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Long bone overgrowth and joint laxity are hallmark features with limbs that are disproportionately long relative to the trunk. Lined by a mucous membrane, it contains three auditory ossicles and communicates with the nasopharynx via the auditory (eustachian) tube. Wright and Giemsa stains, used in hematology for blood and bone marrow smears, contain eosin and methylene blue, so protein stains pink and nuclei, bluish purple. Histologically benign (G0); variable clinical course and biologic behavior Stage 1. At the same time, the calcified septa gradually become thinner until they disappear altogether. High estrogen levels have been associated with increased number of autoreactive B lymphocytes, a predominantly Th2 response, and increased antibody production. Also, obstruction and resultant infection of Meibomian sebaceous glands in the eyelid form a hard, painless, nodular swelling under the palpebral conjunctiva called a chalazion. The apical dendrite of each cell ends as a bulbous olfactory knob, which extends above the epithelial surface. Low-dose aspirin may lower the thrombotic risk, has a low incidence of adverse side effects, and is inexpensive. Although percutaneous needle biopsy is less invasive, open surgical biopsy is usually recommended because a larger specimen can be obtained. A large dendrite projects apically, is oriented at right angles to the surface, and branches repeatedly as it climbs to the surface. The principles of tendon repair therefore include thorough debridement of the wound, precise anatomic reapproximation, and protected active range of motion during healing to help maintain the mobility essential for normal function. Renin is also engaged in feedback control of glomerular filtration rate in individual nephrons via the renin-angiotensin system. The most striking feature of these cells is the presence of numerous vesicles, which are free in the cytoplasm or closely associated with luminal and abluminal cell surfaces and whose main function is to transport fluid and proteins between blood and surrounding interstitium. The rectangle marks a sarcomere, each of which are delineated by successive Z bands (Z). Primary functions of the synovium are to produce synovial fluid and to remove cellular and connective tissue debris from joint cavities. NervousTissue 121 Purkinje cells (inhibitory) Dendrites of Purkinje cell Molecular layer Purkinje cell layer Granular layer White matter Area of the cerebellum delineated by the rectangle is seen in the micrograph below. In tetralogy of Fallot, blood is shunted through a ventricular septal defect from the pulmonary circulation to the systemic circulation because of right ventricular outflow obstruction. Other common sites are the distal radius, proximal humerus, distal tibia, and sacrum. Cutaneous neurofibroma "nodules" (fibroma molluscum), pigmented nevi, elephantiasis, and verrucous hyperplasia are other characteristic skin lesions. They form in many locations, including the vertebral column, neck, shoulders, and knee. Brush cells (Blue) are fewer in number and are thought to represent less than 5% of the epithelial cell volume. If bradycardia does develop, drugs that exert their effect by blocking the parasympathetic branches of the autonomic nervous system. Later, lateral and cephalocaudal folding forms a long, cylindrical endodermal tube extending the length of the embryo; this becomes the primitive gut tube and then the digestive tract. The nutrient artery passes obliquely through the nutrient foramen of the bone, without branching and in a direction that usually points away from the end of the bone, where the greatest amount of growth is occurring at the epiphyseal plate. The synovial proliferation along with the microvascular process called angiogenesis may behave like a benign tumor, which is partly caused by defects of some apoptotic genes and their molecules. The diagnosis of von Recklinghausen neurofibromato sis in a child requires a high index of suspicion. Turnover and transit times may be even more rapid in some diseases, such as psoriasis, in which transit time is about 8 days. Thereafter, a slower, longer-lasting bone loss continued and ended at 32 weeks of immobilization, with bone mass levels reaching a plateau at approximately 50% of original values. Radiographs should be taken with the neck in flexion, extension, and neutral position.
