Lesson3_Unit 1_Tissue Level of Organization.pdf

Tissue Level of Organization Unit 1: Levels of Organization Prof. Girlie L. Perdon-Pineda LEARNING OUTCOMES: At the end of the chapter, the students should be able to: ❖ Identify the main tissue types and discuss their roles the human body; ❖ Identify the four types of tissue memb...

Tissue Level of Organization Unit 1: Levels of Organization Prof. Girlie L. Perdon-Pineda LEARNING OUTCOMES: At the end of the chapter, the students should be able to: ❖ Identify the main tissue types and discuss their roles the human body; ❖ Identify the four types of tissue membranes and the characteristics of each that make them functional; TISSUES: ❖ This is used to describe a group of cells found together in the body. The cells within a tissue share a common embryonic origin. HISTOLOGY ❖ This is the microscopic study of tissue appearance, organization, and function.  TYPES OF TISSUES: TYPE IMAGE FUNCTION “epithelium” — refers to the sheets of cells that cover exterior surfaces of the body, lines internal cavities and EPITHELIAL passageways, and forms TISSUE certain glands. LOCATION: Lining of GI tract organs and other hollow organs Skin surface (epidermis)  TYPES OF TISSUES: TYPE IMAGE FUNCTION - binds the cells and organs of the body together and functions in the protection, CONNECTIVE support, and integration of all parts of the body. TISSUE LOCATION: Fat and other soft padding tissue Bone Tendon  TYPES OF TISSUES: TYPE IMAGE FUNCTION - excitable, responding to stimulation and contracting to provide movement. MUSCLE TISSUE Three major types: skeletal (voluntary) muscle, smooth muscle, and cardiac muscle in the heart.  TYPES OF TISSUES: TYPE IMAGE FUNCTION Also excitable, allowing the propagation of electrochemical signals in the form of nerve NERVOUS impulses that communicate between different regions of TISSUE the body LOCATION: Brain Spinal Cord Nerves  TYPES OF TISSUES: TYPE Additional Video Reference Epithelial Tissue Types of Tissue Part 1_ Epithelial Tissue Connective Tissue Types of Tissue Part 2_ Connective Tissue Muscle Tissue Types of Tissue Part 3_ Muscle Tissue Nerve Tissue Types of Tissue Part 4_ Nervous Tissue Embryonic Origin of Tissue: The zygote, or fertilized egg, is a single cell formed by the fusion of an egg and sperm. After fertilization the zygote gives rise to rapid mitotic cycles, generating many cells to form the embryo. ➔ Totipotent — The first embryonic cells generated that have the ability to differentiate into any type of cell in the body. Germ Layers – from which all the tissues and organs of the human body eventually form Ectoderm – (ecto = “outer”) Mesoderm – (meso = “middle”) Endoderm – (endo = “inner”) Embryonic Origin of Tissue: GERM LAYER GIVES RISE TO: Epidermis, glands on skin, some carnial bones, pituitary and adrenal medulla, the nervous system, the mouth between cheek and gums, ECTODERM the anus Embryonic Origin of Tissue: GERM LAYER GIVES RISE TO: Connective tissues proper, bone, cartilage, blood, endothelium of blood vessels, muscle, synovial membranes, serous membranes lining body MESODERM cavities, kidneys, lining of gonads.  For Embryonic Origin of Tissue: Additional Info, scan this code GERM LAYER GIVES RISE TO: Lining of airways and digestive system except the mouth and distal part of digestive system (rectum and anal canal); glands (digestive glands, ENDODERM endocrine glands, adrenal cortex)  TISSUE MEMBRANES: ❏ This is a thin layer or sheet of cells that COVERS the outside of the body, the organs internal passageways that lead to the exterior of the body, and the lining of the moveable joint cavities. TWO CATEGORIES OF TISSUE MEMBRANES 1. Connective tissue membranes, which include synovial membranes, and 2. Epithelial membranes, which include mucous membranes, serous membranes, and the cutaneous membrane.  1. CONNECTIVE TISSUE MEMBRANE This is formed solely from connective tissue. These membranes encapsulate organs, such as the kidneys, and line our movable joints. Synovial membrane : the type of connective tissue membrane that lines the cavity of a freely movable joint. Synovial fluid: a natural lubricant that enables the bones of a joint to move freely against one another without much friction. 