Histology and Cytology
Histology and Cytology BIO 3163
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EPITHELIAL TISSUES I General De nition Epithelium is atissue composed of closely aggregated cells that are in apposition over a large part of their surface and which have little intercellular substance A Simplest form is a single layer of cells covering a surface or lining a tube or cavity B More often multiple layers develop C Origin of epithelial tissues 1 Embryologically epithelial tissues develop from all three germ layers but the majority develops from the ectoderm and endoderm 2 The epidermis of the skin and the epithelium of the cornea which together cover the entire surface of the body are derived from the ectoderm a Associated with this are the glandular appendages of the skin sweat glands sebaceous glands mammary glands 3 The alimentary tract is lined with epithelium derived from the endoderm a Associated with this are the various digestive glandsliver pancreas gastric intestinal glands 4 The epithelium lining the respiratory tract is endodermal 5 Mesodermal epithelial derivatives include the kidney and reproductive organs and the lining of the ducts of the urinary system and reproductive systems 6 In addition to the above the lining ofthe blood vessels and heart is referred to as endothelium and that lining serous cavities as mesothelium both are mesodermal derivatives 11 Classification of the epithelial tissues A Epithelial tissues can be broadly classified into two groups 1 Covering and lining division 2 Glandular division B Covering and lining division 1 The basis for classifying the covering and lining epithelial tissues is by cell layering and cell types 2 Cell layering a Simple consisting of a single layer of cells b Pseudostratified staggered cell heights give an appearance of layering but all cells are on the basement membrane an apparent layering c Strati ed consisting of several to many layers of cells 3 Cell shapes a Squamous attened cells which are broader than they are thick b Cuboidal cells are short prisms typically siX sided since the vertical view approximates a square they are termed cuboidal c Columnar cells are distinctly taller than they are wide 112 The combination of layering and cell shape leads to the different types of covering epithlia that are seen The different epithelial membranes are specialized for the kinds of functions they perform Simple epithelial membranes a Simple squamous epith occur where the membranes are not subjected to a great dial of wear and tear and where a smooth surface is needed 1 These membranes do not appear to advantage in sections because of their lack of thickness 2 Examples lining of body cavities mesothelium lining of vascular and lymphatic system vessels endothelium thin loops of Henle in kidney smallest ducts of glands terminal respiratory ducts and alveoli Simple cuboidal epith appear where greater amount of wear and tear occur and where underlying structures need more protection that afforded by squamous cells 1 Appearance in sections is a row of approximate squares 2 Examples many ducts of glands majority of the kidney ducts covering of the ovary Simple columnar epith becomes modified some used for protection while others perform secretory or absorptive functions 1 Unmodified simple columnar providing protective role ducts of glands 2 Secretory simple columnar all of the cells are specialized to secrete mucus cells are filled with mucus droplets found in lining of stomach and lining of cervical canal 3 Secretory and absorptive simple columnar lining of small intestine here absorptive columnar cells with microvilli appear interspersed with mucous secretory cells termed goblet cells Pseudostratified epithelia the only cell type involved is the columnar cell Thus all pseudostratified membranes are pseudostratified columnar In this type of membrane all of the cells are in contact with the basement membrane but not all of the cells reach the surface hence the appearance of a stratified membrane a b Pseudostratified columnar non ciliated epith appears in the large ducts of glands e g parotid and in the male urethra Pseudostratified columnar ciliated epith most common type of pseudostratified columnar lines the majority of the respiratory tract 1 In this instance there are also goblet cells interspersed in the membrane mucus that is secreted traps dust and cilia move it to a point where it can be eliminated C Support 1 II 3 c Pseudostrati ed columnar with stereocilia the epithelium is found as the lining for the epididymis Strati ed epithelial membranes appear where a great deal of protection is needed Strati ed membranes derive their name from the uppermost cell in the stratification a Strati ed squamous non keratim39zed epith found on wet surfaces subjected to considerable wear and tear l Kept moist by glandular secretions 2 Locations inside of mouth lining of esophagus lining of vagina 3 Cell arrangements cuboidal or columnar gt irregular cells gt attened squamous cells b Strati ed squamous keratinized epith found on dry surface of the skin ie the epidermis l Resembles non keratinized type except that the superficial cells undergo a metamorphosis to keratin waterproof first line of defense against bacteria 2 Layers a Stratum basale germinativum cuboidal to columnar cells responsible for production of new cells b Stratum spinosum prickle cell layer c Stratum granulosum cells produce keratohyalin granules d Stratum corneum keratin layer c Strati ed cuboidal relatively rare ducts of sweat glands show atrue stratified cuboid al epith graafian follicle of ovary may be considered a stratified cuboidal epith as well as the epithelium lining the seminiferous tubules d Strati ed columnar epith relatively uncommon parts of pharynx larynx urethra largest ducts of salivary glands and mammary glands e Transitional epith appears as stratified cuboidal in the relaxed state but as stratified squamous in the stretched state occurs only in the urinary tract lining the ureter bladder and a portion of the urethra All epithelial membranes are are supported by basement membranes The basement membrane is a thin extracellular structure that consists of two layers a the basal lamina closer to the base of the epithelial cells and secreted by them The basal lamina conists of collagen laminin D II 4 bindtothe39 391 39 r quot andl 39J b the reticular lamina closer to the underlying connective tissue it contains ne reticular bers secreted by broblasts The basal surface is that surface of an epithelial membrane that is in association with the basement membrane while the free surface of epithelial membranes is known as the apical surface Junctions of epithelial cells all covering and lining epithelial membranes are composed of cells joined by cell junctions and supported by connective tissue the basement membrane 1 There are 3 main types of junctions a Tight junctions occludens junctions b Nexus junctions gap junctions c Adherens junctions desmosomes Tight junctions occludens junctions occur particularly between cells in absorptive membranes these junctions function to maintain a seal