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The two growth plates in a typical long bone are peripheral extensions of the primary ossification center. Surface features of olfactory cells that bear tangled cilia (arrows), sustentacular cells with short microvilli, and mucous droplets that had been discharged from glands of Bowman are in the field. The primary focus is preservation of endorgan function to prolong survival and to enhance quality of life. In the later, sustained-loss phase, the periosteal envelope was affected, resulting in a smaller bone with a slightly widened medullary canal and a thinner, more porous cortex. Benzocaine does promote the formation of methemoglobin but is not alone in that regard, as prilocaine also causes formation of methemoglobin. It is characterized by congenital skeletal malformation of the great toes, with episodes of painful soft tissue swelling that lead to severe progressive ossification of the soft tissues usually beginning in late childhood. An abrupt transition (double arrows) from simple columnar (left) to stratified columnar (right) epithelium occurs in this part of the pectinate line. Muscle fibers undergo repair and remodeling via an increase in protein synthesis and activation of satellite cells. Matrix vesicles are rich in various phosphatases, some of which act as a pyrophosphatase to destroy pyrophosphate, another inhibitor of calcium-phosphate precipitation. Within the fascicle are nuclei of occasional fibroblasts, Schwann cells, and capillary endothelial cells between nerve fibers. These injuries can compromise the overlying skin and soft tissue if not addressed surgically and present a risk for infection and a challenge in planning for operative fixation of underlying fractures. A genetic predisposition is an important factor in determining the immune response to the still-unknown initiating factors. In glycolysis, glucose-6-phosphate, derived either from the degradative phosphorylation of glycogen or from the phosphorylation of glucose in serum, is broken down into two molecules of acetyl coenzyme A (CoA). Leydig (interstitial) cells produce testosterone, the hormone responsible for male secondary sex characteristics. Terminal branches of portal veins, about 300 mm in diameter, regularly give off inlet venules, which empty into thin-walled, fenestrated hepatic sinusoids that are in intimate contact with hepatocytes. Axonal swellings have prominent mitochondria and many microtubules for axoplasmic transport. A single impulse in the motor nerve results in contraction of the muscle fiber in an all-or-nothing fashion. It also harbors capillaries and lymphatics plus many lymphocytes and other cells, which aid in immunologic defense 12. They have all organelles needed for two types of secretions-merocrine and apocrine. Chromaffin cells of the adrenal medulla stain yellow-brown, which indicates the presence of epinephrine and related compounds. The nodules, in the lamina propria, protrude into the lumen, thereby narrowing it so it has a slit-like, stellate appearance. The fourth, outer layer is an adventitia (or serosa), which consists mostly of loose connective tissue with autonomic nerves and plexuses, blood vessels, and lymphatics. In addition to the synoviocytes, cell infiltrates including neutrophils, lymphocytes, and plasma cells also contribute to the synovial hypertrophy. If this happens, the vena caval cannula should be withdrawn to a more proximal position, and the adequacy of the venous return from the patient to the cardiopulmonary bypass machine should be confirmed. Each day, lymphatics return about 40% of total plasma protein to veins and permit entry of chylomicrons and immuno- 8. Differentiating these two conditions can be complex, yet is crucial because of contrasting therapy and prognosis. The side effects are similar among all and include injection or infusion reactions, infections, and, rarely, demyelinating diseases and malignancies. Regional bone loss may be seen in post-traumatic events, such as fracture, transient osteopenia, and reflex sympathetic dystrophy. As in other parts of the digestive tract, elements of the enteric nervous system are seen: the myenteric plexus between the two smooth muscle layers, and the submucosal plexus in the submucosa. In lamellar bone, collagen fibers are in parallel layers, which are readily apparent when viewed by polarization microscopy. Protruding into the posterior chamber, it is covered by double-layered epithelium. Photomicrograph of decalcified trabecular bone showing relationship of trabeculae to marrow (H & E, x35).
