L5: Connective tissue cells Flashcards
What is the function of CT?
The CT supports, surrounds, binds, and separates various tissues and organs.
What are the types of CT?
True(proper)β->loose and dense
Supportiveββ>bone and cartilage
Liquidββ>blood
What are the characters of white collagenous fibers?
β Color: the bundles are white in color.
β Strong and resist stretch.
β It forms wavy bundles.
β Can be affected by
ο² converted into gelatin by boiling
ο² Destroyed by acids & alkalies.
What are the components of CT?
-cells, fibres and matrix
How is white collagenous fibres seen under LM?
The bundles can be stained:
ο² Acidophilic with Hx & E.
ο² Blue with Mallory trichrome stain.
ο² Red with Van Giesonβs stain.V
How is white collagenous fibres seen under EM?
β Each collagenous bundle is formed of a group of fibers which are composed of fibrils.
β Each fibril is formed of tropocollagen molecules: -.
ο Synthesized by Fibroblasts
ο Length is 280 nm
ο Each molecule is composed of 3 polypeptide chains twisted around each other to form a triple helix.
ο The arrangement of tropocollagen molecules gives the fibril a cross banding appearance Structure
What are the types and sites of collagen?
What are the characters of yellow elastic fibers?
ο Color: yellow.
ο Elastic in nature
ο The fibers branch & anastomose
How is yellow elastic fibre seen under LM?
ο Hx & E.: acidophilic.
ο Van Giesonβs stain: yellow.
ο Ver-Hoffβs stain: black.
How are yellow elastic fibres seen under EM?
Each fiber is formed of:
ο² Amorphous protein in the center called elastin
ο² Microfibrils in the periphery called oxytalan fibers.
What are the sites of yellow elastic fibres?
ο In the walls of arteries.
ο In the trachea, bronchi, and bronchioles.
ο Ligamentum flavum between vertebrae.
ο Ligamentum nuchae in the back of the neck
οSuspensory ligament of the penis
What is the structure of reticular fibers?
ο They are very thin fibers that branch and anastomose to form a network.
How are reticular fibres seen under LM?
ο Hx & E: not stained.
ο Silver: brown to black (Agyrophilic)
ο PAS: Magenta colored (polysaccharides).
What are the sites of reticular fibers?
ο The stroma of parenchymatous organs e.g. Liver, spleen, and lymph nodes.
ο Reticular lamina of the basement membranes.
What is the matrix composed of?
ο Composed of three components:
1) Amorphous component.
2) Fibrous component
3) Tissue fluid
What is the amorphous part composed if?
ο The amorphous part: formed of two main parts:
1) Glycosaminoglycans (gags)
2) Glycoproteins
GAGS in CT
Non-sulphated type (hyaluronic acid)
Soft jelly-like
Not linked to a core of protein
Can be hydrolyzed by hyaluronidase enzyme
Sulphated type (chondroitin sulphate)
hard
Linked to a core of protein forming proteoglycans.
Not affected.
ο Stain: Metachromatic stain e.g., Toluidine blueβreddish-purple in Color.
Glycoproteins in CT.
Act as adhesive material.
Examples:
ο² Chondronectin in cartilage.
ο² Osteonectin in bone.
ο Stain: PASβ magenta-colored.
What are fixed CT cells?
-undifferentiated mesenchymal cell
-fibroblasts
-adipocytes (fat cells or adipose cells)
-reticular cells
-macrophages (clasmatocyes or histiocytes)
What is the origin of the undifferentiated mesenchymal cell?
Mesodermal cells of the embryo
Can mesenchymal cells divide?
Yes
Are mesenchymal cells differentiated?
No
How is UMC seen under LM?
Cytoplasm: pale basophilic due to little ribosomes
Nucleus:clovesβ->central,vesicular,large,oval,single
Sites: pre-natalβ->in the embryonic CT
Post-natalβ->in decides teeth and in pericytes surrounding the blood capillaries
Shape: Branched with few cell processes which are thin and long
Number: common in embryonic CT (mucoid and mesenchymal)
Size: Tiny
How is UMC seen under LM?
