Lecture 3: Basic cell types Flashcards
What are the four basic tissue types?
Epithelial tissue, supporting tissue, muscular tissue, nervous tissue
What are epithelial tissues?
Diverse group of tissues including surface epithelia and solid organs
What do epithelial tissues cover?
All body surface, cavities and tubes
What are the functions of epithelial tissues?
Containment, selective diffusion/absorption, secretion and physical protection
What do all epithelial tissues contain?
Cytokeratin intermediate filaments (makes them recognizable)
What are all epithelia supported by?
Basement membrane of variable thickness
What does the basement membrane separate the epithelium from?
Underlying supporting tissue
What does the basement membrane not contain?
Blood vessels
What is the consequence of basement membranes not containing blood vessels?
Epithelial cells are dependent on diffusion of nutrients and oxygen from connective tissue
Because of the basement membrane, epithelial cells are ______
polarised
What is the name of the side of the epithelial cells facing the basement membrane?
Basal surface
What is the name of the side of the epithelial cells facing towards the surface (not the basement membrane)
Apical surface
On what three properties are epithelial tissues classified?
No.cell layers, shape of cells, presence of surface specialisations
What are the two types of epithelial tissues based on the number of cell layers?
Single layer: simple
Multilayered: stratified
What are the three shapes of component cells of epithelial tissues?
Squamous (flattened), cuboidal columnar
In stratified epithelia, the shape of which part of the tissues cells determine its name?
The surface shape
Describe the shape of simple squamous epithelium
Flattened, irregular shaped cells, form a continous surface
Simple squamous epithelium is often called…
Pavemented epithelium
What supports simple squamous epithelium?
A delicate underlying basement membrane
Where is simple squamous epithelium found?
Lining surfaces involved in diffusion of gases or fluids (lungs, blood capillaries etc.)
How can simple squamous epithelium be recognized?
Nucleus bulges into the lumen
How is simple cuboidal epithelial tissue recognised?
Nucleus is round and located in the centre of the cell
Where is simple cuboidal epithelial tissue found?
Small ducts that are excretory, secretory or absoptive
Give an example of where simple cuboidal epithelium is found in the body.
Collecting tubules of kidney
What do cell borders of simple cuboidal epithelium look like?
Indistinct
Where are nuclei located in simple columnar epithelium?
Base, apex or centre of cytoplasm: this is polarity of nucleus
Where are simple columnar epithelium found?
Absorptive surfaces (small intestine, gall bladder) or secretory (e.g. stomach)
Name another type of simple epithelia.
Psuedostratified columnar ciliated epithelium
Why is psuedostratified columnar ciliated epithelium classed as simple epithelia?
All cells rest on basement membrane, just nuclei are at different levels
Where is psuedostratified columnar ciliated epithelium found?
Airways: also known as respiratory epithelium
What do the cilia do in psuedostratified columnar ciliated epithelium tissue and what is this called?
Propel mucus to the pharynx
Mucociliary escalator
What function does stratified epithelia have?
Mostly protective (too thick for absorption/secretion)
What are the shape of the cells at the top and bottom of stratified squamous epithelium?
Flattened at the top
Cuboidal at the base
What is the epidermis made of?
Keratinising stratified squamous epithelium
How is the epidermis adapted to withstand constant abrasion/dessication?
Tough non-living surface layer composed of protein keratin wrapped in plasma membrane
What happens as the epithelium within the epidermis matures?
Nuclei are eventually lost
Describe the structure of stratified cuboidal epithelium
Thin, usually 2-3 layers of cuboidal cells only
Where is stratified cuboidal epithelium found?
Lining of larger excretory ducts of exocrine glands (salivary glands etc)
What is the strength of stratified cuboidal epithelium vs simple?
More robust
Is stratified cuboidal epithelium involved in significant secretory or absoptive activity?
No
What name is given to the epithelia found in the urinary tract of mammals?
Transitional epithelium (urothelium)
What is urothelium specialised for?
