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by: Jacinthe Hirthe
Jacinthe Hirthe
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Maria Terreros

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Maria Terreros
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This 166 page Class Notes was uploaded by Jacinthe Hirthe on Monday October 12, 2015. The Class Notes belongs to ZOO 3753 at Florida International University taught by Maria Terreros in Fall. Since its upload, it has received 29 views. For similar materials see /class/221737/zoo-3753-florida-international-university in Animal Science at Florida International University.

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Date Created: 10/12/15
JUNQUEIRA S a51c Hiatglogy Mescher AL Chapter 13 Hemopoiesis Junqueira39s Basic Histology Text amp Atlas 129 l HLemopo iesis Introduction r Mature blood cells have a relatively short life span i and must be continuously replaced with stem cell progeny produced in the he39mopoietic Gr haima blood poiesis a making organs Erythrocytes granulocytes monocytes and platelets are derived from stem cells located in bone marrow The origin and maturation of these cells are termed respectively erythropoiesis Gr erythros red poiesis granulopoiesis monocytopoiesis and thrombocytopoiesis Development of the major types of lymphocytes by lymphopoiesis occurs in the marrow and in the lymphoid organs 4 Stem Cells Growth Factors amp Differentiation 1 Stem cellSare pluripotent cells capable of asymmetric division and selfrenewal i PIU ripotient Hem op oiieti c Stem Cells A blood cexllsariSefrom a single type of stem cell in the bone marrow called a pluripotent stem cell because it can produce all blood cell types Figure 13 1 The pluripotent stem cells proliferate and form two major cell lineages one for lymphoid cells lymphocytes and another for myeloid cells Gr myeos marrow that develop in bone marrow Myeloid cells include granulocytes monocytes erythrocytes and megakaryocytes w Progenitr Precursor Cells The lutrijpotent stem cells give rise to daughter cells with restricted potentials called progenitor cells r colonyforming units CFUs here are four types of progenitorsCFUs w Erythroid lineage of CFUerythrocytes CFUE w Thrombooytic lineage of CFUmegakaryocytes CFUMeg av Granulocyte monocyte lineage of CFU granulocytesmonocytes CFUGM 4 Lymphoid lineage of CPUlymphocytes of all types CFUL All four progenitorCFUs produce precursor cells or blasts Fig 131 f P rgenitor cells divide asymmetrically to produoe both progenitor and precursor cells w Precursor cells produce only cells on the path to differentiation Hemopoiesis depends on favorable microenvironmental conditions and the presence of paracrine or endocrine growth factors w Hemopoietic rowth factors called colonystimulating factors CSF or hemsatopoietins poietins are proteins with complex overlapping functions in stimulating proliferation mitogenic activity of immature mostly progenitor and precursor cells supporting differentiation of maturing cells and enhancing the functions of mature cells Table 132 nte Marrow one marrow and adipocytes are found in the medullry canals of long bones and in the cavities of cancellous bones There are two types of bone marrow based on their appearance at gross examination bloodforming red bone marrow whose color is produced by an abundance of blood and hemopoietic cells and yellow bone marrow which is filled with adipocytes and essentially excludes hemopoietic cells w Red bone marrow Figure 13 2 is composed of a stroma Gr stroma bed hemopoietic cords or islands of cells and sinusoidal capillaries w The matrix of bone marrow also contains collagen type I proteoglycans fibronectin and laminin the latter glycoproteins interacting with integrins to bind cells to the matrix Maturation of Erythrocytes A mature cell is one that has differentiated to the stage at which it can carry out all its specific functions Erythrocyte maturation involves hemoglobin synthesis and formation of a small enucleated biconcave corpuscle Several major changes take place during erythrocyte maturation Figure 13 4 i There a gradual decrease in the number of polytriibosomes basophilia decreases with a simultaneous increase in the amount of hemoglobin an acidophii lic protein within the cytoplasm MitoChondria and other organelles gradually disappear The glycoprotein erythropoietin Epo a growth factor produced in the kidneys stimulates production of mRNA for globin the protein component of hemoglobin and is essential for the production of erythrocytes recgniizalble cell in the erythroid series Figure 1 3 5 is the proerythroblast The next stage is reresented by the basophilic erythroblast The next stage cell volume is reduced and some cytoplasmic areas begin to be filled with hemoglobin producing regions of both bas20phiia and acidophilia in the cell now called a polychromatophilic erythroblast In the next stage no basophilia is evident resulting in a uniformly acidophilic cytoplasm the orthochromatophilic erythroblast Late in this stage this cell ejects its nucleus which is phagocytosed by macrophages The cell is called reticulocyte Reticulocytes pass to the circulation where they may constitute 1 of the red blood cells lose the polyribosomes and quickly mature as erythrocytes Maturation of Granulocytes Granulopoiesis involves cytoplasmic changes dominated by synthesis of proteins for the azurophilic granules and specific granules These proteins are produced in the rough endoplasmic reticulum and the prominent Golgi apparatus in two successive stages Figure 13 6 w The myeloblast is the most immature recognizable cell in the myeloid series Figure 1 In the next stage the promyelocyte is Characterized by its basophilic cytoplasm and azurophi l ic granules containing lysosomal enzymes and myeloperoxidase The first visible sign of differentiation appears in the myelocytes Figure 13 9 in which specific granules gradually increase in number and eventually occupy most of the cytoplasm at the metamyelo39cyte stage Thevas tmajon ty of g ranUlOcytes are neutrophils The total time taken fora myeloblast to emerge as a mature Circulating neutrophil is about 11 days Under normalcircumstances five mitotic divisions occur in the m yel39ob39last promye locyte and neutrophilic myelocyte stages Developing and mature neutrophils Can be considered to exist in four functionally and anatomically defined compartments the granulopoietic compartment in marrow storage as mature cells in marrow until release the circulating population and a marginating population of cells adhering to endothelial cells of postcapillary venules and small veins Figure 13 10 1 Maturation o ngrafn qucytes Monoc39y tes iv The monoblast is a progenitor cell that is virtually identical to the myeloblast in its morph o logic characteristics Further differentiation leads to the promonocyte a large cell with basophilic cytoplasm and a large slightly indented nucleus Promonocytes divide twice as they develop into monocytes Mature monocytes enterthe bloodstream circulate for about eight hours and then enter tissues where