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Venous return from the bronchial cir- culation is by two routes: bronchial veins and pulmonary gree of physiological dead space as well as physiological veins 20 mg tamoxifen otc menstruation gas. About half of the bronchial blood flow returns to the shunt in the lungs purchase 20 mg tamoxifen with visa menstrual cycle calendar. The remainder returns through small shunt and a low regional V˙ A/Q˙ ratio. In healthy individuals, bronchopulmonary anastomoses into the pulmonary veins. It is important to remember that any giogenesis, the formation of new vessels. This is extremely deviation of V˙ A/Q˙ ratio from the ideal condition (0. When a clot or embolus obstructs pul- shunt is that it always leads to venous admixture and re- monary blood flow, the adjacent parenchyma is kept alive duces the amount of oxygen carried in the systemic blood. REVIEW QUESTIONS DIRECTIONS: Each of the numbered (C) Compliance (A) Zone 1 items or incomplete statements in this (D) Flow per minute (B) Zone 2 section is followed by an answer or by (E) Capillary blood volume (C) Zone 3 completions of the statement. The effect of gravity on the (D) Zone 4 ONE lettered answer or completion that is pulmonary circulation in an upright 6. Which of the following best the middle of the lung (A) Zone 1 characterizes the pulmonary (B) Capillary pressure to be greater at (B) Zone 2 circulation? Which of the following best (C) Low Low Low High the lung characterizes alveolar ventilation (D) High Low High High (D) Lower vascular resistance at the apex and blood flow at the base, (E) High Low Low High of the lung compared with the base compared with the apex, of the 2. Pulmonary vascular resistance is (E) Venous pressure to be greater than lungs of a healthy standing decreased alveolar pressure at the apex person? A patient lying on his back and Ventilation- (B) By breathing low oxygen breathing normally has a mean left Ventilation Blood flow perfusion ratio (C) At high lung volumes atrial pressure of 7 cm H2O; a mean (A) Higher Higher Lower (D) With increased pulmonary arterial pulmonary arterial pressure of 15 cm (B) Lower Higher Higher pressure H2O; a cardiac output of 4 L/min; and (C) Lower Lower Lower 3. In healthy individuals, the pulmonary an anteroposterior chest depth of 15 (D) Higher Lower Higher and systemic circulations have the same cm, measured at the xiphoid process. The regional changes seen in (B) Vascular resistance which of the following conditions? The apex of the lungs of a 21-year-old SUGGESTED READING perfusion ratios affect gas tensions in subject is 20 cm above the heart. Oxford, UK: But- (D) Highest at apex Lowest at base monary vascular resistance of 4 mm terworth-Heinemann, 2000. Baltimore: Lippin- output of 5 L/min and mean driving pressure for moving cott Williams & Wilkins, 1998. Pulmonary blood flow limits the transfer of O2 and CO2 in decreases the ability of the blood to carry O2. Diffusing capacity depends on the diffusion properties of HCO in the plasma. Hypoxemia is an abnormally low PO2 or oxygen content in of hemoglobin loaded with oxygen. GAS DIFFUSION AND UPTAKE Oxygen is taken up by blood in the lungs and is trans- ported to the tissues. Oxygen uptake is the transfer of oxygen There are two types of gas movements in the lungs, bulk flow from the alveolar spaces to the blood in the pulmonary capil- and diffusion. Gas uptake is determined by three factors: the diffusion down to the alveoli, by bulk flow, analogous to water coming properties of the alveolar-capillary membrane, the partial out of a faucet, in which all molecules move as a unit. For example, oxygen dif- fuses across the alveolar-capillary membrane because of the Respiratory Gases Cross the Alveolar-Capillary difference in PO2 between the alveoli and pulmonary capil- laries (Fig. The partial pressure difference for oxygen Membrane by Diffusion is referred to as the oxygen diffusion gradient; in the nor- The movement of gases in the alveoli and across the alveo- mal lung, the initial oxygen diffusion gradient, PAO2 (102 lar-capillary membrane is by diffusion in response to partial mm Hg) minus PvO2 (40 mm Hg), is 62 mm Hg. Recall that partial pres- diffusion gradient across the alveolar-capillary membrane sure or gas tension can be determined by measuring baro- for carbon dioxide (PvCO2 PACO2) is about 6 mm Hg, metric pressure and the fractional concentration (F) of the which is much smaller than that of oxygen. At sea level, PO2 is 160 When gases are exposed to a liquid such as blood mm Hg (760 mm Hg 0.