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Nuclear atypia, mitoses, and multiple nuclei not significant in children but suggest malignancy in adults (H & E stain). During the seventh week, the primordia of many of the smaller bones of the hand and foot are present. Provitamin D2 (ergosterol) is ingested or provitamin D3 (7-dehydrocholesterol) is synthesized from cholesterol by the liver, and both are stored in the skin. Their blind ends are initially solid and become the secretory acini by forming a central cavity. The foot is nearly always involved in arthrogryposis; most common is rigid club foot (equinovarus). Superimposed on the basilar membrane is highly specialized epithelium-the organ of Corti-that consists of hair cells and supporting cells. Nodules located over the knuckles, toes, or knees may restrict motion in the underlying joint. The Chvostek or Trousseau sign may be elicited even in patients with asymptomatic hypocalcemia. Ending freely among epithelial cells without any structural specialization, they act as nociceptors or respond to thermal stimuli. Like astrocytes of the central nervous system, pituicytes and their processes ensheath and support axons. In other lacunae, chondrocytes shrank away from walls to leave a clear pericellular halo. Methotrexate has been studied in retrospective trials, with response rates up to 80%, including patients who had failed corticosteroid therapy. Myocardial wall tension is directly related to the end-diastolic ventricular pressure or volume (preload) and systemic vascular resistance (afterload). Near the cell periphery are scattered profiles of sarcoplasmic reticulum and small invaginations of the sarcolemma, or caveolae, that play a role in calcium regulation during contraction. If these parts have normal sensa tion and if the proximal joints can place the hand or foot in the desired position, functional activities can be performed with some skill. Posteriorly, trachealis muscle fibers, stretched between the free ends of the cartilage rings, run in a transverse and oblique longitudinal orientation. The duct of a serous gland of von Ebner delivers watery secretions to the sulcus to cleanse the taste buds. Mild-to-moderate anemia is typical of active disease, with the exception of mild cases, and is largely due to a relative failure of bone marrow production because of increased uptake and abnormal storage of iron by the reticuloendothelial system and the phagocytic cells of the inflamed, hyperplastic synovial membrane. Laboratory tests to identify common causes of secondary osteoporosis include a complete blood cell count and differential, erythrocyte sedimentation rate, routine chemistry profile, 25-hydroxyvitamin D level, thyroid stimulating hormone, parathyroid hormone, and 24-hour urine for measurement of calcium excretion. In general, the speed or onset of action of local anesthetics is related to the pKa of the drug. The veins form an extensive hemorrhoidal venous plexus, which may develop varicosities and lead to internal hemorrhoids. Type B cells are most important because of their ability to secrete prostaglandins, collagenase, hyaluronan, and many other components of joint fluid. Although the fat cell is sometimes thought of as a type of fibroblast, it is increasingly being regarded as a separate cell type that, when it does not contain lipid, resembles a fibroblast. Other parts of the colon, however, are invested by an incomplete serosa and suspended by mesentery. In 1616, he aptly described the heart as a pump and the direction of blood flow in arteries and veins. As development proceeds to the time of birth, hydroxyapatite emerges as the dominant component of bone mineral. This tissue becomes more fibrous and then develops around and between fragment ends to form a bridge, or callus, to unite the fragments. Hormones, such as insulin, and the sympathetic nervous system, which innervates adipose tissue, control these activities. Its core has an axoneme with two central microtubules and nine peripheral microtubular doublets, which provides substrate for sperm tail motility. Note that in skeletal muscle, influx of extracellular calcium is not required for muscle contraction, unlike the case for motor nerve terminals.
