Cells and Tissues - Epithelial Tissue Flashcards
Epithelial tissue description
tissue that covers body surfaces, lines hollow organs, cavities and ducts, and forms glands
Cell junction definition
are contact points between the plasma membrane of tissue cells
Types of cell junctions
Tight junctions, Adherens junctions, Gap junctions, desmosomes and hemidesmosomes
Key functions of epithelial tissues
Selective Barriers (limit uptake of anything into the interior or aid transfer) Secretory (onto a free surface) Protective (it is the interface to the outside - also protects against abrasion)
Apical surface definition
the surface of an epithelial cell that is exposed to the body exterior or to the cavity of an internal organ
Lateral surface definition
the surface of an epithelial cell that is adjacent to other cells
Basal surface definition
is the bottom surface of an epithelial cell that is adjacent to the basement membrane
Types of Lateral junctions
Tight junction, Adherens junction, Gap junction and Desmosome
Types of Basal Junctions
Hemidesmosome
Microfilaments definition
are bundles of protein beneath the cell membrane and the cytoplasm eg. Actin
Microfilament function
To give cells strength, alter cell shape (act as cell skeleton), link the cytoplasm to the cell membrane, connect cells together, allow cell movement and muscle contraction
Intermediate filament
are a type of cytoskeletal element made of multiple strands of fibrous proteins wound together. These are thicker than microfilaments and made of proteins like keratin
Intermediate filament function
to provide strength to cell and allow materials to move through the cytoplasm
Definition of the lumen
the central cavity of a tubular or other hollow structure in an organism or cell (apical surface of a cell faces this)
Tight junction definition
a lateral junction that is made of individual sealing strands of transmembrane proteins
Where are tight junctions mainly found?
In the epithelial tissue that lines the stomach, intestines and urinary bladder (ie where you don’t want any leakage)
The main binding transmembrane proteins in tight junctions
Claudins and occludins
Adherens junction definition
a lateral junction that has a plaque layer of proteins on the inside of the cell to join actin to cadherins
Tight junction function
To maintain cell polarity by preventing the movement of ions and proteins between apical and basal surfaces of cells (they are electrically tight)
Cadherin definition
a transmembrane glycoprotein that joins cells together in adherens junctions and desmosomes.
These insert into the plaque on the opposite side of the plasma membrane, crossing the intercellular space
Plaque definition
a dense layer of proteins on the inside of the plasma membrane that attaches membrane proteins and microfilaments to the cytoskeleton
Adhesion belt definition
The extensive adherens junctions in epithelial cells
Catenins definition
a protein that links the Cadherins to Actin in adherens junctions
Actin definition
a microfilament in the cytoplasm of the cell
Adherens junction function
to prevent cell separation from tension forces like in contractions (eg. when food moves through the intestines)
Desmosome definition
a lateral junction that has a plaque layer on the inside to join keratin to cadherins
Keratin function in desmosomes
To given the cell structural integrity as keratin spans from one desmosome to another on the other side of the cell
Desmosome function
to prevent cells from separating/ pulling apart
Where are desmosomes mainly found?
In the epidermis (to stop separation from tension) and in cardiac muscle cells in the heart (to stop cells pulling apart during contraction)
Gap junction definition
a lateral junction that contains proteins that allow for communication between adjacent cells
Connexin definition
a membrane protein that forms connexons or hemichannels
Connexon/hemichannel definition
consists of 6 connexin protein molecules that make up a gap junction. These are closed and open when docked to a connexon of another cell.
Gap junction function
To allow small molecules and ions to diffuse from one cell to another. It also allows direct communication between cells
Hemidesmosome definition
a basal/basolateral junction that has a plaque layer and has transmembrane glycoproteins (integrin) that attach to the keratin of the cytoskeleton and the laminin of the basement membrane
Integrin definition
a transmembrane glycoprotein that links the keratin to laminin in hemidesmosomes
Laminin definition
a protein that is present in the basement membrane
Junctional complex definition
a combination of a tight junction, adherens junction and a desmosome
Basement membrane definition
is a thin extracellular layer that separates the epithelium from deeper tissue
The parts of the basement membrane
the basal lamina and the reticular lamina
Basal lamina definition
is the layer (in the basement membrane) closest to and secreted by the epithelial cells.
Hemidesmosome function
to connect the epithelial cells to the basement membrane
What is contained in the basal lamina layer of the basement membrane?
Proteins like collagen, laminin and glycoproteins and proteoglycans
Reticular lamina definition
the layer (of the basement membrane) closer to and produced by the connective tissue cells called fibroblasts
Fibroblast definition
collagen produced by connective tissue
What is contained in the reticular lamina layer of the basement membrane?
fibrous proteins such as collagen and fibronectin
Do epithelia have nerves or blood vessels?
Epithelia has nerves but is avascular (does not contain blood vessels). It exchanges nutrients and wastes through diffusion with blood vessels in adjacent connective tissue cells.
