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UKCD Histo Lec 3
learning objectives from histo for connective tissue
| Question | Answer |
|---|---|
| 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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