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They develop in the embryo as invaginations of epidermis, independent from pilosebaceous units, into underlying dermis. The mechanical stresses on the skeleton, as the infant begins to acquire increasing voluntary neuromuscular function during its first 2 years, serve to stimulate skeletal growth, ossification, and especially remodeling. Amputation should be considered only if there is neurovascular insufficiency, loss of skin cover, or infection and never if there is good skin cover with sensation. The mucosa consists of prominent nonkeratinized stratified squamous epithelium, 150-200 mm thick, and an underlying lamina propria. In the radial clubhand the forearm is short, the hand deviates radially, and the thumb is absent (see Plate 446). Example 6 illustrates normal bone resorption paired with an increase in the rate of bone formation, which leads to a net increase in bone mass with time. Involvement of the orbit may compress the optic nerve or interfere with function of the extraocular muscles. Deep infoldings (arrows) of plasma membrane invaginate the basal aspect and interdigitate extensively with those of adjacent cells. Instead of biconcave discs, they become crescent-shaped sickle cells, which lose malleability and malfunction. Fever, malaise, anorexia, or weight loss may occur in about one third of patients. Surgery is reserved for patients with severe tendon damage who are unlikely to respond to other treatments. Power muscles such as the biceps would be trained with high force or load and a low number of repetitions. The muscularis mucosae has two illdefined layers of smooth muscle cells, arranged helically and longitudinally, that contract to allow localized movements and folding of the mucosa. Subepithelial mucous and serous glands liberate their secretions onto the mucosal surface to also aid in entrapment of particulate matter, lubrication, and moistening. The knee appears "back ward" and hyperextended, with the examiner typically able to further extend the leg until it nearly touches the chest. Networks of these small vessels form deep plexuses in the reticular dermis and superficial plexuses in the papillary dermis, which are connected by communicating vessels. Once the triple helix is formed, procollagen is transported from the rough endoplasmic reticulum to the Golgi apparatus and packaged for secretion by exocytosis. Platelets (Pl) are round to oval discs containing a dark-staining central granulomere surrounded by a homogeneous, pale hyalomere. In the polydactylous deficiency, supernumerary bony ele ments are present in the hand, creating a cleft of soft tissue and the appearance of a lobster claw. Each cell has a nucleus that varies in form and may have an oval, kidney, or horseshoe shape. The most striking character istic is the extreme density (increased radiopacity) of the bone. Two proteins associated with actin, tropomyosin and the troponin complex, respond to varying calcium ion concentrations by acting as a switch to enable or disable the interaction and formation of cross bridges between actin and the myosin heads. Inadequate aldosterone levels interfere with renal fluid and electrolyte balance, thereby lowering systemic blood pressure and contributing to circulatory shock. Spine Involvement Degenerative disease of the spine occurs to some degree in almost every person past middle age, but the severity and speed of progression vary greatly. Short upper and lower limbs with relatively long trunk, normal head circumference, and marked knock-knee (genu valgum) Grebe chondrodysplasia Partial cleft of upper lip Acromesomelic dysplasia the rare Grebe chondrodysplasia is transmitted as an autosomal recessive trait. Metastasis after age 40 is usually sec ondary to the primary carcinomas mentioned earlier.
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Additional circumferential lamellae formed by periosteum Area of bone resorption produced by osteoclastic activity of modulated progenitor cells of original osteonal canal and by osteoclastic activity of area osteocytes d1 c1 a2 a1 Marrow cavity b2 b1 c2 c1 Second-generation osteon formed in resorbed area of original primary osteon C. Children with macrophage activation syndrome commonly present with culturenegative septic shock and signs of cardiovascular collapse. They are used for prolonged anaerobic activities with a relatively high force output, such as racing 400 m. This appearance is gradually lost in distal bronchi as cells become simple columnar and then cuboidal. The various nephron segments differ in function, distribution of transport proteins, and responsiveness to hormones and drugs such as diuretics. Therefore, the phrenic nerves and the muscular diaphragm used for breathing, and the sensory nerves of the lips, mouth, and throat, as well as the striated muscle with their motor nerves of the lips, tongue, jaws, and throat used for the complicated reflex functions of suckling and swallowing, are functionally well developed at birth. The major function of calcitonin, a hormone secreted by the parafollicular cells of the thyroid gland, is to inhibit osteoclastic bone resorption in response to elevated serum calcium levels. Similar to melanocytes, they are not linked by desmosomes to adjacent keratinocytes and possess slender dendritic processes emanating from a spherical cell body. Optimum biopsy samples contain both