Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington

Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington Friday, November 6, 2009 Proof: Paige Whitt Dr. Cotlin Connective Tissue Page 1 of 8 Connective Tissue [S1]: I. Functions of Connective Tissue [S2] a. What is the function? Provides structure and maintains shape of the body. b. Basically, connective tissue in one form or another can be thought of as providing a continuum between every other cell types. c. The other cell types are muscle, nerves, and epithelium that are pretty distinct and everything else is connective tissue. II. General Features [S3] a. All of mesodermal origin b. It is very vascular, containing lots of blood vessels c. There are a few exceptions: cartilage is avascular d. Involved defense and protection, we see lots of immune cells roaming around connective tissue e. Storage of fate f. Mediates tissue repair, so if tissue is damaged it’s the cells in the connective tissue that activate and run to that site and start repairing the tissue III.Classification of Connective Tissue [S4] a. In embryonic connective tissue it can be classified as mesenchymal or mucal in origin b. In humans, tissue can be classified as connective tissue proper or specialized connective tissue. c. Connective tissue proper can either be categorized as loose or dense. i. Loose is a loose assortment of proteins and cells ii. Dense is going to be a denser composition of fibers and not cells d. All connective tissue is basically cells and extracellular matrix e. Connective tissue is basically an assortment of cells and matrix, whatever the matrix might be f. Specialized connective tissues are: i. Cartilage: all cartilage is connective tissue including hyaline cartilage and elastic cartilage ii. Bone: is connective tissue, you have cells that lay out a matrix, osteocytes lay out bone tissue or osteoblasts iii. Blood: is a connective tissue, you have cells and the matrix in which they live is the plasma iv. Adipose cells: usually adipose cells or adipocytes are in connective tissue proper or in other large regions in the body they are so concentrated it is like its own tissue g. We will focus on cartilage, bone, and blood later IV. Connective Tissue Proper [S5] a. Loose connective tissue is just a few cells and a loose network of matrix b. Reticular is going to be specialized usually in our immune organs such as our lymph nodes and the spleen that contains a particular type of collagen called reticular fibers and it creates a network for tissue that is highly cellular—the spleen has lots of immune cells roaming around and so does the lymph node c. Adipose is a fat storing cell, insulator, shock absorber, we need healthy supplies of fat in the body d. Dense irregular and dense regular refers to the collagen bundles. So, dense irregular is going to have a dense concentration of collagen but just irregularly arranged versus a dense concentration of collagen that is very structured and organized that is dense regular V. Composition of Connective Tissue [S6] a. Like I said all connective tissue, regardless if it is bone, blood, loose connective or dense connective is composed of your cells and your matrix b. Cells we can have an assortment of cells, the primary cell that lays out your collagen are fibroblasts c. You can also see other cells such as fat cells, mast cells, macrophages, etc. and we will talk about these cells d. Endothelial cells of our blood vessels are also seen VI. Loose Connective Tissue [S7] Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington Friday, November 6, 2009 Proof: Paige Whitt Dr. Cotlin Connective Tissue Page 2 of 8 a. This is a picture of loose connective tissue. b. The thick, orange-brown diagonal line is a blood vessel c. All of these orangish-pinkish cells are collagen bundles d. There are an assortment of cells, the black fibers would be elastic fibers e. Reticular fibers are pretty much going to be found in your immune organs f. Collagen in general and just elastic fibers are found in a lot of loose connective tissue g. Sometime we will see large concentrations of elastic fibers in our large arteries or in cartilage, but in this case usually in connective tissue underlying our skin and supporting our skin is going to be loose connective tissue h. Collagen is a structural component and elastic giving that movement and elasticity to tissues VII. Cells of Connective Tissue [S8] a. We see an assortment of cells, most of those are going to be fibroblasts but also find what we call resident cells and those are the ones that are always present and stay in that tissue. b. In the case of a cell lying down reticular fibers, specifically are called reticulocytes but I just use fibroblasts c. Adipocytes are your fat storing cells d. Pericytes are in connection with blood vessels e. Mast cells and tissue macrophages are immune cells f. Then transient cells are all of your other white blood cells. All of your white blood cells in your vascularture at some point move out and low-level roam the body. We find immune cells, lymphocytes, macrophages lining the epithelium of our oral cavity, lining our digestive tract. Any places that are exposed to the outside world, you are going to have immune cells roaming. You will always see these