CT/Adipose in Class Lec Flashcards
Connective tissues range from liquid (blood) to soft tissue (fascia and adipose tissue) to harder substances (cartilage and bone).
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Common Features of CT?
- Rich ECM, lesser in number of cells per unit area
- Common embryological origin (most from embryonic mesenchyme and some from neural crest like the CT in the head)
never exposed to outside world
ecto/endo form what?
epi cells
mesoderm forms what?
mesenchyme - loose collectio not cells with lots of ECM
what can an undifferentiated mesenchymal cell form?
fibroblast osteocyte osteoblasts chondrocytes chondroblast adipocyte endothelial cell/smooth muscle cells
elements of CT? (3)
fibers
cells
matrix
CT functions?
- structural support (bone/cartilage)
- energy depot and cushioning
- defense: immune responses and inflammation
- repair and wound-healing
- cues for differentiation
Exs of CT functioning as structural support
bone and cartilage
capsules of spleen and lymph nodes
basal laminae
three types of fibers in CT?
collagen
reticular
elastic
things in the matrix of CT?
proteoglycans
glycoproteins
tissue fluid
cells in the CT?
derived from differentiation of mesenchyme: fibroblasts mesenchymal adipocytes chondrocytes osteocytes
arise elsewhere and migrate into CT: macrophages lymphocytes mast cells granulocytes
collagen fibers:
what type of subunits
what diameter
color on H&E?
- collagen subunits
- .5-20 micrometer diameter
- pink/orange on H&E
reticular fibers:
subunits?
diameter?
color on H&E?
- collagen subunits
- .5-2 micrometers in diameter
- not stained by H&E! (silver or PAS)
elastic fibers:
subunits?
diameter?
color on H&E?
- elastin + microfiber glycoproteins (fibrillin +)
- .5-1 micrometer diameter
- poorly stained by H&E (orcein or resorcinol) - sometimes show up as pale pink on H&E
collagen and reticular fibers are very similar. Collagen are thicker, reticular are thinner and not as strong.
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There are about 20 collagen genes… how many collagen types?
28 but we only care about first 4
collagen: glycine repeated every 3 aa.
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collagen type I
forms?
distribution?
COLLAGEN FIBERS
thick fibers
skin, bone, cornea, tendons
collagen type II
forms?
distribution?
fine fibrils
cartilage
collagen type III
forms?
distribution?
RETICULAR FIBERS
thin fibers
loose connective tissue, arteries, smooth muscle, stroma of many glands
collagen type IV
forms?
distribution?
sheets
basal laminae
Different types of collagen result from different combinations of collagen polypeptides. The different types differ somewhat in physical properties and have different tissue distributions - you should know these!
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Type I thick collagen fibers are composed of many fibrils. The fibrils have a striated appearance and form a staggered array.
(thick fibers in skin, bone, cornea, and tendons)
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What do collagen fibers show up as in H&E? (type I)
pink threads!
wispy looking for type I!
what do collagen fibers look like in a EM? (cross section and longitudinally)
cross section - spots/stippled
longitudinally - individual fibrils with characteristic striations that result from staggered but regular polymerization
can tell its NOT skeletal muscle because there are no organelles!
Type I - denser CT
Type III - looser CT
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which fibers cannot be visualized at all on H&E?
reticular! (use silver/ PAS instead)
elastic fibers are also poorly visualized but do show up as pale pink
special stain type I collagen?
trichrome
special stain reticular?
silver
PAS
special stain elastic?
roscorcinol
orcein
what is special about collagen?
It has a high tensile strength - meaning it has resistance to be lengthened/stretched. (NOT THE RESISTANCE TO SHEAR - meaning the ability to resist bending or breaking).
makes sense bc you want your skin to go back after you pull on it (don’t want droopy skin)
how to collagen get its high tensile strength? (3)
- compact triple helix
- ordered polymerization
- cross-linking between lysine residues
which fibers have high tensile strength?
collagen and reticular
ability to resist stretching (put fibers at different angles to prevent stretching from all diff angles)
elastic fiber structure?
elastin core and microfibrils made of fibrillin, MFAP, and emilin
Marfan syndrome caused by what?
mutations in fibrillin
TEM of elastic fiber?
amorphous shape
core doesn’t stain but the microfibrils do!
elastic fibers property?
resiliency or elasticity - the ability to elongate and recoil
this comes from the fact that elastin is made of segments of rigid alpha-helix separated by random coils; the random coils allow the protein to extend, but when released, it recoils to a more globular structure.
cross-links between lysines check the extension so that the fiber is not pulled spar
when stretched, hydrophobic residues get exposed!
what do elastic fibers look like in H&E?
look like doubled wavy lines
resorcin for elastic fibers shows up what color?
black/ purple
the ratio of the different fibers in a tissue (collagen, reticular, elastic) determine the tissues properties!