cortices and intervening cancellous bone in a single, unfragmented cylinder. The presence of a vertebral fracture on a radiographic image is termed prevalent if noted on the first film and incident if a new finding on subsequent radiographs. A prominent muscularis externa consists mainly of smooth muscle oriented in different directions. Lacuna Mineralized bone matrix (organic osteoid and collagen fibers impregnated with hydroxyapatite crystals) Osteocytes (from osteoblasts) Extensions of osteocytes filling canaliculi Early stages of flat (membrane or dermal) bone formation Capillaries in narrow spaces A. The venules are thus more permeable than are capillaries in the cortex, and the medulla has no blood-thymus barrier. On the other hand, phosphate is present in almost all foods and dietary deficiencies are uncommon. Rapid delivery of hormones and regulatory factors to and from the anterior lobe and bloodstream thus occurs. It most often occurs in the distribution of the median nerve in the hand and the medial plantar nerve in the foot. Bone marrow stem cells are small, mononucleated, and not easily identified under the microscope, but their existence is inferred from in vitro cell cultures, which generate more mature, recognizable progenitor cells. Then, coiling of the otocyst, accompanied by a series of complex constrictions and outgrowths, gives rise to the saccule, utricle, three semicircular canals, and cochlea. Creatine kinase is the most sensitive and reliable enzyme tested and may be elevated before muscle weakness. Dosing and route of administration depends on the type and severity of organ involvement. Syndactyly is occasionally hereditary, and this type affects males more often than females and is rare in AfricanAmerican children. At first, symptoms tend to be epi sodic, transient, and fluctuating, but the waddling gait becomes more pronounced as the disorder progresses, and increased discomfort and stiffness force patients to limit their activities. If osteoid seams are deficient in mineral, the osteoid is incapable of binding tetracycline, leading to an absence of fluorescence. Each has a characteristic shape that is circumscribed by a connective tissue sheath. The mucous membrane of the larynx consists mainly of respiratory epithelium, but over the vocal folds it becomes nonkeratinized stratified squamous epithelium; this change is a function of active movement of the folds and wear and tear induced by friction. This drug is rarely used alone in a patient with a poor prognosis or high disease activity. Numerous guidelines have been published for the prevention and treatment of glucocorticoid-induced osteoporosis. They are embedded in fibromuscular stroma, dense with collagen and irregularly arranged smooth muscle.
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Histologic examination shows immature myxoid car tilage with stellate chondrocytes enmeshed in lightly staining myxomatous chondroid matrix. As the spaces accumulate fluid, they enlarge, become confluent, and give rise to a cavity-the follicular antrum. Meticulous detail is necessary to ensure follow-up scans measure the same area and same size region of interest, ensuring that real change has occurred in patients being observed or treated. Interstitial connective tissue shows nerve fibers, Schwann cell nuclei, and capillaries (C). Primary chondrosarcoma occurs most often in adults and tends to affect the pelvis, proximal femur, and shoulder girdle. The final common pathway of dysfunction, in its most extreme form, is termed "vasomotor paralysis. The maternal component of the placenta is the decidua basalis of the endometrium, which is the modified stratum basale in which the embryo is implanted. Defects develop in the surrounding fibrous material (anulus fibrosus), which becomes fibrillated. Many cases of dwarfism are the result of a rare genetic event, the spontaneous mutation. Malformations include deficient thenar muscles; short, floating thumb; deficient carpals, meta carpals, and radius; and classic radial clubhand. One consequence of space flight is a significant loss of bone mass (both matrix and mineral) in a weightless environment. The trapezius muscle, along with the upper five cervical spinal nerves, migrates to attach ultimately to the skull, the nuchal ligament, and the spinous processes of the seventh cervical to twelfth thoracic vertebrae. The outer aspect of the dura attaches to the periosteum of the skull; the inner dural surface is lined by a layer of flattened fibroblasts. The lamina propria is loose fibroelastic connective tissue richly endowed with capillaries, nerves, and small lymphatic channels. Leukocyte counts greater than 2,000/mm3 usually result in loss of transparency in the fluid, but confirmation that this is due to leukocytosis is important. In this type of defect, the epiphysis of the distal humerus is absent and the standard aboveelbow prosthesis is usually appro priate (see Plate 442). A tumor of mammotrophs, it leads to amenorrhea, infertility, osteopenia, and galactorrhea in women and erectile dysfunction and loss of libido in men. It is not a "diagnosis of exclusion" but in fact has a distinct phenotype, its own set of highly specific signs and symptoms. They are composed of aggregates of intermediate (cytokeratin) filaments of the cytoskeleton. This selective barrier, like the blood-brain barrier, sequesters a receptor from the external milieu. People