between the membrane and material being absorbed a Outer lamellae of membranes are fused using proteins known as occludins Nexus junctions gap junctions outer lamellae of membranes approximate each other but a 20 angstrom gap separates them a nexus junctions are communicating junctions ie allow communication between cells a Gap is crossed by structures that abut on membranes of both cells a hollow proteinaceous tube known as a connexon consisting of proteins known as connexins b Appear to function in passing impulses and information from cell to cell Adherens junctions no direct contact occurs between cell but space between cells if lled with cell coat material that binds the cells together There are several types of adherens junctions a zonula adherens junction provides lateral adhesion between epithelial cells This junction type is located below occludens junctions and acts to reinforce the occludens junction The transmembrane adhesion molecule is E cadherin b macula adherens junction desmosome provides spot like welds along the lateral aspects of adjacent epithelial cells The transmembrane adhesion molecules are desmocollin and desmoglein c hemidesmosome anchors epithelial cells to the basement membrane Glandular division 1 Glands are classi ed as being exocrine or endocrine ductless a Exocrine glands deliver their secretions via ducts onto the surface from which they initially formed b a b 115 Endocrine glands deliver their secretion into the vascular system Formation both glands initially start the same way but exocrine glands retain their connection to the surface epithelium while endocrine glands lose that connection Exocrine glands If duct system is unbranched the gland is simple if branched the gland is compound If secretory unit acinus is tubular gland is termed tubular if secretory unit is ask like it is termed alveolar gland can be mixed If secretion of exocrine gland is watery it is said to be a serous gland i f the secretion is a thick mucus the gland is said to be a mucous gland gland can be mixed 1 2 Secreto Serous secretory units cells have a roughly triangular appearance with a lumen in the center of the acinus a Cytoplasm at base of cells is basophilic b Nucleus rounded and near base of cell but not directly on it Mucous secretory units cells are truncated pyramids a Cytoplasm appears pale and vacuolated because of poor staining quality of mucus b Nuclei of secretory cells are attened against the base ofthe cell ry units of exocrine glands appear to be cradled in a myoepithelial basketprobably helps in expression of secretion Support for exocrine glands is from connective tissue which forms a capsu le for the gland partitions of connective tissue septa from the capsule extend into the gland causing areas to be fenced off 1 2 Merocr 1 2 3 Large areas lobes small areas lobules Ducts travel in connective tissue hence there are interlobular and intralobular ducts a Interlobular ducts thick epithelial lining and large lumen surrounded by substantial amounts of connective tissue b Intralobular ducts less heavy and not surrounded by much connective tissue ine apocrine and holocrine glands This classi cation is based on how the glands produce their secretion Merocrine secretion is a product of cell and delivered through the cell membrane via the normal exocytosis mechanism cell membrane is kept intact ex pancreas Apocrine small part of cytoplasm lost with secretion no IIIl CONNECTIVE TISSUES I General A Connective tissue consists of cells and extracellular bers embedded in ground 11 substance containing tissue uid 1 Fibers were originally classi ed as collagenous reticular and elastic a Recent information indicates that collagenous and reticular bers are probably the same Collagenous bers are thicker while reticular bers are thinner b Cells are recognized as being xed or wandering Classi cation of connective tissue is dif cult because of the many subtypes involved The classi cation scheme we will use is as follows 1 Ordinary connective tissue a Loose ordinary connective tissue also referred to as areolar connective tissue b Dense ordinary connective tissue 1 Dense regular connective tissue 2 Dense irregular connective tissue 2 Hemopoietic connective tissue a Blood b Myeloid tissue blood forming tissue 1 Red myeloid tissue active 2 Yellow myeloid tissue inactive c Lymphatic tissue 1 Nonencapsulated lymphatic nodules 2 Lymph nodes 3 Thymus 4 Spleen 3 Supporting connective tissue a Cartilage l Hyaline 2 Elastic 3 Fibrous b Bone l Cancellous immature 2 Mature Ordinary connective tissue A Loose ordinary connective tissue exhibits a common and simple form and may be taken as the prototype of connective tissue Widely distributed in the body encountered to some extent in every microscopical section of the body a Fastens skin to other structures b Conducts vessels and nerves c Binds together muscles and their parts d e III2 Supplies general bedding stroma of many organs Serves as a packing material lls space between organs The two main components of intercellular substances of connective tissue are represented in the loose variety bers and amorphous material ground substance a b Fibers provide strength and elasticity Ground substance provides a diffusion medium for nutrients The bers of connective tissue a Collagenous bers appear in all connective tissue in varying degrees 1 In loose connective tissues they appear as strands of varying thickness l20um and run in all directions wavy bers 2 Under high magni cation with EM the collagen brils are cross striated 3 Collagen is secreted from connective tissue cells broblasts as procollagen a molecule consisting of three helical polypeptides The non helical ends of the procollagen are cleaved from the procollagen molecule after it is secreted to form tropocollagen a molecule of about 260nm long and 15nm thick consisting of three helical polypeptides of molecular weight 10000 The tropocollagen units then attach to form the collagen bril a Contains high content of glycine along with hydroxyproline and hydroxylysine which do not occur in other proteins in large amounts 4 The tropocollagen molecules combine outside the cell with a staggered array of about 14 their length hence the cross striations Elastic bers 1 Provide for the ability of the tissue to be deformed and to recover its original shape 2 Also appear to be formed by broblasts 3 Not composed of subunits as is collagen but are composed of micro brils embedded in an amorphous component called elastin Both elastin and collagen are reported to be capable of inducing formation of nuclei of hydroxyapatite crystals Ca10PO45OHz found in bone Reticular bers form the supporting structure for blood vessels lymphoid and blood forming organs and other epithelial organs 1 Reticular bers have been shown to be identical to collagen but differ in their size thickness from 05um to 2pm Ground substance a b Has the properties of a viscous uid or thin gel Two general kinds chondroitin sulfates and hyaluronic acid 1 Both types consist of alternating saccharides that form chains the chains are then linked to protein 2 Condroitin sulfates disaccharide