2. EPITHELIAL MEMBRANES This is composed of epithelium attached to a layer of connective tissue, for example, your skin. a. Mucous membrane: Sometimes called mucosa, lines the body cavities and hollow passageways that open to the external environment, and include the digestive, respiratory, excretory, and reproductive tracts. Mucous, produced by the epithelial exocrine glands, covers the epithelial layer. EPITHELIAL MEMBRANES b) Serous membrane: composed of mesodermally derived epithelium called the mesothelium that is supported by connective tissue. These membranes line the coelomic cavities of the body, that is, those cavities that do not open to the outside, and they cover the organs located within those cavities. c) Cutaneous membrane : also called as the “skin”. It is a stratified squamous epithelial membrane resting on top of connective tissue. The apical surface of this membrane is exposed to the external environment and is covered with dead, keratinized cells that help protect the body from desiccation and pathogens. EPITHELIAL TISSUE  EPITHELIAL TISSUE: Most epithelial tissues are essentially large sheets of cells covering all the surfaces of the body exposed to the outside world and lining the outside of organs. Epithelium also forms: the glandular tissue of the body; the area of the body exposed to the outside (Skin); other areas exposed to the outside which include the airways, the digestive tract, as well as the urinary and reproductive systems. hollow organs and body cavities that do not connect to the exterior of the body, which includes, blood vessels and serous membranes, are lined by endothelium (plural = endothelia), which is a type of epithelium. EPITHELIAL TISSUE: Important Structure and Features of the Epithelia: 1. Highly cellular — with little or no extracellular material present between cells. Adjoining cells form a specialized intercellular connection between their cell membranes called a cell junction. 2. Polarity — The epithelial cells exhibit polarity with differences in structure and function between the exposed or apical facing surface of the cell and the basal surface close to the underlying body structures. EPITHELIAL TISSUE: Important Structure and Features of the Epithelia: 3. Completely avascular — no blood vessels cross the basement membrane to enter the tissue, and nutrients must come by diffusion or absorption from underlying tissues or the surface. EPITHELIAL TISSUE: Important Structure and Features of the Epithelia: 4. Rapid replacement of damaged/dead cells — sloughing off of damaged or dead cells is a characteristic of surface epithelium and allows our airways and digestive tracts to rapidly replace damaged cells with new cells. GENERALIZED FUNCTIONS OF EPITHELIAL TISSUES: 1. Epithelial tissues provide 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. Some epithelia often include structural features that allow the selective transport of molecules and ions across their cell membranes. 2. Many epithelial cells are capable of secretion and release mucous and specific chemical compounds onto their apical surfaces ❖ For example, the epithelium of the small intestine releases digestive enzymes. Cells lining the respiratory tract secrete mucous that traps incoming microorganisms and particles. A glandular epithelium contains secretory cells. THE EPITHELIAL CELL : Particular structures found in some epithelial cells are an adaptation to specific functions. Cilia — these are microscopic extensions of the apical cell membrane that are supported by microtubules. They 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. ❖ The ciliated epithelium of your airway forms a mucociliary escalator that sweeps particles of dust and pathogens trapped in the secreted mucus toward the throat. ❖ Nasal cilia sweep the mucous blanket down towards your throat. CELL to CELL JUNCTIONS : Three basic types of connections allow varying degrees of interaction between the cells 1. Tight junctions 2. Gap junctions 3. Anchoring junctions 1. TIGHT JUNCTION: ➔ separates the cells into apical and basal compartments CELL to CELL JUNCTION : Three basic types of connections allow varying degrees of interaction between the cells: ANCHORING JUNCTION: ➔ help stabilize epithelial tissues. ➔ common on the lateral and basal surfaces of cells where they provide strong and