A & P Histology

histology

study of tissues and how they are arranged into organs

4 broad categories of tissues

epithelial tissue

connective tissue

nervous tissue

muscular tissue

organ

structure with discrete boundaries that is composed of two or more tissue types

tissue

a group of similar cells and cell products working together to perform a specific role in an organ

ways the 4 tissue types differ

types and functions of their cells

characteristics of the matrix

relative amount of space occupied by cells versus matrix

matrix (extracellular material) is composed of

fibrous proteins

clear gel called ground substance

ground substance also known as

tissue fluid, extracellular fluid, interstitial fluid, tissue gel

fertilized egg becomes

an embryo with layers

3 primary germ layers

ectoderm

endoderm

mesoderm

ectoderm (outer)

gives rise to epidermis and nervous system

endoderm (inner)

gives rise to mucous membrane lining digestive and respiratory tracts, digestive glands, among other things

mesoderm (middle)

gelatinous tissue called mesenchyme

wispy collagen fibers and fibroblasts in gel matrix

gives rise to cartilage, bone, blood, muscle

histologists preserve slice and section tissues

fixative prevents decay (formalin)

histological sections: tissue is sliced into thin sections one or two cells thick

stains: tissue I mounted on slides and artificially colored with histological stain

stains bind to different celular components

sectioning reduces three demential structure to

two dimensional slice

longitudinal section

tissue cut on its long axis

cross section

tissue cut perpendicular to long axis of organ

oblique section

tissue cut at an angle between cross and longitudinal sections

smear

tissue is rubbed across a slide

i.e blood

spread

some membranes and cobwebby tissues are laid out on a slide

i.e areolar tissue

epithelia are sheets of

closely adhering cells, one or more cells thick

epithelial tissue

covers body surfaces and lines body cavities

upper surface usually exposed to the environment or an internal space in the body

constitutes most glands

Avascular

avascular

does not have blood vessels

usually nourished by underlying connective tissue

epithelial tissue functions

protect deeper tissues from injury and infection

produce and release chemical secretions

excrete wastes

absorb chemicals including nutrients

selectively filter substances

sense stimuli → bug crawling on skin

epithelial cells are

very close together

epithelial cells have a

high rate of mitosis

basement membrane

basal surface

apical surface

basement membrane

layer between an epithelium and underlying connective tissue

collagen, reticular proteins, glycoproteins, other protein-carbohydrate complexes

anchors the epithelium to the connective tissue below it

basal surface

surface of epithelial cell facing the basement membrane deepest layer

rapidly, reproducing cells

apical surface

surface of epithelial cell that faces away from the basement membrane

simple epithelia

contain one layer of cells

named by shape of cells

all cells touch basement membrane

stratified epithelia

contain more than one layer

named by shape of apical cells

some cells rest on top of the others and do not touch basement membrane

four types of epithelia with only one layer of cells

1. simple squamous
2. simple cuboidal
3. simple columnar
4. pseudo-stratified columnar

3 and 4 usually contain goblet cells

goblet cells

wineglass shaped mucus secreting cells in simple columnar and pseudo-stratified epithelia

simple squamous epithelium

single row of thin cells

permits rapid diffusion or transport of substance

secretes serous fluid

locations: alveoli, glomeruli, endothelium, serosa

simple cuboidal epithelium

single layer of square or round cells

absorption and secretion, mucus production and movement

locations: liver, thyroid, mammary and salivary glands, bronchioles, and kidney tubules

simple columnar epithelium

single row of tall, narrow cells

oval nuclei in basal half of cell

brush border of microvilli, ciliated in some organs, may possess goblet cells

absorption and secretion; secretion of mucus

Locations: lining of GI tracts, uterus, kidney, and uterine tubes

pseudo stratified epithelium

looks multilayered, but all cells touch basement memebrane

nuclei at several layers

has cilia and goblet cells

secretes and propels mucus

stratified epithelia

range from 2-20 or more layers of cells

some layers rest directly on others

\-only the deepest layer attaches to basement membrane

4 types of stratified epithelia

stratified squamous

stratified cuboidal

stratified columnar

transitional epithelium

stratified squamous is

most widespread epithelium in the body

resists abrasion

deepest layer of stratified squamous undergoes

continuous mitosis

\-daughter cells push toward the surface and become flatter as they migrate upward

\-finally die and flake off- exfoliation or desquamation

two kinds of stratified squamous epithelia

keratinized- found on skin surface, abrasion resistant

nonkeratinized- lacks surface layer of dead cells

keratinized stratified squamous

multiple layers; cells become flat and scaly toward surface

resists abrasion; retards water loss through skin; resists penetration by pathogenic organisms