repeat is composed of a sulfated galactose amine and glucuronate in each repeating unit the multiple chains are linked to protein which makes up about 15 of the molecule a The high amount of protein in this molecule gives III3 chondroitin sulfate the consistency of a gel 3 Hyaluronic acid contains sugars glucosamine and glucuronate linked to protein that accounts for about 2 of the molecule a Tissue Fluid The lower amount of protein in this molecule gives it the consistency of a viscous uid useful in joints where it is known as synovial uid also acts to contain infection by walling off material a Within the ground substance is a large quantity of tissue uid extracellular uid that allow exchange of nutrients and waste products between the blood and cells b Derived from blood plasma produced at arterial ends of capillaries and absorbed at venous ends usually more produced than absorbed excess collected by lymphatics c Ifmore is produced than absorbed edema swelling ensues causes of edema l Obstruction to return of venous blood raises venous pressure bad heart action ie heart cannot pump all blood returned to it congestive heart failure 2 Lymphatic obstruction elephantiasis in ammation 3 Insufficient blood protein from nutritional deficit or a large weeping wound or kidney disease 4 Increased capillary permeability ie capillary damage The cells of loose connective tissue a It is convenient to consider the cells of loose connective tissue as belonging to two categories 1 Fixed cell population a stable population of cells that you expect to see fibroblasts mesenchymal cells perivascular cells fat cells adipocytes macrophages histiocytes and mast cells 2 Wandering cell population involved in short term events in loose connective tissue the wandering cell population consists of white cells that migrate from the blood into the loose connective tissue and also includes plasma cells b Fixed cells 1 Fibroblasts the common frxed cells of connective tissue a b c d Produce the fibers and amorphous ground substances Shape depends on their physical substrate 1 Fusiform when alongside fibers H Stellate in open areas between fibers Nucleus generally ovoid and AopenE Generally agreed that they are differentiated cells that do not give rise to other types 2 3 4 5 1114 Mesenchymal cells Perivascular cells retain embryonic potentialities a Usually around periphery of blood vessels especially capillaries hence the term Aperivascular cells b Can be called on to replace lost cell types of connective tissue ie they are pluripotential Adipose cells Fat cells a Specialized for synthesis and storage of fat b Nucleus becomes attened along side of cell signet ring appearance c When they accumulate in large numbers becoming the predominant cell type the resulting tissue is termed adipose tissue 1 White adipose tissue common body fat having the signet ring type cell 11 Brown adipose tissue less abundant occurs only in certain areas aXilla and nape of the neck very abundant in hibernating animals used for heat generation cells with central nucleus and Afrothy cytoplasm contains large numbers of small fat vesicles Macrophages Histiocytes a Stretched out along bers appear as broblasts but nuclei are smaller and more darkly stained than broblasts b Normally sessile xed but become motile in in ammation c Are derived from monocytes d Are phagocytic cells can be demonstrated with trypan blue I injest extravasated red cells cellular debris bacteria are mobile scavengers e Play a role in immunologic reactions phagocytize and process antigen and then present antigen APCs Antigen Presenting Cells to lymphocytes Mast cells a Originate from a progenitor cell that is released from the bone marrow ie the stem cell is located in the bone marrow b The progenitor cells leave the circulation through capillaries and venules and take up residence in the loose connective tissue where they proliferate and mature c Cytoplasm of mast cells is lled with granules containing heparin and histamine Heparin is a potent anticoagulant but the amount released by mast cells is of little value to whole body in preventing coagulation The heparin released probably causes localized anti coagulation II Histamine is a potent dilator of capillaries also III5 causes constriction of smooth muscle particularly in bronchioles d Mast cells are active in allergic reactions mast cell granules discharge their active substances into the tissue space when antigen attaches to IgE that is attached to IgE receptors on the surface of the mast cell c Wandering cells these are white cells that migrate from the blood into the loose connective tissue space in response to short term in ammatory events cells involved are monocytes lymphocytes plasma cells eosinophils neutrophils Monocytes compose the largest amount of wandering cells in response to in ammation they become phagocytic and appear as macrophages if material is too large to phagocytize they will coalesce around it and become foreign body giant cells a The macrophagic cells of the body form a Acell system formerly known as the reticuloendothelial system but now known as the mononuclear phagocyte system this system comprises a defense line against infection the cells are widely distributed and known by different names depending on tissue ie Kupffer cells of liver microglia of brain Langerhans cells of the integument osteoclasts of the bone alveolar phagocytes 2 Lymphocytes smallest of the wandering cells a Are essential agents in immunological defense of the body b Are not the end stages of differentiation but are in a resting state can differentiate into antibody producing cells plasma cells or cytotoxic cells depending on whether they are B or T lymphocytes 3 Plasma cells a Differentiate from stimulated B lymphocytes b Have highly developed rERs c Are relatively rare in normal connective tissue but are abundant in connective tissue of intestine in the lamina propria and in lymphoid tissues 4 Eosinophils a Increase in number in allergic reactions and parasitic infections b Phagocytize antigenantibody complexes 5 Neutrophils a Phagocytize bacteria B Dense ordinary connective tissue 1 Unlike the loose ordinary connective tissues that consist of about equal amounts of cells ground substances fibers and tissue uid the dense connective tissues represent ordinary connective tissues that are comprised mainly of intercellular III6 bers 2 The only cell type associated with dense ordinary connective tissues is the broblast 3 Dense ordinary connective tissue is divided into dense regular connective tissue and dense irregular connective tissue depending on the arrangement of the bers Dense regular connective tissue In this type the bers are arranged in a plan with the bers all passing in the same direction a l a b C d b 1 2 III Hemopoietic Connective Tissue Tendons the bers form a exible structure but one which resists pulling Fibers are arranged in parallel rows Act to attach muscles to bones Ligaments similar to tends with a bit more irregularity of the bers Act to attach bones to bones Aponeuroses multiple sheets of bers sheets lie next to each other and pass in