Tissues Flashcards
What are the four types of tissues in the human body?
Epithelial, Connective, Muscle, Nervous
What are 3 places that epithelial tissue is found?
- Covering body surfaces
- Lining body cavities
- Forming glands
Epithelial cells rest on a….
basement membrane /basal lamina
What are the 3 major functions of epithelial cells
- Covering and lining (protection)
- absorption
- Secretion
How do epithelial cells receive their nutrition?
All epithelial are avascular (no capillaries).
They are dependent on proximity to loose connective tissue for their nutrient and oxygen supplies and by-product removal
What always lies on the interface between epithelial cells and connective tissue?
a basal lamina
What are 3 chief characteristics of epithelial cells ?
- Form a sheet of closely associated cells held together by junctional complexes with very little intercellular space
- Ability to shed and renew
- Made up by polarized epithelial cells that have specific functions depending on the location in the body
What are the 8 types of epithelial tissue?
- Simple squamous
- Stratified squamous
- Simple cuboidal
- Stratified cuboidal
- Simple columnar
- Stratified columnar
- Pseudostratified columnar
- Transitional
What kind of places are simple squamous epithelia found in? what are some examples?
places where there is a very rapid passage
of chemicals
ex:
1. Endothelium of lymphatic vessels
2. Alveoli of lungs
3. Lining of capillaries
4. Some parts of kidney glomerulus and tubules
What functions can simple squamous epithelium perform?
some simple secretion (such as lubricating substances), and some filtering
Simple squamous epithelium lining blood vessels is called ?
endothelium
The simple squamous epithelium that covers body cavities is called?
mesothelium
What are 2 key differences between simple squamous epithelium and simple cuboidal epithelium?
- thicker (cube shaped) and more protective
- a more complex cytoplasm, and perform more complex functions in terms of secretion and absorption
- still allow passage of chemicals
What are two examples of where simple cuboidal epithelium is found?
The secretory part of most glands (like the thyroid for example)
Most tubules of the kidney
What is the morphology of simple columnar epithelium?
A single layer of tall cells. The nucleus tends to be elongated and localized near the basement membrane
Have microvilli and/or cilia
What tasks are simple columnar epithelium active in?
Secretion and absorption
Where are simple columnar epithelium found? (2 examples)
- Bronchioles (ciliated)
2. Small intestine (microvilli)
What is the distinguishing morphology of pseudostratified columnar epithelium? (2 things)
- Cells are tall and thin, but vary in height – all touch the basement membrane, but not all make it to the apical surface
- The nucleus may be found at different points/levels
Can pseudostratified columnar epithelium have cilia?
Yes
Where is an example of pseudostratified columnar epithelium?
Trachea
What types of cells tend to be intermixed with pseudostratified columnar epithelium?
Mucous secreting goblet cells
How is stratified epithelial tissue named?
based on the type of cell found at the surface
What is the most common type of stratified epithelium?
stratified squamous epithelium
- lower layers may be cuboidal or columnar
what is the main useful feature of stratified epithelium?
protection and durability
What are the two groups of stratified squamous epithelium (based on secretion)
Keratinized and non-keratinized
What makes stratified squamous epithelium keratinized? where is this type found? what does it constitute?
flattened superficial layer loses their nuclei and become filled with keratin (keratinized)
Found on the outside of the body
Constitutes the epidermis
What makes stratified squamous epithelium non-keratinized? where is this type found?
consists of several layers of cells with the most superficial layer composed of flat living cells
-mucosal type
Lines the moist body surfaces, such as mouth, esophagus, vagina
Where is stratified cuboidal epithelium found?
Lines the ducts of sweat glands but otherwise uncommon
- also salivary and mammary..?
Where is stratified columnar epithelium found? is it common or uncommon?
Uncommon but occasionally found in large excretory ducts of some glands and in the cavernous urethra
What is transitional epithelium?
a stratified epithelium which undergoes marked changes in appearance, depending on the degree of stretch
Where is transitional epithelium found?
