Fibrous CT Flashcards
What structure separates CT from the outside environment?
Epithelium
What separates CT cells from each other?
ECM
What is ECM composed of?
A gel like (ground) substance with embedded protein fibers
What is ground substance?
It holds tissue fluid derived primarily from blood
Carries O2, CO2, nutrients and waste
What is connective tissue?
A microscopically and functionally diverse group of tissues that can be classified into major groups such as embryonic and adult CT
What can adult CT be further classified into?
Fibrous and specialized CT
Which classes of CT are considered to be fibrous?
Areolar, dense regular and dense irregular
Which CT classes are considered to be specialized?
Adipose, cartilage, bone and hematopoietic
What are the functions of CT?
Structural framework of the body, protection, supports and interconnects other tissues, energy storage, transport fluids, cells and dissolved chemicals throughout the body and defense against invasion of microorganisms
What are fibroblasts?
Cells of CT that produce collagen, elastin, reticular fibers, proteoglycans and glycoproteins
What are mesenchymal cells?
CT stem cells
What are adipocytes?
A CT cell type that stores and releases fats, provides a reserve for energy sources and removes lipids from the blood, stores it and released it into the blood stream when needed
Describe adipocytes structure
Closely packed with their nuclei pushed to the side by large fat droplets
What are chondrocytes?
A CT cell that produces and maintains cartilage components
What are osteoblasts/osteoclasts?
A CT cell type that produces and removes bone components
What are hematopoietic stem cells?
A CT cell that produces RBCs and immune cells
Which structures are considered to be the fibrous component of ECM of CT?
Collagen fibers, elastin and reticular fibers
What is the function of the collagen?
Resist tension
What is the most common type of collagen?
Type I collagen
Describe the structure of type I collagen
Fibrils are aligned and cross linked to increase tensile strength
Comprised of two collagen type alpha 1 chains and a collagen type alpha 2 chain secreted as procollagen that is processed and crosslinked at the cell surface
What gives collagen fibers their banding appearance on a scanning electron micrograph?
Their fibril arrangement
What is scurvy?
Cells must have sufficient levels of vitamin C in order to properly cross link collagen fibers (is a cofactor in collagen synthesis)
Vitamin C deficiency will weakened collagen and CT in the body causing scurvy
What are some sx of scurvy?
Loss of teeth, blood vessel rupture (easy bruising), and poor healing as maintenance requires continual collagen production
What is Ehlers-Danlos syndrome?
Abnormal collagen synthesis leading to weak collagen fibers (multiple forms) due to mutations in collagen genes or collagen synthesis genes
What is elastin?
Protein fibers that are elastic and recoil back to original state when stretched
They are an assembly of tropoelastin, fibulin 1 and fibrillin-1/2
What are reticular fibers?
Form a supportive meshwork surrounding structures
Join CT to basement membrane
Also form nets surrounding capillaries and support the framework for bone marrow and the spleen
Which structures are considered to be a part of the amorphous ground substance of the ECM of CT?
Proteoglycans, hyaluronan, glycoproteins and extracellular proenzymes
What structures are proteoglycans composed of?
Chondroitin sulfates, heparan sulfates or keratan sulfates
What is the function of hyaluronan and proteoglycans in the ECM?
Primarily responsible for cushioning and resisting compressive forces
Form large sugar and sugar-protein structures
What is the purpose of the carbohydrate group of glycoproteins?
Important in protecting the proteins from destruction and can serve as signaling portion of molecules, structural molecules for ground substance to be built on, etc
What are some examples of glycoproteins found in the amorphous substance of ECM?
Cytokines, growth factors, structural proteins (e.g. fibronectin, laminins, tenascins, link proteins)
Which structures play a role in cell-ECM interactions?
Integrin receptors, syndecans, CD44 receptors, selectins, growth factor receptors and cytokine receptors all play an important role in cell signaling
What role do integrin receptors play in cell-ECM interactions?