odd cells, but if you know there is an infection such as in the lung we see an upregulation of white blood cells. You know if there are a lot of white blood cells in an area, they have been called to fight an infection. We say these are transient, they kind of come and go. VIII. Fibroblasts [S9] a. So the fibroblasts are the major produces or the extracellular matrix—collagen, elastic fibers, and reticular fibers IX. Fibroblasts/fibrocytes [S10] a. Terminology, you will see the term fibrocytes as well and the term “blast” usually means a maturing very active cell where a “cyte” is a mature, steady state resting b. So in bone, newly made bone comes from an osteoblasts and when its mature and kind of fully formed is an osteocyte c. Same thing as a chondroblast and a chondrocytes d. In this case, fibroblast and fibrocyte, most books will just call them fibroblasts because they are always turning over this matrix e. “blast”=active vs. “cyte”=resting f. In this picture, upper right, you can see this loose connective tissue and here is a fibroblast that is spindly shaped. g. The bottom picture is of dense connective tissue and they are so flattened and bound by all of the collagen you just see little sliver of a cell. X. Quiescent Fibroblasts or Fibrocytes [S11] a. Same picture from previous slide on bottom. b. These are just resting fibroblasts or fibrocytes. XI. Adipocytes [S12] a. Here is our adipocytes that can found individually, in clusters or in very large clusters as you can expect. b. Usually, they store lipids. Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington Friday, November 6, 2009 Proof: Paige Whitt Dr. Cotlin Connective Tissue Page 3 of 8 c. They have a very characteristic appearance that they are just full of lipid droplets and since their cytoplasm is predominantly taken over by lipid their nuclei is pushed all the way to the side. d. They are very easy to pick out, usually once you start seeing them you can pick them out anywhere XII. Adipocytes [S13] a. So, just a little bit about adipocytes, they are thought to just be fat cells which is true but there is an important role to them. b. The important role of adipocytes is energy storage, they are our back up storage. We get a lot more ATP from the break down of fats than we do sugars. c. Adipocytes also serve as a site of insulation and protection and cushioning. We need a healthy supply of adipocytes just to kind of insulate and buffer our organs. d. They can be categorized as white or brown, which are unilocular or multilocular cells. e. Lipid mass is usually not membrane bound, they just take up so much its just kind of in their cytosol so you don’t have specific secretory packets or membrane bound organelles f. More and more adipocytes are getting recognized and studied for their role as endrocrine cells and some people now call them an endocrine cell because they do secrete hormones. g. For short-term, ghrelin kind of helps stimulate the appetite and tells the body we need to eat, we need food where as the peptide YY is secreted and gives us our sense of feeling full. So, they say its better to eat slower because it takes a while because this hasn’t kicked in. h. Long-term, insulin is not secreted by adipocytes but leptin is and is thought to help reduce appetite in the long-term i. They just found obese people actually have increased levels of leptin and its thought that they have become resistant so their bodies keep trying to produce leptin but their bodies are resistant to it and feel like they need to have it suppressed. XIII. Fat Absorption and Release [S14] a. Adipocytes take up free fatty acids and package it in triglycerides and then once they are stimulated, they break it back down to mobilize energy b. Fight or flight, so lets say they get a signal saying that they need energy, lets mobilize some of our fat and will break it back down and secrete it and then it will be carried in the bloodstream. XIV. White Adipose Tissue [S15] a. This is just a picture of fat and you can see little capillaries as well. b. There is a lot of vasculature around fat because it is exchanging and taking up fat directly from the blood stream. XV. Mast Cells [S16] a. Mast cells are developed in the bone marrow and resident cells of the connective tissue. b. These are immune modulators and these are going to be involved in our immediate hypersensitivity allergic reactions. c. We all know haparin and histamine, so antihistamine blocks it. If you take an antihistamine you block this histamine which starts a cascade of inflammation and recruitment of secondary immune system. We have an allergen, lets secrete all these factors to increase blood flow and increase inflammation and start saying lets call in some of our white blood cells – neutrophils, eosinophils, basophils and other backup cells. d. These are the first line of defense saying there is something irritating us, secrete this and secondary mediators are some of these growth factors that recruit help to the area XVI. Mast Cells [S17] a. Mast cells are very easy to pick out, especially with their staining. b. They have all of these preformed vesicles with these mediators and are just waiting. c. Their stimulation is by their receptors for IgE, and IgE is their trigger for release. XVII. Mast