Connective Tissue 1

Question 1

Connective Tissue

Answer 1

Connective tissue comprises one of the four basic tissue types

• forms a framework upon which epithelial tissue rests and within which nerve tissue and muscle tissue are embedded
• Blood vessels and nerves travel through connective tissue
• provide a matrix that connects and binds cells and organs

Question 2

Functions of Connective Tissue

Answer 2

• transport nutrients and metabolites
• immunological defense
• ## mechanical support

Question 3

Connective tissue components

Answer 3

• cells
• extracellular matrix : fibers, ground substance
• cells of connective tissue are not directly attached to one another

Question 4

Origin of Connective Tissue

Answer 4

• originate from the mesenchyme, an embryonic tissue formed by elongated cells
• mesodermal cells migrate from their origin site and surround and penetrate developing organs
• connective tissue cell lineage derived from the multipotential embryonic mesenchyme

Question 5

Connective tissues cells can be resident or wandering. What is the difference?

Answer 5

Resident cell population: permanent residents

Wandering or transient cell populations: cells that migrate into CT from blood

Question 6

Fibroblasts

Answer 6

Most common cells in connective tissue and are responsible for the synthesis of extracellular matrix

• only the nucleus is visible in H & E preparations
• Two stages of activity- active and quiescent -are observed in these cells
• a) The active fibroblast has an abundant and irregular branched cytoplasm
• b) The quiescent fibroblast or fibrocyte is smaller than the active fibroblast and tends to be spindle shaped

Question 7

Macrophages

Answer 7

• they are phagocytic cells derived from monocytes
• connective tissue macrophasges are also called histiocytes
• characterized by an irregular surface with pleats, protusions, and indentations, a morphological expression of their active pinocytotic and phagocytic activities
• act as defense elements
• important role in removing cell debris and damaged extracellular components

Question 8

Chronic granulomatous inflammation

Answer 8

• is a specialized form of chronic inflammation characterized by small aggregates of modified macrophages ( epithelioid cell and multinucleated giant cells usually populated by CD4+ Th1 lymphocytes

Question 9

Mast cells

Answer 9

• large ovoid CT cells, with a spherical nucleus and cytoplasm filled with large basophilic secretory granules
• originate from progenitor cells in the bone marrow
• surface of mast cells contains specific receptors for immunoglobulin

Question 10

Immediate hypersensitivity reaction

Answer 10

• release of the chemical mediators stored in mast cells promotes the allergic reactions known as immediate hypersensitivity reactions

Question 11

Adipose Cells

Answer 11

• connective tissue cells that have become specialized for storage of neutral fats or for the production of heat

Question 12

Undifferentiated mesenchymal cells

Answer 12

• present in loose CT, differentiate into cells that are required in repair and formation of new tissue

Question 13

Plasma cells

Answer 13

• ovoid cells that have a basophilic cytoplasm due to their richness in rough endoplasmic reticulum
• derived from B lymphocytes and are responsible for the synthesis of antibodies

Question 14

Leukocytes

Answer 14

The normal connective tissue contains leukocytes that migrate through the walls of capillaries and postcapillary venules from the blood to connective tissue by a process called diapedesis

Question 15

Connective
tissue
fibers

Answer 15

• are present in various amounts depending on the structural needs or function of the connective tissue
• Three main types of connective tissue fibers: collagen, reticular, elastic

Question 16

Collagen fibers and fibrils

Answer 16

1) collagens that form long fibrils: molecules of long fibril-forming collagens aggregate to form fibrils clearly visible in the electron microscope
2) Fibril- associated collagens: short structures that bind collagen fibrils to one another and to other components of the extra cellular matrix
3) Collagen that form networks: The molecules of the network- forming collagen or type 4 collagen assemble in a meshwork that constitutes the structural component of the basal lamina
4) Collagens that form anchoring fibrils: anchoring collagen, or type 7 collagen is present in the anchoring fibrils that bind collagen fibers to the basal lamina

Question 17

Reticular fibers

Answer 17

• particularly abundant in smooth muscle endoneuriu and the framework of hematopoitetic organs,, spleen, lymph nodes, red bone and constitute a network around the cells of parenchymal organs