To accommodate stretch and the toxicity of urine
What types of epithelial cells does transitional epithelium have?
Intermediate between stratified cuboidal and squamous epithelia
When relaxed, what shape are the cells of the urothelium?
Large and rounded
When stretched, what shape are the cells of the urothelium?
Intermediate and surface layers are flattened
What are cilia?
Motile structures projecting from luminal surface of epithelial cells
Where are cilia most notably found? (As a specialisation of epithelia)
Female reproductive and respiratory tract
Cilia are not easily seen under a light microscope. True or false?
False
How do cilia move?
Wave-like synchronous rhythm to propell particles/fluid in a consistent direction
How long may cilia be?
10 micrometers
How many cilia may a cell have?
Up to 300
What are microvilli?
Minute, finger-like projections of the luminal plasma membrane
Where are microvilli found?
Epithelia specialised for absoption
How much can microvilli increase surface area by?
30 fold (may be thousands on one cell)
How long are microvilli?
1 micrometer
How do microvilli appear under a light microscope?
Cannot be resolved, but appear as a brush border
Where are microvilli found within the body?
Small intestine
What are goblet cells?
Modified columnar epithelial cells that synthesise and secrete mucus
Where are goblet cells found?
Scattered amongst simple epithelia, particualarly in the GI and respiratory tract
How do you stain goblet cells?
PAS staining: stains bright pink
What is epithelium primarily involved in secretion often arranged into?
stuctures called glands
What are glands?
Invaginations of the epithelial surface which proliferate into the underlying connective tissue
What do all glands have?
A continous basal rate of secretion which is modulated by nervous and hormonal influences
What comprises exocrine glands?
Solid organs of largely epithelial cells, connected to surface epithelium of GI tract by branching system of ducts
Give examples of exocrine glands
Small sweat glands
Salivary glands
Liver
What are exocrine glands divided into?
Secretory components and duct system
What are the types of secretory component?
Tubular or acinar
Coiled or branched
What may the shape of the duct system be?
Branched (compound) or unbranched (simple)
Where are simple tubular glands found?
Large intestine
What type of gland are sweat glands?
Simple coiled tubular gland
What do simple coiled tubular glands appear as under a microscope?
Different portions seen in each plane of section because of tight coiled shape
Where is simple branched tubular glands found mostly?
In the stomach mucus
How are endocrine glands formed>
Lose their connection to epithelial surface during development
Where do endocrine glands release their secretions?
Directly into blood (and lymph??
Why are most endocrine glands composed of more than one type of secretory cell?
They release more than one hormone product
How is endocrine gland secretion usually controlled?
Metabolic factors (e.g. glucose)
Secretion of other hormones
Nervous system
Describe the general structure of most endocrine glands
Clusters of secretory cells, each with their own basement membrane, surrounded by blood vessel network
Of what origin is supporting tissue?
Mesodermal origin
What does supporting tissue do?
Provide structural and metabolic support for other tissues and organs
What does supporting tissue mediate?
Exchange of nutrients, gases and metabolites between tissues and the circulatory system
Name two forms of specialised supporting tissues
Blood, cartilage and bone
What are supporting tissue composed of?
- Specialised cells
- Extracellular matrix
What is extracellular fluid?
Dominant component of many supporting tissues, which determines physical properties of the tissues
What is the extracellular matrix composed of?
Ground substance
Fibres
In an H&E stain, what does fibrous proteins in the supporting tissues look like?
Wavy bundles of pink-stained material
In an H&E stain, what does ground substance appear as?
Pale, unstained
What is the overall appearance of an H&E stain of supporting tissue?
Generally, cell density is low.
What is the most abundant protein in the body?
Collagen
What does collagen provide?
Tensile strength
In what form is collagen secreted from a cell?
Secreted as tropocollagen
What happens to tropocollagen after it has been secreted into the extracellular matrix?
Polymerises into collagen
Where is type 1 collagen found?
Dermis, tendons, ligaments, bone and fibrous supporting tissue
In what form is type 1 collagen visible under light microscopes?