Cell Degranulation [S18] Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington Friday, November 6, 2009 Proof: Paige Whitt Dr. Cotlin Connective Tissue Page 4 of 8 a. Basically what you are seeing is crosslinking of IgE receptors and antigen will bind, trigger a reaction through adenylate cyclase, cAMP, increase in calcium b. Do you remember where our calcium is high? Outside the cell and in the lumen of the ER. The ER has high calcium concentrations and the outside of the cell has high concentrations. c. Influx of calcium inside the cell from these triggers causes exocytosis and this is usually the case. When you learn nerve terminals and secretion of neurotransmitters, it’s an action potential causing calcium to rush in and cause exocytosis. So calcium is a huge mediator in exocytosis. d. It is triggered by antigen-IgE complex, a chain reaction and you have secretion of mast cells that are sitting there waiting for that signal. XVIII. Pericytes [S19] a. These are found surrounding blood vessels or capillaries I should say. b. Most blood vessels should all be lined by, the lumen of the blood vessel is lined by what? Endothelium. c. Arteries and veins will have smooth muscle around them and connective tissue, some of your large arteries have lots of elastic tissue around them. d. Once you get down to a capillaries bed, they loose all of the muscle tissue around them because if you think about at the capillary is where you see gas exchange and you don’ t want muscle getting in the way of moving that oxygen. e. So your small blood vessels are really just going to be a little vessel surrounded by endothelium and a basement membrane and then you’ll have these cells called pericytes. f. Pericytes are really just capillary supporting cells that put out processes that hug and support. g. Arteries have multiple layers of smooth muscle and once you get to capillaries you loose that and once you get to the veinous system you gain that structure. So at the capillary level the only supporting structure really are these pericytes. h. Pericytes can be induced to help fix capillary damage by kicking in to differentiate into endothelium cells and smooth muscle cells and connective tissue around and are really critical cells in the maintenance of a capillary bed. XIX. Macrophages [S20] a. Macrophages are phagocytic cells specialized to take up large molecules and not just small proteins but bacteria and even red blood cells or cell debris. b. These roam our body and derive from monocytes in the blood, monocytes leave the vascular compartment and go out into the body c. You want them roaming around, under your epithelium you have macrophages roaming around. d. First, they are going to clean up even if you have necrotic or cells that have undergone programmed cell death, macrophages clean up this debris. e. There are places in connective tissue, just in loose connective tissue or dense irregular tissue a macrophage is just a macrophage, but in other areas of the body they need a specialized macrophage that is committed to doing one job and these have different names. i. A kupfer cell is a macrophage in the liver and is specialized to live in sinusoids and help take up some of that material coming from the GI tract. ii. Dust cells or alveolar cells are resident macrophages in the lung, as you imagine depending on where you live such as pollution, you cannot cough it all back up but macrophages help get rid of all the things we take in iii. Langerhans cells in our epidermis that are basically our first line of defense that can capture bacteria before it gets into our active tissue below. iv. Osteoclast is a macrophage in the bone and it resorbs bone v. Microglia are found in the CNS, so they are the resident macrophages of the central nervous system. XX. Macrophages [S21] Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington Friday, November 6, 2009 Proof: Paige Whitt Dr. Cotlin Connective Tissue Page 5 of 8 a. This is what they look like, usually you can tell they are usually odd shaped cells and processes called filopodia that are waiting to engulf stuff. b. The spleen is one of the places that red blood cells go to die and macrophages in there engulf the cells in there. c. These are large, spindly shaped cells XXI. Langerhans Cells [S22] a. These are Langerhans cells of the skin and you can see they put out these long processes. b. Would you say this was keratinized or non-keratinized stratified squamous? Kertanized, the keratin layer is on the top and here are all your stratified squamous cells and these are your Langerhans (red arrows). c. They put out these processes to fill, modulate, and look for invaders. XXII. Kupfer Cells [S23] a. Kupfer cells in the liver, I know this doesn’t look like much to you all but these are hepatocytes, large cells that hang out in sinusoids XXIII. Plasma Cells- Specialized for Antibody Secretion [S24] a. Lastly, are plasma cells and are lymphocytes specialized for secretion of one type of antibody. b. They roam around and are found underlying epithelium and are specialized to secrete antibodies. c. A lot of times once they’ve seen something before, they are right there hanging out so as soon as they seen another thing they can secrete antibody to combat infections. d. They