flexible connections. CELL to CELL JUNCTION : Three basic types of connections allow varying degrees of interaction between the cells: GAP JUNCTION: ➔ Forms an intercellular passageway between the membranes of adjacent cells ➔ These junctions allow electrical and metabolic coupling of adjacent cells, which coordinates function in large groups of cells. CLASSIFICATION OF EPITHELIAL TISSUES: Epithelial tissues are classified according to the shape of the cells and number of the cell layers formed. Cell Shapes ➔ squamous (flattened and thin), ➔ cuboidal (boxy, as wide as it is tall), ➔ columnar (rectangular, taller than it is wide). Cell Layers ➔ simple (one layer), ➔ stratified (more than one), ➔ pseudostratified (single layer of Transitional describes a form of irregularly shaped cells that give the specialized stratified epithelium in appearance of more than one layer) which the shape of the cells can vary. CLASSIFICATION OF EPITHELIAL TISSUES: CLASSIFICATION OF EPITHELIAL TISSUES: CELLS APPEARANCE LOCATION FUNCTION Thin Scales; Air sacs of the lungs Allows materials to 1. Simple Squamous squamous cell and the lining of the pass through by Epithelium nuclei tend to be heart, blood vessels diffusion and flat, horizontal, and and lymphatic filtration, and elliptical vessels secretes lubricating substances Made of single layer Lines vessels of the Allows materials to a. Endothelium of squamous cells lymphatic and pass through by cardiovascular diffusion and filtration system Made of single layer Forms the surface layer Secrete a fluid that b. Mesothelium of squamous cells of the serous membrane that lines body cavities lubricates the and internal organs mesothelium CLASSIFICATION OF EPITHELIAL TISSUES: CELLS APPEARANCE LOCATION FUNCTION 2. Simple Cuboidal The nucleus of the In ducts and Secretes and Epithelium box-like cells secretory portions absorbs molecules appears round of small glands and in kidney tubules 3. Simple Columnar The nucleus of the Ciliated tissues including the bronchi, Absorbs; it also Epithelium tall column-like cells uterine tubes, and secretes mucous tends to be uterus; smooth and enzymes. elongated and (nonciliated tissues) located in the basal are in the digestive end of the cells. tract bladder CLASSIFICATION OF EPITHELIAL TISSUES: CELLS APPEARANCE LOCATION FUNCTION 4. Pseudostratified Appears to be Ciliated tissue Secrete mucous; Columnar stratified but lines the trachea ciliated tissue Epithelium instead consists of and much of the moves mucous a single layer of upper respiratory irregularly shaped tract and differently sized columnar cells; nuclei interspersed between Goblet cell the columnar Mucous-secreting epithelial cells of unicellular “gland” mucous membranes; lining of the small intestine CLASSIFICATION OF EPITHELIAL TISSUES: CELLS APPEARANCE LOCATION FUNCTION 1. Stratified Squamous Top layer may be Lines the Protects against Epithelium covered with dead esophagus, mouth, abrasion cells filled with and vagina keratin 2. Stratified Cube-like cells Sweat glands, Protective tissue Cuboidal Epithelium arranged in layers salivary glands, and mammary glands CLASSIFICATION OF EPITHELIAL TISSUES: CELLS APPEARANCE LOCATION FUNCTION 3. Stratified Columnar column-like cells The male urethra Epithelium and the ducts of Secretes and arranged in layers some glands. protects 4. Transitional Shapes of the apical Lines the bladder, Allows the urinary Epithelium cells; change organs to expand and urethra and gradually as the stretch bladder fills with ureters urine CLASSIFICATION OF EPITHELIAL TISSUES: GLANDULAR EPITHELIUM: A gland is a structure made up of one or more cells modified to synthesize and secrete chemical substances. Most glands consist of groups of epithelial cells. A gland can be classified as: ❖ 1. Endocrine gland — a ductless gland that releases secretions directly into surrounding tissues and fluids (endo- = “inside”) – part of a major regulatory system coordinating the regulation and integration of body responses ❖ Examples: anterior pituitary, thymus, adrenal cortex, and gonads GLANDULAR EPITHELIUM: A gland can be classified as: ❖ 2. Exocrine gland — whose secretions leave through a duct that opens directly, or indirectly, to the external environment (exo- = “outside”). – release their contents