Histology Notes 2

8/6/2019 Histology Notes 2

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Histology Notes

Tissue: A group of similar cells that perform a special function.

It is composed of cells and extracellular matrix such as blood or bone.

Organs consist of 2 parts:

Parenchyma: the cellular part of the organ preforming the main function.Stroma: provides support, made up of connective tissue.

Types of tissues:

Epithelial Tissue

2 types:

Covering: covers all external surfaces and lines the bodys cavities

Glandular: cells that specialise in secretion.

Consists of uninterrupted layer of tightly packed cells. In glands where there are pores, these holes are an invagination of epithelium.

There is always an attached surface (basal layer) and a free surface (apical layer)

Intercellular spaces in epithelium are small and these narrow spaces between cells are sealed off from external environment by cell junctions.

Principal function:

covering, lining and protecting surfaces (i.e. skin, gut)

secretion (glands)

absorption (intestine) sensation (neuroepithelium)

contractibility (myoepithelial cells

Connective tissue is always underlying epithelial tissue to support it.


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Between these 2 tissues is the basement membrane which bounds the lamina propria to the epithelium. The free surface (apical) is exposed to the

outside and the basal surface is connected to the underlying lateral surface of the connective tissue.

Epithelium is avascular. It receives nutrients/oxygen/nerve impulses through the connective tissue that supports it through the basement membrane.

Connective tissue serves a mechanical and metabolic function to epithelial tissue.

Basement Membrane

It is formed by the secretion of both epithelial cells and connective tissue cells.

It separates the epithelium from the underlying connective tissue.

It allows some substances (selectively permeable) from connective tissue to supply epithelial tissue.

Composed of 2 layers:

The basal lamina (20-100 nm thick) and consists of protein filaments (laminin, collagen, glycoproteins, proteoglycans) embedded in the

amorphous matrix. It is produced by epithelial cells.

The reticular lamina consists of reticular fibres embedded in ground substance synthesised by cells of the connective tissue underlying theepithelium.

Specialisations of the cell surface: Microvilli, cilia and flagella.

Microvilli: small, close together protrusions, meaty (thanks Kim), appears like a brush border. Allows for the increase in absorption hence found in G I

tract.

Cilia: numerous, short, hairlike projections. Found on respiratory epithelium to help eliminate foreign particles. This respiratory epithelium also has

goblet cells that produce mucus which will trap foreign particles and cilia will sweep them outside of the system.

Flagella: similar structure to cilia but longer and is limited to one per cell, spermatozoa.


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Summary of Tissue Features

Tissue Justification Location Function Extra notes

Simple Squamous

epithelium

Consists of

single layer offlattened,

irregularlyshaped cells;

with a flat

centrally located

nucleus.

Displays a

mosaic pattern.

Lining of blood ve

ssels

(endothelium), liningbody

cavities (mesothelium),alveoli of lungs and

Bowmans capsule

(kidney)

Diffusion

(easier todiffuse across

one layer) andfiltration.

Secretion in

serous

membranes.

Stratifiedsquamous

epithelium

2 types:

Keratinised:

tougher, dryer;

contains protein

keratin that

strengthens tissue.

Non-Keratinised:

wet; called mucosa

Consists ofseveral layers of

cells, with cells

appearing

squamous

(flattened) at

apical surface

and cells closer

to basement

membrane

appearing

cuboidal tocolumnar.

Has rounded

nucleus,

centrally

located.

Keratinised:epidermis

(upper part of

skin)

Non-

keratinised:

Lining of oral

cavity,

oesophagus,

anus, cervix,

and vagina.

Protect againstmechanical

abrasion.

Keratinised:

protection and

prevents water

loss.

Non-

keratinised:

Protection andsecretion.


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Simple columnar

epithelium

Consists of tall

cells, appear

columnar.

Nuclei are

elongated and

may be located

towards the

base. Will have

microvilli

(appears likebrush border) on

the luminal

surface to help

with absorptive

properties. Will

also have goblet

cells.

Gastro-

intestinal tract,

Small intestine

Absorption

Pseudostratified

columnar

epithelium

Maybe ciliated or

nonciliated, though

majority are usually

ciliated.

Consists of one

layer of cells -

appears to be

more as cells are

at different

heights. All cells

do rest on

basement

membrane.

Columnar shapeof cell. Randomplacement of

rounded nucleus,

from base to cell

surface.