different directions Also act to attach muscles to bones Elastic ligaments elastic bers predominate over collagenous bers leads to a more yellow color 1 Examples vocal cords elastic arteries ligamentum nuchae Dense irregular connective tissue Found in dermis of skin and the capsules of many organs Collagen and elastic bers in all directions planes Allows tissue to resist deformation from stress in any direction Blood has traditionally been classi ed as a connective tissue in which the intercellular substance is uid 1 It is connective not in the sense that it adds to the structural integrity of the body but in the sense that it maintains communication between the tissues of the body 2 The blood is composed of plasma and formed elements formed elements include red cells white cells and platelets thrombocytes Of the formed elements only the red cells and platelets function entirely in the blood vascular system The white cells use the blood as a means of getting from their sites of origin to the tissues where they perform their functions a B The Formed Elements 1 Red cel a ls erythrocytes The minute corpuscles that impart color to the blood are termed erythrocytes or red cells Not true cells because of the lack of a nucleus 1 2 3 They are formed in the marrow as true cells but extrude their nucleus and lose all capacity for DNA directed protein synthesis They function in the uptake of oxygen in the lungs and its transport III7 to tissue and the return of C02 from tissues to the lungs 4 In fish amphibians reptiles and birds the nucleus remains intact but is apparently metabolically inert The normal number in blood is about 54 millionmm3 for males and 48 millionmm3 for females The shape of an erythrocyte is a biconcave disk about 75 pm in diameter and 19 pm in thickness shape provides for larger surface area than a sphere In thick smears stacks of erythrocytes are found termed rouleauX occurs only when blood is stagnant Shape of erythrocyte varies in solutions of different tonicity l isotonic normal cell con guration 2 hypotonic cells swell and lyse hemolysis 3 hypertonic cells shrink crenation Reticulocytes red cells that have remanents of ribosomes ie immature term comes from staining with brilliant cresyl blue normal number 08 of total 1 used clinically as a rough indication of erythrocyte formation Anemia a condition characterized by a lack of erythrocytes or lack of hemoglobin l Anemia due to lack of cells in this case the cells appear normal in size and color hence called normochromic normocytic anemia usually due to hemorrhage 2 If cells are undercolored then the anemia is termed a hypochromic anemia usually from lack of iron to form hemoglobin cells may also be smaller iron deficiency anemia hypochromic microcytic anemia 3 In pernicious anemia the fault is not with hemoglobin production but in cell production due to a lack of Vitamin B12 B 12 not absorbed due to a lack of intrinsic factor intrinsic factor or Castle in stomach hence the cells tend to be larger and over filled with u u i 7 r u 1 anem1a White blood cells leukocytes a Are classified as the presence or absence of granules granular or agranular and according to the shape of their nucleus mononuclear and polymorphonuclear l granular leukocytes are further divided by the staining quality of their granules into neutrophils eosinophils basophils Normally the range of circulating leukocytes is from 5000 to 9000mm3 in the presence of infection their numbers can rise to 20000mm3 The relative proportions of various leukocytes is usually constant 1 Neutrophils 5560 Eosinophils l3 Basophils 007 Lymphocytes 2530 Monocytes 37 III8 Nuetrophils 5560 most abundant leukocyte l Easily recognized from their characteristically lobed nucleus 2 or more lobes 2 Released into blood as young cells with a simple elongated nucleus band neutrophils lobulation occurs with age the number of band forms serves as an index of rate of entry into the blood system a In females the chromatin of the X chromosome forms a minute separate lobule known as a drumstick 3 Contain small granules which have little af nity for dyes speci c granules and a few larger reddish staining granules called azurophil granules l Azurophil granules appear to be modi ed lysosomes containing a peroxidase 2 Speci c granules lack lysosomal enzymes but contain alkaline phosphatase and a poorly characterized group of proteins called phagocytins 4 Neutrophils are phagocytic cells and are active in bacterial infection 5 Normal life span is about 8 days Eosinophils l3 of leukocytes l Recognized by their coarse eosinophilic granules and bilobed nucleus 2 Each granule contains one or more crystals imbedded in an amorphous matrix a granules also contain normal lysosomal enzymes 3 Not normally phagocytic for bacteria but will phagocytize them in the presence of antibacterial antibody 4 Selectively phagocytize antigenantibody complexes Basophils 007 of leukocytes l Recognized by large basophilic granules and elongated nucleus bent in the shape of a U 2 Granules contain histamine and heparin 3 Thought to be a circulating form of mast cell but are derived from a stem cell different from that of the mast cell 4 Actual function unknown Lymphocytes 2530 of leukocytes second most abundant class of leukocytes 1 There are two different classes of lymphocytes that differ in background life span and potentiality but are not different morphologically 2 Lymphocytes are primarily concerned with immunological reactions a Immune reactions occur in response to the entrance of foreign protein or in some cases polysaccharide foreign substances termed antigen 3 The two major classes of lymphocytes are B lymphocytes Bursal 4 lymphocytes and T lymphocytes Thymic lymphocytes B lymphocytes originate and mature in the bone marrow 5 1119 a Are involved in humoral immune responses ie production of circulating antibody b B lymphocytes constitute about 10 of the circulating lymphocytes c B lymphocytes leave the marrow and nest in secondary lymphoid structures lymphatic nodules lymph nodes and spleen d B lymphocytes contain IgM on their cell surface that acts as a receptor for a speci c antigen e When activated they differentiate to plasma cells and memory cells B cells react to soluble antigen or bacterial antigens and also require Thelper substance via Thelper cells to complete their activation f Plasma cells produce antibody while memory cells are long lived and react rapidly to a second exposure to the same antigen T lymphocytes originate in the bone marrow and migrate to the thymus where they proliferate and mature and are carried by the blood to other lymphoid tissues a Are involved in cell bound immune responses ie antigen attached to a cell surface b T lymphocytes constitute about 75 of the circulating lymphocytes c There are three major sub populations of T lymphocytes 1 Thelper cells stimulate the differentiation of B cells into plasma cells and memory cells 2 Tcytotoxic cells act against foreign cells or virus infected cells by recognizing foreign antigen on the cell surface 3 Tmemory cells react to reintroduction of the same antigen h Monocytes 38 of