Basic Cell Types Flashcards
What are the four basic tissues?
- epithelial tissue
- supporting tissue
- muscular tissue
- nervous tissue
What does the epithelial tissue cover?
- Covers and lines all body surfaces, cavities and tubes
What is epithelial tissue involved in?
- containment
- selective diffusion
- absorption
- secretion
- physical protection
How does epithelial tissue play a part in immunohistochemistry?
All epithelial tissue contain cytokeratin intermediate filaments
What are all epithelial supported by?
A basement membrane:
- separates the epithelium from the underlying supporting tissue
- avascular
- polarised, as one side faces the basement membrane (basal surface) and now towards the surface (apical surface)
If its avascular how does the tissue gain nutrients?
The epithelium is dependent on diffusion of nutrients and oxygen from connective tissue for survival
How are surface epithelia classified?
- number of cell layers
- shape of component cells
- presence of surface specialisations such as cilia/keratin
What are the types of cell layers?
- single layer is simple
- multilayered is stratified
What are the shape of component cells?
Based on the appearance at right angles to the epithelial surface
- squamous (flattened)
- cuboidal
- columnar
What are the types of simple epithelial cells?
- simple squamous epithelium
- simple cuboidal
- simple columnar
- pseudostratified columnar ciliated epithelium
Simple squamous epithelium?
- flattened irregular shaped cells forming a continuous surface called pavemented epithelium
- supported by an underlying basement membrane
- found in organs that take part in diffusion of gases or fluids, such as lungs or blood capillaries.
Simple cuboidal epithelium?
- intermediate between simple squamous and simple columnar
- nucleus is round and located in the centre of the cell
- lines small ducts and may have excretory, secretory or absorptive functions like collecting tubules of kidney
Simple columnar epithelium?
- taller than simple cuboidal
- nuclei are elongated and may be located towards the base, apex or centre of the cytoplasm – polarity of the nucleus
- founding adoptive surfaces like the small intestine, gall bladder or in secretory places like the stomach
Psuedostratified columnar ciliated epithelium?
- All cells rest on the basement membrane but nuclei are all at different levels giving the appearance of different cell layers
- found in airways so known as respiratory epithelium
- cilia propel mucus to the pharynx = mucociliary escalator
What do all SIMPLE epithelium have in common?
- All of the cells rest on the basement membrane
- one layer
What is stratified epithelia?
- defined as epithelia consisting of 2 or more layers
- mainly have a protective function
- poorly suited for absorption and secretion due to thickness of all the cell layers
- classification is based on surface cell shape and structure
What are stratified epithelia poorly suited for?
Absorption and secretion due to the thickness of all cell layers
What is classification based on in stratified epithelia?
Surface cell shape and structure
What are the types of stratified epithelia?
- Stratified squamous epithelia
- Stratified cuboidal epithelia
- Transitional epithelium (urothelium)
What is the structure of a stratified squamous epithelium?
- Flattened cells at the top (surface)
- Keratinising stratified squamous epithelium constitutes the epithelium of skin = epidermis
- Cuboidal cells at the base (basement membrane)
How is a stratified squamous epithelium adapted?
- Adapted to withstand constant abrasions and desiccation due to tough non-living surface layer composed of protein keratin wrapped in plasma membrane
- as the epithelium matures, nuclei are eventually lost
What is the structure of stratified cuboidal epithelium?
- It is thin stratified epithelium usually 2 or 3 layers of cuboidal cells only
- more robust than simple epithelium
How is the stratified cuboidal epithelium adapted?
- It is found in the lining of larger excretory ducts of exocrine glands such as salivary glands
- not involved in significant secretory or absorptive activity
What is the structure of transitional epithelium (urothelium)?
- the features are intermediate between stratified cuboidal and squamous epithelia
- when relaxed, surface cells are large and rounded umbrella cells
- when stretched, intermediate and surface layers are extremely flattened
Where are transitional epithelium (urothelium) found?
- only found in urinary tract in mammals and is highly specialised to accommodate stretch and the toxicity is urinecuboidal
What are the membrane specialisations of epithelia?
- Cilia
- Microvilli
- Goblet cells
What is the structure of cilia?
- motile structures that project from the luminal surface of epithelial cells, esp. in the female reproductive and respiratory tract
- may be 10 micrometers long
- easily seen on light microscope
- a cell may have up to 300 cilia
How does cilia function?
They beat with a wave-like synchronous rhythm propelling particles/fluid in a consistent direction over the epithelial surface
What is the structure of microvilli?
- minute finger- like projections of the luminal plasma membrane found int he epithelia that are specialised for absorption
- only 1 micrometer in length
- found in the small intestine
What is the function of microvilli?
- they increase the surface area by x30 fold: may be thousands on one cell
What is the structure of goblet cells?
- modified columnar epithelial cells
- scattered amongst many simple epithelia, particularly the GI and respiratory tract
- stains bright pink with PAS staining
What is the function of goblet cells?
- they synthesise and secrete mucus
What is the Glandular epithelium?
- epithelium that is primarily involved in secretion is often arranged into structures called glands
What are glands?
- Glands are invaginations of the epithelial surface which reproduce rapidly into the underlying connective tissue
- all glands will have a continuous basal rate of secretion, which is then modulated by nervous and hormonal influences
What types of glands are there?
- exocrine glands
- endocrine glands
What are exocrine glands?
