Lecture 6 Flashcards
Connective tissue Function
- Connecting framework of the body
a. Continuous with other basic tissue types
b. Stroma – connective framework of body organs and glands
c. Medium for diffusion of metabolites - Supportive framework of the body
a. Cartilage, bones, ligaments and tendons - Protection and defense
a. Immune and inflammatory responses
b. Tissue repair after injury - Fat storage
Connective tissue components
• Extracellular matrix (ECM) and cells
• ECM contains:
– Ground substance
– Fibers
– It generally contains blood
and lymphatic vessels

What is depicted by the Green and blue arrows

- Ground substance (Blue)
- Fibers (collagen and elastic) (Green)
Ground Substance
- Glycosaminoglycans (GAGs)
- Proteoglycans:
- Glycoproteins

What are the arrows pointing to

- Collagens: tensile strength
- Elastic fibers:ability to return to original shape

What type of fiber is shown in the image

Collagen I fibers
Light microscopy of type I collagen fibers stained pink. F: fibroblasts.
What type of fiber is shown in the image

Collagen I fibers
Electron microscopy of type I collagen fibers:
Fibrils show periodicity at 68 nm (arrow)
What type of fiber is shown in the image

Organization of type I collagen fibers

Collagen I fibers
- Flexible with high tensile strength
- The main structural collagen and is found in fibrous supporting tissue, skin (dermis), tendons, ligaments and bone.
- When examined with the TEM, collagen fibers appear as bundles of fine, thread- like subunits, the collagen fibrils
Reticular Fibers (type III collagen)
- Formstroma(delicate supporting network) around functional cells (parenchyma) of many organs such as endocrine glands, lymph nodes, bone marrow and liver.
- StainpoorlywithH&Ebut stain with silver salts
What type of fiber is shown in the image

Reticular fibers (arrows, silver stain)
What is depicted in the image and what is the arow pointing to

Liver cirrhosis
arrow pointing to collagen build up
Example of fibrosis
Fibrosis
Fibrosis is defined by the overgrowth, hardening, and/or scarring of various tissues and is attributed to excess deposition of extracellular matrix components including collagen.
What does fibrosis result from
• Results from chronic inflammatory reactions induced by a variety of stimuli including persistent infections, autoimmune reactions, allergic responses, chemical insults, radiation, and tissue injury.
What is depicted in each image shown

Elastin fibers (arrows) are seen in the mesentery (a), dermis (b) and in the wall of aorta (c)
Elastic Fibers
- They have rubber-like properties that allow tissues to stretch or bend and recoil
- Present in large amounts in tissues such as lung, skin, urinary bladder and the wall of blood vessels
- They are composite of fibrillin which forms a network of microfibrils, embedded in a larger mass of cross-linked elastin
What is shown in the image

Electron micrographs of Elastin fibers (E). Arrows show the fibrillin microfillaments
What is shown in the image

Fibroblasts (arrows)
What is shown in the image

Myofibroblasts (arrows)
Fibroblasts
- Synthesize collagen, elastic and reticular fibers and the complex carbohydrates of the ground substance in the ECM.
- During wound healing fibroblasts differentiate into myofibroblasts to repair the damaged organ
Permanent supporting (resident cells). They develop and remain in connective tissues
– Fibroblasts
– Adipocytes
Transient defense cells develop elsewhere, migrate into connective tissues for surveillance and in response to specific stimuli
– Macrophages
– Mast cells
– Plasma cells
– Leukocytes
Macrophages
- Phagocytic cells
- Blood-born cells that arise from monocytes
- They have different names in different tissues, e.g. Kupffer cells in the liver, microglia in the CNS, alveolar macrophages in the lung.
What is depicted in the image

M: acrophages
N: neurophils
BV: blood vessel
What is the imagine showing

Electron micrograph of a macrophage
Mast Cells
- They arise from a pluripotential hemopoietic stem cell (HSC) in the bone marrow
- After migrating into the connective tissue, immature mast cells differentiate and produce their characteristic granules
- Granules contain: heparin, histamine, chemotactic factors and leukotrienes They release chemical mediators that promote allergic reactions and inflammation.
- Absent from the CNS
What are the arrows pointing to

