Tissues (general, epithelial, connective Flashcards
Introduction to tissues, connective tissues
What is a tissue?
A group of cells that are similar in structure and perform a similar or related function.
What are the 4 building block tissues?
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
Explain the general function of the epithelial tissue.
- It covers surfaces: almost all surfaces are covered by it
- forms the epidermis (outer most layer of skin)
Explain the general function of the connective tissue.
- supporting and connecting the other tissues
- none of the other tissue types would function, uses it to get where it’s going
Explain the general function of the muscle tissue.
- initiates conscious and unconscious movements
- movement of blood vessels, movement of food in digestive system
Explain the general function of the nervous tissue.
control and coordination
- not only muscles but also glands, digestive systems, etc
how do cells form tissues?
2 ways:
1. cell junctions
- stick really close tgt, hold cell membranes tgt
- Extracellular matrix
- not using cell part- uses extracellular part
- using collagen, elastin, and ground substances to form strong virus structure/ gel
WHere can you find and not find the epithelial tissue?
e.g. inner cavities, e.g. mouth, esophagus, respiratory tract, urinary tract, all lined by it
- only cornea and joint surfaces don’t have epithelium there
What cells use what way to form tissues?
- some tissues use both types- e.g. muscle cells often use both, others only use one
- connective tissue almost always uses extracellular matrix
- epithelial, cardiac and smooth muscles use cell junctions a lot to form tissues
- There is variation in the amount of cell junctions and
extracellular matrix between the different tissue
types.
In depth function of epithelial tissue (what is its function at skin, small intestine, kidney, and glands)?
- Covers the body surfaces both internally
and externally - Acts as a boundary or interface between
different environments (internal and external).
e.g. - internal: chemicals
external: sun
In doing so it may perform a number of
functions:
– protection (skin)
– absorption (small intestine)
– selective permeability
– filtration (kidney)
– excretion (kidney, intestines, skin)
– secretion (glands, small intestine,
kidney)
– sensory reception (skin) or perception
e.g. internal linings: accidentally inhaling food causes coughing, too hot of curry into intestines, gastrointestinal system will signal to get rid of it
- Forms all glands of the body (both exocrine
and endocrine glands).
State cellular, nutritional and shape/ structure-related characteristics of epithelial tissues.
- Highly cellular - very little to no extracellular matrix
(ECM)/ space, cells are very tightly stuck together - Specialised contact between cells - cell junctions
- Polarity – apical (top), lateral (sides) and basal
(bottom) domains
- top is always exposed to a space (outside) or inside of lumen or inside of blood vessel (they always know) - Basal lamina (basement membrane)
- secretes it and lies upon it, sits on the foundation to recognise its 3 fronts - Supported nutritionally and mechanically by an underlying layer of loose connective tissue
- all have it no matter where it’s found
- mechanical: structural support - Avascular (no blood vessels)
- have connective tissue because there are no blood vessels to receive nutrients and get rid of waste, therefore uses underlying connective tissue - Regeneration - can repair itself
- contains stem cells that can undergo mitosis, and cell division, - able to produce new epithelial cells and repair itself
- e.g. liver (a gland) made up of epithelial tissue, great ability of regeneration - Cell membrane specialisations - microvilli, stereocilia,
cilia
- top of cell has microvilli, stereocilia, cilia, lateral: cell junctions, basal: basal lamina
List 5 characteristics of the epithelium. (structural, nutritional, cellular)
- Highly cellular
- Specialised contact between cells
- Polarity
- Basal lamina
- Has underlying layer of loose connective tissue
- Avascular
- Regeneration
- Cell membrane specialisations - microvilli, stereocilia,
cilia
Why do we classify tissues?
- Communicate effectively
- So we can compare normal vs pathological changes
(enables to classify when things goes wrong, when it changes, when homeostasis is disrupted, trying to compensate for it (need to recognise what the normal structure is) - To show relationship between structure vs function
Which two features are the epithelium classified upon?
- number of cell layers present
- Shape of the cell on the apical or free surface
So how do you name epithelia?
Put their two features together
e.g. simple squamous epithelium
- first word: no. of cell layers, second word: shape cell on apical/ free surface
What are the common epithelia found in human body?
