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ORGAN: Human oesophagus (human, child). STAIN: Hematoxylin-Eosin (H/E).
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Oesophagus child (H/E) (2x). One of the layers that make up the esophageal wall is the so-called “submucosa” (Sm), which serves as an example for studying loose connective tissue. The surface of the esophagus that borders the lumen of the organ is lined by a malpigian epithelium (E). Outside the submucosa, the muscular layer (M) can be identified.
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Oesophagus child (H/E) (4x). Loose connective tissue contains a balanced proportion of cells, connective tissue fibres and ground substance, although this type of tissue varies widely in terms of the amount of collagen fibres, depending on the organ in question. In this sample, the submucosa (Sm) is made up of very loose connective tissue, as it corresponds to the oesophagus of a young child. At this magnification, the cell nuclei (arrowhead) dispersed throughout the tissue can be seen, as well as small blood vessels (V). (Lining epithelium: E. Muscular layer: M).
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Oesophagus child (H/E) (10x). In the submucosa, as a loose connective tissue, the cells are separated from each other by wide spaces occupied by intercellular substance, composed of connective tissue fibers (arrowhead) that can be identified at these magnifications, and ground substance. The presence of blood vessels (V) and lymphatic vessels (difficult to distinguish) is a constant in loose connective tissue. The thick eosinophilic zone located next to the submucosa and very close to the lining epithelium (E), corresponds to a layer made up of smooth muscle, the so-called “muscularis mucosae” (asterisk).
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Oesophagus child (H/E) (20x). Most of the nuclei found in the loose connective tissue are fibroblasts (arrow). In the spaces between the cells, elongated or punctate fibrillar structures can be observed, which correspond to collagen fibers (arrowhead) in different sections planes. The pale areas between the fibers are occupied by the grpund substance which, being highly hydrated, is extracted in the dehydration process that requires inclusion in paraffin to make the histological section. (Blood vessel: V).
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Oesophagus child (H/E) (100x). At high magnification, the small number of cell nuclei can be seen, which correspond to fibroblasts (F). Among them, there are many fibers, sectioned both longitudinally (blue arrowhead) and transversely (red arrowhead). The apparently empty spaces between these fibers are filled with amorphous substance, which is lost when it is extracted during the histological technique. It is common to find blood vessels (V) in loose connective tissue, since this is the usual place where these structures are located. They are easily identified thanks to the red blood cells (arrow) that they contain in their lumen.
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ORGAN: Oesophagus. STAIN: Hematoxylin-Eosin (H/E).
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Adult oesophagus (H/E) (2x). Loose connective tissue can present different appearances depending on the greater or lesser quantity of components of the intercellular substance (or extracellular matrix). Thus, in this esophagus of an adult human, the submucosal layer - which also forms the axis of the folds that make relief towards the lumen of the organ - is composed of loose connective tissue (Tc) which, unlike that shown in the previous slide ("Child's esophagus"), is richer in collagen fibers and therefore is more stained with eosinophilic staining appetite. (Lining epithelium: E. Muscular layer: M).
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Adult oesophagus (H/E) (4x). Both the so-called “lamina propria” (asterisk), which supports the lining epithelium (E) of the esophagus, and the submucosa (Sm), which forms the connective axis of the fold shown in the image, are composed of loose connective tissue. This type of tissue is characterized by the presence of blood vessels (arrowhead), of various sizes. Between the lamina propria and the submucosa, a slightly more heavily stained band can be seen, which corresponds to the muscularis mucosae, made up of smooth myocytes (Ml).
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Adult oesophagus (H/E) (4x). Both the so-called “lamina propria” (asterisk), which supports the lining epithelium (E) of the esophagus, and the submucosa (Sm), which forms the connective axis of the fold that appears in the image, are composed of loose connective tissue. The presence of blood vessels (V) of various sizes is characteristic of this type of tissue. Between the lamina propria and the submucosa, a slightly more heavily stained band can be seen, which corresponds to the muscularis mucosae, made up of smooth myocytes (Ml).
