Module4_Tissues.docx

Define the term tissue, and describe the three embryonic germ layers from which tissues arise. A tissue is a group of cells that have a similar embryological origin and are specialized for a particular function. A few weeks after fertilization, a developing embryo is comprised of three distinct lay...

Define the term tissue, and describe the three embryonic germ layers from which tissues arise. A tissue is a group of cells that have a similar embryological origin and are specialized for a particular function. A few weeks after fertilization, a developing embryo is comprised of three distinct layers of cells which give rise to all of the body’s tissues and organs. These three germ layers are the outer, or superficial, ectoderm, middle mesoderm, and innermost, or deep, endoderm. Embryonic Origin of Tissues and Major Organs. Name the four primary adult tissue types, and give a brief description of each. Depending on their function and structure, the various tissues of the body are classified as the following four principal types: Epithelial tissue covers body surfaces; lines hollow organs, body cavities, and ducts; and forms glands—providing protection for underlying tissue. Connective tissue protects and supports the body and its organs, binds organs together, stores energy reserves as fat, and provides immunity. Muscle tissue is responsible for movement and generation of force. Nervous tissue initiates and transmits action potentials (nerve impulses) that help coordinate body activities, monitors the external environment, and contributes to homeostasis. Describe the features, location, and function of epithelial tissue. General Features of Epithelial Tissues Epithelial cells are arranged in sheets, in either single or multiple layers. The epithelium consists mostly of packer cells with little extracellular material. In epithelial tissues, many cell junctions are present, providing secure attachments among cells (see below). An epithelial cell has an apical surface and a basal surface attached to a base membrane. Epithelia adhere firmly to nearby connective tissue through a thin extracellular layer called the basement membrane. Epithelia have a nerve supply and a high capacity for renewal (a high mitotic rate). The basement membrane is made up of a cellular layer of collagen and glycoproteins called the basal lamina; often, it is underlain with a layer of reticular fibres and glycoproteins called the reticular lamina. Epithelial tissue is avascular; the exchange of materials between epithelium and adjacent connective tissue is by diffusion. Functions of epithelia include protection, filtration, lubrication, secretion, digestion, absorption, transportation, excretion, sensory reception, and reproduction. Cell to Cell Junctions Cells of epithelia are closely interconnected by three types of junctions: the barrier-forming tight junctions, stabilizing anchoring junctions, and signal-conducting gap junctions. Note the general structure and relative locations of each of these types of junctions in the following figure: Barrier forming tight junctions separates cells into basal and apical compartments, no extracellular material between the two adjacent cells and controls movement of substances through the extracellular space between the cells is blocked. So they are selective barriers. They therefore protect their underlying tissues from harmful substances such as hydrochloric acid. lining and covering tissues Stabilizing anchoring junctions in the basal and lateral surfaces of cells to provide strong and flexible connections. Desmosomes: lateral surfaces. Occurs in patches on the membranes of cells and these patches are structural proteins (intermediate filaments/keratin) on the inner surface of cell’s membrane. Embedded in these patches are adhesion molecules called cadherins that project through the membrane to link with the cadherin molecules of adjacent cells link the intermediate filaments of adjacent cells important in holding cells together and preventing them from separating superficial layers of skin Hemidesmosomes: same structure as desmosome but instead connect the cells to the extracellular matrix such as basal lamina and the adhesion molecule is integrin instead of cadherin. Adherens: use either integrin or cadherin depending on what they are linking to but they have contractile protein actins on the cytoplasmic surface of their cell membranes and these actin make belt like structures inside the cell influence the shape and folding of epithelial tissue hold endothelial cells together and resist stress by providing strong mechanical attachments between cells Signal conducting gap junctions: intercellular passageways between cells to allow movement of small ions and molecules electrical and metabolic coupling of adjacent cells coordinate functions in large groups of cells Discuss the classification scheme for epithelia. The covering and lining of the epithelia can be classified as a combination of layers and shapes of cells. The name of the specific type of stratified