Cells and Tissues: Epithelial Tissue Flashcards
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Epithelial Tissue description
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tissue that covers body surfaces, lines hollow organs, cavities and ducts, and forms glands
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Cell junction definition
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are contact points between the plasma membrane of tissue cells
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Types of cell junctions
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Tight junctions, Adherens junctions, Gap junctions, desmosomes and hemidesmosomes
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Key functions of epithelial tissues
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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)
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Apical surface definition
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the surface of an epithelial cell that is exposed to the body exterior or to the cavity of an internal organ
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Lateral surface definition
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the surface of an epithelial cell that is adjacent to other cells
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Basal surface definition
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is the bottom surface of an epithelial cell that is adjacent to the basement membrane
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Types of Lateral junctions
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Tight junction, Adherens junction, Gap junction and Desmosome
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Types of Basal Junctions
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Hemidesmosome
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Microfilaments definition
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are bundles of protein beneath the cell membrane and the cytoplasm eg. Actin
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Microfilament function
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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
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Intermediate filament
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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
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Intermediate filament function
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to provide strength to cell and allow materials to move through the cytoplasm
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Lumen definition
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the central cavity of a tubular or other hollow structure in an organism or cell (apical surface of a cell faces this)
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Tight junction definition
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a lateral junction that is made of individual sealing strands of transmembrane proteins. These join the cytoskeletons of adjacent cells and the more strands of transmembrane proteins = the tighter the junction
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Where are tight junctions mainly found?
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In the epithelial tissue that lines the stomach, intestines and urinary bladder
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The main binding transmembrane proteins in tight junctions
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Claudins and occludins
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Adherens junction definition
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a lateral junction that has a plaque layer of proteins on the inside of the cell to join actin to cadherins
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Tight junction function
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To maintain cell polarity by preventing the movement of ions and proteins between apical and basal surfaces of cells (they are electrically tight)
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Cadherin definition
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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
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Plaque definition
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a dense layer of proteins on the inside of the plasma membrane that attaches membrane proteins and microfilaments to the cytoskeleton
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Adhesion belt definition
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The extensive adherens junctions in epithelial cells
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Catenins definition
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a protein that links the Cadherins to Actin in adherens junctions
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Actin definition
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a microfilament in the cytoplasm of the cell
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Adherens junction function
to prevent cell separation from tension forces like in contractions (eg. when food moves through the intestines)
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Desmosome definition
a lateral junction that has a plaque layer on the inside to join keratin to cadherins
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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
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Desmosome function
to prevent cells from separating/ pulling apart
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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)
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Gap junction definition
a lateral junction that contains proteins that allow for communication between cells
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Connexin definition
a membrane protein that forms connexons or hemichannels
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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.
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Gap junction function
To allow small molecules and ions to diffuse from one cell to another. It also allows direct communication between cells
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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
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Hemidesmosome function
to connect the epithelial cells to the basement membrane
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Integrin definition
a transmembrane glycoprotein that links the keratin to laminin in hemidesmosomes
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Laminin definition
a protein that is present in the basement membrane
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Junctional complex definition
a combination of a tight junction, adherens junction and a desmosome
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Basement membrane definition
is a thin extracellular layer that separates the epithelium from deeper tissue
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The parts of the basement membrane
the basal lamina and the reticular lamina
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Basal lamina definition
is the layer (in the basement membrane) closest to and secreted by the epithelial cells.
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What is contained in the basal lamina layer of the basement membrane?
Proteins like collagen, laminin and glycoproteins and proteoglycans
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Reticular lamina definition
the layer (of the basement membrane) closer to and produced by the connective tissue cells called fibroblasts
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Fibroblast definition
collagen produced by connective tissue
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What is contained in the reticular lamina layer of the basement membrane?
fibrous proteins such as collagen and fibronectin
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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.
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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
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Metastasis definition
the growth of cancer in other secondary areas (the chance of this increases if malignant melanoma penetrates the basement membrane)
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ABCD for melanoma
Asymmetry, border irregularity, colour and diameter
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Two types of epithelial tissue
Covering/lining epithelia and glandular epithelia
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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
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What is glandular epithelia?
the epithelia that constitute the secretory portion of glands
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How are covering and lining epithelia classified?
