Tissues of the Body. Epithelium Flashcards
What is the function of Epithelial tissue?
Covers body surface. Lines hollow organs, cavities and ducts. Forms the glands of the body
What are cell junctions?
Cell junctions are connection points between the plasma membranes of adjacent cells. There are 5 types.
What is the 5 types of cells junctions?
- Tight junctions
- Adherens junctions
- Gap junctions
- Demosomes
- Hemidesmosomes
What are the key functions of Epithelial tissue
(S.S.P)
Selective barriers (limit or aid transfer). Secretory (onto a free surface). Protective (especially from abrasion)
What is apical surface?
The edge surface of epithelial tissue facing the body surface, body cavity, lumen of an internal organ, or a tubular duct that receives cell secretions. They may contain cilia or microvilli
What is the lateral surface?
The surface of an epithelial cells which face the adjacent cells on either side- these surfaces contain junctions (gap, desmosome, tight, adherens)
What is the basal surface?
The deepest layer of epithelial cells facing the basement membrane - these may contain hemidesmosomes junctions.
How are epithelial cells arranged?
Epithelial cells are arranged into flat, continuous sheets and can be comprised of single or multiple layers
What is the cystoskeleton?
A structure that helps cells maintain their shape and internal organisation, and it also provides mechanical support that enables cells to carry out essential functions like division and movement.
What are the components of the cytoskeleton?
- Microfilaments - such as actin
- Intermediate filaments - such as keratin
What is ACTIN?
A type of microfilament - protein bundles beneath cell membrane and cytoplasm that determine cell shape and structure and allow for muscle contraction.
What is Keratin?
A type of intermediate filament - structural roles in the cytoplasm of cells, also allow movement of material within cytoplasm
Describe the structure of tight junctions
Located near the apical surface
Strands of transmembrane proteins (claudins and occludins) link adjacent plasma membranes in a ‘sewing-like’ appearance. No gap is left
What is the function of tight junctions?
Joins adjacent plasma membranes tightly together keeping cell polarity (i.e electrically tight) by preventing migration of proteins between apical and basal surfaces
Where are tight junctions found?
Epithelial tissue lining stomach, intestines, and bladder
What are claudins and occludins?
Transmembrane proteins that form the tight junction
Describe the structure of adherens junction
Located near the apical surface. Two plaques (patches of protein tissue) on each membrane linked together by transmembrane glycoproteins (cadherin) - belt-like appearance
Cadherin links to catenins (present in membrane) which link to actin filaments
What is the function of adherens junction?
Adherens junction links the microfilaments of adjacent cells preventing cell separation from tension forces like muscle contraction (strength and structure)
What is cadherin and catenin?
Cadherin is the transmembrane glycoprotein that fills the gap in adherens junction and desmosome junction.
Catenin is a type of protein present in the plasma membrane that links the cadherin to the actin filaments of the cells.
Describe the structure of desmosone junctions?
Button-like shape. Composed of two plaques (walls of tissue) joined together by transmembrane glycoprotein (cadherin)
Cadherin links to the keratin intermediate filaments of each adjacent cell
What is the function of Desmosome junctions?
Link the intermediate filaments (keratin) of adjacent cells providing strength to the junctions between cells. Allows tissue to resist shearing forces. Bind muscle cells
Where are desmosome junctions found?
Found in skin epithelium and cardiac cells of the heart to prevent pulling apart.
Describe the structure of gap junctions
The plasma membrane at gap junctions contain connexin protein molecules which group in numbers of 6 to make connexon (otherwise known as a hemichannel). These connexon molecules move about in the cell membrane until a matching connexon is found in the adjacent membrane and form a tunnel - communication portal.
What is the function of gap junctions?
Allow the cells to communicate with one another (pass chemical and electrical signals). Also allow transfer of ions and small molecules between adjacent cells of tissue
What are connexins and connexons?
Connexins are protein molecules present in plasma membranes that make up connexons (hemichannels).
Connexons are circular molecules made up of 6 connexins and form gap junction.
Describe the structure of hemidesmosome
Junction formed between the basal layer and the basement membrane of epithelial tissue.
