By S. Lukar. University of Rochester.
The cells that produce cartilage are chondrocytes (KON-dro-sites) purchase 50mg dramamine free shipping symptoms uric acid, a name derived from the word root chon- dro purchase 50mg dramamine medications 2 times a day, meaning “cartilage” and the root cyto, meaning “cell. Cells Collagen ◗ Muscle Tissue Muscle tissue is designed to produce Elastic movement by contraction of its cells, fibers which are called muscle fibers because most of them are long and threadlike. The cells in skeletal muscle are very large and are remarkable in having Stored fat multiple nuclei and a pattern of dark and light banding described as C striations. This tissue gradually becomes has branching cells and specialized membranes be- impregnated with salts of calcium and phosphorus that tween the cells that appear as dark lines under the mi- make bone characteristically solid and hard. In the skin and membranes Greek word meaning “glue,” reveals its role as the main struc- covering muscles and organs, collagen fibers are arranged ir- tural protein in connective tissue. The result is a Fibroblasts secrete collagen molecules into the surrounding tissue that can resist stretching forces in many different direc- matrix, where the molecules are then assembled into fibers. Striations Nerves from even the most remote parts of the body come together and form a great trunk cable called the spinal cord, which in turn leads into Nuclei the central switchboard of the brain. Be- cause the outer layer of the brain has ◗ Nervous Tissue large collections of cell bodies and unmyelinated fibers, the brain is popularly termed gray matter, even though its The human body is made up of countless structures, both interior is composed of white matter (see Fig. For all the workers in the corporation to coordinate their ef- Nervous tissue is supported by specialized cells known as forts, there must be some central control, such as the neuroglia (nu-ROG-le-ah) or glial (GLI-al) cells, which president or CEO. Each structure of the body is in direct communica- Some of these cells protect the brain from harmful sub- TISSUES, GLANDS, AND MEMBRANES ✦ 65 4 and the movement of joints. Epithelial Gray matter membranes are of several types: ◗ Serous (SE-rus), membranes line the White matter walls of body cavities and are folded back onto the surface of internal or- gans, forming their outermost layer. The thin epithelium of serous mem- A more detailed discussion of nervous tissue and the branes is a smooth, glistening kind of tissue called nervous system can be found in Chapters 9 and 10. Their properties vary: covers the organs of the abdomen, and forms supporting some are fragile, others tough; some are transparent, oth- and protective structures within the abdomen (see Fig. They may contain cells that secrete lubricants to forms the lining of a closed cavity, while another part ease the movement of organs, such as the heart and lung, folds back to cover the surface of the organ contained in 66 ✦ CHAPTER FOUR that cavity. The relationship between an organ and the fibrous sac (the fibrous pericardium) that encloses the serous membrane around it can be visualized by imagin- heart (see Fig. Because internal organs are called viscera, the portion Your fist is the organ and the serous membrane around it of the serous membrane attached to an organ is the vis- is in two layers, one against your fist and one folded back ceral layer. Portions of the peritoneum that cover organs in the ab- The portion of the serous membrane attached to the domen are named according to the particular organ in- wall of a cavity or sac is known as the parietal (pah-RI- volved. Parietal pleura lines the normally are in direct contact with a minimal amount of thoracic (chest) cavity, and parietal pericardium lines the lubricant between them. The cells that line the nasal cavities and the passageways of the respiratory tract are supplied with tiny, hairlike extensions called cilia, described in Chapter 3. For example, throat infections may travel along mucous Checkpoint 4-8 Epithelial membranes have an outer layer of membranes into other parts of the upper respiratory tract epithelium. TO-sus) (SLE) and rheumatoid (RU-mah-toyd) arthritis, may affect many parts of the body because collagen is the ◗ Synovial (sin-O-ve-al) membranes are thin connective major intercellular protein in solid connective tissue. Fascia is found in two regions: For a variety of reasons, the normal pattern of cell and tis- sue growth may be broken by an upstart formation of cells ◗ Superficial fascia is the continuous sheet of tissue that having no purpose whatsoever in the body. Benign tumors grow as a single mass within a tissue, lending them neatly to We are all familiar with a number of diseases that directly complete surgical removal. These range from the common cold, as growing in situ, meaning that they are confined to their which is an inflammation of the mucosa of the nasal pas- place of origin and do not invade other tissues or spread sages, to the sometimes fatal condition known as peri- to other sites. Of course, some benign tumors can be tonitis, an infection of the peritoneum, which can follow quite harmful; they may grow within an organ, increase rupture of the appendix and other mishaps in the ab- in size, and cause considerable mechanical damage. When the cancer cells reach their destina- voluntary muscle, it is common in some types of invol- tion, they immediately form new (secondary) growths, or untary muscle, particularly in the uterus (womb). In some cases, fluids can be blood are classified differently according to the cells in examined for signs of cancerous cells, as these cells which they originate as well as other clinical features. Usually, Pleural or peritoneal fluids also may be studied for signs a tumor of the nervous system originates in the support of cancerous cells (see Box 4-3, Histotechnologist). This method is most commonly ap- phatic tissue is called a lymphoma (lim-FO-mah), and plied to study of the breasts in the process of mammog- cancer of white blood cells is leukemia (lu-KE-me-ah). Other structures such as the lungs, nervous system, and digestive system also may be examined by Checkpoint 4-9 What is the difference between a benign and a malignant tumor? Everyone should be familiar with certain signs that may ◗ Computed tomography (CT) is the use of x-rays to indicate early cancer and should report these signs for further investigation by their healthcare provider.
Neurons in M1 project to pools of neurons in the brainstem and spinal cord where they directly or indirectly activate motor neurons projecting to muscles order dramamine 50mg mastercard treatment wpw. The experiments on motor system plasticity in rats have concentrated on the organizational changes in M1 that follow peripheral motor nerve injury dramamine 50mg amex treatment lyme disease. The focus of such studies has been to reveal changes in the functional organization of motor cortex in experiments where microelectrodes are systematically used to stimulate arrays of sites within M1. Such stimulations produce muscle movements, and the part of the body moved depends on the location stimulated in M1. Somatosensory inputs to M1 of mammals provide an organized representation or map of the cutaneous receptors of the opposite side of the body,6 and a similarly organized map of the movements of body parts on the opposite side of the body. Thus, the movement map in M1 of rats and other mammals proceeds from hindlimb movements medially, to face and tongue movements laterally. In microstimulation experiments, M1 can be divided into territories devoted to movements within major divisions of the body, such as forelimb or face, and the effects of the loss of motor neuron outputs to these body regions on the organization of the evoked movement map in M1 can be studied. However, the consequences of electrically stimulating any site in M1 depend on the param- eters of stimulation. High levels of current and long trains of current pulses produce complex sequences of movements often involving a number of body parts,8 while low levels of current and short sequences of pulses often produce movements or twitches in a few isolated muscles. Movement maps in M1 are typically based on low current levels that produce just noticeable movements of a body part or muscle. Thus, movement maps in mammals with motor nerve injury need to be interpreted concerning both the somatotopic pattern produced, and the levels of current needed to produce that pattern. The normal organization of M1 in rats is known from a number of studies using microstimulation at threshold levels. Both of these injuries sectioned the axons of a major motor neuron pool that was targeted directly or indirectly by corticospinal neurons in a well-deﬁned zone in M1. One prediction of post-surgical results would be that microstimulation of neurons throughout the deprived zone of M1 would fail to produce movements, unless perhaps very high levels of stimulating current were used. Instead, stimulations of the deprived M1 zone, at normal threshold