Welcome to the practical classes of histology of organs and systems. Introducing lab class (in spanish)
These practical classes aims to provide students with the necessary educational resources so that they acquire basic practical skills of each topic, i.e. recognize, locate and describe the types of cell, tissue and structures specific to each body.
Each of these practical classes are structured in three main elements:
-Definition of learning objectives.
-Notes: Description of structures, tissues and cell types inherent in the system.
-Location of structures exercises / cell types in virtual preparations

LEARNING OBJECTIVES
-Differentiate between thin skin and thick skin.
-Locate the epidermis, dermis and hypodermis, both thin skin and thick skin.
-Locate the layers of the epidermis: basal layer, hawthorns, grain, lucid and horny.
-Locate keratinocytes, melanocytes and Langerhans cells in the epidermis.
-Identify the dermis papillary and reticular dermis.
-Locate and characterize hair follicles
-Identify and differentiate sweat and sebaceous glands.
-Locate the secretory portion and pexcretory orción of sweat glands.
-Locate and characterize Valter-Pacinian and Meissner corpuscles.

NOTES
GENERAL QUESTIONS
The skin or tegument is largest organ of our body, which covers completely. Extended, human skin, occupies approximately 2 m 2.
The skin meets a set of work necessary for the maintenance of life:
-Protection: The skin is the first barrier of protection of the body from external aggressions, such as: microorganisms, ultraviolet light, mechanical or chemical attacks. Also the skin protects from water loss. Skin cells are located antigen-presenting that give the alarm in case of bacterial invasion.
-Sensory perception: the skin has numerous receptors: touch, pressure, temperature and pain.
-Metabolic reserve: skin has a considerable amount of adipose tissue that serves as energy reserve of body. In addition the skin synthesizes an important part of the vitamin D needed.
-Thermoregulation: Subcutaneous adipose tissue serves as an excellent insulator and prevents loss of heat in situations of low environmental temperature. By otRA part, in conditions of high ambient temperature, the evaporation of the sweat and the radiation of heat from the vascular network of the dermis allow a significant loss of heat by the body.
Across its surface skin presents a structure in three layers: Layers & elements of the skin
-Skin
-Dermis
-Hypodermis
The thickness of these layers is not the same across the surface, and that is why, traditionally distinguishes between: Thin skin vs thick skin
-Thick skin: located in the palms of the hands, soles of the feet. His epidermis and dermis are thick and its interface presents a steep ridges.
-Thin skin: located in the rest of the body. Both the epidermis and the dermis of this type of skin are thinner that skin thicker and its interface presents a surface flat.
In addition to these layers in the skin can find a series of adjoining structures, known as faneras, in this line can describe:
-Hair
-Nail (not dealt with in this volume)
-Sweat glands
-Odoriferous glands
-Sebaceous glands
-Sensory corpuscles

EPIDERMIS
The epidermis is the outermost layer of the skin and is trat of a flat epithelium stratified keratinized. Layers of the epidermis
Among other differences, the keratin layer is much thicker than thick skin in the thin skin.
The epidermis is traditionally divided into several layers: Layers and cell types of the epidermis

STRATUM BASALE (BASAL LAYER)
It is the deepest layer of the epidermis and its cells resting directly on the basement membrane that separates the epidermis from the dermis.
It consists of a single line of cells that have a profile, clear, cylindrical rather cubical and thick skin or something flat. This layer corresponds to the germinal layer cells in mitosis are frequent. The nuclei of the cells of this layer often present an oval nucleus whose axis is oriented perpendicular to the basement membrane (portrait orientation).

STRATUM SPINOSUM (ESPINOSA COAT)
It is the next layer of the epidermis and its thickness varies depending on thin skin or thick, being obviously more coarse in the thick skin skin.
The profile of the cells of this layer varies more jar in your area more internal (next to the basal layer) and flatter as we climbed over the layer. The nuclei ofThese cells range from slightly oval (in the deeper areas of the layer) to clearly oval (in the most superficial areas) and its axis is orientated parallel to the basal membrane (horizontal orientation)
To the optical microscope and using conventional staining techniques as the hematoxilina-eosina can be seen that the cells are separated by a zone which stains very little. The TEM (MET) shows that these cells do not exhibit a smooth profile, but that presented a large number of (similar to spines) short cytoplasmic extensions that contact of cells with each other creating this more clear strip that is appreciated to the optical microscope.

