A&P - 4.3 Connective Tissue Supports and Protects

overview of connective tissue

• serves to hold in place, connect, and integrate the body’s organs and systems

• most abundant tissue in the body

• highly variable in structure and function

• never exposed to the outside environment

functions of connective tissues

• binding of organs - tendons and ligaments

• support - bones and cartilage

• physical protection - cranium, ribs, sternum

• immune protection - white blood cells attack foreign invaders

• movement - bones provide lever system

• storage - fat, calcium, phosphorus, energy

• heat production - metabolism of brown fat in infants

• transport - blood, fluid, dissolved materials

main types of connective tissue

• fibrous tissue

• adipose tissue

• cartilage

• bone

• blood

characteristics of connective tissue

• all types of connective tissue originate from mesenchyme

• connective tissues vary widely in appearance and function but all forms share 3 basic components:

  • specialized cells

  • extracellular protein fibers

  • ground substance

• the function of the connective tissue comes from there fibers

mesenchyme

• loose embryonic tissue from which connective tissue cells derive

• contains mesenchymal cells which are undifferentiated stem cells that give rise to various adult connective tissues

specialized cells

• the cells present in each type of connective tissue helps to distinguish the various types from one another

• a few of the cells are listed here:

  • fibroblast cells = produce connective tissue proper

  • chondrocytes = produce cartilage

  • osteocytes = produce bone

  • hemocytoblast cells = produce blood

extracellular protein fibers

three primary fibers are produced in connective tissues

• elastic fibers = slender, straight, and very stretchy

  • contains a high percentage of the protein elastin that allows the fibers to stretch and return to original size

• collagen fibers = thick, straight or wavy, and often forms bundles

  • very strong and resist stretching

• reticular fibers = strong fibers that form a branching network or scaffolding

  • cross-link to form supporting “nets”

ground substance

fluid or semi-fluid material that fills the space between cells and surrounds the extracellular fibers

matrix

extracellular material which is produced by the cells embedded in it

• ground substance and extracellular fibers make up the matrix of connective tissues

connective tissue proper

• connective tissue containing a viscous matrix, fibers, and cells

• includes connective tissues with many types of cells and extracellular fibers in a gel-like substance

  • reticular fibers, adipocytes, mesenchymal cell, elastic fibers, collagen fibers, fibroblast, macrophage

• types of connective tissues

  • loose connective tissues (areolar tissue, adipose tissue, reticular tissue)

  • dense connective tissues (dense regular, dense irregular, elastic)

fibers of fibrous connective tissue

• collagenous fibers

• reticular fibers

• elastic fibers

collagenous fibers

• collagen is most abundant of the body’s proteins - 25%

• tough, flexible, and stretch-resistant

• tendons, ligaments, and deep layer of the skin are mostly collagen

• less visible in matrix of cartilage and bone

• common in dense irregular connective tissue, prevents hyperextension

reticular fibers

• thin collagen fibers coated with glycoprotein

• form framework of spleen and lymph nodes

elastic fibers

• thinner than collagenous fibers

• branch and rejoin each other

• made of protein called elastin

• allows stretch and recoil

• found in elastic tissue which is found in ear, the more elastin we have the more the tissue can stretch

types of fibrous connective tissue

• loose connective tissue

• dense connective tissue

loose connective tissue

• fibers created a loose, open framework

• much gel-like ground substance between cells

• types:

  • areolar tissue!!

  • adipose tissue

  • reticular tissue

areolar tissue

• DESCRIPTION: loosely organized fibers, abundant blood vessels, and a lot of seemingly empty space

• possess all six cell types

• fibers fun in random directions

  • mostly collagenous, but elastic and reticular are also present

• LOCATION: fills the spaces between muscle fibers, surrounds blood and lymph vessels, and supports organs in the abdominal cavity

• FUNCTION: nearly every epithelium rests on a layer of areolar tissue

  • blood vessels provide nutrition to epithelium and waste removal

    • vascular - direct blood supply

  • ready supply of infection-fighting leukocytes (white blood cells) that move about freely

• attaches skin to underlying body parts

lamina propria

areolar connective tissue underlying a mucous membrane

adipose tissue

• DESCRIPTION: loose connective tissue that consists of fat cells with little extracellular matrix

  • adipocytes - fat cells

• FUNCTION: stores fat for energy and provides insulation

• LOCATION: found deep to the skin, especially at the sides of waste, buttocks, and breasts

reticular tissue

• DESCRIPTION: loose connective tissue made up of a network of reticular fibers

• FUNCTION: provides a supportive framework for soft organs and resists distortion

• LOCATION: found in liver, kidney, spleen, lymph nodes, and bone marrow

• reticular fibers create a complex supporting network known as a stroma (framework)

mucous connective tissue

specialized loose connective tissue present in the umbilical cord

dense connective tissue

• fibers are densely packed together

• fibers fill spaces between cells

• fibers provide both elasticity and protection

• types vary in fiber orientation:

  • dense regular!!

