Histology Lecture 5 PDF

24 (II) Connective Tissue Fibers White Collagen Yellow Elastic Reticular Fibers Fibers Fibers Origin Mainly Fibroblasts Fibroblasts Fibroblasts...

24 (II) Connective Tissue Fibers White Collagen Yellow Elastic Reticular Fibers Fibers Fibers Origin Mainly Fibroblasts Fibroblasts Fibroblasts (+ chondroblasts & osteoblasts) LM Wavy branching Thin long Very thin fibers that branch & bundles, formed of branching fibers. anastomose forming a non-branching parallel Run singly not in network fibers bundles. Drawing ‫اﻟﻔ‬ ‫ﺻ‬ ‫ل اﻟ‬ ‫ا‬ ‫ﻟﻔر ﺳﻲ‬ Color & - Colorless when - Yellow in color Brown with Silver stain stain single, white when when fresh. (argyrophilic) ‫درا‬ ‫ﻗﺔ اﻻ‬ condensed. - Pink in H&E - Pink in color in H&E - Brown with (acidophilic) Orcein. ‫اﻻ ول‬ Character Strong , rigid & Stretchable Delicate & flexible not elastic Function Give strength to Give elasticity to Form the stroma ‫و‬ tissues & resist tissues (background) which supports stretching organs ‫ﻟﻲ‬ Types Many types, the most one type one type important are; I, II, III, IV,V, VII. Types of Connective Tissue Proper Classified according to the relative abundance of the basic components into: (I) Loose C.T. (II) Dense C.T. 1- Loose (Areolar) C.T. 1- White Fibrous C.T. 2- Reticular C.T. a-Regular b- Irregular 3- Mucoid C.T. 2- Yellow Elastic C.T. 4- Adipose C.T.  25 (I) Loose Types of C.T. Proper 1- Loose (Areolar) C.T.: (The most common type) Structure: - It contains: - All types of C.T. cells (mainly fibroblasts, fat cells & macrophages) and all types of C.T. fibers (mainly collagen), embedded in a loose matrix. - Contains potential cavities (areolae), which may be filled with fluids or gases. Sites: 1- Present allover the body except the brain. ‫اﻟﻔ‬ 2- Around organs and blood vessels. 3- Under epithelium; in submucosa & ‫ﺻ‬ dermis of skin. Functions: ‫ل اﻟ‬ 1- It binds tissues together & surrounds ‫ا‬ ‫ﻟﻔر ﺳﻲ‬ organs.. 2- It supports epithelium and blood vessels. ‫درا‬ ‫ﻗﺔ اﻻ‬ 2- Reticular C.T.: Structure: It is formed of: ‫اﻻ ول‬ a) Reticular Fibers: fine branching fibers. b) Reticular Cells: These are modified fibroblasts. ‫و‬ They are branched cells with long processes that ‫ﻟﻲ‬ are connected with each other. Reticular cells and fibers form a network (reticulum) which is stained brown by Silver stain (Ag). Sites& functions: Both reticular cells and fibers form the framework (Stroma) of organs (to support the functioning cells) e.g. lymph node, spleen & liver 3- Adipose C.T. It is a loose C.T., in which fat cells predominate. It consists of groups of fat cells, separated by fibrous septa.  26 There are 2 types: White Adipose C.T. Brown Adipose C.T. Structure: - Unilocular fat cells: large - Multilocular fat cells: small with flat peripheral nucleus with central rounded nucleus - Each cell contains a large - Each cell contains many fat single fat droplet. droplets. - Fat is not pigmented. - The fat is pigmented due to: - Poor blood supply a) High vascularity b) Cytochrome pigments in mitochondria ‫اﻟﻔ‬ ‫ﺻ‬ Sites: ‫ل اﻟ‬ - Under the skin *In fetus & newborn: ‫ا‬ ‫ﻟﻔر ﺳﻲ‬ - Mammary gland. - Interscapular region & axilla - Around the kidney *In adults only around thoracic aorta ‫درا‬ Functions: - Storage of fat. ‫ﻗﺔ اﻻ‬ - Heat insulator - Heat generation (in - Support of organs e.g. newly born infants) kidney. ‫اﻻ ول‬ - Forms the body contours, especially in females. ‫و‬ 4- Mucoid C.T.: ‫ﻟﻲ‬ Structure: Formed of: - Large amount of jelly-like ground substance rich in mucus and hyaluronic acid. - UMCs & fibroblasts that communicate by their processes. - Fine collagen fibers Sites: - Umbilical cord (Known as Wharton′s Jelly) - Pulp of.growing teeth - Vitreous humor of the eye Function: It protects near-by structures from pressure.  