tissuelevel.pdf

The term tissue is used to describe a group of cells functioning together in the body. The microscopic study of tissue appearance, organization, and function is called HISTOLOGY. HISTOLOGY is also the foundation for understanding PATHOLOGY, the changes that occur during the course of disease TYPE...

The term tissue is used to describe a group of cells functioning together in the body. The microscopic study of tissue appearance, organization, and function is called HISTOLOGY. HISTOLOGY is also the foundation for understanding PATHOLOGY, the changes that occur during the course of disease TYPES OF CELLS IN THE HUMAN BODY, THEY ARE ORGANIZED INTO FOUR CATEGORIES OF TISSUES: EPITHELIAL, CONNECTIVE, MUSCLE, AND NERVOUS The Four Types of Tissues EPITHELIAL TISSUE are sheets of cells that cover exterior surfaces of the body, line internal cavities and passageways, and form certain glands. CONNECTIVE tissue, our most diverse category of tissue, binds the cells and organs of the body together and functions in the protection, support, and integration of all parts of the body. MUSCLE TISSUE is contractile; it provides movement, whether that means moving the skeleton as in walking, or moving the blood through the body as the heart muscle contracts. NERVOUS TISSUE is capable of short- and long-distance communication throughout the body EXTRACELLULAR MATRIX (ECM) is a network of substances that surround and support the cells in a tissue the ECM of bone tissue is solid while the ECM of the blood is liquid.. MAJOR COMPONENTS of ECM are usually COLLAGEN FIBERS AND PROTEOGLYCANS COLLAGEN is the most abundant protein in the human body. PROTEOGLYCANS are large, negatively-charged molecules that are a combination of carbohydrate and protein. The THREE BASIC TYPES OF CONNECTIONS—TIGHT JUNCTIONS, DESMOSOMES, AND GAP JUNCTIONS (Types of Cell Junctions) At one end of the spectrum is the TIGHT JUNCTION, which fuses the membranes of two neighboring cells together tightly so that there is no extracellular space between them, which blocks the movement of substances through the extracellular space between the cells. DESMOSOMES and their cousins hemidesmosomes are two types of anchoring junction, which are cell junctions that help stabilize cells structural. DESMOSOMES unite two neighboring cells structurally. HEMIDESMOSOMES, which look like half a desmosome, link cells to the extracellular matrix. A GAP JUNCTION forms an intercellular passageway between the membranes of adjacent cells to facilitate the movement of small molecules and ions among the cytoplasm of adjacent cells EPITHELIAL TISSUE is essentially large sheets of cells covering all the surfaces of the body The main function of epithelial tissues is protection, so they are found in locations that are exposed to the outside world such as your skin and the lining of your mouth. For these “INSIDE” STRUCTURES, the epithelial tissue lining them is called eNDOTHELIUM (PLURAL = ENDOTHELIA). The airways, the digestive tract, and the urinary and reproductive systems are all connected to the outside world. It is common to find bacteria in these spaces, and so we give the tissues lining these the name EPITHELIUM (PLURAL = EPITHELIA) EPITHELIA as being polar because they have two sides that are distinct. One of their sides, the APICAL SIDE, is exposed to the external environment or an internal space The BASAL SURFACE is the only side of the tissue facing the ECM. The specialized ECM that supports and anchors the basal epithelium is known as a BASEMENT MEMBRANE.  This supportive membrane consists of TWO LAYERS: the LAMINA LUCIDA, a mixture of glycoproteins and collagen that provides the immediate attachment site for the epithelium, and a LAMINA DENSA, which has a denser and more structural weave of tough collagen fibers; layer that is deepest and connects to the underlying connective tissue EPITHELIAL TISSUES are nearly completely avascular, meaning that they have no blood vessels. GENERALIZED FUNCTIONS OF EPITHELIAL TISSUE Epithelial tissues provides:  the body’s first line of protection from physical, chemical, and biological wear and tear  The cells of an epithelium act as gatekeepers of the body,  controlling permeability and  allowing selective transfer of materials across a physical barrier In enclosed spaces that are lined with epithelia, the enclosed space is called a LUMEN. Many EPITHELIAL CELLS are capable of secretion and release mucus and specific chemical compounds onto their apical surfaces. EPITHELIAL FEATURES:  Highly cellular  Polar  Avascular  Innervated  Adhered to a basement membrane It is a common feature of the apical epithelial surface to have CILIA OR MICROVILLI. CILIA, microscopic extensions of the apical cell membrane, beat in unison and move fluids as well as trapped particles  CILIATED EPITHELIUM lines the ventricles of the brain, where it helps circulate the cerebrospinal fluid. If we consider the function of CILIA (to sweep materials off the apical surface) and the function of MICROVILLI (to expand the surface area of the cell)  MICROVILLI are similar extensions of the apical cell membrane,  but they do not contain cytoskeletal elements  do not have the capacity to move.  to expand the surface area of the cell  to allow more contact with the extracellular fluid on the apical side.  the purpose of this is to allow more membrane transport to occur THE THREE SHAPES OF EPITHELIAL CELLS are:  SQUAMOUS (FLAT),  CUBOIDAL (ROUND), and  COLUMNAR (TALL AND NARROW) 2 CHARACTERISTICS THAT GO INTO EPITHELIAL CELL CLASSIFICATION: THE SHAPE OF THE CELLS AND THE NUMBER OF THE CELL LAYERS  CELL SHAPES can be squamous (flat and thin), cuboidal (boxy, as wide as it is tall), or columnar (rectangular, taller than it is wide with a nucleus closer to its basal side).  