Connective tissues provide support, protection, and structure to the body.
Types of Connective Tissue
1. Loose Connective Tissue:0
I. Areolar Tissue:
Structure: Contains a loose arrangement of fibers and various cell types.
Location: Widely distributed under epithelia, surrounds capillaries.
Function: Provides cushioning, binds tissues, and allows for nutrient diffusion.
II. Adipose Tissue:
Structure: Comprised mainly of adipocytes filled with fat droplets.
Location: Under the skin (subcutaneous layer), around kidneys and eyeballs, within the abdomen, and in breasts.
Function: Stores energy, insulates against heat loss, and cushions organs.
III. Reticular Tissue:
Structure: Network of reticular fibers with supportive cells.
Location: Lymphoid organs (lymph nodes, bone marrow, and spleen).
Function: Provides a supportive framework for soft organs.
2. Dense Connective Tissue:
I. Dense Regular Connective Tissue:
Structure: Parallel collagen fibers with a few elastic fibers; major cell type is fibroblasts.
Location: Tendons, ligaments, and aponeuroses.
Function: Attaches muscles to bones or to muscles and bones to bones; withstands great tensile stress in one direction.
II. Dense Irregular Connective Tissue:
Structure: Irregularly arranged collagen fibers with some elastic fibers; major cell type is fibroblasts.
Location: Dermis of the skin, submucosa of digestive tract, fibrous capsules of organs and joints.
Function: Withstands tension exerted in many directions; provides structural strength.
III. Elastic Connective Tissue:
Structure: Dense regular connective tissue containing a high proportion of elastic fibers.
Location: Walls of large arteries, within certain ligaments associated with the vertebral column, within the walls of the bronchial tubes.
Function: Allows tissue to recoil after stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration.
3. Specialized Connective Tissues
I. Cartilage:
A. Hyaline Cartilage:
Structure: Amorphous but firm matrix with collagen fibers; chondrocytes lie in lacunae.
Location: Embryonic skeleton, ends of long bones in joint cavities, costal cartilages of the ribs, nose, trachea, and larynx.
Function: Supports and reinforces; serves as a resilient cushion; resists compressive stress.
B. Elastic Cartilage:
Structure: Similar to hyaline cartilage, but more elastic fibers in matrix.
Location: External ear (pinna), epiglottis.
Function: Maintains the shape of a structure while allowing great flexibility.
C. Fibrocartilage:
Structure: Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate.
Location: Intervertebral discs, pubic symphysis, discs of knee joint.
Function: Tensile strength allows it to absorb compressive shock.
II. Bone (Osseous Tissue):
Structure: Hard, calcified matrix containing many collagen fibers; osteocytes lie in lacunae. Very well vascularized.
Location: Bones.
Function: Supports and protects (by enclosing); provides levers for the muscles to act on; stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation (hematopoiesis).
III. Blood:
Structure: Red and white blood cells in a fluid matrix (plasma).
Location: Contained within blood vessels.
Function: Transports respiratory gases, nutrients, wastes, and other substances.
Structure:
Connective tissues have fewer cells and more extracellular matrix than other tissues.
The extracellular matrix consists of protein fibers (collagen, elastin, reticular) and ground substance.
Location:
Connective tissue proper: Beneath the skin, around organs, tendons, ligaments, and bone marrow.
Specialized connective tissue: Joints, rib cage, ear, and skeletal system.
Fluid connective tissue: Blood vessels and lymphatic vessels.
Functions:
Support: Connective tissues bind and support other tissues and organs.
Protection: They protect and cushion organs.
Insulation: Adipose tissue stores energy and insulates the body.