STRATUM GRANULOSUM (GRANULAR LAYER)
This layer is located above the thorny stratum and is the last layer composed of cells. These cells have a very flat profile.
Features why cells that compose are seen more intensively dyed in the optical microscope. In addition their cytoplasm notes full of dense granules, which are known as keratohyalin granules. The nuclei of these cells are clearly oval shaped and presented an orienthorizontal action.
It is in these cells where begins the process of keratinization through apoptosis, so the outer cells are already dead cells.

STRATUM CORNEUM (CORNEAL LAYER)
This layer is formed by plates of keratin (which is what turns the cells of the granular layer).
This layer is considerably thick thick skin. A sublayer of the stratum corneum in the area closest to the granular layer is defined in the thick skin, and in some cases of thin skin. This sublayer, using techniques such as the hematoxylin - eosin, stained more intense for what is known as "Stratum lucidum" (lucid layer).

The cells that make up the epidermis are known generically as keratinocytes. In addition to the keratinocyte, other cells in the epidermis can be observed: Layers and cell types of the epidermis
-Melanocytes: These cells are responsible for the synthesis of melanin, which is responsible for the coloration of the skin. The synthesis of melanin is favoured by exposure to ultraviolet light (UV). These cells are exclusively located in the basal layer, scattered among the keratinocytes of this stratum. To the microscoPIO, using techniques such as the hematoxylin-eosin, these cells are very easily distinguished, since their cytoplasm, rounded appearance, just stained, while its core, also Hairpin, stained intensely.
-Langerhaans cells: cells are antigen-presenting with origin in the bone marrow (lineage of macrophages). Although they are most abundant in the spiny layer can be found in all cell of the epidermis, even in the dermis layers. Your profile is very irregular and they have cytoplasmic projections (such as macrophages). Its core presents also an irregular profile.
-Merkel cell: (not shown) are derived from the neural crest cells and have a clear function sensitive (are pressure sensors). To its basal domain arrive sensory nerve terminals. They are located in the basal layer and are scarce and to the optical microscope are very difficult to distinguish from melanocytes.

As it has been said, in the thick skin the interface between the epidermis and the dermis is not flat, and thus the dermis presents some basal projections that sneak into the dermis and are known as "Epidermal ridges". Epidermal ridges and dermal papillae

DERMIS
The dermis is the layer underlying the epidermis and is composed of connective tissue, which is usually very vascularized.
According to the orientation of the fibers collagen and the density of cells distinguish two layers in the dermis: Layers & elements of the skin Epidermal ridges and dermal papillae

PAPILLARY DERMIS
It is the layer adjacent to the epidermis of a moderated, just below the basal membrane thickness.
This layer is formed by very thin Collagen fibers (mainly collagen type III and some elastic fibers) and a moderate number of cells (fibroblasts and some macrophages). This amount of cells has been that some authors define this layer as loose connective tissue, although it is not a unanimous opinion.
This layer is where the folds or "papillae" dermal which are those that are interdigitan with the epidermal ridges. This layer shows a large amount of blood capillaries, which are responsible for feeding the epidermis.

RETICULAR DERMIS
The reticular dermis lies below the papillary dermis and is composed of dense pack of thick collagen fibres (mostly collagen type I and packages of elastic fibers), oriented in different directions, lor that gives the appearance of grid. The number of cells in this layer is very low, and majority are fibroblasts, although they may also see macrophages and other cells of the body defense system.

HYPODERMIS
It is the deepest layer of the skin and also consists of connective tissue, whose main characteristic is the large amount of adipose panicles that contains. Hair (Scanning Electron Microscopy)

HAIR Hair (Scanning Electron Microscopy)
The hair is an annex of the skin, which in mammals (hairy) plays an important biological role, when the hair is erect form a layer of air that isolates the skin of the low and high temperatures; also erect hair makes the animal look bigger, intimidating their opponents.
In humans, and given the lack of hair these biological functions lost sense.
The hair is a cylindrical structure composed of cornificado epithelium (keratinized).
In humans there are two kinds of hair:
-Hair. It is fine, short, soft and without cord. It is located in the torso and members.
-Terminal hair. It is strong, long, hard and with marrow. Such is the hair, the hair of the beard, underarms and pubic.
In podem hairstructurally, you distinguish two zones:

HAIRY Layers of the hair shaft, and the hair follicle Hair follicles, transverse section Layers of the hair follicles, transverse section stem
It is what is commonly referred to as hair.
Three layers, all of them formed by epithelial cells, keratinised, differ in the terminal hair what varies is the level of compaction of keratin. From within outward, these layers are:
-Cord: The central cylinder of the hair, is formed by large cornificadas cells, among which small bubbles of air are located. In old age the number of these bubbles increases what gives the hair the hoary appearance.
-Bark: Is the second layer and the thicker. Consists of very cornificadas cells (hard keratin) that are very close together.
-Cuticle: The outermost layer and is made very flat plates of keratin that are available by way of Texas.
In the hair cortex and cuticle, but not cord are distinguished.