Cytoplasm: pale basophilic due to little ribosomes
Nucleus:clovesβ->central,vesicular,large,oval,single
Sites: pre-natalβ->in the embryonic CT
Post-natalβ->in decides teeth and in pericytes surrounding the blood capillaries
Shape: Branched with few cell processes which are thin and long
Number: common in embryonic CT (mucoid and mesenchymal)
Size: Tiny
how is UMC seen under EM?
Mainly free polysomes (little rER and small Golgi)
What is the function of UMC?
It acts as a multipotent stem mother cell.
What are fibroblasts?
The most common type of C.T. cells that are responsible for the synthesis of C.T. matrix and fibers.
What is the origin of fibroblasts?
develop from pericytes (branched cells around blood capillaries) which develop from U.M.C.
Can fibroblasts divide?
No
Are fibroblasts differentiated?
Yes
How are fibroblasts seen under LM?
Cytoplasm: Deep basophilic with negative Golgi image
Nucleus: oval, vesicular (with fine chromatin and prominent nucleolus), and eccentric in position
Shape: branching spindle-shaped cells.
Sites: The most common type of C.T. cells, very numerous in the loose C.T.
How are fibroblasts seen under EM?
ο The cytoplasm is rich in ribosomes, rER, and prominent Golgi.
ο Some mitochondria
ο Microtubules and microfilaments preserve the shape of the cell.
What is the function of fibroblasts?
1- Synthesis of the components of the C.T. matrix.
2- Synthesis of nearly all types of C.T. fibers (fiber-forming cells).
3- Responsible for the growth of C.T. and healing of wounds.
What are fibrocytes?
Fibrocytes: are old fibroblasts characterized by:
ο² Shape: spindle-shaped but flatter and has fewer processes.
ο² Nucleus: darker.
ο² Cytoplasm: less basophilic (less rER).
ο² Function: preserve and renew the already formed components of the CT matrix and fibers.
What are the steps of the formation of white adipocytes?
UMCs β Lipoblast β Brown adipocyte β White adipocyte.
Can both brown and white adipocytes divide?
No
Are both brow and white adipocytes differentiated?
Yes
How are the brown adipocytes seen under LM?
Cytoplasm: Contains many fat droplets:
Paraffin sections (Hx&E) β Cytoplasm is acidophilic with many vacuoles due to dissolved fat droplets.
Nucleus: single central and rounded nucleus.
Shape: oval
Sites: In sites of Brown adipose CT
Number: The main cells in adipose CT
Size: 10-times smaller than white adipocytes
How are the white adipocytes seen under LM?
Cytoplasm: Contains a large fat globule:
1. Paraffin sections (Hx&E) β an empty space due to dissolved fat globule.
Nucleus: A single flat peripheral nucleus pushed to one side giving a Signet Ring appearance.
Shape: oval
Sites: Mainly in sites of white adipose CT, Also in loose CT.
Number: The main cells in adipose CT
Size: 10 times larger than brown adipocytes.
How are brown adipocytes seen under EM?
Multiple fat droplets.
ο sER and numerous mitochondria are scattered among
the fat droplets
How are white adipocytes seen under EM?
sER & some mitochondria are present in the remaining
cytoplasm beside the nucleus.
What is the origin of white reticular cells?
UMC
Can reticular cells divide?
No
are reticular cells differentiated?
Yes
How are reticular cells seen under EM?
Few organelles include rER, ribosomes, and mitochondria.
How are reticular cells seen under LM?
Cytoplasm: Hx & E β Pale basophilic.
Special stain β Silver stain
Nucleus: central,oval, and pale
Site: reticular stroma of parenchymatous organs.
Shape: branched with many processes
Size: small
Number: most common cell in reticular CT.
What is the function of reticular cells?