epithelium depends on the shape of the surface cells. Layers are arranged as simple (one layer), stratified (several layers), or pseudostratified (one layer that appears as several). Cell shapes include squamous (flat), cuboidal (cube-like), columnar (rectangular), and transitional (variable). Classes of Epithelial Tissue. Simple epithelium is a single layer of cells; stratified epithelium consists of several layers of cells. Note that the name for an epithelium is always a pairing of the layers present and cell shape Describe the structure, location, and function(s) of different epithelial subtypes in the body. Simple squamous epithelium is found in parts of the body that are subject to little wear and tear. Endothelium lines the heart and blood vessels. Mesothelium lines the thoracic and abdominopelvic cavities, and covers the organs within them. Mesothelium: surface layer of serous membrane . Smooth and protective surface with lubrications Simple cuboidal epithelium consists of a simple layer of cube-shaped cells, and performs the functions of secretion and absorption kidney tubules and secretory portions of small glands Simple columnar epithelium can be ciliated or nonciliated/smooth. Ciliated tissue contains cells with cilia—motile, hair-like processes that help to move fluids or particles along a surface fallopian tubes and bronchi nonciliated tissue contains microvilli to increase surface area digestive tract and bladder. Goblet cells secrete mucus. Goblet cells are mucus secreting unicellular gland dispersed between columnar epithelial cells of mucus membranes Stratified epithelium is a more durable and protective tissue. The name of the specific kind of stratified epithelium depends on the shape of the surface cells. Pseudostratified epithelium has only one layer but gives the appearance of many. All cells are attached to the basement membrane, but some do not reach the apical surface. In pseudostratified ciliated columnar epithelium, the cells that reach the surface either secrete mucus (goblet cells) or bear cilia that sweep away mucus and trapped foreign particles trachea and upper respiratory tract. Pseudostratified nonciliated columnar epithelium contains no cilia or goblet cells. Stratified squamous epithelium consists of several layers of cells in which the top layer of cells is flat and the deeper layers of cells vary in shape from cuboidal to columnar. The basal cells replicate by mitosis and ultimately work their way to the surface. In keratinized stratified squamous epithelium, a tough layer of keratin (a protein resistant to friction with a capacity to repel bacteria) is deposited in the surface cells mammalian skin. Nonkeratinized stratified squamous epithelium does not contain keratin and remains moist mouth cavity Stratified cuboidal epithelium is a rare tissue that consists of two or more layers of cube-shaped cells with mainly a protective function salivary, sweat and mammary glands Stratified columnar epithelium consists of several layers of cells of which only the top layer is columnar. It is somewhat rare and functions in protection and secretion male urethra and ducts of some glands Transitional epithelium consists of several layers of cells; their appearance is variable. It is capable of stretching and thus permits the distention of an organ. It lines the urinary bladder and portions of the ureters and the urethra. Goblet Cell. (a) In the lining of the small intestine, columnar epithelium cells are interspersed with goblet cells. Summary of Epithelial Tissue Cells. Define a gland, and differentiate between exocrine and endocrine; merocrine, apocrine, and holocrine; and serous and mucous types. A gland is a single cell or a mass of epithelial cells adapted for secretion. Endocrine glands are ductless; their secretory products (hormones) enter the extracellular fluid and diffuse into the blood. Exocrine glands (sweat, oil, and digestive glands) secrete their products into ducts that empty at the surface of the covering and lining of the epithelium or directly onto a free surface. These types of glands can be classified on the basis of: 1) their mode of secretion, 2) the nature of their secretions, 3) their structure, and 4) the shape of their ducts. Merocrine exocrine glands, the most common type, release their secretions via exocytosis, e.g., the lubricant mucin, and eccrine sweat glands. Apocrine exocrine glands pinch off their apical surfaces along with their secretory vesicles, e.g., apocrine sweat glands release fatty secretions in genital areas that get broken down by local bacteria and cause body odor Holocrine exocrine gland cells lyse and are destroyed after accumulating their products within their cytoplasm, e.g., sebaceous glands that lubricate and protect the skin and hair with oily secretions. Salivary glands are composed of serous or mucous glands, or both. These two types of exocrine glands are named for their products. Serous glands release a thin liquid of water and proteins, such as the digestive enzyme amylase. Mucus is a thicker, more viscous