Lines excretory passages in the urinary system (i.e., the urothelium)
What is the main location and function of simple squamous epithelium?
location: air sacs of the lungs and lining of blood and lymphatic vessels
function: allowing materials to pass by filtration and diffusion. Also secreting lubricating substances
What is the main location and function of simple cuboidal epithelium?
location: in ducts and secretory portions of of small glads and kidney tubules
function: secretion and absorption
What is the main location and function of simple columnar epithelium?
location:
- cillated tissues in the bronchi, uterine tubes, uterus,
- smooth tissues: in the digestive tract and bladder
function: absorption as well as secreting mucous and enzymes
What is the main location and function of pseudostratified epithelium?
location: cilliated tissue lines the trachea and upper respiratory tract
function: secretes and moves mucous
What is the main location and function of stratified squamous epithelium?
location:
- keratinized: constitutes the epidermis
- non-keratinized: lining the esophagus, mouth and vagina
function: protect against abrasion
What is the main location and function of stratified cuboidal epithelium?
location: sweat, salivary, and mammary glands
function: protective tissue
What is the main location and function of stratified columnar epithelium?
location: uncommon but found in some ducts and urethra
function: secretes and protects
What is the main location and function of transitional epithelium?
location: lines the bladder, urethra, and ureters
function: allows urinary organs to expand and stretch
What are 4 specializations of the lateral surface of epithelial cells?
all are junctions
- Occluding (zonula occludens or tight junctions)
- Adhering (zonula adherens)
- Desmosomes (macula adherens)
- Communicating (gap junctions)
What is the function of hemidesmosomes? where are they found?
Found on the basal surface
Attachment to the basal lamina
What are two specializations of the apical surface of epithelial cells?
cilia and microvilli
What are tight junctions? What do they do? what is attached to what?
Appear as “fusions” of the cell membranes to one another
- form a barrier
formed by proteins, like occulin, claudin. Attached to actin
What are adhering junctions? what do they do? what are they made of? what attaches to what?
Sticking adjacent cells together.
Made of proteins such as cadherin. Attached to actin filaments all around the cell.
What are desmosomes? what do they do? what are they made of? what attaches to what?
These are points of attachments.
The cells can have a bit of space between spanned by cadherin and intermediate filaments (cytokeratin in epithelia).
What are gap junctions for? What are they made of?
for cell to cell communication
Pores formed by arrangement of connexin proteins that permit passage of ions and other molecules.
What do tight/occluding junctions greatly reduce the passage of?
water electrolytes and other small molecules
What are the main cell joining proteins in tight/occluding junctions?
Occludin and claudin
- anchored within cell to actin
What is the order of junctions?
- tight/occluding junctions are the most outer ones
- zona adherens is below
- macula adherens/desmosome
- gap junctions
What does the zona adherens do?
Attaches epithelial cells together
How does the zona adherens attach epithelial cells together? what proteins are involved?
Transmembrane cadherins on each cell interact with one another to form a link
Actin on the inside of the cell interact with the junction and form a “belt” all the way around the inside of the cell
How do desmosomes connect? how is it different from the zona adherens?
Cell-cell connection through cadherins
Anchored to intracellular filaments – in epithelia, this is cytokeratin (instead of actin)
What is different with desmosomes compared to other junctions?
there can be more space between cells that with other types of junctions
What is a connexon ? what is it formed by?
A pore formed for gap junctions
formed by 6 connexin proteins
What can pass through connexons?
small water soluble molecules
- not nucleic acids or proteins
What proteins are involved in the hemidesmosome connection between the epithelial cell and the basement membrane?
Keratin filaments anchor the hemidesmosome to the inside of the cell
connected by integrin
anchored to the basement membrane by laminin
Define: gland
one or more cells that make and secrete a fluid or chemical message
What are 3 factors used to classify glands
The development of the gland (exocrine or endocrine)
The shape of the gland
The mechanism of excretion
Define: exocrine
Retain a passage and secrete onto the surface of the epithelium
- ex: salivary glands