Welcome to lab classes in basic histology Introducing lab class (in spanish) .

The aim of these lab classes is to provide students with educational resources to acquire basic practical skills of each subject, recognize, locate and describe cell types and basic tissues.

Each of these practical sessions are structured around three main elements:
- Definition of learning objectives.
- Description of basic tissues and their cell types.
- Exercices location of cell types and basic tissues in virtual slides.

LEARNING OBJECTIVES
- Differentiate cartilage tissue from other body tissues.
- Differentiating the three types of cartilage.
- Identify hyaline cartilage tissue.
- Identify the elastic cartilage.
- Identify the fibrillar cartilage or fibrocartilage.
- Differentiate the extracellular matrix of chondrocytes.
- Identify isogenic groups.
- Locate the perichondrium in the two types of cartilage that arise.

HANDBOOK
The cartilage is a type of connective tissue Hyaline cartilage where the firm consistency of their extracelular matrix allows the tissue withstand mechanical stress. The cartilage is characterized by an extracellular matrix enriched with glycosaminoglycans and proteoglycans, a types of macromolecules that interact with collagen and elastic fibers. The different variations in the composition of the matrix components produced three types of cartilage biomechanically adapted to local needs. For example, in the respiratory system, the cartilage forms a structure of support on soft tissue, either is found in the joints of the bones, where thanks to their smooth surface, cartilage provides a shock absorption and displacement area, facilitating the movement of the bones. In addition, cartilage is essential for the development and growth of long bones that occurs after birth.
Cartilage is formed by a cell type called chondrocyte Chondrocyte TEM and the extracellular matrix that they themselves produce. The chondrocytes are located in cavities within the cartilage matrix called lacuna, while the extensive extracellular matrix is composed of ground substance and fibers of various kinds, among which collagen type II, hyaluronic acid, proteoglycans and other small glycoproteins. Because the collagen and elastin are flexible, solid gel consistency of cartilage depends on the electrostatic bonds between the collagen and glycosaminoglycan said chains attached of the proteoglycans.
Surrounding the cartilage matrix we find the perichondrium Hyaline cartilage , a type of dense connective tissue that is essential for growth and maintenance of cartilage. It consists of numerous fibroblasts and large collagen I fibers. Fibroblasts from the inner layers of the perichondrium are the precursors of chondroblasts, which in turn differentiate into chondrocytes. The perichondrium is vascularized and therefore is responsible for the supply of nutrients and other elements to the cartilage.
Due to the cartilage has no blood vessels, chondrocytes receive low oxygen, reason why chondrocytes metabolize glucose mainly through anaerobic glycolysis producing lactic acid as end product. The nutrients from blood vessels reach the chondrocytes by diffusion through the perichondrium to the deeper cells of the tissue. The water transport and other various solutes is produced by the intermittent pumping of the cartilage due to compression and decompression is submitted.
The three types of cartilage are hyaline cartilage Hyaline cartilage , elastic cartilage Elastic cartilague and fibrous cartilage or fibrocartilage.

HYALINE CARTILAGE Hyaline cartilage Hyaline cartilage
The hyaline cartilage, bluish-white and translucent when observed in fresh, is the most common and best studied of the three. In mammals can be found in the articular surfaces of mobile joints Humerus. General structure of the bone , in the walls of the respiratory tract (nose Nasal Cavities , larynx, trachea General Structure of the trachea , bronchi Lung, Structure of the Bronchus ), in the ventral portion of the ribs where they articulate with the sternum, and the plate epiphyseal Endochondral overview formation , which is responsible for longitudinal growth of bones. During embryonic life, the hyaline cartilage skeleton serves as temporary, to be replaced by bone.

MATRIX
40% of the dry hyaline cartilage corresponds to type II collagen fibers immersed in a network of proteoglycans and structural glycoproteins. Proteoglycans contain chondroitin 4, chondroitin 6, and keratansulfate, covalently bound to a protein core. Hundreds of these proteoglycans are non-covalently bound to large molecules of hyaluronic acid, forming large aggregates of proteoglycans.
The high water of solvation coupled with the negative charges of glycosaminoglycans is responsible for the ability of cartilage to absorb shock and spring work as biomechanical functions of great importance, especially in the articular cartilage.
Besides the type II collagen and proteoglycans, another important component of cartilage matrix glycoprotein is chondronectin, which like the fibronectin in the connective tissue, this macromolecule binds specifically glycosaminoglycans, collagen type II membrane integrins, regulating the binding of chondrocytes to the extracellular matrix.
The basophilic cartilaginous matrix is usually due to the high concentration of sulfated glycosaminoglycans. Staining observed variations are due to differences in the composition of the matrix. The extracellular matrix surrounding the chondrocytes intimately called territorial matrix is rich in glycosaminoglycans and collagen-poor, reason why is viewed differently than the rest of the matrix.
Hyaline cartilage tissue in the presence of perichondrium found in all structures that are safe in articular cartilage, where nutrients and oxygen reach chondrocytes via synovial fluid.

CHONDROCYTES Chondrocyte TEM
Chondrocytes are the resident cells of cartilage tissue. On the periphery of hyaline cartilage young chondrocytes shows an elliptical morphology, with axis parallel to the surface. As we enter the tissue, chondrocytes adopt a more rounded, and usually appear in groups, called isogenic groups Isogenic groups of up to eight cells originating from the successive divisions of a single chondrocyte. Because chondrocytes are responsible for the secretion of the matrix, as it is secreted, they are left isolated from the rest of chondrocytes within the so-called lacuna.
The functions of chondrocytes depend on hormones. The synthesis of glycosaminoglycans is accelerated in the presence of growth hormone, thyroxine and testosterone, while slowed in the presence of cortisone, hydrocortisone and estradiol. A more cartilage growth depends largely on the hormone somatotropin, which promote the release of other factors such as IGF-1 in the liver, which acts directly on chondrocytes, promoting their growth.

ELASTIC CARTILAGE Elastic cartilague
Elastic cartilage is similar to hyaline cartilage except that it contains a large network of fine elastin fibers over fibers of collagen type II. The fresh cartilage has a yellowish color due to the presence of these elastin fibers. The elastic cartilage has perichondrium.
Elastic cartilage is found in the pinna, external channels in the ear canals in the ear tubes or eustachian tube, the epiglottis and cuneiform cartilage in the larynx.

FIBROCARTILAGE
Fibrocartilage or fibrous cartilage is a tissue intermediate between dense connective tissue and hyaline cartilage. It is found in the intervertebral discs, in the union of certain ligaments and symphysis of the pubis. Always associated with dense connective tissue, the limit between the two tissues is never clear, showing a transition zone.
Single chondrocytes or isogenic groups, lined up in long columns axially separated by thick type I collagen fibers and less proteoglycan than other forms of cartilage. The orientation of collagen fibers depends largely on the stress they are subjected fibrocartilage. Do not has a perichondrium.

EXERCICES
- Locate the cartilage in these virtual slides Elastic cartilage H-E 1,5 um Hyaline cartilage H-E 1,5 um .
- Locate chondrocytes in these virtual slides Elastic cartilage H-E 1,5 um Hyaline cartilage H-E 1,5 um .
- Identify the isogenic groups Elastic cartilage H-E 1,5 um Hyaline cartilage H-E 1,5 um .
- Identify the perichondrium in these virtual slides Elastic cartilage H-E 1,5 um Hyaline cartilage H-E 1,5 um .