Lecture 10 Connective Tissue (Part 1) PDF

HNU Faculty of Medicine Histology & Cell Biology Department Year 1 Principle of Human Body Structure HBS-101 Lecture 10 Connective Tissue Proper (Part 1)  objectives By the...

HNU Faculty of Medicine Histology & Cell Biology Department Year 1 Principle of Human Body Structure HBS-101 Lecture 10 Connective Tissue Proper (Part 1)  objectives By the end of this lecture the student will be able to: 1. Define the general character and structure of the connective tissue. 2. Classify connective tissue types. 3. Describe the histological structure (LM and EM) correlated to functions of UMCs, fibroblasts, pericytes , reticular cells. 4. Clinically correlate between keloid and palmar fibromatosis and the defective structures.  Connective tissue General characters: ❖ The connective tissue (C.T.) supports and connects various tissues and organs. ❖ Consists of cells, fibers and intercellular substance (matrix). ❖ It is rich in blood vessels and nerves. ❖ Is derived from the mesodermal embryo only. Types: 1) Connective tissue proper (soft). 2) Cartilage (rigid). 3) Bone (hard). 4) Blood (fluid). Components of C.T Proper: A) Connective tissue fibers: 1- Collagen fibers (Tense): (Most common) Characters: ❖Formed by fibroblast, chondroblast, osteoblast. ❖ White in fresh state. ❖ Strong & resist stretch. ❖ Form wavy bundles. ❖ Bundles branch, but single fiber doesn’t branch. ❖ Digested by pepsin and collagenase enzyme. ❖ Converted into gelatin by boiling. ❖ Affected by boiling. LM: H&E: acidophilic. Mallory trichrome: blue. Van Gieson's stain: red.  Types of collagen According to amino acids sequences, there are at least 28 types of collagen fibers: Major types Sites Type I Tendons, bones, dermis of the skin, dentin, cornea Type II Cartilage matrix Type III Reticular fibers (present in network that supports the organs e.g. spleen) Type IV Basal lamina Type V  E/M of collagen fibers: Collagen fibrils show transverse banding periodicity of 67 nm ( alternating light and dark bands). They represent gap regions and overlap regions between the tropocollagen molecules  Adjacent rod-like collagen subunits are staggered with small gaps between their ends.  TS LS  Medical application ( Collagenopathies) Osteogenesis imperfecta Repeated fractures after minor trauma, brittle bones, abnormal teeth, thin skin, weak tendons, blue sclerae, and progressive hearing loss  Medical application ( Collagenopathies) Keloid: is a local swelling caused by abnormal large amounts of collagen that form in scars of skin. It is common in Africans. 2- Elastic fibers: Characters: Formed by: fibroblast, chndroblast, smooth muscles ❖ Elastic in nature. ❖ Yellow in fresh state. ❖ Thin, long and highly refractile. ❖ Fibers branch and may form elastic membranes (wall of the aorta). ❖ Digested by elastase enzyme. ❖ Not affected by boiling. LM: - H&E: acidophilic. - Van Gieson's stain: yellow. - Brown by Orcein. With EM: they have NO axial periodicity and not made up of fibrils. They are formed of: Amorphous protein: elastin in the centre. Microfibrillar protein: surrounding elastin. Sites: 1. Walls of arteries. 2. Trachea. 3. Ligaments of the back.  Medical application Mutations in genes of fibrilin will results in improper deposition of elstic fibers with weakness in the wall of elastic arteries and formation of swelling called aortic aneurysm and rupture (life threating conditions). This is called Marfan’s syndrome.  Clinical Correlation : Sun Exposure and Photo-aged Skin Sunlight exposure accelerates aging : by altering the cross-linking that occurs between collagen molecules. These result in formation of collagen fibers with abnormal stability and decreased resistance to enzymatic degradation. 3- Reticular fibers: Characters: ❖ Very thin. ❖ Branch and anastomose to form network. LM: H&E: not stained Silver: black. Sites: Stroma of organs e.g. Liver, spleen.  Synthesized by fibroblasts and reticular cells and smooth muscles Formed mainly of collagen type III surrounded by glycoprotein.  E/M Because it is a type of collagen, they show the transverse banding (axial periodicity). B) Connective tissue cells: I. Rounded or oval cells: 1- Fat cells (adipocytes): Origin: U.M.Cs. Site: adipose and loose C.T. Nucleus: flattened & peripheral. Cytoplasm: large fat globule pushing the nucleus at one side. Stain: H&E: signet ring. Sudan III: orange. Sudan black: black. Osmic acid: black. Functions: 1) Storage of energy. 2) Heat insulation. 2- Plasma cells: Origin: activation of B lymphocytes. Site: lymphatic organs. Nucleus: rounded, eccentric & cart-wheel Cytoplasm: deep basophilic & negative Golgi image. Function: Secretion of antibodies (immunity). 3- Mast cells: Site: mucosa of the GIT & respiratory tract. Nucleus: rounded & central. Cytoplasm: Large basophilic granules. Stain: Toluidin blue: (metachromatic) → purple Functions: Secretion of histamine and heparin. 4- Blood leucocytes: Blood leucocytes leave the blood and appear in the C.T. in certain conditions, e.g.: 1) Eosinophils: in allergy. 2) Neutrophils: in acute infections. 3) Monocytes & lymphocytes: in chronic infections. Reference Junqueira's Basic Histology Text and Atlas, 17th edition by Anthony Mescher 26