Connective Tissue serves what purpose?
: provides supportive and connective framework for all tissues in body
CLASSIFICATION OF CONNECTION TISSUE:
what are the 4 types?
1. Connective Tissue Proper
-- Loose connective tissue
-- Dense connective tissue
-- Hyaline cartilage
-- Elastic cartilage
3. Bone Tissue
-- Compact bone
-- Spongy bone
Which are considered specialized connective tissue?
Define Mucous tissue / the umbilical cord
most of the connective tissue between the vessels consists of collagen fibers.
- Between the collagen fibers are small cells staining red, they are fibrocytes and fibroblasts.
- white space is ground substance.
Loose Connective Tissue
characterized by a loose irregular arrangement of connective tissue fibers and
abundant ground substance. Collagen fibers, fibroblasts(most numerous), mast cells and macrophages
predominate in loose connective tissue.
- thickest lighter staining strands are
- thinner darker staining fibers is elastic
- fibroblasts lie along the length of collagen
Dense Connective tissue / Tendon
- Dense regular connective tissue is present in ligaments and tendons.
- consists of long collagen fibers (typically type I)
- between the densely packed collagen fibers are flatten nuclei of
Adipose cells are closely packed and separated by thin strips of connective tissue septa in which are found compressed fibroblasts, arterioles, venules, nerves and capillaries
(non is visible in slide).
- the adipose cell nuclei are located peripherally. (not visible in slide).
- adipocytes are derived from lipoblasts that are derived from mesenchymal cells.
- lipid droplets are present inside the adipose cell.
Unlike the other tissue types (epithelium, muscle, and nerve), which consist mainly of cells, what makes up most of Connective tissue?
composed of fibroblasts and other cells that make up the
extracellular matrix (ECM) of various protein fibers,
all of which are surrounded by watery ground substance
Where does Connective Tissue come from?
Mesenchyme, which are undifferentiated cells with large nuclei, with prominent nucleoli and fine chromatin and are spindle shaped.
What do Fibroblast do in Connective Tissue? other cells found in here, such as macrophages , plasma cells , and mast cells.
originate locally from mesenchymal cells and are permanent residents of connective tissue; and are the most common cells in connective tissue, produce and maintain most of the tissue’s extracellular components. Fibroblasts synthesize and secrete collagen (the most abundant protein of the body) and elastin, which form large fibers, as well as the GAGs, proteoglycans, and multi adhesive glycoproteins that comprise the ground substance.
What else does Fibroblast do for connective tissues?
They are targets of many families of proteins called growth factors that influence cell growth and differentiation.
-involved in wound healing, sometimes called myofibroblasts, have a well-developed contractile function and are enriched with a form of actin also found in smooth muscle cells.
mesenchymally derived cells are specialized for cytoplasmic
storage of lipid as neutral fats, or less commonly for the production
of heat. The large deposits of fat in the cells of adipose
connective tissue also serve to cushion and insulate
the skin and other organs.
Macrophages & the Mononuclear
phagocytic ability and specialize in turnover of protein fibers
and removal of dead cells, tissue debris, or other particulate
A typical macrophage measures between
10 and 30 μm in diameter and has an eccentrically located,
oval or kidney-shaped nucleus.
Macrophages are also secretory cells producing an
array of substances, including various enzymes for
ECM breakdown and various growth factors or cytokines
that help regulate immune cells and reparative
What else does Macrophages able to do in the system?
Macrophages derive from bone marrow precursor cells
that divide, producing monocytes that circulate in the blood.
These cells cross the epithelial wall of venules to penetrate connective
tissue, where they differentiate further, mature, and
acquire the morphologic features of phagocytic cells. Therefore,
monocytes and macrophages are the same cell at different
stages of maturation.
Mast cells are
oval or irregularly shaped connective tissue cells,
between 7 and 20 μm in diameter, whose cytoplasm is filled with
basophilic secretory granules.
Because of their high content of
acidic radicals in their sulfated GAGs, mast cell granules display
metachromasia, which means that they can change the color of
some basic dyes
Mast cells release numerous bioactive substances with the roles in the inflammatory response. Below are 6 of them.
