pgs. 124-134 Flashcards
Ground Substance in Connective Tissue
amorphous, homogeneous material found in connective tissue that can range in texture from a liquid or gel to a calcified solid. It is made up primarily of glycosaminoglycans (GAGs), which are long, unbranched chains of glycoproteins. The most common GAG in connective tissue is hyaluronic acid, which is often combined with proteins. These large molecules help organize the formation of fibers within the tissue.
Functions
Nutrient and waste exchange: Ground substance facilitates the exchange of nutrients and waste between cells and the bloodstream.
Shock absorption: It acts as a cushion, protecting cells from mechanical stress.
Microbial defense: The viscous texture of ground substance prevents the movement of most microorganisms. However, some microbes have developed enzymes like hyaluronidase that degrade hyaluronic acid, enabling easier movement through tissues.
Fibers of Connective Tissue (three major types)
collagenous, reticular, and elastic.
Collagenous fibers
Composed of collagen, which forms strong, thick strands.
organized into parallel fibrils made of microfibrils. highly resistant to pulling forces, making them essential in tissues like tendons and ligaments, which are constantly subjected to tension.
Appearance: Collagen fibers are white and form white tissue when densely packed.
Tensile strength: Collagen fibers can stretch and then return to their original length. When exposed to heat, collagen denatures, softening the tissue (e.g., in meat cooking).
Types of collagen: different types of collagen, with Type I being the most common in connective tissues.
Reticular fibers
These are thin, delicate fibers made of collagen but arranged in branched networks.
They form a “mist net” structure, which provides a supportive framework for organs that contain a high number of cells, such as the liver, spleen, lymph nodes, and bone marrow.
also support blood vessels, nerves, muscle fibers, and capillaries.
Elastic fibers
Made of elastin, these fibers form branched networks but lack the tensile strength of collagen fibers.
Elasticity: These fibers are coiled, allowing them to stretch and recoil like a rubber band.
Found in tissues that undergo regular stretching, such as skin, lungs, vocal cords, and the walls of blood vessels.
Color: Elastic fibers are often called yellow fibers due to their color when fresh.
Major Cell Types in Connective Tissue
Connective tissue contains two categories of cells: fixed cells and wandering cells.
Fixed Cells (fibroblasts, adipocytes, reticular cells)
These cells remain in the connective tissue and are involved in the production and maintenance of the extracellular matrix.
Fibroblasts
The most abundant fixed cells, fibroblasts secrete collagen and ground substance (including GAGs).
They are large, irregularly shaped, metabolically active, and can reproduce.
Specialized fibroblasts include chondroblasts (in cartilage) and osteoblasts (in bone).
As fibroblasts mature and form the matrix, they become less active and are referred to as fibrocytes
Adipocytes (fat cells)
Found throughout connective tissue, adipocytes store lipids.
They resemble fibroblasts when immature but expand as they accumulate lipids. The nucleus is pushed to one side due to lipid storage.
When grouped together, adipocytes form adipose tissue, which stores energy, insulates, and cushions organs.
Common locations include under the skin, around the kidneys, and in the abdomen.
Reticular cells
Star-shaped cells with long, branched processes that form netlike connections with other cells.
Involved in immune responses and the production of reticular fibers.
Found in immune system organs like the lymph nodes, bone marrow, and spleen.
Wandering Cells (leukocytes, mast cells, macrophages)
These cells move in and out of connective tissue and are primarily involved in tissue repair and defense.
Leukocytes (white blood cells)
White blood cells, including neutrophils and lymphocytes, migrate from blood into connective tissue during infection or inflammation.
They protect the body by engulfing microbes (phagocytosis) and producing antibodies.
Mast cells
Oval-shaped cells containing large, dark-staining granules filled with histamine and heparin.
Histamine increases blood flow and makes capillaries leaky, while heparin prevents blood clotting.
These cells are involved in allergic reactions and inflammation. Upon activation, they release their granules, initiating inflammation.
Macrophages
Large, irregularly shaped cells that act as phagocytes, engulfing and digesting dead cells, debris, and pathogens.
Macrophages can be fixed (remaining in one location) or mobile, moving to sites of infection.
They are given different names depending on their location (e.g., Kupffer cells in the liver, microglial cells in the brain).
Connective Tissue
classified into connective tissue proper and specialized connective tissue. primary components of connective tissue are ground substance, fibers, and cells, and the variations of these components lead to different tissue types.
Connective Tissue Proper
This category includes all connective tissues except for bone, cartilage, and blood. It is divided into: Loose and Dense connective tissue
Dense connective tissue
Includes dense regular, dense irregular, and elastic tissue.
Dense Regular
Structure: Characterized by tightly packed, parallel collagen fibers that align with mechanical stress, providing tensile strength in one direction.
Appearance: Silvery-white and avascular, leading to slow healing due to poor blood supply.
Fibroblast Arrangement: Fibroblasts are arranged in rows between fibers, focusing on collagen production with minimal ground substance.
Function: Found in structures requiring resistance to tensile forces along one axis, such as tendons (muscle-to-bone), ligaments (bone-to-bone), aponeuroses (muscle connections), and fascia (muscle and structure support).
Dense Irregular
Structure: Collagen fibers in thicker, randomly arranged bundles form a single sheet.
Function: Resists forces from multiple directions, providing strength in all directions.
Location: Found in areas under stress from various directions, such as the dermis, fibrous capsules of organs (kidneys, liver, spleen), and joint capsules.
Elastic
Structure: Primarily composed of elastic fibers, giving it stretch and the ability to return to its original shape.
*Location: Found in areas requiring elasticity, such as ligaments (vertebral column), the nuchal ligament in horses, and the walls of large arteries, bronchi, bladder, and heart.
connective tissue is made up of 3 components
ground substance, cells, fibers
Loose connective tissue
Includes areolar, adipose, and reticular tissue.
Areolar Tissue
A flexible, supportive tissue with randomly placed fibers and cells suspended in thick ground substance.
Fibroblasts are the predominant cells, and it supports and cushions organs, blood vessels, nerves, and lymph nodes.
Areolar tissue is also found in the subcutaneous layer of the skin and mucous membranes.
It can fill with fluid during injury or infection, causing edema (swelling).
