Connective Tissues Flashcards
What are ‘Connective’/’Supporting tissues’?
its supports , binds and connects other tissues and organs providing structural and metabolic support of them
General Properties of CT
- Strength – tensile strength afforded by structural proteins (e.g. various collagens)
- Space-filling / volume (due to glycoproteins and complex carbs – retain water
- Elasticity – can return to original shape after mechanical distortion – due to elastin fibrils
What are the constituent elements of Connective tissue?
- Cells
- Extracellular Matrix
* Ground substance: Hyaluronate and proteoglycan aggregates
- Fibrillar proteins e.g. Collagen fibres and Elastin
- Extracellular Matrix
Ground substance: highly hydrated – why?
- Composition: ‘Toilet-brushes’ of a proteoglycan core with covalently-bound glycosaminoglycan (GAG) ‘bristles’.
- These ‘brushes’ bind to long, linear hyaluronate (HA) molecules, to form hyaluronate - proteoglycan aggregates
what is CT derived from?
is derived from multipotent embryonic mesenchymal cells.
The mesenchyme
is a type of undifferentiated embryonic connective tissue that develops predominantly in the mesodermal layer of the embryo
what is Collagen
- Most abundant human protein – 30% of our whole body protein content
- 28 types of collagen known in humans
Different collagen types form fibrils and fibre, sheets e.g. Type IV or anchors.
List of the components of CT
1 - Cells: difference types
1. Fibroblasts
2. Macrophages
3. Mast cells
4. Plasma cells
5. Adipose cells
6. Leucocytes
2 - Fibers:
a. Collagenous
b. Elastic
c. Reticular
3 - Matrix:
* The *intercellular substance, in which cells and fibres
* Ground substance Hyaluronate and proteoglycan aggregates
Types Of C.T (Depending On Matrix):
- Soft = C.T Proper
- Rigid (rubbery , firm) = Cartilage
- Hard (solid) = Bone
Fluid (liquid) = Blood
Fibroblast Cells Structure
Flat branched cells (spindle-shaped) with basophilic cytoplasm.
* They can divide.
* Old fibroblasts are called fibrocytes . *fibrocytes are mainly inactive
Function of the plasma cells:
- Formation of proteins of C.T. fibres.
*the cytoplasm of these cells are rich in ribosomes which on the outer surface of Rough ER.
- Formation of C.T. matrix.
- Healing of wounds.
- Responsible for formation of 3 types of fibres (collagen , elastic , reticular ).
Most common cell and found nearly in all types of C.T. proper?
Fibroblasts
Macrophages
Structure?
Basophilic cytoplasm, rich in lysosomes
▪ Irregular outlines (cell membrane)
*pseudopodia of macrophages is the cause of its irregular outlines.
▪ They can divide.
▪ They originate from blood monocytes.
what is the function of macrophages?
phagocytosis
Mast cells structure
cytoplasm contains numerous basophilic cytoplasmic granules.
Function of mast cells
- Secrete heparin (anticoagulant)
- Secrete histamine (allergic reactions)
Active Plasma Cells Structure
- Basophilic cytoplasm with a negative Golgi image.
- *negative Golgi image : lack of ribosomes around Golgi apparatus.
- Nucleus: spherical, eccentric with a clock-face appearance of chromatin.
function of active plasma cells
Function: Secretion of antibodies (immunoglobulins).
Structure of Unilocular Adipose Cells:
- Large spherical , with a single large fat droplet.
- Thin rim of cytoplasm at the periphery.
- Nucleus: flattened , peripheral.
*the large fat droplet squeeze the cytoplasm and nucleus to give them their shape.
function adipose cells
storage of fat
Leukocytes (White Blood Cells) structure
- Appear normally in C.T. proper.
- Neutrophils increase in acute inflammation.
- Lymphocytes and monocytes increase in chronic inflammation.
- Eosinophils and basophils increase in allergic inflammation.
types of fibre
collagen fibres
reticular fibres
elastic fibres
structure and function of collagen fibers
Made of collagen type I
* Non-branched fibre , arranged in bundles
* Bundles form the branch.
