Connective Tissue Flashcards
T or F: Leukocytes from the blood become active once in the CT
T
What are the four functions of CT?
Structural support, medium for exchange, aid in defense and protection of the body, and site of fat storage.
Embryonic CT is composed of what?
Mesenchyme (mostly fibroblasts, source of progenitor cells), mucous CT which sits below the surface of skin and helps in cell development. Wharton’s Jelly, a very watery fluid in the umbilical cord
What is CT mesenchyme?
Mostly fibroblasts and the source of CT progenitor cells
What are the five types of CT proper?
Loose (areolar), Dense irregular, Dense regular, Reticular, and Adipose
How is CT proper type defined?
The density of connective tissue fibers
What are specialized CT?
Cartilage, bone, blood (hemopoietic and lymphatic tissue)
Where is dense irregular CT found?
Dermis of skin, sheaths of nerve, capsules of spleen, kidney, lymph nodes, testes, and ovaries
Where is dense regular CT found?
Tendons and ligaments
Where is loose irregular CT found?
Fills spaces just deep to skin, mesothelial lining of body cavity, blood vessels adventitia, surrounds parenchyma of glands, lamina propria of GI tract
What are the two general components of CT organization?
ECM and cells
What composes the ECM of CT?
Ground substance (no stain) and fibers (synthesized by fibroblasts)
What are the two types of CT cells?
Fixed/Resident (fibroblasts and adipocytes) and Transient/wandering (Macrophages of plasma cells that come from elsewhere e.g. blood)
What are the three major components of the ground substance?
Glycosaminoglycans, Proteoglycans, Glycoproteins
T or F: The fibers in the ground substance are visible in LM
F
What are GAGs?
Polysaccharides of repeating disaccharide subunits
What type of GAGs are in the CT ground substance?
Sulfated…e.g. keratin, chondroitin, and dermatan sulfate and unsulfated…e.g. hyaluronic acid
What is the function of GAGs in the CT ground substance?
Attracts water and resists compression (attracts water via its negative charge by attracting sodium)
What is the function of hyaluronic acid in the ground substance of CT?
Long chain, very large to make backbones for proteoglycan attachement, non-sulfated
What are proteoglycans?
Protein core with covalently bound sulfated GAGs
What is the function of PG in the CT ground substance?
Important for binding and activation of growth factors
What type of glycoproteins are in the ground substance of CT?
Fibronectin, laminin, and entactin
What is the function of glycoprotein in the ground substance of CT?
Contains domains for the components of ECM and integrins to bind, important for transport
What are the three types of CT fibers?
Collagen, reticular, elastic
T or F: Collagen fibers are visible in LM
T
What are the characteristics/function of collagen fiber in CT?
Major fibrous protein of CT and is flexible with extremely high tensile strength
What is the approximate size of collagen fibers?
Less than 10 microns in diameter with wavy structure that stains pink in H&E
Describe the structure of collagen fibers
Formed by an assembly of tropocollagen molecules. Each tropocollagen molecule is made up of a triple helix of 3 alpha-chains (alpha-chain subunits give the collagen its characteristics)
T or F: Every third AA in tropocollagen is glycine
T
What are the major AA of tropocollagen?
Proline, hydroxyproline, hydroxylysine, and glycine
What gives collagen its banding pattern?
Gap regions due to periodic gaps of the tropocollagen which lead to light (less dense) and dark bands
General CT, tendon, bone, ligament, and capsules or organs is covered by what type of collagen?
Type I
Morphology of Type I collagen
Large banded collagen fiber
What is the function of Type I collagen?
Resists tension (very strong)
What is Type II collagen?
Small banded collagen fiber that makes up hyaline and elastic cartilage and is in the vitreous of the eye
What is the function of Type II collagen?
Resists pressure
What is Type III collagen?
Small banded collagen fiber that makes up lymphoid tissue, bone marrow, spleen, liver, lung, cardiovascular system, and skin
What is the function of Type III collagen?
Forms a structural framework
What is Type IV collagen?
Sheet-like layers that make up the basement membrane and basal lamina
What is the function of Type IV collagen?
Forms meshwork of lamina densa and provides support and filtration function
What is Type V collagen?
Thin fibrils that make up the dermis, tendon, bone ligament, capsules of oran, and placenta
What is the function of Type V collagen?
Associates with Type I collagen, placental ground substance
What is Type VII collagen?
Thin fibrils that serve as the junction between the epidermis and dermis
What is the function of Type VII collagen?
Anchors fibrils in the basement membrane
Where is collagen synthesized?
Fibroblast
Follow the production of collagen
Transcription in nucleus, translation of preprocollagen in RER with the alpha chains having propeptides at amino and carboxy terminal ends, Hydroxylation in RER, Glycosylation in RER, Formation of procollagen triple helix in RER (spontaneous),
secretion of procollagen via trans Golgi network, Cleavage of propeptides by procollagen peptidase to form tropocollagen molecule. Spontaous self assembly of tropocollagen to form collagen fibril
What prevents collagen from forming inside fibroblasts?
Propeptides on the preprocollagen
Where are propeptides located on preprocollagen?
Carboxy and amino terminals
Where is the procollagen triple helix formed?
RER
What secretes procollagen?
Trans golgi network
Where does cleavage of procollagen to tropocollagen take place?
