By A. Ur-Gosh. Chicago School of Professional Psychology.
D2 purchase 120mg sildigra overnight delivery erectile dysfunction pump how to use,D3 and D4) receptors (a) D1 D5 D2 D3 D4 Agonist Bromocriptine 440* 440* 8* 5* 290* Quinpirole 1900 ± 5 24* 30* 7-OH-DPAT 5000* ± 10 1* 650 SKF 38393 1 0 discount sildigra 50mg guaranteed erectile dysfunction treatment. SYNAPTIC EFFECTS Because DA is very much localised to one brain area (striatum) and as there is such a pronounced DA pathway from the substantia nigra to the striatum it would be reasonable to assume that the effect of this pathway on striatal neuron activity is well established. Over the years a large number of studies using extracellular recording in the striatum have shown that iontophoretic DA depresses 75±100% of all neurons responding to it, irrespective of whether spontaneous, excitatory amino acid-induced, or synaptic-evoked activity was being monitored. This inhibitory response is slow in onset (up to 15 s) and long in duration (possibly minutes). Stimulation of the substantia nigra can produce inhibition, excitation or mixed effects but it is possible, despite the high proportion of 150 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION DA neurons in this nucleus, that not all the effects are elicited by the release of DA. Most neuroleptics block the inhibitory effects of applied DA but some, e. Generally these studies lacked specific agonists and antagonists used microintophoresis which is not really quantitative and with extracellular recording gave little information on the state of polarisation of the neuron. Unfortunately the picture was not clarified by intracellular recordings from striatal neurons which, as these need to be large to take an electrode, are not necessarily typical (only 10%) of most striatal neurons innervated by DA afferents. Stimulation of the substantia nigra invariably produces a monosynaptic depolarisation in them that is blocked by haloperidol, but which may proceed to a hyperpolarisation, if the stimulus is strong enough. DA iontophoresced onto the same neuron may also cause depolarisation (Kitai, Sugimori and Kocsis 1976) but can still reduce its discharge. Mixed effects are often seen with DA and when it is infused in increasing concentrations into the striatum through a push±pull cannula it generally depresses extracellularly recorded cell firing but low concentrations can produce excitation or bimodal excitation±inhibition (Schoener and Elkins 1984). Voltammetry studies with an electrode that can also be used for recording neuronal firing have shown that increasing nigrostriatal stimulation induces not only an increase in DA release but also an inhibition of neurons (after some initial but variable excitation of large neurons), which outlasts the rise in extracellular DA. Thus the effects of endogenous DA appear to be critically dependent on its extracellular concentration and it may be that while synaptic effects can be excitatory, extrasynaptic ones are inhibitory. Some of this effect may also be indirect through reducing the release of excitatory NTs such as glutamate from cortico-striatal fibres or ACh from intrinsic neurons. In view of the known cellular actions of DA, such as increased K efflux and reduced Ca2 currents associated with D receptor activation in cell lines, inhibition would be 2 the expected response to DA, especially as cyclic AMP, which is increased by D1 receptor activation also inhibits striatal neurons. In fact although many DA synaptic effects are blocked by D2 antagonists like haloperidol, the role of D1 receptors should not be overlooked. Iontophoretic studies on rat striatal neurons (Hu and Wang 1988) showed that while the release of DA by low currents facilitated glutamate-induced activation, high current efflux inhibited it. Although these effects were reduced by the D2 antagonist haloperidol it was the D1 agonist SKF 38393 which mimicked them, causing activation when released by low currents but inhibition at higher ones. By contrast, the D2 agonist quinpirol produced a less marked biphasic effect in which inhibition dominated. Intracellular recording from striatal neurons in rat brain slices show a cAMP-mediated D1-dependent (blocked by SCH 23390) suppression of a voltage-dependent sodium current which make the cell less responsive. An observed D1-sensitive suppression of the sodium current and a shift of the inactivating voltage in a hyperpolarising direction, together with a depression of certain Ca2 currents, would make the neuron less excitable. The D effect in these measures is 2 less clear with reports of both a depolarising and hyperpolarising shift of the DOPAMINE 151 Figure 7. Reproduced by permission from Dalley (1992) inactivation curves and an