located, spherical nuclei

where is simple cuboidal located?

kidney tubules

simple cuboidal function?

secretion and absorption

describe transitional cells

• specialized to change in response to increased tension

• irregularly shaped cells that flatten when stretched

transitional cells functions

• behaves as an expandable lining

• acts as a check valve - forms a barrier that helps prevents the contents of urinary tracts from diffusing back

examples of transitional cells

inner lining of the urinary bladder, ureters, and superior urethra

describe glandular epithelium

• specialized to produce and secrete substances into ducts or body fluids

• usually columnar or cuboidal epithelium

what are the different types of glands?

exocrine and endocrine

define exocrine; examples

• secretes products into ducts that open into surfaces

• can be multicellular or unicellular

• ex: skin or digestive tract

define endocrine; examples

secrete products into tissue fluid or blood; thyroid or ovaries

how are exocrine gland types classified?

classified according to the ways they secrete their products

merocrine

release fluid by exocytosis

examples of merocrine

salivary glands, pancreatic glands, sweat glands of the skin

apocrine

lose small portions of their glandular cell bodies during secretion

examples of apocrine

mammary glands, ceruminous glands (ear wax)

holocrine

release entire cells

examples of holcrine

sebaceous glands of the skin