ECM
T or F: Collagen fibril assemble requires energy
F (spontaneous)
T or F: Procollagen triple helix forms spontanously in the RER
T
What color does collagen stain in an H&E?
Pink due to high affinity for eosin
What type of CT is located at myotendinous junctions?
Dense regular CT
What composes Reticular fibers?
Type III collagen
What is the structure of reticular fiber?
Thin (0.5 micron to 2 micron), branched
What stains reticular fibers?
H&E is poor, usually use silver and PAS stains
Reticular fibers are often prevalent in what tissue?
Lymphatic, hematopoietic, spleen, liver, and other glands
Elastic fibers in skin have what function?
Allow for resilience
T or F: Elastic fibers stain in H&E
F, require their own stain
Describe the structure of elastic fibers
Flexible elastin core with fibrillin skeleton. Elastin is deposited on the fibrillin core
What are two locations elastin is often found?
Ligaments and walls of arteries
What is scurvy?
Vitamin C deficiency leading to lack of proline hydroxylase leading to weak and unstable tropocollagen/collagen.
What is Ehlers-Danlos syndrome?
Mutation in collagen gene or enzyme related to collagen metabolism (general disease type). The gut is often ruptured in this syndrome
What is Marfan’s syndrome??
Defect in fibrillin gene which can lead to rupturing of the gut or issue with artery walls. Can get aortic rupture.
Name five fixed resident cells in CT
Fibroblasts, pericytes, adipocyte, mast cell, histiocyte (macrophage)
Name 4 transient cells in the CT
Macrophage, monocyte, lymphocyte, granulocytes (neutrophils, eosinophils, basophils)
What is the principal cell of CT?
Fibroblasts
What are the two subtypes of fibroblasts in the CT?
Myofibroblasts and pericytes
What are myofibroblasts?
Resemble smooth muscle cells and play a role in wound closure and healing. Have very dense nuclei (not active)
What are pericytes?
Undifferentiated mesenchymal cells associated with capillaries and small venules. Left over mesenchymal cells that can be stimulated to make new fibroblasts or adipocytes. These cells are transcriptionally active (can see some euchromatin)
What are the two types of adipocytes?
Unilocular and Multilocular
What are unilocular adipocytes?
Single lipid droplet. White/yellow fat. Serve to store lipids
What are multilocular adipocytes?
Brown fat. Found in infants and newborns. Thermogenic. Multiple lipid droplets
Unilocular adipocytes store lipids as…?
TAGs that are synthesized in the adipocyte or synthesized in the liver and imported as VLDL
What happens in unilocular adipocytes upon mobilization of lipids by hormonal of neurogenic control?
TAGs broken down to FA and glycerol
T or F: Adipocytes produce leptin
T
What is leptin?
Produced by adipocytes to decrease food intake and increase metabolism
What percentage of newborn body weight is multilocular adipocyte?
2-5%
Why is multilocular adipocyte brown?
Due to high amoud of cytochrome present in mitochondria
How is heat generated in multilocular adipocyte?
Mitochondria contain thermogenin which allows flow of H back into MM from IM without producing ATP
T or F: Multilocular adipocytes are located in a rich capillary bed
T
How is heat production controlled in multilocular adipocytes?
Sympathetic innervation
What are the two types of obesity?
Hypertrophic (adult onset increase in cell size, liposuction!) and Hypercellular (childhood onset increase in cell number, harder to deal with because cells tend to retain ability to replicate)
What are histiocytes/macrophages?
Principal phagocytic cells of CT
Where do histiocytes come from?
Originate in bone marrow as monocytes. Part of the mononuclear phagocyte system (MPS)
T or F: Histiocytes can fuse to form foreign body giant cells
T (often multinucleate)
Where are histiocytes located?
CT
Where are Kupffer cells located?
Liver
Where are alveolar macrophages found?
Lung
Where are macrophages found?
Bone marrow, lymph node, spleen, and thymus
Where are pleural ad peritoneal macrophages found?
Serous cavities
Where are osteoclasts found?
Bone
Where are microglia found?
CNS
Where are langerhan’s cells found
Epidermis
T or F: Plasma cells are transient
T
Where do plasma cells originate from?
B lymphocytes (become plasma cells upon interaction with antigen)
What is characteristic of plasma cells?
Cartwheel nucleus and basophilic cytoplasm
Where are plasma cells abundant? What is their function?
Sites of chronic inflammation and synthesize and secrete immunoglobulins.
Why is the cytoplasm of the plasma cell basophilic?
Huge Golgi apparatus
What are mast cells?
20-30 micron diameter cells that mediate inflammatory response
Where do mast cells originate from?
Bone marrow
What are the characteristics of mast cells?
Basophilic granules with primary mediators of inflammation (heparin, histamine, eosinophil, and neutrophil chemotactic factors).
Synthesize and secrete secondary mediators (leukotrienes, thromboxanes, and prostaglandins to cause contraction)
What is a hypersensitivity reaction facilitated by mast cells?
Anaphylactic shock
Generally describe mast cell activation
Binding of antigen, cAMP cascade leading to release of calcium to trigger release of primary mediators (histamine and heparin among others). Phospholipases are also activated to release secondary mediators like prostaglandins
What is the function of neutrophils?
Phagocytic and digest bacteria
What is the function of eosinophils?
Attack parasites
What is the function of basophil?
Inflammatory response