leukocytes 1 Have the appearance of large lymphocytes but with more abundant cytoplasm in addition the cytoplasm stains a grayish blue rather than pale blue of lymphocytes 2 Nucleus tends to be eccentrically located and oval 3 Produced in bone marrow and use blood as a transport to the tissues where they take up residence as macrophages 4 Are essential for processing many antigens prior to activation by immunocompetent lymphoid cells Platelets a Small colorless anucleate corpuscles in blood b Round or oval biconveX disks number 250000 to 300000mm3 ofblood c Have an agranulated outer region known as the hyalomere and intemal granulated region known as the granulomere d Produced in the marrow from cytoplasmic fracture of large cells known as III 10 me gakaryocytes Principle function is in blood clotting l Damage to endothelium causes adherence of platelets causes platelet thrombus 2 Released from platelets is a substance called platelet thromboplastin similar to tissue thromboplastin 3 r39 quot causes 39 ofr quot to thrombin Thrombin then acts as an enzyme to cause conversion of fibrinogen to brin clot C Plasma liquid portion of the blood 1 Constitutes about 55 of the total blood volume and contains water dissolved foods and waste products various ions and several proteins 2 There are three major types of plasma proteins a Albumin produced in the liver and responsible for maintaining the colloid osmotic pressure of the blood b Globulins l Gammaglobulin IgG produced by plasma cells and more commonly known as antibodies 2 Beta globulins function in the transport of hormones metal ions and lipid in the blood c Fibrinogen synthesized in the liver and is important in clotting mechanism D Myeloid Tissue blood forming tissue Occupies the medullary cavities of long bones it has an aggregate volume equal to that of liver with about half that volume active in the adult 2 Active marrow is red while inactive contains many adipose cells and has a yellow appearance 3 The marrow consists of blood cells their precursors and adipose cells packed within the meshes of a loose stroma a The stroma consists of loose reticular bers supporting primitive reticular cells b The blood supply is via the nutrient artery of the bone which eventually breaks down into a system of sinusoids c Active erythropoiesis and myelopoiesis occurs between the sinusoids cells then pass into the sinusoids and then into the general circulation 4 Hypotheses of hemopoiesis and cell lines a The polyphyletic hypothesis considered hemopoietic activity to be caused by several different stem cells 1 Erythrocytes intravascularly from erythroblasts 2 Granular leukocytes from myeloblasts 3 Agranularl 1 f from 39 J 39 39 39 and 39 39 b The monophyletic hypothesis considered hemopoietic activity to result from a single stem cell capable of differentiating into any of the cell types the pluripotential stem cell was called a hemocytoblast c Current hypothesis is a modification of the monophyletic hypothesis 5 Current scheme of Hemopoiesis a PPSC Pluripotential Stem Cell gives rise to III 11 l Multipotential lymphoid stem cell CFUL colony forming unit lymphocytes a Tcells b B cells 2 Multipotential myeloid stem cell CFUGEMM a CFUE colony forming uniterythrocyte b CFUGM colony forming unitneutrophilsmonocytes c CFUEo colony forming uniteosinophil d CFUBa colony forming unitbasophil e CFUMeg colony forming unitmegakaryocyte 6 Regulation of hemopoiesis is believed to be under the control of various poietic hormones a Erythropoietin produced in the kidney b Colony Stimulating Factors 7 produced by endothelial cells and fibroblasts of bone marrow and some c Thrombopoietin 7 produced in the liver E Lymphatic tissue consists of non encapsulated lymphatic nodules lymph nodes thymus and spleen 1 Non encapsulated lymphatic nodules a Appear behind wet epithelial membranes that line the respiratory and digestive tracts may occur as single nodules ie Peye1ss patches in the ileum or as con uent nodules as in tonsils b Appear as roughly spherical structures supported by reticular bers and packed with lymphocytes c More common after birth thus the presence and recognition of antigens may in uence their development d Sometimes acquire germinal centers which are lighter stained areas exhibiting increased mitotic activity e Function as a defense line against antigen entrance through moist epithelial membranes f Are populated with both B and T lymphocytes 2 ymph nodes a Small organs occurring along lymphatic vessels consisting of highly organized accumulations of lymphoid tissue which recognizes antigenic materials in the lymph that percolates through them 1 Also rich in macrophages which clear lymph of undesirable cells microorganisms and particulate matter b Are commonly attened and ovoid in shape with a slight indentation the hilus where blood vessels enter leave and efferent lymphatics leave Afferent lymphatics enter the convex side of the node c Nodes consists basically of a parenchymal mass of lymphoid tissue traversed by lymph vessels or sinuses 1 Covered by a collagenous capsule which is thickened near the hilus and invests the node as trabeculae 2 Parenchyma between trabeculae is supported by a stroma of reticular fibers parenchyma consists of lymphocytes both B and T plasma III 12 cells and macrophages 3 Under low power the general organization of an outer deeper staining cortex can be differentiated from a lighter staining medulla Afferent lymphatics drain into a marginal or subcapsular sinus radially disposed sinuses penetrate the cortical parenchyma and continue to branch into the medulla l Sinuses are freely permeable to lymph and are continually crossed by wandering cells 2 Sinuses finally regroup in the medulla to form efferent lymphatics cords of parenchymal tissue between medullary sinuses are known as medullary cords The cortex of the nodes contains primary lymphatic nodules with germinal centers the cortex is populated with B lymphocytes when stimulated by antigen the primary nodules develop lighter staining secondary nodules or Agerminal centers Between the cortex and the medulla is a region referred to as the Adeep cortex or the Aparacortex This region is populated chie y by T lymphocytes Thymus a median organ situated in the superior mediastinum it consists of two lobes arising as separate structures in the embryo but becoming closely joined by connective tissue a The only primary lymphatic structure to be identified in mammals It is the first organ to become lymphatic during embryonic life being seeded with stem cells from the yolk sac Thymic lymphocytes undergo extensive antigen independent proliferation l A portion of the cells degenerate in the thymus while the others pass to the blood and populate the other lymphatic structures and differentiate into thymus dependent or T lymphocytes that are active in Acell mediated immune responses Germinal centers are lacking and there is no antibody production in the thymus Removal of the organ before the immune system has developed leads to impairment of the bodys immune defenses Histological structure 1 Each lobe is divided into lobules each