Bundles
Where is type 2 collagen found?
Hyaline cartilage
What is the appearance of type 2 collagen under a light microscope?
Fine fibrils dispersed in the ground substance
What is type 3 collagen also called?
Reticulin
What is the structure of type 3 collagen/reticulin?
Delicate branching supporting meshwork in highly cellular tissues
Where is type 3 collagen found?
Liver, bone marrow and lymphoid organs
How is type 3 collagen stained under a light microscope?
Absorb metallic silver, by which they are stained black
What does type 4 collagen do?
Forms a mesh-like structure in basement membranes
What is type 7 collagen?
Anchoring fibrils that link to the basement membrane
What cells are derived from mesenchyme?
Fibroblasts, myofibroblasts, chondrocytes, adipocytes, defence and immune cells
What are the most common cells?
Fibroblasts
What do fibroblasts do?
Responsible for secreting extracellular matrix
What is the function of myofibroblasts?
Contractile function and secretion of extracellular fluid
What cells are responsible for secreting the extracellular matrix in cartilage?
Chondrocytes
What cells are responsible for secreting the extracellular matrix in bone?
Osteocytes
What are adipocytes specialised for?
Storage and metabolism of fat, collectively form adipose tissue
What cells make up defence and immune cells?
Mast cells, tissue macrophages and plasma cells
What is the name given to the embryonic tissue from which all connective tissue is derived?
Primitive mesenchyme
What shape are mesenchymal cells?
Stellate shaped
Delicate branching cytoplasmic extensions
What shape are the nuclei of mesenchymal cells?
Oval
Describe the extracellular matrix of mesenchyme cells
Mainly ground substance,very few fibres
How does mature fibroblasts collagen fibres appear in an H&E stain?
Dense and very pink
What is the shape of mature fibroblast nuclei?
Condensed and elongated in the direction of collagen bundles
What is the main function of mature fibroblasts?
Maintain integrity of the tissue by slow turnover of extracellular matrix
Where might supporting tissue be loose?
Bowel submucosa
What is the basement membrane made of?
Sheet like arrangements of extra-cellular matrix proteins
What is the basement membrane an interface between?
Support tissue and parenchymal cells
What name is given to the basement membrane in nerve and muscle tissue?
External lamina
What do basement membranes act as a barrier to?
Downward epithelial growth
Where is the selective permability of supporting tissue of particular importance?
Kidney
What are the main constituents of basement membranes?
Collagen type 4
Structural glycoproteins laminin, entactin and fibronectin
What produces the main constituents of basement membranes (except fibronectin)
Epithelial cells
What produces fibronectin?
Fibroblasts
What three layers make up the basement membrane?
Lamina lucida, lamina densa and lamina fibroreticularis
What is the lamina lucida?
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 electrolucent layer which merges with supporting tissue underneath
What does lamina densa and lucida mainly consist of?
Type 4 collagen and laminin
What does lamina fibroreticularis mainly consist of?
Type 3 collagen and fibronectin
Adipose tissue generally has a rich blood supply. True or false? Why?
True
For releasing energy
What might influence fat metabolism of adipocytes?
Hormones, nervous system, diet and energy expenditure
What proteins are adipocytes responsible for releasing?
Adipocytokines
Give an example of an adipocytokine.
Leptin, tumour necrosis factor alpha
What does adipocytokines do?
Regulate body mass and influence general metabolism
What % body weight does white adipose tissue make up in adults?
20% males
25% females
Where is white adipose tissue distributed?
Throughout the body, especially deep in the dermis
What other function does white adipose tissue have?
Thermal insulator and a cushion against mechanical shock (e.g. in kidney)
What receptors do adipocytes have?
Insulin, cortisol, growth hormone and noradrenaline
What shape does fat cells have?
Signet ring shape
What is brown adipose tissue?
Highly specialised type found in newborn mammals
What is the role of brown adipose tissue?
Temperature regulation
How is brown adipose tissue arranged?
Lobules separated by fibrous septae which convey blood vessels and nerves
