Connective tissues are composed of cells separated by an extracellular matrix. The matrix contains protein fibers like collagen, elastic fibers, and reticular fibers which are secreted by fibroblasts. Connective tissue includes specialized types like cartilage, bone, blood, as well as loose and dense connective tissue. Cartilage provides structure and protection to joints, bone forms the skeleton, and blood transports cells and proteins throughout the body.
2. Characteristics of Connective Tissues (CT)
Cells are separated by non-cellular material, called the
extracellular matrix
Most connective tissues have good blood supply
Most cells divide (to recover from injury)
Elastic Cartilage
Extracellular
matrix
nucleus of cell
3. Cell Types
Cells of CT may either be fixed in place (resident cells) or they
may be wandering cells
Examples of fixed cells
Fibroblasts
Secretes protein fibers into matrix
Fibroblast
Mast Cells
Secretes histamine & heparin into blood
Mast Cell
4. Wandering cells move throughout the tissues.
Example of a wandering cell: Macrophages
Macrophages actively move about during infection
phagocytizing bacteria & debris.
macrophages
5. extracellular matrix of connective tissues
The matrix of most CT contains protein fibers &
a non-protein ground substance
Protein Fibers
Protein fibers are secreted by fibroblasts.
3 types of protein fibers include
elastic fibers, collagen fibers, and reticular fibers
6. Protein Fibers
1. Collagenous fibers
Thick bands of protein
Collagen fibers are flexible, but only slightly elastic
They exhibit great tensile strength that resists pulling
Collagenous fibers forms the bulk of ligaments & tendons
Most abundant protein in mammals
Ligaments connect bone to bone
Tendons connect muscle to bone
7. Protein Fibers
2. Elastic Fibers
Composed of a spring-like protein, called elastin.
Elastic fibers are weaker than collagen, but exhibit elastic recoil
Elastic fibers can be easily stretched or deformed and they retain their
shape.
Locations: vocal cords, respiratory tract, blood vessels
8. Figure 5.17 Scanning electron micrograph of collagenous fibers and elastic fibers
9. Protein Fibers
3. Reticular Fibers
Consist of thin strands of collagen fibers
Reticular fibers form an interwoven matrix, called a reticulum.
Reticular fibers fill the spleen, liver, and lymph nodes
Reticular fiber
10. Types of connective tissue
Connective tissue is often divided into two categories
1. CT proper
2. Specialized CT
Connective Tissue Proper
Loose Connective Tissue
Areolar
Adipose
Reticular
Specialized Connective Tissue
Cartilage
Bone
Blood
Dense Connective Tissue
Dense Regular C.T.
Dense Irregular C.T.
Elastic C.T.
11. Areolar Tissue
Areolar tissue consist of a loose network of collagen
and elastic fibers produced by fibroblasts.
Areolar tissue forms delicate membranes that loosely
bind organs together
Locations
subcutaneous layer of skin
between muscles
surrounds organs
Functions
anchors skin to underlying organs
holds organs in place
12. Adipose Tissue (fat)
Structure
Precursor cells resemble fibroblasts, but
as they accumulate fat droplets in the
cytoplasm they become adipocytes.
Functions of adipose
stores energy
insulation
cushions organs
secretes estrogens
Locations
Beneath the skin – subcutaneous fat
Within abdominal cavity – visceral fat
Surrounds kidneys & eyeballs
Surface of heart
13. Reticular Connective Tissue
Structure
Reticular CT contains fibroblasts along with a network
of thin collagenous fibers arranged into a reticulum.
Locations include the framework of
Spleen
Liver
Lymph nodes
Functions of reticular CT
forms the framework of some organs
reduces the flow of fluid through an
organ
14. Dense Regular Connective Tissue
Structure:
Dense Regular CT contains relatively few fibroblasts with
densely packed collagenous fibers in parallel arrangement.
Functions:
Great tensile strength that withstands pulling forces
especially in one direction
Locations:
Tendons & Ligaments
Dense CT has a poor blood supply so
they are slow to heal following an injury.
15. Dense Irregular Connective Tissue
Structure
Dense Irregular CT contains fibroblasts with a dense
network of interwoven collagenous fibers
Functions
Dense Irregular CT withstands pulling forces in all
directions
Location
Dermis of skin
Dermis (deep layer) of skin
16. Elastic Connective Tissue
Structure
Elastic CT contains fibroblasts along with a dense
arrangement of elastic fibers, with a few collagen fibers.
Functions
Elastic recoil
Locations
Walls of larger arteries
and the respiratory tract
17. Cartilage Overview
Functions of cartilages
Provides attachments
Protects tissue
Structural model for developing bone
General structure of cartilages
Mature cartilage cells are called chondrocytes
The extracellular matrix of cartilage consists of
1. An abundance of collagen fibers
2. a gel-like ground substance
3. Lacunae = cavities containing chondrocytes
In addition, each of the three types of cartilages have
unique characteristics.
18. Hyaline Cartilage
Structure
Hyaline cartilage contains very fine collagenous fibers and the
ground substance gives hyaline cartilage a glossy appearance.
Functions
Hyaline cartilage provides durable protection and
supports movable joints
Locations
end of bones
embryonic skeleton
costal cartilages of the ribs
end of the nose
19. Elastic Cartilage
Structure
Elastic cartilage contains a dense network of elastic fibers in its
extracellular matrix in addition to the gel-like ground substance
and collagen proteins.
Function
Elastic cartilage provides flexible support that helps maintain the
shape of the organs.
Locations
framework of external ear and
portions of the larynx
20. Fibrocartilage
Structure
Hyaline cartilage contains very fine collagenous fibers and the
ground substance gives hyaline cartilage a glossy appearance.
Function
Fibrocartilage acts like a shock absorber
Locations
within intervertebral discs
meniscus of the knees
pubic symphysis
21. Bone
Structure
Bone is composed of
1. Cells called osteocytes within lacunae (cavities)
2. Collagen fibers that offer pliability to bone
3. Mineral Salts that provide hardness
Functions
1. support and protection
2. movement
3. blood cell production
Locations
skeleton of the body
22. Blood
Structure
Blood is composed of red blood cells, white blood cells, and
platelets suspended in a fluid matrix, called plasma.
Functions
1. RBCs – transport gasses
2. WBCs – fight infection and remove debris
3. Platelets – blood coagulation (clotting)
4. Plasma – transports nutrients, wastes, hormones, etc.
Location
Within blood vessels