with a cortex and medulla 2 The medulla is a central core that sends a lateral projection into each lobule 3 The cortex surrounds the medullary projections 4 A capsule encloses each lobe and septa mark off the lobules trabeculae come off at right angles to septa and capsule they traverse the cortex but not the medulla 5 The parenchyma consists of reticular cells bounding compartments filled with lymphocytes a The reticular cells are like those of the other lymphatic structures but their origin is endodermal and not mesodermal are known as epithelioreticular cells ercs III 13 b Inthe medulla one class of epithelioreticular cells erc V1 is organized into concentric structures known as Hassalls corpuscles probably the site of thymosin and thymopoietin 6 Cortex contains lymphocytes of varying size with larger ones near the periphery and smaller ones deep in the cortex Degenerating small lymphocytes are also seen in the deep cortex Macrophages are seen scattered throughout the cortex and may congregate at the border of the cortex and medulla 7 Medulla lymphocytes are less abundant and chie y of the small lymphocyte type 8 Lymphocytes enter the blood in the postcapillary venules of the medulla In the cortex the capillaries are highly impermeable to macromolecules and provide a bloodthymus barrier to antigens 4 Spleen an abdominal organ on the left side sheltered by the 9th 10th and 11th ribs lying beneath the stomach and above the kidney a It is a complex lter in the blood stream concerned with clearing the blood of particulate matter and damaged cells and with immune responses to blood borne antigens With a fresh section elongate or round gray areas are scattered throughout a soft dark red mass the gray areas represent white Mp and are lymphoidal in nature while the red areas represent pulp irregularly spaced vessels of large caliber The spleen has a collagenous capsule with inward extensions or trabeculae The capsule is thickened at the hilus where it is attached to peritoneal ligaments and where arteries and veins enter and leave White pulp forms peria1terial lymphoid sheaths about the arteries where they penetrate the parenchyma The lymphatic structures follow the arteries almost to the point of their becoming capillaries Occasional germinal centers are found and these contain predominantly B lymphocytes while the remainder of the lymphoid tissue is composed of T lymphocytes Red pulp a network of branching and anastomizing sinuses separated by pulp cords The stroma consists of reticular fibers that branch from trabeculae 1 Pulp cords are filled with a number of free cells macrophages leukocytes and red cells 2 The filtering action of the spleen depends on the large number of macrophages associated with the splenic cords 3 Open and closed circulation of the spleen a Open circulation capillaries deliver blood to pulp cords blood percolates through cords and renters circulation by passing through walls of venous sinuses b Closed circulation capillaries open into venous sinuses Blood can then pass from the sinuses to the cord space and then back again into the sinuses c Most likely both circulatory schemes are operating at the same time in the spleen III 14 111111111116 responses 1 Immune system protects the 39 39 39 39 from 39 39 The system encompasses all of the lymphatic tissue of the body Lymphocytes have the ability to recognize antigens macromolecules and foreign cells and set up a speci c defensive reaction termed the immune response Clonal selection theory holds that lymphocytes arise that can recognize a limited number or perhaps a single antigen On meeting an antigen the lymphocyte is stimulated causing it to undergo transformation which results in proliferation and differentiation a Proliferation leads to expansion in numbers of relevant cells clonal expansion b Differentiation results in appearance of effector cells and memory cells Effector cells cause antigen removal Of crucial importance in immune responses are molecules known as MHC Major Histocompatibility Complex molecules that are associated with cell surfaces two types exist a MHCI associated with the surface of all cells This molecule allows the cells of our immune system specifically cytotoxic T cells CD8 T cells to recognize selffrom unself b MHCII associated with B lymphocytes and macrophages antigen presenting cells This molecule is recognized by helper T cells CD4 T cells and causes these cells to release a substance that completes activation of an immunologically competent cell Abbreviated CD8 response a Cytotoxic T cell CD8 recognizes a foreign MHCI as might occur in a tissue transplant or a modified MHCI as might occur when a viral fragment or parasite fragment is attached to the MHCI of normal body cells b Some viral or parasite antigen is most likely also processed by macrophages and these cells place the antigen fragments on their MHCII molecules that then attract appropriate helper T cells CD4 T cells 1 When a helper T cell recognizes an altered MHCH it attaches to it and secretes Thelper substance a complex mix of cytokines which allows for complete activation of an immunologically competent cell c An activated Cytotoxic cell undergoes proliferation clonal expansion with the production of large numbers of cytotoxic cells and memory cells 1 Cytotoxic cells attach the altered or foreign MHCIs and cause destruction of the cells bearing the altered or foreign MHCIs by release of porforins than cause perforation of the cell and subsequent cell death 2 Memory cells remain in the circulation and reside the peripheral lymphatic organs for a long time Abbreviated Bcell response a Antigen attaches to receptor IgM on surface of B cell Antigen is processed by B cell and is attached to MHCII ofthe B cell Antigen is also most likely r J by 39 and the 39 also attaches r r IV 111 15 pieces ofprocessed antigen to its MHCII molecules b Thelper cells CD4 T cells recognize the altered MHCII molecules on the B cell and Macrophage and secrete T helper substance that completes the activation of the initially stimulated B cell c Activated B cell undergoes proliferation with the resultant production of plasma cells and memory cells 1 Plasma cells produce antibody IgG which neutralizes the offending antigen 2 Memory cells remain in circulation and take up residence in peripheral lymphatic organs Supporting connective tissue 003 These connective tissues have a large amount of intercellular substance in form of ground substance and a paucity of cells The intercellular substance is actually performing the support function of this tissue The two major types of supporting connective tissue are cartilage and bone Cartilage l Consists of cells chondrocytes and fibers embedded in an amorphous gel like matrix composed of chondroitin sulfate a mucopolysaccharide glycosaminoglycan 2 Except where it is exposed to uid as injoints it is enclosed by a dense fibrous connective tissue called the perichondrium 3 General characteristics of the tissue a During embryonic life the mesenchyme around an area that is to become cartilage remains closely applied to the developing cartilage and becomes