Anatomy and Physiology A Tissues, Glands, and Membranes PDF

ANA 1 ANATOMY AND PHYSIOLOGY A Mark Joseph V. Liwanag, MSN, RN Course facilitator MODULE 4 TISSUES, GLANDS AND MEMBRANES  OVERVIEW ▪ TISSUE – is group of similar cells with similar functions ▪ Structure is a reflection of its function ▪ HISTOLOGY –microscopi...

ANA 1 ANATOMY AND PHYSIOLOGY A Mark Joseph V. Liwanag, MSN, RN Course facilitator MODULE 4 TISSUES, GLANDS AND MEMBRANES  OVERVIEW ▪ TISSUE – is group of similar cells with similar functions ▪ Structure is a reflection of its function ▪ HISTOLOGY –microscopic study of tissue structure CHANGES IN TISSUES CAN RESULT IN: 1. Development 2. Growth 3. Aging 4. Trauma 5. Disease  FOUR BASIC TISSUE TYPES Epithelial Connective Muscle Nervous  EPITHELIAL TISSUE/EPITHELIUM ▪ Is found throughout the body where it covers external and internal surfaces throughout the body ▪ outer layer of the skin and the lining of cavities, such as the digestive tract, airways, and blood vessels. ▪ It also forms most glands. HALLMARKS OF EPITHELIUM Epithelium generally has the unique characteristics listed below: 1. Mostly composed of cells 2. Covers body surfaces 3. Nonvascular 4. Capable of regeneration  HALLMARKS OF EPITHELIUM Epithelium generally has the unique characteristics listed below: 5. DISTINCT CELL SURFACES. ▪ FREE SURFACE - which is not in contact with other cells ▪ BASAL SURFACE - adjacent to a basement membrane, which attaches the epithelial cells to underlying tissues ▪ BASEMENT MEMBRANE – is a thin, glue - like layer that holds the epithelium in place while remaining highly permeable to water and other substances ▪ MICROVILLI: are cylindrical extensions of the cell membrane that increase the free surface area ▪ involved in absorption or secretion, such as the cells lining the small intestine. ▪ CILIA: propel materials along the free surface of cells. ▪ nasal cavity and trachea are lined with pseudostratified columnar ciliated epithelium. ▪ Intermixed with the ciliated cells are specialized mucus-producing cells called GOBLET CELLS  HALLMARKS OF EPITHELIUM Epithelium generally has the unique characteristics listed below: 6. CELL AND MATRIX CONNECTION ▪ Epithelial cells fit closely together to form continuous sheets. ▪ Neighboring cells are bound together at many points by specialized cell junctions, including desmosomes and tight junctions ▪ TIGHT JUNCTIONS: bind adjacent cells together and form permeability barriers.  HALLMARKS OF EPITHELIUM Epithelium generally has the unique characteristics listed below: 6. CELL AND MATRIX CONNECTION ▪ DESMOSOMES: are mechanical links that bind cells together. ▪ Modified desmosomes, called HEMIDESMOSOMES, also anchor cells to the basement membrane. ▪ GAP JUNCTIONS: are small channels that allow small molecules and ions to pass from one epithelial cell to an adjacent one.  1. Protecting Underlying Structure. Functions of Epithelia: Protect the underlying skin from abrasions E.g. include outer layer of the skin, and the epithelium of the oral cavity, which protects the underlying tissues from abrasion. 2. Acting as a Barrier Prevents the movement of many substances through the epithelial layer E.g. the epithelium of the skin acts a barrier to water and reduces water loss from the body as well as prevents entry of toxic molecules and microorganisms  Functions of Epithelia: 3. Permitting the Passage of Substances. allows many substances to move through it. E.g. Carbon dioxide and oxygen are exchanged between the air and blood by diffusion through the epithelium in the lungs. 4. Secreting Substances. Sweat glands, mucous glands, and the enzyme secreting portion of the pancreas all composed of epithelial cells.  5. Absorbing substance. Functions of Epithelia: ▪ cell membrane of certain epithelial tissues contain carrier proteins that regulate the absorption of materials ▪ E.g. the epithelial cells of the intestines absorb digested food molecules, vitamins and ions.  