[2] Connective Tissues

• Connective tissue develops from mesenchyme and consists of cells and extracellular matrix.
• The matrix of connective tissue consists of tissue fluid, the ground substance.
• Ground substance is a medium for the exchange of nutrients, oxygen, and waste.
• Ground substance is a jelly-like substance that protects the body from foreign material.
• Due to its consistency, ground substance serves as a barrier to pathogenic molecules.
• Ground substance contains numerous cells that protect and defend the body against bacteria and foreign bodies.
• Connective tissue is classified as loose connective tissue and dense connective tissue.
• Embryonic connective tissue originates from embryonic mesenchyme and develops mainly from the middle layer of the embryo (mesoderm).
• Mesenchyme consists largely of this viscous ground substance with few collagen fibers.
• Mesenchymal cells are surrounded by an extracellular matrix (ECM) that they produced and consists largely of simple ground substance which is rich in hyaluronic acid and has very little collagen.
• Proteoglycans consist of a core protein to which sulfated GAGs are attached.
• High magnification: Fibroblasts are quite numerous.
• Glycosaminoglycans (GAGs) are long polymers of repeating disaccharide units.
• Ground substance is amorphous, transparent and fibrous.
• The ground substance can easily return to its original shape due to its ease of compression and deformation.
• The ground substance has a jelly or marshmallow-y characteristic.
• Lower magnification section of Human Umbilical Cord.
• Fine collagen fibers can be found in between.
• Ground substance is a mixture of three major kinds of macromolecules: Glycosaminoglycans (GAGs), Proteoglycans, and Multiadhesive Glycoproteins.
• Loose connective tissue, also known as areolar tissue, contains multidirectional weaves of a variety of different connective tissue fibers.
• Certain compression and deformation may occur without affecting blood flow towards the fetus due to the composition of the ground substance.
• Multiadhesive Glycoproteins have multiple binding sites for cell surface integrins, matrix macromolecules.
• Fibers are embedded into a soft gelatinous material (ground substance) which allows tissue to be elastic and flexible.
• Dense regular connective tissue is found in ligaments and tendons.
• Collagen fibers are the thickest and are of type I collagen.
• Nuclei are interspersed/packed between fibers and are basophilic in nature.
• The capsule (upper part) of dense irregular connective tissue is covered by simple squamous epithelium.
• Dense regular connective tissue has the presence of a direction or orientation of fibers, with a parallel orientation that allows the connective tissue to be strong and stretchable.
• Dense regular connective tissue is composed primarily of bundles of collagen and a few fiberblasts interspersed in between.
• Dense irregular connective tissue is widely distributed in the body and is not properly arranged in comparison to dense regular connective tissue.
• If there is no nucleus in the thick part of the connective tissue, it is collagen fibers, otherwise, it is a fiberblast.
• The function of dense irregular connective tissue is support and protection of organs through tearing resistance.
• Dense irregular connective tissue is composed primarily of a small amount of ground substance and is not multi-layered.
• Components of connective tissue include collagen fibers, elastic fibers, and nuclei (fiberblast nuclei).
• Elastic fibers are thinner strands and are interspersed/packed between fibers.
• Higher objective dense irregular connective tissue is composed of collagen fibers which are tough, thick, fibrous proteins that do not branch and are the most abundant fibers, found in almost all the connective tissues of organs.
• Specialized connective tissues include adipose tissue, which is found in the intestine and is composed of adipocytes, which are fat cells, and is characterized by adipocytes being closely packed together and usually separated by strips of connective tissue septa.
• Reticular fibers are found in the lungs, bladder, skin, and walls of large blood vessels.
• Collagen fibers are usually large and tightly packed.
• Collagen fibers are large, tightly packed, and oriented in one direction for maximal tensile strength.