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Example research essay topic: White Blood Cells Connective Tissue - 3,064 words

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... site Connective tissues have three main elements: ground substance, fibers, & cells. Ground substances make up the extracellular matrix. (Note: that the term matrix indicates the ground substance. ) Ground Substance - is an amorphous (unstructured) material that fills the space between the cells & contains the fibers. It is composed of interstitial fluid, cell adhesion proteins, & proteoglycans. Cell adhesion proteins, a group that includes fibronectin & lamina, sever mainly as a connective tissue glue that allows connective tissue cells to attach themselves to matrix elements. The proteoglycans consists of a protein core to which glycosaminoglycans (GAGs) are attracted.

The strand-like GAGs which are large, negatively charged polysaccharides, stick out from the core protein like the fibers of a bottle brush. Important examples of GAGs in connective tissues are chondroitin sulfate, keratin sulfates, & hyaluronic acid. The GAGs intertwine & trap water, forming a substance that varies from a fluid to a semi-stiff hydrated gel. The relative amounts & kinds of GAGs help determine the properties of the matrix. Example - The higher the GAG content, the stiffer the ground substance is.

The ground substance holds fluids & functions as a molecular sieve, or medium, through which nutrients & other dissolved substances can diffuse between the blood capillaries & the cells. The fibers embedded in the ground substance makes it less pliable & impede diffusion somewhat. The fibers of the connective tissue provide support. Three types of fibers are found in connective tissue matrix: Collagen Fibers - (white fibers), are constructed primarily of the fibrous protein collagen. Collagen molecules are secreted into the extracellular space, where the are assembled spontaneously into cross-linked fibers. Collagen fibers are extremely tough & provide high tensile strength to the matrix.

Stress test show that collagen fibers are stronger than steel fibers of the same size. Collagen fibers are the Elastic Fibers - (yellow fibers), are formed largely from another fibrous protein, elastin. Elastin has a randomly coiled structure that allows it to stretch & recoil like a rubber band. The presence of elastin in the matrix gives it a rubbery, or resilient, quality. Connective tissue can stretch only so much before its thick, rope-like collagen fibers become taut. Then, when the tension lets up, elastic fibers snap the connective tissue back to its normal length & shape.

Elastic fibers are found where greater elasticity is needed (ex. skin, lungs, & blood vessel walls). Reticular Fiber - are fine callagenous fibers & are continuous with collagen fibers. They branch extensively, forming delicate networks that surround small blood vessels & support the soft tissue of organs.

They are particularly abundant where connective tissue abuts other tissue types, for example, in the basement membranes of epithelial tissues, & around capillaries, where they form fuzzy nets. Each major class of connective tissue has a fundamental cell type that exists in immature & mature forms. The undifferentiated cells, indicated by the suffix blast, are actively mitotic cells that secrete the ground substance & the fibers characteristics of their particular matrix. The primary blast cell types by connective tissue class are: Connective tissue proper: fibroblast.

Blood: hemocytoblast or hematopoietic stem cell. Once they synthesize the matrix, the blast cells assume their less active, mature mode, indicated by the suffix city. The mature cells maintain the health of the matrix. However, if the matrix is injured, they can easily revert to their more active state to repair & regenerate the matrix. (The hemocytoblast, the blood-forming stem cell found in bone marrow, always Additionally, connective tissue is home to an assortment of other cell types, such as nutrient-storing fat cells & mobile cells that migrate into the connective tissue matrix from the bloodstream. The latter include white blood cells (neutrophils, eosinophils, lymphocytes) & other cell types concerned with tissue response to injury, such as mast cells, macrophages, & antibody-producing plasma cells.