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Adult oesophagus (H/E) (20x). The loose connective tissue of the submucosa is the site of vessels of different types, both blood vessels (Vs) and lymphatic vessels (Vl). The cell nuclei observed, generally elongated and dark, correspond mostly to fibroblasts (arrowhead). In the intercellular substance (extracellular matrix) there are abundant connective tissue fibers with eosinophilic staining (arrow), with collagen fibers predominating.
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Adult oesophagus (H/E) (40x). Although the submucosa of the esophagus is rich in collagen fibers of the intercellular substance, which could cause confusion with other types of connective tissue (see the following preparations), the presence of an appreciable quantity of cells, mainly fibroblasts (arrow), arranged in no apparent order, indicates that it is a loose connective tissue. The larger lumens observed in the image are lymphatic vessels (Vl). Part of the wall of a collapsed blood vessel (Vs) can be seen on the top right..
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Adult oesophagus (H/E) (100x). At high magnification, the different cell populations that make up the loose connective tissue can be distinguished. The elongated nuclei with dark chromatin, which are more abundant, are fibroblasts (F). While some rounded nuclei could belong to a histiocyte (macrophage) (arrow), the few cells with granular cytoplasm are unmistakably mast cells (arrowhead). Between the cells there is a considerable quantity of connective fibres (asterisk) stained with eosin, sectioned in different planes, which correspond mainly to collagen fibres. (Blood capillary: C).
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ORGAN: Skin (thick) (human). STAIN: Hematoxylin-Eosin (H/E).
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Thick skin (H/E) (2x). Plexiform connective tissue, also called dense irregular connective tissue, is located in the deep dermis (Dp). Above it is the superficial dermis (Ds), formed by loose connective tissue, which supports the epidermis (E). Below the deep dermis, adipose tissue (A) can be seen, which belongs to the hypodermis (Hp). The secretory portions of the sweat glands (Gs) can also be seen.
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Thick skin (H/E) (4x). The border between the superficial dermis (Ds) and the deep dermis (Dp) is very diffuse, since both are eosinophilic and contain collagen fibers. However, a certain limit (arrow) can be established between the two, since the superficial dermis is more cellular, being a loose connective tissue. On the contrary, the deep dermis is made up of a plexiform connective tissue, formed by a plexus of thick, intersecting bundles of collagen fibers, with few cells and amorphous substance. (Epidermis: E).
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Thick skin (H/E) (10x). Plexiform connective tissue is predominantly stained with eosine due to the abundant collagen fibres that form a plexus of intertwined bundles, interspersed with a smaller but noticeable quantity of elastic fibres, which cannot be distinguished from collagen fibres with H/E as they are also eosinophilic. In the small spaces left by the fibre bundles, there are some cell nuclei (arrowhead), especially of fibroblasts. Plexiform connective tissue is traversed by both blood vessels (V) and sweat gland excretory ducts (C).
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Thick skin (H/E) (20x). Proof that collagen fiber bundles intersect to form a plexus in plexiform connective tissue is provided by the fact that bundles are sectioned longitudinally (L), transversely (T) and obliquely (O) in the histological section. The spaces between the fiber bundles are slightly dilated as a result of sample processing, and this is where the few fibroblasts, whose elongated and dark nuclei (arrowhead) are easily visible, and the ground substance are located.
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Thick skin (H/E) (40x). At high magnification, plexiform connective tissue has an irregular “puzzle” appearance, with thick collagen fiber bundles appearing as elongated eosinophilic bands when cut longitudinally (L) or as circles when sectioned transversely (T). Elastic fibers are also present, but are not visible when stained in the same way as collagen fibers. However, they are easily visible with the Gallego technique (see the following slide). Fibroblasts (arrow) with typical elongated, dark nuclei are located between the connective fibers.
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ORGAN: Skin (thick) (human). STAIN: Cajal-Gallego.
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Thick skin (Cajal-Gallego) (2x). Plexiform connective tissue (Pl), or irregular fibrous connective tissue, is part of the deep dermis that provides consistency to the skin (conveniently treated industrially, it is the “leather”). It has abundant fibers that form a complex interlaced plexus, where abundant bundles of collagen fibers are mixed, which with the Cajal-Gallego technique are stained greenish blue (turquoise blue), with a smaller amount of red elastic fibers. Both cells and amorphous substance are scarce, and are not demonstrated with this technique. (Epidermis: E. Hypodermis: Hp).
