Descriptive Histology CLS 222 Ch 3: Connective tissue Descriptive Histology CLS 222 Saida Almashharawi

Objectives Definition of connective tissue Function of connective tissue Structure of connective tissue Characteristics of connective tissue Cells of connective tissue Extra cellular matrix

Introduction DEFINITION It is one of the four general classes of animal tissues- as well as epithelial, muscle and nervous tissues. Is a kind of animal tissue that connects, supports, binds, or separates other tissues or organs of the body. It is the most diverse tissue and is found throughout the body Unlike epithelial tissue, connective tissue has relatively little intimate contact between the cells that make up part of its structure

Function Storage of energy Protection of organs Provision of structural framework for the body Connection of body tissues Connection of epithelial tissues to muscle fiber. Transportation of fluids and dissolved substances Defend the body against microorganisms Repair of body tissue

Structure of connective tissue Structurally, connective tissue  is made up of cells and extracellular matrix. The extracellular matrix is made up of protein fibers in and polysaccharide matrix, secreted and organized by cells in the extracellular matrix. Variations in the composition of the extracellular matrix, determines the properties of the connective tissue. For example, if the matrix is calcified, it can form bone or teeth.

Characteristics of connective tissue Cells are spread through an extracellular fluid. Ground substance - A clear, colorless, and viscous fluid containing glycosaminoglycans and proteoglycans to: fix the body water and the collagen fibers in the intercellular spaces, fills the space between the cells and contains the fibers. Ground substance slows the spread of pathogens. Fibers. Not all types of CT are fibrous. Examples of non-fibrous CT include adipose tissue and blood.

Cells of connective tissue A variety of cells with different origins and functions are present in connective tissue Fibroblasts Mast cells Macrophages plasma cells Adiposities cells

Cell types Extracellular matrix Ground substance Macrophage Fibers • Collagen fiber • Elastic fiber • Reticular fiber Fibroblast Lymphocyte Capillary Fat cell Mast cell Neutrophil

Cells of connective tissue Origin of cells : Fibroblasts : Originate from undifferentiated mesenchymal cells spend all their life in connective tissue mast cells, macrophages, and plasma cells : Originate from hematopoietic stem cells in bone marrow These are all types of Immune cell. circulate in the blood, and then move into connective tissue where they remain and execute their functions.

Cells of connective tissue Fibroblasts They are mainly responsible for secreting the non-rigid extracellular matrix including the fibers collagen, elastin or fibronectin. Two stages of activity: active fibroblasts inactive fibroblasts. Cells with synthetic activity are morphologically distinct from inactive fibroblasts that are scattered within the matrix they have already synthesized.

Cells of connective tissue Active fibroblast Large, euchromatic, oval nucleus Cytoplasm not usually visible but contains abundant rough endoplasmic reticulum and Golgi apparatus Elongated, spindle-shaped cells High synthetic activity

Active fibroblast

Cells of connective tissue Inactive fibroblast Small, heterochromatic, flattened nucleus. Reduced cytoplasm and organelles. Low synthetic activity.

Cells of connective tissue 2.Macrophages Derived from blood monocytes Enter connective tissue from the bloodstream and rapidly transform into macrophages Are large cells with more cytoplasm than lymphocytes or plasma cells. They have no granules and function to ingest other cells and bacteria by phagocytosis, antigen processing, and cytokine secretion.

Cells of connective tissue 3.Mast cells Releasing immune modulators from cytoplasmic granules, in response to antigen binding with cell surface antibodies. Mast cells secrete histamine, heparin and other factors. They are important in the uptake of fatty acids from the blood into fat cells.

Cells of connective tissue 4.Plasma cells Secrete antibodies to provide humeral immunity Derived from B-lymphocytes take up residence in lymph nodes, bone marrow, and loose connective tissue where they synthesize and secrete specific antibodies.

Cells of connective tissue 5. Adipose cells Adipocytes are connective tissue cells that have become specialized for storage of neutral fats or for the production of heat.

Extracellular matrix Fibers: Collagen fibers Reticular fibers Elastic fibers

Collagen fiber Collagen is the most common protein found in the human body. It is found in almost all organs and body parts. In general, collagen winds itself into a fiber mesh that adds structural stability to that specific body part. It is commonly associated with skin integrity, but is critical for proper function of many other body parts too. At least 12 types of collagen exist, four of which are commonly found in different body parts. Type I collagen is the most abundant type

Reticular fiber  Composed of type III collagen secreted by reticular cells. Reticular fibers crosslink to form a fine meshwork (reticulin). This network acts as a supporting mesh in soft tissues such as liver, bone marrow, and the tissues and organs of the lymphatic system.

Elastic fiber  Are bundles of proteins (elastin) found in extracellular matrix of connective tissue  produced by fibroblasts and smooth muscle cells in arteries. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed. Elastic fibers include elastin, elaunin and oxytalan.

Extracellular matrix Ground substances It is a jelly like substance having proteins and sugars, -in bone the ground substance include minerals, and - in blood the ground substance is the plasma

Homework #2 1- Define the connective tissue? 2-What are the functions of the connective tissue? 3- What are the types of cells present in connective tissue ? 4- What are the types of fibers present in the C.T.?