This wide variety of cells is particularly obvious in our prototype, areolar connective tissue. The oval mast cells are typically found clustered in tissue spaces deep to an epithelium or along blood vessels. These cells act as sensitive sentinels to detect foreign substances (ex, bacteria, fungi) & initiate local inflammatory responses against them. In the mast cell cytoplasm are conspicuous secretory granules containing: Heparin - an anticoagulant (a chemical that prevents the blood clotting) when free in the bloodstream, but its significance in human mast cells Histamine - is released during inflammatory reactions, makes the Macrophages are large, irregularly shaped cells that avidly phagocytic a broad variety of foreign materials, ranging from foreign molecules to entire bacteria to dust particles. Macrophages also engulf & dispose of dead tissue cells, & they are central actors in the immune system. In connective tissues, they may be attached to connective tissue fibers or they may migrate freely through the matrix.

Macrophages are peppered throughout loose connective tissue, bone marrow, & lymphatic tissue. Those in certain sites are given specific names. They are called histiocytes in loose connective tissue, Kupffer cells in the liver, & micro glial cells in the brain. Although all these cells are phagocytes, some have selective appetites. For example, macrophages of the spleen primarily dispose of aging red blood cells, but they will not turn down other delicacies that Classwork (pgs. 128 - 134) February 18, 1999 Bone, Blood, Membranes, Nervous, & Muscle Tissues Bone (osseous) - due to its rock hardness it has the ability to support Blood - the fluid within blood vessels; functions as the transport vehicle Membranes - a continuous multicellular sheet composed of at least two primary tissue types: an epithelium bound to an underlying layer of Cutaneous Membranes - are your skin. Mucous Membranes - lines cavities open to the exterior.

Serous Membranes - are moist membranes found in closed ventral body cavities (ex. pericardium, pleura). Nervous Tissue - Has two major cell types. Neurons - specialized cells that generate & conduct nerve Muscle Tissue - made up of muscle fibers.

Muscle cells possess Skeletal Muscle - attached to bone, voluntary or stratified (lines); Cardiac Muscle - occurs in the heart, it is striated & contains intercalated discs (junctions of branching cells). Smooth Muscle - visceral or involuntary; found in hallow internal Homework (pgs. 136) February 18, 1999 Tissue repair requires that cells divide & crawl, activities that are initiated by growth factors (wound hormones) released by injured cells. It occurs in two major ways: by regeneration - the replacement of destroyed tissue with the same kind of tissue- & by fibrosis - involves proliferation of fibrous connective tissue called scar tissue. Each of these occurs depends In skin, the tissue we will use as our example, repair involves both Inflammation sets the stage. The process begins while the inflammatory reaction is still going on. Let us briefly examine what has happened up to this point.

Tissue injury sets the following inflammatory events into motion. First, because of the release of histamine & other inflammatory chemicals by injured tissue cells, macrophages, mast cells, & others, the capillaries dilate & become very permeable. This allows white blood cells & plasma fluid rich in clotting proteins, antibodies, & other substances to seep into the injured area. Then the leaked clotting proteins construct a clot, which stops the loss of blood, holds the edges of the wound together, & effectively walls off, or isolates, the injured area, preventing bacteria, toxins, or other harmful substances from spreading to surrounding tissues. The portion of the clot exposed to the air quickly dries & hardens, forming a scab.

The inflammatory events leave excess fluid, bits of destroyed cells, & other debris in the area. Most of this material is essentially removed from the area via lymphatic vessels or phagocytized by macrophages. At this point, the first step of tissue repair, Organization restores the blood supply. During organization the temporary blood clot is replaced by granulation tissue. Granulation tissue is a delicate pink tissue composed of several elements. Thin, extremely permeable capillaries bud from intact capillaries nearby & enter the damaged area, laying down a new capillary bed; they protrude nub-like from the surface of the granulation tissue, giving it a granular appearance.

These capillaries are fragile & breed freely, as demonstrated when someone picks at a scab. Also present in granulation tissue are scattered macrophages & fibroblasts that synthesize new collagen fibers to bridge the gap permanently. As organization continues, macrophages digest & remove the original blood clot. The granulation tissue, destined to become scar tissue (a permanent fibrous tissue patch), is highly resistant to infection because it produces bacteria-inhibiting substances. Regeneration &/or fibrosis effects permanent repair. While organization is going on, the surface epithelium begins to regenerate.

