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connective tissue histology
MS1/Mod 1: histology, connective tissue
What are connective tissues derived from?
splanchic mesoderm (walls of GI tract)
somatic mesoderm (body walls)
What composes the ECM?
fibers and ground substance
What comprises connective tissues?
collagen and proteoglycans
What comprises proteoglycans?
glycosaminoglycans and protein core
How do GAGs make a hydrated gel?
GAGs have lots of negative charges and are attracted to Na+ which brings water with it
What is the purpose of the hydrated gel of GAGs?
hydrated gel allows rapid diffusion of water-soluble molecules through ground substance but slows the passage of lg molecules and bacteria...creates turgor of ECM to resist stress
What is the pathway of making collagen?
preprocollagen (rER)--->procollagen (rER)--->tropocollagen/collagen (outside the cell via protease)--->collagen fibrils--->collagen fibers
Where are collagen fibers found?
CT and reticular laminae of basement membranes
What makes collagen?
fibrocytes/blasts, sm muscle cells, chondrocytes/blasts, osteocytes/blasts
Collagen type 1
most common, "classic collagen"
Collagen type 2
in hyaline, elastic cartilage and fibrocartilage (intervertebral disks)
Collagen type 3
assoc w/ type 1; called "reticular fibers", characteristic structural scaffolding of lymphoid tissues and bone marrow
Collagen type 7
Collagen type 4
Where are reticular fibers synth?
fibrocytes/blasts in LCT and by reticular cells in lymphoid tissues and in bone marrow
What are some physical characteristics of reticular fibers?
highly glycosylated; delicate silver-staining networks (vs thick bundles)
What are the functions of reticular fibers?
supportive lattices in LCTs near epithelium and adipose tissue; hematopoietic and lymphoid tissues
What makes up elastic fibers?
elastin and fibrillin (glycoprotein)
What makes elastin?
sm muscle cells come' elastic arteries...NOT fibroblasts
What type of tissue has elastic fibers?
tissues subject to stretching or expansion (elastic arteries, interalveolar septa, bronchi and bronchioles, elastic cartilage of ears)
What is an example of CT damage?
What makes elastic fibers?
smooth muscle cells, fibrocytes/blasts, chondrocytes/blasts
What are some physical characteristics of elastic fibers?
not easily seen w/ reg staining techniques; highly pliable and elastic
What happens if ECM damaged?
fibrocytes--->fibroblasts--->repair---fibrocytes (same for chondrocytes/blasts, osteocytes/blasts)
special variant of fibroblast
What are the differences between fibrocytes and fibroblasts?
: in LCT and CT in repair
both synth and secrete ECM components but diff is activity level
What is the job of a reticular cell?
produce reticular fibers in hematopoietic and lymphoid tissues; phagocytize Ag and debris; collect Ag on cell surface
What lives with reticular cells?
lymphocytes, macrophages, FCD
fewer cells, thick matrix
Dense irregular CT
dense matrix is nondirectional
i.e. deeper CT of skin; organ trabeculae
Dense regular CT
dense matrix is directional (tendons, ligaments)
i.e. tendons, ligaments
What are some specialized CTs?
cartilage and bone
What are the functions of adipose tissue?
store E in the form of stored lipids
cushions and insulates body
lots of mit but oxidative phosphorylation step deactivated so heat is made instead of ATP in order to keep baby warm
aka functional tissue
What is subcutaneous fat?
makes "panniculus adiposus" (superficial fascia)
varies in thickness depending on adults
What is intra-abdominal fat?
in retroperitoneal areas
variable amts surrounding blood/lymphatic vessels in omentum and mesenteries
What does adipose tissue make?
What lives in CT?
* do not originate here, migrate here after mature
derived from bone marrow precursors
has abundant basophilic granules in cytoplasm- heparin and histamine
several can fuse to make multinuc giant cell
lg, irregular cell w/ lg, pale staining nuc; "junky" cytoplasm
abundant in areas susceptible to bact invasion (GI tract)
lg, ovoid w/ eccentric nuc and lots rER
clock face nuc w/ lots of heterochromatin on nuc env
present in variable numbers
sm, round cell w/ dk, round nuc, think cytoplasm
migratory, phagocytic, short-lived
bright-red cytoplasmic granules (lysosomes)
internum and externum in specific granules
What makes GAGs and collagen?
aka glycosamine in GAGs
connective tissue diseases
Ehlers-Danlos syndrome, Stickler syndrome