Types of Tissue 1: Epithelia Flashcards
4 Basic Types of tissue
- Epithelia
– Connective tissue (e.g. Connective
tissue proper, Bone, Cartilage, Blood,
Lymph)
– Muscle
– Nervous tissue
Tissue Definition
an assemblage of similarly specialized cells united in performing a
specific function
how many tissues are needed to make an organ
2 or more
what are the two types of epithelium
Proper epithelium
Glandular epithelium
proper epithelium function
covers and lines your outer and inner body
Glandular epithelium definition
forms your glands and secretes hormones and other substances
Where is epithelia found
Interface between compartments
Lines / covers all body surfaces and tubes
Glands
Epithelium functions
Covering, lining and protecting surfaces
Performs absorption
Secretion
Epithelia specialised characteristics
Specialised cell to cell junctions
Polarised
Basement membrane
Avascular - don’t have own blood supply - rely on connective tissues
3 epithelium cell types
Squamous cells, Cuboidal cells, Columnar cells
Squamous cell function
Lining and diffusion
make thin membranes - fast absorption and diffusion
Endothelium = blood vessels and lymph
Mesothelium = body cavities linings
Cuboidal cell function
absorb nutrients
produce secretions
columnar cell functions
absorb nutrients
produce secretions
- more organelles, larger
What is simple epithelium
one layer of cells
What is stratified epithelium
multiple layers of cells built on top of each other, like bricks
What is pseudostratified epithelium
mostly just one layer of cells
cells with different shapes and sizes
What is transitional epithelium
stratified epithelium that can accommodate stretching e.g. the bladder
Selective diffusion definition
transfer of gases, nutrients and waste products
between the blood and surrounding tissues.
What epithelia cells are used in selective diffusion
Usually simple squamous epithelia, to provide the smallest barrier to diffusion.
What epithelia are used for absorption /secretion.
For example absorption of nutrients from the gut, and secretion of enzymes for digestion.
usually columnar epithelia, as the
cells contain lots of endoplasmic reticulum, and Golgi, for secretion. They often have microvilli, to
increase the surface area of the apical surface for absorption.
What type of epithelia cells are used for physical protection.
For example, protecting underlying tissues from sunlight, heat, cold, abrasion, etc.
always stratified epithelia (many layers), and can
sometimes be keratinised on its apical surface, as in skin.
The keratin helps to waterproof the skin.
What are the 3 different polarities of the cells?
- Apical (lumen, modifications, microvillia, cilia etc)
- Lateral (connect to neighbouring cells)
- Basal (connect to basal lamina/basement membrane and underlying connective tissue)
What is the basement membrane?
Basal surfaces of all epithelia rest on the basement membrane
Functions of the basement membrane
Separates the epithelia from underlying connective tissue
Acts as a semipermeable filter
Important for the avascular cells
What are the 4 apical cell specialisations
- Microvilli
- Cillia
- Stereocillia
- Keratin
They have specialised structures
projecting from their apical side to aid absorption or to move substances along the cell’s surface
Functions of microvilli
Increase the apical surface area in cells.
Most developed in cells specialised for absorption (e.g. intestinal cells).
What is celiac disease caused by?
No microvilli in the intestines
Structure of microvilli
Fine, finger-like projections which contain a central core of microfilaments.
Structure of cilia
Long, motile projections of the apical surface. longer than microvilli. They contain a core of
microtubules and beat synchronously.
Location of cilia
They are found on cells lining the upper respiratory tract for example, where their rhythmic beating moves mucus upwards in the respiratory tract.
Stereocilia definition
Mechano-sensing organelles of hair cells (found in the inner ear and male reproductive tract.)
A much less common type of apical process
Different from cilia, more closely related to
microvilli.
Secrete and reabsorb fluid in epididymis to transport spermatozoa.
Stereocilia location
Found in inner ear and male reproductive tract
Keratin location
found in areas susceptible to abrasion and water loss (i.e. skin).
Keratin function
Layers of the intermediate filament protein keratin are found on the apical surface.
In the skin, basal cells divide and move out into the layers above.
As they reach the outer layers, they start to lose their nuclei and cytoplasmic organelles, the cells
degenerate and become ‘keratinized squames’ of the outer keratinized layer.
Proper epithelium function
covers and lines your outer and inner body
Glandular epithelium definition
forms your glands and secretes hormones and other substances
Endocrine glands
secrete hormones straight into the bloodstream or nearby cells
Exocrine glands
secrete juices into tubes or ducts that lead to the outside of the body
Secretory epithelia function
Secretory cells synthesize, store and release:
* Proteins- e.g. in the pancreas
* Lipids- e.g. adrenal, sebaceous glands
* Complex of carbohydrates and proteins- e.g. salivary glands
* All the above - e.g. lactating mammary glands
Exocrine glands remain in connection to the surface epithlium so that it delivers its secretions as and when. Endocrine glands have lost that
connection completely.
Cell to Cell junctions example
Desmosomes
How are epithelial layers connected
Epithelial layers consist of packed and
continuous cells.
Little to no extracellular material- unlike connective tissue
So are connected by specialised cell to cell junctions e.g. desmosomes
Desmosomes definition
Desmosomes are molecular complexes of cell adhesion proteins and linking proteins
Desmosomes function
Specialized for cell-to-cell adhesion.
Lateral domain of the cells.
Help to resist shearing forces found in simple and stratified squamous epithelium.
Desmosomes location
Scattered, spot-like attachment sites
Basal membrane connections
In the basal domain there are a variation called Hemidesmosomes, an anchoring junction.
Very small stud- or rivet-like structures
Hemidesmosomes
Contain a dense plaque on inner surface of the plasma membrane with keratin containing filament coursing out into the cytoplasm
What is the stratum basale?
The deepest layer of the skin
Separated from the dermis by the basement membrane, attached to basement membrane by hemidesmosomes.
What is the stratum corneum?
The outermost layer of the epidermis.
Is the barrier that prevents unwanted materials from entering the body and excessive loss of water.
What is the stratum spinosum?
8-10 cell layers (known as prickle cell layer)
Helps make skin flexible and strong.
What is the stratus lucidum?
Smooth, seemingly translucent layer of the epidermis.
Reduces friction
(located above stratum granulosum and below stratum corneum)
What is the stratum granulosum?
3-5 cell layers
Forms waterproof barrier helps to prevent fluid loss from the body.