CLASSFICATION OF EPITHELIUM A. ACCORDING TO THE NUMBER OF CELL LAYERS 1. SIMPLE – includes all tissues that have exactly one layer of cells 2. STRATIFIED – this group include epithelia with more than one layer (or stratum) of cells 3. PSEUDOSTRATIFIED – the name of this category is “false stratified” epithelium looks as it is stratified but it is really only one layer deep.  CLASSFICATION OF EPITHELIUM B. ACCORDING TO THE NUMBER OF CELL LAYERS 1. SQUAMOUS – shaped like fish scales, these cells are much wider than they are tall when viewed in across section. Nuclei may be absent in cross section 2. CUBOIDAL – cells are roughly cube-shaped, being about as tall as wide. More often resemble rounded squares or even circles. 3. COLUMNAR – these column-like cells are taller than they are wide when viewed in a cross section 4. TRANSITIONAL - cells change shape as the need arises, being stretched or compressed.  SIMPLE SQUAMOUS EPITHELIUM ▪ is a single layer of thin, flat cells ▪ Often found where diffusion or filtration take place ▪ allows exchange of gases through diffusion ▪ filtration membranes of the kidneys ▪ prevents abrasion between organs  Simple Cuboidal Epithelium ▪ Single layer of cube-shaped cells; some cells have microvilli (kidney tubules) or cilia (terminal bronchioles of the lungs) ▪ common in glands and their associated small tubes called ducts ▪ have a greater secretory capacity than simple squamous epithelial cells. Simple Columnar Epithelium ▪ is a single layer of tall, thin cells ▪ the simple columnar epithelium of the small intestine produces and secretes mucus and digestive enzymes ▪ cells have cilia (bronchioles of lungs, auditory tubes, uterine tubes, and uterus) or microvilli (intestines) ▪ Goblet cells - produce a lubricating mucus  Pseudostratified columnar epithelium ▪ this epithelium gives the false (pseudo) impression that it is stratified ▪ secretes mucus*, which covers its free surface. ▪ A ciliated variety (more precisely called pseudostratified ciliated columnar epithelium) lines most of the respiratory tract STRATIFIED SQUAMOUS EPITHELIUM ▪ is the most common stratified epithelium in the body. ▪ It usually consists of many cell layers. ▪ The cells at the free edge are squamous cells, whereas those close to the basement membrane are cuboidal or columnar. ▪ Stratified squamous epithelium is found in sites that receive a good deal of abuse or friction  STRATIFIED SQUAMOUS EPITHELIUM 1. KERATINIZED squamous epithelium ▪ forms the outer layer of the skin ▪ thick layer of cells provides protection ▪ keratin reduces the loss of water from the body. 2. NON - KERATINIZED (moist) stratified squamous ▪ forms the tissues of the mouth ▪ composed of living cells with a moist surface. STRATIFIED CUBOIDAL EPITHELIUM ▪ consists of more than one layer of cuboidal epithelial cells. ▪ relatively rare ▪ found in sweat gland ducts, ovarian follicular cells, and the salivary glands. ▪ It functions in absorption, secretion, and protection. STRATIFIED COLUMNAR EPITHELIUM ▪ are columnar cells, but its basal cells vary in size and shape. ▪ found mainly in the ducts of large glands. ▪ Location: Mammary gland ducts, larynx, a portion of the male urethra  ▪ special type of stratified epithelium that can be greatly stretched TRANSITIONAL ▪ a highly modified, stratified squamous epithelium EPITHELIUM that forms the lining of only a few organs ▪ the urinary bladder, the ureters, and part of the urethra. GLANDS ▪ gland consists of one or more cells that make and secrete a particular product. ▪ a secretion, typically contains protein molecules in an aqueous (water-based) fluid. Two major types of glands develop from epithelial sheets: 1. Exocrine glands 2. Endocrine glands  GLANDS 1. EXOCRINE GLANDS ▪ with ducts and tubes to carry secretions away from the gland ▪ can be simple, with ducts that have no branches, or compound, with ducts that have many branches ▪ secretions from exocrine glands pass through the ducts onto a surface or into an organ. STRUCTURE OF EXOCRINE GLANDS  GLANDS: classified according to how products leave the cell 1. MEROCRINE: products are released, but no actual cellular material is lost Sweat and digestive enzymes produced by the pancreas 2. APOCRINE: the secretory products are released as fragments of the gland cell Milk secretion by the mammary glands utilizes some apocrine secretion. 