Connective Tissue

Question 1

• Most abundant and widely distributed of the primary tissues, but its amount in particular organs varies
• main classes: ___ ___ proper,cartilage, bone, and blood
• connects body parts
• Major functions include: binding and supoorting, protecting, insulating, storing and reserve fuel, and transporting substances within the body
• All ____ tissue arise from mesenchyme which is an embryonic tissue.
• may be avascular (such as cartilage), poorly vascularized (as in tendons and ligaments), or have a rich supply of blood vessels (as in adipose tissues). All have an extracellular matrix which separates the living cells from each other within the tissue. This makes the tissue able to withstand tension and trauma that no other tissue could.
• Structurally, there are three components: (1) cells, (2) fibers, (3) ground substance. Together the ground substance and fibers make up the non-living extracellular matrix.

Answer 1

Connective Tissue

Question 2

• immature cells that can be enlisted to secrete fibers and ground substance, or divide mitotically to replace damaged cells, or to support growth and general turnover of the tissue.
• Cells that end in the suffix _____ are actively dividing cells that have the ability to secrete the ground substance and fibers of their particular extracellular matrix. The primary ____ cell types are fibroblasts found in CT proper, chondroblasts found in cartilage, osteoblasts of bone, and a variety of hematopoietic stem cells which produce our circulating red and white blood cells.

Answer 2

blast

Question 3

• a mature form that carries on the day-to-day business of the particular tissue

Answer 3

cyte

Question 4

• “Womb”
• separates the living cells of the tissue

Answer 4

extracellular matrix

Question 5

• the unstructured material that fills the space between the cells and contains the fibers
• composed of interstitial (tissue) fluid, cell adhesion proteins (fibronectin, laminin, and others), and proteoglycans
• consists of large amounts of fluid and functions as a molecular sieve, or medium, through which nutrients and other dissolved substances can diffuse between the blood capillaries and the cells
• It can be fluid like maple syrup, a semifluid, or gelatinous like jello.
• contains water, electrolytes, fine collagen fibrils and a diversity of large molecules, especially glycoproteins or proteoglycans. Proteoglycans consist of a protein core to which are attached glycosaminoglycans or GAGs. The GAGs are negatively charged polysaccharides (like sugars) that stick out from the protein making microscopic “bottle brushes”. There are two main types of GAGs, chondroitin sulfate and hyaluronic acid.
• surrounds and supports the cells and fibers of the CT.
• It provides a medium for diffusion of nutrients and metabolites exchanged between blood and tissue. One of its major roles is to act as a molecular sieve; it allows for diffusion, but prevents the spread of larger materials such as bacteria.

Answer 5

ground substance

Question 6

• The most abundant cell type found in connective tissue proper are ____ which secrete the fibers and most of the ground substance.
• Their shape is variable and depends on how synthetically active they are, as well as in what type of CT they are found in.

Answer 6

fibroblasts

Question 7

Once a fibroblast finishes its synthetic work, they become less active and are called ___ However, if the matrix is injured, they can become active fibroblasts again in order to repair the damage.

Answer 7

fibrocytes

Question 8

• are derived from monocytes (yellow arrow) from the blood.
• They are phagocytic and are attracted to areas of infection.
• appear irregular in shape on histological slides. This is because their shape changes as they “crawl” through the tissue on their way to engulf bacteria, cellular debris, or any other kind of foreign material, living or dead.
• are derived from a type of circulating white blood cell (WBC) called a monocyte.
• “Big eaters”

Answer 8

macrophages

Question 9

• Energy reserve, padding, insulation, etc.
• These are large, ovoid cells. Their cytoplasm is filled with a huge droplet of stored fat in the form of triglyceride. The triglyceride takes up all of the cytoplasm pushing the nucleus out of the center and up against the inner surface of the plasma membrane. In histological sections, ____ can be easily recognized because they look like the outline of an empty circle. The reason for this is because when tissues are prepared for sectioning, they must be dehydrated in ethyl alcohol which dissolves the fat.

