11/18/2014 Microscopic Anatomy Connective Tissue Thomas Poole Flashcards
What is connective tissue?
The tissue that forms a continuum with the other 3 major tissues to maintain a functionally integrated body
What is the function of connective tissue?
- mostly structural
- characterized on the basis of its extracellular matrix
What are some examples of connective tissue?
organ capsules
tendons and ligaments
areolar tissue filling spaces
fat
cartilage
bone
What does connective tissue develop from?
embryonic mesoderm
*in the head, from the neural crest by the migration of mesenchymal cells
Describe mesenchymal cells’ morphology
- oval nucleus with prominent nucleoli
- small amount of cytoplasm
- multiple thin processes that make it difficult to see the limits of the cytoplasm in the light microscope
What is connective tissue composed of?
extracellular matrix (ECM) and connective tissue cells
The extracellular matrix can be divided into ___, ___ and ___
ground substance
protein fibers
tissue fluid
What types of cells form connective tissue?
resident or fixed
*derived locally and present in relatively constant numbers
immigrant or wandering
*migrate in from the blood or bone marrow
What are some examples of resident cells?
mesenchymal cells, fibroblasts, reticular cells, and adipose cells
What are some examples of immigrant cells?
macrophages, mast cells, plasma cells, and other blood-derived CT cells (lymphocytes, monocytes, neutrophils, eosinophils, and basophils)
Some mesenchymal cells remain ___ in adult connective tissue and serve as ___ for new fibroblast, smooth muscle, or endothelial cell differentiation
undifferentiated; stem cells
What are mesenchymal cells called when found near blood vessels?
pericytes or adventitial cells
Mesenchymal cells typically have a ___ nucleus with prominent nucleoli and ___ cytoplasm than the fibroblasts that they otherwise resemble
large; less
What are fibroblasts?
The most numerous and ubiquitous of all connective tissue cells
What do fibroblasts synthesize and secrete?
ECM including CT fibers
Can we morphologically distinguish between the synthetically and mitotically active fibroblast and the inactive, resting fibrocyte?
Yes
Describe fibroblasts
Oval, euchromatic nucleus with several prominent nucleoli and a basophilic cytoplasm due to a well-developed RER
Describe the fibrocyte
Shorter and more spindle-shaped with a more heterochromatic nucleus and acidophilic cytoplasm
Fibrocytes may revert to the fibroblast state to participate in ___
tissue repair
During adult wound healing, a special type of fibroblast appears called a ___ that shares features of a fibroblast and a smooth muscle cell
myofibroblast
Describe reticular cells
Stellate shape with long thin processes and a centrally placed, euchromatic nucleus shaped like an Idaho potato with a prominent nucleolus
What do reticular cells do?
Produce reticular fibers that form the netlike stroma of hematopoietic, lymphoid and adipose tissues
What are white adipose cells or adipocytes?
Cells specialized for lipid storage
Why are adipocytes called signet ring cells?
Because the single droplet of lipid displaces both the nucleus and the cytoplasm to the edge of the cell
The lipid is lost during routine histological preparation, but can be preserved by ___ fixation
osmium tetroxide
Describe macrophages
Smaller than fibroblasts, have a heterochromatic, kidney shaped nucleus, and numerous vacuoles and granules in their cytoplasm from phagocytic activity
They are most easily identified in tissue from animals that have been injected (while alive) with a colloidal dye such as ___
trypan blue
Describe mast cells
Largest of the CT cells (20 to 30 microns in diameter). Their cytoplasm is filled with basophilic granules and they have a small, central nucleus
Mast cells are frequently found around ___
blood vessels
Describe plasma cells
- large, ovoid cells with an eccentric nucleus and an abundant RER
- nucleus has a characteristic clock face appearance because of a central nucleolus and heterochromatin clumps spaced around the inner surface envelope of the nucleus
- cytoplasm exhibits a clear zone due to the active Golgi complex
Where are plasma cells found?
Medulla of lymph nodes and in the lamina propria of the stomach and intestines
What is ground substance?
Colorless and transparent mixture that binds cells to connective tissue fibers
*formed mainly of glycosaminoglycans (GAGs) and structural glycoproteins
The majority of glycosaminoglycans GAGs (except hyaluronic acid) are bound covalently to a protein core forming a ___
proteoglycan molecule
What are the three main types of connective tissue fibers
collagen
reticular
elastic
Describe collagen fibers
- composed of fibrils greater than 50 nm in diameter
- made of type I collagen
Is collagen the most abundant protein in the human body?
Yes
What are the three groups into which the family of proteins called collagens are divided?
Fibril forming collagens
Linking/anchoring collagens
Sheet-forming collagen (Type IV)
Describe reticular fibers
- composed of fibrils less than 50 nm in diameter
- composed mainly of collagen type III
Ehlers-Danlos type IV disease
Caused by faulty transcription or translation of type III collagen and results in aortic and intestinal ruptures in areas where reticular fibers normally reinforce smooth muscle layers
Describe elastic fibers
- composed mainly of the protein elastin
- abundant in elastic ligaments and arteries
What are the 3 different types of elastic fibers?
Oxytalan fibers (fibrillin)
Elaunin fibers
Elastin fibers
Marfan’s syndrome
Mutations in the fibrillin gene where patients risk aortic rupture and hypermobile joints
Describe loose connective (areolar) tissue
Consists of a loose network of different fiber types in which many fixed and wandering cells are suspended
Describe dense connective tissue
Contains collagen fibers that predominate over cells
- regular
- ropelike arrangement of fiber bundles
- irregular
- fabric-like arrangement
What is the predominant cell of the dense connective tissue?
Fibrocyte (mature fibroblast)
Describe reticular connective tissue
Previously called hematopoietic tissue of the subgroup connective tissue with special properties is made of reticular cells and reticular fibers
Describe unilocular (common, yellow or white) adipose tissue
Composed of cells with a single large droplet of fat
Describe multilocular (brown) adipose tissue
Composed of cells that contain many lipid droplets per cell and abundant mitochondria around a centrally placed nucleus
Which one is much more abundant, unilocular fat or multilocular fat?
Unilocular fat
Where does fat develop from?
Undifferentiated mesenchymal cells via lipoblasts
Multilocular fat occurs primarily in the ___
human fetus