Epithelial cells migrate across the granulation tissue just beneath the scab, which soon detaches. As the fibrous tissue beneath matures & contracts, the regenerating epithelium thickens until it finally resembles than of the adjacent skin. The end result is a fully regenerated epithelium, & an underlying region of scar tissue. The scar may be invisible, or visible as a white thin line, depending on the Classwork (pgs. 189 - 203) February 24, 1999 The adult Skeleton has 206 separate bones. There are two main divisions: Axial Skeleton - has 80 bones; the upper axis has 74; the inner ear has 6. Contains the skull.

There are two major divisions: 2. / 3. Parietal Bones - bulging top side of the cranium. 4. / 5. Temporal Bones - house the middle & inner ear structures. 6. Occipital Bone - creates the framework of the lower back part 7.

Sphenoid Bone - resembles bat wings. 8. Ethmoid Bone - forms bony area between the nasal cavity & 1. / 2. Maxillae Bones - upper jaw (upper lip); one on each side. 3. Mandible Bone - lower jaw. 6. / 7. Nasal Bones - bridge of the nose; one on each side. 8. / 9. Lacrimial Bones - helps form tear ducts. 10. / 11.

Inferior Nasal Conchae Bones - ledge protecting the nasal 12. Vomer Bone - completes the nasal septum. 13. / 14. Palatine Bones - hard plate within the mouth. Appendicular Skeleton - consists of 126 bones. Classwork (pgs. 204 - 213) February 25, 1999 Hyoid Bone - is below the skill, attached to the bottom of the tongue; single bone in the neck above the larynx & below the mandible; not attached to any other bone in the body (sesam oid).

Spinal Column; divided into three types of vertebrae: Cervical Vertebrae - neck (has 7 bones). Thoracic Vertebrae - found in the posterior part of the chest or the Lumbar Vertebrae - found in the small of the back (has 5 bones). Sacrum - below the vertebral column, a single bone resulted by a fusion Atlas - is at the top of the vertebral column, the head sits upon it; has no Axis - is below the atlas; has a body & a spinous processes. Coccyx - is below the sacrum, consists of 4 bones fused together (is a tail Sternum - is the media part of the anterior chest. Ribs - 12 pairs or 24; in front (anterior), each of the first 7 ribs joins a costal cartilage that attach to the sternum. Then the next 3 join the cartilage of the ribs before, so they are attached to the sternum directly.

The 11 th & 12 th pairs do not attach & are called floating ribs. Classwork (pgs. 214 - 227) February 26, 1999 Bones of the limbs & their girdles are collectively called the appendicular skeleton because they are appended to the axial skeleton that forms the Shoulder Girdle - consists of two bones, the anterior clavicle & the Clavicles - collar bones, are slender, doubly curved long bones that can be felt along their entire courses as they extend horizontally across the Scapulae - shoulder blades, are thin, triangular flat bones. Humerus - (arm) articulates proximally with the scapula at the shoulder, & distally with the radius & ulna at the elbow. Radius - on the thumb side, has two proximal articulations, the humerus, Ulna - on the little finger side, articulates proximally with the humerus & the radius, & distally with cartilage. 5 metacarpals- framework of the hand. Hip Girdle- formed by a pair of coal bones, which consists of three bones, which are separate during childhood & fused together during adulthood): Ilium - the large flaring bone that forms a major portion of a coal Ischium - forms the posteroinferior part of the hip bone.

Pubis - forms the anterior portion of the os coxa. Femur - (thigh bone), is the largest, longest, & strongest bone in the body. Tibia - the longest & strongest bone in the lower leg; articulates proximally with the femur, & distally with the fibula & talus. Fibula - is smaller & more deeply placed, proximally articulates with the 5 metatarsals - flat part of the foot. Classwork (pgs. 261 - 262) March 05, 1999 General Function of the Muscular System There are four general functions of the skeletal system.

