Are fasciae innervated by nerves
Fascia and connective tissue
The value and importance of connective tissue used to be held very high. Then it has been more forgotten in recent years to celebrate a renaissance now. In this article, the tissues that make up our body should be briefly explained, then specifically the connective tissue and the fasciae, whereby the first question arises, what a fascia is. Actually, this is not entirely clear, and so I would like to leave the definition of a fascia to macroscopy. In my examinations, I will process and interpret the fascia samples defined by the macroscopist.
The tissues of the body
Our body is made up of 4 basic tissues. A tissue is an association of similarly differentiated cells that are connected to one another by cell contacts. These 4 tissues are firstly the epithelial tissue, secondly the muscle tissue, thirdly the nerve tissue and a tissue that connects them all, the connective and supporting tissue.
1. Epithelial tissue
Definition of epithelial tissue: cell to cell without essential intercellular substance, the cells are polar differentiated. Where does epithelial tissue occur? Epithelial tissue lines external and internal surfaces and is found in the organs of secretion. I would like to say right away that in most books the epithelial tissue is defined as a tissue that lines inner and outer surfaces. However, this is the occurrence, not the definition. Epithelial tissue is of various origins in our body and can arise from all three cotyledons. The epithelium usually sits on a basement membrane and has no blood vessels, but it does have nerves and lymph vessels. The epithelial tissue has to perform many functions. Only a few are mentioned here. First of all, protection against mechanical loads; we only think of our cornified, multilayered squamous epithelium of the skin. The epithelium must also protect against osmotic damage, if we only think of the lining of the urinary bladder. Third, protection from ultraviolet radiation. Fourth, an absorption function, e.g. in our intestines. Fifth: transport function, so the surface movement in our airways. However, the epithelium can also perform contractile functions, if we only think of the “pouring in of the milk” during the breastfeeding period, where so-called myoepithelial cells around the tubules in the mammary gland transport the milk onwards. The epithelial tissue can also absorb stimuli (sensory epithelium). Eighth, the epithelial tissue also has to line internal surfaces, if we only think of our body cavities. The ninth function is the secretory function up to and including the structure of the glands. Here are just a few examples, whereby our squamous epithelium accomplishes several of these functions as one possibility. The squamous epithelium of our skin has to protect against mechanical influences, against osmotic damage and against ultraviolet radiation; it can also perform an absorption function - so you can see that a tissue can also perform several functions.
2. muscle tissue
In the case of muscle tissue, we distinguish between 3 types:
- The intestinal muscles or smooth muscles, a non-fatiguing musculature that is innervated by the autonomic nervous system and is essential for our vital functions.
- The skeletal muscles, a highly specialized tissue that, with few exceptions, is subject to our will.
- The heart muscles. Here the term striated muscles should be avoided as far as possible, because skeletal muscles and heart muscles differ significantly in their submicroscopic structure, i.e. in the area of calcium ion storage, in the area of innervation and cellular structure; the only thing these two tissues have in common is the horizontal stripes, but everything else is different. It is essential that the excitation system of our heart is not a nerve tissue.
A look at the embryology shows that when the first functioning heart muscle tissue appears at the end of the 3rd embryonic week, nothing functional is yet available from the nervous system. Therefore, the heart muscles are stimulated by specialized excitation muscles.
3. Nerve tissue
This tissue, in turn, has a special position and is actually made up of two components that are directly linked to one another and one component is not viable without the other. These components are on the one hand the neuron and on the other hand the glia. The glia could be described as a separate connective tissue of the nerve tissue under quotation marks. This nerve tissue is different from the rest of the tissue in many areas. So in nutrition, but also in your immune system and also due to the lack of lymph vessels in our central nervous system. Without the glia, the nervous system would not function, as there is no insulation, but nutrition and defense would also not be possible.
4. Connective and supporting tissue
This tissue is defined as being made up of cells and intercellular matter. In the case of cells, a distinction is made between the so-called fixed cells, i.e. the cells that build up the tissue (e.g. fibroblasts, fibrocytes, chondroblasts, chondrocytes, osteoblasts, osteocytes) and the free connective tissue cells, which are the cells of the defense, which on the one hand in the connective tissue and, secondly, as cells that are delivered via our transport system, the blood, migrate out of the blood and then carry out their function in the connective tissue.