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It is clear that there are several proteins in- can result in activation or inhibition of the postsynaptic neu- volved in this process cheap tamoxifen 20 mg overnight delivery pregnancy body pillow. Alterations in the membrane potential that occur in the are anchored to cytoskeletal components in the terminal by postsynaptic neuron initially take place in the dendrites and synapsin buy tamoxifen 20mg without a prescription menopause 1800s, a protein surrounding the vesicle. Still other proteins cause the vesicles to the influx or efflux of specific ions (Fig. Tetanus toxin and botulinum toxin the activation of a synapse leads to the influx of positively exert their devastating effects on the nervous system by dis- charged ions, the postsynaptic membrane will depolarize. Exposure to these toxins can be fatal because the repolarize back to the resting level. The rate at which it re- failure of neurotransmission between neurons and the mus- polarizes depends on the membrane time constant, , which cles involved in breathing results in respiratory failure. To is a function of membrane resistance and capacitance and 2 complete the process begun by Ca entry into the nerve represents the time required for the membrane potential to terminal, the docked and bound vesicles must fuse with the decay to 37% of its initial peak value (Fig. The vesicle mem- time constants because the increase in membrane resistance brane is then removed from the terminal membrane and re- and/or capacitance results in a slower discharge of the cycled within the nerve terminal. The slow decay of the repolarization allows ad- Once released into the synaptic cleft, neurotransmitter ditional time for the synapse to be reactivated and depolar- molecules exert their actions by binding to receptors in the ize the membrane. In some, the receptor forms part of an ion channel; in oth- ers, the receptor is coupled to an ion channel via a G pro- tein and a second messenger system. In receptors associated A with a specific G protein, a series of enzyme steps is initi- ated by binding of a transmitter to its receptor, producing a second messenger that alters intracellular functions over a longer time than for direct ion channel opening. These EPSP membrane-bound enzymes and the second messengers they produce inside the target cells include adenylyl cy- clase, which produces cAMP; guanylyl cyclase, which pro- duces cGMP; and phospholipase C, which leads to the for- mation of two second messengers, diacylglycerol and inositol trisphosphate (see Chapter 1). When a transmitter binds to its receptor, membrane conductance changes occur, leading to depolarization or B hyperpolarization. An increase in mem- brane conductance that permits the efflux of K or the in- flux of Cl hyperpolarizes the membrane. In some cases, membrane hyperpolarization can occur when a decrease in membrane conductance reduces the influx of Na. Each of IPSP these effects results from specific alterations in ion channel function, and there are many different ligand-gated and voltage-gated channels. A, The depolarization of the mem- in the Dendrites and Soma brane (arrow) brings a nerve cell closer to the threshold for the initiation of an action potential and produces an excitatory post- The transduction of information between neurons in the synaptic potential (EPSP). B, The hyperpolarization of the mem- nervous system is mediated by changes in the membrane po- brane produces an inhibitory postsynaptic potential (IPSP). The rate of decay of membrane po- Axon hillock tential (Em) varies with a given neuron’s membrane time constant. Axon The responses of two neurons to a brief application of depolariz- ing current (I) are shown here. Each neuron depolarizes to the same degree, but the time for return to the baseline membrane po- tential differs for each. Neuron 2 takes longer to return to baseline than neuron 1 because its time constant is longer ( m2 m1). Con- EPSP 1 EPSP 2 sequently, longer periods of depolarization increase the likelihood of summating two postsynaptic potentials. The process in which postsynaptic membrane potentials are added with time is called temporal summation (Fig. If the magnitude of the summated depolarizations is above a threshold value, as detected at the axon hillock, it will generate an action potential. Action Action Time The summation of postsynaptic potentials also occurs potential 1 potential 2 with the activation of several synapses located at differ- ent sites of contact. When a synapse is activated, causing an influx of positively charged ions, a depolarizing electrotonic po- EPSP 2 C tential develops, with maximal depolarization occurring at the site of synaptic activation. The electrotonic poten- EPSP 1 tial is due to the passive spread of ions in the dendritic cytoplasm and across the membrane. The amplitude of the electrotonic potential decays with distance from the synapse activation site (Fig.