Answer 9

Adipocytes

Question 10

• Stem cells that can differentiate into other CT cell types if tissue becomes injured or infected
• stem cells that have the ability to differentiate into other types of CT cells if the tissue becomes injured or infected

Answer 10

Mesenchymal cells

Question 11

are most abundant in the skin, but can also be found in the CT of the eye.

Answer 11

Melanocytes

Question 12

• They include several types of white blood cells that leave the bloodstream to come to the aid of macrophages and mast cells in fighting infection or an injury.
• Phagocytic neutrophils and eosinophils that are attracted to injury sites by chemicals released by macrophages & mast cells
• “Small eaters”

Answer 12

microphages

Question 13

• ____ of connective tissue provide strength and support.
• There are three main types of CT ___; (1) collagen which comes from a word meaning glue, (2) elastic, and (3) reticular whose root word means “net”. Of these, collagen is by far the most abundant and the strongest.

Answer 13

fibers

Question 14

• the most abundant protein in the vertebrate body (25-30%).
• Tough and strong
• Breaking point greater than steel
• Allows for some degree of flexibility
• Synthesized by fibroblasts

Answer 14

Collagen fibers

Question 15

• Composed of the protein elastin
• Thinner than collagen; branched & wavy
• Fibers can stretch up to 150% of their relaxed state without breaking.
• Abundant in tissues subject to stretching: Arteries, parts of the lungs, some ligaments, skin, blood vessels, Synthesized by fibroblasts in CT, Synthesized by smooth muscle cells in blood vessels.

Answer 15

Elastic Fibers

Question 16

• Actually thin collagen fibers coated with a glycoprotein.
• Arranged in a tough but flexible network instead of bundles.
• Can be visualized with the light microscope only if stained with a silver-containing stain.
• Form a net-like meshwork for many organs
  Stroma
  Lymphoid organs such as spleen, lymph nodes, bone marrow.

Answer 16

Reticular Fibers

Question 17

• cluster along blood vessels
• detect foreign microorganisms and initiate local inflammatory responses against them
• These cells are large and ovoid in shape and are common along blood vessels in areolar CT which is where they have their greatest effect on the body. Their cytoplasm is filled with granules of heparin and histamine.

Answer 17

Mast cells

Question 18

an anticoagulant chemical that prevents blood clotting when free in the bloodstream

Answer 18

heparin

Question 19

• a substance that makes capil
• It causes blood vessels to get bigger in diameter and makes them “leaky”

Answer 19

histamine

Question 20

neutrophils, eosinophils, lymphocytes, and other cell types that are concerned with tissue response to injury

Answer 20

White blood cells

Question 21

store nutrients

Answer 21

fat cells

Question 22

• a common embryonic tissue
• CT arise from this
• has a fluid ground substance containing fine sparse fibers and star-shaped mesenchymal cells

Answer 22

mesenchyme

Question 23

• is the most widely distributed connective tissue in the body.
• small open space. This tissue appears to have a lot of “open space” between fibers and cells. In actuality, the space is filled with clear ground substance giving it an “airy” appearance.
• FUNCTION: Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid.
• Besides being the most widely distributed form of CT, ____ connective tissue is the least specialized. It contains all three fiber types, and many of the types of cells we discussed previously.
• Its ground substance accounts for most of its volume, and it can change shape and is resilient to pressure.
• ____ CT supports most epithelia. It also comprises the stroma (supportive network) of many organs and is found in the core of mesenteries.
• It binds body parts together while allowing them to move freely over one another; it wraps around small blood vessels and nerves, surrounds glands, and forms the subcutaneous tissue. It also connects skin to underlying tissues & allows muscles to contract without pulling on the skin. It supports mucous membranes (to be discussed later) where it is referred to as the lamina propria.
• is highly vascularized so it is a common site for injection of drugs.