by the arrangement of cells in layers and the shapes of the cells
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Simple definition (in epithelia)
a single layer of cells
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Simple epithelium function
diffusion, osmosis, filtration, secretion and absorption
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Stratified definition (in epithelia)
two or more layers of cells
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Stratified epithelium function
to protect underlying tissue in locations where damage may occur (considerable wear and tear)
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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
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Goblet cells definition
Pseudostratified columnar cells that swell up with mucus
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Pseudostratified epithelium function
Secretion
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Secretion definition
the production and release of substances like mucus, sweat or enzymes
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Absorption definition
the intake of fluids or other substances such as digested food from the intestinal tract
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Squamous definition (in epithelia)
flat and thin cells
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Squamous epithelium cell function
allow rapid passage of substances through them (diffusion)
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Cuboidal definition (in epithelia)
cells that are as tall as they are wide
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Cuboidal epithelium cell function
secretion and absorption
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Columnar definition (in epithelia)
cells that are more tall than wide
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Columnar epithelium cell function
protect underlying tissue as well as secretion and absorption
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Transitional definition (in epithelia)
a stratified epithelium where cells change from stratified cuboidal (in relaxed state except apical layer which is large and rounded) to stratified squamous (when cells are stretched)
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Transitional epithelium cells location
In the urinary bladder where they stretch to a larger size then collapse back into a smaller size
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Transitional epithelium function
to allow urinary organs to stretch and maintain protective lining while holding variable amounts of fluid without rupturing
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Simple squamous epithelium description
is the most delicate epithelium that is made from a single layer of flat cells (like a tiled floor when viewed from the apical surface). They have a flat nucleus
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Simple squamous epithelium function
Filtration (blood filtration in kidneys), diffusion (oxygen into blood vessels of the lung), secretion (outer layer of serous membranes)
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Mesothelium
a subtype of simple squamous epithelium
that covers the serous membranes (pericardial (outside heart cavity), pleural (lungs), peritoneal (gut) cavities) of an adult
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Endothelium
a subtype of simple squamous epithelium that lines the cardiovascular and lymphatic system (heart, blood vessels, lymphatic vessels)
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Simple squamous epithelium location
Kidney, the lining of cardiovascular and lymphatic systems, inside eye, alveoli of lungs, inside blood vessels and heart
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Simple cuboidal epithelium description
is a single layer of cube-shaped cells. They have a round nucleus
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Simple cuboidal epithelium function
secretion and absorption
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Simple cuboidal epithelium locations
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pancreas ducts
kidney tubules
Smaller ducts of many glands
Secretory chambers of thyroid
Anterior surface of lens of the eye
Pigmented epithelium at posterior of retina Secretory part of some glands like thyroid
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Microvilli definition
a large number of minute cytoplasmic projections from the surface of epithelium cells that are non-motile (no movement). They are notably found at the intestinal brush border and in the proximal convoluted tubule of the kidney
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Simple columnar epithelium description
a single layer of column-like cells that have more cytoplasm within them, therefore, has more organelles (more metabolically active than cuboidal cells). Can come in two forms: non-ciliated and ciliated. Simple columnar epithelium can have cilia or microvilli
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Non-ciliated simple columnar epithelium description
is a single layer of column-like cells that have microvilli on the apical surface for the increased surface area. Can contain goblet cells
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Non-ciliated simple columnar epithelium function
lubrication (mucus in goblet cells), absorption and secretion (high capacity than cuboidal cells due to more organelles)
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Non-ciliated simple columnar epithelium location
Lines gastrointestinal tract (from the stomach to the anus to prevent the destruction of the stomach lining from acidic gastric juice), the ducts of many glands and the gallbladder.
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Cilia definition
actively motile processes with a complex internal structure found on the epithelial lining of the respiratory tract and the female reproductive tract
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Ciliated Simple Columnar Epithelium description
is a single layer of column-like cells that have cilia on the apical surface. Can contain goblet cells
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Ciliated Simple Columnar Epithelium function
The cilia have synchronous movement which assists in moving mucus and foreign particles to the throat where they can be expelled. Can also move oocytes through uterine tube into the uterus
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Ciliated Simple Columnar Epithelium location
Some bronchioles (small tubes) of the respiratory tract, uterine tubes, some paranasal sinuses, the central canal of the spinal cord, ventricles of the brain
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Pseudostratified columnar epithelium description
appears to have several layers of column-like cells because of the nuclei not aligning, but all cells are attached to the basement membrane so it is actually simple epithelium. Can be ciliated or non-ciliated
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Ciliated- Pseudostratified columnar epithelium description
column-like cells that bear cilia or contain goblet cells
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Non-ciliated Pseudostratified columnar epithelium description
contains cells without cilia or goblet cells
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Ciliated- Pseudostratified columnar epithelium function and location
to secrete mucus that traps foreign particles and cilia sweep away mucus for elimination from the body in the respiratory tract
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Non-ciliated Pseudostratified columnar epithelium function and location
Absorption and protection in the ducts in glands, epididymis and male urethra
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Stratified squamous epithelium description
has two or more layers of flat cells in apical layer. Cells may become cuboidal or columnar in lower layers. Can be keratinised and non-keratinised
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Keratinised Stratified squamous epithelium description
Stratified squamous epithelium that has a tough layer of keratin in apical layers and several layers deep
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Non-keratinised Stratified squamous epithelium description
Stratified squamous epithelium that does not contain keratin and is moistened by mucus from salivary and mucous glands
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Keratinised Stratified squamous epithelium location
Skin
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Stratified squamous epithelium function
To protect against abrasion, water loss, ultraviolet radiation and foreign invasion. Both types are the first line of defence against microbes
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Non-keratinised Stratified squamous epithelium location
Wet surfaces (mouth, pharynx, esophagus, anus, and vagina) and the tongue
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Stratified Cuboidal Epithelium description
has two or more layers or cells that look cube-shaped in apical layer (fairly rare)
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Stratified Cuboidal Epithelium location
Ducts of adult sweat glands; esophageal glands, male urethra
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Stratified Cuboidal Epithelium function
protection and has limited secretion and absorption abilities
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Stratified Columnar Epithelium description
only the apical layer has columnar cells. Lower layers consist of shortened and irregular shaped cells (RARE)
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Stratified Columnar Epithelium location
Part of urethra; some large gland ducts such as oesophageal glands; anal mucosal membrane, part of the conjunctiva of the eye
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Stratified Columnar Epithelium function
protection and secretion
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What does a gland consist of?