have a very distinct, clock face appearance and all the nucleus of all of these cells usually has a central nucleolus and this very organized heterochromatin pattern called a clock face pattern. XXIV. Extracellular Matrix [S25] a. Lets talk a few minutes about the matrix, matrix is basically our fibers and ground substance XXV. Ground Substance [S26] a. Connective tissue has a supporting role, but also a buffering and lots of fluid and there are places where we want the connective tissue to be more spongy or less spongy. b. The ground substance is specialized to be like a gel that can become more or less hydrated. c. The main components are these glycosaminoglycans which are sugars and the proteoglycans which are proteins and basic glycoproteins. d. A glycoprotein is a protein with a carbohydrate modification as opposed to a proteoglycan which is a protein with all of these glycoaminoglycans modifications. XXVI. Ground Substance [S27] a. So the whole role of this as you can imagine is that it is highly acidic and can recruit the water and basically form a sponge and can arrange with all of these proteoglycan monomers and these aggregates has a very spongy appearance and can compress when needed. XXVII. Fibers [S28] a. Collagen b. Elastic c. Reticular XXVIII. Collagen [S29] a. We have many types of collagens b. The most that we find in regular connective tissue are I and III c. Usually, II is found in cartilage d. I is predominant in bone, but don’t worry about those so much. e. Some of them are more fibrillar meaning that they form long fibers f. Some of them are crosslinking, or anchoring fibrils and these are not involved in bundles. g. If you see collagen in a bundle it is one of these fibril collagens (I,II,III,V,XI) h. IV is specialized collagen found in the basement membrane Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington Friday, November 6, 2009 Proof: Paige Whitt Dr. Cotlin Connective Tissue Page 6 of 8 i. All of your fibroblasts will produce these, so a fibroblasts determines what type of collagen it secretes based on where it is located XXIX. Aggregate of Collagen Molecule [S30] a. I think you all went through this, processing of collagen so its kind of a specialized protein and one of these unique features is the hydroxylation of proline molecules. b. It is formed as a pro-collagen in this triple helix formation and its packaged in the RER and Golgi c. Secreted in pro-collagen form and extracellular, once it is secreted, we will see cleavage of the nonhelical ends and polymerization into what we know of as their collagen bundles. d. This is to remind you of constitutive vs. regulated secretion that mast cell that has all those granules secretes in a regulated fashion, it has those vesicles and waits to get the signal before secreting the granules and this is the same for neurotransmitters. Fibroblasts making collagen is constitutive secretion, as soon as they make the collagen it is secreted from the cell. So these are constitutively secreting collagen as a low level. e. The cleavage happens once its extracellular and then we get polymerization. XXX. Collagen [S31] a. This is a nice picture of this triple helix and here is a lateral view versus a cross-section view. b. You can this is a very regular structure. They may be arrayed in an irregular fashion, but the molecules themselves are pretty regular. XXXI. Collagen [S32] a. All of these fibers here, all of these bundles are just collagen bundles. b. Would you say this is dense regular or dense irregular connective tissue? Irregular because we see a lot of irregular tissue like all of them supporting tissue under our epidermis is dense irregular tissue, our mouth is dense irregular tissue. c. So these guys are just going to be fibroblasts lay (purple) and some small blood vessles, but other than that these are just fibroblasts laying down that material XXXII. Elastic Fibers [S33] a. Elastic fibers are a type of collagen synthesized from fibroblasts. b. It has an accessory molecule called fibrillin that gives it its elastic nature c. It is processed similarly to collagen d. The molecules are called elastin, but when they form these fibers they are called elastic fibers e. There are elastin molecules crosslinked by fibrillin and that keeps all of these molecules together and gives it its elastic properties f. The individual monomers have a little bit of elasticity, but it is the assortment or aggregation of the fibers as a whole. It is not like one elastin molecule is stretched that long, it’s the whole fiber. g. This stain makes them appear blackish, and is not just one molecule but it is really a collection of these that have this property of expansion collectively due to the fibrillin crosslinking. XXXIII. Elastin Fiber Image [S34] a. You have elastin molecules crosslinked by fibrillin which keeps all of these molecules together and that gives it its elastic properties XXXIV. Reticular Fibers – Collagen Type III [S35] a. Reticular fibers is a collagen type III and I will not say much more about that. b. This is what it looks like, all of these fibers—it stains specifically as well. c. Its found in a lot of our immune organs, particularly our spleen and lymph nodes. d. Fibroblast secretes the collagen and has nothing more to do with