through a duct that leads to the epithelial surface. Examples of secretion: mucous, sweat, saliva and breast milk METHODS AND TYPES OF SECRETION: ❏ 1. Merocrine secretion : the most common type of exocrine secretion. The secretions are enclosed in vesicles that move to the apical surface of the cell where the contents are released by exocytosis. ❏ 2. Apocrine secretion : accumulates near the apical portion of the cell. That portion of the cell and its secretory contents pinch off from the cell and are released. The sweat glands of the armpit are classified as apocrine glands. METHODS AND TYPES OF SECRETION: ❏ 3. Holocrine secretion : involves the rupture and destruction of the entire gland cell. The cell accumulates its secretory products and releases them only when it bursts. New gland cells differentiate from cells in the surrounding tissue to replace those lost by secretion. ❏ - The sebacious glands that produce oils on the skin and hair are holocrine glands/cells. METHODS AND TYPES OF SECRETION: Glands are also named after the products they produce. ✓ The serous gland produces watery, blood-plasma-like secretions rich in enzymes such as alpha amylase, whereas ✓ The mucous gland releases watery to viscous products rich in the glycoprotein mucin. METHODS AND TYPES OF SECRETION: Connective Tissue: Supports and Protects THE CONNECTIVE TISSUE: Connective tissue cells are dispersed in a matrix, unlike epithelial tissue, which is composed of cells closely packed with little or no extracellular space in between. Matrix — includes a large amount of extracellular material ➔ The major component of the matrix is a ground substance often crisscrossed by protein fibers. This ground substance is usually a fluid, but it can also be mineralized and solid, as in bones. FUNCTIONS OF CONNECTIVE TISSUES: 1. Support and connect other tissues 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 2. Protection In the form of fibrous capsules and bones that protect delicate organs and, of course, the skeletal system. Specialized cells in connective tissue defend the body from microorganisms that enter the body. FUNCTIONS OF CONNECTIVE TISSUES: 3. Transport of fluid, nutrients, waste and chemical messengers Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and lymph. 4. Storage of surplus energy and insulation Adipose cells store surplus energy in the form of fat and contribute to the thermal insulation of the body. CLASSIFICATION OF CONNECTIVE TISSUES: The three broad categories of connective tissue are classified according to the characteristics of their ground substance and the types of fibers found within the matrix 1. Connective Tissue Proper: Includes loose connective tissue and dense connective tissue. Both tissues have a variety of cell types and protein fibers suspended in a viscous ground substance. ➔ Dense connective tissue is reinforced by bundles of fibers that provide tensile strength, elasticity, and protection. ➔ Loose connective tissue, the fibers are loosely organized, leaving large spaces in between. CLASSIFICATION OF CONNECTIVE TISSUES: 2. Supportive Connective Tissue: Includes bone and cartilage—provide structure and strength to the body and protect soft tissues. ➔ In bone, the matrix is rigid and described as calcified because of the deposited calcium salts. 3. Fluid Connective Tissue: Includes lymph and blood, various specialized cells circulate in a watery fluid containing salts, nutrients, and dissolved proteins.  CONNECTIVE TISSUE EXAMPLES Connective tissue proper Supportive connective tissue Fluid connective tissue Loose connective Cartilage tissue Hyaline Blood Areolar Fibrocartilage Adipose Elastic Reticular Dense connective Bones tissue Compact bone Lymph Regular elastic Cancellous bone Irregular elastic CONNECTIVE TISSUE PROPER: Fibroblasts are present in all connective tissue proper. Fibrocytes, adipocytes, and mesenchymal cells are fixed cells — which means they remain within the connective tissue. Other cells move in and out of the connective tissue in response to chemical signals. Macrophages, mast cells, lymphocytes, plasma cells, and phagocytic cells are found in connective tissue proper but are actually part of the immune system protecting the body. CELL TYPES: 1. Fibroblast - The most abundant cell in connective