TOPIC: EPITHELIUM
Ciliary activity is based on the movement of the doublet microtubules in relation to one another. Each doublet exhibits a pair of "arms". The Dynein arms extend unidirectionally from one microtubule of each doublet microtubule and interact with adjacent doublets to form temporary cross-bridges, so that they slide past one another. The arms contain Dynein, an ATPase. ATPase splits ATP to liberate the energy necessary for active movement of a cilium.
Immotile cilia syndrome: This results from a genetic defect causes an abnormal ciliary beat or the absence of any beat. It is characterized by cilia that lack Donnan arm and is associated with recurrent respiratory infections, reduced fertility in women, and sterility in men. This may be associated with situs inversus, in this case the condition is known as Kartagener's syndrome.
GLANDS
Glands are composed of epithelial cells specialized to synthesize and secrete a specific product. They originate from an epithelium that penetrates the connective tissue and forms secretory units. They consist of a functional portion of secretory and ductal epithelial cells (parenchyma), which is separated by a basal lamina from supporting connective tissue elements (stroma). Glands are classified into two major groups based on how their products are distributed.
Adenoma is a simple gland-forming tumor, where the cells arrange themselves in acini. Adenocarcinoma has more invasive characters of the same tumor. Lack of differentiation is called anaplasia, and such anaplastic tumors are highly malignant. Highly undifferentiated tumors are more malignant. Thyroid gland adenocarcinoma or pituitary adenocarcinoma is two examples of undifferentiated tumors. In some instances, adenomas retain the secretions and form a cyst, when it is called cystadenoma, which may reach enormous sizes sometimes, eg., cystadenoma of the ovary.
Exocrine glands secrete their products onto a surf ace through ducts or tubes.
Endocrine glands lack a duct system and have lost their original embryonic connections to the surfaces from which they invaginated. They often lack a true surface. They secrete their products into the connective tissue from which they enter the bloodstream in order to reach their target cells. The products of endocrine glands are called hormones. Endocrine glands are ductless, and secrete into the blood.
In some epithelia, individual cells secrete a substance that does not reach the bloodstream but has an effect on other cells within the same epithelium. Such secretory cells or glands are known to be acting in a paracrine fashion. The secretory material reaches the target cells by diffusion through the extracellular space. Exocrine glands are classified as either unicellular or multicellular.
Unicellular glands are the simplest in structure. In this instance, the secretary component consists of single cell distributed among other cells that are not secretary. A typical example is the Goblet cell. The Goblet cell secretes mucus and is located among other columnar cells in the surface lining and glands of the intestine and in certain passages of the respiratory tract.
TOPIC: CARTILAGE
Cartilage is the connective tissue type that has a consistency in between loose connective tissue like adipose and dense like bone. It is not as hard, but is flexible. Cartilage functions in giving architectural support. All fetal bones for instance, are built upon cartilage prototype called hyaline cartilage. Hyaline cartilage skeleton forms the basis of long bones as well.
Chondrocytes along with a firm, gel-like extracellular matrix form the basic components of a cartilage. Nerves and blood vessels do not penetrate cartilage. Cartilage types are distinguished on the basis of the amount of ECM and collagen or elastin in it. Hyaline cartilage is the archetype form. Hyaline cartilage is seen in tracheal rings, nose, larynx, joints, ventral rib ends. Hyaline cartilage is also seen in articular surfaces and epiphyseal plate.
Hyaline cartilage seen in the articular cartilage and growth plates are devoid of perichondrium thereby, lacking a steady source of chondrogenic cells.
Fracture of articular cartilage and growth plate is considered prognostically poor, as there is no perichondrium. Appositional growth is not possible in such fractures. There is limited regeneration of cartilage by interstitial growth. However, infusion of chondroblasts from a different site can form new cartilage.
Cartilage degeneration is common in old age, and may often lead to loss of mobility and pain in the articular areas. When cartilage degenerates, it frequently leads to calcification of the cartilage. Cartilage regeneration is usually poor in adults.
Elastic cartilage: Is seen in several locations, such as pinna of external ear, walls of auditory and eustachian canals, epiglottis, and larynx (cuneiform and corniculate cartilages). The matrix has abundant frequentlybranching elastic fibers. Elastic fibers give a yellow tinge to the elastic cartilage. In contrast to hyaline cartilage, elastic cartilage has fine, crisp cartilage fibers and the isogenous groups are indistinct and numerous in number.
Fibrocartilage: At sites of insertion of ligaments and tendons to bone, in intervertebral disks and pubic symphysis, fibrocartilage is the type seen. These are the areas where there is extreme stress due to mechanical pull. These sites need to resist the extreme forces of weight and tension. There is predominance of collagen Type I, hence it stains more acidophilic. It has little amorphous matrix rich in Chondroitin SO4 and Dermatan SO4. Chondrocytes are alligned as linear arrays, rather than as clusters. In intervertebral disk, the hyaluronic acid rich nucleus pulposus is surrounded by the annulus fibrosus, which is the fibrocartilage. As there is no perichondrium in fibrocartilage, fractures or damage to this is also considered of poor prognostic value.
Intervertebral disk rupture is due to tearing of the laminae of annulus fibrosus. The nucleus pulposus extrudes out of the posterior aspect of the disk rupture. Frequently, the disk may slip or dislocate. The disk compresses on the spinal nerves.
Chondrosarcoma is commonly seen in the ends of long bones and may also develop from benign enchondromas in the small bones of hands or ilium. They are more likely to be seen in adults. Areas of intermitent cartilage alternates with sarcomatous tissue. Chondrosarcomas tend to be locally malignant and frequently not metastatic.
TOPIC: NERVOUS TISSUE Composition of Gray & White matter
Gray matter is composed of neuron cell bodies, dendrites, non-myelinated axons, neuroglial cells and blood vessels. Absence of myelin causes this region to have a gray color. White matter is composed of mostly myelinated nerve fibers along with some unmyelinated nerve fibers, neuroglial cells, but no neuron cell bodies. Its white color comes from abundance of myelin surrounding the axons. Myelin which is rich in lipid appears white in fresh tissue.
Cerebral infarction (softening), is caused by failure of the suply of oxygen and glucose to maintain ghe viability of the tissues in the territory of a cerebral arterial branch. Infarct is a local lesion of necrosis in the affected area. Arterial stenosis due to atheroma, leads to potential reduction in the luminal diameter and along with systemic circulatory defects can lead to infarction.
1
8
|