they mature as macrophages or other phagocytic cells and function for several months Lymphocytes All lymphocyte progenitor cells originate in the bone marrow Some of these lymphocytes migrate to the thymus where they acquire the full attributes of T lymphocytes Subsequently T lymphocytes populate specific regions of peripheral lymphoid organs Other bone marrow lymphocytes differentiate into B lymphocytes in the bone marrow and then migrate to peripheral lymphoid organs I The rst identi able progenitor of lymphoid cells is the Iymphroblijast a large cell capable of dividing two or three times to form prolymphocytes Prolymphocytes are smaller and have relatively more condensed chromatin but none of the cellsurface antigens that mark T or B lymphocytes In the bone marrow and in the thymus these cells synthesize cellsurface receptors characteristic of the B or T lymphocyte Hneages MEDICAL APPLICATION 4 Abnormal stem cells in bone marrow can produce diseases based on cells derived from that tissue Leukemias are malignant clones of leukocyte precursors They occur in lymphoid tissue lymphocytic leukemias and in bone marrow myelogenous and monocytic leukemias In these diseases there is usually a release of large numbers of immature cells into the blood t origin of Platelets I y in adults the membraneenclosed cell fragments called plateleth originate in the red bone marrow by dissociating from mature megakaryOCytes Gr megas big karton nucleus kytos which in turn differentiate from megakaryOblasts in a process driven by thrombopoietin To form platelets megakaryocytes extend several long gt100 m wide 2 4 m branching processes called proplatelets These extending proplatelets penetrate the sinusoidal endothelium and appear as long processes disposed lengthwise with the blood flow in these vessels Figure 13 3 Mature megakaryocytes have numerous imaginations of plasma membrane ramifying throughout the cytoplasm called demarcation membranes Figure 13 12 which were formerly considered quotfracture linesquot or quotperforationsquot for release of platelets but are now thought to represent a membrane reservoir that facilitates continuous rapid proplatelet elongation Each megakaryocyte produces a few thousand platelets after which the remainder of the cell shows apoptotic changes and is removed by macrophages JUNQUEIRA S a51c Hiatglogy Mescher AL Chapter 11 The Circulatory System Junqueira39s Basic Histology Text amp Atlas 12e The Circulatory System Introduction i The Circulatory system includes both the blood and lymphatic vascular systems The blood vascular system Figure 11 1 is composed of the following structures i The heart it The arteries The capillaries and w The veins The lymphatic vascular system begins with the lymphatic capillaries which are closedended tubules that merge to form vessels of steadily increasing size these vessels terminate in the blood vascular system emptying into the large veins near the heart One of the functions of the lymphatic system is to return the fluid of the tissue spaces to the blood The circulatory system is considered to consist of the macrovasculature vessels that are more than 01 mm in diameter large arterioles muscular and elastic arteries and muscular veins and the microvasculature arterioles capillaries and postcapillary venules Heart The heart is a muscular organ that contracts rhythmically pumping the blood through the circulatory system Figure 11 3 The right and left ventricles pump blood to the lungs and the rest of the body respectively right and left atria receive blood from the body and the pulmonary veins respectively The walls of all four heart chambers consist of three major layers or tunics the internal endocardium the middle myocardium and the external epicardium w The endocardium is a thin layer of connective tissue lined by simple squamous endothelium Between the endocardium and myocardium is a layer of variable thickness called the subendocardial layer containing veins nerves and branches of the impulseconducting system of the head The myocardium is the thickest of the tunics and consists of cardiac muscle cells arranged in layers that surround the heart chambers in a complex spiral w The heart is covered externally by simple squamous epithelium mesothelium supported by a thin layer of connective tissue that constitutes the epicardium A subepicardial layer of loose connective tissue contains veins nerves and many adipocytes Figure 11 5 The epicardium corresponds to the visceral layer of the pericardium the serous membrane in which the heart lies The cardiac valves consist of a central core of dense fibrous connective tissue containing both collagen and elastic fibers lined on both sides by endothelial layers The bases of the valves are attached to strong fibrous rings that are part of the fibrous skeleton The heart has a specialized system to generate a rhythmic stimulus for contraction that is spread to the entire myocardium This system Figure 11 3 consists of two nodes located in the right atrium the sinoat rial SA node pacemaker and the atrioventricular AV node and the atrioventricular39 bundle of His wt Distally fibers of the AV bundle become larger than ordinary cardiac muscle fibers and acquire a distinctive appearance These conducting myofibers or Purkinje fibers have one or two central nuclei and their cytoplasm is rich in mitochondria and glycogen Both parasympathetic and sympathetic neural components innervate the heart Ganglionic nerve cells and nerve fibers are present in the regions close to the SA and AV nodes where they affect heart rate and rhythm such as during physical exercise and emotional stress Tissues of the Vascular Wall 4 Walls of larger blood vessels contain three basic structural components a simple squamous endothelium smooth muscle and connective tissue with elastic elements in addition to collagen The amount and arrangement of these tissues in vessels are influenced by mechanical factors primarily blood pressure and metabolic factors reflecting local needs of tissues at The en dothelium is a special type of epithelium that acts as a semipermeable barrier between two internal compartments the blood plasma and the interstitial tissue fluid Structural Plan of Blood Vessels Blood vessels are usually composed of the followmg layers or tUnics L tunica coat as shown in Figures 11 1 and 11 7 The tunica intima has one layer of endothelial cells supported by a thin subendothelial layer of loose connective tissue with occasional smooth muscle cells In arteries the intima is separated from the media by an internal elastic lamina the most external component of the intima w The tunica media the middle layer consists chiefly of concentric layers of helically arranged smooth muscle cells Figures 11 7 and 118 The tun ica adventitia or tunica externa principally of type I collagen and elastic Figures 11 7 and 118 a Figurej 17 Figures118 usually have vasa vasorum the vesselquot which consist of capillaries and venules in the adventitia and the outer part of the media Figure 11 9 a Larger vessels are supplied with a network of unmyeli nated sympathetic nerve