Veterinary Foundation: Connective Tissue PDF

Systems 1 Veterinary Foundation: Connective Tissue Dr. Rhea St. Louis  What statement accurately describes the macrophage? A. They are elongated cells that wrap around endothelial cells lining small blood vessels. B. They produce heparin and histamine. C. They are phagocytic...

Systems 1 Veterinary Foundation: Connective Tissue Dr. Rhea St. Louis  What statement accurately describes the macrophage? A. They are elongated cells that wrap around endothelial cells lining small blood vessels. B. They produce heparin and histamine. C. They are phagocytic and contain lysosomes. D. They are stellate-shaped cells that produce reticular fibers. Learning Outcomes By the end of this session, students will be able to: Identify the location of various connective tissue cells and various types of connective tissue. Recognize the structure, location, and function of various connective tissue cells like mesenchymal cells, fibroblasts, reticular cells, adipocytes, pericyte, mast cells, plasma cells, macrophages, pigment cells, and fibers like collagen, elastic, and reticular fibers and amorphous ground substances. Connective Tissue One of four types of basic tissue. Consists of cells and an extracellular matrix ○ Extracellular matrix includes structural fibers and specialized proteins, which constitute the ground substance CT forms a vast and continuous compartment throughout the body bounded by the basal laminae of epithelia and external laminae of muscle and nerve cells. Different types of CT are responsible for a variety of functions ○ To provide structural and mechanical support for other tissues ○ To mediate the exchange of nutrients and waste between circulation and other tissues  Embryonic Connective Tissue All CT is derived from the mesodermal layer of the embryo. The first CT to develop in the embryo is mesenchyme, the stem cell line from which all CT is later derived. Clusters of mesenchymal cells are scattered throughout adult tissue, particularly blood vessels, and supply cells needed for replacement and repair after a CT injury. Components of Connective Tissue Extracellular matrix (ECM) ○ Ground substance Aqueous gel of glycoproteins and proteoglycans that occupies the space between cellular and fiber elements of CT ○ Variety of fibers Variety of supportive cells ○ Cells which produce and maintain the ECM ○ Cells that migrate from the associated vasculature to reside in the ECM Components of Connective Tissue: Cells Fibroblasts ○ The most common native cell type of CT. ○ Metabolically active: Synthesize collagen, elastic fibers, reticular fibers, and ground substance of the ECM. ○ Fibrocytes are mature fibroblasts (less active) ○ Chondroblasts and osteoblasts are the primary specialized cell types found in cartilage and bone. ○ Appear elongated cell with pale staining flattened processes  Components of Connective Tissue: Cells Macrophages ○ Phagocytic cells derived from monocytes. ○ Monocytes migrate from the bloodstream, where they differentiate into macrophages. ○ Essential component of the immune system (body’s defense system). Components of Connective Tissue: Cells Mast cells ○ Large ovoid CT cells with spherical nucleus and cytoplasm filled with basophilic granules containing histamine and heparin. ○ When triggered, mast cells release histamine, an inflammatory mediator that causes vasodilation and increased blood flow at a site of injury or infection, along with itching, swelling, and redness – an allergic response. ○ Derived from hematopoietic cells and are part of the immune system  Components of Connective Tissue: Cells Adipocytes ○ CT cells specialized to store neutral fat/lipids and produce a variety of hormones. ○ Differentiate from mesenchymal stem cells and gradually accumulate fat in their cytoplasm. ○ Located throughout loose CT as individual cells and as groups of cells. ○ Create adipose tissue when they accumulate in large numbers. ○ Exist in two basic forms White adipocytes Store lipids as single large droplet and are less metabolically active Brown adipocytes Store lipids as many small droplets and have high metabolic activity  Components of Connective Tissue: Cells Leukocytes ○ These are white blood cells which are frequently present in small numbers in normal CT. ○ Lymphocytes Round cell with thin rim of cytoplasm and large round deeply staining nucleus. Important for adaptive immunity response. ○ Neutrophils Rarely seen in CT, more commonly observed in inflammatory states. ○ Plasma cells Prominent constituent of loose CT where pathogens tend to enter the body; e.g., GI and respiratory tracts. Derived from B-lymphocytes. Large basophilic, ovoid cell, with considerable cytoplasm and spherical eccentrically positioned nucleus.  What statement is accurate about fibroblasts? A. They are cells which are specialized to store fat. B. They are large ovoid cells with basophilic granules in their cytoplasm. C. They migrate from the bloodstream and then differentiate. D. They rarely seen in CT and are commonly observed in inflammatory states. E. They are the most common CT cell and usually appear with processes. Break Time Components of Connective Tissue Fibers Present in varying amounts depending on the structural needs or the function of the CT. Each type of fiber is produced by fibroblasts and is composed of proteins consisting of long peptide chains. Fibers can be ○ Collagen fibers ○ Reticular fibers ○ Elastic fibers Components of Connective Tissue: Fibers Type I (most common) found in every CT Type II found in hyaline and elastic cartilage and the vitreous body of eye. Collagen fibers The five most Type III found in reticular fibers, healing wounds, smooth muscle, and fetal skin. common types Type IV found in basal laminae of epithelia Type V found in placental basal laminae, tendons and muscle sheaths. https://www.histology.leeds.ac.uk/tissue_types/connective/connective_fibres.php Components of Connective Tissue: Fibers Collagen fibers ○ Collagen is the most common fibrous protein in the ECM, and it is important for resisting tensile forces. ○ It is