A plaque (wall of tissue) is connected to the basement membrane via a transmembrane glycoprotein called integrin.
Integrin acts as the linker protein between the keratin of the basal layer cell and laminin in the basement membrane
What is the function of the hemidesmosome?
Link between basal layer epithelial cells and basement membrane preventing movement of the epithelial layer over the basement membrane - fixation of cell
What is integrin and laminin?
Integrin is the transmembrane glycoprotein forming the hemidesmosome junction
Integrin forms the link between keratin and laminin (a protein) present in the basement membrane
What are the 4 lateral junctions?
- Gap, tight, desmosomes, and adherens
What are the 4 lateral junctions?
- Gap, tight, desmosomes, and adherens
What is only the basal junction?
Hemidesmosome
What is the junctional complex?
The combination of tight junction, adherens junction and desmosome.
What is a basement membrane?
A layer underlying all epithelial tissue composed of two layers - basal lamina and reticular lamina. Located in between the basal layer of epithelial tissue and connective tissue
What is basal lamina?
The top layer of the basement membrane made up of proteins that are secreted from the basal layer of the epithelial tissue. Contains collagen, laminin, glycoproteins
What is the reticular lamina?
The lower layer of the basement membrane made up for proteins produced by connective tissue cells below the basement membrane called firboblasts. Contains: fibronectin, collagen.
What are fibroblasts?
Cells of connective tissue blow the basement membrane responsible for the production of proteins that make up the reticular lamina
What is the function of the basement membrane?
Support for overlying epithelial tissue. Formation of surface for wound healing. (allows epithelial cells to move across new basement membrane reforming cuts and tears in skin). Filtration of blood in kidneys. Protection of inner layer from passage of large molecules
Does Epithelial layer have nerves?
Yes
Does the epithelial layer contain blood vessels
No - The epithelial tissue is avascular
How does the epithelial layer receive nutrients and get rid of waste?
Diffusion across the basement membrane between the blood vessels present in the connective tissue and the epithelial tissue
What are the two main types of epithelial tissue?
Covering and lining epithelia. Glandular epithelia
What is covering and lining epithelia?
Epithelia tissue that forms the outer covering of skin and internal organs. Also forms the inner lining of blood vessels, ducts, and body cavities, and the interior of the respiratory, digestive, urinary, and reproductive system
What is glandular epithelia? (Name the two types)
Constitute the secretory portion of glands. Two types include endocrine (hormones into blood) and exocrine (secretion onto external surfaces and ducts)
What are the further classifications of covering and lining epithelia made based on their arrangement?
- Simple: Single layer of cells
- Stratified: multiple layer of cells
- Psuedostratified: single layer of cells however not all cells reach the apical surface
What are the further classifications of covering and lining epithelia made based on the shape of the cells?
- Squamous: Flat and thing (diffusion)
- Cuboidal: Same height and width (secretion; absorption)
- Columnar: Long and thing (secretion; absorption)
- Transitional - always stratified where the cells are able to change shape from cuboidal to flat depending the shape of organ
What are the further classifications of covering and lining epithelia made based on the shape of the cells?
- Squamous: Flat and thing
- Cuboidal: Same height and width
- Columnar: Long and thing
- Transitional - always stratified where the cells are able to change shape from cuboidal to flat depending the shape of organ
What are the features of the simple squamous epithelium
A single layer of thin, flat cells. Present at sites of filtration, diffusion and secretion in serous membranes (soft tissue). E.g lining cv and lymphatic system (known as endothelium). Cells are fried egg shaped
What is endothelium?
Layer of simple squamous epithelium lining the vessels of the cardiovascular system and lymphatic system
What is mesothelium?
Specialised type of simple squamous epithelium that lines the serous membranes of the heart, lungs, and abdominal areas
What are the features of simple cuboidal epithelium?
A single layer of cuboidal cells. Present at sites of secretion and absorption. Found in the secreting portion of glands like the thyroid gland
What are microvilli?
Finger-like cytoplasmic extensions from the membrane that increase surface area for absorption and exchange of materials
What are cilia?
