LECTURE III
Learning Objective: To identify the components of
connective tissue and describe their structure, composition &
function.
–
Connective
tissue is made up of specialized cells and extracellular matrix composed of
extracellular protein fibers and a ground substance
–
Underlies
epithelium, supports capillaries, small nerves
- Functions of connective tissue
1.
Establishing
a structural framework
2.
Transporting
fluids and dissolved materials
3.
Protecting
delicate organs
4.
Supporting,
surrounding and interconnecting tissues
5.
Storing
energy reserves e.g. fat
6.
Defending
the body from microorganisms
7.
Cell
growth and differentiation
Structural
Elements of Connective Tissue
-
Extracellular matrix (ECM) is composed of three structural elements:
A. Protein fibers
B. Ground substance
C. Cells/Fluid
A.
Ground Substance
–
Is
an interstitial (tissue) fluid within which are one or more of the molecules
listed below:
a)
Hyaluronic
acid: a very slippery polysaccharide which serves as a good lubricant for joints.
– Gelatinous, separates
cells, traps extracellular fluid; lubricates joints; gives shape to eyeballs;
fills body spaces
b)
Proteoglycans:
Large polysaccharide molecules bound to a protein core.Polysaccharides
called glyocosaminoglycans (chondroitin sulfate,keratin sulfate).Protein part
attaches to hyaluronic acid. Able to trap
large amounts of water.
§
Glycosaminoglycans
(GAGs) are attached to proteoglycans
ü They trap water. As GAGs
increase, so does viscosity
•chondroitin
sulfate – capable of being mineralized; found in cartilage, bones, skin, blood
vessels
•dermatin
sulfate – harder; found in skin, tendons, blood vessels, heart valves
•
keratin
sulfate - still harder; bone, cartilage, cornea of the eyes
c. Adhesive molecules: hold proteoglycan
aggregates together.
i.
Chondronectin in cartilage,
ii.
osteonectin in bone,
iii.
fibronectin in fibrous connective tissue (Binds cells,
collagen and GAG)
iv.
Laminin mediates attachment of epithelial cells to
basal laminae
–
Cells
have membrane receptors, integrins, that bind collagen,
fibrinectin, laminin and other extracellular structural components
–
Functions
as a molecular sieve through which nutrients diffuse between blood capillaries
and cells
B.
Fiber
-
Long,
rope-like protein extracellular polymers embedded in the ground substance
-
Present
in variable proportions in the different types of connective tissues
-
Fiber
provide structural support, adhesion, connect cells
-
Three
types: collagen, reticular and elastic
fibers.
-
Collagen
and reticular fibers are composed of various types of collagen, elastic
fibers are composed mainly of elastin
1.
Collagen
fibers (white fibers)
-
Large
fibers made of the protein collagen
-
The
most abundant fibers (collagen type I)
-
Un-branched
-
Promote
tissue flexibility.
-
Localized in tendons, ligaments, cartilages
-
Identified
in histological sections by staining with various acidic dyes.
2.
Elastic
fibers (yellow fibres)
-
Intermediate
fibers made of the protein elastin.
-
Branching
fibers that allow for stretch and recoil
-
can
be stretched to 150% of its original length
-
Localized
in lung, urinary bladder, skin, large blood vessels (aorta)
- Stained
using elastin-specific dyes, such as resorcin-fuchsin, aldehyde-fuchsin, or orcein.
3.
Reticular
fibers
- Small
delicate, branched fibers that have same chemical composition of collagen (predominantly collagen type III)
-
Branched
-
Fill
spaces between tissues and organs.
-
Localized
in liver, spleen, lymph nodes,
haematopoietic organs
-
Stained
using silver salt impregnation
C.
Cells
-
Fewer,
rarely touching, surrounded by a matrix
-
Immature
forms (-blasts) secrete the matrix and can still divide
-
Once
the matrix is secreted, the cells mature into -cytes which have decreased cell
divisions and secrete less matrix material- chondro- cartilage, osteo- bone,
fibro – connective, etc. Fibroblasts – connective tissue proper
- Fibroblasts - secrete the proteins needed for fiber synthesis and components of the extracellular matrix
- Adipose (adipocytes) - Common in some tissues (dermis of skin); rare in some (cartilage)
- Mast cells - Common beneath membranes; along small blood vessels. Can release heparin, histamine, and proteolytic enzymes in response to injury.
- Leukocytes (WBC’s) - Respond to injury or infection
- Macrophages - Derived from monocytes (a WBC). Phagocytic; provide protection
- Chondroblasts - form cartilage
- Osteoblasts - form bone
- Hematopoietic stem cells - form blood cells
- Undifferentiated mesenchyme (stem cells) - Have potential to differentiate into adult cell types
–
Have
a common mesenchymic origin
Types
of Connective Tissues
- True (Proper) CT
a)
Loose
CT
i.