Answer 23

Connective Tissue Proper: loose connective tissue, areolar

Question 24

Because of its loose structure, areolar CT serves as a reservoir of water & salts for surrounding tissues. Amazingly, areolar CT can hold about as much fluid as the entire bloodstream. When a body region is inflamed, the areolar CT in the area soaks up excess fluids like a sponge & the area swells. This condition is called ___

Answer 24

edema

Question 25

• FUNCTION: Provides reserve food fuel: insulates against heat loss; supports and protects organs
• “fat tissue” is a type of loose CT comprised of special cells called adipocytes which account for 90% of this tissue’s mass. As mentioned previously, adipocytes store fat in the form of triglycerides. Adipocytes are among the largest cells in the body, however they can swell and shrink as they take up or release fat. The photomicrograph on the right of the diagram above was taken from some adipocytes that were not full of fat giving them a wrinkly appearance. In full adipocytes, the cytoplasm and nucleus are pushed to the periphery of the cell. Adipocytes are derived from fibroblasts.
• located through out the body; it is located under the skin, it fills in eye sockets, surrounds kidneys, it is common beneath the mesothelial lining of the pericardial and abdominal cavities, it is found in the core of mesenteries, and other places. The fat beneath the skin serves the general energy needs of the entire body, whereas smaller, localized deposits serve local energy needs of highly active organs like the heart. Because fat is a poor conductor of heat, it helps insulate the body; it prevents heat loss.

The type of fat just described is called white fat, but babies have a second type of fat called brown fat. Brown fat differs from white fat in that the cells contain many mitochondria (giving it the brownish coloration), and is highly vascularized. Instead of using lipids to make ATP, the mitochondria of brown fat use the lipid fuel to make heat. This is important, because new born babies lack the ability to produce body heat by shivering. Brown fat is located mainly between the shoulder blades, on the anterolateral neck, and on the anterior abdominal wall.

Answer 25

Connective tissue proper: loose connective tissue, adipose

Question 26

• FUNCTION: Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages
• As the name indicates, ___ CT contains only reticular fibers which form an interlacing network that supports the cells of certain kinds of organs. The supportive network formed by reticular fibers is called the stroma which literally means bed or mattress.
• The stroma supports the functional cells (collectively referred to as the parenchyma) of the organ.
• _____ CT is found in lymphoid organs such as lymph nodes, spleen, bone marrow, as well as the liver and kidney.

Answer 26

Connective Tissue proper: loose connective tissue, reticular

Question 27

• Has a greater proportion of fibers, fewer cells and less ground substance than loose CT.
• Two major kinds: Dense Regular CT & Dense Irregular CT

Answer 27

Dense CT

Question 28

• FUNCTION: attaches muscle to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction
• contains closely packed parallel bundles of collagen fibers and very little ground substance.
• The cells found in __ __CT are fibroblasts which appear as dark-staining, elongated ovals, found squeezed between the fiber bundles that they secrete. The fibers and fibroblasts (or fibrocytes) are highly ordered, but the tissue is poorly vascularized because there is no room for capillaries. Consequently, when damaged __ ___ CT is very slow to heal.
• is found where strength is required in a specific direction; the fibers run parallel to the direction of pull. Notice that the bundles of collagen fibers appear wavy. This allows some limited stretch or give to the tissue. However, when the fibers are fully straightened out by a force pulling on them, there is no further stretch.
• Common examples of __ __ CT include tendons which connect muscle to bone and ligaments that connect bone to bone. An aponeurosis is a tendinous sheet that attaches a broad, flat muscle to another muscle or to bones.
• also makes up the cornea of the eye which needs to be strong, but remain clear.

Answer 28

CT Poper: Dense CT, Dense regular

Question 29

• FUNCTION: Withstands tension exerted in many directions; provides structural strength
• has the same structural elements as dense regular CT except that the bundles of collagen fibers are much thicker and are arranged irregularly meaning that they run in multiple directions.
• This irregular random weave of thick collagen fibers makes the tissue very strong and resistant to tension or stress coming from more than one direction.
• It also helps to prevent over expansion of some hollow organs such as the urinary bladder.
• makes up the dermis of skin, capsules of organs, heart valves, sheaths of tendons, sheaths surrounding bone (periosteum) and cartilage (perichondrium), and the submucosa of digestive tract.