  • dense irregular!!

  • elastic

dense regular connective tissue

• DESCRIPTION: consists of collagenous fibers packed into parallel bundles

  • densely packed, parallel collagen fibers

  • compressed fibroblast nuclei

• FUNCTION: provides strength along the axis of the collagen fibers

• LOCATION: found in cords (such as tendons) or sheets (ligaments)

difference between tendons and ligaments

• tendons connect muscle to bones

• ligaments connect bones to bones

dense irregular connective tissue

• DESCRIPTION: consists of collagenous fibers interwoven into a mesh-like network

  • densely packed, randomly arranged (non-parallel), collagen fibers and few visible cells

• FUNCTION: provide strength in many directions and are particularly important in areas subjected to stress from many directions such as the dermis of the skin

  • withstands unpredictable stress

• LOCATION: deeper layer of skin (dermis); capsules around organs

elastic tissue

• DESCRIPTION: when elastic fibers outnumber collagen fibers, the tissue has a springy, resilient nature 

• FUNCTION: elasticity allows it to tolerate cycles of extension and recoil

• LOCATION: bound between vertebrae of the spinal column and the erectile tissues of the penis

fluid connective tissue

specialized cells that circulate in a watery matrix that contains salts, nutrients, and dissolved proteins

• types:

  • blood

  • lymph

blood

• DESCRIPTION: fluid connective tissue containing erythrocytes and various types of leukocytes that circulate in a liquid extracellular matrix

• LOCATION: flows within the cardiovascular system

• FUNCTION: hemocytoblasts (specialized cell) gives rise to three formed elements suspended in plasma:

  • erythrocytes; red blood cells - transport oxygen and carbon dioxide

  • leukocytes; white blood cells - help defend the body from infection and disease

  • thrombocytes; platelets - cell fragments that are involved in the clotting response that seals broken blood vessels

lymph

• DESCRIPTION: forms as interstitial fluid enters a lymphatic vessel

• FUNCTION: lymph passes through lymph nodes where it is cleaned and filtered

• LOCATION: flows within the lymphatic system

supporting connective tissue

• type of connective tissue that provides strength to the body (supports the weight of the body) and protects soft tissue

• less diverse cell population and a matric containing much more densely packed fibers

• types:

  • cartilage

  • bone

cartilage

• connective tissue consisting of collagenous fibers embedded in a firm, solid, rubbery matric containing chondrocytes; stiff connective tissue with flexible matrix

• no (rarely) blood vessels

  • diffusion brings nutrients and removes wastes

  • heals slowly (because it doesn’t have the supply of nutrients since its avascular)

• types of cartilage vary with fiber composition:

  • hyaline cartilage

  • elastic cartilage

  • fibrous cartilage

chondroblasts

cartilage cells that produce the matrix that will trap them

chondrocytes

cartilage cells that are trapped in lacunae (cavities) - chondroblast is sealed off in a lacunae within the matrix

• contains a reserve population of chondroblasts that contribute to cartilage growth throughout life

lacunae

(singular = lacuna) small spaces in bone or cartilage tissue that cells occupy

hyaline cartilage

• DESCRIPTION: most common type of cartilage, smooth and made of short collagen fibers

• FUNCTION: provides support with some flexibility and reduces friction between bony surfaces

• LOCATION: found connecting the ribs to the sternum, covering the articular surface of long bones, supporting the respiratory passageways such as the trachea, and forming the tip of the nose and part of the nasal septum 

  • trachea (rings) and the part of the bone in joints is covered in hyaline

fibrocartilage

• DESCRIPTION: tough form of cartilage, made of thick bundles of collagen fibers

• FUNCTION: provides some compressibility and can absorb pressure

• LOCATION: found within the intervertebral discs, the meniscus of the knee, and pubic symphysis

elastic cartilage

• DESCRIPTION: type of cartilage, with elastin as the major protein

• FUNCTION: provides firm but elastic support; characterized by rigid support as well as elasticity

• LOCATION: found in the ear and epiglottis