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Delta waves—recorded on the scalp over all the cerebral lobes while a person is asleep; rhythmic oscillation at about 1 to 5 cycles/sec; typical in an awake infant buy discount tamoxifen 20 mg on line women's health care policy issues, but its presence in an awake adult indicates brain damage order tamoxifen 20 mg with amex menstruation nausea and vomiting. The cessation of brain-wave patterns (a “flat EEG”) may be corpus callosum and anterior commissure (fig. Deviations from these patterns are of clinical significance that transmit impulses from the cerebrum to other parts of in diagnosing trauma, mental depression, hematomas, tumors, in- the brain and spinal cord and from the spinal cord and fections, and epileptic lesions. Normally, there are four kinds of other parts of the brain to the cerebrum. Basal Nuclei White Matter of the Cerebrum The basal nuclei are specialized paired masses of gray matter located The thick white matter of the cerebrum is deep to the cerebral deep within the white matter of the cerebrum (figs. The corpus stria- connections within the brain by which information is transmit- tum is composed of several masses of nuclei. The caudate nucleus is ted to the appropriate places in the form of electrical impulses. A thick band of white matter lies between the cau- The three types of fiber tracts within the white matter are named date nucleus and the next two masses underneath, collectively called according to location and the direction in which they conduct the lentiform nucleus. Association fibers are confined to a given cerebral hemi- sphere and conduct impulses between neurons within that corpus striatum: L. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 369 (a) (b) FIGURE 11. It is a thin layer of gray matter, Knowledge of the brain regions involved in language has been lying just deep to the cerebral cortex of the insula. The globus pallidus regulates the muscle tone necessary left inferior gyrus of the frontal lobe. Neural diseases or motor speech area causes selective stimulation of motor im- physical trauma to the basal nuclei generally cause a variety of pulses in motor centers elsewhere in the frontal lobe, which in motor movement dysfunctions, including rigidity, tremor, and turn causes coordinated skeletal muscle movement in the phar- rapid and aimless movements. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 370 Unit 5 Integration and Coordination Corpus callosum Intermediate commissure Septum pellucidum Genu of corpus Choroid plexus of third ventricle callosum Splenium of corpus callosum Posterior commissure Anterior commissure Pineal gland Thalamus Corpora Hypothalamus quadrigemina Optic chiasma Pituitary stalk Cortex of Pituitary gland cerebellum Mammillary body Arbor vitae of Pons cerebellum Medulla oblongata FIGURE 11. Motor cerebral cortex Thalamus Claustrum Putamen Basal nuclei Lentiform nucleus Globus Corpus pallidus striatum Caudate nucleus Cerebellum Spinal cord FIGURE 11. The thalamus is a relay center be- tween the motor cerebral cortex and the other brain areas. The combined muscular stimulation translates a sentence but cannot read it, presumably because of damage to thought patterns into speech. Some recovery usually occurs after damage to the motor Language comprehension has been destroyed in people with speech area, but damage to Wernicke’s area produces more severe Wernicke’s aphasia; they cannot understand either spoken or and permanent aphasias. It appears that the concept of words to be spoken origi- Knowledge Check nates in Wernicke’s area and is then communicated to the motor speech area through the arcuate fasciculus. Diagram a lateral view of the cerebrum and label the four ate fasciculus produces conduction aphasia, which is fluent but superficial lobes and the fissures that separate them. How are these patterns The angular gyrus, located at the junction of the parietal, monitored clinically? Describe the arrangement of the fiber tracts within the integration of auditory, visual, and somatesthetic information. Describe the aphasias that result from damage to the motor damage to the left angular gyrus can speak and understand spo- speech area and Wernicke’s area from damage to the arcuate fasciculus and from damage to the angular gyrus. Wernicke’s area: from Karl Wernicke, German neurologist, 1848–1905 Van De Graaff: Human V. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 372 Unit 5 Integration and Coordination Pituitary stalk FIGURE 11. DIENCEPHALON The cerebral cortex discriminates pain and other tactile stimuli, The diencephalon is a major autonomic region of the brain that but the thalamus responds to general sensory stimuli and pro- consists of such vital structures as the thalamus, hypothalamus, vides crude awareness. The thalamus probably plays a role in the epithalamus, and pituitary gland. Objective 17 Describe the location and structure of the pituitary gland. It forms the floor and part of the lateral walls of the bral hemispheres of the telencephalon. Despite its small size, the hypothalamus performs mus, hypothalamus, epithalamus, and pituitary gland. Thalamus The hypothalamus acts as an autonomic nervous center in accelerating or decelerating certain body functions.