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Thick skin (Cajal-Gallego) (4x). Plexiform connective tissue (Pl) is located deep in the dermis, predominantly staining turquoise blue due to the abundance of collagen fibers, which are mixed with elastic fibers, which are stained red. At low magnification, such as the one in the image, the elastic fibers do not stand out, although they can be seen using the “Virtual microscope” option. Above the plexiform connective tissue is the superficial dermis, formed by loose connective tissue (asterisk). (Epidermis: E. Hypodermis: Hp).
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Thick skin (Cajal-Gallego) (10x). The epidermis (E) rests on the loose connective tissue (Cl) of the superficial dermis. The dermo-epidermal junction is irregular, with connective tissue papillae (asterisk) and epidermal ridges (arrow). Beneath the superficial dermis, without precise boundaries, is the plexiform connective tissue (Pl) of the deep dermis. The proximity of both types of connective tissue allows them to be compared and to see how in the plexiform the collagen fibres (turquoise blue) are more abundant and are arranged in thick, intersecting bundles, while the elastic fibres (red) are scarcer.
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Thick skin (Cajal-Gallego) (20x). In the network that forms the plexiform connective tissue, the turquoise blue colour of the collagen fibres (arrow), sectioned in different planes, predominates. Interspersed with them are the elastic fibres (arrowhead), which are much finer and stained red using the Cajal-Gallego technique.
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Thick skin (Cajal-Gallego) (40x). Since plexiform connective tissue consists of a network of collagen fibre bundles mixed with elastic fibres, both collagen fibre bundles (red letters) and elastic fibres (blue letters) can be observed in different section planes - longitudinal (L), transverse (T) and oblique. The cells are not stained with this technique. As a technical artefact, the clear spaces (asterisk) between the fibrillar components of the tissue appear slightly dilated. (Blood vessel with red blood cells: V).
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ORGAN: Tendon (human). STAIN: Hematoxylin-Eosin (H/E).
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Tendon (H/E) (4x). Fibrous connective tissue is characterized by being very rich in collagen fibers arranged in bundles that are oriented parallel to each other, which is why it is also called dense regular connective tissue. An example is the tendon (T), which is eosinophilic due to the abundance of collagen fibers. The narrow pale band seen in the image is a small sheet of loose connective tissue that belongs to the so-called “peritenom” (P), where the few blood vessels that nourish the tendon are located.
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Tendon (H/E) (10x).In the longitudinal section of this human tendon, thick, parallel eosinophilic bands can be seen, which correspond to the bundles (H) of collagen fibres. Between these bundles there are narrow, elongated nuclei with dark chromatin, which belong to fibroblastic cells called “tenocytes” (arrowhead). Outside the tendon there is a loose connective tissue called the external peritenom (Pe), from which thin septa extend towards the interior of the tendon and are introduced between the bundles of fibres, constituting the internal peritenom (Pi).
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Tendon (H/E) (20x). The collagen fiber bundles (arrow) appear as thick eosinophilic bands parallel to each other and to the long axis of the tendon. Sometimes, these bands are separated by narrow gaps (asterisk), which appear as an empty space, an artifact that frequently occurs in this type of tissue. Between the fiber bundles are the tenocyte nuclei (arrowhead), which are narrow, elongated and have dark chromatin, similar to those of fibroblasts.
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Tendon (H/E) (40x). The appearance of small indentations (asterisk) between the collagen fiber bundles (arrow), an artifact produced by the histological technique, makes it easier to see their remarkable parallelism in the fibrous connective tissue. Between the fiber bundles, tenocytes can be seen, cells whose laminar processes cannot be seen in the preparation. Of these tenocytes, only their nuclei (arrowhead) can be identified, narrow and elongated, with dark chromatin, arranged with their major axis parallel to the longitudinal axis of the tendon.
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ORGAN: Elastic artery (aorta). STAIN: Hematoxylin-Eosin (H/E).
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Elastic artery (H/E) (2x). Elastic arteries, such as the aorta, have a thick wall, where the so-called “tunica media” (M) predominates, which in the image is the most eosinophilic part. It is made up of elastic connective tissue, very rich in elastic elements that provide elasticity to the vessel wall. From a functional point of view, elastic arteries transform the discontinuous blood flow produced by the rhythmic contractions of the heart into a continuous flow.