a single cell or a group of cells that secrete substances into ducts, onto a surface or into the blood.
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How are glands classified?
According to where they secrete their substances too
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Glandular epithelia function
Secretion
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Endocrine Gland description
Secrete directly into the bloodstream without a duct usually traversing interstitial fluid
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Endocrine Gland function
Produces hormones that regulate many metabolic and physiological activities to maintain homeostasis
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Endocrine Gland location
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Pituitary Gland (at base of the brain)
Pineal Gland (inside brain)
Thyroid and parathyroid (near larynx)
Adrenal gland (above kidneys)
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Exocrine Gland description
Secretes into ducts that empty onto the surface of a covering or lining epithelium
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Exocrine gland function
produce substances such as sweat (regulate body temp), oil, earwax, saliva and digestive enzymes
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Exocrine Gland location
Sweat and salivary glands; oil glands; wax glands; pancreas
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Mucous cell (Single-cell gland) description
in epithelia, there are independent gland cells scattered around that secrete mucin. The apical cytoplasm is filled with large secretory vesicles that look clear or foamy
An example of this is the exocrine goblet cells
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Islets of Langerhans
Areas of pancreatic cells that produce insulin and glucagon
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Characteristics that describe multicellular glands
The structure of the duct
The structure of the secretory area
The relationship between the two
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Multicellular gland description
A gland composed of many cells
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Simple definition (glands)
A gland that has a single duct that does not divide in any way on its way to the gland cells
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Tubular definition (glands)
A gland whose glandular cells form tubes (straight or coiled)
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Branched definition (glands)
A gland with several secretory areas that share a duct (only used in simple glands)
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Acinar/aveolar definition (glands)
A gland whose secretory portion is rounded
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Compound definition (glands)
A gland whose duct divides one or more times on its way to the gland cells
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Tubuloalveolar definition (glands)
glands whose secretory cells form both tubes and sacs
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Simple tubular definition
A straight tubelike gland that opens directly onto the surface.
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Simple branched tubular definition
The tubular secretory part is branched and attaches to a single unbranched duct.
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Simple coiled tubular definition
The tubular secretory part is coiled and attached to a single unbranched duct
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Simple acinar definition
Secretory portion is rounded and attaches to a single unbranched duct
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Simple branched acinar definition
The rounded secretory part is branched and attaches to a single unbranched duct
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Compound tubular definition
Secretory portion is tubular and attaches to a branched duct
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Compound acinar definition
Secretory portion is rounded and attaches to a branched duct
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Compound tubuloalveolar definition
Secretory portion is both tubular and rounded and attaches to a branched duct
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Glands in the large intestine
Example of a simple tubular gland
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Gastric gland
Example of simple branched tubular gland
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Sweat gland
Example of a simple coiled tubular gland
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Glands of penile urethra
Example of a simple acinar gland
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Sebaceous gland
Example of a simple branched acinar gland
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Bulbourethral gland
Example of compound tubular gland
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Mammary gland
Example of a compound acinar gland
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Acinar glands of the pancreas
Examples of compound tubuloacinar glands
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Pineal gland
Produces melatonin, controls day/night cycle
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Hypothalamus and pituitary gland
Work together to control other endocrine glands, regulates growth and fluid balance
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Thyroid Gland
Produces hormones that regulate metabolism and calcium levels
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Parathyroid gland
Regulates calcium levels
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Thymus
Site of T cell maturation
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Adrenal glands
Secrete adrenaline (increases action in cardiovascular and respiratory systems), cortisol (regulates metabolism) and aldosterone (mineral balance)
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What is an apocrine gland?
Exocrine glands that have cytoplasm in their secretions. glands that accumulate their secretory product at the apical surface of the secreting cell. Then that portion pinches off by exocytosis from the rest of the cell to release the excretion. The cell repairs itself and repeats this process.
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Example of apocrine glands
Mammary gland
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What is a merocrine gland?
glands that secrete products by exocytosis during production (the majority of exocrine glands). Exocrine glands that secrete without losing cellular material.
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Example of the merocrine gland
Salivary and sweat glands, pancreas
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What is a holocrine gland?
Exocrine glands whose secretions are made up of disintegrated cells. glands that accumulate their secretory product in their cytosol. As cell matures, it ruptures and becomes the secretory product
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Example of a holocrine gland
Sebaceous gland in skin.
