Histology- Connective Fibers

What is the defining characteristic of connective tissue regarding its origin?

It is a diverse group of tissues sharing a common embryonic origin, the mesenchyme (mesoderm).

How does connective tissue differ from epithelial tissue in terms of cellularity?

Connective tissue has few cells, whereas epithelial tissue is highly cellular.

Contrast the adherence of cells between connective tissue and epithelial tissue.

Cells in connective tissue are not adherent, while epithelial cells are tightly adherent.

Regarding vascularity, how do connective tissue and epithelial tissue compare?

Connective tissue is vascular, whereas epithelial tissue is avascular.

How does the extracellular matrix differ between connective tissue and epithelial tissue?

Connective tissue has an abundant matrix, while epithelial tissue has little.

What is the primary germ layer origin for connective tissue compared to epithelial tissue?

Connective tissue is derived mostly from mesoderm, while epithelial tissue is derived from all germ layers.

Which tissue type bears mechanical stress in connective tissue versus epithelial tissue?

In connective tissue, the matrix bears mechanical stress, whereas in epithelial tissue, the cells bear it.

What are the three main components that compose connective tissue?

It is composed of fibers, cells, and ground substance.

What are the two main categories of connective tissue?

Connective tissue proper and specialized connective tissue.

What are the two main types of connective tissue proper?

Loose connective tissue and dense connective tissue.

Describe the characteristics and locations of loose connective tissue.

It has abundant ground substance and typically supports epithelia, nerves, and blood vessels, forming the lamina propria.

Distinguish between dense regular and dense irregular connective tissue.

Dense regular has collagen fibers arranged in parallel bundles, providing great tensile strength in one direction (e.g., tendons, ligaments). Dense irregular has collagen fibers interwoven randomly, providing strength in multiple directions (e.g., dermis, organ capsules).

Name some types of specialized connective tissue.

Adipose tissue, cartilage, bone, and blood.

What is the most abundant structural fiber of connective tissue?

Collagen is the most abundant structural fiber.

Describe the typical diameter of collagen fibers.

Their diameter ranges from 0.5 to 10\,mm.

What property does collagen provide to connective tissue?

It provides tensile strength.

How do collagen fibers appear when stained with eosin, Mallory, or Masson’s?

They are acidophilic, staining pink with eosin, blue with Mallory, and green with Masson’s.

What distinctive pattern does collagen exhibit under electron microscopy when stained with heavy metals?

It exhibits a banding pattern that repeats every 68\,nm along its length, reflecting the structure of tropocollagen.

What is the polymerized form of Collagen Type I?

Fibril (fibrillar).

Where is Collagen Type I primarily distributed?

It is found in bone, skin, tendon, ligaments, cornea, and internal organs, accounting for 90\% of body collagen.

What properties are associated with Collagen Type I?

It is fibril-forming, typical and most common, with a rope-like structure, and clearly visible with electron microscopy and light microscopy.

What is the polymerized form of Collagen Type II?

Fibril.

Where is Collagen Type II largely distributed?

It is found in cartilage, intervertebral disc, notochord, and vitreous humor of the eye.

What is the polymerized form of Collagen Type III?

Fibril (reticular fibers).

What are the tissue distributions for Collagen Type III?

They are located in skin, blood vessels, and internal organs (stroma of the spleen, lymph nodes, and bone marrow).

What is the polymerized form of Collagen Type IV?

Sheet-like network.

Where is Collagen Type IV primarily located and what is its function?

It forms the basal laminae.

What are the similarities between collagen and reticular fibers?

Both are types of collagen fibers; reticular fibers are essentially very thin Type III collagen fibers. Both provide structural support.

What are the key differences between collagen (Type I) and reticular fibers (Type III)?

Collagen Type I fibers are thicker, generally unbranched, and provide tensile strength in dense connective tissues. Reticular fibers are thinner, branched, form delicate networks, and are stained with silver or PAS, providing support in lymphatic and hematopoietic organs and acting as a scaffold in embryonic tissue/wound healing.

Characterize the diameter and branching pattern of reticular fibers.

They are thin fibers (0.5 - 2\,mm in diameter) that exhibit a branching pattern.

What type of collagen constitutes reticular fibers?

They consist of Type III collagen.

What are reticular fibers coated with?

They are coated with proteoglycans.

What special stains are used to visualize reticular fibers?

They stain with silver salts or PAS.

Which cells synthesize reticular fibers?

Fibroblasts, reticular cells, Schwann cells, and smooth muscle cells of blood vessels and the alimentary canal synthesize them.

What is the function of reticular fibers in reticular organs?

