By W. Masil. North Carolina School of the Arts.
Cytology © The McGraw−Hill Anatomy buy 250 mg famciclovir with amex antiviral for cold sores, Sixth Edition of the Body Companies, 2001 Chapter 3 Cytology 61 (a) (b) FIGURE 3. Peroxisomes also contain the enzyme catalase, Fibrils and Microtubules which breaks down excess hydrogen peroxide into water and Both fibrils and microtubules are found throughout the cyto- oxygen so that there is no toxic effect on other organelles within plasm. The fibrils are minute rodlike structures, whereas the mi- the cytoplasm. Both provide the cell with support by forming Centrosome and Centrioles a type of cytoskeleton. Specialized fibrils called myofilaments are The centrosome (central body) is a nonmembranous spherical particularly abundant in muscle cells, where they aid in the con- mass positioned near the nucleus. Microtubules are also involved in the of rodlike structures called centrioles (sen′tre-o¯lz) (fig. The wall of each centri- They are especially abundant in the cells of endocrine organs, ole is composed of nine evenly spaced bundles, and each bundle where they aid the movement of hormones to be secreted into contains three microtubules. Microtubules in certain cells provide flexible support Centrosomes are found only in those cells that can divide. During the mitotic (replication) process, the centrioles move away from each other and take positions on either side of the nu- Cilia and Flagella cleus. They are then involved in the distribution of the chromo- Although cilia and flagella appear to be extensions of the cell somes during cellular reproduction. Mature muscle and nerve membrane, they are actually cytoplasmic projections from the in- cells lack centrosomes, and thus cannot divide. These projections contain cytoplasm and sup- portive microtubules bounded by the cell membrane (fig. Vacuoles Cilia and flagella should not be confused with microvilli or with Vacuoles (vak′yoo-o¯lz) are membranous sacs of various sizes that stereocilia, both of which are specializations of cell membranes. They are formed when a Cilia (sil′e-a˘) are numerous short projections from the ex- portion of the cell membrane invaginates and pinches off during posed border of certain cells (fig. Vacuolation is initiated either by pinocytosis (pin″o˘- spersed with mucus-secreting goblet cells. There is always a film si-to′sis), in which cells take in minute droplets of liquid through of mucus on the free surface of ciliated cells. Ciliated cells line the cell membrane, or by phagocytosis (fag″o˘-si-to′sis), in which the lumina (hollow portions) of sections of the respiratory and re- the cell membrane engulfs solid particles (fig. The function of the cilia is to move the mucus may contain liquid or solid materials that were previously outside and any adherent material toward the exterior of the body. Flagella (fla˘-jel′a˘) are similar to cilia in basic microtubular structure (see fig.
Naturally occurring cellular death discount 250 mg famciclovir with mastercard acute hiv infection neurological symptoms, disease, or trauma division rates, or it may be a matter of days or even years for from surgery or injury may necessitate mitosis in these organs. At the end of G1, the centrioles replicate in prepara- Still other cells, such as muscle or nerve cells, lose their mitotic tion for their role in cell division. Trauma to these cells fre- phase, the DNA in the nucleus of the cell replicates, so that the quently causes a permanent loss of function. During the G2 (second growth) phase, the enzymes and dence suggests that mitotic ability is genetically controlled and, other proteins needed for the division process are synthesized, for those cells that do divide, even the number of divisions is and the cell continues to grow. If this is true, it may be a factor in the aging The actual division of a cell is referred to as the mitotic process. Physical stress, nutrition, and hormones definitely have phase, or simply M phase (fig. It is thought that the replication ac- ther divided into mitosis and cytokinesis. Mitosis is the period tivity of cells might be controlled through a feedback mechanism of a cell cycle during which there is nuclear division and the involving the release of a growth-inhibiting substance. Such a sub- duplicated chromosomes separate to form two genetically iden- stance might slow or inhibit the cell divisions and growth of par- tical daughter nuclei. The process of mitosis takes place in four ticular organs once they had amassed a certain number of cells or successive stages, each stage passing into the next without had reached a certain size. These stages are prophase, Except for cells on exposed surfaces, most cells of the body metaphase, anaphase, and telophase (fig. Cytokinesis are located in a fairly homogeneous environment, where contin- (si″to-kı˘nésis) is division of the cytoplasm, which takes place ual adaptation to change is not necessary for survival. Prolonged exposure to sunlight, for example, stimulates the syn- cytokinesis: Gk. Cytology © The McGraw−Hill Anatomy, Sixth Edition of the Body Companies, 2001 Chapter 3 Cytology 71 FIGURE 3. Cytology © The McGraw−Hill Anatomy, Sixth Edition of the Body Companies, 2001 72 Unit 3 Microscopic Structure of the Body friction to the skin stimulates mitotic activity and the synthesis Energy deficit means that more energy is required by a cell of a fibrous protein, keratin, which results in the formation of a than is available. Hypertrophy (hi″pe′rtro˘-fe) refers to an in- when the cells do not have enough glucose or oxygen to allow crease in the size of cells resulting from increased synthesis of for glucose combustion. Examples of energy deficits are low levels protein, nucleic acids, and lipids. Cellular hypertrophy can be ei- of blood sugar (hypoglycemia) and the impermeability of the cell ther compensatory or hormonal. Compensatory hypertrophy oc- membrane to glucose (as in diabetes mellitus).