Areolar
(loose fibrous) connective tissue
ii.
Adipose
tissue
iii.
Reticular
connective tissue
a)
Dense
CT
i.
Dense
(fibrous) regular connective tissue
ii.
Dense
(fibrous) irregular connective tissue
- Support CT
a)
Cartilage
i.
Hyaline
cartilage
ii.
Elastic
cartilage
iii.
Fibrocartilage
- Liquid CT
i.
Blood
ii.
Lymph
1.
True or Proper Connective Tissue
a)
Loose Connective Tissue:
i.
Areolar
tissue-Widely distributed under epithelia
ii.
Adipose
tissue-Hypodermis, within abdomen, breasts
iii.
Reticular
connective tissue-Lymphoid organs such as lymph nodes
- Areolar (loose fibrous) connective tissue
Description:
Gel-like matrix with all three fiber types: Cells: fibroblast, macrophages, mast cells, and some
white blood cells.
Function: Wraps and cushions organs: its macrophages
phagocytize bacteria: plays important role in inflammation:
holds and conveys tissue fluid.
Location: Widely distributed under epithelia of body,
e.g forms lamina propria of mucous membrane; packages organs:
surrounds capillaries, nerves
ii.
Adipose loose connective
tissue
Description: Consists of adipocytes;
"signet ring" appearing fat cells. They store energy in the form of triglycerides
(lipids). have nucleus pushed to the side by large fat droplet
Function:
Provides reserve fuel; insulates against heat loss; supports and protects organs
Location:
Found in subcutaneous layer, around organs and in the yellow marrow of long bones
iii.
Reticular CT
Description: Consists of fine interlacing
reticular fibers and reticular cells
Function:
Forms the framework (stroma) of organs and binds together smooth muscle
tissue cells
Location: Liver, spleen and lymph nodes
b.
Dense Connective Tissue:
i.
Dense
regular connective tissue:
ii.
Dense
irregular connective tissue:
i.
Dense
regular Connective Tissue
-
Consists
of bundles of collagen fibers and fibroblasts
-
Forms
tendons, ligaments and aponeuroses
-
Function
= provide strong attachment between various structures
ii.
Dense Irregular CT
-
Consists
of randomly-arranged collagen fibers and a few fibroblasts
-
Found
in fasciae, dermis of skin, joint capsules, and heart valves
-
Function
= provide strength
2.
Supportive Connective Tissue:
•
Cartilage and bone support the rest of the body
•
Cartilage
–
Grows via interstitial and appositional growth
–
Matrix is a firm gel containing chondroitin sulfate
–
Cells called chondrocytes
–
Cells found in lacunae
–
Perichondrium separates cartilage from surrounding
tissues
–
Three types: hyaline, elastic and fibrocartilage
a)
Cartilage
i.
Hyaline
Description: Amorphous
but firm matrix; collagen fibers form an imperceptible network;
chondroblasts produce the matrix and then mature (chondrocytes) lie in lacunae
Function: Supports and reinforces: has resilient
cushioning properties; resists compressive stress
Location: Forms most of the embryonic skeleton;
covers the ends of long bones in joints cavities; forms costal
cartilages of the ribs; cartilages of the nose, trachea, and larynx.
ii.
Fibrocartilage
-
Matrix
similar to but less firm that that in hyaline cartilage
-
Thick
collagen fibre oredominate
-
Found
in the pubic symphysis, intervertebral discs, discs in synovial joints (menisci
of the knee) & Bone-tendon junction
-
Function
= support and fusion, and absorbs shocks.
-
Deceptively
similar to dense CT- Lacunae
-
iii.
Elastic Cartilage
-
Threadlike network of elastic fibers within the
matrix.
-
Similar to hyaline cartilage
-
Found in external ear, auditory tubes, and
epiglottis.
-
Function = gives support, maintains shape,
allows flexibility
Fluid
connective tissues
•
Distinctive
collections of cells in a fluid matrix
•
Blood
–
Formed elements and
plasma
•
Red blood cells, white
blood cells and platelets
–
Arteries carry blood
away, veins carry to the heart
–
Capillaries allow
diffusion into the interstitial fluid
•
Lymph
–
Interstitial fluid
entering the lymphatic vessels
Membranes
Membranes
are simple organs
-
Form
a barrier
-
Composed
of epithelium and connective tissue
-
Four
types
1.
Cutaneous
- Covers the body surface
2.
Synovial-
Incomplete lining within joint cavities
3.
Serous-Line
sealed internal cavities
-Form transudate
4.
Mucous
- Line cavities that communicate with the exterior
-Contain lamina propria
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