W2 - Epithelium Flashcards
LO1: Name the primary germ layers that epithelial tissue is derived from
Epithelial tissue is derived from all three primary germ layers, depending on the type and location of the tissue.
LO2: Describe the characteristics and functions of epithelium
Cellularity: Tightly packed cells with little extracellular space
Polarity: Distinct apical (top) and basal (bottom) surfaces
Attachment to a membrane: Cells are attached to a basement membrane
Avascularity: Lacks blood vessels; nourished by diffusion
Innervation: Often richly supplied with nerve endings
High Regeneration Capacity: Rapid cell turnover and repair
Physical Protection: Shields underlying tissues from damage
Selective Permeability: Controls movement of substances in and out
Secretion: Produces fluids like mucus, enzymes, and hormones
Sensation: Contains sensory receptors for detecting stimuli
LO3: Describe how epithelium is classified
simple vs stratified (based on the number of cell layers)
squamous, cuboidal, columnar (based on the shape of the cells)
keratinised vs non-keratinised (dry vs porous and wet)
also pseudostratified epithelium where nuclei are at different levels but all in contact with membrane
LO4: Simple squamous epithelium
- composed of a single layer of squamous cells.
Functions:
diffusion and filtration, as it allows for the rapid movement of substances across its surface.
Found in:
- lining the alveoli of the lungs where gas exchange occurs and lining blood vessels where the movement of substances in and out of the blood occurs (called endothelium when lining blood + lymphatic vessels and heart chambers)
- membranes lining internal body cavities, where the cells secrete a lubricating fluid (mesothelium, as it originates from mesoderm)
LO4: Simple cuboidal epithelium
- composed of a single layer of cuboidal cells.
Functions: absorption and secretion.
Found in:
- lining the kidney tubules where substances are either reabsorbed into the blood or secreted into the tubular fluid
- lining the ducts of glands which produce secretions.
LO4: Simple columnar epithelium
- composed of a single layer of columnar cells.
Two forms: ciliated and non-ciliated.
- non-ciliated form often have microvilli
on their apical surfaces.
both often have mucous-secreting cells called goblet cells
Functions: absorption and secretion.
Found in:
- lining most of the gastrointestinal tract, the uterine tubes in the female reproductive tract and the bronchioles in the respiratory tract.
LO4: Pseudostratified columnar epithelium
- composed of a single layer of columnar cells, but varying levels of the nuclei make it look stratified.
Two forms: ciliated and non-ciliated
Function:
- protection + ciliated form also has a secretory function (has goblet cells)
Found in:
- ciliated form is much more common, found lining most of the respiratory tract.
- non-ciliated is rare, found lining parts of the male urinary and reproductive tracts.
LO4: Stratified squamous epithelium
- composed of multiple layers of cells with the apical cells being squamous and the basal cells being more cuboidal or polyhedral.
Two forms:
- keratinised (apical cells are dead, lack nuclei and other organelles and are filled with a protein called keratin)
- non-keratinised (the cells are all living, contain nuclei and other organelles and lack keratin (this is the form that is shown on the image).
Function:
protection, prevents the underlying tissue from damage caused by abrasion (basal cells undergo division + migrate to surface to replace damaged/lost cells)
Found in:
- keratinised = epidermis of skin
- non-keratinised = oral cavity, part of pharynx, oesophagus, anal canal, vagina
LO4: Stratified cuboidal epithelium
- composed of only a few layers of cells (apical cells being cuboidal)
Functions: protection and secretion.
Found: lining the ducts of sweat and salivary glands.
LO4: Stratified columnar epithelium
- composed of only a few layers of cells, (apical cells being columnar)
Functions: protection and secretion.
Found: primarily lining the large ducts of some glands (it is rare)
LO4: Transitional epithelium
- composed of multiple layers of cells capable of changing shape depending on degree of stretch
- When relaxed, the basal cells resemble cuboidal cells and the apical cells are large and rounded.
- When stretched, the apical cells resemble squamous cells.
Function: specialised for distension (allowing for swelling, like when bladder is full)
Found: lining most of the urinary tract.
LO4: Summary table 1
LO4: Summary table 2
LO5: Briefly describe the classification and function of glands (describe glands)
- Formed by invaginations of epithelial tissue into the underlying connective tissue.
Glands can either be individual cells such as goblet cells or multicellular organs such as sweat and salivary glands.
LO5: Briefly describe the classification and function of glands (classification and function)
Epithelial cells that constitute glands are specialised for producing secretions such as mucous, enzymes and hormones.
Exocrine glands maintain connection to the epithelial surface via ducts which carry their secretions to the surface, e.g sweat, and salivary glands
Endocrine glands lack ducts and release their secretions (hormones) directly into the bloodstream.
- The ducts are the conducting portions of the glands
- secretory portions which produce the secretions are called acini