Mast cell (arrows)
What is depicted in the image

Electron micrograph of a mast cell
Plasma cells
- Plasma cells are antibody- producing cells derived from B lymphocytes
- The Golgi apparatus is usually prominent because of its relatively large size and lack of staining.
- The cytoplasm displays strong basophilia because of an extensive rER
- The nucleus is spherical and typically offset or eccentrically positioned
What type of cell is shown in this image

Plasma cell
What type of cell is shown in this image

Plasma Cell
Leukocytes
- White blood cells that include lymphocytes (B lymphocytes, T lymphocytes) monocytes and granulocytes (neutrophils, eosinophils,basophils)
- Transient cells that enter the connective tissue in response to specific stimuli
What type of cell is depicted in the image

Leukocytes (neutrophils, arrows) normally found in the lamina propria of the small intestine
Adipocytes
- Specialize in storage
- Found isolated or in groups within loose and dense irregular connective tissue
- Predominate in the adipose tissue:
– Unilocular adipocytes: in white adipose tissue
– Multilocular adipocytes: in brown adipose tissue
What type of cell is shown

Adipocyte
What type of cell is shown

a. White adipose tissue b. Higher magnification. A: adipocyte
- Unilocular: Found in white adipose tissue
- Contain one huge lipid droplet
What type of cell is shown

Adipocytes
- Multilocular: Found in brown adipose tissue
- Contain many small lipid droplets and numerous mitochondria
Embryonic connective: Mesenchyme
- Embryonic connective tissue that produces all types of connective tissue
- Consists of mesenchymal cells that are:
– undifferentiated cells
– elongated cells with large nuclei
• ECM consists mostly of ground substance rich in hyaluronan (hyaluronic acid) and very little collagen
What type of cell is shown

Mesechymal cells (arrows)
Embryonic connective tissue: Mucous (or mucoid) connective tissue
- Presentinumbilicalcord
- Gelatinouswithfew fibroblasts and collagen fibers and abundant ground substance known as Wharton’s jelly
- Manymesenchymalstem cells among fibroblasts
What type of tissue and cells are depicted in the image

Embryonic connective tissue: Mucous (or mucoid) connective tissue
Loose (areolar) connective tissue
- Large amount of ground substance and less collagen
- Contains numerous fibroblasts
- Forms a layer beneath the epithelial lining of many organs
- Fills spaces between muscle and nerve fibers
- Flexible but not very resistant to stress
- Well vascularized
- Site of inflammatory and immune reactions
What type of connective tissue is depicted

Loose (areolar) connective tissue
Dense connective tissue
- Fewer cells but many collagen fibers and less ground substance than loose connective tissue
- It protects organs and strengthens them structurally
What type of tissue is depicted

• Dense irregular connective tissue
– Fibers arranged in multiple directions
– Resistance to stress from all directions
What type of tissue is depicted

• Dense regular connective tissue
– Collagen fibers and fibroblasts arranged in parallel
– Resistance to prolonged or repeated stress from the same direction
Elastic connective tissue
- Dense connective tissue rich in elastic fibers
- Provides resistance to tissue allowing them to recoil after stretching
- They stain poorly with H&E and require special staining (e.g orcein, fuchsin)
What type of connective tissue is this

Elastic connective tissue
What type of connective tissue is this

Elastic connective tissue
Reticular connective tissue
Contains type III collagen (reticular) fibers produced by specialized fibrobasts (reticular cells)
- They create a delicate scaffolding (stroma) for lymphoid organs (lymph nodes and spleen), bone marrow and liver
- Reticular fibers are enveloped by reticular cells.
- Contains transient cells (macrophages and dendritic cells)
What is shown in the images below

a) Reticular fibers (arrows). b) Reticular fibers (arrows, silver staining)
Adipose Tissue
- Fat-storingcells (adipocytes) predominate
- Typesofadiposetissue:
– White adipose tissue: contains mostly unilocular adipocytes mostly
– Brown adipose tissue: contains mostly multilocular adipocytes
White Adipose Tissue
- It typically forms 20% of the body weight in adults
- Long-term energy storage
- Provides thermal insulation for the body
- Fills spaces between other tissues, helps keeps organ in place, acts as a cushion in regions subject to repeated mechanical stress (e.g. palms, heels)
- Produces various hormones, growth factors and other important substances
Brown Adipose Tissue
- Constitutes 2%-5% of the newborn body
- Serves for heat production, but not for energy storage
What type of tissue is the arrow pointing to, be specific

Brown adipose tissue