Answer 29

CT Proper: Dense CT, dense irregular

Question 30

• FUNCTION: Allows tissue to recoil after stretching; maintains pulsatile flow of blood through arteies, aids passive recoil of lungs following inspiration
• has a much more limited distribution. It is found mainly in a few ligaments between the vertebrae (ligamenta nuchae and ligamenta flava) that need to stretch as the trunk bends and twists.
• contains many branching elastic fibers. It appears yellowish in the fresh state. When stretched, elastic connective tissue can snap back into shape thereby providing both stretch and strength

Answer 30

CT PROPER: Dense CT, elastic

Question 31

• is able to withstand both tension and compression; it is tough but flexible and so provides a resilient rigidity to the structures it supports. Think about your trachea or windpipe. It is comprised largely of cartilaginous rings. These prevent the collapse of the windpipe when you take a deep breath, but also permits the neck to be flexible.
• located on the ends of bones absorbs and cushions the compression when we jump, and allows bones in our joints to glide smoothly when we move.
• lacks nerves and is avascular. It is nourished via diffusion from a surrounding covering of dense irregular connective tissue called the perichondrium.
• About 80% of the ___ matrix is made up of water, which enables it to rebound after being compressed, and provides a means of diffusion of nutrients to the cartilage cells. The ground substance contains large amounts of the GAGs chrondroitin sulfate and hyaluronic acid, and fibers of collagen and sometimes elastin.
• Because ___ is avascular and aging choncrocytes lose their ability to divide, __ heals slowly when injured. This is why sports injuries involving damage to ___ take so long to heal. During later life, ___ tends to calcify or even ossify (become bony). This causes the chondrocytes to die because diffusion of oxygen and nutrients is eliminated.
• There are three major types: hyaline, elastic and fibrocartilage, so named because of the main type of fibers in the matrix.

Answer 31

cartilage

Question 32

• The cells of cartilage are called ____
• They may occur singly or in clusters of 2-4 cells.
• They sit in “holes” in the organic matrix called lacunae. As the ____ secrete the fibers and ground substance of the cartilage, they become trapped in the matrix. Therefore, when they divide they form clusters or nests of cells surrounded by extracellular matrix.
• Each cluster of ___ represents the descendents of a single __
• Unlike other connective tissues, cartilage has no blood vessels or nerves within it. __ receive nutrients and oxygen via diffusion through the matrix from the perichondrium.

Answer 32

chondrocytes

Question 33

• FUNCTION: Supports and reinforces; serves as resilient cushion; resists compressive stress
• Of all three types of cartilage, ___ cartilage is the most abundant and wide spread.
• appears glassy, shinny, and whitish-blue when fresh. About 40% of the matrix is comprised of collagen fibers which give it strength, but they are fine and indistinguishable. The remainder of the matrix is ground substance. The primary proteoglycan of the ground substance is chondroitin sulfate.
• is the main type of cartilage found supporting and reinforcing body structures and joints.
• It covers the ends of long bones in joint cavities, it is found on the ends of the ribs that join the sternum, it supports the trachea, nose and most of the voice box or larynx. Most of the fetal skeleton forms from a __ cartilage model that is eventually replaced by bone.

Answer 33

Hyaline cartilage

Question 34

• FUNCTION: Maintains the shape of a structure while allowing great flexibility
• has a much more restricted distribution. It appears yellow when fresh. The organic matrix of __ cartilage contains less ground substance and is filled with elastic fibers. As we learned previously, elastic fibers branch.
• In ___ cartilage they form a network within the matrix which can be visualized using a microscope because the matrix does not appear smooth and glassy. In the picture above, the fibers appear purple to black. This is because a special stain was you so they can be seen.
• Another distinguishing histological feature of ___ cartilage is that the chrondrocytes are more abundant and more closely packed compared to hyaline cartilage.
• is found where support is required, but the structure is subject to distortion. For example, you can twist and turn your outer ear called the pinna, but it will spring back to its original shape.
• is also found comprising some of the cartilages of the larynx.