They form the supporting framework for the spleen, lymph nodes, and bone marrow.

How do reticular fibers contribute to boundaries between epithelia and connective tissue?

They provide attachment of epithelial cells to the underlying connective tissue.

What role do reticular fibers play in embryonic tissue and wound healing?

They are present in embryonic tissue and wound healing, later being replaced by stronger type I fibers.

How do elastic fibers compare in diameter to collagen fibers?

They have a smaller diameter than collagen.

What is a notable characteristic of their structural organization?

They branch and form loose 3-D networks, fenestrated sheets, or parallel bundles.

What structural components make up elastic fibers?

They are composed of elastin (main component, amorphous core) and microfibrils (containing fibrillin, organize the fiber).

What is the role of fibrillin microfibrils?

Fibrillin microfibrils organize the growing elastic fiber.

Which cells synthesize elastic fibers?

Fibroblasts and smooth muscle cells synthesize them.

How do elastin molecules contribute to the elasticity of fibers?

Each elastin molecule is randomly coiled due to its hydrophobicity and can expand and retract due to covalent bonds forming a network.

What is the primary function of elastic fibers in the body?

They are primarily found in organs that must stretch and return to their original shape.

List specific locations where elastic fibers are abundant.

Locations include elastic arteries (e.g., aorta), dermis of skin, lung, elastic ligaments, and vocal folds.

What specific structures do elastic fibers form in elastic arteries?

They form fenestrated sheets in concentric layers between layers of smooth muscle cells.

Compare the physical appearance of collagen and elastic fibers under light microscopy.

Collagen fibers are thick, wavy, and unbranched, often appearing in bundles; elastic fibers are thinner, branch, and form networks or sheets.

What are the primary protein components of collagen and elastic fibers?

Collagen fibers are primarily composed of tropocollagen (forming fibrils), whereas elastic fibers are composed of elastin and fibrillin microfibrils.

How do collagen and elastic fibers differ in their functional properties?

Collagen provides high tensile strength but is relatively inelastic; elastic fibers provide elasticity and recoil capabilities.

What deficiency leads to Scurvy, and what is its role in collagen synthesis?

It results from a vitamin C deficiency, which is required for the synthesis of collagen molecules.

What are the common symptoms of Scurvy?

Symptoms include fragile blood vessels, loose teeth/tooth loss, swollen and bleeding gums, sore/stiff joints, and slow wound healing.

What is Ehlers-Danlos Syndrome classified as?

It is a heterogeneous group of heritable connective tissue disorders.

What range of symptoms can be associated with Ehlers-Danlos Syndrome?

Symptoms may include joint hypermobility, subluxations, soft-velvet-like skin, easy bruising, and poor wound healing.

Why can mutations in Type III collagen mutations (vascular type) of Ehlers-Danlos Syndrome be severe?

They can be severe because they affect blood vessels.

What genetic mutation is responsible for Marfan’s Syndrome?

It results from mutations in the fibrillin gene.

What are the characteristic physical symptoms of Marfan’s Syndrome?

Skeletal defects (tall, lanky individual, long limbs, spider-like fingers, chest abnormalities, spinal curvature) and cardiovascular abnormalities, such as aortic dilation.

Describe the physical characteristics of ground substance.

It is a viscous, clear substance with a high water content.

What happens to ground substance during tissue preparation?

It is lost during tissue preparation.

What does ground substance contain?

It contains proteoglycans and multiadhesive glycoproteins.

What are the primary functions of ground substance?

Its functions include mechanical support, withstanding compressive forces, rapid diffusion of water-soluble molecules, regulating growth factors and secreted proteins, and regulating molecular trafficking in the extracellular matrix.

What is the most abundant component of the ground substance?

Glycosaminoglycans (GAGs).

What property of ground substance are GAGs responsible for?

They are responsible for the physical properties of ground substance.

What makes GAGs highly negatively charged?

They are highly negatively charged.

Name some examples of GAGs.

Examples include Hyaluronic acid, Heparin sulfate, Chondroitin sulfate, Heparin, Dermatan sulfate, and Keratan sulfate.

How does Hyaluronic acid differ from other GAGs?

Is not bound to protein, meaning it does not form a proteoglycan.

What are proteoglycans composed of?

They are composed of core proteins covalently bound to glycosaminoglycan molecules.

Where are proteoglycans found?

They are found in the ground substance of all connective tissues.

What are the functions of multiadhesive glycoproteins?

They stabilize the extracellular matrix (ECM), link cells to ECM components, regulate cell movement, and stimulate cell proliferation and differentiation.