Connective Tissue II Flashcards
What is an essential role of bone in cell signaling?
Bone is the body’s largest storehouse of Ca2+ and is continuously remodeled to maintain blood calcium levels. 99% of the body’s calcium is stored in bone, which also stores and protects hematopoietic tissues.
What are cartilages primary functions?
It forms the initial template that will be replaced by bone, and as a very pliable, hydrated support structure throughout life.
How does cartilage form?
It begins to form within connective tissue that has a layer of cells containing mesenchymal stem cells (MSC) the are stimulated to produce chondrocytes. Chondrocytes secrete the matrix that forms cartilage and entomb themselves within it in sites called lacunae.
What cellular processes continue within the lacunae?
The chondrocytes maintain the ability to divide and replicate themselves, forming strings of cloned chondrocytes that produce cartilage matrix and eventually separate themselves within it.
What is the perichondrium?
The surface layer of the cartilage that contains a dense layer of connective tissue. Contains mesenchymal stem cells and fibroblasts and collagen fibers. It is continuous with and connected to the overlying connective tissue.
What are the two ways that cartilage can grow?
Through interstitial growth, by the production of chondrocytes and ECM internally. Or by appositional growth, growth at the surface produced by mesenchymal cell production of chondrocytes that add to the cartilage. This growth stops in early adulthood.
What is the most prominent and common type of cartilage in the body?
Hyaline cartilage. Appears very smooth in histological samples. Loaded with hyaluronic acid, and thin collagen fibers. Forms most of the fetal skeleton, still found in the joints.
What are the two other common types of cartilage and where are they often found?
Elastic cartilage - loaded with elastic fibers. Need specialized stains to see. Found in the ears and nose.
Fibrocartilage - a merger between very dense connective tissue and cartilage. Commonly found at the junction of muscles and bone, where the tendon and the bone meet.
What are osteoprogenitor cells?
Osteoprogenitor cells are a subclass of stem cells produced by mesenchymal stem cells which are restricted to producing osteoblasts. Osteoprogenitors are capable of self-renewal, cell division, proliferation, and differentiation into osteoblasts.
How are bones formed?
In the connective tissue, osteoblasts are produced which line up and secrete watery secretions full of collagens and proteoglycans specific to bone called osteoid. Osteoblasts may divide and produce clones of themselves which continue to secrete osteoid, eventually encasing themselves in lacunae.
What are osteocytes?
Unlike cartilage, when the osteoblasts become encased they further differentiate into osteocytes. Osteocytes extend long processes of themselves into channels in the bone called calaliculi. The cellular processes are connected to the processes of neighboring cells through gap junctions. All of the osteocytes of a line are connected to each other and to the osteoblasts that created them.
What are the differences between osteoblasts and osteocytes?
Osteoblasts secrete the matrix (osteoid) that creates the bone and divide into osteocytes. Osteocytes do not secrete osteoid nor do they divide. Osteocytes monitor the condition of the bone and communicate it to the osteoblasts. This also means that bone can only grow appositionally, it cannot grow interstitially.
What is the process that creates the solid bone structure?
Matrix vesicles are secreted by osteoblasts and contain huge amounts of calcium and phosphate. Together, calcium and phosphate form hydroxyapatite, a crystalline structure that breaks the vesicle and deposits throughout the bone matrix. This is the storage form of Ca2+ and PO4- in the body.
What are osteoclasts and where do they come from?
Osteoclasts are effectively macrophages for bone. Hematopoietic cells give rise to monocytes (macrophage precursors) which enter the bone matrix and differentiate into multinucleated cells called osteoclasts. They degrade the bone matrix with enzymes, and transcytose it into the CT containing blood vessels.
What are five major roles of osteoclasts?
1 - They degrade bone matrix 2 - they can degrade cartilage matrix during bone formation 3 - they stimulate vascularization of bone. (Bone is highly vascularized compared to cartilage) 4 - Nerves also follow osteoclasts into bone 5 - they mobilize calcium from the bones.