Acidophilic
reticular fibres structure
Made of collagen type III
* Branch and form a network
* Stained black with silver
elastin fibres function
Made of Elastin
Branched
Stained brown with orcein
How do cells make collagen?
RER
Synthesis of pre-procollagen alpha-chains (glycine every third residue allows helical conformation)
Golgi
* Packing into secretory vessels
Cytoplasm
* Constitute exocytosis
Extracellular environment
* Non-helical terminal peptides cleaved
Collagen molecules assemble into fibrils
Some Important examples of collagen types
Type 1-5
Type 1 collagen fibre
90% of all collagen. Fibrils aggregate into fibres and fibre bundles e.g. in tendons, capsules of organs and dermis. Organic component of bone.
Type 2
fibrils do not form fibres, hence form a very fine mesh present in hyaline and elastic cartilage.
Type 3
Fibrils form branching fibres, (but not bundles) around muscle and nerve cells, and within lymphatic tissues and organs, where they are called reticulin. Also found in the skin in the papillary dermis.
Type 4
Type 4 – unique sheet form present in basal lamina of basement membrane.
Type 5
Type 5 - Anchors basal lamina to underlying reticular lamina.
Disorders of Collagen Synthesis:
- Ehlers-Danlos
- Scurvy
- Osteogenesis imperfecta
Type 1 collagen Assembly
- Each collagen subunit is approximately 300nm long and 1.5nm wide
- Each fibril is composed of staggered collagen molecules with a periodic banding which repeats every 67 nm.
Fibrils assemble into fibres (which are visible under light microscopy), and fibres can assemble into larger bundles.
structure of Dense collagenous C.T.
Predominance of collagen fibres + fibroblasts.
sites of dense collagenous CT
Sites:
1- Dense irregular: e.g. dermis of the skin, capsules.
2- Dense regular: e.g. tendons, ligaments.
Function: tough tissue : resistant to stretch
Structure of Elastic tissue (Dense)
Predominance of elastic fibres (sheets or membranes) + fibroblasts.
Sites and function of Elastic Tissue (Dense)
Sites:
Large arteries, e.g. Aorta
Function: elastic tissue : stretchable.
Structure Reticular tissue (Loose)
Predominance of reticular fibres + reticular cells (specialized fibroblasts).
Sites and Function of Reticular Tissue
Sites:
Stroma of organs: e.g. liver , lymph node , spleen.
Function: structural support.
Structure Unilocular adipose tissue (Loose) (white adipose tissue)
Structure:
* Predominance of unilocular fat cells.
Sites and Function of Unilocular adipose tissue
Sites:
* Subcutaneous tissue , especially in:
1. Buttocks.
2. Abdominal wall.
3. Female breast.
* Around the kidney.
Function:
4. Synthesis , storage and release of fat.
5. Supports organs , e.g. kidney.
Heat insulation.
Loose Areolar CT Structure
❖ Contains all the main components of C.T.P.
❖ all types of C.T. cells & fibers + abundant matrix.
❖ No predominant element in loose C.T.
site of loose areolar CT
Sites:
e.g. Subcutaneous tissue.
Function of the ECM:
The connective tissues non cellular portion is known as the extracellular matrix (ECM), giving the physical scaffolding for the cells.
- The ECM is able to hold water, provide appropriate hydration of the tissue and form part of a selective barrier to the external environment.
Composition: ‘Toilet-brushes’ of a proteoglycan core with covalently-bound glycosaminoglycan (GAG) ‘bristles’. These ‘brushes’ bind to long, linear hyaluronate (HA) molecules, to form hyaluronat- proteoglycan aggregates - *Highly polar, hence attract water (90% of ECM is water)
- Gel-like, inflexible and resistant to compression (useful in cartilage)
ECM dysfunction can result in various medical conditions:
Abnormal remodelling of tissues results in alterations in ECM structure and function, which ultimately promotes the development of common diseases such as fibrosis, osteoarthritis, and cancer.