the perichondrium outer layer develops into fibroblasts and produces the outermost layer of the perichondrium the brous perichondrium the inner layer contains chondroblasts and becomes the chondrogenic perichondrium b Cells of cartilage are termed chondrocytes and reside in chambers in the matrix known as lacunae may be several cells in a lacuna cell nest or isogenous group lacunae develop from chondroblasts secreting ground substance and collagen fibers around themselves c Growth of cartilage occurs by two methods appositional growth and interstitial growth 1 Appositional growth cells and ground substance added to surface by activity in the chondrogenic layer of the perichondrium 2 Interstitial growth growth via mitosis of lacunar cells causing expansion of the lacuna occurs only in young cartilage d Nutrition of cartilage cartilage is avascular thus nutrition and removal of waste products is via diffusion 4 There are three types of cartilage hyaline elastic and fibrous a Hyaline cartilage has a pearly white translucent appearance matrix appears uniform 1 Most commonly occurring type of cartilage 2 Embryonically it is used as the basis for most of the skeleton Bone III 16 ultimately replace by bone 3 In the adult it is found on the ventral ends of ribs tracheal rings larynx and the articulating surfaces of bones Elastic cartilage has elastic bers in addition to collagen bers in the matrix allows the tissue to be deformed and then return to its original shape 1 Found in the extema ear ear pinna and the epiglottis Fibrocaltilage contains large numbers of collagen bers in the matrix 1 The only cartilage type that lacks a perichondrium 2 Never occurs alone but merges with hyaline cartilage or brous tissue 3 Examples are intervertebral disks insertions of tendons and ligaments Although the precursor of most bone appears as cartilage in the embryo bone is not calci ed cartilage The two tissues are similar in that their cells lie in lacunae and the matrix is similar However when cartilage becomes calci ed the cells are shut off from their nutrition and die This is not the case in bone Differences between bone and cartilage a Bone has a canalicular mechanism 1 The intercellular substance of bone unlike that of cartilage has a canal system to provide nourishment to the bone cells or osteocytes 2 The canaliculi arise from protoplasmic processes of the osteoblasts during development of bone 3 As the osteoblasts secrete ground substance the areas around the cell processes remain open thus forming the canal system 4 Since bone is laid down from inside to out the last canal opens into atissue space containing tissue uid Tissue uid thus ows through the canal system to nourish the bone cells osteocytes Waste products also follow the canal system out from the lacunae to the tissue space Bone is vascular 1 As might be expected the canal system is not very ef cient thus no osteocyte can remain alive it is any distance from a capillary 2 Bone is thus exceedingly well supplied with capillaries and even that which appears to the eye as being very dense shows on microscopic examination that no bone cell is more than a few millimeters from a capillary Bone can grow only by the appositional method 1 Under normal conditions the intercellular substance becomes calci ed as soon as it is laid down Because of this the matrix cannot expand 2 Furthermore osteocytes are so differentiated that they have lost all capacity to divide 3 Thus the only way in which bone can grow is by adding to the III 17 surface appositional growth 4 Structure of bone a Compact bone 1 The tissue is covered with a brous connective tissue known as the periosteum a b c d e The periosteum consists of two layers an external brous portion known as the brous periosteum and internal layer containing osteoblasts known as the osteogenic layer Compact bone is composed of cylindrical units known as osteons or Haversian systems Consist of concentric lamellae around a central canal the Haversian canal which contains blood vessels and nerve supply I canaliculi open into the Haversian canal Between osteons are remnants of previous concentric lamellae called interstitial lamellae Circumferential lamellae are located underneath the periosteum outer circumferential lamellae and line the marrow cavity inner circumferential lamellae 2 Because of the various levels of lamellae compact bone is said to have a lamellar structure 3 Canals containing blood vessels that run perpendicular to the Haversian canals are known as Volkmanns canals a These travel from the endosteal periosteal outer surface to the endosteal surface inner surface of the bone 4 The lining of the marrow cavity is known as the endosteum a b Cancellous bone Is one cell in thickness and contains cells that can differentiate into osteoblasts ie the cells are osteoprogenitor cells more commonly called endosteal cells 1 Lacks the osteon structure of compact bone 2 Consists of trabeculae if the trabeculae are sufficiently thick osteons will develop 3 Cancellous bone does have a periosteum and endosteum like compact bone 5 Ossi cation Processes intramembranous endochondrial and heterotropic ossi cation a Intramembranous ossi cation this process is used in the formation of the at bones of the skull and the clavicle l Seen in connection with development of at bones of the skull 2 Process is so termed because of the fact that the area in which bone 3 4 5 6 III 18 develops initially has a membranous character a Membrane does not turn to bone it is replaced by bone Process begins when a clump of mesenchymal cells differentiate into osteoblasts a After osteoblasts appear it is not long before some of them secret the characteristic organic intercellular substance of one Not all the cells of the osteoblastosteocyte series differentiate immediately the youngest least differentiated cells proliferate into new osteoblasts a Both cells remain at the edge of the newly formed bone and continue to enlarge the area 1 Growth becomes differential in that it is greater in some directions than others resulting in the formation of spicules Well developed spicules thicken and are then known as trabeculae resulting in the formation of cancellous bone Cancellous bone becomes compact on the top and bottom surfaces of the developing bone resulting in two plates of compact bone with cancellous bone between them The area of cancellous bone is known as the diploe Endochondral ossi cation process responsible for the formation of the majority of the bones of the body 2 3 4 5 6 7 In sites to be occupied by most of the bones of the body cartilage models of the bones to be are formed first Subsequently the cartilage models are replaced by bone again cartilage does not turn into bone cartilage is replaced by bone Process begins with the formation of the cartilage model that grows in extent by both interstitial and appositional grth As the cartilage models grows the centermost cells mature and become calcified a Also at this time blood vessels begin to impregnate the area the appearance of blood vessels changes the environment of the model so that osteoblasts differentiate