3. HOLOCRINE: involves the shedding of entire cells Sebaceous (oil) glands of the skin utilize holocrine secretion. GLANDS 2. ENDOCRINE GLANDS ▪ glands have no ducts and empty their secretions into the blood. ▪ HORMONES: are carried by the blood to other parts of the body. ▪ Endocrine glands include the thyroid gland and the insulin-secreting portions of the pancreas. CONNECTIVE TISSUE ▪ Connective tissue - connects body parts. ▪ most abundant and widely distributed of the tissue types. ▪ perform many functions, primarily involved in protecting, supporting, and binding together other body tissues. HALLMARKS OF CONNECTIVE TISSUE VARIATIONS IN BLOOD The distinguishing characteristics of SUPPLY. connective tissue include the following: ▪ Most connective tissues are well vascularized (that is, they have a good blood supply). Except for: ▪ Tendons and ligaments - have a poor blood supply ▪ Cartilages - avascular  HALLMARKS OF CONNECTIVE TISSUE The distinguishing characteristics of connective tissue include the following: EXTRACELLULAR MATRIX ▪ Connective tissues are made up of many different types of cells ▪ With varying amounts of a nonliving substance found outside the cells, called the extracellular matrix. Functions of Connective Tissue ▪ Enclosing and separating other tissues. Sheets of connective tissue form capsules around organs, such as the liver and the kidneys. Connective tissue also forms layers that separate tissues and organs. ▪ Connecting tissues to one another. Tendons and ligament connects other structure ▪ Supporting and moving parts of the body. Bones of the skeletal system provide rigid support for the body, and semirigid cartilage supports structures.  ▪ Storing compounds. FUNCTIONS OF Adipose tissue (fat) CONNECTIVE TISSUE stores high-energy molecules, and bones store minerals ▪ Cushioning and insulating. Adipose tissue cushions and protects the tissues it surrounds and provides an insulating layer beneath the skin that helps conserve heat.  FUNCTIONS OF ▪ TRANSPORTING. Blood transports gases, CONNECTIVE TISSUE nutrients, enzymes, hormones, and cells of the immune system throughout the body. ▪ PROTECTING. Cells of the immune system and blood provide protection against toxins and tissue injury, as well as against microorganisms. Bones protect underlying structures from injury  CELLS OF CONNECTIVE TISSUE ▪ The specialized cells of the various connective tissues produce the extracellular matrix. ▪ name of the cell identifies the cell functions by means of one of the following suffixes: -blast, -cyte, or -clast. 1. Blasts - create the matrix 2. Cytes - maintain it 3. Clasts - break it down for remodeling CELLS OF CONNECTIVE TISSUE 1. BONE CELLS ▪ Osteoblasts - which form bone (osteo-, bone) ▪ Osteocytes - which maintain it ▪ Osteoclasts - which break it down CARTILAGE CELLS FIBROUS TISSUE CELLS 2. CARTILAGE CELLS ▪ Chondroblasts - which form cartilage (chondro-, cartilage) ▪ Chondrocytes - which maintain it. 3. FIBROUS TISSUE CELLS ▪ Fibroblasts - which form fibrous connective tissue ▪ Fibrocytes - which maintain it BONE CELLS  CELLS OF CONNECTIVE TISSUE ▪ ADIPOCYTES – adipose cells, contain large amounts of lipid. ▪ rare in some connective tissue types, such as cartilage, but abundant in others, such as loose connective tissue. ▪ MAST