The NUMBER OF CELL LAYERS in the tissue  can be one (in this type, called a SIMPLE EPITHELIUM, every cell rests on the basal lamina), or more than one (in this type, called a STRATIFIED EPITHELIUM, only the basal layer of cells rests on the basal lamina). STRATIFIED EPITHELIA, the cells in the basal layer often have a cuboidal shape, simply because the cells are stem cells SIMPLE EPITHELIAL TISSUE is the name for tissue with a single layer of cells SIMPLE SQUAMOUS EPITHELIUM have the appearance of a fried egg.  Squamous Cell Nuclei tend to be flat and horizontal, mirroring the form of the cell  alveoli of lungs where gasses diffuse, segments of kidney tubules, and the lining of capillaries  Simple Cuboidal Epithelium, the nucleus of the boxlike cells appears round and is generally located near the center of the cell.  lining of the ducts of glands  In Simple Columnar Epithelium, the nucleus of the tall column-like cells tends to be elongated and located in the basal end of the cells.   active in the absorption and secretion of molecules  PSEUDOSTRATIFIED COLUMNAR EPITHELIUM is a type of epithelium that appears to be stratified, but instead consists of a single layer of irregularly-shaped and differently sized columnar cells; found in the respiratory tract STRATIFIED EPITHELIAL TISSUE is the name for tissue consisting of several layers of cells; the cells at the apical layer are the oldest  Stratified Squamous Epithelium is by far the most common type of stratified epithelium in the human body; keratinized (topped with keratin-filled dead cells) or nonkeratinized (top layer is moist living cells  Lines the esophagus, mouth, and vagina  Stratified Cuboidal Epithelium (Sweat glands, salivary glands, and the mammary glands) and  Stratified Columnar Epithelium ( male urethra and the ducts of some gland)are uncommon in the human body, appearing only as a lining in a few of the larger glands and ducts. A GLAND is a structure that synthesizes and secretes chemicals. Most glands are composed of groups of epithelial cells, but some are unicellular. the inside is a sterile place where no bacteria are found outside is those spaces continuous with the outside world, including the lining of the gut. GLAND can be classified as an ENDOCRINE GLAND if it secretes within the body and bloodstream, or as an EXOCRINE GLAND if it secretes onto an epithelium to the outside of the body; Sweat glands and the glands of the digestive system example Endocrine Glands The secretions of endocrine glands are called HORMONES. HORMONES are released into the interstitial fluid, diffused into the bloodstream, and delivered to targets—in other words, cells that have receptors to bind the hormones. The ENDOCRINE SYSTEM is part of a major regulatory system coordinating the regulation and integration of body responses.  anterior pituitary, thymus, adrenal cortex, and gonads EXOCRINE GLANDS release their contents through a duct that leads to the epithelial surface.  Mucus, sweat, saliva, and breast milk are all examples of secretions from exocrine glands. EXOCRINE GLAND STRUCTURE exocrine glands are either unicellular or multicellular; classified as simple or compound, and as acinar or tubula The unicellular glands are single cells such as goblet cells scattered among the epithelial cells. The multicellular exocrine glands consist of a single layer of epithelial cells that folds into the deeper tissues below METHODS AND TYPES OF SECRETION  THREE MODES OF EXOCRINE SECTION: MEROCRINE, APOCRINE, AND HOLOCRINE  MEROCRINE SECRETION, the most common type of exocrine secretion, is accomplished through exocytosis; so materials secreted by this method include sweat and watery mucus.  APOCRINE SECRETION, the material to be secreted accumulates near the apical portion of the cell;  HOLOCRINE SECRETION involves the rupture and destruction of the entire gland cell. SEROUS GLAND produces watery secretions derived from blood plasma and typically rich in enzymes MUCOUS GLAND releases watery to viscous products rich in the glycoprotein mucin. A) In MEROCRINE SECRETION, the cells share their contents through exocytosis. (B) In APOCRINE SECRETION, the apical half of the cell fills with the secre tory product and then separates from the basal half of the cell. (C) In HOLOCRINE SECRETION, the secretory cell is consumed with the secretory product and the whole cell is destroyed as it releases its product. CONNECTIVE TISSUES  are the most structurally diverse category of tissues in the human body.  three characteristic components:  CELLS,  LARGE AMOUNTS OF GROUND SUBSTANCE, AND  PROTEIN FIBERS  The types of CELLS found in any given connective tissue can change periodically  The most abundant cell in connective tissue proper is the FIBROBLAST. Adipocytes (fat cells) are cells that store lipids as droplets that fill most of the cytoplasm.  cells are rarely found touching each other  connect tissues and organs; from the connective tissue sheath that surrounds muscle cells, to the tendons that attach muscles to bones, and to the skeleton that supports the positions of the body  protection  defend the body from microorganisms that enter the body.  Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues  TWELVE TYPES OF CONNECTIVE TISSUES CAN BE SORTED INTO BROAD CATEGORIES BASED ON GENERAL PROPERTIES CONNECTIVE TISSUE PROPER Semisolid, flexible connective tissues are typically grouped together The structural connective tissues— bone and cartilage—are grouped together in a category called SUPPORTIVE CONNECTIVE TISSUE. Liquid connective tissues (blood and lymph) are grouped together in the category called FLUID CONNECTIVE TISSUE MACROPHAGES AND MAST CELLS are the most common types of wandering cell-do not stay put; rather, they may be found in various concentrations.; immune defense role and so immune cells are found patrolling these tissues. MACROPHAGES are large immune cells that wander through tissues searching for waste, debris, or unwanted visitors such as bacteria. Macrophages release CYTOKINES, small proteins that act as chemical messengers; recruit other cells of the immune system to infected sites and stimulate their activities MAST CELLS are immune cells that secrete chemicals in order to activate immune responses CONNECTIVE TISSUE FIBERS AND GROUND SUBSTANCE Three main types of fibers are secreted by fibroblasts: collagen fibers, elastic fibers, and reticular fibers. COLLAGEN FIBERS are flexible but also have great tensile strength, resist stretching, and give ligaments and tendons their characteristic resilience and strength. ELASTIC FIBERS contain the protein elastin along with lesser amounts of other proteins and glycoproteins. The main property of elastin is that after being stretched, compressed, or twisted it will return to its original shape. RETICULAR FIBERS are formed from the same protein subunits as collagen fibers; however, reticular fibers remain narrow and are arrayed in a branching network. LOOSE CONNECTIVE TISSUE is found between many organs where it acts both to absorb shock and bind tissues together. It allows water, salts, and various nutrients to diffuse through to adjacent or imbedded cells and tissues  AREOLAR TISSUE is a loose connective tissue that resembles a loosely-woven web. It is characterized by predominantly collagen fibers with smaller amount of elastin fibers. Areolar connective tissue is found surrounding blood and lymph vessels, as well as supporting organs in the abdominal cavity  ADIPOSE TISSUE consists mostly of packed cells with few fibers between the cells. The cells within adipose tissue are known as ADIPOCYTES; these are specialized and modified for fat  storage. The two varieties of adipose tissue are called white and brown, white adipose actually appears more of a dull yellow. RETICULAR TISSUE is tissue composed of reticular fibers, loosely woven together to form a meshlike supportive framework for the cells of some organs such as lymphatic tissue, the spleen, and the liver DENSE CONNECTIVE TISSUE does not allow for as much communication of nutrients and fluids through the tissue, but is more resistant to pulling forces; dense connective tissue is harder to stretch TWO TYPES OF DENSE CONNECTIVE TISSUE 1. In DENSE IRREGULAR CONNECTIVE TISSUE, the collagen fibers are woven together in random, net like patters as we saw in areolar tissue. The fibers, while netlike, are very tightly packed together, and this arrangement gives the tissue tremendous strength. 2. DENSE REGULAR CONNECTIVE TISSUE the collagen fibers are parallel to each other, enhancing tensile strength and resistance to stretching in the direction SUPPORTIVE CONNECTIVE TISSUES The two major forms of supportive connective tissue—cartilage and bone—allow the body to maintain its posture and protect internal organs.  CARTILAGE is a semisolid material that is able to offer structure and protection to the body while maintaining some flexibility. The ribcage functions to protect the vulnerable heart and lung organs Chondrocytes. These cells are responsible for generating the chondroitin sulfates and other components of the cartilage matrix. 1. HYALINE CARTILAGE, the most common type of cartilage in the body, consists of short and dispersed collagen fibers and contains large amounts of proteoglycans 2. FIBROCARTILAGE has thick bundles of collagen fibers dispersed through its matrix. These collagen fibers lend fibrocartilage a toughness and durability to resist impact. 3. ELASTIC CARTILAGE contains collagen and proteoglycans, but this tissue type has far more elastic fibers than the other forms of cartilage  BONE is the hardest connective tissue. It provides protection to internal organs and supports the body. There ARE TWO TYPES OF BONE in the body: COMPACT BONE, which forms the periphery of most bones, and SPONGY BONE, which is composed of trabeculae and marrow-filled spaces and forms the deeper portion and the epiphyses of most bones FLUID CONNECTIVE TISSUE In the fluid connective tissues—blood and lymph—cells circulate in a liquid extracellular matrix called plasma  BLOOD is a fluid connective tissue containing erythrocytes, five types of leukocytes, and platelets that circulate in a liquid extracellular matrix  Erythrocytes (commonly called red blood cells) transport oxygen and other gasses, increasing the efficiency of carrying gasses in a liquid  Leukocytes (commonly called white blood cells) are immune cells.  LYMPH is a liquid collected from body tissues with excess interstitial fluid. MUSCLE TISSUE is all about movement