The Tissue Level of Organization

Transcription

1 The Tissue Level of Organization August 31, Connective Tissues Describe the general features of connective Describe the structure, location, and function of the various types of connective General Features of Connective Tissues Connective Tissues are the most abundant and widely distributed in the body they are also the most heterogeneous of the tissue groups They perform numerous functions: Bind together Support and strengthen tissue Protect and insulate internal organs Compartmentalize and transport Energy reserves and immune responses Collagen is the main protein of CT and the most abundant protein in the body, making up about 25% of total protein content Connective tissue is usually highly vascular and supplied with many nerves The exception is cartilage and tendon - both have little or no blood supply and no nerves Although they are a varied group, all CT share a common theme Sparse cells Surrounded by an extracellular matrix The extracellular matrix is a non-cellular material located between and around the cells It consists of protein fibers and ground substance (the ground substance may be fluid, semifluid, gelatinous, or calcified) Connective Tissue Cells Fibroblasts are the most numerous cell of connective These cells secrete protein fibers (collagen, elastin, & reticular fibers) and a ground sub stance which varies from one CT to another Chondrocytes make the various cartilaginous C.T. Adipocytes store triglycerides Osteocytes make bone White blood cells migrate from the blood in response to infections Macrophages are the big eaters that swallow and destroy invaders or debris via phagocytosis They can be fixed or wandering Neutrophils are also macrophages ( small eaters ) that are numerous in the blood Mast cells and Eosinophils play an important role in inflammation by producine histamine Plasma cells (lymphocytes) secrete antibody proteins and attack invaders Connective Tissue of Extracellular Matrix CT cells secrete 3 common fibers which provide strength and support Collagen fibers composed of collagen Found in bone, tendons, ligaments Elastin fibers composed of elastin, fibrillin, and other glycoproteins Found in skin, blood vessel walls, and lungs Reticular fibers composed of collagen and glycoprotein Found around fat cells, nerve fibers, and skeletal and smooth muscle tissue

2 Classification of Connective Tissues Embryonic Connective Tissues Embryonic connective tissue Mesenchyme Mucous connective tissue Primarily present in the embryo, the developing human from fertilization through the first two months of pregnancy, and in the fetus, the developing human from the third month of pregnancy to birth Mesenchyme gives rise to all other connective Mucous CT (Wharton's Jelly) is a gelatinous substance within the umbilical cord and is a rich source of stem cells Mature connective tissue Loose connective tissue Dense connective tissue Cartilage Bone Liquid Mature Connective Tissues Mature Connective Tissues are present in the newborn Cells arise primarily from the mesenchyme Loose Connective Tissues Dense Connective Tissues Cartilage Areolar Connective Tissue is the most widely distributed in the body It contains several types of cells, all three fiber types (collagen, elastic, and reticular), and a semifluid ground substance It is found in the subcutaneous layer, mucus membranes, and around blood vessels, nerves, and body organs It is used to attach skin and underlying, and as a packing between glands, muscles, and nerves Adipose Tissue consists of adipocytes, which store triglycerides It is located in the subcutaneous layer, around organs and joints, and yellow bone marrow It reduces heat loss and serves as padding and as an energy source Brown Adipose tissue generates heat Bone Tissue Liquid Connective Tissue Reticular Connective Tissue is a network of interlacing reticular fibers and cells It forms a scaffolding used by cells of lymphoid such as the spleen and lymph nodes Found in the liver, spleen, and lymph nodes Dense Irregular Connective Tissue consists predominantly of fibroblasts and collagen fibers randomly arranged It provides strength when forces are pulling from many different directions It is found in fasciae, the dermis of the skin, and membrane capsules around organs Dense Regular Connective Tissue consists of parallel bundles of collagen fibers and fibroblasts It forms tendons, ligaments, and other strong attachments where the need for strength along one axis is mandatory (a muscle pulling on a bone)