CELLS - play important roles in inflammation. ▪ contain chemicals - heparin, histamine, and proteolytic enzymes, that are released in response to injury, such as trauma and infection. ▪ WHITE BLOOD CELLS, OR LEUKOCYTES - continuously move from blood vessels CELLS OF into connective tissues. CONNECTIVE TISSUE ▪ The rate of movement increases dramatically in response to injury or infection. ▪ MACROPHAGES - are large, phagocytic cells found in some connective tissue types. ▪ phagocytize foreign and injured cells, and they play a major role in protecting against infections. ▪ PLATELETS - function in the clotting process to reduce bleeding from a wound.  EXTRACELLULAR MATRIX: Protein Fibers of the Matrix Three types of protein fibers help form most connective tissues. ▪ Collagen fibers, which resemble microscopic ropes, are flexible but resist stretching. ▪ Reticular fibers, are very fine, short collagen fibers that branch to form a supporting network. ▪ Elastic fibers, have a structure similar to that of coiled metal bed springs; after being stretched, they can recoil to their original shape. Extracellular Matrix: Ground Substance of the Matrix 1.GROUND SUBSTANCE: consists of nonfibrous molecules. “shapeless” background against which the collagen fibers are seen through the microscope. 2. PROTEOGLYCAN: resemble the limbs of pine trees, with proteins forming the branches and polysaccharides forming the pine needles. trap large quantities of water between the polysaccharides. CLASSIFICATION OF CONNECTIVE TISSUE ▪ Two major categories of connective tissue are embryonic and adult connective tissue. ▪ Adult connective tissue consists of three types: 1. CONNECTIVE TISSUE proper (loose and dense) 2. SUPPORTING CONNECTIVE tissue (cartilage and bone) 3. FLUID CONNECTIVE tissue (blood).  CONNECTIVE TISSUE PROPER 1. Loose connective tissue ▪ consists of relatively few protein fibers that form a lacy network, with numerous spaces filled with ground substance and fluid. ▪ Three subdivisions of loose connective tissue are areolar, adipose, and reticular. 2. Dense connective tissue ▪ has a relatively large number of protein fibers that form thick bundles and fill nearly all of the extracellular space. ▪ protein fibers are produced by fibroblasts. ▪ There are two major subcategories of dense connective tissue: collagenous and elastic.  LOOSE CONNECTIVE TISSUE AREOLAR: has extracellular matrix consisting mostly of collagen fibers and a few elastic fibers. ▪ the most widely distributed connective tissue ▪ It functions as a universal packing tissue and connective tissue “glue” ▪ it helps to hold the internal organs together and in their proper positions.  Areolar Connective Tissue  LOOSE CONNECTIVE TISSUE ADIPOSE: consists of adipocytes, or fat cells, which contain large amounts of lipid for energy storage ▪ composed of large cells and a small amount of extracellular matrix, which consists of loosely arranged collagen and reticular fibers with some scattered elastic fibers. ▪ cells are large and closely packed together ▪ pads and protects parts of the body and acts as a thermal insulator. ADIPOSE TISSUE  RETICULAR: tissue forms the framework of LOOSE CONNECTIVE lymphatic tissue TISSUE such as in the spleen and lymph nodes, as well as in bone marrow and the liver RETICULAR TISSUE ▪ Dense connective tissue has a relatively large number of protein fibers, which form thick bundles and fill nearly all of the extracellular space. ▪ Dense connective tissue can be subdivided into two major groups: regular and irregular. ▪ DENSE REGULAR: collagen fibers that are oriented in the same direction, e.g., in tendons and ligaments ▪ DENSE IRREGULAR: fibers are oriented in many different directions, e.g., in the dermis and organ capsules DENSE CONNECTIVE TISSUE  DENSE REGULAR COLLAGENOUS CONNECTIVE ▪ has abundant collagen TISSUE fibers, which give this tissue