3. Integrating Cell Into Tissues Flashcards
Define tissue
Groups of cells that are similar in structure and function and adapted to perform a specific function
Define an organ
Estate where two or more tissues are combined to create a structural unit that has a particular function that or some of its parts
Which three types of cells in the body remain separated from each other?
The ova, The spermatozoa and the corpuscles of the blood (red and white blood cells)
During very early embryo development which three layers of the embryo are formed from the surface inwards?
The ectoderm,mesoderm and the endoderm
From which layers of the embryo are epithelium cells divide from?
All three layers
Which layer of the embryo are nerve cells derived from?
The ectoderm
Which layer of the embryo or muscle and connective tissue derived from?
Mainly the mesoderm
Which layer of the embryo are the mucosa derived from?
The Endoderm
How are surface proteins produced at the early developmental stage and what do they facilitate?
They are produced by cells of the same type congregating together to produce surface proteins that anchor cells together and facilitate cell-to-cell communication. The cells are basically woven together with extracellular and intracellular proteins to create discrete tissue
What are the four main categories of body tissue?
1) epithelial tissue
2) connective tissue (includes blood, cartilage, bone, teeth and fat)
3) muscle tissue
4) nerve tissue`
When do cells first coalesce?
During embryogenesis when they stick together after dividing, as opposed to separating out
What does the human blastocyst consist of?
The blastocyst cavity, the trophoblast and the inner cell mass (embryoblast)
What does the inner cell mass develop into?
The embryo
What does the trophoblast become?
The placenta
What cell does all cells of the body come from?
The epiblast
What four things hold cells together?
1) Cell-cell adhesion molecules
2) Extracellular matrix proteins (fibres)
3) Internal-external scaffolding
4) Close proximity of cells- pressure effects
What are the three main component of connective tissue?
1) cells - mainly mature fibroblasts/ fibrocytes, fixed adipocytes, reticular cells (found in lymphatic tissue)
2) fibres - collagen, elastin, reticular fibres
3) ground substance - glucosaminoglycans e.g. hyaluronic acid
What part of the connective tissue bears the mechanical stress?
The extracellular matrix, made up of fibres and ground substance.
What is the primary cell of connective tissue and what ability does it have?
Mesenchymal stem cells (immature fibroblast cell).
Have the ability to inter-convert between different connective tissue cell types.
What are the six functions of connective tissue?
- Binding and supporting.
- Protecting.
- Insulation.
- Storing reserve fuel and cells.
- Transporting substances within the body.
- Separation of tissues.
What type of tissue are nerves found in?
Connective tissue with branches that go to the edge of the epithelium (but epithelium itself has no nerves) and smooth muscle
What does connective tissue consist of?
- Extracellular matrix is plentiful
- Cells are sparsely distributed within in
- Matrix is rich in fibrous polymers especially collagen, and it is the matrix rather than the cells that bear most of the mechanical stress
How do connective tissue cells interact?
Direct attachments between one cell and another are rare
What does epithelial tissue consist of?
- cells are tightly bound into single layered sheets called epithelia
- extracellular matrix is scant, consisting mainly of the basal lamina which underlies the epithelium
What is the function of the basal lamina?
Anchor down epithelium and connect the cells to underlying connective tissue thus stabilising the basal ends of the epithelial cells.
How are epithelial cells attached to each other?
- Cell to cell adhesion molecules.
- strong intracellular protein filaments (part of the cytoskeleton) cross the cytoplasm of each cell and attach to specialised junctions in the plasma membranes to prevent the cells from stretching too much
- these junctions in turn attach adjacent cells to each other or to the underlying basal lamina
What part of the epithelium bears the most mechanical stress?
The cell to cell adhesion molecules.
What can mesenchymal stem cells produce?
Bone, cartilage, muscle, marrow, tendon/ligament, adipose tissue and connective tissue: produces most of the extracellular fibres that anchor cells into place or make tissue
In culture what do mesenchymal stem cells convert into and what do these produce?
Quickly converts to a mature fibroblasts and produces fibronectin, laminin and collagen that allows cells to adhere to plastic or glass surfaces
Why is hyaluronic acid put into cosmetics?
To moisturise as it is full of sugars so water is drawn into the skin and gets into the dermal layer and makes the skin expand
Why is collagen put into cosmetics?
Draws water in which prevents wrinkles
What happens to bone marrow with age?
It stores fat and is gradually replaced by it
Where are epithelial tissues found?
Lining all the cavities and free surfaces of the bodyq
What do the specialised junctions between epithelial cells help to do?
Help to form tissue barriers and inhibit the movement of water, solutes and cells from one compartment to another
What do epithelia rest on?
A supporting bed of connective tissue which is via a basement membrane that contains many different proteins
What is formed when the supporting bed attaches the epithelial layer to other tissues such as muscle tissues?
Tissues join together in various combinations to form larger functional units called organs
Why are epithelial cells described as polar cells?
Have distinct apical, lateral and basal surfaces which each have different specialised structures for different functions.`
What are apical domain modifications on epithelial cells?
- Microvilli,
- Stereocilia,
- Cilia.
What are the lateral surface specialisations in epithelial cells?`
- Tight junctions,
- Adherens junctions,
- Desmosomes (Adhesion plaques),
- Gap junctions,
- Cell adhesion molecules.
What are the basal surface specialisations in epithelial cells?
- Hemi Desmosomes,
- Focal adhesions,
- Integrins,
- Proteoglycans,
- Cell adhesion molecules.
What are tight junctions?
- near apical end of cell on lateral borders
- long cell to cell fusion point
function of tight junctions?
- Seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them
- Prevent movement of larger molecules from the lumen into deeper tissue layers of the organ.
• Eg tight junctions near the apical surfaces of cells lining the digestive tract help to keep enzymes, acids and wastes in the lumen from reaching the base lateral surfaces and damaging the underlying tissues and organs. - But in the gut, can transiently open to allow small molecules (sugars, AAs, water) to cross to underlying tissues - paracellular trans
What are adhesion junctions?
Almost always found 1/3rd distance from luminal surface
• Found in pairs
• Formed from intracellular actin filaments
• Linked to E-cadherin proteins
• E-Cadherins cross the intercellular space and bind with transcellular E-cadherins from adjacent cells.
• Found throughout this region as ‘a belt of adhesion’
Sometimes called ‘adhesion belt’
In what tissue are adhesion junctions found and what is their main function?
Only found in epithelial and endothelial cells.
Functions as tissue stabilising factor and additional transport barrier.- important in blood brain barrier
What are desmosomes?
- The strongest of all the cell-to-cell adhesions
- Found ~ ½ way between top and bottom of cells
- Random distribution pattern
- Cytokeratin fibres intracellularly, E-cadherins intercellularly (spring-like)
- joins the intermediate filaments in one cell to those in a neighbour
In what tissue are desmosomes found and what is their main function?
Found in tissues that experience intense mechanical stress (e.g. cardiac muscle, bladder tissue).
Provide mechanical strength and prevent tissue destruction.
it is the only adhesion found in skin cells