- Simple squamous
- when good gas exchange, simple diffusion, smoothly slippery surface is required - Stratified squamous
- keratinised or non-keratinised
- keratinised= dead on surface e.g. skin
don’t contain nuclei cuz dead
- non-keratinised, e.g. inside of cheek, cells aren’t dead in inner cheeks - Simple cuboidal
- Simple columnar
- Pseudostratified ciliated columnar (with goblet cells)
- has cilia on top creating currents
- globet cells= glandular cells - Urinary or transitional
- enables cells to expand and is water-tight
What are the possible variations of the number of cell layer present?
- One cell layer thick (all cells touching basal lamina)= simple epithelium
- More than one cell thick (if not all cell touching basal lamina, it is no longer a simple epithelium-> now a stratified epithelium (strata= layers)
- Not all cells reach surface, but only one cell thick: pseudo= fake
pseudostratified epithelium
What are the possible variations of the shape of cell on apical/ free surface?
- in a stratified epithelium, cells closest to lumen or external surface are how you classify the shape.
1. cells are elongated and thin (wider than tall): squamous - scale like!
- all sitting on basal lamina depending on whether stratified
2. as wide as tall: cuboidal cells
3. tall and thin like columns (taller than wide)-> columnar cells
What are some examples of where the simple squamous epithelium can be found? Explain with functions and how they relate to structure.
- Have flattened, long nuclei with little cytoplasm
- Much, much wider than they are tall
- Line the surface where passive transport of gases or fluids
occurs: simple squamous lining
- E.g. alveoli of lungs (gas exchange), glomerulus of kidneys, capillaries (endothelium- epithelium within blood vessels), GIT (gastrointestinal tract) - Provide smooth, frictionless surface
- called mesothelium: when used to cover organ
- e.g. fluid part outside of GIT, lungs and heart: so when moving around, abrasion won’t be caused
- Lines the lumina of the heart chambers, blood and
lymphatic vessels-> known as endothelium
What are some examples of where the simple cuboidal epithelium can be found? Explain with functions and how they relate to structure.
- Have a spherical (round) and centrally placed nucleus
- Nuclei form a single row
- They are cube-shaped (square) (tall as they are wide)
- All cells contact basal lamina
- Many ducts are lined by this type of
epithelium
– e.g., ducts in the kidneys and salivary glands
*ducts= cubes
What are some examples of where the simple columnar epithelium can be found? Explain with functions and how they relate to structure.
large amount of cytoplasm on surface because of having many villi for absorption
- Have elongated (sausage shaped)
nuclei
- usually found in a basal position forming a single row
- They are elongated cells (taller than they are wide)
* All cells contact basement membrane
* Found lining the parts of the GIT, reproductive system and the larger ducts.
What are some examples of where the stratified squamous epithelium can be found? Explain with functions and how they relate to structure.
Have many layers of nuclei that show a progressive change
of nuclear shape.
non-keratinised: nuclei present all the way to top
if not: kera
if they are: non-kera
- no other epithelial that are keratinised
- non-kera: skin, kera: high friction: mouth, vagina
- Not all cells contact the basal lamina
- Found in areas that require a protective surface (epidermis of
skin, ) - moist area, high friction: non-keratinised stratified squamous epithelium is found, e.g. mouth, vagina, anal canal
- epidermis of skin is where the keratinised type is found
What are some examples of where the transitional epithelium can be found? Explain with functions and how they relate to structure.
- sometimes referred to urothelium (lining urinary
- lots of specialised junctions to prevent leakage
- Stratified with domed cuboidal cells on surface of the relaxed epithelium
- Nuclei can change shape depending upon if the organ is stretched or not, e.g. umbrella cells
The more volume, cells flatten out more, lines the ureter (urinary bladder) - Cell membrane specialisations to allow for expansion of the organ
- Found exclusively in the excretory passages of the urinary system
- E.g. Renal calyces (first part of urinary system that collects urine), renal pelvis (within the kidney), ureters and urinary bladder
Epithelial surface specialisation
- Epithelia are characterised as having polarity
– That is, they have an apical, lateral and basal
surface - Each surface may have membrane
specialisations