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Occupa- ties designed to maintain or improve their tional therapists may help individuals current level of function 20mg tamoxifen for sale womens health uiuc. Speech therapists ed to behavioral changes may result in may help individuals maximize their unsafe situations for the individual discount tamoxifen 20mg menstrual water retention. Those speech capability as well as their ability to who are in denial about their condition swallow. In some instances cognitive and their limitations may also be exposed retraining and memory training may be to situations that could result in unsafe useful. Individuals are usually affected in cult, social interactions also become more middle or later life, with males affected difficult, resulting in increasing social iso- more frequently than women. Personality changes that may pro- duce violent or hostile behaviors further Manifestations of ALS stress support systems. Because Huntington’s disease has a Symptoms of ALS depend on the area of genetic component, family members may the nervous system affected; both upper be under the additional stress of knowing and lower extremities are affected. There that they may themselves be at risk for are two primary forms of ALS: developing Huntington’s disease. Coun- • Spinal form seling, education, and support can help to • Bulbar form reduce the stress that family members may be experiencing. The spinal form of ALS is characterized by muscular weakness, muscle atrophy Vocational Issues in Huntington’s Disease (decrease in size), spasticity, and hyperac- tive reflexes. Individuals may first com- Huntington’s disease is a progressive, plain of tripping, stumbling, or awk- degenerative disease; however, in the ear- wardness when walking or running. In the bulbar condition progresses and individuals have form individuals may first notice difficul- increasing difficulty with memory, com- ty in breathing, slurring of speech or low- munication skills, and physical ability, ered volume when speaking, or difficulty sheltered employment may be the most with swallowing. As the condition progresses, symptoms become worse, spreading to other parts of Amyotrophic Lateral Sclerosis the body so that eventually, whether the (ALS; Lou Gehrig’s Disease) individual first experienced the bulbar or spinal form of ALS, he or she eventually Amyotrophic lateral sclerosis (ALS), also experiences all the symptoms. Individuals sometimes referred to as Lou Gehrig’s dis- become increasingly weak and immobile. They may experience respiratory mus- current medical theory suggests a multi- cle weakness leading to breathing factorial etiology that may include genet- problems, and in later stages of the con- ic, viral, autoimmune, and neurotoxic fac- dition they may require ventilatory assis- Neuromuscular Conditions 101 tance in order to breathe. Cognitive func- Psychosocial Issues in ALS tion, sensation, vision, hearing, and bow- el and bladder function are usually not The social, economic, and psychologi- affected. It is common for individuals with ALS to Diagnosis of ALS experience fear, anxiety, and depression, especially as the condition progresses There is no reliable laboratory test to and the individual recognizes rapid pro- detect the presence of ALS. Diagnosis is gressive deterioration of physical func- usually based on the symptoms the indi- tion. Because of loss of mobility and in- vidual exhibits and their progression and creased dependency, feelings of helpless- the individual’s medical history, and by ness and powerlessness are also common. Some individuals may experience discour- agement and become angry as their phys- Treatment and Management of ALS ical limitations increase. They may ex- perience grief with each subsequent loss of There is no cure for ALS, and no effec- function. There may be loss in social rela- tive treatment is currently available. They may feel vidual with ALS to remain independent as guilty because of their increased depend- long as possible, be comfortable, and ence on others and may express concern avoid complications. Treatment of symp- and frustration over the burden they feel toms is used to maintain muscle function, is being placed on family members. Medications to reduce Since individuals with ALS need sub- spasticity may be used; however, these stantial help with most activities of daily can also increase muscle weakness and living, family members most often find cause sedation. Physical therapy may be themselves in a caregiving role even in helpful to maintain function and to the early stages of the individual’s condi- reduce the painful symptoms brought on tion. If the individ- Occupational therapists can provide sup- ual with ALS is also the major breadwin- port and help individuals to adapt their ner, financial issues may become a major environment in order to maximize func- concern. Individuals with speech difficul- to assume the caregiving role, which fur- ties may utilize speech therapists to help ther contributes to financial distress. Family members may also have feelings of Speech pathologists may be utilized to help powerlessness, anger, or anxiety about the individuals who have difficulty with swal- future. Using special techniques and equipment that enhance Guillain-Barré syndrome is an inflam- their functional capacity and independ- matory condition of the peripheral nerves ence in self-care can help them exert per- (nerves lying outside the central nervous sonal control over their life and thus system). Since communica- syndrome is unknown, but symptoms are tion is usually significantly affected, almost always preceded by an infectious equipment such as voice amplifiers, or illness that has occurred about 10 days be- techniques such as eye blinking if individ- fore.

