Anatomy I - Connective Tissue Flashcards
Connective Tissue
Connective Tissue Characteristics
- Cells, though few when compared with epithelial tissue
- Most abundant and widely distributed tissue in the body
- Present in many different forms throughout the body
- Highly vascular (with some exceptions)
Connective Tissue Proper
1) Loose (areolar) CT
2) Dense CT
a) Irregular CT (alias: Dense Irregular CT)
b) Regular CT (alias: Dense Regular CT)
Special CT
a) Elastic CT
b) Adipose CT
(c) Reticular CT
(d) Embryonic CT
Supporting Tissue
1) Cartilage
2) Bone
Connective Tissue Functions
- Binds, supports, and strengthens other body tissues
a. Underlies all epithelia
b. Fills in spaces - Protects, insulates, and repairs internal organs
a. Encases vulnerable organs, e.g., the brain being housed in the cranium
b. Provides soft beds of fat, e.g., the kidneys embedded in lumbar fat
c. Assists in temperature regulation
d. Source of undifferentiated cells for repair purposes
3 - Compartmentalizes structures
a. Isolates separate groups of skeletal muscle
b. Provides filtration spaces in certain organs, e.g., the glomerulus of the kidney - Transport system
a. Blood cells and plasma
b. Fluids within the extracellular matrix - Site of stored energy reserves, e.g., fat
Connective Tissue Composition
- Consists of two basic elements
a. Cells
b. Extracellular matrix (ECM, or simply, matrix)
Mesenchymal cell (a type of embryonic cell)
Ancestral cell to most of the cells of adult CT: a. Fibroblast b. Adipocyte c. Chondroblast d. Osteoblast e. Odontoblast (teeth)
Bone marrow
Precursor cells give rise to other cell types:
a. Mast cell
b. Macrophage
Fibroblasts
large, fusiform-shaped, branching cells present in most types of connective
tissue; most numerous of the connective tissue classes of cells; secretes and maintains
the matrix; acts as a type of stem cell which is capable of migrating throughout matrix
secreting new ground substance and matrix (as required) for wound and tissue repair
Adipocytes
aka Fat Cells, or Adipose Cells
a. Large spherical cells
1) In profile view, they look like a signet ring
b. Synthesize and store triglycerides
1) Actually, a large vacuole of fat
c. Essential for life – a filler, food, insulator
Mast Cells
a. Mast cells contain numerous granules
1) Granules contain primary mediators of immune/inflammatory response:
a) Heparin (chondroitin sulfate – a sulfated
glycosaminoglycan [GAG])
b) Histamines
c) Proteases
d) Eosinophil chemotactic factor (ECF)
e) Neutrophil chemotactic factor (NCF)
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b. Mast cells also produce (synthesize) secondary mediators that are not stored in
the cell, but rather released immediately
1) Secondary mediators from membrane arachidonic acid precursors
a) Leukotrienes
b) Thromboxanes
c) Prostaglandins
d) Cytokines (to numerous to mention)
c. Mast cells function in the immune system by initiating an inflammatory response
known as the immediate hypersensitivity reaction (systemically, referred to as
anaphylactic reaction)
Macrophages – alias: Histiocytes
a. Irregularly shaped cells
1) Contains many finger-like filopodia for phagocytosis
b. Arise from bone marrow precursor cells of the mononuclear phagocyte system
1) This system phagocytic cells having different names for their location
a) Kupffer cells – liver
b) Dust cells – lungs
c) Langerhans cells – skin
d) Monocytes – blood
e) Osteoclasts – bone
f) Microglia – neural tissue
g) Macrophages – CT
Function of macrophages
1) Phagocytose (and digest) dead and damaged cells, cellular debris
2) Assist in ‘defense’ by phagocytizing and destroying foreign substances,
including microorganisms
3) During immune response, factors released by lymphocytes activate
macrophages; become motile (exhibit increased locomotion)
Wandering Cells
- Plasma cells
2. Leukocytes
Plasma cells
a. Large ovoid cells
b. Present throughout all CT, though present in greatest numbers in CT subject to
chronic inflammation
c. Produce and secrete antibodies
Leukocytes
The class of circulating cells (WBC) that respond to inflammation and the immune system a. Lymphocytes b. Monocytes c. Neutrophils d. Eosinophils e. Basophils (similar to mast cells)
Lymphocytes
WBC’s that circulate in the bloodstream, migrating through the
capillary walls and into the CT during times of inflammation
Monocytes
the macrophages of the blood
Neutrophils
phagocytose and digest bacteria in areas of acute inflammation,
resulting in the formation of pus – the accumulation of dead neutrophils and
debris
Eosinophils
combat parasites by releasing cytotoxins; moderate allergic
reactions and phagocytose antibody-antigen complexes
Basophils (similar to mast cells)
release primary and secondary mediators
that initiate, maintain, and control the inflammatory process
Matrix (Extracellular Matrix)
Composed of ground substance and fibers; resists compressive and stretching forces
Ground Substance
the component of connective tissue that occupies the space
between the cells and fibers; a hydrated, amorphous material
Ground Substance
Typically absent in histological preparations as processing washes ground substance away b. Ground substance is composed of: 1) Glycosaminoglycans (GAGs) 2) Proteoglycans 3) Adhesive glycoproteins
Glycosaminoglycans (GAGs)