it in a sense and just secretes out there into the matrix and doesn’t hold on to it or anything, but reticular fibers are secreted by reticulocytes (are fibroblasts but are called reticulocytes) because they are a little more specialized. XXXV. Reticular Fibers [S36] Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington Friday, November 6, 2009 Proof: Paige Whitt Dr. Cotlin Connective Tissue Page 7 of 8 a. The fibers are extracellular, but what happens is the reticulocytes hold onto the fibers as they are secreting it so what happens is that it makes this network of all of these cells and fibers making a meshwork. b. The fibers are extracellular but stay in close contact with the cell, so all these cells and fibers form a continuum that provides scaffolding for cells in the lymph nodes and spleen. c. Reticular fibers are specialized for structural support and also bone marrow. XXXVI. Rat Mesentery/Polarized Image [S37] a. This is a polarized image here, here are our collagen bundles of various thickness. b. So you can see this would probably be a loose because there is a lot more loose space here c. The red is the collagen and the black is the elastic fibers XXXVII. Areolar (Loose) Connective Tissue [S38] a. Loose connective tissue, all of the space is sometimes called lamina propria but don’t worry about that right now. b. All of that space is filled with ground substance because all connective tissue is are cells and extracellular matrix, and in this case you have fibroblasts and loose assortment of cells and collagen bundles and ground substance XXXVIII. Loose Connective Tissue [S39] a. This is another picture showing elastic fibers XXXIX. Loose Connective Tissue [S40] a. Another picture showing elastic fibers XL. Dense Irregular CT – in the Dermis of the Skin [S41] a. Dense irregular tissue, so these would be of the epidermis b. There is a keratinized stratified squamous layer c. All of this below is the dermis and is packed with collagen XLI. Skin (Dense Irregular) [S42] a. Here it is as well, the stain shows collagen and elastic fibers XLII. Dense Irregular Connective Tissue [S43] a. Here is another one as well closer up b. The bundles are irregularly arranged and they are also very varied in their size, so not every bundle is going to be the same size c. The long, horizontal bundles are in longitudinal and the circular bundles are in cross-section XLIII. Collagen and Adipocytes [S44] a. Here is some denser irregular connective tissue with some adipocytes in there, so you can see the very distinguishable fat cells and always with a big blob with the nucleus on the periphery XLIV. Tendon (Dense Regular) [S45] a. Dense regular tissue is predominantly found in our tendons b. All of these are just bundles of collagen and a supply of fibroblasts XLV. Muscle-Tendon Junction [S46] a. Here is a nice picture at the muscle-tendon junction b. This is bundles of collagen and you can see very regularly arranged usually in this parallel array c. This is skeletal muscle over here with striations but you will learn that later XLVI. Elastic CT [47] a. Lastly, elastic tissue is going to be found in loose and dense irregular tissue underlying our skin giving it its property b. This s a slice of the aorta, our large arteries have a lot of elastic fibers in them as you would expect blood leaving the heart is under a lot of pressure and your large arteries are going to be surrounded by elastic fibers c. There are specialized areas where you will find elastic fibers in all of these bands d. Shown are endothelium, smooth muscle with concentrated elastic fibers interspersed Fundamentals I: 11:00-12:00 Scribe: Ashley Brewington Friday, November 6, 2009 Proof: Paige Whitt Dr. Cotlin Connective Tissue Page 8 of 8 XLVII. Reticular Connective Tissue [S48] a. This is just reticular fibers, so they have a more cellular composition than other connective tissue but these fibers that look like they are still associated with the reticulocytes XLVIII. Reticular Fibers in the Lymph Node [S49] a. This is a lymph node, all of these cells here and here are loose free roaming cells b. So now you can see how that cell and reticular fiber network provide a scaffolding for this loose assortment of cells because they need something to roam around on XLIX. Diseases Involving Connective Tissue [S50] a. There are lots of diseases b. Artherosclerosis is a thickening of connective tissue c. Diabetes can develop and compromise basement membranes and alteration of transport of sugars d. Connective tissue is critical for cancer and metastasis. What is metastasis? When cancer moves around. So if you have a squamous carcinoma, cancer of skin cells as long as that cancer is contained until it gets across the basement membrane. Once it gets across the basement membrane it can free flow and move. So metastasis is a case where those cells are free flowing through connective tissues and move around. e. Fibrosis is usually when you have a thickening or enrichment of connective tissue meaning there are too many fibers there. There are dental diseases involved. f. Emphysema, you have some elastic fibers in the respiratory tract so when we breathe our alveoli can expand and elastin is damaged by smoking, you loose elasticity and you compromise your breathing.