fibers vasomotor nerves whose neurotransmitter is norepinephrine Figure 11 9 ischarge of norepinephrine from these nerves produces vasoconstriction Because these efferent nerves generally do not enter the media of arteries the neurotransmitter must diffuse for several micrometers to affect smooth muscle cells where gap junctions propagate the response to the inner layers of muscle cells i i i Vasculatu re of the macrovasculatu re are classified arbitrarily as follows Large Elastic Arteries large elastic arteries help to stabilize the blood flow The elastic arteries include the aorta and its large branches The intima is thicker than the corresponding tunic of a muscular artery An internal elastic lamina although present may not be easily discerned since it is similar to the elastic laminae of the next layer Figures 11 8 and 11 10 The media consists of elastic fibers and a series of concentrically arranged perforated elastic laminae whose number increases with age there are about 40 in the newborn 70 in the adult Between the elastic laminae are smooth muscle cells reticular fibers proteoglycans and glycoproteins The tunica adventitia is relatively underdeveloped r lar rte rites Thre muscular arteries can control blood flow to organs by contracting or relaxing the smooth muscle cells of the tunica media The intima has a very thin subendothelial layer and the internal elastic lamina the most external component of the intima is prominent Figure 11 11 4 Arterial Sensory Structures Carotid sinuses are slight dilatations of the internal carotid arteries which contain baroreceptors detecting increases in blood pressure r carotid bodies are small ganglia like structures paraganglia near the bifurcation of the common carotid arteries that contain chemoreceptors SensitiVe to blood 002 and 02 concentrations A network of sinusoidal capillaries is intermixed with glomus type I cells containing numerous dense core vesicles with dopamine serotonin and adrenaline Figure 11 12 Dendritic fibers of cranial nerve IX the glossopharyngeal nerve synapse with the glomus cells The sensory nerve is activated by neurotransmitter release from glomus cells in response to changes in the sinusoidal blood increased 002 decreased 02 or increased H levels Aortic bodies located on the arch of the aorta are similar in structure and function to carotid bodies t rte rioles it The smallest arteries branch as arterioles have one or two smooth muscle layers and indicate the beginning of an organ39s microvasculature Figure 11 13 where exchanges between blood and tissue fluid occur Arterioles are generally less than 05 mm in diameter with lumens approximately as wide as the wall is thick Figures 11 2 and 11 14 4 Fwiw ure 111 Structure of microvasculature Figure 1 13914Artenioles certain tissues and organs arteriovenous shunts orna nastomioses regulate blood flow by allowing direct communication between arteriolesand venules Arterioles in such shunts have a relatiVely thick capsulelike adventitia and a thick smooth muscle layer Arteriovenous shunts are richly innervated by the sympathetic and parasympathetic nervous systems These interconnections are abundant in skeletal muscle and in the skin of the hands and feet Capillari es Capillaries permit different levels of metabolic exchange between blood and surrounding tissues They are composed of a single layer of endothelial cells rolled up in the form of a tube The average diameter of capillaries varies from 5 to 10 m and their individual length is usually not more than 50 m Altogether capillaries comprise over 90 of all blood vessels in the body I The capillaries are often referred to as exchange since it is at these sites that 02 002 substrates and metabolites are transferred from blood to the tissues and from the tissues to blood In general endothelial cells are polygonal and elongated in the direction of blood flow Figure 11 7 The nucleus causes that part of the cell to bulge into the capillary lumen The cytOplasim contains a small Golgi appraratus mitochondria free ribosomes and sparse cisternae of RER Junctions of the tight zonula occludentes type are present between most endothelial cells conferring the wall with variable permeability to macromolecules that plays significant roles in both normal and pathologic conditions w Capillaries can be grouped into three types depending on the continuity of the endothelial cells and the external lamina Figure 1 1 16 Types of capillaries anmmenal cell b Fenas lraled capillary 439 Venules 439 A characteristic feature of all venules is the large diameter of the lumen compared to the overall thinness of the wall Figure 11 20 w Veins lood entering veins is under very low pressure nd moves toward the heart by contraction of the tunica media and external compressions from surrounding muscles and other organs Valves project from the tunica intima to prevent backflow of blood Most veins are small or medium veins Figure 11 21 The big venous trunks paired with elastic arteries elose to the heart are large veins Figure 11 8 Large veins have a welldeveloped tunica intima but the tunica media is relatively thin with few layers f smooth muscle and abundant connective tissue e Most veins have valves but these are most prominent in large veins Valves consist of paired semilunar folds of the tunica intima projecting across part of the lumen Figures 11 21 and 11 22 They are rich in elastic fibers and are lined on both sides by endothelium The valves which are especially numerous in veins of the legs help keep the flow of venous blood directed toward the head Lymphatic Vascular System n addition to blood vessels the ody has a system of thin walled endotheli39al channels that collect excess interstitial fluid from the tissue spaces and return it to the blood This fluid is called lymph unlike the blood it flows in only one direction toward the heart The lymphatic capillaries originate in the various tissues as thin closed ended vessels that consist of a single layer of endothelium and an incomplete basal lamina Lymphatic capillaries are held open by bundles of anchoring filaments of the elastic fiber system which also bind the vessels firmly to the surrounding connective tissue Figure 11 23 The thin lymphatic capillaries converge into larger lymphatic vessels With rare exceptions such as the CNS and the bone marrow lymphatic are found in almost all organs 1 The larger lymphatics have a structure similar to that of veins except that they have thinner walls and lack a clear cut separation between tunics They also have more numerous internal valves Figure 11 24 2 Figure 1124 Lymphatic vessels and valve Lymphatic vessels ultimately end Up as two large trunks the thoracic duct and the right lymphatic duct which respectively empty lymph into the junction of the left internal jugular vein with the left subclavian vein and into the confluence of the right subclavian vein and the right internal jugular vein 4 Besides gathering interstitial fluid as lymph and returning it to the blood the lymphatic system of vessels is a major distributor of lymphocytes antibodies and other immune components