Question 18

Elastic fibers

Answer 18

• allow tissues to respond to stretch and distension
• composed of two structures , a central core of elastin and surrounded by fibrillin microfibrils
• elastin: is a protein that forms fibers of varibale thickness or lamellar layers as in elastic arteries
• fibrillim: is a glycoprotein that forms fine microfibrils; the microfibrils are formed first, elastin material is then deposited on the surface of microfibrils

Question 19

Ground Substance

Answer 19

• occupies the space between the cells and fibers

- Ground substance is a highly hydrophilic, viscous complex of: 1) anionic macromolecules 2) multiadhesive glycoproteins

Question 20

Glycosaminoglycans

Answer 20

• linear polysaccharides formed by repeating disaccharide units usually composed of a uronic acid and a hexosamine

Question 21

Proteoglycans

Answer 21

• composed of a core protein associated with the four main glycosaminoglycans: dermatan sulfate, chondroitin sulfate, keratan sulfate, heparan sulfate
• have been shown to be bound to a hyaluronic acid chain forming larger molecules- proteoglycan aggregates called aggrecan
• aggrecan: responsible for hydration of ECM of cartilage
• decorin: collagen fibrilogenesis, regulates thickness of the fiber
• versican: cell to cell and cell to ECM interaction
• syndecan: transmembrane proteoglycan binds collagen, heparing, tenacin, and fibronectin tointercellular cytoskeletal actins

Question 22

Multiadhesive glycoporteins

Answer 22

• compound that contain a protein moiety to which carbohydrates are attached
• functions: attachment, adhesion, motility, and growth & differentiation
• fibronectin is a glycoprotein synthesized by fibroblasts and some epithelial cells
• laminin is a large glycoprotein that participates in the adhesion of epithelial cells

Question 23

Degradation of the extracellular matrix

Answer 23

• can be degraded by matrix metalloproteinases, a family of zinc-dependent proteases
• the activity pf matrix metalloproteinases in the extracellular space can be speciffically inhibited by tissue inhibitors of metalloproteinases

Question 24

Member of the family of matrix metalloproteinases

Answer 24

• Collagenases: MMP-1, MMP-8, and MMP13 can degrade types 1,2,3,5 collagens
• Gelatinases can degrade a number of ECM molecules including type 4,5,6 collagens, laminin, and aggrecan core proteins
• Stromelysins degrade basement membrane components
• Matrilysins

Question 25

Classification of Connective tissues

Answer 25

1) Embryonic connective tissue: mesenchyme, mucous connective tissue 2) connective tissue proper: loose connective tissue, dense connective tissue 3) Specialized connective tissue: adipose tissue, cartilage and bone, blood and hemopoietic tissue, lymphatic tissue

Question 26

Mesenchyme

Answer 26

- embryonic connective tissue primarily found in embryo

Question 27

Mucous connective tissue

Answer 27

- has an abundance of ground substance composed primarliy of hyaluronic acid and are mainly in the fibroblast

Question 28

Loose Connective Tissue

Answer 28

- loosely arranged fibers and abundant cells of various type - supports many structures that are normally under pressure and low friction - fills space between groups of muscle cells - moderate amount of collagen elastic and reticular fibers

Question 29

Dense CT

Answer 29

- less flexible and far more resistant to stress than is loose connective tissue - Dense irregular connective tissue: contains more fibers and the collagen fibers are arranged in bundles without a definite orientation; found in reticular dermis and capsules of various organs - Dense regular tissue: characterized by ordered and densely packed arrays of fibers and cells; aligned witht the linear orientation of fibroblasts in response to prolonged stresses exerted in the same direction

Question 30

Tendons:

Answer 30

elongated cylindrical structures attach striated muscle to bone

Question 31

Adipose tissue

Answer 31

- specialized connective tissue that plays an important role of energy homeostasis - one of the largest organs in the body - very efficient energy storage tissue - continuous turnover and is sensitive to both nervous and hormonal stimuli

Question 32

Unilocular ( white) adipose

Answer 32

- composed of cells that when completely developed, contain one large central droplet of yellow fat in their cytoplasm for reserves of long term energy and also as endocrine organ - found throughout the human body except for the eyelids, the penis, the scrotum, and the entire auricle of the external ear - age and sex determine the distribution - subdivided into incomplete lobules by a partition of connective tissue containing a rich vascular bed and network of nerves

Question 33

Multilocular (brown) adipose

Answer 33

composed of cells that contain numerous lipid droplets and abundant brown mitochondria