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Elastic artery (H/E) (4x).The arterial wall is made up of three layers, starting from the lumen: “intima” (I), “media” (M) and “adventitia” (A). The middle layer, which is thicker and more eosinophilic, contains the elastic connective tissue, which is very rich in elastic laminae. Although these laminae cannot be seen at this magnification, they can be clearly distinguished using the “Virtual microscope” option. The adventitia (A) is made up of loose connective tissue that usually appears more or less frayed due to the handling of the piece.
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Elastic artery (H/E) (10x). The elastic connective tissue that forms the middle layer (M) of the wall of elastic arteries has an intercellular substance with abundant elastic elements, mainly in the form of sheets, which are arranged in concentric layers. There are also elastic fibers that go unnoticed with H/E. Between the sheets, cell nuclei are observed, mostly belonging to smooth myocytes that, despite their muscular nature, are responsible for synthesizing the components of the intercellular substance in this type of connective tissue. (Intima: I. Adventitia: A).
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Elastic artery (H/E) (20x). In the elastic connective tissue of the media layer (M) of elastic arteries there are numerous elastic laminae that are observed as wavy lines that are intensely eosinophilic and shiny (arrow). The elongated nuclei between these laminae correspond to smooth myocytes (arrowhead). The limit of the media layer with the intima (I) is defined by a thick elastic lamina, although this situation does not always occur. To the left of the image is the adventitia (A), composed of a loose connective tissue rich in fibers, where the elastic laminae disappear.
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Elastic artery (H/E) (20x). In the middle layer of elastic arteries, the numerous wavy, eosinophilic lines that are shiny and wavy are striking. These lines correspond to elastic lamellae (arrow) arranged in concentric layers around the lumen of the vessel. Their sinuous appearance is due to the loss of tension to which they are subjected in the living individual. The spaces between the lamellae are occupied by a small amount of ground substance, some collagen fibers, elastic fibers that go unnoticed with H/E, and cells (smooth myocytes and occasional fibroblasts).
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Elastic artery (H/E) (40x). High magnification image of the elastic connective tissue of the aortic wall. The abundant elastic, eosinophilic and wavy laminae are prominent. These are perforated laminae (P) through which nutrients diffuse through the artery wall. Between the laminae there are elongated nuclei with rounded edges that are smooth myocytes (arrow). Some darker nuclei with sharp ends could correspond to fibroblasts (arrowhead). Between the elastic laminae there are also collagen and elastic fibers (these go unnoticed with H/E), as well as little ground substance.
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ORGAN: Elastic artery (aorta). STAIN: Cajal-Gallego.
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Elastic artery (Cajal-Gallego) (4x). The different staining between the collagen fibres (turquoise blue) and the elastic component (red) highlights the abundance of elastic elements in the elastic connective tissue that makes up the middle layer (M) of the elastic arteries. The adventitia, however, is made up of a loose connective tissue relatively rich in collagen fibres, which explains its turquoise blue colour with the Cajal-Gallego technique. (Lumen of the artery: L).
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Elastic artery (Cajal-Gallego) (10x). The abundant elastic lamellae (arrow) of the elastic connective tissue of the tunica media of the elastic arteries are stained red using the Cajal-Gallego technique. These lamellae follow an undulating path when they are relaxed and do not have to withstand the pressure they receive in the living individual. They are parallel to each other, since they are arranged in concentric layers around the vascular lumen. Although there are few elastic fibers in the adventitia (A), distinguishable by their red color, the turquoise blue color of the collagen fibers predominates. (Blood vessel in the adventitia: V. Lumen of the artery: L).
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Elastic artery (Cajal-Gallego) (20x). Among the elastic laminae there are elastic fibres (arrowhead) that follow a more or less oblique path, connecting some laminae with others. Also observed, in very small quantities, some collagen fibres (arrow) stained turquoise blue. With the Cajal-Gallego technique only the fibrillar component of the extracellular matrix is ​​demonstrated, so the cells between the elastic laminae are not visible (see the previous slide, stained with an H/E).