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properties of the ECM?
fibers (3)
proteoglycans
glycoproteins
fibers are embedded within the ECM - a gell composed of proteoglycans and glycoproteins that hold the tissue fluid
what are proteoglycans composed of?
a protein component and a glycan.
the glycan is a glycoaminoglycan (GAG) built up from repeating disaccharides (alternating glucose and amino glucose residues)
different GAGs are composed of different pairs of sugars
ex. GAG = dermantan sulfate or heparin
the carboxyl groups of GAGs are negatively charged and most are sulfated - overall negative!!
Thus, GAGs are highly-charged, long, unbranched chains of repeating disaccharides
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what is the key feature of GAGs?
the negative charge!
The long, charged chains repel each other - thus tissues rich in GAGs resist compression.
GAGs on proteins assume what appearance?
proteoglycans look like bottle brushes because they stick out at right angles to maximize distance from each other!
Because the GAG chains repel each other, they occupy large volumes and cannot readily be compressed. The “empty space” between GAG chains allows for diffusion of tissue fluid.
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Two properties of proteoglycans?
rigidity and porosity
proteoglycans are classic in synovial fluid, cartilage, and important to the immune system.
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elastic fibers show up as thin purply lines when close up on resorcinol or orcein
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type I collagen is found where in skin?
dermis
CT is like an intelligent building because it can sense its environment, reach decisions about the state of that environment, and communicate those decisions.
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Embryonic mesenchyme gives rise to ________ (the main cells of CT proper) and to cells of various specialized tissues..
fibroblasts
fibroblast characterisitcs (4)
- elongated or fusiform cells
- ovoid nuclei
- prominent nucleoli
- eosinophilic cytoplasm
if they are actively synthesizing, they will have lots of RER! but that usually goes away and most fibroblasts are resting. if you are injured, it will go back to synthesizing.
vast majority of bone marrow derived cells are found in CT
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CT provides surveillance and security services for the body… (2)
1) immune response: specific - nonself antigens recognized by lymphocytes
2) inflammation: nonspecific - foreign substances engulfed by phagocytes
CT is just under epi… so if you get cut, the CT has stuff (immune cells) to combat damage/infection
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macrophages derived from?
monocytes
found in many tissues through the body
named big eater
macrophage characterisitcs?
- active in phagocytosis (frothy cytoplasm and irregular membrane)
- involved in in inflamm responses
- ag presentation during immune responses
lots of euchromatin!! very active with big nucleus
lots of lysosomes that appear dark on EM
what causes metachromasia?
proteoglycans/GAGs (heparin sulfate)
granules in mast cells
dye originally blue turns purple/red
what are in granules of mast cells?
Granules contain bioactive substances: Histamine Leukotrienes Proteoglycans e.g. heparin sulfate (metachromasia) ECF-A proteases
slow release of granules in mast cells cause….
slow release of granule contents and cytokines regulates innate immune response
rapid release of granule contents in mast cells?
anaphylactic shock!/allergic reactions
mast cells are found..?
basophils…?
mast - tissues
basophil - blood
mast cells are concentrated near blood vessels in tissues where they will likely encounter foreign pathogens.
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Histamine causes what two things?
- bronchoconstriction by inducing contraction of smooth muscle - can cause death rapidly
- vasodilation - lowers BP rapidly and causes loss of consciousness
both affect smooth muscle but cause opposite effects in diff places (reap =contract; vasc = dilation)
epinephrine binds to what type of receptor?
causes what action?
adrenergic
its actions vary by tissue type depending on the expression of adrenergic receptors
causes smooth muscle relaxation in the airways and contraction of muscle in the arterioles
reverses effect of histamine
epinephrine (Adrenaline) is the choice of tx of patients with…?
anaphylaxis
what happens in the first exposure to an allergen?
slow immune response - 10-14 days
then the IgE bind to receptors on mast cell surfaces
induces a weak immune response - that is some lymphocytes are stimulated to proliferate and differentiate into plasma cells which secrete ab (IgE) - takes several days after exposure
what happens during a second exposure to allergen? (2)
- the allergen again triggers an immune response, which is more powerful and slightly quicker (may now occur within 3 days rather than 7-10)
- In susceptible individuals, the allergen also binds directly to IgE on the “primed” mast cells, causing anaphylaxis, which is rapid (within minutes) and life-threatening.
Binding of allergen to IgE on mast cells causes….
immediate release of cytoplasmic granules
constriction of airways
diverse diseases with CT!
joint hyper mobility
rheumatoid arthritis
autoimmune diseases
anaphylactic shock