- exocrine glands compromise solid organs of largely epithelial cells which are connected tot he surface epithelium of GI tract by branching system of ducts, e.g. vary from small sweat glands to salivary glands to the liver
- What categories can exocrine glands be divided into?
secretory compartment:
- tubular or acinar
- coiled or branched
duct system:
- branched (compound) or unbranched (simple)
Any combinations of the 2 can occur
exocrine glands : simple tubular glands
- found in the large intestine
- single straight tubular lumen into which the secretory products are discharged
- secretory cells line the entire duct
exocrine glands: simple coiled tubular glands
- found in sweat glands only
- tightly coiled in 3D so different portions seen in each plane of section
exocrine glands: simple branched tubular glands
- found in the stomach mucus secreting glands
- several tubular secretory portions which converge onto a single unbranched duct
what is the structure of endocrine glands?
- endocrine glands lose they connection to the epithelial surface during development and release secretions directly into blood e.g. thyroid gland
- they contain clusters of secretory cells each with their and they are surrounded by a rich network of blood vessels.
how do endocrine glands function?
- most endocrine glands release more than one hormone product, so often are composed of more than one type of secretory cell
- the secretion is controlled by metabolic factors e.g glucose, the secretion of other hormones and the nervous system
- release hormones into the intercellular spaces from whence they diffuse rapidly into the blood
What are supporting tissues?
tissue of mesodermal origin which provides structural and metabolic support for other tissues and organs
What are supporting tissues comprised of?
- specialised cells
- extracellular matrix: ground substance and fibres
- generally contain blood and lymphatic vessels
- many different forms with different physical properties
- physical properties of the tissue are determined by the extracellular matrix component
What is the function of supporting tissues?
- mediates exchange of nutrients, gases and metabolites between tissues and circulatory system
How many types of collagen are there?
collagen is a type of fibre:
- type 1 collagen
- type 2 collagen
- type 3 collagen (reticulin)
- type 4 collagen
- type 7 collagen
What is collagen?
- the main type of fibre
- most abundant protein in the body
- provides tensile strength
- secreted as tropocollagen into the extracellular matrix where it polymerises to form collagen
Where is type 1 collagen found?
Dermis, tendons, ligaments, bone and fibrous supporting tissue. Bundles visible with light microscopy
Where is type 2 collagen found?
Hyaline cartilage, fine fibrils dispersed in the ground substance
Where is type 3 collagen (reticulin) found?
Delicate branching supporting meshwork in highly cellular tissues e.g. liver, bone marrow and lymphoid organs, absorb metallic silver by which they are stained black
Where is type 4 collagen found?
Forms a mesh-like structure in basement membranes
Where is type 7 collagen found?
Anchoring fibrils that link to the basement membrane
Cells are derived from mesenchyme and include:
- fibroblasts; secreting extracellular matrix
- myofibroblasts: contractile function + secretion of extracellular matrix
- chondrocytes/osteocytes: responsible for secreting extracellular matrix in cartilage and bone respectively
- adipocytes: highly specialised for the storage and metabolism of fat
- defence and immune cells: mast cells, tissue macrophages and plasma cells; may be static or migrating elsewhere
What is primitive mesenchyme?
- Embryonic tissue from which all connective tissue is derived
- Mesenchymal cells are stellate shaped with delicate branching cytoplasmic extensions
- Oval nuclei
- The extracellular matrix is mainly ground substance with very few fibres, permits free diffusion
What are mature fibroblasts?
- Collagen fibres are dense and very pink
- fibroblast nuclei are condensed and elongated in the direction of collagen bundles
- little cytoplasm
- main function is to maintain the integrity of tissue by slow turnover of the extracellular matrix constituents
What is the basement membrane?
- Sheet-like arrangements of extracellular matrix proteins which act as interface between support tissue and parenchymal cells
- Called external lamina in nerve and muscle tissue
What is the function of the basement membrane?
- Provides metabolic support & binds to underlying support tissue
- Controls epithelial growth and maturation – acts as a barrier to downward epithelial growth
- Selective permeability especially important in the kidney
What is the structure of the basement membrane?
- fibrous protein collagen 4 and structural glycoproteins laminin, entactin and fibronectin
- These appear to be produced by the epithelial cells, except for fibronectin, which fibroblasts produce
The basement membrane is composed of 3 layers:
Lamina lucida
Lamina densa
Lamina fibroreticularis
What is the Lamina Lucida?
Relatively transparent layer abuts the plasma membrane of the basal epithelial cells
What is the Lamina Densa?
Intermediate electron-dense layer
What is the Lamina fibroreticularis?
Broad relatively electrolucent layer which merges with supporting tissue underneath. Mainly type 3 collagen & fibronectin
What are lamina lucida and dense mainly made up of?
Both lamina lucida and densa are largely made up of type 4 collagen and laminin
What are adipose tissues?
- Adipocytes are cells adapted for the storage of fat
What is the structure of adipose tissues? and where can they be found?
- Generally has a rich blood supply as important for releasing energy
- May be found in isolation or clumps, or make up the bulk of the tissue, as in adipose tissue
How do the adipose tissues function?
- Adipocytes also are responsible for releasing several proteins = adipocytokines e.g. leptin, tumour necrosis factor alpha, which regulate body mass and influence general metabolism
- Hormones and the nervous system, diet and energy expenditure will all influence the fat metabolism of adipocytes. Adipocytes are responsible for your health and they have an influence on health.
What types of adipose tissue are there?
- white adipose tissue
- brown adipose tissue
What is white adipose tissue?
- 20% of body weight in normal male adults and 25% in females
- Distributed throughout the body especially deep in the dermis
- Thermal insulator and a cushion against mechanical shock in sites like the kidney
- Pale staining as it is occupied by lipid, leaving thin rim of cytoplasm and cell membrane. Adipocyte nucleus is squashed to one side
- Adipocytes have receptors for insulin, cortisol, growth hormone and noradrenaline
What is brown adipose tissue?
- Highly specialised type found in newborn mammals
- Important role in temperature regulation
- Adult humans have very little brown adipose tissue
- Arranged in lobules separated by fibrous septae which convey blood vessels and nerves