Movement - either body as a whole or parts of the body. Heat Production - muscles produce heat -- - since there are so many muscles, they are one of the most important parts of the mechanisms Posture - continual partial contraction of muscles allow for standing, Stabilizing Joints - muscles help keep everything in place. There are four characteristics that enable skeletal muscle tissue to Excitability - the ability to be stimulated, this causes them to be able to respond to regulatory mechanisms, such as nerve signals. Contractility - the ability to shorten, which allows muscles to pull on Extensibility - the ability to stretch & return to the resting length. Elasticity - the ability of the muscle fiber to resume to its resting length Skeletal muscle cells, are composed of bundles of skeletal muscle fibers that extend the length of the muscle. They are long cells.

They have the same structural parts as other cells, but they have different names: Sarcoplasmic Reticulum - endoplasmic reticulum. Sarco plasm - cytoplasm, it contains mitochondria & many nuclei. Myofibril's, are bundles of long fibers. They are made up of thick & thin Homework (pgs. 263 - 265) March 05, 1999 Most muscles span joints & are attached to bones (or other structures) in at least two places & when a muscle contracts, the movable bone, the muscles insertion, moves toward the immovable are less movable bone, the muscles origin. In the muscles of the limbs, the origin usually lies Muscle attachments, whether origin or insertion, may be direct or indirect.

In direct attachments, the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage. In indirect attachments, the muscles connective tissue wrappings extend beyond the muscle as a rope-like tendon or a flat, broad aponeurosis. The tendon or aponeurosis anchors the muscle to the connective tissue covering of a skeletal element (bone or cartilage) or to the fascia of other muscles. The temporal muscle of the head has both direct & indirect (tendinous) Of the two, indirect attachments are much more common in the body because of their durability & small size. Since tendons are mostly tough collagen ic fibers, they can cross rough bony projections which would tear apart the more delicate muscle tissues.

Because of their relatively small size, more tendons than fleshy muscles can pass over a joint -- - thus, When viewed at high magnification, each muscle fiber is seen to contain a large number of rod-like myofibril's that run in a parallel fashion & extend the entire length of the cell. Each are 1 - 2 m in diameter, the myofibril's are so densely packed that the mitochondria & other organelles appear to be squeezed between then. There are hundreds to thousands of myofibril's in a single muscle fiber, depending on its size, & they account for about 80 % of the cellular volume. The myofibril's are the contractile elements of the Striations, Sarcomere's, & Myo filaments Striations - a repeating series of dark & light bands, are evident along the length of each myo fibril. The dark bands are called A bands because they are anisotropic; that is, they can polarize visible light. The light bands, called I bands, are isotropic, or non polarizing.

In an intact muscle fiber, the myo fibril bands are nearly perfectly aligned with one another & this gives the cell as a whole a stripped (striated) appearance. Each A band has a lighter stripe in the midsection called the H zone (bright). The H zones are visible only in relaxed muscle fibers. Each H zone is bisected by a dark line called the M line. The I bands also have a mid-line interruption, a darker area called the Z discs. A sarco mere is the region of the myo fibril between two successive Z discs.

About 2 m long, the sarco mere is the smallest contractile unit of a muscular fiber. Thus, the functional units of the skeletal muscle are actually very minute proportions of the myofibril's, & the myofibril's are chains of sarcomere's aligned end-to-end like boxcars in a train. If we examine the banding pattern of a myo fibril at the molecular level, we see that it arises from an orderly arrangement of two types of even smaller structures, called filaments or myo filaments, within the sarcomere's. The thick filaments extend the entire length of the A band.

The more lateral thin filaments extend across the I bands & part way into the A band. The Z discs, also called a Z line, is a coined shaped protein sheet that anchors the thin filaments & also connects each myo fibril to the next throughout the width of the muscle cell. The H zone of the A band appears less dense when viewed microscopically because the thin filaments do not overlap the thick ones in this region. The M line in the center of the H zone is slightly darker because of the presence of fine strands that hold adjacent thick filaments together in that area.

A longitudinal view of the mylo filaments is a bit misleading because it gives the impression that each thick filament interdigitate's with only four thin filaments. In areas where thin & thick filaments overlap, each thick filament is actually surrounded by a hexagonal arrangement of six thin Bibliography: none


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Research essay sample on White Blood Cells Connective Tissue

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