27 (II) Dense Types of C.T. Proper 1- White Fibrous C.T.: Structure: Formed of: Bundles of collagen fibers and fibroblasts with minimal ground substance. Types: 2 types according to the arrangement of collagen bundles: Regular White Fibrous C.T. Irregular White Fibrous C.T. Structure Parallel collagen bundles with Irregulary arranged collagen bundles fibroblasts in-between with fibroblasts in-between ‫اﻟﻔ‬ ‫ﺻ‬ ‫ل اﻟ‬ ‫ا‬ ‫ﻟﻔر ﺳﻲ‬ Sites - Tendons - Cornea - Periosteum - Perichondrium - Dermis of skin - Capsule of organs ‫درا‬ ‫ﻗﺔ اﻻ‬ Function Withstand stretch in one direction Withstand stretch in different directions ‫اﻻ ول‬ 2-Yellow Elastic C.T.: ‫و‬ Structure: Formed of: ‫ﻟﻲ‬ - Mainly elastic fibers (so appears yellow in fresh state) - Fibroblasts. Sites: - Aorta - Bronchi & bronchioles - Ligaments Function: Recoil after stretch.  28 Chapter 4 Cartilage Intended Learning Outcomes (ILOs) By the end of this chapter, the student should be able to: 1- Describe the histological structure of different types of cartilage (hyaline, yellow elastic & white fibrocartilage). 2- Differentiate between the three types of cartilage. ‫اﻟﻔ‬ 3- Elucidate the sites of each type of cartilage. ‫ﺻ‬ Definition: It is a specialized type of C.T. in which the matrix is rubbery (firm but flexible) to bear mechanical stress. ‫ل اﻟ‬ Characters of cartilage: ‫ا‬ ‫ﻟﻔر ﺳﻲ‬ Being a type of C.T., cartilage is formed of cells, fibers and ground substance (matrix). ‫درا‬ ‫ﻗﺔ اﻻ‬ The cells are widely separated by a considerable amount of intercellular substance (matrix). Cartilage is avascular (non-vascular), nourished by diffusion of O2 & nutrients ‫اﻻ ول‬ from surrounding C.T. or synovial fluid in the joint cavities. ‫و‬ It has no lymph vessels or nerves. ‫ﻟﻲ‬ Types of cartilage: There are three types of cartilage based on the amount of ground substance and the type of fibers embedded in it. These types are hyaline, yellow elastic and white fibrocartilage. Hyaline cartilage has the typical structure of cartilage. The other types are considered as variants of its basic structure. 1- Hyaline Cartilage The most common type. It appears translucent, with glassy appearance, (Hyalo = glass).  29 Sites: 1- Fetal skeleton 2- Epiphyseal plate 3- Costal cartilage 4- Articular surface of joints 5- Respiratory passages (nose, larynx, trachea & bronchi). Structure: A) Perichondrium: it is a capsule-like structure formed of dense fibrous C.T. that surrounds the hyaline cartilage except at the articular surface of joints. It is formed of two layers: 1- Outer fibrous layer: white fibrous C.T. formed of fibroblasts, collagen fibers (Type I), it is rich in blood vessels & nerves. ‫اﻟﻔ‬ 2- Inner chondrogenic (cellular) layer: rich in chondrogenic cells and chondroblasts. ‫ﺻ‬ Functions of Perichondrium: Nutrition of non-vascular cartilage (by diffusion). ‫ل اﻟ‬ Provides attachment for muscles. ‫ا‬ ‫ﻟﻔر ﺳﻲ‬ Formation of new cartilage cells during growth. ‫درا‬ ‫ﻗﺔ اﻻ‬ ‫اﻻ ول‬ ‫و‬ ‫ﻟﻲ‬ B) Cartilage Cells: 1- Chondroblasts (immature cartilage cells): Origin: arise from UMCs. Site: always on the surface of cartilage, at the inner aspect of perichondrium.  