Connective Tissue Flashcards
What are the 2 main components that make up connetive tissues?
Cells and the extracellular matrix
What are resident cells?
Originates in connective tissue like fibroblast or spends most of life in connective tissue like mastocyte.
What are migrating cells?
Arrive in connective tissue from blood under specific conditions, e.g. inflammation.
What ground substances are present in the intercellular matrix?
GAGs
Proteoglycans
Glycoproteins
What fibers are present in the intercellular matrix?
Collagen
Elastic
Distinguish the different types of extracellular matrix.
gelatinous; solid; liquid
Where do connetive tissues originate from?
Connective tissue originates from mesoderm.
What is the mesenchyme?
The mesenchyme is the connective tissue of the embryo. It contains very fine and sparse collagen fibers and abundant ground substance and cells.
The collagen fibers reflect that this connective tissue does not undergo intensive mechanical stress.
It’s also the progenitor of all cells of connective tissues.
Describe the features of fibroblasts.
Metabolically active cells with basophilic cytoplasm which actively synchronise and shape the extracellular matrix.
Synthesis of all components of the intracellular substance.
Most common cells of the connective tissue.
When needed, they can become mobile and proliferate.
Describe the size and components of fibroblasts.
Length 12-14μm; width 5-7μm
Can be seen under a light microscope.
There is an abundant GA and ER associated with ribosomes inside the cell.
Abundant heterochromatin indicates active transcription.
What happens when fibroblasts become fibrocytes?
The shape of cell changes and the amount of ER and GA decreases, thus the cell becomes less active.
What is a reticular cell?
The reticular cell is a type of fibroblast that synthesizes type II collagen and uses it to produce reticular fibers.
What are the functions of white fat cells?
Energy storage sites
Insulation - particularly relevant when adipocytes associate to form adipose tissue.
Cushioning - involves adipose cells.
Endocrine functions
Where are white fat cells located?
Commonly found in scattered groups in loose connective tissue.
In some areas, they can form a true tissue called the adipose tissue.
Describe the structure of white fat cells and how this is formed.
Through a multistep differentiation process, a lipoblast (adipoblast) is formed in which small droplets containing 3 glycerides are evident.
These droplets fuse to form a single big droplet which occupies the whole cytoplasm. They are not surrounded by a true membrane, but a phospholipid monolayer with polar heads towards the cytoplasm.
Then the cytoplasm is confined at the peripheral as a thin layer containing the organelles and the nucleus.
Describe the appearance of white fat cells in a histological section, explain why it takes this appearance.
In a histological section, fat cells appear empty except from the visible thin cytoplasm ring.
This is because of the lipid content of droplets being extracted by treatment with alcohol (dehydration) for preparation for paraffin.
Describe the proliferative abilities of white fat cells.
Adipose cells have limited proliferation ability in adult cells.
They proliferate during the 1st year of life and we live life with a number of cells set at 3 or 4 years of life.
Why can white adipose cells be considered endocrine cells?
They produce the hormone leptin, which is important as shown in mice. If its activity is abolished, the mice lose sense of safety and continuously eat until obesity.
Therefore leptin signals to the hypothalamus a sense of safety.
What are the functions of brown fat cells.
They are involved in thermoregulation, forming brown fat tissue and are abundant in hibernating mammals.
In humans, they are abundant in newborns that do not shiver in order to maintain body temperature.
Describe the structure of brown fat cells.
Their cytoplasm is filled with many small lipid droplets instead of one big one, they also have a high number of mitochondria.
How do brown fat cells regulate temperature?
In mitochondria a protein called UCP catalyzes re-entry of protons into the matrix, thereby reducing the synthesis of ATP while generating heat.
Where are macrophages derived from?
They are derived from circulating monocytes which leave the bloodstream and differentiate into macrophages.
In connective tissue proper they are also called osteocytes.
What are the receptors on phragocytes that recognises bacterial presence?
TOLL-like, Fc and C3b.
Describe TOLL-like receptors.
TLR(TOLL-like receptors) are single membrane spanning receptors able to recognize specific antigens common to several pathogens, their binding activates internal signalling, which leads to the expression of membrane proteins and eventually the activation of t-lymphocytes.
Describe hoe Fc receptors contribute to phagocytosis.
Macrophages also use receptors for the Fc portion of antibodies. The antibodies recognise and bind to microbes leading to microbe opsonization.
The variable fragment binds and decorates the microbe. Fc fragments are free for binding to macrophage, their binding activates the macrophage, which internalizes the opsonized microbe into phagosome and fuses with lysosomes making phrag-lysosome.
What are complement components?
The complement component is a group of plasma proteins usually in an inactive form, and becomes activated with the presence of a foreign body by a cascade mechanism and binds to a target.
This causes either its lysis and/or recognition by phagocytes.
How do complement components work?
Complement components can bind to the membrane of the pathogen and form MAC (Membrane Attack Complex), this makes holes in the PM, disrupting the integrity and eventually leading to death.
Otherwise it can bind to complementary receptors on macrophages and activate phagocytosis.
How so macrophages respond to large foreign bodies?
If foreign body is large, macrophages can fuse to form a giant poly-nucleated cell.
Describe the functions of macrophages.
Innate immunity (chemotaxis/phagocytosis)
Presentation of antigens to T-helper lymphocytes (MHC-II) - allows macrophage to expose specific antigens derived from foreign bodies presented to T-lymphocytes.
Synthesis and release of substances in inflammation, e.g. prostaglandins or necessary to the activation of lymphocytes, e.g. IL-1.
How do macrophages present antigens?
Part of the pathogen is exposed by the macrophage, antigens are recognised by CD4 T-helper cells which starts immune response.
