Title Basic Tissue Types – Connective Tissue by jizhen1947


									Title: Basic Tissue Types – Connective Tissue

  1- Connective tissue is the most abundant and widely distributed tissue in the body.
     In its various forms, connective tissue

         a- binds together

         b- strengthens and supports

         c- protects and insulates

         d- compartmentalizes

         e- stores energy

         f- transports within the blood

         g- provides immunity

  2- Connective tissues – General features

         a- Connective tissue consists of two basic elements: Cells and
            extracellular matrix

         b- The extracellular matrix – is the material located between the widely
            spaced cells. The matrix consists of protein fibers and ground substance
            (the material between the cells and the fibers)

         c- The extracellular matrix is produced and secreted by the connective tissue
            cells. These cells determine the tissues qualities. For example
            chondrocytes (cartilage cells) produce an ECM that is hard but pliable,
            whereas osteocytes (bone cells) produce an ECM that is hard but not

         d- Unlike epithelium- Connective tissue are not found at body surfaces,
            with the exception of cartilage they are highly vascular (tendons are only
            slightly vascular) cartilage also does not have a nerve supply

  3- Connective tissue cells –

         a- Each type of connective tissue cell, contains a class of immature cells that
            end in “blast” which means to “bud or sprout” for example: fibroblasts in
            loose CT, osteocytes in bone, chondrocytes in cartilage. Blast type cells
            are capable of dividing and secrete the matrix
       b- Once these cells secrete the matrix they differentiate into the mature form
          of the cell, ending in “cyte” as in chondrocyte and adipocyte (fat cell).
          These cells have lost most of their ability to divide and are responsible for
          maintaining the ECM

       c- There are six types of connective tissue cells

          1- Fibroblasts – Large flat, branching cells found in most connective
             tissue. These are the most numerous of the CT cells

          2- Macrophages – engulf bacteria and cell debri through phagocytosis
             (cell eating)

          3- Plasma cells – secrete antibodies (proteins that attack foreign bodies)

          4- Mast cells – produce histamine, dilates small blood vessels as part of
             the inflammatory response

          5- Adipocytes – also called fat cells, CT cells that store triglycerides

          6- White blood cells (leukocytes) – not found in significant numbers in
             CT, however found in large numbers at areas where an immune
             response is occurring

4- The Extracellular matrix – Each type of connective tissue has unique properties,
   based on the ECM that the cells produce and found between the cells. The ECM
   consists of cells and ground substance

       a- Ground Substance – The ground substance is the component of the CT
          found between the cells and the fibers.

       b- The ground substance may be

          1- fluid

          2- semifluid

          3- gelatinous

          4- calcified

       c- The ground substance, stores water, binds tissue together, supports the
          cells and provides a medium that allows for exchange of materials
          between the blood and the cells
          d- The ground substance contains water and large organic compounds which
             are combinations of polysaccharides and proteins)

              1- The polysaccharides are collectively called glycosaminoglycans or
                 GAG’s, the most important of which is hyaluronic acid

              2- Hyaluronic acid – is a viscous, slippery substance that helps to
                 lubricate joints, holds cells together and maintains the shape of the eye

              3- White blood cells, sperm and bacteria produce Hyaluronidase, which
                 breaks apart the hyaluronic acid, making the ground substance more
                 liquid. This allows white blood cells to reach infections more easily,
                 allows sperm to enter the egg and unfortunately allows for the rapid
                 spread of bacteria though CT

5- The Fibers of the ECM – Fibers in the ECM strengthen and support CT. These fibers
include collagen, elastic and reticular