30 L.M.: Flat to oval or spindle in shape, with deeply basophilic cytoplasm. Flat, pale stained nucleus, with prominent nucleolus. They can divide. EM: Features of protein forming cells (euchromatic nucleus, abundant ribosomes, rER, large Golgi apparatus & many mitochondria). Functions: 1- Formation of cartilage matrix and change into chondrocytes. 2- Formation of cartilage collagen (type II). 3- Cartilage growth from outside (appositional growth). ‫اﻟﻔ‬ 2- Chondrocytes (mature cartilage cells): Origin: They develop from chondroblasts. When chondroblasts mature, ‫ﺻ‬ they secrete enough matrix to be completely surrounded by it and imprisoned in lacunae, they are now called chondrocytes. ‫ل اﻟ‬ L.M.: ‫ا‬ Rounded with pale basophilic cytoplasm. ‫ﻟﻔر ﺳﻲ‬ Rounded, darkly-stained, central nucleus. ‫درا‬ ‫ﻗﺔ اﻻ‬ Embedded in the matrix inside spaces called lacunae, either singly or in groups and surrounded by capsule of condensed matrix. The superficial cells are small, oval and single in their lacunae & ‫اﻻ ول‬ parallel to the surface. ‫و‬ The older cells become deeper in the matrix. They are rounded or triangular. They divide once or twice giving clusters of cells formed of 2 ‫ﻟﻲ‬ or 4, up to 8 cells (isogenous groups) surrounded with darkly stained capsule of condensed matrix. This group of cells is called cell nest. They account for interstitial growth of cartilage. E.M.: Features of protein forming cells. Functions: Maintain the cartilage matrix, by continuous secretion of new matrix around them. C) Fibers: Collagen fibers (type II). They can’t be seen by LM, so the matrix appears homogenous, and transparent. This is because: – Fibers are very thin. – Fibers have the same refractive index as the surrounding matrix.  31 D) Ground substance (Matrix): It is produced by chondroblasts and chondrocytes. It is rubbery, homogenous, transparent and deeply basophilic. The matrix consists of: proteoglycans, glycoproteins and water. 2- Yellow Elastic Cartilage It is yellow in fresh state, more opaque & flexible. Structure: Covered by perichondrium. ‫اﻟﻔ‬ Has the same structure of hyaline cartilage, but with large number of branching ‫ﺻ‬ elastic fibers embedded in the matrix forming a network that gives this type the yellow color, with few collagen fibers (type II). ‫ل اﻟ‬ Chondrocytes form small cell nests (mostly 2 cell isogenous groups). ‫ا‬ ‫ﻟﻔر ﺳﻲ‬ Sites: it is found where support with flexibility is required: ‫درا‬ Ear pinna. ‫ﻗﺔ اﻻ‬ Eustachian tube. ‫اﻻ ول‬ Epiglottis and some laryngeal cartilages External auditory canal. ‫و‬ ‫ﻟﻲ‬ White fibrocartilage Elastic cartilage  32 3- White Fibro Cartilage It is not surrounded with perichondrium. It is a tough type of cartilage which is important in bone to bone attachment. Structure: It is formed of dense collagen fibers (type I), present in parallel thick bundles. Cartilage cells (chondrocytes) inside lacunae are present in rows between collagen bundles, embedded in very scanty matrix around them. Sites: Intervertebral disc. Mandibular joint. ‫اﻟﻔ‬ Symphysis pubis. Sternoclavicular joint. ‫ﺻ‬ Growth of Cartilage 1- Appositional Growth: It is the growth resulting from the addition of new layers of cartilage to the surface by the activity of the inner cellular layers of ‫ل اﻟ‬ ‫ا‬ perichondrium (chondroblasts). ‫ﻟﻔر ﺳﻲ‬ 2- Interstitial Growth: It is the growth of cartilage from inside by division of chondrocytes which proliferate and produce matrix around them. ‫درا‬ ‫ﻗﺔ اﻻ‬ ‫اﻻ ول‬ ‫و‬ ‫ﻟﻲ‬