levels of current, produced movements of body parts adjacent to the missing or denervated body part. When the motor nerve to the muscles that move the facial vibrissa was cut, stimulation of the deprived vibrissa cortex produced forelimb, eye, and eyelid movements. After forelimb amputation, stimulation of the deprived forelimb cortex moved the shoulder and stump of the missing limb (Figure 9. In a second set of experiments with a chronically implanted stimulating elec- trode, changes in muscle targets did not appear immediately after the stimulated location was deprived by nerve section, but forelimb activity could be evoked from vibrissa cortex within hours of vibrissa nerve section. Because of the rapid change in the organization of M1, the reorgani- zation was attributed to a rapid strengthening of existing synaptic contacts, rather than the formation of new connections that would likely take longer to grow and become functional. One mechanism proposed for such reorganization was the long-term potenti- ation (LTP) of horizontal connections that are intrinsic to M1 and interconnect functionally distinct sectors of M1. A dorsolateral view of a brain of a rat (above) shows the location of M1 relative to primary somatosensory cortex (S1) primary visual cortex (Vis. In normal M1 (left), electrical stimulation of microelectrode site in caudomedial M1 produces hindlimb movements, and more rostrally, trunk movements. A large caudal region is devoted to forelimb movements, including a medial zone for shoulder movements. More rostrally, a large region relates to facial vibrissa movements, and a narrow zone is for eye movements and eye blinks. Reduced neural activity in M1 would result in activity dependent reductions in the expression of the inhibitory neural transmitter, GABA, and receptors for GABA. However, sectioning sensory neurons only, while leaving motor nerves intact, would also reduce the activity in M1, but peripheral sensory nerve section by itself does not appear to produce reorganization in M1 of rats. Reorganization of motor cortex (M1) in rats has also been studied after the descending corticospinal tract in the lower thoracic spinal cord was cut. In these experiments, there were no rapid reorganizations of the motor cortex, as microstimulation of the hindlimb cortex after two days of recovery continued to produce no motor responses. However, after 4 weeks of recovery, microstimulation of the hindlimb cortex produced whisker, forelimb, and trunk movements, demonstrating a functional reorganiza- tion of the motor cortex. Anterograde tracing of corticospinal axons from the reorganized hindlimb portion of M1 indicated that many of these axons had sprouted into the cervical spinal cord. Thus, much of this slowly emerging reor- ganization of the motor cortex could be attributed to the growth of new connections so that corticospinal axons reached new motor neuron pools. In related experiments, transected hindlimb corticospinal axons sprouted to contact propriospinal neurons that projected past the lesion to lumbar motor neurons for the hindlimb.
The action ﬂow and glom erular ﬁltration m ay fall transiently cheap 50mg dramamine fast delivery medicine in balance, they of the nitrovasodilators depends on the intracellular generally return to predrug levels within an hour 50mg dramamine otc treatment plant. Clinical Uses Absorption, M etabolism, and Excretion D iazoxide is adm inistered intravenously for the treat- The onset of the hypotensive action of sodium nitro- m ent of hypertensive em ergencies, particularly m alig- prusside is rapid, within 30 seconds after intravenous nant hypertension, hypertensive encephalopathy, and adm inistration. Therefore, sodium nitro- whom it is adm inistered and rarely reduces blood pres- prusside m ust be adm inistered by continuous intra- sure below the norm otensive range. A fter the infusion is stopped, blood In patients with coronary insufﬁciency, a -blocker pressure returns to predrug levels within 2 to 3 m inutes. H owever, -blockers by the kidney, toxicities due to this com pound are m ost potentiate the hypotensive effect of diazoxide, and likely in patients with im paired renal function. The dose of diazoxide should also be lowered if Pharmacological Actions the patient has recently been treated with guanethidine or another drug that depresses the action of the sym pa- In contrast to hydralazine, m inoxidil, and diazoxide, thetic nervous system. Such drugs perm it a greater hy- sodium nitroprusside relaxes venules as well as arteri- potensive effect because they