increased opening of a potassium conductance (see Calabresi et al. What is clear from all these experiments is that DA can have a bimodal effect depending on how much is applied or released, and which receptors are involved. Excitation is more common at low concentrations and inhibition at higher ones. What happens in vivo is not clear but in vivo voltammetry certainly suggests that the extracellular concentration of DA can be very high and this would favour the more commonly observed inhibition. In other brain areas which receive a DA input, such as the nucleus accumbens and prefrontal cortex, it appears to be inhibitory and predominently D2-mediated. These are, of course, extracellular recordings but more recent intracellular studies in both rat and guinea pig accumbens slices show that DA produces a D2-mediated depolarisation and a D1 hyperpolarisation which appear to be dependent on decreased and increased K conductances respectively. This would certainly fit in with the belief that DA mediates the positive effects of schizophrenia by a D2-mediated stimulation of the nucleus accumbens (see Chapter 17). The D1 receptor is primarily linked to the activation of adenylate cyclase and then protein kinase A. The response to its activation will therefore depend on the ion channels and other proteins modulated by the kinase which can vary from one neuron to another. Since the D2 receptor is not so closely associated with just one G-protein, this gives it the potential for even more effects (see Greenhoff and Johnson 1997). Those modifying the synthesis, storage, release, uptake and metabolism of DA have been covered above in the appropriate sections on neurochemistry. The actions and uses of agonists and antagonists are outlined in Table 7.
It is beyond the scope of this text to attempt a com- prehensive discussion of the numerous diseases and dysfunctions of these organs discount sildigra 25 mg with mastercard erectile dysfunction viagra not working. Some general comments will be made buy 100mg sildigra with mastercard erectile dysfunction doctors san antonio, however, Snellen’s chart: from Herman Snellen, Dutch ophthalmologist, 1834–1908 Van De Graaff: Human V. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Developmental Exposition mesoderm,and endoderm—are involved in the formation of the The Ear ear. Both types of ectoderm (neuroectoderm and surface ecto- derm) play a role. The ear of an adult is structurally and functionally divided EXPLANATION into an outer ear, a middle ear, and an inner ear, each of which The ear begins to develop at the same time as the eye,early dur- has a separate embryonic origin. All three embryonic germ layers—ectoderm, from deep embryonic tissue as one might expect,but rather be- (a) (a1) (a2) (b1) (b2) (b) (c) (d) (e) EXHIBIT II The development of the inner ear. Toward the end of the fourth week,the outer edges of the invaginated otic fovea come together and fuse to form an otocyst. The otocyst further differentiates to form a dorsal utricular portion and a ventral saccular portion. Three separate diverticula extend outward from the utricular por- tion and develop into the semicircular canals, which later func- tion in balance and equilibrium. A tubular diverticulum called the cochlear duct extends in a coiled fashion from the saccular portion and forms the membranous portion of the cochlea of the ear (exhibit II). The spiral organ, which is the functional por- tion of the cochlea,differentiates from cells along the wall of the cochlear duct (Ex. The sensory nerves that innervate the inner ear are derived from neuroectoderm from the developing brain. The differentiating otocyst is surrounded by mesodermal tissue that soon forms a cartilaginous otic capsule (exhibit III). As the otocyst and surrounding otic capsule grow, vacuoles con- taining the fluid perilymph form within the otic capsule. The vacuoles soon enlarge and coalesce to form the perilymphatic space, which divides into the scala tympani and the scala vestibuli. Eventually, the cartilaginous otic capsule ossifies to form the bony (osseous) labyrinth of the inner ear. The middle- ear chamber is referred to as the tympanic cavity and derives from the first pharyngeal pouch (exhibit IV). The auditory ossi- cles, which amplify incoming sound waves, derive from the first and second pharyngeal arch cartilages. As the tympanic cavity enlarges, it surrounds and encloses the developing ossicles (ex- hibit IV). The connection of the tympanic cavity to the pharynx gradually elongates to develop into the auditory (eustachian) tube, which remains patent throughout life and is important in maintaining an equilibrium of air pressure between the pharyn- geal and tympanic cavities. The outer ear includes the fleshy