Basement membrane function
To support the overlying epithelium
Provide a surface where epithelial cells can migrate during growth or wound healing (wounds disrupt epithelia and BM and need to be reconstituted during healing)
Acts as a physical barrier (especially for malignant melanoma)
Participates in the filtration of substances in the kidney
Metastasis definition
the growth of cancer in other secondary areas (the chance of this increases if malignant melanoma penetrates the basement membrane)
ABCD for melanoma
Asymmetry, border irregularity, colour and diameter
Two types of epithelial tissue
Covering/lining epithelia and glandular epithelia
Types of covering/lining epithelia
the outer coverings of skin and some internal organs
the inner linings of blood vessels, ducts, cavities and the interior of the respiratory, digestive, urinary and reproductive systems
What is glandular epithelia?
the epithelia that constitute the secretory portion of glands
How are covering and lining epithelia classified?
by the arrangement of cells in layers and the shapes of the cells
Simple definition (in epithelia)
a single layer of cells
Simple epithelium function
diffusion, osmosis, filtration, secretion and absorption
Stratified definition (in epithelia)
two or more layers of cells
Stratified epithelium function
PROTECTION of underlying tissue in locations where damage may occur (considerable wear and tear)
Pseudostratified definition (in epithelia)
appears to have multiple layers of cells because the nuclei of the different cells are in different layers but because all cells connect to basement membrane it is in fact simple epithelium. Not all cells reach the apical surface
Goblet cells definition
Pseudostratified columnar cells that swell up with mucus
Pseudostratified epithelium function
Secretion
What are glandular epithelia?
Glands are made up of a single cell or group of cells that secret substances into blood
What are the two classifications of glandular epithelia?
Exocrine and Endocrine
Explain the process of exocrine glands?
Secrete substances or hormones into a duct which will then empty their contents onto a surface
It produces local effects
What is an example of an exocrine gland working?
Sweat glands
Sweat is made in the dermis, it needs to get on the surface for thermoregulation, it does so through a duct
Explain the process of endocrine glands
Secrete substances or hormones directly into the blood via interstitial fluid (ie have NO ducts)
What is an example of an endocrine gland working?
Thyroid gland
Hormones migrate through the epithelia and straight into a blood vessel nearby
What are the two sub-types of exocrine glands?
Single cell or multicellular
What is a single cell exocrine gland?
Goblet cells
Secrete mucinin which is hydrated to form mucous
What are the two classifications for the DUCT of a multicellular exocrine gland?
Simple (has a single duct that doesn’t divide)
Compound (duct that branches)
What are the classification of the SECRETORY portion of a multicellular exocrine gland?
Tubular if it forms tubes either straight or coiled
Alveolar if it forms sac-like pockets (roundish)
What are the 5 simple multicellular exocrine glands?
Simple tubular Simple coiled tubular Simple branched tubular Simple alveolar Simple branched alveolar
Where are simple tubular glands found?
Intestinal glands
What are simple coiled tubular glands used as?
Sweat glands
Describe simple branched tubular glands
Gastric glands
Mucous glands of oesophagus, tongue, duodenum
Describe simple alveolar glands
A stage in the embryonic development of simple branched glands
Describe simple branched alveolar glands
Sebaceous glands
What are the two subtypes of where simple squamous epithelium is located?
Endothelium and mesothelium
What does endothelium line?
Line blood vessels + heart (CVS system)
Barrier and allows for rapid diffusion
What does mesothelium line?
Pleura, Pericardial and peritoneal cavities (ALL SEROUS MEMBRANES)
Secret serous fluid, especially to prevent friction in the heart
Where else is simple squamous epithelium found apart from the mesothelium and endothelium?
Alveoli of the lungs - rapid diffusion
Bowman’s capsule of the kidney - filtration barrier
What is the function of simple squamous epithelium?
Diffusion (lungs), filtration (kidneys) and secretion (in serous membrane)
What is the function of the serous fluid?
To allow organs to ‘slip and slide’ past against each other without any friction
What is the function of stratified squamous epithelium?
PROTECTION
What are the two sub-types of stratified squamous epithelium?
Keratinised and non-keratinised
Where and what is the function of keratinised stratified squamous epithelium?
SKIN!!
Waterproof, protects from abrasion
Where and what is the function of non-keratinised stratified squamous epithelium?
Found in the ‘naughty places’ - mouth, tongue, throat, oesophagus, vagina and anus
Protects from abrasion of mechanical/chemical stresses
What is the function of the simple cuboidal epithelium?
Secretion and absorption
Where is simple cuboidal epithelium found?
Pancreatic ducts (because pancreas secretes digestive fluids)
Lens surface
Kidney tubules
Surface of the ovary
Where is stratified cuboidal epithelium found and what is its function?
Found in oesophageal glands, adult sweat glands and male urethra
Protection, secretion, absorption
What are the modifications found on simple columnar epithelium?
Cilia and microvilli
What is the function of the cilia?
To move substances
What is the function of the microvilli?
Increase absorption through an increase in surface area