the most abundant protein in mammals - 25% of total protein mass! ○ It is a protein composed primarily of the amino acids glycine & proline, and it also contains sugar groups. ○ It is acidophilic and stains with eosin in H&E-stains (to look pink in sections). ○ It is secreted by fibroblasts as procollagen, and amino acid residues at the ends of the protein are cleaved off outside the cell to form collagen, which then aggregates into fibers, etc. This prevents the formation of large fibers in the cell (which would not be good for the cells!). ○ Collagen consists of three protein chains that wrap around each other in a helical arrangement. The collagen molecules are often crosslinked for extra strength - tensile strength. https://www.histology.leeds.ac.uk/tissue_types/connective/connective_fibres.php Components of Connective Tissue Fibers – Collagen Fibers Most abundant structural component of CT Flexible and have high tensile strength Typically appear wavy with light microscopy Components of Connective Tissue: Fibers Elastic fibers ○ Composed of elastin proteins and are usually organized into parallel sheaths. Reticular fibers ○ Composed of collagen type III. ○ Form a thin reticular network https://www.histology.leeds.ac.uk/tissue_types/connective/connective_fibres.php  Components of Connective Tissue Fibers – Elastic Fibers Allow tissues to respond to stretch and distension. Typically, thinner than collagen fibers, they are arranged in a branching pattern to form a three- dimensional network. Interwoven with collagen fibers to prevent tearing from excessive stretching. Do not stain very well with H&E. Prominent in elastic tissues. Components Of Connective Tissue Fibers – Reticular Fibers Composed of type III collagen. Identified using silver salt method - appear black. Found throughout the body but are most abundant in the reticular tissue. In loose CT, found at the boundary between CT and epithelium, as well as surrounding adipocytes, small blood vessels, nerves, and muscle cells. Prominent in the initial stages of wound healing and scar tissue formation. Create the supportive stroma of hemopoietic and lymphatic tissues. Produced by fibroblasts except for in reticular tissue, which is produced by reticulocytes. What type of fiber is most associated with wound healing during the initial stages of scar formation? A. Elastic fibers B. Reticular fibers C. Collagen fibers  Classification of Connective Tissue Connective Tissue proper Supportive/ specialized Fluid connective Tissue Connective Tissue Loose connective Tissue Cartilage Blood Areolar Hyaline Adipose Fibrocartilage Reticular Elastic Dense Connective tissue Bone Lymph Regular Compact bone Irregular Spongy bone Elastic Loose/areolar Connective Tissue Found in close association with most epithelia. It contains loosely arranged collagen, elastic, and reticular fibers in its ECM and numerous cells. Fibroblasts form and maintain the ECM, but many cells are migrants from the vascular system. (enter loose CT in response to specific stimuli) Often the site of inflammatory and immune reactions. Body location: Surrounds vessels and nerves, also found in lamina propria of mucous membranes and subcutaneous tissue. Adipose Tissue Consists mostly of fat storage cells, with little extracellular matrix. ○ White adipose tissue is most abundant, contributes mostly to lipid storage, and can serve as insulation from cold temperatures White Adipose tissue and mechanical injuries. ○ Brown adipose tissue is more common in infants, hence the term “baby fat”. Brown adipose tissue has many mitochondria within the cells and is thermogenic, therefore, it releases heat on the breakdown of fats. Brown Adipose tissue  Reticular Connective Tissue Mesh-like supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver. Reticular fibers form the network to which other cells attach. Dense Irregular Connective Tissue It mostly contains collagen fibers, which provide significant strength. Cells are sparse and are typically of a single type, the fibroblast. Contains relatively little ground substance. The fibers are arranged in bundles oriented in different directions Dense Regular Connective Tissue Body location: The main functional component of tendons, ligaments, and aponeuroses. The fibers are the prominent feature, and there is little ECM. Fibers are arranged in parallel arrays and are densely packed to provide maximum strength. The cells that produce and maintain these fibers are packed and aligned between the fiber bundles. ○ Tendons attach muscle to bone and consist of parallel bundles of collagen fibers. ○ The fibroblasts of tendons are called tendinocytes and are found between the bundles of collagen fibers. Mucous connective tissue Mucous connective tissue is a primitive (embryonic) connective tissue that persists in the umbilical cord. Mucous connective tissue is composed of fibroblast-like cells, which can be spindle or stellate-shaped. They produce the surrounding, abundant, gelatinous ground substance (Wharton’s jelly) and delicate collagen and reticular fibers. https://digitalhistology.org/tissues/connective/special/mucous/mucous- 1/#:~:text=Mucous%20connective%20tissue%20is%20a,be%20spindle% 20or%20stellate% 20shaped.  Under the microscope, a tissue specimen shows cells located in spaces scattered in a transparent background. This is likely ________. A. Loose Connective Tissue B. Reticular Connective Tissue. C. Dense regular Connective Tissue D. Dense regular Connective Tissue Lesson Summary We identified the location of various connective tissue cells and various types of connective tissue. We can now recognize the structure, location, and function of various connective tissue cells like mesenchymal cells, fibroblasts, reticular cells, adipocytes, pericyte, mast cells, plasma cells, macrophages, pigment cells, and fibers like collagen, elastic, and reticular fibers and amorphous ground substances. Questions?? Please feel free to email me with any questions! Next lesson we will cover a few specific types of connective tissue. Please review the pre-lesson content for lesson 18.