If ciliated, will

have goblet cells

Respiratory

system

including

trachea,

bronchi, nasal

cavity and

sinuses.

Exclusively

limited torespiratory area.

Protection,

secretion and if

ciliated,

movement of

particles outside

of airways.


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(release mucus).

Simple cuboidal

epithelium

Consists of one

layer of cells,

with cells being

cubed shaped.

Rounded,centrally located

nuclei.

Lining of

uterine tubes,

ducts of

salivary glands

and lines thekidney tubules.

Absorption and

secretion

Transitionalepithelium

So called as it

transitions between

stratified cuboidal

and stratified

squamous epithelia.

In a relaxed(contracted)

state, cells

appear more

rounded on

surface layer

(with prominent

strained central

nuclei) and more

cuboidal at

basement layer.

There mayappear to beabout 4 to 5 cell

layers thick. In a

stretched state,

will only appear

2 to 3 layers

Lines urinarybladder and

ureters.

Permitsdistention.


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thick (though

no. of cell layers

has remained

constant) and the

cells appear

extremely

flattened.

Surface cells

may have a

scalloped

outline.

Remember: All connective tissue has ground substance, fibres and cells

Looseconnectiv

e tissue

(areolar)

Consists of alarge amount

of ground

substance

with fibres

randomly

placed. Purple

stained line is

the elastic

fibre and pink

strained line

is the collagenfibre. Roundfibres are the

fibroblasts

(which

produce

collagen)

Found in thedeepest layer

of the skin:

the

subcutaneou

s layer.

Also around

blood

vessels.

Providesstrength,

support

and

elasticity.


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Dense

irregular

connectiv

e tissue

Random

placement of

densely

packed fibres

that show

both

transverse and

longitudinal

aspects of

collagenfibres. Not

much ground

substance

evident.

Found in

dermis of

skin and

around heart

valves.

Provides

strength

Dense

regular

tissue

Densely

packed,

regularlyarranged,

collagen fibre

(appear wavy)

with scattered

fibroblasts

(stained as

purple)

present inbetween rows.

Cells go in

one direction.

Not muchground

substance

evident.

Found in

tendons and

ligaments

Provides

strong

attachment between

structures.


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Adipose

tissue

Fat storagecell.

Lots of

ground

substance

between cells.Cell

(adipocyte) is

roundish and

stores a large

droplet of

triglycerides

inside which

displaces

nucleus is to

the side of the

cell.

Cytoplasm isaround the

rim of the cell

periphery

(cell

membrane).

Found in

subcutaneou

s layer.

Paddingaround

joints,

around heart

and kidneys.

Serves as

an energy

reserve,

supportsand

protects.


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Hyaline

Cartilage

Roundish

lacuna

containing

chondrocyte

appears

whitish

embedded

within ground

substance.Nucleus

within

chondrocyte

found off-

centre.

Cells within

the

perichondrium are called

chondrocytes.

Most

common

type of

cartilage.

Found in the

larynx, nose

and end of

long bones.

Creates a

smooth

surface for

ease of

movement

at joints.

Flexibility

and

support


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Compact

Bone

Concentric

bony layers or

lamellae are

located

around the

central

haversian

canal. Fine

canaliculi

radiate fromeach lacunae

which are

little cavities

filled with

osteocytes.

Found in

long bones

Support,

protection

and

storage.

House

blood

forming

tissue.


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Skeletal

Muscle

Striated

muscle fibres

light and

dark (with

NO

intercalated

discs).

Numerous

nucleuses,

positioned onperiphery of

cell. Presence

of connective

tissue

between

muscle fibres.

(Connective

tissue appearsas blue

scraggly lines

under

microscope).Thick fibres

are myosin

and thin fibres

are actin.

Usually

located to

bones by

tendons

Involved

in muscle

contractio

n

motion,

posture,

heat

production

and

protection.


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Smooth

muscle

Spindle

shaped fibres

thick in

middle and

tapered at

ends. No

striations.

Nuclei are

centrally

located andoval shaped.

Constriction

of blood

vessels and

airways,

propulsion

of food

through

gastro

intestinal

tract.

Internal

structures

such as

blood

vessels,

stomach,

intestines.


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Cardiac

muscle

Striated

muscle fibres

with

intercalated

discs joining

neighbouring

fibres.

Branched

cylindrical

fibres withone centrally

located

nucleus.

Heart wall Pumps

blood to

all parts of

the body.

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Histology Notes 2