               1- Collagen –

              a- Are strong and resistant to pulling. They are not stiff and allow for

              b- Collagen is the most abundant protein in the body about 25% of
                 all proteins

              c-Collagen is most often found in cartilage, bone, tendons and ligaments

               2- Elastic fibers –

              a- Are smaller than collagen and form a dense network

              b- They contain the protein elastin and can stretch up to 150% of their
                 length without breaking

              c- They bounce back without losing elasticity

              d- They are found in blood vessels, skin and lungs

               3- Reticular fibers –

              a- Provide support in the walls of blood vessels

              b- Surround adipose tissue and smooth muscle

              c- Much thinner than collagen – found in spleen and lymph nodes
5- Types of Connective Tissue

      a- Connective tissue can be divided into 2 major groups: Embryonic and
         mature. Embryonic CT is generally only found in the embryo from
         fertilization until birth. Mature CT is present after birth and includes: 1-
         Loose CT, 2- Dense CT, 3- Cartilage, 4- Bone and 5- Liquid CT (Blood
         and lymph)

         1- Loose Connective Tissue – LCT the fibers are loosely held together
            with many cells present

               a- Areolar CT – is the most widely distributed CT in the body, it is
                  the layer of tissue that connects the skin to the underlying tissue
                  and organs (grip and rip)

               b- Adipose CT – adipose tissue is made from specialized cells
                  called adipoctyes (fat cells) and they store triglycerides (fat) Fat
                  helps to insulate the body, is a major energy reserve and protects
                  many organs of the body

               c- Reticular CT – Has a very lacy appearance and helps to support
                  the liver and spleen and helps to filter worn out red blood cells

         2- Dense Connective Tissue – DCT has many more fibers but a lot fewer
            cells than LCT

                     a- Dense Regular CT – Thick bundles of collagen fibers
                        arranged parallel to each other. They are very strong when
                        pulled on the long axis this is what most tendons and
                        ligaments are made up of

                     b- Dense Irregular CT – The collagen fibers are packed
                        somewhat tightly, however they are arranged irregularly
                        (not like in dense CT). They are found in areas of the body
                        that are pulled in many directions, such as the skin and the
                        heart valves

                     c- Elastic CT – Elastic CT is very strong and bounces back
                        after it has been stretched (think rubber band) it is found in
                        the lungs and in arteries that are always expanding and
3- Cartilage – This is my personal hang up! Cartilage is replaced by bone
   it never becomes bone! Cartilage consists of collagen fibers embedded
   in chondroitin sulfate (very popular supplement at places like GNC to
   promote joint health) Cartilage is gel-like and can with stand a lot of
   stress, much ore than bone can, hence it acts like a shock absorber at
   the ends of long bones

         a- Hyaline cartilage – The most abundant, yet the weakest of the
            three types, it is found wherever a joint is present in the body.
            It helps to reduce friction and absorb shock

         b- Fibrocartilage – This is the strongest type of cartilage in the
            body. It can be very rigid and is located between the
            vertebrae, the menisci of the knees and at the pubic

         c- Elastic cartilage – Highly flexible and resilient helps to
            maintain the shape of structure such as the tip of the ear
            (pinnae) and the auditory tubes.

4- Osseous Connective Tissue (Bone) – Bones support the soft tissue of
   the body, protect delicate structures and work with skeletal muscle to
   generate movement. Bone store calcium and phosphorous
   (Importance of the Ca:P ratio) and store red and yellow marrow. They
   store fat and produce blood cells

         a- Bones are classified as either spongy or compact

         b- Osteoblasts are immature bone cells that lay down the ECM,
            Osteocytes are mature cells that maintain the integrity of the
            bone and osteoclasts break down bone and are important in

5- Liquid Connective Tissue – In liquid CT the cells are suspended in a
   liquid medium. The two types of liquid CT are blood and lymph

         a- Blood – Blood is a liquid CT with an ECM called Plasma.
            Within the plasma are the “formed elements” which are the
            red blood cells (erythrocytes) the white blood cells
            (leukocytes) and the platelets

              1- Red blood cells carry oxygen and carbon dioxide

              2- White blood cells are involved in immunity and allergic
       3- Platelets allow for blood clotting

2- Lymph – Lymph is similar to blood plasma, its transports lipids
and helps in the immune response. Most lymph glands are found in
the axilla (armpit), the groin and the small intestine

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