auricle attached to the side of the head and the tubular external acoustic canal that ex- tends into the external acoustic meatus of the temporal bone of the skull. The external acoustic canal forms from the surface ec- toderm that covers the dorsal end of the first branchial groove (Ex. A solid epithelial plate called the meatal plug soon develops at the bottom of the funnel-shaped branchial groove. The meatal plug is involved in the formation of the inner wall of the external acoustic canal and contributes to the tympanic membrane (eardrum). The tympanic membrane has a dual origin from surface ectoderm and the endoderm lining the first pharyn- geal pouch (exhibit IV). EXHIBIT III The formation of the cochlea and the spiral organ from the otic capsule. Successive stages of development of the perilymphatic space and the spiral organ from the eighth to the twentieth week. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 (concluded) EXHIBIT IV The development of the outer- and middle-ear regions and the auditory ossicles (malleus, incus, and stapes). An embryo afflicted with rubella is 30% more likely to be Other severe malformations, which are incompatible with life, aborted, stillborn, or congenitally deformed than one that is not are generally expressed with this condition. Rubella interferes with the mitotic process, and thus causes underdeveloped organs. An embryo with rubella may suf- Ear fer from a number of physical deformities, including cataracts and Congenital deafness is generally caused by an autosomal reces- glaucoma, which are common deformities of the eye. The actual functional impairment is generally either a defective Eye set of auditory ossicles or improper development of the neurosen- Most congenital cataracts are hereditary, but they may also be sory structures of the inner ear. In this condition, the lens is abnormalities are not uncommon, especially in infants opaque and frequently appears grayish white. Functional Impairments of the Eye Emmetropia No correction necessary (normal vision) Few people have perfect vision.
In such cases discount sildigra 120 mg free shipping erectile dysfunction young causes, corti- chromosome purchase 25mg sildigra with mastercard erectile dysfunction treatment home veda, an individual with a 47,XXY karyotype has sol production is low, causing increased production of normal testicular function in utero in terms of testosterone ACTH by activating the hypothalamic-pituitary axis and AMH production and no ambiguity of the genitalia at (Fig. The extra X chromosome, however, interferes with perplasia and an abnormal production of androgens and the development of the seminiferous tubules, which show corticosteroid precursors. These infants are born with am- extensive hyalinization and fibrosis, whereas the Leydig biguous external genitalia (i. The degree of virilization de- azoospermic, and often exhibit some eunuchoidal features. When aldosterone levels are also affected, a life- with a 45,XO karyotype will have no gonadal development threatening salt-wasting disease results. Untreated patients during fetal life and is presented at birth as a phenotypic fe- with congenital adrenal virilism develop progressive mas- male. Given the absence of ovarian follicles, such patients culinization, amenorrhea, and infertility. These in- differentiated testes but underdeveloped and/or absent dividuals have neither male nor female internal genitalia wolffian-derived structures and inadequate virilization of and phenotypic female external genitalia, with the vagina the external genitalia. They are reared as females and un- testosterone biosynthesis, metabolism, or action. The 5 - dergo feminization during puberty because of the periph- reductase deficiency is an autosomal recessive disorder eral conversion of testosterone to estradiol. Disorders of puberty are classified as precocious pu- Such infants have ambiguous or female external genitalia berty, defined as sexual maturation before the age of 8 and normal male internal genitalia (Fig. They are years, and delayed puberty, in which menses does not start often raised as females but undergo a complete or partial by age 17 or testicular development is delayed beyond age testosterone-dependent puberty, including enlargement of 20. True precocious puberty results from premature activa- the penis, testicular descent, and the development of male tion of the hypothalamic-pituitary-gonadal axis, leading to psychosexual behavior. The most frequent causes are CNS lesions cessive disorder caused by end-organ insensitivity to an- or infections, hypothalamic disease, and hypothyroidism. These 46,XY males have abdominal testes that secondary sex characteristics without gametogenesis. Because of androgen in- result