Lecture 5 - Connective Tissue

What are the main functions of connective tissue?

*most abundant and widely distributed primary tissue

Connective tissue proper: bind and support, insulate, store reserve fuel

Bone: protect, bind and support

Cartilage: protect, bind and support

Blood: transport substances

Defining Characteristics of all Connective Tissues

1. originated from mesenchyme tissue

2. varying degrees of vascularity

3. cells suspended in extracellular matrix (ground substance + fibers

• allows tissue to bear weight, withstand tension, etc

What are the types of connective tissue cells?

“Blasts” are immature form of cells that secrete ground substance and ECM fibers

“Cytes” are mature form of cells that maintain the health of the matrix

• Fibroblasts/cytes: in connective tissue proper

• Chondroblasts/cytes: in cartilage

• Osteoblasts/cytes: in bone

What are the types of connective tissue fibers?

1. Collagen: strongest and most abundant, tough, high tensile strength

2. Elastic fibers: long, thin elastin fibers that allow for stretch and recoil

3. Reticular: made of same proteins as collagen fibers but are shorter and highly branched which allows for more “give”/stretch

What is ground substance made of?

• gel-like material that fills the space between cells

• Made of:

  • cell adhesion proteins (act like glue)

  • Sugar proteins (proteoglycans)

  • water & interstitial fluid

Types of Connective Tissue Proper

1. Loose connective tissues

   1. areolar

   2. adipose

   3. reticular

2. Dense connective tissues

   1. dense regular

   2. dense irregular

   3. elastic

Cell type of all: fibroblasts/cytes

White Fat of Adipose Tissue (loose connective)

• Cell type: adipocytes

• stores nutrients, very small matrix (little room between cells), highly vascular

• Functions: shock absorption (found surrounding joints), insulation, & energy storage

Brown Fat of Adipose Tissue (loose connective)

• Cell type: fibroblasts/cytes

• lots of mitochondria = produces ATP

• heats bloodstream

Dense Regular Tissue (dense connective)

Cells: fibroblasts/cytes

• make/secrete collagen fibers and ground substance

Fibers: collagen

• thick bundles of collagen fibers all running in the same direction

• high resistance to pulling, fibers are wavy so they stretch, low vascularity

Where is dense regular tissue found?

tendons and ligaments

What does dense regular tissue look like?

Dense Irregular Tissue (dense connective)

Cells: fibroblasts/cytes

Fibers: collagen

• fibers of collagen are thicker and randomly arranged, form sheets

• resist tension from MANY directions

Where is dense irregular tissue found?

Dermis of skin (under epidermis)

Fibrous joint capsules

What does dense irregular tissue look like?

Elastic Tissue (dense connective)

Cells: fibroblasts/cytes

Fibers: elastic

• allows tissues to recoil after stretching

• maintains blood flow by allowing the arteries to stretch when blood enters and recoil when blood goes out

Where is elastic tissue found?

walls of large arteries (ex: aorta)

some ligaments (ex: ones that connect vertebrae)

What does elastic tissue look like?

Cartilage as a Connective Tissue

Cells: chondroblasts/cytes

• think C in cartilage - C in chondroblasts

Fibers: collagen and elastic (in some)

• tough, flexible material with NO nerves

• No blood vessels = no blood flow so receives nutrients from the surrounding membrane

• Perichondrium produces the fibroblast/cyte cells

• matrix made of water, collagen fibers, and sugar proteins

Hyaline Cartilage

• most abundant

• has collagen and elastic fibers

• locations: tips of long bones, nose, trachea, larynx, cartilage of ribs

Elastic Cartilage

• more elastic fibers than hyaline

• has collagen and elastic fibers

• locations: ears and epiglottis (flap in the throat behind the tongue)

Fibrocartilage

• the middle man of properties of hyaline and elastic cartilages

• only has collagen fibers

• locations: intervertebral discs and knee

Blood as a Connective Tissue

Cells: red blood cells, white blood cells, platelets

• does not contain fibers

• matrix is called plasma

• transports nutrients, wastes, gases, etc

Bone as a Connective Tissue

Cells: osteoblasts/cytes

• think osteoporosis is a bone disease, and cell name is similar

Fibers: collagen

• called osseous tissue

• matrix is ground substance calcified with inorganic calcium salts

• more collagen fibers than cartilage

• LOTS of blood vessels

• stores calcium and fat

• bone marrow inside is where blood cells are created

• has cavities in the matrix called lacunae - tiny “canals” where nutrients/waste move through

  • osteocytes are housed in lacunae

What is bone remodeling?

the replacement of bone through both bone deposition (creation) and bone resorption (getting rid of old bone)

Where does bone remodeling occur?

• both spongy and compact bone

• both outer and inner surfaces of bones

  • periosteum: outer surface

  • endosteum: inner surface

Bone Deposition

osteoblasts creating new bone

Bone Resorption

osteoclasts digesting old bone

• secrete lysosomal enzymes that digest the matrix

• acidity dissolves calcium salts

• also phagocytize dead osteocytes and demineralized matrix

Hormonal Controls of Bone Remodeling

• dictates WHEN bone addition/resorption occurs

• Parathyroid Hormone is produced by the parathyroid glands when there are low blood calcium levels

  • stimulates osteoclasts to resorb bone —> takes the calcium from it and releases it into the bloodstream to raise levels

  • PTH secretion stops when homeostatic level is reached again

  • negative feedback response

Mechanical Stress Impact on Bone Remodeling

• dictates WHERE to add/remove bone

• bones directly reflect the stresses that they encounter

• The segments of bone experiencing tons of stress will react by adding new bone and making that area thicker