To the intercellular substance
This amorphous intercellular substance, also known as the extracellular matrix, consists mainly of proteoglycans, a substance that is responsible for the ability to bind water and which decreases with age. This extracellular matrix also contains the interstitial fluid, which contains electrolytes, hormones, plasma proteins, but also nutrients and waste products. In addition, there is another component, the glycoproteins, in the basic substance. We find a specialization of this basic substance in the basement membranes. We find these basement membranes as a base in epithelial tissues, but also in many other tissues such as muscles and nerve tissue.
The formed, intercellular substance is the fibers. We distinguish between 3 groups:
1. The collagen fiber
When we talk about collagen fibers, we always mean immunological type I. This fiber is found in skin, tendons, organ capsules and bones. Collagen is derived from Kolla, glue, so it is a glue-forming fiber, i.e. it is converted into glue by hot water. This type I fiber is strongly anisotropic, which speaks for a parallel arrangement of submicroscopic structures. In terms of its behavior, it dissolves in dilute acids, it is not branched and it is extremely strong. A load of 6 kg per square mm² corresponds to the norm. If we imagine an Achilles tendon, the load capacity corresponds to 500 kg. This collagen fiber is formed from amino acids in the fibroblasts and excreted by the cells as procollagen molecules. This procollagen molecule has a non-helical arrangement, which means that fibril formation is not yet possible. These procollagen molecules change in the extracellular space and become tropocollagen, a 280 nanometer long building block. These tropocollagen molecules then combine in register form end to end and side to side, their length being shifted by 25% in each case, to form the so-called procollagen filaments. A combination of procollagen filaments forms a protofibril, another combination of many protofibrils makes a microfibril, many microfibrils make a fibril, and many fibrils make a fiber. As I said, this fiber is unbranched. When several fibers unite, a fiber bundle is created, this fiber bundle now shows the possibility of branching. There are then other types of collagen, e.g. type II collagen, which we find in the cartilage tissue and in the vitreous humor of our eyes. In the case of collagen fiber type III, the better name is reticulin fiber, lattice fiber or mesh fiber. We find this flexurally elastic fiber as the most important fiber in the so-called reticular connective tissue of our defense organs, but we also find it as sheaths around cells, for example in smooth muscles, where every smooth muscle cell has a stocking made of reticulin fibers around it, and there this fiber is branched, can be sheared from a stocking into the stocking of the neighboring cell, which is what makes the formation of tunicae, i.e. muscle skins, possible in the first place. We also find this fiber as a network around fat cells, e.g. so that these cells do not burst when exposed to pressure as a pressure cushion. This reticulin fiber is formed by the fibroblasts and in our immune tissue by the fibroblastic reticulum cell. Collagen of the immunological type above 3 have no fibrillar or fiber structure and are therefore popular in the cosmetic industry to be introduced between the individual cells and there to attract water and thereby tighten the tissue. The elastic fiberIt occurs mainly in the form of a network or in membranes; we find them in our ligamentum nuchae, in the ligamenta flava, in organ capsules, in the lungs, in vessels. It is 100 - 150% stretchable and can withstand a tensile load of 20 kg per cm². When stretched, it will increasingly show the phenomenon of anistotropy. It is also produced by the fibroblasts.
The connective tissue
After we have got to know the building blocks of connective tissue, we now have to ask the question about the tasks of connective tissue.
The connective tissue in the stroma of the organs has an important function to structure the parenchyma. Another task is of course the formation of the organ capsules and a protective function around vessels and organs. The transfer of force must also be mentioned as a function when the force is transferred from a muscle to a bone. Furthermore, the metabolic function, water balance and the defense. In general, it must be said that the connective tissue is a connecting tissue, epithelial tissue can never sit directly on a muscle, so there must be a connecting tissue in between, i.e. the connective tissue, which is absolutely necessary for nutrition.
Where does the connective tissue come from?
The first connective tissue, the so-called embryonic connective tissue or mesenchyme, arises in our development in the 3rd week. Cells migrate from the primitive stripe into the depths and push themselves between hypoblasts and epiblasts. This development only relates to the so-called intraembryonic mesoderm. This mesenchyme is characterized by the fact that there are wide intercellular spaces and the cells form a spatial network with one another via intercellular connections. These mesenchymal cells are not yet capable of fiber formation, but they show a lively mitotic activity and good amoeboid mobility in order to form blastema in the embryonic body, i.e. the basis for the development of organs. The embryonic connective tissue cell is extremely variable and they differentiate into osteoblasts, chondroblasts, but also blood cells, hemocytoblasts. The muscles also develop from them. During our development we then find another tissue that is made up of mesenchymal-like cells like the fetal connective tissue, as we find it classically in an umbilical cord. Umbilical cord has a more gelatinous texture, which is why this fetal connective tissue is also known as gelatinous tissue. They are wide intercellular spaces with a lot of intercellular substance, which, however, also contain collagen fibers.
