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UKCD Histo Lec 3

learning objectives from histo for connective tissue

QuestionAnswer
From which specific precursor are all CT proper and its specialized form derived? Mesenchyme
What are the two main characteristics of CT? High ratio of ICS to cells (except adipose CT); 2. Varying vascularity (except cartilage).
How do these two features compare with epithelium? In epithelium there is low ICS to high cellularity (like adipose CT); epithelium is avascular (like cartilage).
What are the two most important functions of CT? Support (connection/adhesion) and diffusion.
What are the main components of CT? Cells, fibers and amorphous ground substance.
What is the predominant cell of CT? Fibroblasts/cytes
What does this cell do? Secretes all 3 fiber types as well as the ground substance of CT
How does the active form of this cell differ in name and appearance from its inactive form? Active
White/yellow/unilocular single unified lipid droplet within the cytoplasm
brown/multilocular lipid droplets do not coalesce and are found randomly within the cytoplasm.
What are the specific functions of these adipocytes? White: store lipid for energy; brown: store lipid as a source of heat.
How are adipocytes organized as a tissue? Cells held in place by a reticular fiber meshwork, highly vascularized, low ICS content.
Endothelial cells They form the walls of the numerous capillaries that vascularize adipose CT.
How does the structural composition of adipose tissue relate to its function? Lots of blood supply for the efficient exchange of lipid between the blood and the adipocytes.
From which cell type do macrophages arise? Monocytes
From where do they migrate before becoming macrophages? Monocytes leave the circulating blood and become macrophages.
What is the function of a macrophage? They ingest interstitial debris.
How are macrophages structurally equipped for this function? They are ameboid (can move), form pseudopodia (for ingesting material) and contain numerous lysosomes (to digest the ingested particles).
What is the function of a mast cell? They secrete anticoagulants and can also make blood vessel walls leaky (facilitate edema).
What do the granules of mast cells contain? Heparin (anticoagulant) and histamine (causes BV’s to become leaky).
Where are mast cells localized in CT? Why? Close to blood vessels. Their secretions deal primarily with these structures.
How does the IgE antigen-antibody binding in mast cells work? IgE receptors for previously ingested antigens presented on surface of a mast cell, 2nd exposure to antigens binds w/ antibody sites, causes rapid release of histamine from stored cytoplasmic granules, Histamine makes blood vessels leaky -edema
How do antihistamines affect this binding? Antihistamines compete for binding sites on these cells preventing the antigen-antibody cross-linking resulting in stabilization of the membrane-bound cytoplasmic granules of histamine - therefore they are NOT released.
From which cell type do plasma cells arise? From B lymphocytes (B cells).
What the function of plasma cells? They produce antibodies (humoral response to antigens).
How is their morphology related to this function? Their cytoplasm is packed with rough endoplasmic reticulum (protein manufacturing organelles – as antibodies are protein-based).
Which other types of cells are common to CT? Most other blood cells (eosinophils, basophils, neutrophils, lymphocytes, etc.).
List the three types of fibers found in CT. Collagen(ic), elastic, and reticular.
Which fiber type is the most abundant? Collagen(ic).
Of what is a collagen fiber composed? Tropocollagen subunits arranged in a 1/4 length overlap morphology.
Outline the steps in collagen synthesis. Hydroxylysine and hydroxyproline are amino acids incorporated into procollagen, this is secreted, upon entering ECM in intercellular space cleaved into active subunit, tropocollagen, assembled into collagen fibers
Which cell is responsible for forming collagen fibers in connective tissue proper? In connective tissue only fibroblasts,. In other tissues osteoblasts, chondroblasts, odontoblasts, and cementoblasts can secrete collagen fibers.
How many different types of collagen are there? More than five at this point.
What is the reason for these numerous variations in collagen fiber composition? Varying diameters - they are arranged in varying fiber size; Type I being the thickest; Type V being the thinnest.
Which one is most common in connective tissue proper (loose areolar, dense). Type I.
How do reticular fibers differ from collagen fibers? Predominantly size - they are smaller, type III collagen fibers covered with associated glycoproteins so they stain differently than collagen fibers.
Which type of collagen do they contain? Type III collagen fibers.
