Describe the general functions of connective tissues.

Functions of CT - COMMS

Connect tissues and cells

Organ support  

Mechanical support and protection

Metabolic support as medium for diffusion

Signaling to other cells

Give a description of each type of connective tissue cell, including ultrastructure, any special conents (e.g. granules) and function: fibroblast/fibrocyte

fibroblasts (blast = younger, more metabolic)

structure:

– most common CT cell

– abundant basophilic cytoplasm with long cytoplasmic processess

– abundant rER, Golgi
- large ovoid euchromatic nucelus, prominent nucleolus

fibrocyte (cyte = older, less metabolic)

structure:

– smaller quiescent fibroblasts
– spindle-shaped, less processes
– smaller, darker nuclei
– cytoplasm more acidophilic

development: Mesenchymal development

function:

• synthesize and secrete components of ECM

• respond to growth factors

• post-mitotic, except during tissue damage

clinical:

• fibroblasts secrete scar tissue after tissue damage

• quiescent fibrocytes can revert to fibroblasts

• wound contraction brought about by myofibroblasts, cells that have features of fibroblasts, but also with contractile properties due to having increased amounts of actin/myosin

What type of fiber is this?

[image]

Collagen

description:
most abundant protein in body (30%), secreted by various cell types (fibroblasts, osteoblasts, chondroblasts, odontoblasts, smooth muscle cells, etc.)

structure: triple helix of pre-procollagen α chains, forming a procollagen fibril (10.4 nm/turn, 67 nm periodicity)-> collagen

categories of collagen:
– collagens that form fibrils (types I, II, III, V and XI)
– fibril-associated collagens (types IX, XII and XIV)
– collagen forming anchoring fibrils (type VII)
– collagen that forms networks (types IV, VII)

clinical:

• osteogenesis imperfecta – defect of type I collagen; leads to brittle malformed bones
• progressive systemic sclerosis – excessive collagen production; leads to fibrosis of tissues
• keloid – excessive collagen deposited in scars
• scurvy – vitamin C deficiency, leading to degeneration of CT

Explain the synthesis of collagen fibers, and their degradation.

synthesis:

• pre-procollagen α chains produced by ribosomes and
released into rER cisternae
• lysine and proline residues hydroxylated yielding
hydroxylysine and hydroxyproline (vitamin C dependent)
• some hydroxylysine residues are glycosylated
• α chains coil around each other to form a triple helix

• triple helices form procollagen fibrils, that can be
homotrimeric or heterotrimeric
• procollagen molecules are sent to Golgi, where
molecules are modified, packaged in secretory vesicles
and shipped
• once secreted, procollagen peptidases cleave terminal peptides, converting procollagen -> collagen

• cross-linking of collagen molecules is catalyzed by lysyl oxidase

degradation: Cortisol stimulates degradation of (skin) collagen into amino acids.

Describe the components of ground substance -- their chemical composition and properties.

ground substance is amorphous, transparent, highly hydrated, viscous that fills spaces between cells and fibers, and acts as barrier to microbes It is made of:

1. glycosaminoglycans (GAGs) - unbranched disaccharide polymers of a uronic acid (glucuronic or iduronic acid) and a hexosamine (glucosamine or galactosamine). examples include: 

• hyaluronan – polymers of glucosamine/glucuronate (of integral membrane)
• dermatan sulfate
• chondroitin sulfate
• keratan sulfate
• heparan sulfate

2. proteoglycans (mostly saccharides)

• formed of a core protein to which are attached sulfated GAGs
• acidic groups on proteoglycans cause binding to basic amino acid residues on collagen molecules
• aggrecan (cartilage) – syndecan (cell surface)

3. multiadhesive glycoproteins (mostly protein)

• similar to proteoglycans, but protein moiety
predominates
• play role in adhesion of cells to substrate, or cells to cells

• examples: involved in embryonic development
– fibronectin » binds to collagen, GAGs and integrins on cell membranes
– laminin » binds to type IV collagen, GAGs and integrins; involved in binding of epithelial cells to basal lamina

- both allow cancer cells to invade tissues

Note: integrin: cell surface receptors which bind collagen, fibronectin and laminin, bind to the cytoskeleton (to actin filaments) via talin and vinculin

Give a description of each type of connective tissue cell, including ultrastructure, any special conents (e.g. granules) and function: adipoctye

adipocyte structure:

– large cells ranging in size from 50-150 μm in diameter
– contain single large lipid droplet (85% of cell’s weight)
– in tissue prep, solvents dissolve out fat (chicken-wire)
- thin rim of cytoplasm with nucleus on periphery

– cells are surrounded by external (basal) lamina

development: Mesenchymal development

function:

- storage of neurtral fats

- heat production by "brown" fat (infants)

Give a description of each type of connective tissue cell, including ultrastructure, any special conents (e.g. granules) and function: mast cells

mast cell structure:

– large ovoid cells, 20-30 μm diam.
– granules demonstrate metachromasia

– central spherical nucleus

– cytoplasm filled with basophilic granules containing:

• heparin
• histamine
• serine proteases
• leukotrienes
• eosinophil and neutrophil chemotactic factors

development: hematopoietic

functions: release stored chemical mediators which promote immediate hypersensitivity reactions in response to allergens, causing mast cells to degranulate

clinical: anaphylaxis -  antigen binding to IgE attaced on mast cells causes degranulation, leading to:

• itching, flushing and swelling of skin (hives)
• s.o.b. due to tracheal and bronchial swelling
• abdominal cramping, diarrhea, vomiting
• coronary artery spasm leading to arrhythmia or infarction
• loss of consciousness, loss of bladder control and muscle tone

Give a description of each type of connective tissue cell, including ultrastructure, any special conents (e.g. granules) and function: plasma cells

plasma cell structure:

– large ovoid activated B lymphocytes cells (antigen⁺)
– basophilic cytoplasm
– juxtanuclear Golgi apparatus (stains pale in H&E)
– spherical eccentric nucleus with “clock face” pattern of
heterochromatin

development: hematopoietic

functions: manufacture and release immunoglobulins (antibodies), which bind to specific antigens to destroy or inactivate them, or produce some other immune response

Give a description of each type of connective tissue cell, including ultrastructure, any special conents (e.g. granules) and function: leukocytes/WBC

leukocyte (WBC) structure:

– don’t contain hemoglobin (RBCs do)
– originate in bone marrow, travel in the blood to sites of activity using diapedesis (squeeing thru capillary walls)

development: hematopoietic

functions: involved in various aspects of
inflammatory and immune responses

types:

• agranulocytes
     – monocytes -> macrophages
     – lymphocytes (B and T cells)
• granulocytes
     – neutrophils
     – eosinophils
     – basophils

What type of fiber is this?

[image]

Elastic fiber

structure:

• thinner than type I collagen fibers
• formed of microfibrils made of fibrillin and other
glycoproteins, which surrounds the fiber in a sheath
• elastin is deposited between the microfibrils, forming
larger fibers, which is digested by pancreatic elastase

• desmosine and isodesmosine cross-link elastin
molecules

clinical: Marfan syndrome: defect in fibrillin gene

What type of fiber is this?

[image]

Reticular fiber

structure:

• formed of type III collagen
• form networks of thin, heavily glycosylated fibers
• stain with silver (argyrophilic) stains or PAS
• form supporting meshwork for liver, marrow and  lymphatic organs