under the perichondrium These lay down a shell of bone around the model the perichondrium is now called a periosteum b The calcification center is now known as an ossification center The first bone formed is cancellous with trabeculae and later this is replaced by compact bone The cartilage at each end of the model continues to grow thus increasing the length of the bone More of the cartilage matures is invaded with blood vessels and bone is formed so that eventually a marrow cavity is formed In long bones a second center of ossification arises in the epiphyses Heterotropic ossi cation V Joints A III 19 l The formation of bone in places where it shouldnt be ie scar tissue loose connective tissue etc 2 Occurs when for some unknown reason conditions occur that allow for mesenchymal cells to differentiate to osteoblasts that begins the formation of bone Bone cell types a Osteoprogenitor develops from the mesenchyme It is the initial bone formation cell that develops b Osteoblast immature bone cell that develops from the osteoprogenitor This cell is responsible for the formation of the ground substance and fiber content of bone This cell has many cell processes that allow for the formation of canaliculi Osteocyte a mature bone cell residing in a lacuna d Osteoclast a bone resorption cell This cell is a large multinucleate cell that forms from the fusion of several monocytes 0 The words articulate articulare to connect and joint jungere to join are used synonymously with those structural arrangements that exist to connect one or more bones at their site of meeting 1 Although many joints permit movement the permitting of movement is not essential for a connecting structure to be termed a joint Besides joining bones together to form a skeleton joints make it possible for the structures they connect to grow in extent Classification of joints 1 Joints may be classified on the basis of how they develop according to their structure or according to the type of movement they permit We shall classify them according to their structure and accordingly there are 5 kinds a Syndesmoses b Synchondroses c Synostoses d Symphyses e Synovial 1 a I 1 On the basis of U and Synostoses are all Synalthroses permit little or no movement Symphyses are Amphiarthroses permit limited movement and Synovial joints are Diarthroses permit a wide range of movement this type of j oint is what generally comes to mind when someone mentions the term joint a v u u u The structural types 1 Syndesmoses a Desmosis refers to a band in this case a band of dense connective tissue b Syndesmoses are joints in which the bones are held together by a band of dense connective tissue 1 In this type of joint the dense connective tissue extends from one bony surface to another c Examples INTRODUCTION I De nition of Histology A The word histology is derived from two Greek words 1 Histos tissue web 2 Logia study of B The term is practically useless without a de nition of the word tissue Tissue is a derivation from the French tissu which means a weave or texture 2 The word tissue came into anatomic use through the work of Marie Francois Xavier Bichat 17711802 a French anatomist who was impressed that the various layers and structures he saw on gross dissection had various textures a Bichat classi ed tissues into 21 different types Essentially he classi ed every organ or structure as a different tissue type 3 Today tissues are classi ed into only four types a Epithelial tissue b Connective tissue c Muscle Nerve C The study of histology also involves the learning of function 1 Tissues have functions as well as structure 2 If one knows the function of an organ heshe can anticipate its structure Likewise a knowledge of an organs structure reveals much about its function II The methods of Histology A Methods for direct observation of living tissues and cells 1 Exteriorization and transillumination a Organs with a long vascular pedicle can be brought out of the body and maintained in moist chambers b Small animals used because of thinner organs c Allows study of circulation in organs release of secretory material ie secretion in the pancreas or the process of ovulation d Technique is limited in number of organs that can be studied and magni cation used 2 Transparent chamber methods a Installation of chambers of metal or glass in long ears of rabbits 1 Tissue to be studied is placed in chamber and can be observed microscopicallyhas been used for study of capillary growth and for observing leukocyte migration b Use of anterior chamber of the eye as a transparent chamber 1 Used for study of early embryonic growth cyclic uterine changes in monkeysdemonstrated that menstruation is a hormonal and not a nervous event 3 Cell and organ culture a Growth of cells and organs in vitro using synthetic growth medium for tissue uid 1 Allows one to follow embryologic development of organs 2 Provides and ethically acceptable means of experimenting on human tissues 4 lVIicromanipulation a Removal of cell parts or injection of minute quantities of chemicals can be used to study cells in culture 5 Vital and Supravital staining a Use of dyes of low toxicity injected into living vital animals or applied to surviving cells and tissues removed from the body supravital l Alizarinntaken up selectively by calcifying matrix of bone Hence this is a good dye to following bone repair following fracture 2 Trypan blueuse for study of phagocytosis 3 Neutral reduse for studying leukocytes B Preparation and examination of killed tissue 1 Study of structure of tissues is hindered by their lack of transparency and thickness a Has led to use of chemically preserved materials that are cut into thin slices called sections b Sections can be stained with various dyes to increase contrast of tissue parts c The goal is to get a method that results in minimum deviation from normal 111 Physiological properties of cells The body is composed of three main components 1 Cellsindividual living entities with a jellylike consistency 2 Intercellular substancesnon living substances made by cells and often lying between cellssome are soft but many are fum 3 Fluidsthe important ones are blood lymph and tissue uid B Cells may be described as the smallest unit of protoplasm capable of independent existence The simplest animals consist of a single cell but higher animals may be thought of as a society of interdependent cells of many kinds 2 Cells serving the same general function are grouped together into tissues 3 Two or more tissues can combine to form larger functional units known as organs 4 Organs with interrelated functions constitute a system C Functional physiological properties of cells 1 It should be kept in mind that the following list in reality pertains only to single celled organisms In multicellular organisms cells have become specialized for one or more of the functions listed 2 The general functional properties of cells are given as a Irritabilitynthe sensitivity of a cell to a stimulus ie pressure light chemicals Nerve cells exhibit highly developed irritability b C0nductivityability to conduct a wave of excitability over the cell surface