which it picks up at lymph nodes and other lymphoid tissues JUNQUEIRA S a51c Hiatglogy Mescher AL quotChapter 3 The cell nucleus Mescher AL Junqueira39s Basic Histology Text amp Atlas 12e The Cell Nucleus Introduction The nucleus contains a blueprint for all cell structures and activities encoded in the of the chromosomes it also contains the molecular machinery to replicate its DNA and to synthesize and process all types of RNA Macromolecular transfer between the nuclear and cytoplasmic compartments is regulated Because functional ribosomes do not occur in the nucleus no proteins are produced there The numerous protein molecules needed for the activities of the nucleus are imported from the cytoplasm Components of the Nucleus w The nucleus frequently appears as a rounded or oval structure usually in the center of the cell Figure 3 1 Its main components are the nuclear envelope chromatin consisting of DNA and asSociated proteins and a specialized region of chromatin called the nucleolus Figures 3 2 and 3 3 The size and morphologic features of nuclei in a specificnormal tissue tend to be uniform In contrast the nuclei in cancer cells often have irregular shapes variable sizes and atypical chromatin patterns Suurne Mischa NL Junquefra39s Basic Himlagy Text and A as 12th Edm hm iwwancessmed lcinemm 39 Cu riht Q The McGrawHiil Cum ies Inc All rihls FEEWECJ clear Envelope Electron microscopy shows that the nucleus is surrounded by two parallel unit membranes separated by a narrow perinuclear space Figure 3 2 Together the paired membranes and the intervening space make up the nuclear envelope Polyribosomes are attached to the outer nuclear membrane indicating continuity of the nuclear envelope with the endoplasmic reticulum Closely associated With the inner nuclear membrane is a mesh39work of fibrous proteins called the nuclear lamina Figure 3 4 which helps to stabilize the nuclear envelope Major components of this lamina are intermediate filament proteins called lamins which bind to membrane proteins and associate with chromatin in nondividing cells w Atsiteswhere the inner and outer membranes of the nuclear envelope fuse the resulting lipidfree spaces contain nuclear pore complexes or NPCs Figures 3 5 3 6 and 3 7 which contain the machinery that regulates most bidirectional tranSport between the nucleus and thecytoplasm The nucleus of a typical mammalian cell contains 3000 4000 such pore complexes each composed of subunits with some 30 different NPC proteins or nucleoporins Figure 3 7 EChromat im l39n non39d iyiding nuclei chromatin is the chromosomal material in a largely uncoiled state Two types of chromatin can be distinguished With boththe light and electron microscopes which reflect the degree of chromosomal condensation Heterochromatin heteros other chroma color which is electron dense appears as coarse granules in the electron microscope and as basophilic clumps in the light microscope Euchromatin is the less coiled portion of the chromosomes visible as finely dispersed granular material in the electron microscope and as lightly stained basophilic areas in the light microscope cw Chromatin is composed mainly of coiled strands of DNA bound to basic proteins called histories and to various nonhistone proteins The basic structural unit of chromatin and histones is the nucleosome Figure 3 8 which has a core of eight small histones two copies each of histones H2A HZB H3 and H4 around which is wrapped DNA with about 150 base pairs Each nucleosome also has a larger linker histone H1 that binds both wrapped DNA and the surface of the core The series of nucleosomes in chromatin is also associated with many diverse nonhistone proteins with a wide variety of enzymatic functions Figure 38 rm rt 1 highm radian ll39l 1115 N as q wag 1r 39 n39 7 Chromosome is the structure within the nucleus of a cell that contains protein an the genetic DNA Chromosomes occur in pairs in diploid cells ordinary body cells haploid cells gametes or sex cells have only one of each pair in chromosomes in their nuclei In humans the somatic cells cells of the body contain 22 pairs of autosom es plus the pair of sex chromosomes X amp Y r Of chromosomes themselves usually usescells grown in vitro and the arrest of mitot icceIIs dtiring metaphase using colchicine which binds tubulin and disrupts microtubules Arrested Cells are then immersed in a hypotonic solution which causes swelling stained in various ways and then flattened between a glass slide and a coverslip The mitotic chromosomes from one nucleus are then photographed under the light microscope cut individually from the photograph and arranged to produce a karyotype in which the stained chromosomal bands can be analyzed Figure 3 11 i NUCIe OIUS quot The nucleolus is a generally spherical highly baSOphilic structure present in the nuclei of cells active in protein synthesis Figure 3 12 The intense basophilia of nucleoli is due not to heterochromatin but to the presence of densely concentrated rRNA which is transcribed processed and complexed into ribosomal subunits in that nuclear region Nucleoli are always associated with nuclei of cells that are intensely synthesizing proteins for growth or secretion Figure 312 Cell Division f Gefll diVision or mitosis Gr m iz os a thread can be observed with the light microscope During this process the parent cell divides and each of the daughter cells receives a chrOmosomal Set identical to that of the parent cell Essentially a longitudinal duplication of the chromosomes takes place and these chromosomes are distributed to the daughter cells The period between mitoses is called interphase during which the DNA is replicated and the nucleus appears as it is most commonly seen in histological preparations The process of mitosis is subdivided into four phases Figures 3 14 and 3 15 The Cell Cycle Mitosis is the visible manifestation of cell division but other processes play fundamental roles in cell multiplication Principal among these is the phase in which DNA is replicated DNA replication occurs during interphase The cyclic alternation between mitosis and interphase known as the cell cycle occurs in all tissues with cell turnover r The cell cycle has four distinct phases mitosis and three interphase periods termed G1 the time gap between mitosis and DNA replication 8 the period of DNA synthesis and G2 the gap between DNA duplication and the next mitosis The approximate times of these phases in rapidly dividing human cells are illustrated in Figures 3 18 and 3 19 Figure 318 The cell Cycle i Cells and Tissue Renewal w Thro ughoutian individual39s lifetime many tissues and organs contain a small population of undifferentiated stem cells whose cycling serves to renew the 2differerntiated cells of the tissues as needed Many stem cells divide infrequently but the divisions are always asymmetric that is one daughter cell remains as a stem cell while the other becomes committed to a path that leads to differentiation MeIOSIs Mieiiosijsi is a specialized process involving two clasely associated cell divisions that occurs only in the cells that will form sperm and