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Elastic artery (Cajal-Gallego) (40x). This high-magnification image shows the difference between the middle layer (M), made up of elastic connective tissue rich in elastic laminae (arrow), and the adventitial layer, made up of loose connective tissue with abundant collagen fibers. Red elastic fibers (arrowhead) can be identified in the adventitia, interspersed with turquoise-colored collagen fibers. By enlarging the image with the “Virtual microscope” option, the unstained nuclei of the cells located between the elastic laminae can be seen.
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Elastic artery (Cajal-Gallego) (40x). The thick elastic lamellae (L), which are stained red, follow a wavy course and are interrupted at certain points (arrow) because they are perforated lamellae. Thanks to these fenestrations, nutrients can diffuse through the thickness of the artery wall, since the elastic component is very impermeable. Fine elastic fibres can be seen joining the lamellae together (arrowhead). Some turquoise-blue collagen fibres (asterisk) can also be seen. The clear, unstained spaces are occupied by cells, mainly smooth muscle cells.
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Elastic artery (Cajal-Gallego) (100x). High magnification detail of the elastic laminae (L), stained red. Their wavy course and the presence of fenestrations (arrows) are notable. Thinner elastic fibres, also stained red, can be seen between the laminae, which connect some laminae to others. Collagen fibres (arrowhead) can also be seen, although they are few in number. The cells are not stained with this technique and are located in the clear spaces (asterisk) between the laminae. By enlarging the image with the “Virtual microscope” option, the nuclei of these cells can be seen.
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ORGAN: Elastic artery (aorta). STAIN: Orcein.
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Elastic artery (Orcein) (2x). Orcein is a dye that selectively stains elastic fibres in an ochre-brown colour (similar to the colour of bricks). For this reason, the middle layer (M) stands out in the wall of elastic arteries, since it is composed of elastic connective tissue with abundant elastic elements. With this technique, the cells are not stained, and the collagen fibres are stained lightly and non-specifically. The clear spaces (arrow) that seem to break the structure of the middle layer in its outer part correspond to the entry of blood vessels that irrigate the arterial wall itself.
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Elastic artery (Orcein) (4x). In the middle layer or tunica media (M) of the elastic artery, at this magnification, a large number of wavy, ochre-brown lines can be seen, which correspond to elastic laminae, the characteristic and predominant element of the elastic connective tissue of the vascular wall. Outside the middle layer is the adventitia (A), with very few elastic fibers. (Blood vessel entrance into the middle layer: arrow).
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Elastic artery (Orcein) (10x). Orcein reveals the presence of elastic fibres in the three layers of the arterial wall: intima (I), media (M) and adventitia (A). The staining is clearly concentrated in the middle layer, which is made up of elastic connective tissue with elastic lamellae (arrow) arranged in concentric layers around the vascular lumen. These lamellae appear in the preparation as closely spaced wavy lines. In the intima and adventitia, the elastic fibres (arrowhead) are embedded in loose connective tissue.
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Elastic artery (Orcein) (20x). The elastic lamellae (arrow) of the elastic connective tissue are stained ochre-brown by orcein and appear as wavy lines, close to each other. They are lamellae arranged in concentric layers parallel to the lumen of the vessel. Their sinuous appearance is due to the fact that they are relaxed, having lost the tension to which they are subjected in the living individual.
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Elastic artery (Orcein) (40x). In the elastic connective tissue of the arterial wall, the predominant elastic component is arranged in the form of elastic lamellae (arrow) of uniform thickness. Between them, with orcein, the existence of elastic fibers (arrowhead) can be seen, which join some lamellae with others, providing greater cohesion to the vessel wall. In the clear spaces (asterisk) between the lamellae and elastic fibers, there are cells (mainly smooth myocytes), which do not stain with this technique, as well as some collagen fibers, which do so nonspecifically in a very pale color.
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Elastic artery (Orcein) (100x). The elastic laminae (L) of the arterial wall, in addition to having an undulating course, have fenestrations (arrow) to allow the passage of nutrients. Elastic fibers (arrowhead) can be identified between the elastic laminae, which connect some laminae with others. In the clear spaces (asterisk) there are cells, whose nuclei can be seen, as well as some pale and nonspecifically stained collagen fibers. The cells correspond in their vast majority to smooth myocytes.