a white appearance. ▪ forms structures such as tendons, which connect muscles to bones and most ligaments, which connect bones to bones ▪ collagen fibers of dense - resist stretching and give the tissue considerable strength in the direction of the fiber orientation. DENSE REGULAR ELASTIC CONNECTIVE TISSUE ▪ has abundant elastic fibers among its collagen fibers. ▪ elastic fibers allow the tissue to stretch and recoil. ▪ Examples include the dense elastic connective tissue in the vocal cords  DENSE IRREGULAR COLLAGENOUS CONNECTIVE TISSUE ▪ forms most of the dermis, which is the tough, deeper portion of the skin ▪ as well as the connective tissue capsules that surround organs such as the kidney and spleen. DENSE IRREGULAR ELASTIC ▪ found in the walls CONNECTIVE TISSUE of elastic arteries. ▪ In addition to collagen fibers, oriented in many directions, the layers of this tissue contain abundant elastic fibers. CARTILAGE ▪ is composed of chondrocytes, or cartilage cells, located in spaces called lacunae within an extensive matrix. ▪ Collagen in the matrix gives cartilage flexibility and strength. ▪ is resilient because the proteoglycans of the matrix trap water, which makes the cartilage relatively rigid and enables it to spring back after being compressed. ▪ provides support, but if bent or slightly compressed, it resumes its original shape. ▪ heals slowly after an injury Supporting Connective Tissue Supporting Connective Tissue HYALINE CARTILAGE is the most abundant type of cartilage and has many functions. forms the cartilage rings of the respiratory tract, the nasal cartilages, and the costal cartilages, which attach the ribs to the sternum (breastbone). HYALINE CARTILAGE ▪ covers the ends of bones where they come together to form joints. ▪ In joints, hyaline cartilage forms smooth, resilient surfaces that can withstand repeated compression. SUPPORTING CONNECTIVE TISSUE FIBROCARTILAGE has more collagen than does hyaline cartilage, and bundles of collagen fibers can be seen in the matrix. withstanding compression, it is able to resist pulling or tearing forces. is found in the disks between the vertebrae (bones of the back) and in some joints, temporomandibular (jaw) joints. FIBROCARTILAGE  Supporting Connective Tissue ELASTIC CARTILAGE ▪ contains elastic fibers in addition to collagen and proteoglycans. ▪ elastic fibers appear as coiled fibers among bundles of collagen fibers. ▪ Elastic cartilage is able to recoil to its original shape when bent. ▪ external ear, epiglottis, and auditory tube contain elastic cartilage. BONE SUPPORTING CONNECTIVE TISSUE ▪ is a hard connective tissue that consists of living cells and a mineralized matrix ▪ Osteocytes (osteo, bone), or bone cells, are located within lacunae. ▪ strength and rigidity of the mineralized matrix enables bones to support and protect other tissues and organs. ▪ two types of bone are compact bone and spongy bone  BLOOD FLUID CONNECTIVE ▪ is unique because the TISSUE: BLOOD matrix is liquid, enabling blood cells to move through blood vessels ▪ Some blood cells even leave the blood vessels and wander into other tissues. ▪ liquid matrix enables blood to flow rapidly through the body, carrying nutrients, oxygen, waste products, and other materials. MUSCLE TISSUE ▪ main characteristic of muscle tissue is its ability to contract, or shorten, making movement possible. ▪ contraction results from contractile proteins located within the muscle cells ▪ length of muscle cells is greater than the diameter. ▪ MUSCLE FIBERS - cells of muscle tissues; resemble tiny threads. SKELETAL MUSCLE ▪ about 40% of a person’s body weight. ▪ attaches to the skeleton and enables the body to move. ▪ described as voluntary (under conscious control) ▪ nervous system can cause skeletal muscles to contract without conscious involvement, as occurs during reflex movements and the maintenance of muscle tone. SKELETAL MUSCLE ▪ tend to be long and cylindrical, with several nuclei per cell. ▪ extend the length of an entire muscle. ▪ cells are striated, or banded, because of the arrangement of contractile proteins within the cell  ▪ is the muscle of the CARDIAC MUSCLE heart; it is responsible for pumping blood ▪ is under involuntary (unconscious) control, although a person can learn to influence the heart rate by using techniques such as meditation and biofeedback ▪ cylindrical but much shorter than skeletal muscle cells.  