HAIR follicle Hair follicles & related structures Layers of the hair shaft, and the hair follicle Hair follicles, transverse section Layers of the hair follicles, transverse section
The hair follicle is an intussusception of the surface of the skin which houses the follicle stem.
Several layers can be distinguished:
-Internal root sheath: is that is closest to the follicle stem. Is in nature andpitelial and are found only in the deepest part of the follicle, the follicle bulb and the area where drain the sebaceous glands.
-External root sheath: it is also of epithelial nature and is located just below the internal root sheath. It is much thicker and is located in the entire length of the hair follicle, the epidermis is continued in the most external part.
-Vitreous membrane: corresponds to the basal lamina under all epithelium, with the particularity that is especially thick.
-Dermal sheath: is cohesive nature and in its upper portion continuous with the papillary dermis. It has high concentration of nerve fibers.
The basal part of the hair follicle is known as follicle bulb and is the area responsible for the growth of the hair. This terminal segment is thickened and in its lower part shows an intussusception occupied by a dermal papilla of connective tissue with lots of blood vessels which aims to nurture the basal epithelial cells that form a Crescent around the dermic papilla. This area is known as matrix, shows a high mitotic activity (responsible for the growth of the)(hair) and is comparable to the stratum basale of the epidermis. Hair bulb
On the dermal sheath at the height of a lump of the external root sheath known as follicular bulb fits the erector muscle of hair, that leads in oblique path to the papillary dermis. This muscle is composed of smooth muscle fibers and its innervation is by the autonomic nervous system. Hair follicles & related structures

GLANDS OF THE SKIN
The skin can be distinguished three types of glands:

SWEAT GLANDS Hair follicles & related structures Skin, Sweat glands Skin, Sebaceous and sweat glands
The sweat glands are simple tubular glands rolled, whose mission is the secretion of sweat, a hypotonic liquid formed primarily by water and a small amount of NaCl (0, 2-0, 3%) and traces of some organic substances such as mucinas. Sweat has a function thermoregulatory sweat evaporates causes a decrease in temperature. These glands are distributed throughout the skin.
The glandular body (adenómero) is very wrapped forming a ball located in the depths of the reticular dermis, even in the hypodermis. This glandular body part the excretory duct that leads in a way, moreor less rectilinear, towards the surface, through the reticular dermis, the papillary dermis and the epidermis.
The wall of the glandular body (adenómero) is formed by cells of cubic to slightly cylindrical profile and leave a small light. Traditionally defined two types of cells:-clear cell and - dark cells. Using conventional staining techniques as the hematoxylin - eosin, not these two cell types can be distinguished and the use of special techniques such as the PAS technique is necessary. These cells are secretory ecrina. Myoepithelial cells can be seen around these cells.
The cells that form the wall of the excretory duct are clear cubic profile with hematoxylin - eosin stained more intensely than the wall of the adenómero cells.

ODORÍFERAS GLANDS (not shown)
Odoriferous glands can be considered modified sweat glands. Secrete a particular kind of sweat which contains substances that they emit a strong smell to be degraded by bacteria. These glands are, primarily, in the armpits, groin area, Mammary areola, perianal region, etc...
Histológicamente these glands have a morphology similar to the sweat, i.e. are of simple coiled tubular type. This class with the branched adenómero glands are occasionally described. Under the microscope these glands are easily distinguished from the sweat glands in the adenómero light is much larger. The wall of these glands only describes a cell type of variable profile (from flat to cylindrical). Myoepithelial cells are also described to her around. This type of gland cells are secretory apocrina.

SEBACEOUS GLANDS Hair follicles & related structures Skin, Sebaceous glands Skin, Sebaceous and sweat glands
Sebaceous glands is secrete sebum, whose biological function is the form an oily film on the surface of the skin that reduces the permeability to water of the skin. These cells are found in the skin thin and usually associated with hair follicles, whose birth tend to drain their short excretory ducts.
The microscope shows that these glands are alveolar (acinar) composed composed of cells weakly stained with conventional techniques, given the high number of lipids in their cytoplasma. These glands are secretion holocrina.

