ground substance

Connective Tissue
General Features
Two basic elements: CELLS and an
extracellular MATRIX
The MATRIX is made with a ground
substance and fibers
Not very cellular compared to the other types of
Does not occur on body surfaces
Has a nerve supply, except cartilage
Usually highly vascular except cartilage
(avascular) tendons and ligaments
Various tissue types confer a variety of
Types of Connective Tissue Cells
Fibroblasts- produce and
secrete fibrous proteins and
ground substance
Macrophages- phagocytic
cells that engulf and digest foreign
Plasma Cells- produce
Mast Cells- produce
histamine, which dialates blood
vessels, and heparin, an
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
Chondroblasts- produce
and secrete fibers and ground
substance in cartilage
Chondrocytes- maintains
the matrix of cartilage
Osteoblasts- produce and
secrete fibers and ground
substance in bone
Osteocytes- maintains the
extracellular matrix of bone
Connective Tissue Extracellular
Ground substance can be
Three Types of Fibers
Collagen – strong, thick yet flexible
Elastic – smaller in diameter than collagen, branch to
form a network within the tissue, very elastic
Reticular – also made with collagen, but much thinner
than collagen fibers, provide support and strength and
form the basement membrane
Two Major Types
of Connective Tissue
 Embryonic
– found in the embryo and
 Mature
– present in newborns to adults
Types of Mature Connective Tissue
Loose Connective Tissue
Dense Connective Tissue
Loose Connective Tissue
In Loose Connective Tissue, the fibers in the
extracellular matrix are loosely arranged. Lots
of ground substance. The ground substance in
semifluid (viscous). Cells are scattered
throughout the tissue. Not very cellular. 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 and cells of the immune system, are
embedded in a semifluid ground substance
Areolar is the most abundant type of connective
Found in the subcutaneous layer deep to skin,
superficial part of dermis, mucus membranes,
around blood vessels, nerves and body organs
Function: supports glandular epithelium and
mesothelial layers of mesentery, supports
immune cells
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
macrophages and other cells involved in
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
Function: provides storage for energy-rich
lipids, cushioning and insulation for organs
Adipose Tissue
Dense Connective Tissue
The extracellular matrix consists of tightly
packed fibers that form bundles. Very little
semi-fluid (viscous) ground substance.
Fibroblasts are squeezed between the
fiber bundles
Three types of Dense CT
 Dense Regular CT
 Dense Irregular CT
 Dense Elastic CT
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
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
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
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
Does not have a nerve supply
Hyaline Cartilage
Contains collagen fibers which are thin and not
visible with a compound light microscope, where
the matrix appears smooth and homogenous.
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
Extracellular matrix is packed with thick
collagen fibers. Has fewer lacunae and
chrondrocytes than the other types of
Found in intervertebral discs and the
menisci of the knees
Function: provides cushioning and reduces
Compact Bone
The extracellular matrix consists of collagen fibers
and a hard ground substance in which inorganic
salts, mostly calcium and phosphorus salts, are
deposited. Osteocytes are located in lacunae,
much like the spaces in cartilage. Because the
ground tissue is hard in bone and diffusion and
osmosis is nearly impossible, little canals, or
canaliculi serve as passages ways for nutrients
and wastes as they connect the lacunae to
larger canals that contain blood vessels.
The matrix is organized and develops in layers called
lamellae. The lamellae form concentric rings that make
up a structure called an osteon. A single bone may have
several hundreds and even thousands of osteons. 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
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
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