living at such altitudes show a high incidence of carotid body tumors, named chemodectomas. Each gland, in the superior temporal part of the orbit, has the size and shape of an almond. Their density, location, and distribution in muscle fibers depend on muscle fiber type. Rhabdomyosarcomas occur primarily in children, and there has been a significant improvement in survival rates in patients with rhabdo myosarcomas primarily owing to the efficacy of multipleagent chemotherapy. For example, chronic urinary bladder inflammation (cystitis) caused by repeated urinary tract infections increases the risk for transitional cell carcinoma-the most common form of bladder cancer. Some perichondrium is retained at the periphery of the articular cartilage, which continues to form cartilage until the articular surface of the joint attains adult size. The lens placode bulges inward to become the lens vesicle, which then separates from corneal epithelium to become the biconvex lens. Pressure should be applied to the wound at once to stop bleeding, and tetanus prophylaxis must be confirmed or provided and in certain situations. The capsule comprises regularly arranged collagen and elastic fibers and provides external support and shape to the liver.
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Bone defect plugged with cement Specimen may be used for frozen section, fixation for histopathologic study, electron microscopy and study with special stains. Surrounding each fascicle is a very condensed layer of specialized connective tissue called the perineurium, which is made of multiple concentric layers of flattened perineurial cells with intervening, longitudinal collagen fibrils. Arteries and veins are classified into types that differ mainly in size, microscopic structure, and location; the scheme is arbitrary because gradual histologic changes occur along the length of the vessels. By the second trimester, the characteristic form and anatomic parts of the inner ear are established. Stimulation of the deep peroneal nerve causes extension of the toes by stimulating the extensor digitorum brevis muscles. High daily doses of antioxidants such as vitamin A may help slow disease progression. Surrounding myoepithelial cells (My) at the base of the acinus share a basement membrane with secretory cells. The functional characteristics of paracellular transport are determined by the tight junction, which differs greatly in its elaboration in the various tubular segments. The nuclei of the muscle fibers themselves, once in place, do not divide mitotically or amitotically; consequently, in order to increase their number, the incorporation of new myoblasts into the syncytia is required, especially when the fibers grow in length. The notochordal cells become temporarily intercalated in the endoderm, which forms the roof of the yolk sac. This area, known as the transformation zone, is subject to tumor formation and is the site of most cervical carcinomas. More commonly, however, the hips are both stiff and dislocated and radiographs reveal advanced and adaptive changes similar to those seen in the older child with classic congenital dislocation of the hip. Heat of sufficient intensity and duration causes coagulation necrosis and cell death, but the cell damage due to heat of lesser intensity is potentially reversible. A small Golgi complex, small numbers of mitochondria, and occasional lysosomes are also present. Exo External os External os Transformation zone Endo Cervical gland Endocervix Exocervix Schematic of the cervical squamocolumnar junction. On cross section, each thick filament is surrounded by six thin filaments and each thin filament is equidistant to three thick filaments. The secretory protein is thought to interact with spermatozoa and affect their mobility. These children usually develop compensatory skills at a very early age and they frequently become very adept at using their feet for prehension (see Plate 438). The first step in management is to assess the extent, depth, and stage of the lesion. Endothelium covering each leaflet is continuous with that lining the vessel lumen. Erythema and/or scaly, papular eruption around fingernails and on dorsum of interphalangeal joints Patients with idiopathic inflammatory myopathies usually present with an insidious progressive painless muscle weakness over a course of several weeks to several months. A macula hair cell has one kinocilium and many stereocilia that project into the gelatinous otolithic membrane. Defective chloride ion transport results in copious amounts of thick and sticky mucus, which predisposes patients to chronic lung infections, among other symptoms. After several attacks the gouty episodes tend to be more severe, last longer, and involve several additional joints, tendons, or bursae. At such sites, innervation of the cell has a relatively simple structure, and synapses are en passant (along its course). The latex fixation tests commonly used in the diagnosis of rheumatoid arthritis detect only the IgM class of rheumatoid factor, which is most prevalent; however, IgG and, to a lesser extent, IgA rheumatoid factors are also found. Epstein Barr virus causes hairy leukoplakia, which consists of white mucosal lesions on the tongue. Lamina propria of loose connective tissue underneath the epithelium contains numerous blood and lymphatic vessels, nerves, and scattered mononuclear connective tissue cells.