Let us now consider the connective tissue of an adult: We distinguish between loose collagenous connective tissue. We find it as a protective device, built like cotton wool, around nerves and blood vessels. It is characterized by a high proportion of basic substance - few cells and few fibers. In contrast to this, the tight collagenous connective tissue is, in extreme cases, a tendon or fascia. Above all, there are collagen fibers arranged in parallel with little amorphous basic substance. The cells have little space between the individual fibers - an essential tissue for power transmission.
An important tissue is the reticular connective tissue, as we find it in our defense organs and in the bone marrow. It is a wide mesh of reticulum cells and the reticulin fibers. The cells of the defense can ideally move in these meshes. We distinguish several types of cells that make up the reticular connective tissue.
1. The fribroblastic reticular cell, a cell that is capable of fiber formation (reticulin fiber).
The second cell type is the histiocytic reticulum cell, a cell type capable of phagocytosis. This cell can pull in its extensions in the tissue, ball itself off and then appear as a monocyte, a transport form of a macrophage in our blood. We can now imagine very well in a lymph node how the lymph seeps through these meshes between the cells and the cells can control the lymph and remove substances through the phagocytosed reticular cells.
Another important cell type is the interdigitating and the dendritic reticular cell. They are signpost cells, i.e. antigen-presenting cells, which are of the greatest importance in the context of our specific defense. What can this reticular connective tissue do?
1. Phagocytosis, ie eating behavior, 2. the formation of fibers, reticulin fibers, 3. the signpost function within the framework of our defense, 4. the formation of blood and tissue macrophages, it can also form the so-called hemocytoblasts in the bone marrow, i.e. a preliminary stage for our blood, and also the formation of fat cells is possible in the reticular connective tissue. There is another important connective tissue in women, it is the spinocellular connective tissue in the ovary. This is almost entirely made up of cells to protect the sensitive egg cells in their waiting position.
The next form of connective tissue is adipose tissue. In the case of adipose tissue, we have to differentiate between brown and yellow or white adipose tissue. We find the brown adipose tissue in newborns, small remnants can be found in the neck region in adults.
This brown fat tissue is a so-called plurivacuolar tissue, i.e. there are lots of small fat droplets in a fat cell. This brown adipose tissue has the ability to produce heat directly, and in the cold it does not have to take the detour via muscle tremors. We also find brown adipose tissue in animals that go into hibernation, just think of the well-known marmot fat. This marmot fat is also used therapeutically in laypersons, as it contains a high proportion of the body's own cortisol. However, the concentration of it is not known, which can lead to dangerous uses.
In the case of white or yellow adipose tissue, we differentiate between building fat and storage fat.
1. The building fat: We find it retrobulbar in the area of the head, i.e. behind the eyeball, further in the area of the cheek fat plug. The building fat around organs is also important, especially the kidney fatty tissue, where it serves to protect the organ. We also have this construction fat on the palm and soles of the feet to cushion them.
2. The storage adipose tissue is gender-specific. In women we find it mainly in the lower half of the body and subcutaneously. In men, on the other hand, it is found in the upper half of the body (bull neck) and in the inner area of the body around organs. The subcutaneous fat tissue is less developed. The man can therefore develop a stronger muscle relief. This storage fat tissue is genetically determined in the number of cells and 2. if there is enough food available, new fat tissue can be generated from fibroblasts, which are converted into lipoblasts. The fat stored in these cells is exchanged for new fat approximately every 35 days.
The next connective tissue that we have is a special form; it is the only liquid tissue in us, i.e. the blood. Why is blood a connective tissue? The blood is made up of free and fixed cells. On the one hand from fixed cells, the erythrocytes, which do not leave the vascular system, and the free cells, which are transported in the blood and then perform their function in the connective tissue, the leukocytes. The intercellular substance, the blood plasma, is made up of the serum, i.e. the amorphous intercellular substance and the fibrinogen, a fibrous component. The erythrocytes are actually no longer real cells because they have no metabolism, they have neither a nucleus nor mitochondria. In the case of white blood cells, we differentiate between neutrophils, segmented granulocytes. The cells known as microphages are capable of phagocytosis and represent the most important cell of the unspecific defense. These cells are also known as pus formers. Their non-stainable granules located in the cells are lysosomes in order to digest the phagocitated material. The eosinophilic segmented granulocytes have the function of breaking down antigen-antibody complexes after an antigen-antibody reaction.These red granules in the cells are also lysosomes with degrading enzymes.