egg cells in the gonads germ cells 0 gametes Two key features Characterize meiosis 1 The cells produced are haploid with just one chromosome from each pair present in the rest of the body39s somatic cells Union of haploid eggs and sperm cells at fertilization forms a new diploid cell the zygote which can develop into a new individual 2 Early in the process the homologous chromosomes of each pair one from the mother one from the father physically associate along their lengths in an activity termed synapsis i As shown in Figure 3 21 the important Apotosis 4 The process of cell suicide or programmed cell death is called apoptosis Gr apo off uptosisr a falling Apoptosis is a highly regulated cellular activity that occurs rapidly and produces small membrane e39ncl osed apoptotic bodies which quickly undergo phagocytosis by neighboring cells or macrophages specialized for debris removal Unlike cells undergoing necrosis as a result of accidental injury apoptotic cells do not rupture and release none of their contents Some examples of39apoptosis will illustrate its significance Inside the thymus T lymphocytes with the potential to react against Selfantigens receive signals that activate the apoptotic program and they die before leaving the thymus see Chapter 14 In the mature ovary apoptosis is the mechanism of both the monthly loss of luteal cells and the removal of excess oocytes and their follicles JUNQUEIRA S a51c Hiatglogy Mescher AL Chapter 10 Muscle Tissue Junqueira39s Basic Histology Text amp Atlas 12e Muscle Tissue Introduction Three types of muscle tissue can be distinguished on the basis of morphologic and functional characteristics Figure 10 1 and the structure of each type is adapted to its physiologic role Skeletal muscle Cardiac muscle Smooth muscle Figure 101 The three types of muscle I it 65 39 The cytoplasm of mUScle cells is called S39arc oplasm Gr sarkos flesh plasma thing formed 39 The smooth ER is called sarcoplasmic reticulum r The sar fcolemma sarkos Gr lemma husk is the cell membrane or plasmalemma 1 Skeletal Muscle Skeletal muscle consists of muscle fibers which are long cylindrical mUIti nucleated cells with diameters of 10 100 m Multinucleation results from the fusion of embryonic mesenchymal cells called myoblasts Figure 10 2 Figure 102 Development of skeletal muscle Figure 103 Organization and of skeletal muscla Figure 104 Skeletal muscle r the of the most important roles of this connective tissue is to transmit the mechanical forces ge nerated by the contracting muscle cellfibers because individual muscle cells seldom extend from one end of a muscle to the other Blood vessels penetrate the muscle within the connective tissue septa and form a rich capillary network in the end omysium Figure 10 5 Lymphatic vessels and larger blood vessels are found in the other connective tissue layers Figure 106 Myfotendinous junction Muscle Fibers w Longitudinally sectioned skeletal muscle fibers show crossstriations of alternating light and dark bands Figure 10 7 The darker bands are called A bands anisotropic or birefringent in polarized light the lighter bands are called I bands isotrOpic do not alter polarized light In the TEM each band is seen to be bisected by a dark transverse line the Z line Ger ZWischenscheibe between the discs The repetitive functional subunit of the contractile apparatus the sarcomere extends from Z line to Z line Figure 10 8 and is about 25 m long in resting muscle Figure 107 Striated skeletal muscle in longitudinal section quot ELQ7 3 7 H i 7 H g M I 39 all 39 IN39JHW HKQ lJ 39 I v wd Figure 10 8 f S39tructiu re of a myofibril a series of sa rcomeres The sarcoplasm has little RER or free ribosomes and is filled primarily with long cylindrical lamentous bundles called myofibrils running parallel to the long axis of the fiber The myofibrils consist of an endto en39d repetitive arrangement of sarcomeres Figure 10 8 w The A and l banding pattern in sarcomeres is due mainly to the regular arrangement of two types of myofilaments thick and thin that lie parallel to the long axis of the myofibrils in a symmetric pattern w The thick filaments are 16 m long and 15 nm E iwide they occupy the A band the central portion of the sarcomere The thin filaments run between and parallel to the thick filaments and have one end attached to the Z line Figure 10 8 the A band shows the presence of a lighter zone in its center the H zone that corresponds to a region cOnsisting only of the rodlike portions of the myosin molecule with no thin filaments present Figure 10 8 Bisecting the H zone is the M line Ger Mitte middle a region where lateral connections are made between adjacent thick filaments Figure 10 8 Figure 109 Molecules composing thin and thick filaments f39 tropomyosin subunit is a long thin molecule aboute4039 in length containing two polypeptide chains Which assembles to form a long polymer located in the groove betWeen the Mo twisted actin strands Figure 10 9 Troponin is a complex of three subunits TnT which attaches to tropomyosin TnC which binds calcium ions and Tnl which inhibits the actinmyosin interaction Troponin complexes are attached at specific sites at regular intervals along each tropomyosin molecule Figure 10 9 Myosin is a much larger complex molecular mass 500 kDa Myosin can be dissociated into two identical heavy chains and two pairs of light chains 6 i gr Sarcoplasmjc Reticulum amp Transverse Tubule System w in muscle the smIOOth endoplasmic reticulum SER is specialized for Ca2 ion seq uestratiOn 39 To provide for a uniform contraction skeletal muscle fibers have a system of transverse T tubules Figure 10 10 Figure 1010 Transverse tubule system Muscleicon traiction depends on the availability of ions and musCle relaxation is related to an absence of ca392 The sarcoplasmic reticulum specifically regulates calcium flow which is necessary for rapid contraction and relaxation cycles ThesachpIasmic reticulum system consists of a branChin g netWOrk of small cisternae surrounding efaCh myofibri Figure 10 10 After a neurally mediated depolarization of the sarcoplasmic reticulum membrane Ca2 ions concentrated within these cisternae are passively released into the vicinity of the overlapping thick and thin filaments whereupon they bind to troponin and allow bridging between actin and myosin molecules When the membrane depolarization ends the sarcoplasmic reticulum actively transports the Ca2 back into the cisternae ending contractile activity Mechanism of Contraction I Key molecular events in muscle Contraction are summarized in Figure 10 11 Innervation Myelinated motor nerves branch out within the perimysium connective tissue where each nerve gives rise to several terminal twigs At the site of innervation the axon loses its myelin sheath and forms a dilated termination situated within a trough on the muscle cell surface This structure is called the motor endplate or the neuromuscular junction Figure 10 13 mm rillluscer Spindles amp Tendon Organs Striated mus39CIe s and myotendinous junctions contain sensory receptors that are encapsulated proprioceptors L proprius one39s own capio to