The 4 Types of Tissues: connective Connective Tissue General structure of CT cells are dispersed in a matrix matrix = a large amount of extracellular material produced by the CT cells and plays a major role in the functioning matrix component = ground substance often crisscrossed by protein fibers ground substance usually fluid, but it can also be mineralized and solid (bones) CTs = vast variety of forms, but typically 3 characteristic components: cells, large amounts of amorphous ground substance, and protein fibers. Connective Tissue GROUND SUBSTANCE In connective tissue, the ground substance is an amorphous gel-like substance surrounding the cells. In a tissue, cells are surrounded and supported by an extracellular matrix. Ground substance traditionally does not include fibers (collagen and elastic fibers), but does include all the other components of the extracellular matrix . The components of the ground substance vary depending on the tissue. Ground substance is primarily composed of water, glycosaminoglycans (most notably hyaluronan ), proteoglycans, and glycoproteins. Usually it is not visible on slides, because it is lost during the preparation process. Connective Tissue Functions of Connective Tissues Support and connect other tissues Protection (fibrous capsules and bones that protect delicate organs and, of course, the skeletal system). Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and lymph. Adipose cells store surplus energy in the form of fat and contribute to the thermal insulation of the body. Embryonic Connective Tissue All connective tissues derive from the mesodermal layer of the embryo . The first connective tissue to develop in the embryo is mesenchyme , the stem cell line from which all connective tissues are later derived. Clusters of mesenchymal cells are scattered throughout adult tissue and supply the cells needed for replacement and repair after a connective tissue injury. A second type of embryonic connective tissue forms in the umbilical cord, called mucous connective tissue or Wharton’s jelly. This tissue is no longer present after birth, leaving only scattered mesenchymal cells throughout the body. Connective Tissue Classification of CTs 3 broad categories of CT are classified according to the characteristics of their ground substance and the types of fibers found within the matrix Connective Tissue Connective Tissue Proper CELLS . Fibroblasts present in all CT proper . Fibrocytes, adipocytes, and mesenchymal cells are fixed cells (remain within the connective tissue). Other cells move in and out in response to chemical signals: macrophages, mast cells, lymphocytes, plasma cells, and phagocytic cells (actually part of the immune system) Connective Tissue Connective Tissue Proper Connective Tissue Fibers and Ground Substance (all secreted by fibroblasts) 3 main types : • Collagen fiber = made from fibrous protein subunits linked together to form a long and straight fiber, while flexible, have great tensile strength, resist stretching, and give ligaments and tendons their characteristic resilience and strength. • Elastic fiber = protein elastin (that after being stretched or compressed, it will return to its original shape) along with lesser amounts of other proteins and glycoproteins. • Reticular fiber = also formed from the same protein subunits as collagen fibers, but arrayed in a branching network. • All of these fibers embedded in ground substance = made of polysaccharides, specifically hyaluronic acid, and proteins (combined to form a proteoglycan with a protein core and polysaccharide branches) . The proteoglycan attracts and traps available moisture forming a clear, viscous, colorless matrix. Connective Tissue Connective Tissue Proper Loose Connective Tissue found between many organs where it acts both to absorb shock and bind tissues togethe + allows water, salts, and various nutrients to diffuse through to adjacent or imbedded cells and tissues. 1. Adipose tissue = mostly of fat storage cells, with little extracellular matrix. White fat contributes mostly to lipid storage and can serve as insulation from cold temperatures and mechanical injuries. Brown adipose tissue is more common in infants (“baby fat”) and is thermogenic Connective Tissue Connective Tissue Proper Loose Connective Tissue 2. Areolar tissue shows little specialization and fills the spaces between muscle fibers, surrounds blood and lymph vessels, and supports organs in the abdominal cavity. Areolar tissue underlies most epithelia and represents the connective tissue component of epithelial membranes. 