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ORGAN: Umbilical cord (human). STAIN: Hematoxylin-Eosin (H/E).
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Umbilical cord (H/E) (2x). In the mucous connective tissue (M), ground substance predominates, with few fibres and cells, and it is similar to the mesenchyme (connective tissue of the embryo). In the umbilical cord, it forms the so-called Wharton's jelly, which fills the space between the two arteries (A) and the vein (V), located in the centre, and the surface of the cord, covered by an epithelium (E) derived from the amnion. The scarcity of collagen fibres and the high hydration of the mucous connective tissue are responsible for the soft consistency and gelatinous appearance of the umbilical cord.
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Umbilical cord (H/E) (4x). This cross section of a human umbilical cord shows the mucous connective tissue (M) occupying the space between an artery (A) and the surface of the cord, which is lined by an epithelium (E). Numerous hollow spaces (asterisk) appear, apparently empty, due to the predominance of the ground substance, very rich in water, which is inevitably extracted during dehydration, a mandatory step in the histological processing of the piece. The few cells are widely separated from each other and at this magnification are identified by the staining of the nucleus (arrowhead).
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Umbilical cord (H/E) (10x). In the mucous connective tissue there are few cells (arrow), with a mesenchymal appearance, with elongated nuclei. Between the cells there is an intercellular substance in which the ground substance predominates, with very few fibers. The empty spaces (asterisk) observed in the image are due to the fact that the ground substance is eliminated in the histological processing of the piece, during dehydration.
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Umbilical cord (H/E) (20x). The cells of the mucosal connective tissue have the same characteristics as mesenchymal cells, which are similar to fibroblasts. Their nuclei (arrows) are elongated, with a relatively dark chromatin. They are cells that emit fine processes (arrowheads), which are already identifiable at this magnification. Between these cells there are remains of a very amorphous ground substance (asterisk), partially removed by the histological processing of the sample.
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Umbilical cord (H/E) (40x). In the mucous connective tissue, the predominant element is a very abundant intercellular substance, with a great predominance of ground substance that appears as clear spaces (asterisk) with some remains of slightly basophilic material. The connective fibers (arrowhead) are immature and very scarce. The few cells that can be seen in the image emit extensions, adopting a more or less star-shaped form.
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Umbilical cord (H/E) (100x). The cells of the mucous connective tissue are star-shaped, as they emit fine processes (arrow). They have little cytoplasm and the nucleus is elongated, with rounded ends and relatively dark chromatin. Between the cells, some fibrillar components can be identified (arrowhead) that correspond to immature collagen fibers, and the clear spaces with small amounts of basophilic material (asterisk) are remains of ground substance, which has been almost completely removed by dehydration during the histological processing of the piece.
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ORGAN: Lymph node. STAIN: Hematoxylin-Eosin (H/E).
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Lymph node (H/E) (2x). The lymph node has a stroma made up of reticular connective tissue, distributed throughout the lymph node, which is difficult to see with H/E because it is mixed with parenchymal cells. At low magnification, a cortex (C) can be distinguished at the periphery, which is very basophilic due to the high cell density, where rounded structures corresponding to the lymphoid follicles (F) stand out. Deeper in the lymph node is the medulla (M), which is less basophilic, and it is here, above all, where, at high magnification, the cells of the reticular connective tissue can be identified.
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Lymph node (H/E) (10x). Medullary region (M) of the lymph node close to the cortex (C). In the medulla, the reticular connective tissue is divided into two areas: the medullary sinuses (Sm) (large, clear areas with low cell density, through which lymph circulates within the node), and the medullary cords (Cm) (elongated, branched structures, more basophilic because they contain parenchyma, which has a high cell density). It is in the medullary sinuses where the cells of the reticular connective tissue are best identified. (Use the “Virtual microscope” option.)
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Lymph node (H/E) (20x). Reticular connective tissue in the lymph node medulla is found in both the medullary cords (Cm) and sinuses (Sm). With H/E, and at this magnification, the loose cellular arrangement of the medullary sinuses allows the reticular cells (arrow) to be distinguished, which are identified by their star-shaped shape, as they emit processes. They can be seen more clearly using the “Virtual microscope” option.