What is the function of reticular fibers? They form supporting meshworks to hold parenchymal cells within an organ.
Which cells can secrete reticular fibers? Fibroblasts, smooth muscle cells and reticular cells.
How do elastic fibers differ structurally from collagen? They are formed of two components – microfibrils embedded in an amorphous protein matrix
What is the glycoprotein that composes these microfibrils? Fibrillin.
What is the specialized function for elastic fibers? Resilience (stretch and return to original shape) – flexibility.
Which cell(s) secrete these fibers? Fibroblasts and smooth muscle cells.
Which other fiber types are contained within this class of fibers? Oxytalan and elaunin fibers belong to the same “class” as elastic fibers.
How do they differ? Where are they found? They are formed of microfibrils with little or no amorphous material embedding them. As a result they are less elastic. They are commonly found in the dermis, tooth socket and suspensory ligaments of the lens (eye).
What is the main molecular component of the ground substance? Proteoglycans – glycoprotein cores with extensive side chains of glycosaminoglycans (GACs).
For what does ground substance have an affinity? Water.
What happens when it absorbs this substance? It changes from a gel state into a sol (watery) state.
What is the function(s) of ground substance? Hydrate cells and promote a diffusion medium for oxygen/nutrient transport to and from blood vessels.
Which three major components comprise the extracellular matrix (ECM)? Fibronectin, laminin and chondroitin sulfate.
What are the predominant proteoglycans? glycoproteins? Fibronectin and laminin are glycoproteins; chondroitin sulfate and hyaluronic acid are proteoglycans.
Which cells secrete, maintain and turn over ECM? Fibroblasts.
Which cells are common in loose CT? Fibroblasts, macrophages, mast cells, lymphocytes, plasma cells.
Where is loose CT found? Within the mesentery of the small intestine as well as in the lamina propria of the tubular gastrointestinal and respiratory systems.
What can be said about its cell:fiber ratio? High cellularity:low fiber ratio.
How does dense CT differ from loose CT? More fibers in dense CT, fewer cells and cell types.
How does dense regular CT differ from dense irregular CT? reg CT- many collagen fibers arranged in regular bundles,squeezing majority of other cell types out, basically avascular irreg CT- collagen fiber bundles are thinner and more irregularly arranged – with a higher cellularity – and variable vascularity.
What is the most predominate cell in dense CT? Fibrocytes.
What is the foremost fiber type in dense CT? Collagen(ic).
How are these fibers arranged in dense irregular? vs. dense regular? Dense regular CT has large numbers of collagen fibers arranged in a parallel fashion in thick bundles; in dense irregular CT the collagen fiber bundles are thinner and more irregularly arranged (more woven-like).
Which other fiber type may be found in smaller amounts in dense CT? Elastic fibers.
Which form of dense CT composes ligaments and tendons? Dense regular CT.
How are the collagen fibers arranged within this structure? In thick parallel bundles
Describe the morphology and arrangement of the most common cell type in this structure. The fibrocyte. Flattened, spindle-shaped and with a drak, inactive nucleus.
What are the four basic characteristics of inflammation? Caolr, dolor, robo, tumor - or heat, pain, redness and swelling.
During the onset of infection by bacteria, which cell type in connective tissue releases cytokines and chemokines? Macrophages
What accounts for tissue swelling during inflammation? Increased vascular permeability and leakage of fluid from blood vessels into surrounding tissue.
What causes pain during inflammation? Release of inflammatory mediators from neutrophils and lymphocytes.
As well as adipocytes, what other cell types are found in white adipose tissue? Preadipocytes, undifferentiated mesenchymal cells, macrophages and capillary endothelial cells.
Which cell type(s) secrete adipokines? Adipocytes, preadipocytes and macrophages.
Name and describe the function of two adipokines. Leptin decreases food tntake, increases energy expenditure, influences puberty, immune responses and insulin sensitivity. Adiponectin increases insulin sensitivity, inhibits atherosclerosis and suppresses inflammation.
What are two definitions of obesity? 1. Body fat greater than 25% of total body mass; 2. BMI greater than 30 kg/m2.
In obesity, which adipose tissue cell type exhibits hypertrophy? The adipocyte.
In severe obesity, which cell types found in adipose tissue are present in higher numbers. Adipocytes and macrophages.
Name four illnesses that are associated with obesity. Diabetes, cardiovascular disease, osteoarthritis and cancer.
Created by: wiechartm
 

 



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