take Among the muscle fascicles are stretch detectors known as muscle spindles Figure 10 14 These structures consist of a connective tissue capsule surrounding a fluidfilled space that contains a few thin nonstriated muscle fibers densely filled with nuclei and called intrafusal fibers w Muscle Fiber Types Skeletal muscle fibers of humans are classified into three types based on their physiological biochemical and h ri st OChemical characteristics Figure 10 15 All three fiber types are normally found throughout most muscles Type or slow red oxidative fibers contain many mitochondria and abundant myoglobin a protein with iron groups that bind 02 and produce a dark red color a Type Ila or fast intermediate oxidative i glycolytic fibers have many mitochondria and much myogl0bin but also have considerable glycogen They39util ize both oxidative metabolism and anaerobic glycolysis and are intermediate between the other fiber types both in color and in energy metabolism Type llb or fast white glycolytic fibers have fewer mitochondria and less myoglobin but abundant glycogen making them very pale in color They depend largely on glycolysis for energy and are adapted for rapid contractions but fatigue quickly Cardiac MUSCIe 439 Figure 1016 shows a diagram of cardiac muscle cells indicating characteristic features of this muscle type Thefstfructufrle and function Off the Contractile proteins in cardiac Cells QBSSthIialJy39 the same as in skeletal muscle The T tubule system and sfa39rcoplasm ic retiCulu m however are not as regularly arranged in cardiac fiber The T tubules are more numerous and la rger invcardia c muscle than in skeletal muscle an d th e39 sarcoplasmis reticulum is less well developed Figure 10 1 Cardiac muscle cells contain numerous mitochondria vizh iCh OCCupy 40 or mOre of the cytoplasmic volume Figure 10 18 reflecting the need for continuous aerobic metabolism in heart muscle By comparison only about 2 of skeletal muscle fiber is occupied by mitochondria Fatty acids transported to cardiac muscle cells by lipoproteins are the major fuel of the heart and are stored as triglycerides in numerous lipid droplets seen in many cardiac muscle cells Glycogen particles may also be present Lipofuscin pigment granules are often found near the nuclei of cardiac muscle cells 4 Smooth Muscle 4 Smooth muscle fibers are elongated tapering and nonstr i ated cells each of which is enclosed by a thin basal lamina and a fine network of reticular fibers Figure 10 19 The connective tissues serve to combine the forces generated by each smooth muscle fiber into a concerted action eg peristalsis in the intestine Each cell has a single nucleus located in the center of the cell39s broadest part Concentrated near the nucleus are mitochondria polyribosomes cisternae of rough ER and the Golgi apparatus P inocyt otic vesicles are frequent near the cell surface quotA rudimentary sarcoplasmic reticulum is present in smooth muscle cells but T tubules are not Figure 1021 Smooth muscle contraction Contraction of smooth muscle is not under voluntary control but is regulated by autonomic nerves certain hormones and local physiological conditions such as the degree of stretch 4 In addition to contractile activity smooth muscle cells also synthesize collagen elastin and proteoglycans extracellular matrix ECM components normally synthesized by fibroblasts Regeneration of Muscle Tissue 1 The three types of adult muscle have different potentials fOr regeneration after injury J In skeletal musCle although the nuclei are incapable of undergoing mitosis the tissue can undergo limited regeneration The source of regenerating cells is the sparse population of mesenchymal satellite cells that lies within the external lamina of each mature muscle fiber Satellite cells are inactive reserve myoblasts that persist after muscle differentiation muscle lacks satellite cells and has virtually no regenerative capacity beyond early childhood Defects ordamage eg infarcts in heart muscle are generally replaced by fibroblast proliferation and growth of connective tissue forming myocardial scars Smooth muscle composed of simpler mononucleated cells is capable of a more active regenerative response After injury viable smooth muscle cells undergo mitosis and replace the damaged tissue JUNQUEIRA S a51c Hiatglogy Mescher AL Chapter 12 Blood Junqueira39s Basic Histology Text amp Atlas 12e we lood Introduction it i Blood a specialized connective tissue in which cells are suspended in fluid extracellular material called plasma Thesocalled formed elements circulating in the plasma are erythrocytes red blood cells leukocytes white blood cells and platelets When blood leaves the circulatory system either in a test tube or in the ECM surrounding blood vessels plasma proteins react with one another to produce a clot which includes formed elements and a yellowish liquid called serum Serum contains growth factors and other proteins released from platelets during clot formation which confer biological properties very different from those of plasma r Composmon of Plasma r laslma isvan aqueous solution pH 74 containing substances of low or high molecular weight that make u 8 1 of its volume Plasma proteins account for approximately 7 of the dissolved components with the remainder including nutrients nitrogenous waste products hormones and many inorganic ions collectively called electrolytes The composition of plasma is usually an indicator of the mean composition of the extracellular fluids in tissues r The major plasma proteins include the following Albumin the mostab undant plasma protein is made iin39th e liverand serves primarin in maintaining the Osmoticpressure Of39the blood I 39and agiobulins made by liver and other cells incl ude tra n39sferrin and other transport factors fibronectin prothrombin and other coagulation factors l ipoproteins and other proteins entering blood from tissues glob ulins which are immunoglobulins antibodies secreted by lymphocytes in many locations Complement proteins a system of factors important in inflammation and destruction of microorganisms Fibrinogen the largest plasma protein 340 kD Blood Cells Erythrocytes human erythrocytes IsuSpenided in an isotonic medium are flexible biconcave disks Figure 12 4 They are approximately 75 m in diameter 26 m thick at the rim and only 075 m thick in the center This biconcave shape provides a large surfacetovolume ratio and facilitates gas exchange The normal concentration of erythrocytes in blood is approximately 39 55 million per microliter in women and 41 6 million per microliter in men Figure 124 Normal human erythrocytes HMEDICAL APPLICATION decreased number of erythrocytes in the blood is usually associated with anemia An increased number of erythrocytes eryth39rocytosis or polycythemia may be a physiologic adaptation found for example in individuals who live at high altitudes where 02 tension is low Polycythemia Gr polys many kytos cell haima blood usually an increase in hematocrit is often associated with diseases of varying degrees of severity and increases blood viscosity when severe it can impair