product released from mucous glands and rich in glycoprotein mucin. Modes of Glandular Secretion. Sebaceous Glands. Describe the general characteristics of connective tissues (CTs), and discuss their major structural differences from epithelial tissue. Connective tissue is the most abundant and widely distributed tissue in the body. Unlike epithelia, connective tissues do not occur on free surfaces. Unlike epithelium, connective tissue is highly vascular (except for cartilage and tendons). Except for cartilage, connective tissue, like epithelium, has a nerve supply. Cells are not packed tightly but are dispersed in a matrix extracellular materials produced by cells that are embedded within it. The matrix plays a major role in their functioning. Explain how CTs are composed of cells plus an extracellular matrix composed of ground substance and fibres. Connective tissues support and connect all other tissue types and consist of the following three basic elements: Cells Ground substance – fluid or semi-fluid viscous component of matrix that is secreted by fibroblast – hyaluronic acid and proteins that together they combine and form a proteoglycan with protein as its core and polysaccharides branching out of it which then they attract and trap moisture to form to form the clear and colorless fluid to viscous ground substance. Protein fibres The latter two components combine to form the matrix. Connective tissue is classified into three categories based on the nature of their matrices: CT proper, supportive CTs, and fluid CTs. All three classes are derived from mesenchyme—a stem cell line derived from embryonic mesoderm. The firsts connective tissue to develop in embryo are mesenchymes. The second type of embryonic connective tissue forms in umbilical cord and is called mucus connective tissue or wharton’s jelly. All connective tissue proper have fibroblasts. Fibrocytes, adipocytes and mesenchymal cells are fixed cells and remain within the tissue. Other cells such as macrophages, mast cells, plasma cells and etc are part of immune system but they move in and out of tissues in response to chemical signals. Describe matrix and ground substance; list the three CT fibre types; and name the types of cells of which CT can be composed. The matrix is abundant with relatively few cells, and tends to prevent tissue cells from touching one another. The matrix of a connective tissue—which can be fluid, semifluid, gelatinous, fibrous, or calcified—is usually secreted by the connective tissue cells and adjacent cells, and determines the qualities of tissues. Cell types: Fibrocytes, adipocytes and mesenchymal cells are fixed cells and remain within the tissue. Other cells such as macrophages, mast cells, plasma cells and etc are part of immune system but they move in and out of tissues in response to chemical signals. Most abundant cell in the connective tissue proper is fibroblasts. Fibroblasts secrete polysaccharides and proteins that combine with extracellular fluid and produce a viscous ground substance that together with protein fibers make the matrix secrete fibers and matrix. Fibrocytes are second common cells in connective tissue proper. Adipocytes: cells that store lipid as droplets that fill their cytoplasm. White and brown. Brown stores in multiple droplets and has high metabolic activity. Whites store in a single large drop and are less active. Their amount and types depends on tissue, location and individuals. Mesenchymal cells are multipotent adult stem cells. Macrophages: large cells derived from monocytes, a type of blood cell, which enters the matrix from blood vessels. Immunity from pathogen and degraded host cells. When stimulated they release chemical messenger cytokines that recruits other immune system cells to the infected site and activate them. They can either be fixed in tissues or be free cells that move by amoeboid movements that engulf pathogens and cellular debris. Mast cells: also derived from blood stem cells and are part of immune system. They are found in connective tissue proper. They have many cytoplasmic granules filled with chemical signals histamine and heparin. Histamine is an inflammatory mediator that gets released if the tissue is irritated. They cause vasodilation and increase blood flow to the site and also cause itching, redness and swelling. Immature cells have names that end in blast (e.g., fibroblast, chondroblast), whereas mature cells have names that end in cyte (e.g., osteocyte). Most mature cells have a reduced capacity for cell division and matrix formation, and are mostly involved in maintaining the matrix. The types of cells found in various connective tissues include fibroblasts (which secrete fibres and matrix), macrophages or histiocytes (which develop from monocytes and are phagocytic), mast cells (which are abundant alongside blood vessels and produce histamine), and adipocytes or fat cells (which store energy in the form of fat). Connective Tissue Proper. Fibroblasts secrete this fibrous tissue which contains fibrocytes, adipocytes, and mesenchymal cells. The