Answer 34

Elastic Cartilage

Question 35

• FUNCTION: Tensile strength allows it to absorb compressive shock
• is intermediate in structure between hyaline cartilage and dense regular connective tissue.
• It does not have much ground substance, instead the matrix is laced with dense collagen fibers arranged in parallel bundles. The chondrocytes are located in rows between the collagen bundles.
• is found where strong support and ability to withstand heavy pressure are required.
• Examples of locations in the body where its found include the cartilages of the knee (menisci), intervertebral discs which are cushions between the vertebrae, and the cartilage between the two pubic bones (pubic symphysis).

Answer 35

Fibrocartilage

Question 36

• stem cells in the perichondrium divide mitotically (make an identical copy of themselves). One of the daughter cells stays a stem cell in the perichondrium, the other becomes an immature chondrocyte (more appropriately, a chondroblast). The immature chondrocytes begin secreting new matrix (shown in dark blue in the diagram). As more and more matrix is secreted, the young chondrocytes are displaced from the surface and are now mature chondrocytes.

Answer 36

appositional growth

Question 37

• involves cell division of mature chondrocytes within the matrix. The chondrocyte divides mitotically in its lacuna. This time, both daughter cells remain as chondrocytes. As they secrete additional matrix, they move apart expanding the cartilage from within. This explains why it is common to see clusters of 2-4 chondrocytes together—they are essentially all clones.

Answer 37

interstitial growth

Question 38

• is a very special kind of connective tissue.
• FUNCTION: Supports and protects (by enclosing); provides levers for the muscles to act on; stores calcium and other minerals and fat; marrow inside ___ is the site for blood cell formation (hematopoiesis)
• The matrix contains very little ground substance and the GAG is chondroitin sulfate.
• Over 90% of the matrix is made up of collagen which makes ___ very strong.
• Packed around the collagen fibers are small crystals of calcium phosphate salt called hydroxyapatite. The crystals make bone hard; if chemically decalcified, ___ can be tied in a knot.
• Unlike cartilage, __ is highly vascularized. This is because, the hydroxyapatite crystals impede diffusion of nutrients to the bone cells.
• Just like cartilage, most of the___ is covered by a dense irregular connective tissue carrying blood vessels and nerves. In __, this layer is called the periosteum.
• comes in two forms, spongy and compact.
• The mature cells of bone are called osteocytes and they are found in lacunae just like cartilage.
• The histological section shown in the picture above is of compact ___. The osteocytes are the tiny cells that somewhat resemble ants because of the appearance of fine lines leaving the main cell body. The fine lines are actually extensions of the cytoplasm that lie in tiny channels called canaliculi. They keep the osteocytes connected to one another and to a nearby blood supply. Recall that the matrix is calcified and therefore prevents diffusion.
• Besides functioning to support and protect the body and some of its vital organs, __ forms the levers upon which muscle acts to create movement.
• also functions as a major storage site of minerals particularly calcium, therefore bone plays a primary role in calcium homeostasis.
• There are other vital minerals stored in ___ as well.
• Some store adipose tissue in their marrow cavities which functions as an energy reserve.
• Other have sites in their marrow cavities for the production of both red and white blood cells, a process called hemopoiesis.

Answer 38

Bone

Question 39

• oes not connect things or give mechanical support.
• It is classified as a connective tissue because it develops from mesenchyme and contains cells surrounded by a nonliving fluid matrix called plasma.
• To qualify as a CT, the matrix must contain fibers. The “fibers” of blood plasma are soluble proteins that only come out of solution when __ clots.
• Plasma makes up about 55% of whole __, and the cellular component makes up the remaining 45%.
• The cells consist of both red and white __ cells, called erythrocytes and leukocytes, respectively.
• Erythrocytes make up over 99% of the cells.
• When__ is removed from the body, and spun in a centrifuge, the red __ cells pack to the bottom of the tube, and the lighter white __ cells form a thin layer called the buffy coat that floats on top of them. The buffy coat also contains cell fragments called platelets that aid in clot formation. The plasma is found on the top of the column. Plasma from which the fibrin has been removed is called serum and this represents the ground substance component of the extracellular matrix of __.

Answer 39

Blood