Tissues of the Body - Week 3 Flashcards
What is epithelia?
-Covering and lining membranes of the body, so every part of body exposed to free surface is epithelium.
-Many types of epithelium, described by the shape of the cell.
-All epithelial cells are separated from surrounding tissue by basement
membrane, a collection of extracellular matrix fibres that act to separate it physically from other tissue around it.
-Epithelial cells are specialised according to function, so often the epithelial cells of an organ are the ones carrying out its function.
-So for example, the cells that line the lumen of the small intestine that food come in contact with are the ones that will absorb nutrients of food, so they’re doing the function of the tissue.
-Also, in lungs, as you breathe in, cells lining air sacs will exchange gases, so it’s the epithelial cells that line air sacs that are performing the function of the tissue.
-So cells are
specialised according to function, so may have surface specialisations like microvilli and cilia, and will almost always have cell junctions.
-Role is to protect underlying tissue from outside world, protect and separate areas within body, help hold tissues together, and perform functions of tissue like thermoregulation, hormone release and absorption and secretion.
What is endothelium?
Lining of inner surface of blood vessels.
What is mesothelium?
Lining of body cavities, e.g. the pleura, peritoneum and pericardium.
What is simple squamous epithelium?
- Composed of flattened, irregularly shaped cells forming a continuous surface, sometimes called pavemented epithelium.
- Like all epithelia, this delicate lining is supported by an underlying basement membrane.
- Found lining surfaces involved in passive transport (diffusion) of either gases or fluids.
- Also forms delicate lining of pleural, pericardial and peritoneal cavities.
What is simple cuboidal epithelium?
- Epithelial cells appear square.
- Nucleus usually round and located in centre of cell.
- Usually lines small ducts and tubules that may have excretory, secretory or absorptive functions, e.g. collecting tubules of the kidney.
What is simple columnar epithelium?
- Nuclei elongated and may be located towards base, centre or apex of cytoplasm.
- Found on absorptive surfaces such as small intestine, as well as secretory surfaces such as that of the stomach.
What is simple columnar ciliated epithelium?
Mainly found in female reproductive tract, e.g. fallopian tube.
What is pseudostratified columnar ciliated epithelium?
- Pseudostratified as looks like many layers of cells, but actually only one layer, as all cells lay on basement membrane.
- Majority of cells ciliated.
- Nuclei at different levels.Almost exclusively confined to airways of respiratory system.”
What is stratified squamous epithelium?
-Consists of a variable number of cell layers, with the ones at the bottom near the basement membrane being cuboidal,
and the ones near the top being flattened and squamous.
-Stratified epithelium usually named by whatever cells at top look like.
-Cells at bottom regenerate epithelium, dividing and producing layers above, and usually these are regenerating
epithelia, so constant turnover of cells.
-Find in skin for example.
-So top layers of skin eventually wear off, but bottom cells dividing.
-This type lines oral cavity, pharynx, oesophagus, anal canal and vaginal canal for example.
What is transitional epithelium?
-Form of stratified epithelium found only in the urinary tract, where it is highly specialised to accommodate a great degree of stretching.
-Named this way as transitions between stratified cuboidal and stratified squamous epithelium.
-Almost domes of cells.
-These cells line bladder and are relaxed as bladder empty.
-As bladder fills up, top cells stretch out and become
flat as bladder fills.
-When bladder empties reverts back to dome like cells.
What is the basement membrane?
-Sheets of matrix at interface of functional tissue (epithelium) and support tissue (connective tissue).
-All epithelium sit on a
basement membrane.
-Composed mainly of type IV collagen, glycoproteins (laminin secreted by epithelial cells, and
fibronectin from fibroblasts that belong to connective tissue) and glycosaminoglycans (GAGs).
-So basement membrane
supported by cells produced by cells above and below it.
What are pathologies of the basment membrane?
-Disorders are renal disease, cancer and genetic diseases.
-Skin pathology - skin is a stratified squamous epithelium, and it’s attached to dermis by basement membrane.
-There are certain genetic disorders where this doesn’t happen, like epidermolysis bullosa, where epithelium gets separated from underlying tissue very easily.
-In renal disease, kidney filter composed of number of elements, one of which is basement membrane of capillaries in glomerulus of kidney.
-If things get stuck in there and get clogged up, that’s basis for range of renal diseases.
-Tumour can arise in epithelial cells.
-While tumorous cells are still contained within epithelium and haven’t breached basement membrane, they are much easier to deal with.
-When they have broken into basement membrane and acquired ability to invade tissue underneath,
more difficult to deal with.
-This is because get into blood vessels or lymphatic vessels and can then migrate around body and set up secondary tumour sites.
-Epithelium doesn’t have blood vessels in it, just cells.
-So it gets nutrition via diffusion, and therefore a tumour that is confined to the epithelium won’t be able to pop its cells into the blood stream and become
invasive and metastatic.
What are examples of glands?
-Simplest one is a single cell, just secreting something onto a surface, like a goblet cell.
-If fold epithelium to make a gland, the very simplest one is a simple tubular one.
-Will produce its secretions and release onto surface.
-Also have simple acinar - the bits secreting are columnar epithelial cells and the bits conveying that secretion to surface are the duct
epithelial cells and they are cuboidal.
-So columnar in the secretory part and cuboidal in the duct part.
-So those are simple
glands that just increase the SA for secretion.
-If increase folding more, get more complex structure like compound tubular
gland.
-Prostate gland - whole organ is a gland.
What are exocrine glands?
Secrete their products onto the epithelial surface directly or via a duct for local action, e.g. sweat glands, liver.
What are endocrine glands?
Release their secretions directly into the blood to act on different tissues, e.g. pituitary and thyroid glands.