ground substance and fibres, deposited in the space between the cells, comprise the matrix of connective tissue. Substances found in the ground substance include: Hyaluronic acid Chondroitin sulfate Dermatan sulfate Keratan sulfate The three types of fibres embedded in the matrix between the cells of connective tissues and all are secreted by fibroblalsts are the following: Collagen fibres, composed of the protein collagen that are linked together to make the long and straight collagen fibers, are very tough and have tensile strength and resistant to stretching, yet allow some flexibility in the tissue; they are found in bone, cartilage, tendons, and ligaments. hold connective tissues together even during movements of body Elastic fibres, composed of the protein elastin, provide strength and stretching capacity and are found in the skin, blood vessels, and lungs and elastic ligaments of vertebral column they return to their original shape after being stretched or compressed Reticular fibres, consisting of collagen and glycoprotein and make a branching network provide support in the walls of the blood vessels and form a strong, supporting network/ structural support around fat cells, nerve fibres, and skeletal and smooth muscle fibres. For each of the following CTs, describe its structure, name a key body location, and identify its function(s). Five types of CT include: Loose connective tissue Dense connective tissue Cartilage Bone Liquid (blood and lymph) Loose connective tissue consists of all three types of fibres, several types of cells, and a semi-fluid ground substance. Loose Connective Tissue – found between organs to absorb shock and bind the tissues. Allow diffusion of water, salts and nutrients to adjacent or imbedded cells and tissues Areolar connective tissue is a prime example of loose connective tissue. It presents all of the typical loose connective tissue features. All types of fibers and various cells randomly distributed in a web like fashion and it is not a very specialized tissue. The ground substance aids the passage of nutrients from the blood vessels of the connective tissue to adjacent cells and tissues. It is found in the subcutaneous layer connective tissue component of epithelial membranes Fill spaces between muscle fibers Adipose tissue is a loose connective tissue consisting of adipocytes, which are specialized for storing triglycerides. It reduces heat loss through the skin; serves as an energy reserve; and supports, protects, and generates considerable heat to help maintain proper body temperature in newborns (brown fat). Found protecting kidneys and also cushioning the back of the eye Adipose Tissue. This is a loose CT that consists of fat cells with very little matrix. It stores fat for energy and provides insulation. Reticular connective tissue consists of a fine interlacing of reticular fibres and reticular cells. It forms the stroma of certain organs, and helps to bind together the cells of smooth muscle. Meshlike supportive framwork made of retircular fibes and reticular cells around soft organs such as lymphatic vessels (spleen and liver) Reticular Tissue is a loose CT composed of a network of reticular fibres which create a structural framework for soft organs. Reticular fibers form the network onto which other cells attach Dense Connective Tissue Dense connective tissue contains thicker, denser, and more numerous fibres than loose connective tissue, but considerably fewer cells. More collagen fibers so greater resistance to stretching and strength. Dense regular connective tissue consists of bundles of collagen fibres in a regular, orderly, and parallel arrangement that confers great strength and resistance to stretching in one direction. ligaments and tendons Dense irregular connective tissue contains collagen fibres that are irregularly arranged; it is found in parts of the body where tensions are exerted in various directions. It usually occurs in sheets, such as the dermis of the skin. It also is found in the heart valves, the perichondrium, the tissue surrounding cartilage, and the periosteum Elastic connective tissue consists of elastic fibres and fibroblasts. It is quite strong and can recoil back to its original shape after being stretched. It is found in lung tissue and elastic arteries. Dense regular elastic tissues: both elastin and collagen ligaments in the vocal folds and ligaments between the vertebrae Dense irregular elastic tissues: arterial walls : Dense Connective Tissue. Dense regular CT consists of collagenous fibres organized into parallel bundles (b) Dense irregular CT contains an interwoven mesh of these same fibres, Cartilage : Cartilage is a connective tissue consisting of collagenous fibers embedded in a firm matrix of chondroitin sulfates. Cartilage is a dense network of collagen and elastic fibres in chondroitin sulfate.