tissue proper - Polysaccharides and proteins secreted by fibroblasts combine with extra-cellular fluids to produce a viscous ground substance that, with embedded fibrous proteins, forms the extra-cellular matrix. a. Fibrocyte — a less active form of fibroblast, is the second most common cell type in connective tissue proper. CELL TYPES: 2. Adipocytes - cells that store lipids as droplets that fill most of the cytoplasm. Two basic types of adipocytes a. White fat adipocytes – store lipids as a single layer drop and are metabolically less active b. Brown adipocytes – store lipids as many droplets and have high metabolic activity. The number and type of adipocytes depends on the tissue and location, and vary among individuals in the population. CELL TYPES: 3. Mesenchymal cell – is a multipotent adult stem cell. - These cells can differentiate into any type of connective tissue cells needed for repair and healing of damaged tissue. CELL TYPES: 4. Other Cells present that are part of Immune System a. Macrophage cells – enter the connective tissue matrix from the blood vessels – essential component of the Immune system – when stimulated, they release cytokines, small protein that act as chemical messengers. Cytokines recruit other cells of the immune system to infected sites and stimulate their activities. Roaming/ Free Macrophages – move rapidly by amoeboid movement, engulfing infectious agents and cellular debris Fixed Macrophages – permanent residents of their tissues CELL TYPES: 4. Other Cells present that are part of Immune System b. Mast cells – has many cytoplasmic granules (these granules contain the chemical signals histamine and heparin) – when irritated or damaged, mast cells release histamine, an inflammatory mediator, which causes vasodilation and increased blood flow at a site of injury or infection, along with itching, swelling, and redness you recognize as an allergic response. CONNECTIVE TISSUE FIBERS AND GROUND SUBSTANCE: Three main types of fibers are secreted by fibroblasts: 1. collagen fibers, 2. elastic fibers, and 3. reticular fibers. 1. Collagen Fiber - made from fibrous protein subunits linked together to form a long and straight fiber. - Collagen fibers, while flexible, have great tensile strength, resist stretching, and give ligaments and tendons their characteristic resilience and strength. These fibers hold connective tissues together, even during the movement of the body. CONNECTIVE TISSUE FIBERS AND GROUND SUBSTANCE: 2. Elastic Fiber - contains the protein elastin along with lesser amounts of other proteins and glycoproteins. The main property of elastin is that after being stretched or compressed, it will return to its original shape. - prominent in elastic tissues found in skin and the elastic ligaments of the vertebral column CONNECTIVE TISSUE FIBERS AND GROUND SUBSTANCE: 3. Reticular Fiber - is also formed from the same protein subunits as collagen fibers; however, these fibers remain narrow and are arrayed in a branching network. - most abundant in the reticular tissue of soft organs such as liver and spleen CONNECTIVE TISSUE FIBERS AND GROUND SUBSTANCE: All of these fiber types are embedded in ground substance. Secreted by fibroblasts, ground substance is made of polysaccharides, specifically hyaluronic acid, and proteins. These combine to form a proteoglycan with a protein core and polysaccharide branches. The proteoglycan attracts and traps available moisture forming the clear, viscous, colorless matrix known as GROUND SUBSTANCE. CONNECTIVE TISSUE FIBERS AND GROUND SUBSTANCE: LOOSE CONNECTIVE TISSUE: 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. 1. Adipose tissue — consists mostly of fat storage cells, with little extracellular matrix. – A large number of capillaries allow rapid storage and mobilization of lipid molecules. LOOSE CONNECTIVE TISSUE: a. White adipose tissue - contributes mostly to lipid storage - can serve as insulation from cold temperatures b. Brown adipose tissue - more common in infants, hence the term “baby and mechanical injuries. fat” - can be found - contains a number of mitochondria which protecting the kidneys explains its efficiency at metabolizing stored fat. and cushioning the back - thermogenic,as it breaks down fats, it releases of the eye metabolic heat, rather than producing ATP LOOSE CONNECTIVE TISSUE: 2. Areolar tissue - It contains all the cell types and fibers previously described; - distributed in a random, web-like fashion. - It fills the spaces between muscle fibers, - surrounds blood and lymph vessels, and - supports organs in the abdominal cavity. 