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Lymph node (H/E) (40x). In the medullary sinuses (Sm), the cells of the reticular connective tissue contact each other by means of processes arranged in a very loose three-dimensional network, leaving wide spaces through which the lymph circulates with its corresponding cells, especially lymphocytes (arrowhead). In the medullary cords (Cm), however, the reticular cells form a somewhat tighter mesh that goes almost unnoticed as they mix and blend in with the large number of parenchymal cells. There are also blood vessels inside the medullary cords (V).
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Lymph node (H/E) (100x). The greater laxity of the medullary sinuses allows us to perfectly identify the processes (blue arrow) that emit the reticular cells (R). They are star-shaped cells, which have a rounded nucleus of relatively loose chromatin, with an evident nucleolus (arrowhead). In the spaces of the meshwork that forms the reticular connective tissue there are small free cells, especially lymphocytes (red arrow), which travel through the lymph that is circulating inside the node. (Medullary cord: Cm).
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Lymph node (H/E) (100x). The star-shaped cells that make up the reticular connective tissue contact each other by means of their processes (arrows), forming a delicate mesh that is closely related to a network of reticular fibers, on which they rest, covering them. These fibers, synthesized by the reticular cells themselves, go unnoticed with H/E, but can be demonstrated with special silver techniques, as can be seen in the following slide. (Medullary cord: Cm. Spaces through which lymph circulates: asterisk).
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ORGAN: Lymph node. STAIN: silver.
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Lymph node (silver) (2x). The reticular fibers of the reticular connective tissue that form the stroma of the lymph node are arranged in different ways depending on the region of the node, and are demonstrated with silver techniques, proving their organization in a three-dimensional mesh. With these techniques, however, the reticular cells are not impregnated or stained. On the other hand, both the capsule (C) that covers the node and the connective tissue trabeculae (T) located inside, have abundant collagen fibers that are impregnated with a blackish brown color.
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Lymph node (silver) (4x). Inside the lymph node, an extensive network of reticular fibers can be observed. There are regions where the mesh is somewhat denser (arrow), leaving small gaps, while in other areas the network is looser (asterisk), with wider spaces. The rounded formations with a brown background and few reticular fibers inside correspond to lymphoid follicles (F). (Capsule: C. Connective tissue trabeculae: T).
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Lymph node (silver) (10x). In the medulla of the lymph node, the network formed by the reticular fibers of the reticular connective tissue is best seen. The areas where the network of fibers is somewhat denser correspond to the medullary cords (Cm), while the areas where the mesh is looser belong to the medullary sinuses (Sm). The darker structures are connective tissue trabeculae (T) rich in collagen fibers, blackish brown in color, and contain blood vessels (V) inside.
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Lymph node (silver) (20x). The parenchyma of the lymphoid organ is located in the spaces left by the reticular fiber mesh. The image corresponds to the medulla of the lymph node, where two regions can be distinguished: the medullary cords (Cm), which contain numerous closely grouped cells that are not impregnated with silver, and the medullary sinuses (Sm), which consist of a very loose network of reticular fibres. The lymph circulates through the medullary sinuses within the lymph node. (Conjunctive trabeculae: T).
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Lymph node (silver) (40x). The reticular connective tissue, present throughout the lymph node, plays different roles depending on its location. In the medullary cords (Cm) it forms a somewhat more compact mesh, which is occupied by parenchymal cells, while in the medullary sinuses (Sm) the network is looser, constituting a system of spaces traversed by reticular fibers and cells, through which lymph is circulating. (Connective tissue trabecula: T).
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Lymph node (silver) (100x). At high magnification, the three-dimensional appearance of the reticular fibre network in the reticular connective tissue is evident. This network is covered by reticular cells that are not silver-stained, but are stained with H/E (see previous slide). Parenchymal cells are located in the spaces between the reticular fibres of the medullary cords (Cm), while lymph flows through the wide spaces in the medullary sinuses (Sm). (Connective tissue trabecula: T).
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ORGAN: Ovary. STAIN: Hematoxylin-Eosin (H/E).