circulation through the capillaries The presence of a high percentage of erythrocytes with great variations in size is called anisocytosis Inherited alterations in hemoglobin molecules are responsible for several pathologic conditions an example of whiCh is sickle cell disease This inherited disorder is caused by a mutation of one nucleotide a point mutation in the gene for the chain of hemoglobin The triplet GAA for glutamic acid is changed to GUA which specifies valine The consequences of this substitution of a single amino acid are profound When the altered hemoglobin called HbS is deoxygenated in venous capillaries it polymerizes and forms rigid aggregates that give the erythrocyte a characteristic sickle shape Figure 12 5 II in i ib Leukocytes Leukocytes white blood Cells migrate to the tissues where they beCome functional and perform various actiwtizes Figure 12 6 According to the type of cytoplasmic granules and the shape of their nuclei leukocytes are divided into two groups polymorphionuclear granulocytes and mononuclear agranulocytes Grantulocytes possess two types of granules the specific granules that bind neutral basic or acidic stains and have specific functions and the azurophilic granules which are specialized lysosomes stain darkly and are present at some level in all leukocytes r Iv i I The major protein components of specific and azurop39hili39c granules are listed in Table 12 1 Granulocytes have polymorphic nuclei with two or more lobes and include the neutrophils eosinophils and ba sgophils Figures 12 1 and 12 6 AgranUIOCytes do not have specific granules but they do contain azurophilic granules Iysosomes The nucleus is round or indented This group includes lymphocytes and monocytes Figures 12 1 and 12 6 The differential count of all types of leukocytes is presented in Table 12 2 All leukocytes are key players in the defense against invading microorganisms and in the repair of injured tissues we Atrs iteisof injury or infection various substances termed cytokines are released that trigger lbosening of intercel39lular junctions in the endothelial cells of local postcapillary venules and the rapid appearance of Pselectin on their flumina l surfaces from WeibelPalade bodies Neutrophils and other leukocytes have on their surfaces ligands for Pselectin and interaction between these proteins causes cells flowing through the venules to slow down like rolling tennis balls arriving at a patch of velcro Other cytokines stimulate the now slowly rolling leukocytes to express integrins and other adhesion factors that produce firm attachment to the endothelium Figure 11 20d In a called diapedesis Gr dia through pedesis to leap the leukocytes send extensions into the new intercellular openings migrate out of the venulegs into surrounding tissue spaces and head directly for the bacterial cells The attraction of neutrophils to bacteria involves chemical mediators in a process of chemotaxis which causes leukocytes to rapidly concentrate where their defensive actions are specifically needed 339 The number of leukocytes in the blood varies according to age sex and physiologic conditions Neutrophiils Po l ymorphon uclear Leukocytes Neutroph39ils constitute 60 70 of circulating leukocytes They are 12 15 m in diameter in blood smears with nuclei having two to five lobes linked by thin nuclear extensions Figures 12 1 12 6 and 12 7 W Ne utrophils are shortlived cells with a halflife of 6 7 hours in blood and a life span of 1 4 days in connective tissues before dying by apoptosis 5 Eloisiniop hi lfs Eosinophils are far less numerous than neutrophils constituting only 2 4 of leukocytes in normal blood In blood smears this cell is about the same size as a neutrophil but with a characteristic bilobed nucleus Figures 12 1 12 6 and 12 9 The main identifying characteristic is the abundance of large red specific granules about 200 per cell that are stained by eosin Basophils also about 12 15 m in diameter make up less than 1 of blood leukocytes and are therGfore difficult to find in smears of normal blood The nucleus is divided into two or more irregular lobes but the large specific granules overlying the nucleus usually obscure its shape Lymphocytes They can be subdivided into functional groups according to distinctive surface molecules markers that can best be distinguished immunocytochemically notably T lymphocytes B lymphocytes and natural killer NK cells Lymphocytes have diverse functional roles related to immune defense against invading microorganisms foreign or abnormal antigens and cancer cells Figure 121 1 Lymphocytes Monocytes Monrocytes are bone marrow derived agranulecytes with diameters varying from 12 to 20 m The nucleus is large off center and may be oval kidneyshaped or distinctly Ushaped Figure 12 12 Platelets 4 Platelets are cell fragments 2 4 m in diameter derived from megakaryocytes of bone marrow Their primary function is to rapidly release the content of their granules upon contact with collagen or other materials outside of the endothelium to begin the process of clot formation and reduce blood loss from the vasculature Figure 1213 Platelets The role of platelets in controlling hemorrhage be summarized as follows Primary aggregation Disruptions in the microviascular endothelium which are common allow platelet aggregation to collagen via Collagenbinding protein in the platelet membrane Thus a platelet plug is formed as a first step to stop bleeding Figure 12 13c Secondary aggregation Platelets in the plug release an adhesive glycoprotein and ADP both of which are potent inducers of platelet aggregation increasing the size of the platelet plug Blood coagulationDuring platelet aggregation fibrinogen from plasma von Willebrand factor and others from damaged endothelium and various factors from platelets promote the sequential interaction cascade of plasma proteins giving rise to a fibrin polymer that forms a threedimensional network of fibers trapping red blood cells and more platelets to form a blood clot or thrombus 4 Clot retraction The clot that initially bulges into the blood vessel lumen contracts slightly because of the interaction of platelet actin and myosin i Clot removal Protected by the clot the vessel wall is restored by new tissue and the clot is then removed mainly by the proteolytic enzyme plasmin MEDICAL APPLICATION 4 Hemophilia A and B are clinically identical differing only in the deficient factor Both are due to sexlinked recessive inherited disorders Blood from hemophiliac patients does not coagulate normally the blood clotting time is prolonged Persons with this disease bleed severely even after mild injuries such as a skin cut and may bleed to death after more severe injuries The blood plasma of patients with hemophilia A is deficient in clotting factor VIII or contains a defective factor VIII one of the plasma proteins involved in fibrin generation in hemophilia B the defect is in factor IX JUNQUEIRA S a51c Hiatglogy Mescher AL Chapter 6 Adipose Tissue Junqueira39s Basic Histology Text amp Atlas 12e AdiposeTissue Introduction 4 Adipose tissue is a specialized type of Connective