- chondroitin sulfates are bound with ground substance proteins Cartilage growth is accomplished by interstitial (endogenous—from within) growth and appositional (exogenous—from without) growth. Their cells are called chondrocytes Its collagen fibers give it strength, and its chondroitin sulfate gives it resilience. Embedded within the matrix are chondrocytes occur within spaces called lacunae in the matrix. Cartilage is surrounded by a dense irregular connective tissue membrane called the perichondrium. Unlike other connective tissues, cartilage has no blood vessels or nerves (except in the perichondrium). The three major types of cartilage are the following: Hyaline cartilage is the most abundant but weakest type of cartilage. It has short and dispersed collagen fibres embedded in a gel-type matrix. It provides flexibility and support, and at the joints, reduces friction and absorbs shock. Also found in nose, ribcage and end of the bones to allow growth. Fibrocartilage contains bundles of collagen fibres in its matrix. It does not have a perichondrium. Due to its combined strength and rigidity, it is the strongest of the three types of cartilage.menisci in the knee joint and intervertebral disc Fibrocartilage provides some compressibility and can absorb pressure. Elastic cartilage contains a threadlike network of elastic fibres within the matrix as well as collagen fibers. A perichondrium is present. Elastic cartilage provides strength and elasticity and maintains the shape of certain organs.external ear/ ear lobe Elastic cartilage provides firm but elastic support Types of Cartilage Cartilage is a connective tissue consisting of collagenous fibers embedded in a firm matrix of chondroitin sulfates. (a) Hyaline cartilage provides support with some flexibility. The example is from dog tissue. (b) Fibrocartilage provides some compressibility and can absorb pressure. (c) Elastic cartilage provides firm but elastic support. Bone: hardest tissues to provide protection and support, help provide movement, store minerals and they have blood forming tissues Bone (osseous tissue) consists of a matrix containing mineral salts and collagenous fibres and cells called osteocytes.--> hardest, protect and support the body Osteocytes / bone cells are also located within lacunae Rigid extracellular matrix collagen fibers embedded within the mineralized ground substance that contain calcium phosphate. Without minerals very little support Without collagens brtille and shatter easily Bone is classified as either compact or spongy, depending on how the matrix and cells are organized. The basic unit of compact bone is the osteon or Haversian system, which consists of four parts and make them solid and provide greater structural strength. The lamella are concentric rings of matrix that consist of mineral salts that give bone its hardness, and collagen fibres that give bone its strength. Lacunae are small spaces between the lamellae that contain mature bone cells called osteocytes. Canaliculi are minute canals—containing the processes of osteocytes—which provide routes for nutrient and waste transport. A central (Haversian) canal contains the blood vessels and nerves. Spongy bone has trabeculae rather than osteons.--> lighter than compact bones and are found in the interior of some bones and end of long bones have empty spaces between trabeculae which are arches of bone proper Blood Blood (vascular tissue) consists of a liquid matrix called plasma, and formed elements that are derived from stem cells located in the bone marrow: Red blood cells (erythrocytes) function in transporting respiratory gases. White blood cells (leukocytes) are involved in phagocytosis, immunity, and allergic reactions. Platelets (thrombocytes) function in blood clotting Plasma has nutrients, wastes and salts dissolved in it to transport throughout the body. Lymph: drain into blood vessels in order to deliver molecules to it that otherwise could not directly enter the bloodstream their specialized capillaries that are very permeable that allow large molecules and excess fluids from interstitial spaces to enter their vessels transport fats absorbed in intestine to deliver them to blood. Lymph is the interstitial fluid flowing in the lymph vessels. Liquid matrix + white blood cell Compare and contrast the three types of muscle tissue in terms of their structure, control, location in the human body, and function. Muscle tissue consists of fibres (cells) that are modified for contraction, and thus provide motion, maintenance of posture, and heat production. Skeletal muscle tissue is attached to bones, is striated, and is voluntary. Cardiac muscle tissue forms most of the heart wall, is striated, and is usually involuntary. Smooth (visceral) muscle tissue is found in the walls of hollow internal structures (blood vessels and viscera), is nonstriated, and is usually involuntary. It provides motion (e.g., constriction of blood vessels and airways, propulsion of foods through the gastrointestinal tract, and contraction of the urinary bladder and gallbladder). Identify the major cell of nervous tissue; denote the location of nervous tissue in the body, and discuss its function. nervous tissue mediates perception and response The nervous system is composed