In a second study of 33 patients with osteogenic methylene diphosphonate uptake in primary osteosarcoma cheap famciclovir 250mg on-line an antiviral agent quizlet. J sarcoma or Ewing’s sarcoma, the ratio of pre- Nucl Med 43:1012-1017 therapy/post-therapy SUVs significantly correlated with 19. Wolf RE, Enneking WF (1996) The staging and surgery of musculoskeletal neoplasms. Orthop Clin North Am 27:473-481 histological outcome of neoadjuvant therapy. Schulte M, Brecht-Krauss D, Heymer B et al (2000) Grading Ultimately, 18-FDG PET may provide the means to as- of tumors and tumorlike lesions of bone: evaluation by FDG sess effectiveness of therapy early after initiation, and PET. J Nucl Med 41:1695-1701 therefore direct changes in treatment regimens in order 21. Aoki J, Watanabe H, Shinozaki T et al (2001) FDG PET of pri- to achieve optimal pre-surgical necrosis. Aoki J, Watanabe H, Shinozaki T et al (1999) FDG-PET in dif- ferential diagnosis and grading of chondrosarcomas. Ries LAG, Kosary CL, Hankey BF et al (1999) SEER Cancer Quantitative evaluation of skeletal tumors with dynamic FDG Statistics Review 1973-1996. CA Cancer J Clin 50:7-33 (2002) The role of quantitative (18) F-FDG PET studies for the 3. J Nucl Sim FH (ed) Diagnosis and management of metastatic bone Med 43:510-518 disease: a multidisciplinary approach. Robbins SG, Lane JM, Healey JH et al (1993) Metastatic bone cutaneous needle biopsy in the management of primary bone disease. Cancer 43:735-744 Lane JM, Healey JH (eds) Diagnosis and management of 26. Fraser-Hill MA, Renfrew DL (1992) Percutaneous needle pathologic fractures. Fraser-Hill MA, Renfrew DL, Hilsenrath PE (1992) Classification of Tumors of Bone: Introduction. CDM, Unni KK, Mertens F (eds) World Health Organization Cost-effectiveness. Stoker DJ, Cobb JP, Pringle JAS (1991) Needle biopsy of mus- soft tissue and bone. IARC, Lyon, pp 226-232 culoskeletal lesions: A review of 208 procedures.
Any opening in the vascular network membrane by cellular processes set in motion by factors may lead to massive bruising or blood loss if left unrepaired buy cheap famciclovir 250 mg on line hiv infection rate unprotected. In turn, activated endothelial cells injury, components of the hemostatic system are activated. They may be activated on exposure to for- forming a bridge between cell surface receptors and colla- eign surfaces during bleeding, or by torn tissue at the site of gen in the subendothelial matrix. The protein thrombin, injury, or by products released from the interior of dam- which is generated by the plasma coagulation cascade, is a aged cells. Hemostasis can be viewed as four separate but potent activator of platelet adherence and secretion. Rup- interrelated events: tured cells at the site of tissue injury release adenosine • Compression and vasoconstriction, which act immedi- diphosphate (ADP), which causes platelets to aggregate at ately to stop the flow of blood the damaged site. These aggregates effectively stop the • Formation of a platelet plug flow of blood from the ruptured vessels. The fibrin network traps red cells, leuko- exerted by the tissue around the injured area, and vasocon- cytes, platelets, and serum at sites of vascular damage, striction. The degree of compression varies in different tis- thereby forming a blood clot. The stable, fibrin-based sues; for example, bleeding below the eye is not readily de- blood clot eventually replaces the unstable platelet ag- terred because the skin in this area is easily distensible. Fibrin is Back-pressure increases as blood which leaks out of the dis- an insoluble polymer of proteolytic products of the rupted capillaries accumulates. Fibrin molecules are cleaved uterus after childbirth, contraction of underlying muscles from fibrinogen by thrombin, which is generated in compresses blood vessels supplying the tissue and mini- plasma during clotting. Damaged cells at the site of tissue injury mation, thrombin cleaves four small peptides (fib- release potent substances that directly cause blood vessels rinopeptides) from each molecule of fibrinogen. The fib- to constrict, including serotonin, thromboxane A2, epi- rinogen molecule devoid of these fibrinopeptides is nephrine, and fibrinopeptide B. The fibrin monomers sponta- neously assemble into ordered fibrous arrays of fibrin, resulting in an insoluble matrix of fibrous strands. At this Platelets Form a Hemostatic Plug stage, the clot is held together by noncovalent forces. First, they form plasma enzyme, fibrin stabilizing factor (Factor XIII), multicellular aggregates linked by protein strands at sites of catalyzes the formation of covalent bonds between CHAPTER 11 Blood Components, Immunity, and Hemostasis 207 strands of polymerized fibrin, stabilizing and tightening the blood clot. Blood clotting is mediated by the sequential activation of a series of coagulation factors, proteins synthesized in the liver that circulate in the plasma in an inactive state. They are referred to by number (designated by a Roman numeral) in a sequence based on the order of the discovery of each factor. The plasma coagulation factors and their common names are listed in Table 11. The sequential activation of a series of inactive mole- cules resulting in a biological response is called a metabolic cascade. The sequential activation of coagulation factors resulting in the conversion of fibrinogen to fibrin (and, hence, clotting) is called the coagulation cascade.
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