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On entering the tuft, the afferent glomerular arteriole immediately divides into up to five primary capillary branches, each of which gives rise to an anastomosing capillary network representing a Inner medulla 4 5 12 1. Scoliosis and anomalies of the mandible, teeth, and small bones of the hands and feet occur in severely affected patients. Each cell has a basal euchromatic nucleus and cytoplasm filled with many tightly packed organelles. Large, pleomorphic Purkinje fibers stain intensely red to magenta due to abundant glycogen in their sarcoplasm. In the cervical spine, compression of the spinal cord from large osteophytes or from displaced degenerated discs may lead to serious neurologic complications manifested by upper motor neuron or long tract signs. In the fingers, some or all of the proximal interphalangeal joints are often bilaterally affected whereas the distal interphalangeal joints are seldom involved. They are holocrine glands in which part of the secretory product, known as sebum, is made of lipid-rich decomposed cells. They have no connection with the ribs or with each other, and their formation is independent of any sclerotomal derivatives. Goblet cells constitute about 20%-30% of cells in the more proximal airways and decrease in number distally. The initial block wears off over a 24-hour period, during which time neurolysis occurs. A round central nucleus sits in cytoplasm containing many mitochondria (Mi) and an extensive canalicular system (Ca) of smooth-surfaced membranes. In bone, osteoclastic activity is stimulated via a complex "coupling" mechanism involving interactions with osteoblasts. Congenital megacolon (Hirschsprung disease)-the most common gut motility disorder caused by failure of migration of neural crest cells to the hindgut during weeks 5-12 of gestation-leads to partial or complete obstruction, usually of the sigmoid colon and rectum, with aganglionic segments that lack Meissner and Auerbach plexuses. During fetal development, the space between the two layers disappears when they become apposed, but they may separate if fluid (such as vitreous, blood, or exudate) accumulates in the potential space. Both open and closed patterns likely operate at different times, according to physiologic conditions. Although patients will benefit to various degrees from nonpharmacologic approaches, most patients, unfortunately, will require analgesic and antiinflammatory medicines. The tendinous intersections (inscriptions) are indicative of the original segmental character of the rectus abdominis muscle (see Plate 1-16). The diagnosis is via endoscopic ultrasonography and fecal elastase-1 assay to evaluate steatorrhea. Interdigitation of thick and thin filaments allows sarcomere contraction, which is best explained by the sliding filament model in which actin filaments slide along myosin filaments. The skeleton plays a vital role in the regulation of calcium metabolism, which is fully described in Section 3, Metabolic Diseases. The skeletal deformities that can result include bowing of the long bones, increased skull size, dilated skull veins, hearing loss, and increased skin temperature over the affected long bones. Osteomalacia is the consequence of insufficient mineralization, so undecalcified sections show an increase in the proportion of unmineralized bone compared with normal bone. Interdigitating lateral borders of two perineurial cells (Pe) show focal adherens junctions (rectangle). Adventitial reticular cells, which are modified fibroblasts, have many branching processes and produce the reticular fiber network that supports hematopoietic cells. The most common adult muscular dystrophy, it often occurs in early adulthood and has an extremely variable degree of severity. The synovial membrane becomes edematous and infiltrated primarily with neutrophils and mononuclear cells. Through the process of coupling, bone formation increases and osteoblasts are stimulated to fill in the resorption defect, although this repair may not be complete in the elderly. The palpebral epithelium rests on richly vascularized dense connective tissue replete with elastic fibers and lymphocytes.
