Epithelial and connective tissue Flashcards
What are characteristics of epithelium?
They are avascular, highly cellular with little intercellular space. Rest on a basement membrane, lines all surfaces.
And they form the parenchyma of exocrine and endocrine glands.
What are three functions of the epithelium?
- Protection: they will protect underlying connective tissue, they keep surfaces moist/lubricated, and they feature intraepithelial lymphocytes.
- Selective Permeability Barrier: in blood vessels they control the passage of ions and fluids
- Absorption (small intestines)
nutrients are absorbed, cells can release gland products, mucus - Secretion (glands) and excretion (kidney tubules)
- Sensory Reception
- Formation of male and female germ cells
- transport of material via apical modifications.
What is the order of tissue types?
There is lumen, epithelium, basement membrane, and CT.
What is the basement membrane?
The BM supports tissue and forms the boundary between epithelium and CT.
The BM is made of three kinds of lamina,
(closest to epithelium)
1. lamina lucida
2 lamina dense
3. lamina reticularis
Use a PAS stain because it stains specifically for glycoproteins.
Describe simple squamous epithelium
Endothelium always refers to blood vessels
Endocardium is lining the ventricles and atria of the heart.
Mesothelium lines the walls of closed cavities of the body.
They function in fluid transport, gas exchange, lubrication and reducing friction.
One cell layer, nuclei are flattened.
Simple cuboidal epithelium, where is it usually found.
It is located in ducts like sweat ducts and kidney collecting ducts.
Where is simple columnar epithelium usually found and describe them.
The nuclei are elongated in shape, and they are usually found in large ducts where you need more protection.
It also sometimes feature microvilli and goblet cells, and sometimes a few lymphocyte above the BM.
You would be able to see the terminal web and the glycolax (digestion of proteins and sugars) via an EM.
Describe stratified epithelium
Usually two layers of cell except for squamous, never have cilia or sterocilia (could possibly have microvilli)
The bottom layer can have any shape so look at what is closest to the surface.
The keratinized epidermis of the skin is special kind of Stratified squamous, where the top layer is flattened and lacks nuclei, forming keratin.
Stratified cuboidal is found in the ducts of sweat glands.
Stratified columnar are in the salivary glands. They feature myoepithelial cells which are full of actin and have a different coloration on LM. They are small and just below the columnar cells.
Describe pseudostratified epithelium
All cells will touch the basement membrane but not all of them will touch the luminal surface. The nuclei will appear in all different levels, apical area is always devoid of nuclei.
WILL ALWAYS have surface modification. cilia or stereocilia.
It is found in the trachea and epididymus.
Describe transitional epithelium
Top layer of cells is either dome shaped or stretched out and become flat. The nuclei however are much rounder than in squamous and you will occassionally see binucleated cells.
FOUND IN URINARY TRACT.
You may also see unit membrane (UM) which are invaginations of the plasma membrane, in the bladder carry fluids
Describe the epithelial junction.
The terminal bar or junctional complex is on the lateral surface of cells. Hemidesmosomes - half a desmisome and intermediate filaments are on the basal side.
It goes in the order of
zonula occludins (tight junction)
zonula adherens (belt desmosome)
Macula adherens: (spot desmosomes)
Communicating junction
and Hemidesmosome.
Describe tight junction
belt desmosomes
spot desmosomes
Gap junctions.
Hemidesmosomes
They feature occludin and claudin transmembrane proteins which link the two sides together, maintaining selective passage of substances from one side to another.
Belt desmosomes anchor cell to cell and feature actin filaments, cadherins and catenins. They wrap around the cell like a belt and will attach when come into contact with another cell.
- Spot desmosomes - show up as spots in a LM, a ladder like
They are made up of desmogleins, desmoplakin, intermediate filaments.
- Signals are passed from one cell to another via connexons. 6 connexons form one gap junction.
- Hemidesmosomes are cell to matrix attachment.
Describe secretory glands
The epithelial cells are known as parenchyma.
CT are known as stroma.
Exocrine glands secrete products via ducts to the surface.
Endocrine duct secretes directly to the blood vessels so they don’t feature ducts.
Glands surround the ducts. Ducts are the openings and glands surround the lumen. So glands can have complex shapes that when sliced will have different looks.
which cells are found in loose connective tissue?
fibroblasts, neutrophils and eosinophils, macrophages and mast cells, brown and white adipose cells.