The third cell type, the basophilic granulocytes, do not contain lysosomes in their granules, but heparin and histamine - substances that we need in inflammation. So there are mediator cells in inflammation. The juvenile forms of these 3 are the so-called rod-like granulocytes.
The next type of cell is the monocyte. The monocyte actually represents a form of transport of a macrophage. The macrophage is thus transported in the blood as a monocyte. It emigrates and can then fulfill its function in the tissue. The most important way for the disposal of the macrophages is via the alveolar macrophages in the lungs, as there is an ideally small connection between the blood and the outside world. The lymphocytes, where we differentiate between large and small, B cells, T cells, helpers, suppressors and many more, are important cells in our specific defense system.
The supporting fabric
Cartilage and bone tissue
1. The cartilage tissue
We differentiate between 3 types, hyaline cartilage, elastic cartilage and fiber cartilage. The cartilage tissue is characterized by the fact that it is free of vessels, so it is a so-called bradytrophic tissue, has no lymphatic vessels and must therefore be nourished from the environment. Like all connective tissue, it naturally also consists of cells and intercellular substance. The cells, the chondroblasts, chondrocytes, are grouped together in small groups called chondrons. A chondron is formed by a cell through division. We also call these cells of a chondron isogenic cells. Between the chondrons there is the interterritorial substance, which consists of the basic substance, the chondromucoid, with a high proportion of proteoglycans and a fiber proportion of mainly type II collagen fibers. The hyaline cartilage is found in the area of our rib cartilage as nasal cartilage (with a special feature, it cannot calcify), but also in the bronchi. Articular cartilage is a special form of hyaline cartilage. This is characterized by the lack of a perichondrium. This perichondrium, which e.g. possesses the costal cartilage, consists of 2 parts - a cellular and a fibrous layer. This cellular layer has precursors of cartilage cells and can therefore carry out regeneration. This layer is missing in the articular cartilage. Therefore the articular cartilage is incapable of regeneration. This perichondrium for nutritional processes is also missing. The articular cartilage has to be nourished by the synovia on the one hand and by the bone on the other. Intermittent pressure loads are very important in order to pump the tissue fluid through the cartilage. The collagen fibers of the articular cartilage also have special features in their course in order to counteract the strong shear forces during the movement of the ball and socket.
The next cartilage is the elastic cartilage. We find it in the area of the auricle, the external auditory canal and parts of the larynx. It is characterized by an additional component, the elastic fibers. If the mechanical stress is too great, this cartilage can tend to form scars.
The third type of cartilage is fiber cartilage. We find it in the symphysis, in the area of the intervertebral disc, in the disci and menisci but also as articular cartilage in the temporomandibular joint.
This cartilage is characterized by the additional content of type I collagen fibers in addition to the naturally occurring type II fibers. Unfortunately, the resilience of this fiber cartilage is not as high as we would like it to be. The reduced resilience is explained by the individual movement sequences, since in this case not all collagen fibers are taut and can thus absorb these pressure forces.
The next supporting tissue is the bone tissue. Since it is also a connective tissue, it in turn has cells and intercellular substance. In the case of the intercellular substance, there is also an inorganic component in addition to an organic component. This inorganic component, the hydroxyapatite, which consists mainly of calcium phosphate. In the organic part we find collagen fibers and the osteoid, the amorphous basic substance. When it comes to bones, we distinguish between two types, the so-called braided bone and the lamellar bone. We find the braided bone in development, but also in the context of healing processes after bone fractures. The lamellar bone is characterized by its minimum / maximum principle, i.e. a minimum amount of building material means maximum load-bearing capacity. However, this presupposes that bones, i.e. supporting pillars, arise in us wherever there is a high load.
These supporting pillars are the lamellar system or Haversian system. They have a Haversian canal in the middle, in which arteries, veins, blood vessels, lymph vessels and nerves are located. These are surrounded by osteocytes, and in between there are collagen fibers in steep spirals, which no longer have any elasticity; so they are biased. This principle allows compressive and tensile forces to be optimally distributed in the bone. We also have to keep in mind that our bones are extremely living tissue and are in constant transformation.
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