Bind specific ECM components and initiate intracellular signaling cascades such as tyrosine kinase activity
What role do syndecans play in cell-ECM interactions?
Co-receptors containing multiple heparan sulfate proteoglycans needed for binding growth factors
What role do CD44 receptors play in cell-ECM interactions?
Bind to hyaluronan
What role do selectins play in cell-ECM interactions?
Cell surface receptors that recognize specific sugar residues
What are characteristics of embryonic CT?
Rich in ECM and mesenchymal stem cells (multipotent)
Some but not as many collagen or reticular fibers
What is embryonic CT referred to the umbilical cord?
Warton’s jelly
What are stem cells?
Self renewing cell population serving as a source for production of differentiated cells throughout life
What are adult MSCs?
Multipotent stem cells that differentiate into a variety of cell types including fibroblasts, muscle cells, osteoblasts, chondroblasts and adipocytes
What are the three types of loose fibrous CT?
Areolar, adipose and reticular
What are some characteristics of areolar CT?
Low density tissue with both fixed and wandering cells
Widespread and surrounds nerves, muscles, and blood vessels
Underlies most epithelia
Well vascularized
What are the fixed cell types in areolar CT?
Fibroblasts, adipocytes, mesenchymal cells
What are the wandering cell types found in areolar CT?
Macrophages, mast cells, plasma cells and leukocytes/lymphocytes
What are macrophages?
Differentiate from blood monocytes
Functions include phagocytosis, destruction of bacteria, damaged or sick cells, removal of cell debris in addition to Ag processing and presentation
What do mast cells secrete?
Chemicals such as histamine that mediate the allergic response and heparin (an anti coagulant of blood)
What are plasma cells?
Differentiate from B cells
Function is to produce Abs that mediate immunity
What are characteristics of adipose?
Characterized by abundant adipocytes and sparse ECM
Richly vascularized
Provides reserve energy source and insulates against heat loss
Supports and protects organs (by padding and cushioning organ or filling space)
Where is adipose CT found?
Under skin, around organs (e.g. kidneys, eye balls, etc), within abdomen, breasts and buttocks
What is white fat?
Functions in energy storage, insulation, cushioning vital organs and hormone secretion
What is brown fat?
Key thermogenic tissue, abundant in newborns but greatly reduced in adults
Describe characteristics of reticular CT
Rich in reticular fibers
Forms an open framework to create a supportive mesh/labyrinth for holding free cells
Where is reticular CT found?
In liver, bone marrow, LNs, and spleen where the meshwork it forms houses blood cells and immune cells outside the blood and lymphatic vessels
What are the three types of dense CT?
Dense regular, irregular and elastic
Describe dense irregular CT
Fibers are deposited in a random pattern
ECM of tightly packed, interwoven collagen fibers running in a random pattern
What is the principle cell type of dense regular and irregular CT?
Fibroblasts
Where is dense irregular CT found?
In dermis of skin, capsules around internal organs, perichondrium, periosteum and fascia
Describe dense regular CT
Fibers are deposited in a highly regular pattern
ECM of tightly packed regularly arranged collagen fibers
Resists pulling forces
Poorly vascularized
Has wavy appearance
Where is dense regular CT found?
In tendons, ligaments, aponeuroses, dense fascia and joint capsules
Describe elastic CT
Rich in elastic fibers
Allows recoil of tissue following stretching
Where is elastic CT found?
In blood vessel walls, bronchiole tubes and special ligaments (e.g. ligamentum nuchae)
What is Marfan’s syndrome?
Autosomal dominant disorder where elastin is weak due to a mutation in fibrillin-1 gene, a component of elastin fibers
Pts tend to be tall with long arms/legs (skeletal defects)
What are the principle target organs for Marfan’s syndrome?
Ocular, skeletal and cardiovascular systems which can be life threatening (ex. Dissecting aneurysms or mitral prolapse)