Heparin, a sulfated GAG that acts locally as an anticoagulant
■■ Histamine, which promotes increased vascular permeability
and smooth muscle contraction
■■ Serine proteases, which activate various mediators of
■■ Eosinophil and neutrophil chemotactic factors,
which attract those leukocytes
■■ Cytokines, polypeptides directing activities of leukocytes
and other cells of the immune system
■■ Phospholipid precursors for conversion to prostaglandins,
leukotrienes, and other important lipid mediators
of the inflammatory response.
mast cells are especially numerous near small blood vessels in the skin and
mesenteries (perivascular mast cells) and in the tissue that lines
digestive and respiratory tracts.
mast cells place themselves strategically
to function as sentinels detecting invasion by microorganisms.
Mast cells originate from progenitor cells in the bone
marrow. The progenitor cells circulate in the blood, cross
the wall of venules and capillaries, and penetrate connective
tissues, where they differentiate.
Release of certain chemical mediators stored in mast cells
also promotes the allergic reactions, also known as
hypersensitivity reactions because they occur within a
few minutes after the appearance of an antigen in an individual
previously sensitized to the same or a very similar antigen.
Plasma cells are:
are B-lymphocyte–derived, antibody-producing
These large, ovoid cells have basophilic cytoplasm due
to their richness in RER
They have a clock like face.
They are also specific antibodies.
White blood cells: Leukocytes
Leukocytes, or white blood cells, make up
a population of wandering cells in connective tissue. They
leave blood by migrating between the endothelial cells lining
venules to enter connective tissue by a process called diapedesis.
The fibrous components of connective tissue are elongated
structures formed from proteins that polymerize after secretion
from fibroblasts: Name them:
collagen, reticular, and elastic fibers.
Describe the realtion of the 3 main types of fibers.
reticular fibers are both formed by proteins of the collagen family,
and elastic fibers are composed mainly of the protein elastin.
These fibers are distributed unequally among the different types
of connective tissue, with the predominant fiber type usually
responsible for conferring specific tissue properties.
Collagen is a key element in all connective tissue as well as epithelial basement membranes and the external laminae of muscle and nerve cells.
It is also the most abundant protein.
They constitute a family of proteins selected during
evolution for their ability to form a variety of extracellular
structures. The various fibers, sheets, and networks made
of collagens are all extremely strong and resistant to normal
shearing and tearing forces.
Collagen type I, the most abundant and
widely distributed collagen, forms large, eosinophilic
bundles usually called collagen fibers. These often
densely fill the connective tissue, forming structures such
as tendons, organ capsules, and dermis.
Sheet-forming collagens such as type IV collagen
have subunits produced by epithelial cells and are the
major structural proteins of external laminae and the
basal lamina in all epithelia.
are short collagens that
link fibrillar collagens to one another (forming larger
fibers) and to other components of the ECM. Type VII
collagen binds type IV collagen and anchors the basal
lamina to the underlying reticular lamina in basement
Collagen synthesis occurs in many cell types but is a
specialty of cells that produce the various kinds of connective
tissue. Where is the intial part of them made?
The initial procollagen α chains are made in the cells’
is a local swelling caused by abnormally large
amounts of collagen that form in scars of the skin.
Keloids occur most often in individuals of African descent
and can be a troublesome clinical problem to manage.
Not only can they be disfiguring, but excision is almost
always followed by recurrence.
Key steps in Collagen formation:
2. Procollagen peptidase
3. Lysyl Oxidase
Hydroxylase enzymes in the ER cisternae add hydroxyl
groups to some prolines and lysines in important reactions
that require O2, Fe2+, and ascorbic acid (vitamin C)
Outside the cell, specific proteases called procollagen
peptidases remove the terminal globular peptides, converting
the procollagen molecules to collagen molecules.
Fibrillar structure is reinforced and disassembly is prevented
by the formation of covalent cross-links between
the collagen molecules, a process catalyzed by the enzyme
initiated by specific enzymes called collagenases, which are
members of an enzyme class called matrix metalloproteinases
(MMPs). Collagenases clip collagen fibrils or sheets in
such a way that they are then susceptible to further degradation
by nonspecific proteases.
Found in delicate connective tissue of many organs, they consist mainly of collagen type III. This collagen forms an extensive network (reticulum) of extremely thin heavily glycosylated fibers. Reticular fibers are seldom
visible in hematoxylin and eosin. They are termed argyrophilic.