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It is present in the brain but its precise location and role are unclear best 20mg tamoxifen womens health 81601. In parallel with the identification of distinct transporters for GABA there has been continued interest in the development of selective blockers of these transporters and the therapeutic potential that could result from prolonging the action of synaptically released GABA generic tamoxifen 20mg amex women's health clinic brisbane northside. It has been known for a long time that certain pro-drugs of nipecotic acid (e. More recently,several different systemically active lipophillic compounds have been described that act selectively on GAT- 1,GAT-2 or GAT-3 (Fig. Of these,tiagabine (gabitril),a derivative of nipecotic acid that acts preferentially on GAT-1,has proved clinically useful in cases of refractory epilepsy. METABOLISM OF GABA Once recovered into GABAergic nerve terminals or glia,GABA is metabolised to succinic semialdehyde and then to succinate. As detailed above,these reactions are catalysed by GABA-T and SSADH,respectively. Aminotransferase reactions are reversible but GABA-T breaks down GABA,rather than producing it,because the irreversible action of SSADH rapidly oxidises the product SSA to succinate (Fig. SSA may also be reduced by the enzyme succinic semialdehyde reductase (SSAR) to form g-hydroxybutyric acid (GHB). Inhibitors of GABA-T include aminooxyacetic acid,5-amino-1,3-cyclohexadi- enenecarboxylic acid (gabaculine), g-vinyl GABA (vigabatrin) and 2-propylpenatanoic acid (valproate). The first two are PLP antagonists and are of experimental interest only. Vigabatrin is an irreversible inhibitor of GABA-T and has been used clinically as an anticonvulsant. Valproate is a widely used anticonvulsant but it is not clear to what extent inhibition of GABA-T contributes to its therapeutic properties,as it also inhibits SSADH and SSAR,and inhibits Na‡ currents,thus limiting neuronal firing. GABA RECEPTORS The actions of GABA are mediated by receptors belonging to three distinct classes, termed GABAA,GABAB and GABAC. GABAA and GABAC receptors form membrane channels (ionotropic receptors) and their activation leads to an increased permeability to chloride (ClÀ) and bicarbonate (HCOÀ) ions. GABA receptors belong 3 B to the family of G-protein-coupled receptors (metabotropic receptors) and can modify the activity of the enzyme adenylate cyclase,suppress transmitter release by directly inhibiting calcium channels or hyperpolarise postsynaptic cells by directly activating potassium channels. GABAA RECEPTORS GABAA receptors are the most widely expressed of the GABA receptors in the CNS and are found at the vast majority of GABAergic synapses. Binding of two molecules of GABA to the receptor causes the opening of an integral transmembrane anion channel (Bormann,Hamill and Sakmann 1987). As the ClÀ permeability of the channel is approximately five times that of HCO À,under most circumstances the net flux is 3 dominated by ClÀ. Because of this the amplitude and direction of GABA-gated currents,and the resultant transmembrane potential changes,are determined largely by the sign and magnitude of the difference between the membrane potential (Vm) and the chloride equilibrium potential (ECl). If ClÀ were passively distributed across the neuronal membrane E would equal V. Cl m However,neurons possess a variety of transport mechanisms for extrusion or uptake of ClÀ (Kaila 1994). The value of E is dictated by the net result of these chloride- Cl extruding or accumulating mechanisms. Mature central neurons tend to maintain a low intracellular ClÀ through the activity of a ClÀ-extruding K‡/ClÀ co-transporter (KCC2). Thus,in many neurons,ECl is more negative than Vm (although variable, typical values would be À70 and À65 mV,respectively). Under these circumstances,an increase in chloride conductance (g ) leads to an influx of ClÀ that results in membrane Cl hyperpolarisation (a movement towards ECl). This is the classic GABA-mediated inhibitory postsynaptic potential (IPSP). The IPSP transiently (tens of milliseconds) moves the membrane potential to a more hyperpolarised value,away from the threshold for action potential initiation (Fig. In cells in which the net ClÀ extrusion is less (because KCC2 or other ClÀ-extruding mechanisms are less active), E Cl may be very close to,or slightly positive to,Vm. The effect of GABA is still inhibitory, 234 NEUROTRANSMITTERS,DRUGS AND BRAIN FUNCTION as the increase in gCl tends to hold the membrane potential close to ECl,thus making it more difficult to trigger an action potential. Activity of NKCC1 can result in ECl being positive to Vm,such that an increase in gCl leads to chloride exit from the cell and membrane depolarisation. GABA may still be inhibitory,as long as ECl is below the threshold for spike initiation.

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