Locations: epidermis; palms and soles heavily keratinized

nonkeratinized stratified squamous

same as keratinized epithelium without surface layer of dead cells

resists abrasion and penetration of pathogens

Locations: tongue oral mucosa, esophagus, and vagina

stratified cuboidal epithelium

two or more cell layers; surface cells square or round

secretes sweat; produces sperm, produces ovarian hormones

Locations: sweat gland ducts; ovarian follicles and seminiferous tubules

transitional epithelium (urothelium)

multilayered epithelium with surface cells that change from round to flat when stretched

allows for filling of urinary tract

Locations: ureter and bladder

cell junctions

connections between two cells

most cells are anchored to

each other or their matrix

cells communicate with

each other

cells resist

mechanical stress

cells control

what moves through the gaps between them

tight junctions

linkage between two adjacent cells by transmembrane cell-adhesion proteins

in epithelia, tight junctions

form a zone that completely encircles each cell near its apical pole

tight junctions seal off

intercellular space, making it difficult for substance to pass between cells

desmosome

patch that holds cells together (like a clothing snap)

keeps cells from pulling apart→ resist mechanical stress

desmosomes are

hook-like, j-shaped proteins that arise from cytoskeleton

anchor cytoskeleton to membrane plaque

transmembrane proteins from each cell joined by cell adhesion proteins

hemidesmosomes

half desmosomes that anchor basal cells of a epithelium to underlying basement membrane

epithelium cannot easily peel away from underlying tissue

gap (communicating) junctions

formed by ring-like connexons

ions, nutrients, and other small solutes pass between cells

located in cardiac and smooth muscle, embryonic tissue, lens and cornea

connexon consists of

6 transmembrane protein arranged like segments of an orange around water-filled pore

gland

cell or organ that secretes substances for use elsewhere in the body or releases them for elimination form the body

glands are usually composed of

epithelial tissue im a connective tissue framework and capsule

secretion

product useful to the body

i.e saliva production

excretion

waste product

i.e urination

endocrine glands

have no ducts; secrete hormones directly into blood

some organs have both endocrine and exocrine functions

liver, gonads, pancreas

hormones

chemical messengers that stimulate cells elsewhere in the body

i.e. thyroid, adrenal, pituitary glands

exocrine glands

maintain their contact with surface of epithelium by way of a duct

surfaces can be external (sweat, tear glands) or internal (pancreas, salivary glands)

unicellular glands

found in an epithelium that is predominately nonsecretory

can be exocrine or endocrine

i.e mucus-secreting gobet celles

capsule

connective tissue covering of exocrine gland

septa or trabeculae

extensions of capsule that divide interior of Gand into compartments (lobes and lobules)

stroma

connective tissue framework of the gland

supports and oranges glandular tissue

parenchyma

cells that perform the tasks of synthesis and secretion

typically cuboidal or simple columnar epithelium

classification of glands

duct shape

gland shape→ tubular, acing, tubuloacinar

duct shape

simple (unbranched) vs compound (branched)

tubular

narrow secretory portion

acinar

secretory cells form dilated sac (acinus vs alveolus)

tubuloacinar

both tubular and acing portions

serous glands

produce thin, watery secretions

perspiration, milk, tears, digestive juices

mucous glands

produce glycoproteins, mucin, which absorbs water to form mucus

goblet cells: unicellular mucous glands

mixed glands

contain both serous and mucous cell types and produce a mixture of the two types of secretion

apocrine secretion “budding”

lipid droplet covered by membrane and cytoplasm buds from cell surface

mode of milk fat secretion by mammary gland cells

merocrine secretion

used by eccrine glands

uses vesicles that release their secretion by exocytosis

i.e. tear glands, pancreas, gastric glands, and others

holocrine secretion

cells accumulate a product until they disintegrate

secrete a mixture of cell fragments and synthesized substances

i.e. oil glands of scalp and skin

glands of eyelids

cell autolysis

increase viscosity

cells may be ONLY

epithelial, connective, or a mix of epithelial, connective, and muscular tissue

examples of membranes of only connective tissue

dura mater, synovial membranes, lens of eye

examples of membranes of only epithelium

anterior surfaces of cornea and lens of eye

cutaneous membrane

the skin

largest membrane in the body

stratified squamous epithelium(epidermis) resting on a layer of connective tissue (dermis)

relatively dry layer serves protective function

mucus membrane (mucosa)

lines passages that open to the external environment

i.e digestive tract

often have mucus producing goblet cells

sublayers or mucus membrane

epithelium. lamina propria(areolar tissue), muscular mucosa (smooth muscle)

functions of mucous membrane

absorptive, digestive, secretor and protective (respiratory)

serous (serosa) membrane

internal membrane

double membrane with watery fluid between

simple squamous epithelium resting on a layer of areolar tissue

serous membrane produces

serous fluid that arises from blood

serous membrane covers

organs and lines walls of body cavity

endothelium

mesothelium

endothelium lines

blood vessels and heart

mesothelium lines

body cavities (pericardium, peritoneum, pleura)ti

tissue growth

increasing number of cells or size of existing cells

hyperplasia

tissue growth through cell multiplication

hypertrophy

enlargement of preexisting cells

muscle growth through exercise

accumulation of body fat

neoplasia

development of a tumor (neoplasm)

benign or malignant

composed of abnormal, nonfunctional tissue

tissues can change

types within certain limits

differentiation

development of more specialized form and function by unspecialized tissue

i.e embryonic mesenchyme becoming cartilage and bone