SENSORY CORPUSCLES
Different types of sensory corpuscles, which, in this chapter we will focus on two of them can be distinguished in the skin:

CORPUSCLES of MEISSNER Skin, Meissner corpuscle
They are responsible for the fine touch encapsulated tactile receptors. They are distributed irregularly being much more abundant in the pulpejos of fingers of hands, plants of feet, nipples, eyelids, lips, and genitalia.
They are oval-shaped and are located in the dermal papillae, just under the epidermis. They are covered with a thin connective tissue capsule and presented cells in disc form, modified Schwann cells.
Meissner corpuscle introduces axons myelinated that display sensitive nerve endings between the discoidal cells. These axons and endings sensitive nerve are not stained with conventional techniques such as the hematoxylin - eosin and require special techniques to be revealed in the samples.

CORPUSCLES of VALTER-PACINI (PACINIAN CORPUSCLE) Skin, Pacinian corpuscle Skin, Pacinian corpuscle 1
They are responsible for most rude touch encapsulated tactile receptors: pressure, vibration, tension.
In the center of the corpuscle is located a single fibers sensitive nerve, which pierces the capsule of the corpuscle in the basal portion. A couple or three compact concentric sheets of modified Schwann cells can be seen around the nerve fiber and its around are numerous concentric sheets of very flat cells (related to the endoneuro). ETAS sheets are separated by a few small spaces filled with similar to lymph fluid. Wrapping everything as a whole stands out a layer of connective tissue.
Valter-Pacini corpuscles may exceed the mm in greatest diameter and are located in the deeper reticular dermis and hypodermis.

In addition to these sensory corpuscles in the skin we can find other sensory corpuscles, both encapsulated as free.
Thus we can find nerve endings in the dermis, some of which arrive at the epidermal basal lamina, just at the height of Merkel cells.
We can also find Ruffini corpuscles in the dermis, bulbs Krausse terminals, or nerve fibres peritriquiales that surround the base of the folhairy ículo.

EXERCISES
SHOWS 1: Human skin (thick), Hematoxilina-Eosina 1.5 um Skin (thick) H-E 1,5 um
-Difference between epidermis and dermis.
SHOWS 2: Skin (thick), Hematoxilina-Eosina 7um Skin (thick) H-E 7 um
-Distinguish between epidermis and dermis and locate dermal papillae.
-Differentiate each of the layers of the epidermis: basal, spiny, granular, lucid and horny.
-Locate melanocytes.
SHOWS 3: Skin (thin), Hematoxilina-Eosina 7um Skin (thin) H-E 7 um
-Identifies epidermis and dermis.
-Find the differences between the thin skin and thick skin.
SHOWS 4: Skin, Masson 7 Tricrómico um Skin Masson's trichrome 7 um
-Distinction between epidermis and dermis
-In the epidermis, locates keratinocytes, melanocytes and Langerhans cells.
-Distinction between papillary dermis and reticular dermis.
-Located and characterized a Sebaceous Gland.
SHOWS 5: Hair follicles (skin), Hematoxilina-Eosina 10 um Hair follicles (skin) H-E 10 um
-Distinguished epidermis, dermis and hypodermis.
-Located and difference sweat and sebaceous glands.
-Located hair follicles and characterized his wall.
SHOWS 7: Scalp, Hematoxilina-Eosina 10 um Scalp (skin) H-E 10 um
-Find hair follicles (in cross-section).
-Characterizes thes-layer of the wall of the follicles follicle.
-It features layers of hair.
SHOWS 8: Skin (ear), 8 Hematoxilina-Eosina um Skin (ear) H-E 8 um
-Distinguish between epidermis and dermis and locate dermal papillae.
-Differentiate each of the layers of the epidermis: basal, spiny, granular, and horny.
-Locate melanocytes.
-Difference between papillary dermis and reticular dermis.
-Located and characterized hair follicles.
SHOWS 9: Meissner Corpuscle (skin), 7 Hematoxilina-Eosina um Meissner corpuscle (skin) H-E 1,5um
-Distinguish between epidermis and dermis and locate dermal papillae.
-Difference between papillary dermis and reticular dermis.
-Locate dermal papillae.
-Located and characterized Meissner's corpuscles.
SHOWS 10: Pacinian Corpuscle (skin), 1.5 Hematoxilina-Eosina um Pacinian corpuscle (skin) H-E 1,5um
-It is characterized the structural elements of the Pacinian corpuscle.