of only two principal kinds of cells: neurons (nerve cells) and neuroglia (protective and supporting cells). Most neurons consist of a cell body and two types of processes called dendrites and axons. Neurons are sensitive to stimuli; convert stimuli into nerve impulses; and conduct nerve impulses to other neurons, muscle fibres, or glands. Neuroglia protect and support neurons, and are often the sites of tumors of the nervous system. The Neuron. The cell body (or soma) contains the nucleus and mitochondria. Electrical impulses are received by dendrites and passed to the cell body. The axon relays the impulse to another excitable cell. Define the term epithelial membrane, and discuss the structure, location, and function of its four different types-cutaneous, mucous, serous, and synovial. Membranes are thin layers of cells that make flat sheets of flexible tissue that cover or line a part of the body. Epithelial membranes consist of an epithelial layer and an underlying connective tissue layer. These membranes include mucous membranes, serous membranes, and the cutaneous membrane or skin. Synovial membranes line joints and contain only connective tissue. Mucous membranes (mucosae) line cavities that open to the exterior, such as the gastrointestinal tract. The epithelial layer of a mucous membrane have exocrine glands that secrete mucus and is an important aspect of the body’s defense mechanisms, acting as a barrier to pathogens and a trapping surface for particles. The connective tissue layer of a mucous membrane is called the lamina propria that supports the epithelial layer. A serous membrane, or serosa, lines a body cavity that does not open directly to the exterior, and covers the organs that lie within the cavity. Examples of this membrane include the pleura, pericardium, and peritoneum. These membranes consist of parietal and visceral portions. The epithelial layer secretes a lubricating serous fluid that reduces friction between organs and the walls of the cavities in which they are located. They form double sheets of mesenteries that suspended the digestive organs in abdominal cavity. Their epithelial membrane is derived from mesoderm and it is called mesothelium. And it is a simple squamous layer. Synovial membranes are connective tissue membranes and lack the epithelium line joint cavities, bursae, and tendon sheaths, and do not contain epithelium; they also secrete a lubricating synovial fluid to reduce friction between movable joints. They also constantly exchange water and nutrients with blood. Cutaneous: stratified keratinized squamous membranes on top of connective tissues. Protect body from pathogens and external world. Serous Membranes. One serous membrane lines the pericardial cavity and reflects back to cover the heart—much the same way that an underinflated balloon would form two layers surrounding a fist. Tissue Membranes. Synovial membranes contain only connective tissue. Epithelial membranes consist of cutaneous, serous, and mucous membranes Describe the nature of cancer and how tissues respond to injury. Inflammation is a tissue’s initial response to injury in an attempt to control and limit the extent of the damage caused, and initiate the repair and regenerative processes. Tissue repair is the process of replacing dead or damaged cells, which can only occur if an inflammation has been contained. 4 signs: Redness – erythema Swelling Local heat Pain Possible 5th sign could be loss of some organ or tissue function Histamine released by mast cells and other inflammatory mediators released by damaged cells cause increased blood flow to the injured tissue through vasodilation, which produces an apparent reddening and local hyperthermia. They also recruit white blood cells These mediators including histamine also cause the endothelium of local blood vessels to become leaky so neutrophiles, macrophages and fluid move from blood to interstitial tissue space and this excess fluid cause a local edema, or interstitial swelling. The swollen tissues squeeze pain receptors, causing the sensation of pain. An acute inflammation resolves itself, but chronic inflammations persist and lead to disease states. Cancer is not a disease of inflammatory origin, but instead arises from cells that have acquired a genetic abnormality or mutation. Such mutated cells can become cancerous if they escape the signals for regulation and undergo uncontrolled cell growth, penetration into adjacent tissues and cause local blood vessel proliferation, and readily spread to other tissues or organs and colonize them. The cancerous cells form tumors that take the blood supply away from normal healthy cells and organs. The cancerous mutations affect key proteins that are involved in controlling and regulating the cells ability to divide properly so they start dividing abnormally and the affected cells accumulate but they are not capable of forming a regular tissue. Symptoms of both local and systemic inflammatory processes can be seen as a consequence of this form of tissue injury if early treatment is delayed.