reduce the increase in oles. Thus, it decreases both peripheral vascular resist- cardiac output that norm ally partially counteracts the ance and venous return to the heart. This direct action, coupled with the neuroen- sym pathetic reﬂexes, so heart rate m ay increase follow- docrine reﬂexes that are activated by a decrease in pe- ing its adm inistration even though cardiac output is not 20 Antihypertensive Drugs 231 increased. Renal blood ﬂow rem ains largely unaffected that this therapeutic approach corrects the cause of the el- by sodium nitroprusside, because the decrease in renal evated pressure. O nly in a few speciﬁc cases, such as vascular resistance is proportional to the decrease in pheochrom ocytom a, can hypertension be directly re- m ean arterial pressure. A s with all vasodilators, plasm a lated to abnorm alities in the functioning of the sym pa- renin activity increases. Clinical Uses Sodium nitroprusside is used in the m anagem ent of hy- ADRENOCEPTOR ANTAGONISTS pertensive crisis. A lthough it is effective in every form The adrenoceptor-blocking agents are described in detail of hypertension because of its relatively favorable effect in Chapter 11, although their use in the treatment of hy- on cardiac perform ance, sodium nitroprusside has spe- pertension is brieﬂy described here. Drugs of this group cial im portance in the treatm ent of severe hypertension are subdivided into -adrenoceptor antagonists ( - with acute m yocardial infarction or left ventricular fail- blockers) and -adrenoceptor antagonists ( - blockers). Because the drug reduces preload (by venodila- tion) and afterload (by arteriolar dilation), it im proves ventricular perform ance and in fact is som etim es used -Blocking Drugs in patients with refractory heart failure, even in the ab- Phenoxybenzam ine and phentolam ine have been avail- sence of hypertension. The frequency of their use for Adverse Effects the treatm ent of prim ary hypertension has greatly di- The m ost com m only encountered side effects of sodium m inished in recent years because of the developm ent of nitroprusside adm inistration are nausea, vom iting, and drugs such as prazosin that are relatively selective for headache, which quickly dissipate when the infusion is 1-receptors. Thus, the stim ulation of the heart and tends for several days, there is som e danger of toxicity renin release, actions that lim it the usefulness of classi- owing to the accum ulation of its thiocyanate m etabo- lite. Thiocyanate intoxication includes signs of delirium cal -blockers, are less with 1-selective antagonists. If nitro- U nlike the vasodilators, which have a m ore prom i- nent effect on arterial beds than on venous beds, the - prusside is adm inistered for several days, thiocyanate blockers prevent vasoconstriction in both vascular beds. Prazosin and its derivatives that are selective for 1- adrenoceptors are quite useful for the m anagem ent of prim ary hypertension. The 1-receptor–selective antag- DRUGS THAT IM PAIR SYM PATHETIC onists can be used alone in m ild hypertension. W hen hy- NERVOUS SYSTEM FUNCTIONING pertension is m oderate or severe, prazosin is generally The drugs discussed in this section reduce blood pres- adm inistered in com bination with a thiazide and a - sure by depressing the activity of the sym pathetic nerv- blocker. This is accom plished in four ways: (1) by re- considerably potentiated by coadm inistration of thi- ducing the num ber of im pulses traveling in the azides or other types of antihypertensive drugs. Since prazosin does not signiﬁcantly inﬂuence diverse and m ay best be appreciated by considering the blood uric acid or glucose levels, it can be used in hy- sym pathetic arc concerned with blood pressure regula- pertensive patients whose condition is com plicated by tion (Fig. Prazosin treatm ent is associ- W hile there m ay be som e involvem ent of the adren- ated with favorable effects on plasm a lipids. Thus, it m ay ergic nervous system in prim ary hypertension, there is be of particular im portance in m anaging patients with no clear evidence that a m alfunction of this system is hyperlipidem ia. Therefore, Further inform ation about the pharm acokinetics, even though drugs m ay depress the sym pathetic system adverse reactions, and preparations of -blockers is and thus lower blood pressure, it should not be assum ed given in Chapter 11. NTS, nucleus of the tractus solitarii; VMC, vasomotor center; ACh, acetylcholine; NE, norepinephrine;, -adrenoceptors;, - adrenoceptors; P2,P 2-purinoceptors; ATP, adenosine triphosphate.