3 Elastic Connective Tissue consists of fibroblasts and freely branching elastic fibers It allows stretching of certain like the elastic arteries (the aorta) Is found in the walls of large arteries, lungs, trachea, and bronchial tubes Elastic cartilage consists of chondrocytes located in a threadlike network of elastic fibers and also has a perichondrium Maintains the shape of organs Makes up the malleable part of the external ear, auditory tubes, and the epiglottis Blood and lymph are two types of liquid CT Blood tissue consists of blood plasma, RBC, WBC, and platelets Transport oxygen and carbon dioxide, carry on phagocytosis, participate in allergic reactions, provide immunity, and bring about blood clotting Lymph is the extracellular fluid that flows in lymphatic vessels Is a clear fluid similar to blood plasma but with less protein Cartilage contains chondrocytes and has a rubbery extracellular matrix containing collagen and elastic fibers It is a tissue with poor blood supply that grows slowly and when injured or inflamed, repair is slow Hyaline cartilage is the most abundant type of cartilage and is found in embryonic skeletons, the ends of long bones, and parts of the ribs, nose, trachea, bronchi, and larynx Consists of a gel-like ground substance and appears bluishwhite in the body It provides a smooth surface for joint movement, is flexible, allows movement, provides support, and is usually surrounded by the perichondrium Fibrocartilage, with its thick bundles of collagen fibers, is a very strong, tough cartilage It contains chondrocytes scattered among bundles of collagen fibers It is found in the pubic symphysis, invertebral discs, and menisci of the knee joint Fibrocartilage discs in the intervertebral spaces and the knee joints support the huge loads up and down the long axis of the body Bone consists of an extracellular matrix of mineral salts and collagen fibers, and osteocytes that are located in the lacunae Bone supports and protects the body, provides a surface for muscle attachment, helps the body move, stores minerals, and houses blood forming tissue 4.6 Membranes Define a membrane Describe the classification of membranes Epithelial Membranes Combining two creates an organ Epithelial membranes are the simplest organs in the body, constructed of only epithelium and a little bit of connective tissue

4 Epithelial membranes consist of an epithelial layer overlying a connective tissue layer Mucous membranes Serous membranes Cutaneous membrane Mucous membranes line interior body surfaces open to the outside: Digestive tract Respiratory tract Reproductive tract Serous membranes line closed cavities and covers organs in those cavities Consist of parietal and visceral layers Parietal layer next to body wall Serous fluid between layers Visceral layer next to organ Pleura, pericardium, peritoneum Synovial Membranes Synovial membranes line joint cavities and consist of areolar connective tissue They do not have an epithelial layer 4.7 Muscular Tissues Describe the general features of muscular Contrast the structure, location, and mode of control of skeletal, cardiac, and smooth muscle tissue Consists of muscle fibers or myocytes that are specialized for contraction Provide motion, maintenance of posture, heat production, and protection Skeletal muscle tissue is attached to bones and is striated and voluntary Cardiac muscle tissue, which forms most of the heart wall is striated and involuntary Smooth muscle tissue is found in walls of hollow internal structures and is nonstriated and involuntary 4.8 Nervous Tissue Describe the structural features and functions of nervous tissue The nervous system is composed of neurons and neuroglia Neurons respond to stimuli by converting the stimuli into electrical signals called nerve action potentials and conducting nerve impulses to other cells Most neurons consist of a cell body and two types of processes, dendrites and axons 4.9 Excitable Cells Explain the concept of electrical excitability Neurons and muscle fibers are considered excitable cells because they exhibit electrical excitability, the ability to respond to certain stimuli by producing electrical signals such as action potentials Action potentials can propagate (travel) along the plasma membrane of a neuron or muscle fiber due to the presence of specific voltage-gated ion channels

5 4.10 Tissue Repair: Restoring Homeostasis Describe the role of tissue repair in restoring homeostasis A convenient way to refer to certain cells when discussing a tissue is Parenchyma or Stroma The parenchymal cells of an organ consist of that tissue which conducts the specific function of the organ Cells of the stroma are everything else connective tissue, blood vessels, nerves Tissue repair is the replacement of worn-out, damaged, or dead cells by healthy ones Stem cells may divide to replace lost or damaged cells When tissue damage is superficial, tissue repair involves parenchymal regeneration When tissue damage is extensive, return to homeostasis depends on active repair of both parenchymal cells and stroma Fibroblasts divide rapidly New collagen fibers are manufactured New blood capillaries supply materials for healing All of these processes create an actively growing connective tissue called granulation tissue 4.11 Aging & Tissues Describe the effect of aging on Tissue heals faster in young adults than in the aged Surgery of a fetus normally leaves no scars Young have a better nutritional state, blood supply, and higher metabolic rate Extracellular components also change with age Changes in the body s use of glucose, collagen, and elastic fibers contribute to the aging process