3. Reticular tissue = mesh-like, supportive framework for soft organs such as lymphatic tissue, spleen, and liver. Connective Tissue Supportive Connective Tissues allow the body to maintain its posture and protect internal organs + 2 major forms: 1. Cartilage The distinctive appearance of cartilage is due to polysaccharides called chondroitin sulfates, which bind with ground substance proteins to form proteoglycans. Embedded within the cartilage matrix are chondrocytes and the space they occupy are called lacunae (singular = lacuna). A layer of dense irregular connective tissue, the perichondrium, encapsulates the cartilage. avascular very slow healing. 3 main types: 2. Bone the hardest CT with rigid extracellular matrix contains mostly collagen fibers embedded in a mineralized ground substance containing hydroxyapatite. Osteocytes are located within lacunae. highly vascularized tissue. Connective Tissue Fluid Connective Tissue = blood and lymph where cells circulate in a liquid extracellular matrix Connective Tissue The following types of connective tissue are covered in this activity: 1. Loose (areolar) connective tissue (delicate thin layers between tissues; present in all mucous membranes) 2. Adipose tissue (fat) 3. Dense connective tissue (tendons/ligaments) 4. Hyaline cartilage (nose/ends of long bones/ribs) 5. Elastic cartilage (outer ear/epiglottis) 6. Fibrocartilage (between vertebrae/knee joints/pubic joint) 7. Bone (skeletal system) 8 Blood (bloodstream) Connective Tissue Table 4.1 Comparison of Classes of Connective Tissues (1 of 2) Connective Tissue Table 4.1 Comparison of Classes of Connective Tissues (2 of 2) Figure 4.8a Connective tissues. (a) Connective tissue proper: loose connective tissue, areolar Description: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some Elastic white blood cells. fibers Function: Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in Collagen inflammation; holds and conveys fibers tissue fluid. Location: Widely distributed under epithelia of body, e.g., forms lamina propria of mucous membranes; Fibroblast packages organs; surrounds nuclei capillaries. Epithelium Photomicrograph: Areolar connective tissue, a Lamina soft packaging tissue of the body (300x). propria Copyright © 2010 Pearson Education, Inc. Figure 4.7 Areolar connective tissue: A prototype (model) connective tissue. Cell types Extracellular matrix Ground substance Macrophage Fibers • Collagen fiber • Elastic fiber • Reticular fiber Fibroblast Lymphocyte Fat cell Capillary Mast cell Neutrophil Copyright © 2010 Pearson Education, Inc. Figure 4.8b Connective tissues. (b) Connective tissue proper: loose connective tissue, adipose Description: Matrix as in areolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet. Function: Provides reserve food Nucleus of fuel; insulates against heat loss; fat cell supports and protects organs. Location: Under skin in the hypodermis; around kidneys and eyeballs; within abdomen; in breasts. Adipose Vacuole tissue containing fat droplet Photomicrograph: Adipose tissue from the Mammary subcutaneous layer under the skin (350x). glands Copyright © 2010 Pearson Education, Inc. Figure 4.8c Connective tissues. (c) Connective tissue proper: loose connective tissue, reticular Description: Network of reticular fibers in a typical loose ground substance; reticular cells lie on the network. Function: Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages. White blood cell Location: Lymphoid organs (lymph (lymphocyte) nodes, bone marrow, and spleen). Reticular fibers Spleen Photomicrograph: Dark-staining network of reticular connective tissue fibers forming the internal skeleton of the spleen (350x). Copyright © 2010 Pearson Education, Inc. Figure 4.8d Connective tissues. (d) Connective tissue proper: dense connective tissue, dense regular Description: Primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast. Collagen Function: Attaches muscles to fibers bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction. Location: Tendons, most ligaments, aponeuroses. Nuclei of fibroblasts Shoulder joint Ligament Photomicrograph: Dense regular connective tissue from a tendon (500x). Tendon Copyright © 2010 Pearson Education, Inc. Figure 4.8e Connective tissues. (e) Connective tissue proper: dense connective tissue, dense irregular Description: Primarily irregularly arranged collagen fibers; some elastic fibers; major cell type is the fibroblast. Nuclei of Function: Able to withstand fibroblasts tension exerted in many directions; provides structural strength. Location: Fibrous capsules of organs and