Motile projections from columnar epithelia cells that can act in a sweeping motion to move substances along surfaces
What are the modifications of the cells that make up a columnar epithelia?
Cilia, Mircovilli, and globlet cells
What are the features of non-ciliated simple columnar epithelium?
Made up of a single layer of rectangular cells. These epithelial cells can have microvilli on the apical surface and goblet cells which are modified columnar epithelial cells containing mucous. Increased surface area means this type of epithelia tissue exists at sites of secretion, lubrication (mucus goblet cells) and absorption. Found in the ducts of many glands
What are the features of ciliated simple columnar epithelium?
Single layer of rectangular cells containing goblet cells. These cells have cilia which are motile projections that can move in a sweeping motion to move substances along surfaces. The cilia allows for synchronous movement assisting with the movement of mucus and foreign objects or oocytes. Found in bronchioles, uterine, fallopian tubes, sinuses; central canal of spinal cord, ventricles of brain.
What are goblet cells?
Modified columnar epithelial cells containing mucous for secretion
What are the two types of stratified squamous epithelia?
Keratinsed and non-keratinised
What are the features of keratinised stratified squamous epithelium?
Multiple layers of epithelial cells where the top layer is thin, and flat cells (bottom layer could be made up of columnar and cuboidal cells).
Contains keratin making surface tough and waterproof- therefore structural and strength roles. Found in skin
What are the features of non-keratinised stratified squamous epithelium?
Layers of multiple cells with squamous epithelial cells on the top layer. These cells do not contain keratin therefore lines wet surfaces such as the mouth, oesophagus, vagina, pharynx, and tongue. They are moistened by mucous. Protects from abrasion, defence from microbes, require secretions from glands
What are the features of psuedo-stratified columnar epithelium
Made up of a single layer of rectangular epithelial cells that all touch the basement membrane however do not all reach the apical surface of the epithelial tissue. There are two types : ciliated and non-ciliated
What is the difference between ciliated and non-ciliated psuedo-stratified columnar epithelia?
Ciliated has goblet cells (modified columnar cells which contain mucous). Non-ciliated has no goblet cells. Therefore ciliated form lines most of upper airways (secretes mucous) and non-ciliated lines larger ducts of glands, epididymis, part of male urethra (absorption and protection). (No cilia and lack goblet cells)
What is the features of stratified cuboidal epithelium?
Made up of cuboidal cells that are arranged in multiple layers. Usually for protection - limited secretion and absorption. Found in ducts of sweat glands and oesophageal glands, part of male urethra
What are the features of stratified columnar epithelium?
Apical layer cells are columnar with irregular shaped cell layers below them. Protection and secretion. Found in part of urethra, large excretory ducts of some glands, small areas in anal mucous membrane
What are the features of transitional epithelium?
Apical layer has large rounds cells and the cells below them are subject to change in shape (resembling cuboidal and squamous and different states). Allow urinary organs to stretch and maintain protective lining while holding variable amounts of fluid without rupturing. Found in the lining of the urinary bladder.
What is a gland?
Gland consists of a single or a cell group of cells that secret substances into ducts, onto a surfaces or into blood.
What is Endocrine Glands?
Glands that secret directly into blood usually via traversing interstitial fluid. Examples are Pituitary pineal, thyroid, and parathyroid glands. Generally distant strong effects
What are Exocrine gland
Glands that secrete into ducts that empty onto the surface of a covering or lining epithelium. Examples are sweat and salivary glands; oil glands; wax glands; pancreas. Generally local effects
What are the 3 characteristics of multicellular ducts to be considered?
- Structure of the duct
- Structure of secretory area
- Relationship between the two
Name and picture the different shape of multicellular ducts 8 total.
- Simple tubular : tear shapes
- Simple branched tubular: 3 tears from single duct
- Simple coiled tubular: tube that is coiled
- Simple acinar (Alveolar): a single sac-like shape
- Simple branched acinar: 3 saces from one duct
- Compound tubular: multiple branched tubular secretory portions
- Compound acinar: multiple branched acinar secretory portions
- Compound tubloacinar: multiple branched mix of acinar and tubular secretory portions