3. Reticular tissue - a mesh-like, supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver. - Reticular cells produce the reticular fibers that form the network onto which other cells attach. DENSE CONNECTIVE TISSUE: Dense connective tissue contains more collagen fibers than does loose connective tissue. As a consequence, it displays greater resistance to stretching. Two Major Categories 1. Dense regular connective tissue - fibers are parallel to each other, enhancing tensile strength and resistance to stretching in the direction of the fiber orientations. - Ligaments and tendons are made of dense regular connective tissue, but in ligaments not all fibers are parallel. DENSE CONNECTIVE TISSUE: Dense connective tissue contains more collagen fibers than does loose connective tissue. As a consequence, it displays greater resistance to stretching. Two Major Categories 2. Dense irregular connective tissue - the direction of fibers is random. This arrangement gives the tissue greater strength in all directions and less strength in one particular direction. - In some tissues, fibers crisscross and form a mesh. SUPPORTIVE CONNECTIVE TISSUES: Two major forms of supportive connective tissue, cartilage and bone, allow the body to maintain its posture and protect internal organs. CARTILAGE: ❖ The distinctive appearance of cartilage is due to polysaccharides called chondroitin sulfates, which bind with ground substance proteins to form proteoglycans.  SUPPORTIVE CONNECTIVE TISSUES: Chondrocytes (cartilage cells) - embedded within the cartilage matrix Lacunae (singular = lacuna) - the space chondrocytes occupy Perichondrium – encapsulates the cartilage Cartilaginous tissue is avascular; thus, all nutrients need to diffuse through the matrix to reach the chondrocytes. This is a factor contributing to the very slow healing of cartilaginous tissues. SUPPORTIVE CONNECTIVE TISSUES: Three main types of Cartilage Hyaline cartilage: tissue: The most common type of cartilage in the body, consists of short and dispersed collagen fibers and contains large amounts of proteoglycans. Under the microscope, tissue samples appear clear. The surface of hyaline cartilage is smooth. Fibrocartilage: This is tough because it has thick bundles of collagen fibers dispersed through its matrix. The knee and jaw joints and the the intervertebral discs are examples of fibrocartilage. Elastic cartilage: Contains elastic fibers as well as collagen and proteoglycans. This tissue gives rigid support as well as elasticity. SUPPORTIVE CONNECTIVE TISSUES: BONE - hardest connective tissue - provides protection to internal organs - supports the body. - contains mostly collagen fibers embedded in a mineralized ground substance - highly vascularized tissue - highly vascularized tissue - Unlike cartilage, bone tissue can recover from injuries in a relatively short time. Cancellous bone looks like a sponge under the microscope and contains empty spaces between trabeculae, or arches of bone proper. It is lighter than compact bone and found in the interior of some bones and at the end of long bones. Compact bone is solid and has greater structural strength. FLUID CONNECTIVE TISSUE: Blood and lymph are fluid connective tissues. Cells circulate in a liquid extracellular matrix. The formed elements circulating in blood are all derived from hematopoietic stem cells located in bone marrow. Erythrocytes, red blood cells, transport oxygen and some carbon dioxide. Leukocytes, white blood cells, are responsible for defending against potentially harmful microorganisms or molecules. Platelets are cell fragments involved in blood clotting. FLUID CONNECTIVE TISSUE: Lymph contains a liquid matrix (plasma) and white blood cells. Lymphatic capillaries are extremely permeable, allowing larger molecules and excess fluid from interstitial spaces to enter the lymphatic vessels. Lymph drains into blood vessels, delivering molecules to the blood that could not otherwise directly enter the bloodstream. MUSCLE