long, unbranched polymers of
repeating disaccharides
Proteoglycans
protein cores to which various GAGs are
covalently linked… for example to
a) Hyaluronic acid, thus forming huge macromolecules
called aggrecan aggregates
b) Responsible for the gel state of the extracellular matrix
Adhesive glycoproteins
large
macromolecules responsible for
fastening the various components of the
extracellular matrix to one another and to
integrins and dystroglycans of the cell
membrane; occur as various types:
a) Laminin – localized at the
basement membrane
b) Chondronectin – localized in cartilage
c) Osteonectin – localized in bone
d) Fibronectin – generally dispersed throughout matrix
Fibers
derived from fibroblasts
Collagen fibers
very strong and resist pulling forces (possess great tensile
strength); promote tissue flexibility; arranged in parallel bundles and composed of
fine subunits by tropocollagen molecules
Collagen fibers
Each collagen fiber is composed of three (alpha)-chains wrapped around
each other in a helical configuration
Though present in as many as 15 different types, six major types are
generally recognized
a) Type I – in CT proper, bone, dentin, tendon, joint capsule, and
dermis of skin
b) Type II – in hyaline and elastic cartilages
c) Type III – reticular fibers
Collagen fibers - Significance
a) Provides the basis for tissue strength and resiliency
b) Production and degradation rates change with age
- Production outpaces degradation in young
- Degradation outpaces production in aged
- Production necessary for wound healing
– Dependent upon proper nutrition
— Vitamin C
— Key amino acids
— Minerals, e.g., copper, zinc
— Growth factors
— Hormones
c) Defects in synthesis and/or degradation of collagen may
contributes to numerous diseases, e.g.,
- cancers
- arthritis
- emphysema
- osteoporosis
- fibrotic diseases (including heart valves)
Elastic fibers
small, branching fibers that form a network; derived from
fibroblasts
Elastic fibers
1) Highly distensible – though resist stretching 2) May be stretched up to 150% of their relaxed length, then return to original length 3) Composed from elastin and microfibrils
Reticular fibers
fibers that form an
extensive network in certain organs, primarily lymphatic organs.
Connective Tissue Proper
The recognized types of CT Proper, which differ in their location, function, and histology, are: Loose, or areolar, CT Dense CT Special CT Supporting Tissue
Loose, or areolar, CT
Fills in the spaces of the body; few fibers
1) Located:
- Deep to the skin
- Deep to the lining of the internal body cavities
- Associated with the adventitia (outer covering) of the blood vessels
- Surrounds the parenchyma of glands
2) Loose CT of the mucous membranes is called the lamina propria
3) Loose CT is characterized by an abundance of ground substance and
extracellular fluid
4) Scattered throughout this tissue are:
- Fibroblasts
- Fat cells
- Macrophages
- Mast cells
- Undifferentiated cells
- Loosely woven collagen fibers
- Lacey reticular fibers
- Some loosely scattered elastic fibers
Dense CT
like Loose CT but with more fibers than cells; fiber arrangement
forms, or gives rise to, two different types of Dense CT:
1) Dense Irregular CT
2) Dense Regular CT
Dense Regular CT
a) Contains coarse collagen fibers densely packed and oriented
into parallel cylinders or sheets that resists tensile forces
b) Again, little space is left for ground substance or cells
c) Some fibroblasts are located between the bundles of collagen,
with their long axis parallel to the bundles of fibers (appear to be
squeeze in)
d) Located in:
- Tendons
- Ligaments
- Aponeuroses
Dense Irregular CT
a) Contains mostly coarse collagen fibers interwoven into a
meshwork in order to resists stress from all directions
b) Collagen fibers are so tightly packed that there is little space for
ground substance of cells
c) A fine network of elastic fibers are often found in this tissue
d) Fibroblasts, as well as all other cell types, are found scattered
amongst the collagen fibers
e) Located:
- Dermis of skin
- Sheath of nerves
- Capsule of spleen
- Gonads (testes and ovaries)
- Kidney
- Lymph nodes
Special CT
1) Elastic CT
2) Adipose CT
3. Reticular Tissue
4. Embryonic CT
Elastic CT
a) Contains coarse, branching elastic fibers with only a few
collagen fibers present
b) Elastic fibers are arranged parallel to each other and form either
sheets or fenestrae (fenestrated membranes)
c) Some fibroblasts are present in the interstitial spaces
d) Located:
- Large blood vessels
- Ligamenta flava (of vertebral column)
Adipose CT
a) Contains (each cell) a single droplet of lipid
b) Heavily supplied with blood vessels
c) Cell membranes contain receptors (for the uptake and release
of free fatty acids and glycerol) which include:
- Insulin
- Growth hormone
- Norepinephrine
- Glucocorticoids
d) Adipose CT is locally
stored differently between the
sexes
Reticular Tissue
a very delicate tissue that forms a 3-D network that supports
cells. This is a specialized type of loose connective tissue that provides the
architectural framework and creates a special environment for hematopoietic
organs and lymphoid organs (bone marrow, lymph nodes and nodules, spleen).
Embryonic CT – alias: Mesenchyme
1) Associated with a fetus and related organs