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Ovary (H/E) (2x). The fusocellular connective tissue is characterized by being very rich in cells and having little intercellular substance. It is found exclusively in the cortex (C) of the ovary. Almost the entire extension of the section that we are observing corresponds to cortex; only a small pale region, on the left, is medulla (M). In the ovarian cortex, the spindle connective tissue cells fill the spaces between large rounded formations called “ovarian follicles” (F). This tissue is similar to the cytogenic connective tissue of the endometrium of the uterus (see next slide).
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Ovary (H/E) (4x)The fusocellular connective tissue can be identified at low magnification by the high density of nuclei (asterisk). It fills, in the cortex, the spaces between the ovarian follicles (F), which are in different stages of maturation. (Blood vessel: V).
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Ovary (H/E) (10x). Ovary cortex (C) where ovarian follicles (F) of different sizes are located and, among them, a large number of cells with elongated nuclei belonging to the fusocellular connective tissue (Fs). In the lower part of the image, a small part of the medulla can be seen, where blood vessels (Vs) and lymphatic vessels (Vl) appear immersed in a loose connective tissue.
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Ovary (H/E) (20x). The fusocellular connective tissue is made up of a large concentration of fibroblast-like cells with elongated nuclei (arrow) of relatively dark chromatin. These cells are often arranged in a swirling pattern, following the so-called “storiform pattern”. Within this connective tissue, small blood vessels (arrowhead) can be found, which are identified by the eosinophilia of the red blood cells that occupy their lumen. (Lining epithelium: E. Ovarian follicles: F).
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Ovary (H/E) (20x). The fusocellular connective tissue is made up of a high concentration of fibroblast-like cells with elongated nuclei (arrow) of relatively dark chromatin. The characteristic arrangement of cells in the fusocellular connective tissue, appearing as irregular clusters (asterisk) of elongated and dense nuclei, indicates that they are cells with narrow cytoplasm and that the intercellular substance is scarce. The eosinophilic dots observed in this tissue are red blood cells that occupy the lumen of small vessels (arrowhead). In the thickness of the spindle cell connective tissue, the different ovarian follicles mature (F). (Lining epithelium: E).
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ORGAN: Uterus (human). STAIN: Hematoxylin-Eosin (H/E).
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Uterus (H/E) (10x). The cytogenic connective tissue is found exclusively in the endometrium, the layer that lines the uterine cavity. It is similar to the fusocellular connective tissue of the ovarian cortex, as the cells predominate over the intercellular substance, but the nuclear density is less pronounced. The image shows part of the endometrium of a human uterus, where the cytogenic connective tissue (C) occupies the wide spaces between the tubular glands (G) that branch off from the lining epithelium. The eosinophilic areas correspond to blood vessels filled with red blood cells. (Lumen of the uterus: L).
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Uterus (H/E) (20x). The most superficial area of ​​the endometrium where the cytogenic connective tissue (C) has a high cellular density. It provides support for the blood vessels (V) and endometrial glands (G), which originate (arrow) from the lining epithelium (E).
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Uterus (H/E) (20x). Deep zone of the endometrium. Cytogenic connective tissue is characterized by a high concentration of cells with oval or rounded nuclei, with different chromatin densities. These cells are arranged in a disorderly manner, with more compact areas (arrowhead), while in others the cells are grouped more loosely (asterisk). (Cross sectioned glands: G. Blood vessels: V).
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Uterus (H/E) (40x). Deep zone of the endometrium where the cytogenic connective tissue shows a high concentration of cells, serving as support for the tubular glands (G) and blood vessels (V). Functionally, the cytogenic connective tissue is very sensitive to female sex hormones, whose concentrations vary cyclically. Its appearance changes in each phase of the menstrual cycle, varying both the cell density, depending on the amount of intercellular substance, and the shape of the cells. It also undergoes important modifications (“decidual reaction”), when there is pregnancy.
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Uterus (H/E) (100x). High magnification detail of the cytogenic connective tissue of the endometrium. This is a region with a relatively homogeneous distribution of cells. Cells with rounded nuclei (arrow) can be seen, interspersed with others with more elongated nuclei (arrowhead). It can be seen that the density of nuclear chromatin shows notable differences between cells.
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