TISSUE AND MOTION MUSCLE TISSUE: Muscle tissue is characterized by properties that allow movement. Muscle cells - are excitable; - they respond to a stimulus. - they are contractile, meaning they can shorten and generate a pulling force. When attached between two movable objects (bones) contractions of the muscles cause the bones to move. Some muscle movement is voluntary, which means it is under conscious control. MUSCLE TISSUE CLASSIFICATION: ✓skeletal, ✓cardiac, and ✓smooth 1. SKELETAL MUSCLE: ❏ This is attached to bones and its contraction makes possible locomotion, facial expressions, posture, and other voluntary movements of the body. TYPES OF MUSCLE TISSUES: Forty percent of your body mass is made up of skeletal muscle. Skeletal muscles generate heat as a byproduct of their contraction and thus participate in thermal homeostasis. Shivering is an involuntary contraction of skeletal muscles in response to perceived lower than normal body temperature. The muscle cell, or myocyte, develops from myoblasts derived from the mesoderm. Myocytes and their numbers remain relatively constant throughout life. TYPES OF MUSCLE TISSUES: 2. CARDIAC MUSCLE: ❏ This forms the contractile walls of the heart. The cells of cardiac muscle, known as cardiomyocytes, also appear striated under the microscope. Cardiomyocyte attach to one another with specialized cell junctions called intercalated discs. Intercalated discs have both anchoring junctions and gap junctions. TYPES OF MUSCLE TISSUES: SMOOTH MUSCLE: ❏ This is responsible for involuntary movements in the internal organs. It forms the contractile component of the digestive, urinary, and reproductive systems as well as the airways and arteries. STRUCTURE AND PROPERTIES OF MUSCLE TISSUES: TISSUE HISTOLOGY FUNCTION LOCATION Long cylindrical fiber, Voluntary movement, Attached to bones and striated, many peripherally produces heat, around entrance SKELETAL located nuclei protects organs points to body (e.g., mouth, anus) CARDIAC Short, branched, striated, Contracts to pump Heart single central nucleus blood Short, spindle-shaped, no Involuntary movement, evident striation, single moves food, nucleus in each fiber involuntary control of Walls of major organs SMOOTH respiration, moves and passageways secretions, regulates flow of blood in arteries by contraction  NERVOUS TISSUE MEDIATES PERCEPTION AND RESPONSE NERVOUS TISSUE MEDIATES PERCEPTION AND RESPONSE: Nervous tissue is characterized as being excitable and capable of sending and receiving electrochemical signals that provide the body with information. Two main classes of cells make up nervous tissue: 1. Neurons : propagate information via electrochemical impulses, called action potentials, which are biochemically linked to the release of chemical signals. 2. Neuroglia : play an essential role in supporting neurons and modulating their information propagation. NERVOUS TISSUE MEDIATES PERCEPTION AND RESPONSE: Neurons three main parts: 1. Cell body — includes most of the cytoplasm, the organelles, and the nucleus. 2. Dendrites — the branch off the cell body and appear as thin extensions. 3. Axon – A long “tail,”, extends from the neuron body and can be wrapped in an insulating layer known as myelin, which is formed by accessory cells. NERVOUS TISSUE MEDIATES PERCEPTION AND RESPONSE: Neuroglia or Glial cells - characterized as having a simple support role. The word “glia” comes from the Greek word for glue. 1. Astrocyte cells : star shape, and are abundant in the central nervous system. Functions: ➔ regulation of ion concentration in the intercellular space, ➔ uptake and/or breakdown of some neurotransmitters, and ➔ formation of the blood-brain barrier, the membrane that separates the circulatory system from the brain. NERVOUS TISSUE MEDIATES PERCEPTION AND RESPONSE: 2. Oligodendrocyte cell → produces myelin in the central nervous system (brain and spinal cord) 3. Schwann cell →produces myelin in the peripheral nervous system.  References: Bautista, M. G. (2019). Human Anatomy and Physiology (3rd ed). National University. Sampaloc Manila Drake, R., Vogl, A. W., & Mitchell, A. W. M. (2013). Gray’s Anatomy for Students. Elsevier. OpenStax College, Anatomy & Physiology. OpenStax College. 19 June 2013. < http://cnx.org/content/col11496/latest/>