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Name the five functions of connective tissue.
- 1) structural support
- 2) medium for exchange - transfer of water, nutrients, waste
- 3) defense
- 4) protection
- 5) storage of lipids
What germ layer does connective tissue originate from?
How do collagen fibers appear by electron microscopy?
appear striated due to the overlapping of tropocollagen
Name the type of collagen in collagen fibers and the type of collagen in reticular fibers.
- collagen fibers - Type I
- reticular fibers - Type III
Where are reticular fibers found?
in connective tissue of highly cellular organs ie. lymphoid nodules
What are elastic fibers and where are they found?
- formed of distensible elastin polymers wrapped wth microfibrils of glycoprotein
- found in tissues where stretch/recoil required (ie. elastic arteries)
Describe the structure of collagen fibers.
- Tropocollagen (triple helix) subunits overlap to form 67nm banding pattern on fibrils
- Fibrils aggregate to form thicker fibers (2 µm in diameter) and very thick bundles (10-20 µm in diameter)
How are reticular fibers stained?
need to use a silver histochemical stain because H&E staining isn't effective to see the reticulum
Which two lineages do connective tissue cell types come from?
- 1) Mesenchymal Stem Cells
- 2) Hematopoetic Stem Cells
What are the 6 cell types in connective tissue?
- Derived from mesenchymal stem cells:
- Derived from hematopoietic stem cells:
- mast cells
- plasma cells
What are fibroblasts?
- most abundant cell in CT
- produces almost all the ECM
- elongated in shape
- prominent and extensice RER and Golgi
- nucleus contains abundant euchromatin
What are adipocytes?
- cytoplasm is filled with lipid droplets - either one big vesicle or many little ones
- nuclei appear pushed to side by cytoplasmic lipid
- clustered in groups = lobules separated by connective tissue sleeves (=septae)
What are pericytes?
- cells associated with the walls of small blood vessels in CT
- stabilize the vessel walls; have some control over vessel diameter
- have some pleuripotent stem cell properties
What are macrophages?
- motile, phagocytic cells
- numerous vacuoles, lysosomes, endosomes, and vesicles in cytoplasm
- nucleus is kidney shaped
- derived from monocytes
What are mast cells?
- Cells that initiate non-specific inflammatory responses
- Repond rapidly to pollens, venoms, etc
- cytoplasm packed with secretory vesicles filled with histamine, heparin, and WBC chemoattractants
What are plasma cells?
- transient cell type
- antibody factories
- cytoplasm binds hematoxylin due to abundant RER
- prominent Golgi apparatus
- 'clockface' nucleus with alternating areas of euchromatin and heterochromatin
- differentiated B-lymphocytes, secrete antibodies
What are the five classifications of connective tissue proper?
- 1) Loose (areolar) CT: highly cellular, abundant ground substance, few fibers, high diffusion index - gel like and malleable, prominent in the lamina propria underneath mucosal membranes, little tensile strength
- 2) Dense Irregular CT: fewer cells, less ground substance, many fibers (mostly collage type I), fibers are irregularly arranged in all directions so tissue is resistant to stress in all directions, prominent in dermis of skin and outer capsules of organs
- 3) Dense regular connective tissue: similar to dense irregular CT but fibers are arranged in parallel arrays so tissue is very resistant to stress in one direction, prominent in tendons and ligaments
- 4) Adipose tissue: high number of adipocytes in groups (lobules) separated by sleeves of dense irregular CT (septa)
- 5) Reticular tissue: highly cellular with many reticular fibers (Collagen Type III), prominent in lymphoid structures and organs
Surface epithelial cells penetrate underlying connective tissue and are specialized to secrete a substance they synthesize
the epithelial secretory units of a gland
Define stroma (as it relates to glands)
The connective tissue around glands that is inductive and supportive
What is the difference between exocrine glands and endocrine glands?
In exocrine glands, secretory product is released apically into a duct or onto a free surface while in endocrine glands, secretory product is release basally into stroma, picked up bloodstream (= 'hormone); factors that act locally on nearby cells after diffusing within the same tissue are called 'paracrine' factors
What are the two types of exocrine glands?
- unicellular glands = single cells embedded in a surface/lining epithelium (eg. goblet cells)
- multicellular glands = clusters of secretory parenchymal cells surrounded by stroma; secrete into a duct (eg. salivary glands)
What are the three ways that multicellular glands are classified?
- 1) duct morphology (simple = unbranched ducts; compound =branched ducts)
- 2) secretory portion morphology (tubular=same diameter as duct; acinar/alveolar=expanded diameter compared to duct)
- 3) nature of secretion (serous = proteinaceous, enzyme rich; mucous = proteoglycan, lubicricating)