tissue in which adipocytes or fat cells predominate These cells can be found isolated or in groups within loose or irregular connective tissue often in large aggregates where they are the major component of adipose tissue Located in many areas throughout the body adipose tissue represents 15 20 of the body weight in men of normal weight in women of normal weight 20 25 of body weight Adipose tissue is the largest repository of in the form of triglycerides the neutral rats in the body r Adi pocytes themselves release hormones and a number of important factors and adipose tissue is now recognized as a major endocrine and signaling organ 39 Adipose tissue or fat is a poor heat conductor and it contributes to the thermal insulation of the body Adipose tissue also fills up spaces between other tissues and helps to keep some organs in place w There are two types of adipose tissue with different locations structures colors and pathologic characteristics w White adipose tissue the more common type is composed of cells that when completely developed contain one large central droplet of Whitishyellow fat in their cytoplasm 39 Brown adipose tissue contains cells with multiple lipid droplets interspersed among abundant mitochondria which give these cells the darker appearance Both types of adipose tissue have a rich blood supply Adipose Tissue iv White adipocytes are called unilocular because triglycerides are stored in a single locus Since quotlipid is removed from cells by the alcohol and xylene used in routine histological techniques a unilocular adipoCyte appears in standard microscope preparations as a thin ring of cytoplasm surrounding the empty vacuole left by the dissolved lipid droplet sometimes referred to as the signet ring cell The large droplet causes these cells to have eccentric and flattened nuclei Figure 6 1 Figure 61 White adipose tissue Storage Mobilization of Lipids 5The White adipose tissue is a large depot of energy for the organism The lipids stored in adipose cells are chiefly triglycerides ie esters of fatty acids and glycerol Triglycerides stored by these cells originate in dietary fats brought to adipocytes as circulating chylomicrons in triglycerides synthesized in the liver and transported to adipose tissue in the form of very lowdensity lipoproteins VLDLs and by the local synthesis of free fatty acids and glycerol from glucose to form triglycerides Figure 62 Lipid storage and mobilization from adipocytes i4 theiadipocyte the fatty acids combine with glycerol phoSphate Supplied by glucose metabolism to form triglycerides Once again These are then deposited in the triglyceride droplets Mitochondria a n39dsmooth ER participate actively in the process of lipid uptake and storage Adi pOSe cells can synthesize fatty acids from glucose a process accelerated by insulin Insulin also Stimulates the uptake of glucose into adipocytes and increases the synthesis of lipoprotein lipase Insulin inhibits the hormonesensitive lipase reducing fatty acid release and also stimulates enzymes for lipid synthesis Glucagon and growth hormone promote triglyceride breakdown and release of fatty acids tissue also functions as an important endocrine organ Ad ip ocytes are the sole Source crime 116 kDa polypeptide hormone leptin Gr leptos thin a quotsatiety factorquot With target cells in the hypothalamus and other organs which regulates the appetite under normal conditions and participates in regulating the amount of adipose tissue w Histogenesis of White Adipose Tissue 9 Like the fiberproducing cells of connective tissue adip ocytes undergo differentiation from embryonic mesenchymal cells Such differentiation is first seen with the appearance of lipoblasts Early lipoblasts have the appearance of fibroblasts but are able to accumulate fat in their cytoplasm Lipid accumulations are isolated from one another at first but soon fuse to form the single larger droplet that is characteristic of unilocular adipose tissue cells Figure 6 3 Figure Development of white and brown fat cells i I Visceral Hfumanssareones few mammals born with fat quot begin to accumulate at week 30 of on and a frequotwelldeve0ped by birth in both the and subcutaneous compartments After birth thedevejlopmen tjof new adipocytes is common around small blood vessels where undifferentiated mesenChymal cells are fairly abundant 39EXi csfezsstiVe formation of adipose tissue or obesity oscurs when energy intake exceeds energy expenditure Although fat cells can differentiate from mesenchymal stem cells throughout life adultonset obesity is generally believed to involve largely increased size or hypertrophy in existing adipocytes h ypertrophic obesity Childhood obesity can involve both increased adipocyte size and formation of new adipocytes by differentiation and hyperplasia of preadipocytes from mesenchymal cells This early increase in the number of adipocytes may predispose an individual to hyperplastic obesity in later life tl Brown Adipose Tissue The color of brown adipose tissue or brown fat is due to both the numerous mitochondria containing colored cytochromes scattered through the adipocytes and the large number of blood capillaries in this tissue Adipocytes of brown fat contain many small lipid inclusions called multilocular Figure 63 The many small lipid droplets abundant mitochondria and rich vasculature all help mediate this tissue39s principal function of heat production In comparison with white adipose tissue which is present throughout the body brown adipose tissue has a much more limited distribution Cells of brown adipose tissue cells are polygonal and generally smaller than cells of white adipose tissue but their cytoplasm contains a great number of lipid droplets of various sizes Figure 6 4 These a39dip39ocytes have spherical and central nuclei and the numerous mitochondria have abundant long cristae Function of Brown Adipocytes The main function ofthe m ultilocular adipose cells to produce heat by nonshivering t hermogenesisv Heat productiOn is increased in these cells because the mitochondria have in their inner membrane a transmembrane protein called thermogenin or uncoupling protein UCP1 a marker unique to brown fat Thermogenin permits the backflow of protons previously transported to the intermembranous space without passing through the ATPsynthetase system in the mitochondrial globular units Histogenesis of Brown Adipose Tissue Brown adipose tissue also develops from embryonic mesenchyme that emerges earlier than white fat during fetal development lts cells become arranged differently from white adipose ssue The number of brown adipocytes increases agaijnjaoil39uiring cold adaptation usually appearing clusters Ofmultilocular cells in white adipose tissue This likely represents differentiation of mesenchymal stem cells within the white adipose tissue Transformation of one type of adipose tissue directly to the other apparently does not occur Besides stimulating thermogenic activity autonomic nerves also promote brown adipocyte differentiation and prevent apoptosis in mature brown cells


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