CARDIAC MUSCLE ▪ striated and usually have one nucleus per cell. ▪ often branched and connected to one another by intercalated disks. ▪ intercalated disks, which contain specialized gap junctions, are important in coordinating the contractions of the cardiac muscle cells SMOOTH MUSCLE ▪ forms the walls of hollow organs (except the heart) ▪ is controlled involuntarily. ▪ are tapered at each end, have a single nucleus, and are not striated. SMOOTH MUSCLE ▪ it is also found in the skin and the eyes ▪ is responsible for a number of functions, such as moving food through the digestive tract and emptying the urinary bladder. NERVOUS TISSUE ▪ Nervous tissue forms the brain, spinal cord, and nerves. ▪ It is responsible for coordinating and controlling many body activities. ▪ Action potentials – ability of nervous tissue cells to communicate with one another by means of electric signals  NERVOUS TISSUE ▪ Neurons – responsible for conducting action potentials ▪ Cell Body – contains the nucleus; site of general cell functions ▪ Dendrites – receive electric impulses ▪ Axon – conduct electric impulses  TISSUE MEMBRANES BODY MEMBRANES - cover surfaces, line body cavities, and form protective (and often lubricating) sheets around organs. TWO MAJOR GROUPS: 1. EPITHELIAL MEMBRANES, which include the cutaneous, mucous, and serous membranes 2. CONNECTIVE TISSUE MEMBRANES, represented by synovial membranes.  EPITHELIAL MEMBRANES: Cutaneous Membrane ▪ cutaneous membrane - is composed of two layers, the superficial epidermis and the underlying dermis. ▪ epidermis is composed of stratified squamous epithelium, whereas the dermis is mostly dense (fibrous) connective tissue. ▪ Unlike other epithelial membranes, the cutaneous membrane is exposed to air and is a dry membrane EPITHELIAL MEMBRANES: Mucous Membranes ▪ consist of various kinds of epithelium resting on a thick layer of loose connective tissue. ▪ line cavities that open to the outside of the body, such as the digestive, respiratory, and reproductive tracts ▪ have mucous glands, which secrete mucus. EPITHELIAL MEMBRANES: Mucous Membranes ▪ FUNCTION: protection, absorption, and secretion. ▪ stratified squamous epithelium of the oral cavity (mouth) ▪ simple columnar epithelium of the intestine ▪ mucous membranes also line the nasal passages  ▪ consist of simple EPITHELIAL MEMBRANES: squamous epithelium resting on a delicate layer Serous Membranes of loose connective tissue ▪ line the trunk cavities and cover the organs within these cavities ▪ secrete serous fluid, which covers the surface of the membranes a. Pleural – lungs b. Pericardial – heart c. Peritoneal – abdominopelvic cavity : Serous Membranes ▪ When the suffix - itis is added to the name of a structure, it means that the structure is inflamed ▪ PERICARDITIS - inflammation of the pericardial membranes ▪ PERITONITIS – inflammation of the peritoneal membranes ▪ PLEURISY - inflammation of the pleural membranes.  ▪ are made up of only Synovial MEMBRANES connective tissue. ▪ line the inside of joint cavities (the space where bones come together within a movable joint) ▪ produce synovial fluid, which makes the joint very slippery ▪ Synovial fluid - reducing friction and allowing smooth movement within the joint  INFLAMMATION ▪ INFLAMMATION - occurs when tissues are damaged ▪ For example, when bacteria/viruses infect epithelial cells of the upper respiratory tract, inflammation and the symptoms of the common cold are produced. ▪ Inflammation can also result from the immediate and painful events that follow trauma, such as closing your finger in a car door or cutting yourself with a knife. INFLAMMATORY INFLAMMATORY RESPONSE RESPONSE - is a defense mechanism that mobilizes the body’s immune cells to isolate and destroy microorganisms and other injurious agents, and remove foreign materials and damaged cells allows tissue repair to occur.  STAGES OF THE INFLAMMATORY RESPONSE 1. Chemical mediators released: ▪ A splinter in the skin causes damage and introduces bacteria. ▪ Chemical mediators of inflammation are released or activated in injured tissues and adjacent blood vessels. ▪ Some blood vessels rupture, causing bleeding.  STAGES OF THE INFLAMMATORY RESPONSE 2. TISSUE SWELLING: ▪ Chemical mediators cause capillaries to dilate and the skin to become red. ▪ Chemical mediators also increase capillary permeability, and fluid leaves the capillaries, producing swelling  STAGES OF THE INFLAMMATORY RESPONSE 3. RECRUITMENT OF IMMUNE CELLS: White blood cells (e.g., neutrophils) leave the dilated blood vessels and move to the site of bacterial infection, where they begin to phagocytize bacteria and other debris. Inflammation has five major manifestations: (1) redness, (2) heat, (3) swelling, (4) pain, and (5) disturbed function. CARDINAL SIGNS OF INFLAMMATION CHEMICAL MEDIATORS IN INFLAMMATORY RESPONSE CHEMICAL MAJOR ACTION Histamine Immediate vasodilation and increased capillary permeability Chemotactic factors Attract neutrophils to site Platelet activating factor (PAF) Activate neutrophils and plt. aggregation Prostagladin Vasodilation, inc. permeability Pain, fever, potentiate histamine effect ▪ Healing is a quality of living tissue WOUND HEALING ▪ regeneration (renewal) of tissues. Types of Wound Healing 1. Primary intention healing: occurs where the tissue surfaces have been approximated (closed) and there is minimal or no tissue loss ▪ It is also called primary union or first intention healing. ▪ An example: closed surgical incision.  WOUND HEALING 2. Secondary intention healing: wound that is extensive and involves considerable tissue loss, and in which the edges cannot or should not be approximated. Example: pressure ulcer. ❖ Secondary intention healing differs from primary intention healing in three ways: ▪ repair time is longer, scarring is greater, susceptibility to infection is greater Phases of Wound Healing 1. INFLAMMATORY PHASE: begins immediately after injury and lasts 3 to 6 days. Two major processes occur during this phase: Hemostasis: (the cessation of bleeding) results from vasoconstriction of the larger blood vessels in the affected area Phagocytosis: cell migration, leukocytes (specifically, neutrophils) move into the interstitial space macrophages engulf microorganisms and cellular debris; secrete an angiogenesis factor  PHASES OF WOUND HEALING 2. PROLIFERATIVE PHASE: second phase in healing, extends from day 3 or 4 to about day 21 post-injury. ▪ Fibroblasts (connective tissue cells), which migrate into the wound starting about 24 hours after injury, begin to synthesize collagen. ▪ Collagen is a whitish protein substance that adds tensile strength to the wound. ▪ Capillaries grow across the wound, increasing the blood supply.  Phases of Wound Healing 3. MATURATION/REMODELING PHASE: begins on about day 21 and can extend 1 or 2 years after the injury. ▪ Fibroblasts continue to synthesize collagen. ▪ wound is remodeled and contracted. ▪ scar becomes stronger but the repaired area is never as strong as the original tissue. ▪ abnormal amount of collagen, can result in a hypertrophic scar, or keloid. REFERENCES: VanPutte C. et.al. (2019). Seeley’s Essentials of Anatomy & Physiology. 10th edition. New York: McGraw Hill Co. Inc.