Tissues (5) Flashcards
What is a tissue?
Groups of cells similar in structure and perform a common/related function
What are the 4 types of tissue?
Epithelial- lining of digestive tract organs, glands and skin surface
Connective- Bones, tendons and fat
Muscular- Muscles attached to bones and muscles of heart
Nervous- brain, spinal cord and nerves
Characteristics of epithelium- polarity
> All have an apical surface (upper free surface exposed to the body exterior or the cavity of an internal organ).
Many apical surfaces are smooth and slick but most have microvilli (extensions on the plasma membrane) which massively increase the SA.
All have a basal surface which consist of a thin supporting sheet called the basal lamina which acts as a selective barrier and selectively allows molecules to enter the epithelium
Basal layer also acts as scaffolding along which epithelial cells can migrate to repair a wound
Some epithelial, such as that lining the trachea have cilia that propel substances along their free surface
Characteristics of epithelium- specialised contacts
> Cells fit tightly together to form continuous sheets
Sides of adjacent cells are tied together by tight junctions (prevent substances from leaking through spaces between cells) and desmosomes (keep cells from pulling apart).
Characteristics of epithelium- avascular but innervated
> Contains no blood vessels but is supplied by nerve fibres
> Nutrients are provided to cells from the underlying connective tissue
Characteristics of epithelium- regeneration
> Has high regenerative capacity
Some cells rub off through friction
Some damaged by harmful substances in the external environment e.g. smoke and bacteria
As long as they receive adequate nutrition, they can replace lost cells by cell division.
What is epithelial tissue/epithelium?
A sheet of cells that cover a body surface or lines a body cavity
> Epithelia form boundaries between different environments
> Nearly all substances have received/given off by the body must pass through epithelial tissue
What are the two types of epithelium?
1) Covering and lining epithelium- forms the outer layer of the skin; dips into and lines the open cavities of the Genito-urinary, digestive and respiratory systems and covers the walls of the abdominal cavity
2) Glandular epithelium- forms the glands of the body
Characteristics of epithelium- supported by connective tissue
> Forms the basement membrane which reinforces the epithelium
Helps it to resist stretching and tearing
Defines the epithelium boundary
What are the functions of epithelium?
1) Protection
2) Absorption
3) Filtration
4) Excretion
5) Sensory reception
How is epithelium classified?
> Each has 2 names- the first indicates the number of cells present and the second describes the shape of the cells
What is simple epithelium?
> Consists of a single cell layer
> Usually found where absorption, secretion and filtration occur
What is stratified epithelium?
> Composed of 2 or more layers stacked on top of each other
> Common in high abrasion areas where protection is important such as skin surface, lining of mouth and vagina
What are the three shapes of epithelial cells?
1) Squamous- flattened and scale like
2) Cuboidal- as tall as they are wide
3) Columnar- tall and column shape
In each, the nucleus forms the same shape as the cell
What is simple squamous epithelium?
> Single cell layer
Very thin
Protection is not one of their specialities
Flattened cells with disc-shaped nuclei and little cytoplasm
What are the functions of simple squamous epithelium?
> Found where filtration/exchange of substances by rapid diffusion is a priority
In the kidney it forms part of filtration membrane
In lungs it forms the walls of the air sacs across which gaseous exchange occurs
In the CVS it provides a slick, friction-reducing lining, where its thinness encourages efficient exchange of nutrients and wastes between bloodstream and surrounding tissue cells (endothelium)
What is simple cuboidal epithelium?
> A single layer of cells, as tall as they are wide, with large, spherical and central nuclei
Functions are secretion and absorption
Found in kidney tubules, ovary surface and ducts of small glands
What is simple columnar epithelium?
> Single layer of tall, closely packed cells with round/oval nuclei
Many have microvilli and some have cilia
Mostly associated with absorption and secretion- cilia type propels mucus
Non-ciliated type lines most of digestive tract (stomach to rectum), gallbladder and ducts of some glands
Ciliated type lines small bronchi, uterine tubes and some parts of uterus
What is stratified squamous epithelium?
> Most widespread of stratified epithelium
Thick and well suited for a protective role in the body
It’s free surface are squamous while cells of deeper layers are cuboidal or columnar
Found in areas subject to wear and tear where surface cells are constantly being rubbed away and replaced by dividing cells from the basal layer
Epidermis of skin, lining of oesophagus, mouth and vagina.
What is stratified cuboidal epithelium?
> Rare
Mostly found in large glands (e.g.sweat glands and mammary glands)
Typically 2 layers thick
What is stratified columnar epithelium?
> Rare
> Small amounts found in pharynx, male urethra and lining of some glandular ducts
What is transitional epithelium?
> Forms lining of hollow urinary bladder which stretches as it fills with urine
Cells of basal layer are cuboidal/columnar
Apical cells vary depending on degree of distension (stretching) of organ
When distended, thins from 6 layers to 3 and apical cells flatten and become squamous like
This ability allows a greater volume of urine to be stored.
What is pseudostratified columnar epithelium?
> Single layer of cells with different heights, some not reaching the free surface
Nuclei seen at different levels
May contain mucus-secreting cells and have cilia
Function is to secrete substances, mostly mucus and to propel it by ciliary action
Ciliated type line trachea and most of upper respiratory tract
Non-Ciliated type in male sperm-carrying ducts and ducts of large glands