It acts as a multipotent stem (mother) cell for:
1. Supportive function: with reticular fibers, they both form a delicate network that supports parenchymal cells.
- Antigen Presenting Cells (APCs): present antigens to T-Helper lymphocytes to activate the immune system.
- Phagocytic function.
What is the origin of macrophages?
From migrating blood monocytes (that originally develop from UMCs in bone marrow).
Can macrophages divide?
No
Are macrophages differentiated?
Yes
How are macrophages seen under LM?
Cytoplasm: Hx & E: Pale basophilic and not clear.
ο Special stains:
ο² Vital stain e.g. trypan blue.
ο² Supravital stain e.g. neutral red.
Nucleus: Eccentric, small, kidney-shaped oval or irregular, single and pale.
Site: mainly in loose CT
Shape: rounded with pseudopodia
Number: the 2nd most common in loose CT
Size:large
How are macrophages seen under EM?
Many lysosomes, few rER and free polysomes, small Golgi, and few mitochondria.
ο Pseudopodia, phagosomes, and pinocytotic vesicles.
What are the types and functions of macrophages?
A) M1 βkillerβ macrophages:
- Phagocytic function: can phagocytize foreign bodies e.g. bacteria.
- Many phages may fuse together to form multinucleated foreign body giant cells to attack a large foreign body
- Antigen Presenting Cells (APCs): present antigens to T-Helper lymphocytes to activate immunity
- Secretory function: they secrete enzymes (e.g. collagenase and elastase) and cytokines.
B) M2 βrepairβ macrophages: function in constructive processes like wound healing and tissue repair, they secrete growth factors and other cytokines
What are the types of skin?
β Thick (non-hairy) skin: found in palms and soles.
β Thin (hairy) skin: covers the rest of the body.
What is the function of adipocytes?
Same as adipose connective tissue
What are free connective tissue cells?
ο Mast cells.
ο Plasma cells.
ο Melanophores = Chromatophores = Melanophages.
ο Migrated Blood leucocytes.
ο Wandering (Free) macrophages.
What is the origin of mast cells?
UMC
Can Mast cells divide?
No
Are mast cells differentiated?
Yes, Fully differentiated
How are Mast cells Seen under LM?
How are Mast cells Seen under LM?
What is the shape of Mast cells under EM?
ο The cell border is irregular with short process.
ο The cytoplasm contains: Much membrane-bounded electron dense granules, ribosomes, rER and mitochondria
What are the functions of Mast cells?
ο Secretion of Heparin: natural anticoagulant.
ο Synthesis, storage and secretion of Histamine: in cases of allergy and inflammation.
ο Secretion of Slow Reacting Substance of Anaphylaxis (SRS-A): has similar action as histamine but longer in duration.
ο Secretion of Eosinophil Chemotactic Factor (ECF): attract eosinophils
What is the origin of plasma cells?
Activation of B-lymphocytes (originating from UMCs) by specific antigen leads to formation of plasmablasts which mature into plasma cells.
Do plasma cells divide and are they differentiated?
- Cannot divide.
- Fully differentiated.
What is the Shape of plasma cells under LM?
What is the shape of plasma cells under EM?
ο Cell border is irregular.
ο The cytoplasm is rich in rER, ribosomes, prominent Golgi and mitochondria.
What are the functions of plasma cells?
Secretion of antibodies (responsible for humoral immunity).
What are melanophores? (Pigment cells)
Melanin-containing C.T. macrophage that engulfs melanin made by melanocytes.
What is the site of melanophores?
Found in the choroid of the eye and dermis of skin.
What is the shape and structure of Melanophores?
Branched with melanosomes in the cytoplasm.
what are migrated leukocytes?
Blood leucocytes leave the blood stream and accumulate in the C.T. in certain conditions, e.g.:
(i) Eosinophils: in allergy or parasitic infestation.
(ii) Neutrophils: in acute infections.
(iii) Monocytes & lymphocytes: in chronic infections.
