Connective Tissue General Features  Two basic elements: cells and an extracellular matrix  Types of cells listed on next slide  The matrix is made with a ground substance and fibers  Not very cellular compared to the other types of tissue  Does not occur on body surfaces  Has a nerve supply, except cartilage  Usually highly vascular except cartilage (avascular) and tendons  Various tissue types confer a variety of functions

Types of Connective Tissue Cells  Fibroblasts- secrete collagen and other fibrous proteins  Macrophages- phagocytic cells that engulf and digest foreign particles  Plasma Cells- produce antibodies  Mast Cells- produce histamine, which dialates blood vessels, and heparin, an anticoagulant  Adipocytes- store fat  Erythrocytes- red blood cells, transport oxygen  Leukocytes- white blood cells, several different types, function in immunity  Thrombocytes- blood platelets, aid in blood clot formation  Chondroblasts- forms the extracellular matrix of cartilage  Chondrocytes - maintains the matrix of cartilage  Osteoblasts- forms the extracellular matrix of bone  Osteocytes - maintains the extracellular matrix of bone -blast – a cell that produces and secretes elements of the extracellular matrix -cyte – typically a mature cell that preforms the function of the tissue

Connective Tissue Extracellular Matrix  Ground substance can be Fluid Fluid Semifluid Semifluid Gelatinous Gelatinous Hard Hard  Three Types of Fibers Collagen – thick, provide strength Collagen – thick, provide strength Elastin – thick and stretchy, provide strength and elasticity Elastin – thick and stretchy, provide strength and elasticity Reticular – fine branching collagen fibers, provide a net-like framework Reticular – fine branching collagen fibers, provide a net-like framework

Two Major Types of Connective Tissue  Embryonic – found in the embryo and fetus  Mature – present in newborns to adults

Types of Mature Connective Tissue  Loose Connective Tissue  Dense Connective Tissue regular regular irregular irregular elastic elastic  Cartilage hyaline hyaline elastic elastic fibrocartilage fibrocartilage  Bone  Blood  Lymph

Loose Connective Tissue In Loose Connective Tissue, the fibers in the extracellular matrix are loosely arranged. The ground substance in semifluid (viscous). Some cells reside permanently in the matrix; cells involved in immunity enter the matrix from blood and are transient. Loose Connective Tissue includes:  Areolar Connective Tissue  Adipose Tissue  Reticular Connective Tissue

Areolar Connective Tissue All three fibers (collagen, elastin and reticular) and several kinds of cells, including fibroblasts, adipocytes, macrophages and mast cells are embedded in a semifluid ground substance Areolar is the most abundant type of connective tissue Found in the subcutaneous layer deep to skin, superficial part of dermis, mucus membranes, around blood vessels, nerves and body organs Function: supports and connects

Areolar Connective Tissue

Reticular Connective Tissue The dominant fiber is recticular fiber. Reticulocytes are fibroblasts that produce more reticular fiber than collagen. The ground substance is semifluid. Found in lymph nodes and other nonmuscular organs Provides a support structure for cells including (in lymph nodes) macrophages and other cells involved in immunity.

Reticular Connective Tissue

Adipose Tissue Contains fibers, fibroblasts and adipocytes embedded in a semifluid ground substance. Has a great number of adipocytes and very little matrix. Adipocytes can appear “empty” on slides. Surrounds organs, abundant in the greater omentum, subcutaneous layer deep to the dermis of the skin Function: provides storage for energy-rich lipids, cushioning and insulation for organs

Adipose Tissue

Dense Regular Connective Tissue The extracellular matrix consists of tightly packed parallel bundles of collagen fibers with very little ground substance. Fibroblasts are squeezed between the collagen bundles Makes up tendons and ligaments Function: provides resistance to pulling forces while providing flexibility

Dense Regular Connective Tissue Tendon

Dense Irregular Connective Tissue The matrix has little ground substance and few fibroblasts. The matrix is packed with bundles of collagen fibers which are irregularly arranged (i.e. not in parallel to each other). Found in the dermis of the skin Function: Provides strength and support of organs

Dense Irregular Connective Tissue

Dense Elastic Connective Tissue Extracellular matrix is packed with elastic fibers, which mostly run parallel to each other, few fibroblasts and consists of very little ground substance. Found in the aorta Function: allows tissue to be stretched and then regain its original size and shape

Elastic Connective Tissue in the Aorta

Cartilage The extracellular matrix consists of collagen and elastic fibers embedded into a gelatinous ground substance. Chondroblasts secrete fibers and ground substance and become isolated in spaces called lacunae (little lakes or pools) and then transform into chodrocytes. Cartilage is avascular and receives nutrients through diffusion from adjacent vascular tissue

Hyaline Cartilage Contains collagen fibers which are thin and not visible with a compound light microscope. Hyaline cartilage appears glassy to the eye. Chondrocytes are found in lacunae. The most abundant type of cartilage in the body. Found at the end of bones (articular), attaching ribs to the sternum (costal), in the nose (nasal) and in the trachea and bronchi. Function: provides support, reduces friction from moving bones, provides flexibility that allows movement without fracture

Hyaline Cartilage

Elastic Cartilage The matrix is packed mostly with elastic fibers. Chondrocytes are located in lacunae. Ground substance is gelatinous. Found in the external ear and epiglottis of the larynx Function: provides flexible support

Elastic Cartilage

Fibrocartilage Extracellular matrix is packed with thick collagen fibers. Has fewer lacunae and chrondrocytes than the other types of cartilage. Found in intervertebral discs and the menisci of the knees Function: provides cushioning and reduces friction

Fibrocartilage

Compact Bone The extracellular matrix consists of collagen fibers and a hard ground substance in mostly calcium salts, are deposited. Osteocytes are located in lacunae. Little canals, or canaliculi serve as passages ways for nutrients and wastes.

The has layers called lamellae. The lamellae form concentric rings that make up an osteon. In the center of each osteon is a large central canal, sometimes referred to as a Haversian Canal, which contains blood vessels and nerves Found in the skeleton of all vertebrates. Function: protects and provides support for body organs, provides levers to make movement possible, support for the body.

Ground Compact Bone

Blood The ground substance is a straw-colored fluid called plasma. Suspended in the plasma are erythrocytes, or red blood cells, leucocytes, or white blood cells, and thrombocytes, or platelets. Fibers are only present during clotting. Found in blood vessels throughout the body. Function: transports nutrients and vital molecules, wastes and molecular signals (hormones, etc.) throughout the body.

Human Blood