Module 7: Epithelial Tissue

Tissue

group of specialized cells and their surrounding tissue

How are tissues classifed?

1. structure and layers of cells

2. Function

3. Composition of extracellular matrix

Epithelial Tissue vs Connective Tissue

Epithelial tissue

• Lots of cells with little extracellular matrix

• densely packed

• arranged in layers

Connective tissue

• Little cells with lots of extracellualr matrix

• arranged irregularly

where is epithelial tissue found

• Protective covering of surfaces inside and outside the body’

example:

—> Lines the respiratory tract

—> lines the urogenital tract

—> Lines digestive tracts

—→ lines body cavities

—> Found as outside surface of body; skin

—> Found in arteries and blood vessels; endothelium

What are the 3 surfaces of eputhelial cells

apical surface: top of the cell, it is the msot exposed layer

Basal surface: bottom or base of cell. attached to basment membrane

Lateral surface: side of cell

Basement Membrane

It is a fibrous layer of extracellualr matrix but has no cells in it. It is found between the connective tissue and the epithelial tissue and has no cells. It is secreted by the connective and epithelial tissue

Functions

1. Holds epithelial cells together; acts as glue

2. Adheres connective tissue to epithelial tissue

3. porous; allows substances to get to the epithelial layer

How do epithelial cells get their blood supply

Epithelial cells are avascular, meaning they don’t have their own blood supply and instead, they get it from supporting tissue

For Example: the dermis gets its blood supply from underlying connective tissue

What happens if epithelial cells get damaged

Epithelial cells are able to regenerate, which basically means undergo mitosis to produce more cells. this is good as epithelial cells are often easily prone to injury (like the skin, gastrointestinal tract and reproductive tract)

Functions of epithelial tissue

• Barrier: skin protects body from foreign particles

• Protecting underlying tissue: epithelium in lining of the mouth

• Permitting the passage of substances. e.g. kidneys- filter toxins

• secretion: e.g. pancreas, mucus, sweat

• absorbing substances: microvilli in small intestines

what are the cell surface modifications?

• microvilli: finger like projections that increase surface area for absorption and secretion: stationary and found in small intestine

—> brush border

• cilia: sways back and forth to move substances along the surface

Classification of epithelial tissue: cell layers

• simple epithelial tissue: one layer

• stratified: more than one layer, only layer on bottom attached to basement membranbe

• pseudostratified: single layer of epithelial tissue but appears as more than one layer as the cells are at different heights so some reach apical surface while some don’t and nuclei are at different heights as well

Classification of epithelial tissue: cell shape

• squamous: flat disk shaped

• cuboidal: cube shaped

• columnar: longer in height then width

Functional characteristics of cel shapes and layer and shapes

• simple: allows for quick diffusion, filtration of blood, secretion, and absorption

• Stratified: protection, particularly against abrasion

• Pseudostratified: modification of simple layer, secretes and moves mucus

• Squamous: quick diffusion or filtration

• cuboidal and columnar: secretion or absorption. May include goblet cells, which produce and secrete mucus

which cell types are very rare in body

stratified cuboidal and columnar

Simple squamous epithelium

A single layer of flat cells

quic tranposrt, diffusion that facilitates efficient gas exchange and filtration. Its thin structure allows for rapid passage of substances.

Location: lining of blood vessels (endothelium), alveoli of lungs, bowman’s capsule of kidneys, and lining of serous membramne

Simple cuboidal

A single layer of cube-shaped cells

Function: secretion and absoption

Location: kidney tubules, glands and their ducts, and the surface of the ovaries

simpe columnar

Single layer of tall, narrow cells. some have cilia or microvilli

Location: glands (cerebrospinal fluid), bronchioles, uterus, uterine tubes, stomach, intstines, gallbladder, and verntricles of the brainfunctions

If cilia, then helps move particles out of bronchioles, moves oocyte throughout uterine tubes,

If microvilli then secretions by glands of the stomach and the intestine, absorption by cells of the intestine

pseudostratifed columnar

Structure: all cells reach the basement membrane. Almost always ciliated and associated with goblet (mucus-producing) cells.

Found in the respiratory tract (ciliated), epidermis (non-ciliated), and male uretha

what epithelial tissue type produced globlet cells

pseudostratified epithelium

transitional epithelium

stratified cells that change shape depending upon detention of organ

found in lining of urinary system

function: accolades functions of fluid in organ or tube, like when their ir urine in urinary bladder.

—> also protects against caustic effects of urine

startied sqaumous

multiple layer and as they go up the cells become more flat

function: protect against abravasions

keratinized: skin (protects against ultra violet radiation, infection and water loss)

non-keratinzed: where fluid/mucus is found lining the structure: vagina, mouth, throat, esophagus, and anus. keep area moist

Glands

epitheluim with supporting networks of connective tissue

can be a single cell or amss of apethilia cells that adapt for secretion

endocrine gland

ductless gland that produce hormone and release it to blood vessels or internal networks

exocrine glands

ducts that lead to exterior, like sweat glands, mammary gland (produce milk),