from the abnormal exposure of immature boys to an- sensitivity, the wolffian ducts regress, and the external gen- drogens and of immature girls to estrogens. The presence of AMH steroid production can be of gonadal or adrenal origin. The next ovulatory cycle after (A) Androgens produced from items or incomplete statements in this implantation is postponed because of cholesterol in the placenta section is followed by answers or by (A) High levels of PRL (B) Estradiol as a precursor from the completions of the statement. Select the (B) The production of hCG by mother’s ovary ONE lettered answer or completion that is trophoblast cells (C) Androgenic substrates from the BEST in each case. The suckling reflex (D) The depletion of oocytes in the mother (A) Has afferent hormonal and efferent ovary (E) Estradiol to be produced in the neuronal components (E) Low levels of progesterone placenta (B) Increases placental lactogen 5. One benefit of insulin resistance in the secretion the mother during pregnancy is (C) Increases the release of dopamine (A) Cortical reaction (A) A reduction of her plasma glucose from the arcuate nucleus (B) Enzyme reaction concentrations (D) Triggers the release of oxytocin by (C) Acrosome reaction (B) The blockage of the development stimulating the supraoptic nuclei (D) Decidual reaction of diabetes mellitus in later life (E) Reduces PRL secretion from the (E) Inflammatory reaction (C) The increased availability of pituitary 6. Implantation occurs effective in preventing pregnancy by (D) A reduction of pituitary function (A) On day 4 after fertilization (A) Blocking ovulation (E) Increased appetite (B) After the endometrium undergoes a (B) Altering the uterine environment 10. The primary reason that the female decidual reaction (C) Thickening the cervical mucus phenotype develops in an XY male is (C) When the embryo is at the morula (D) Reducing sperm motility (A) The secretion of progesterone stage (E) Inducing a premature LH surge (B) Adrenal insufficiency (D) Only after priming of the uterine 7. The maternal recognition of pregnancy (C) The lack of testosterone action endometrium by progesterone and occurs as a result of the (D) Increased inhibin secretion estrogen (A) Prolonged secretion of estrogen by (E) The secretion of antimüllerian (E) On the first day after entry of the the placenta hormone (AMH) embryo into the uterus (B) Production of human placental 3. Upon contact between the sperm head lactogen and the zona pellucida, penetration of (C) Increased secretion of SUGGESTED READING the sperm into the egg is allowed progesterone by the corpus luteum Carr BR. Fertilization, implantation, and because of (D) Secretion of hCG by the endocrinology of pregnancy. Textbook of En- (B) The zona reaction (E) Activation of an inflammatory docrine Physiology. New York: (C) The perivitelline space reaction at implantation Oxford University Press, 2000;265–285. The CHAPTER 39 Fertilization, Pregnancy, and Fetal Development 705 Encyclopedia of Reproduction. Essential Repro- East Norwalk, CT: Appleton & Lange, Spencer TE: Maternal recognition of preg- duction. CASE STUDY FOR CHAPTER 37 Answers to Case Study Questions for Chapter 38 Steroid Abuse 1. There are two laboratory tests that indicate a problem, the A 30-year-old man and his 29-year-old wife have been try- low late follicular phase plasma estradiol concentration and ing to have a baby. She has been having regular menstrual the low midluteal phase plasma progesterone concentra- cycles. The low estradiol could be due to the development of a time of her ovulation. The reduced number of granulosa cells The husband’s physical examination reveals a muscular would not contain sufficient aromatase to synthesize the man with an excellent physique who works out regularly to high levels of estradiol required during the late follicular build his body. In addition, low estradiol could be due to inadequate sults indicate that his plasma testosterone is 1850 ng/dL FSH receptors on the granulosa cells or inadequate FSH se- (normal, 300 to 100 ng/dL) and LH 2 U/mL (normal, 3 to cretion. What is the major reason for the failure of the wife to get The low progesterone during the luteal phase might be due pregnant?
Since trials remain rare 120mg sildigra for sale erectile dysfunction and heart disease, and screening panel findings are seldom factually definitive purchase 100mg sildigra otc erectile dysfunction treatment unani, they also seem to be an inefficient way to improve the quality of evidence at trial in comparison with better use of court-appointed experts, modification of trial presentations, jury learning aids, and the like. Specialized medical courts have attracted recent attention from phy- sicians and general tort reformers, and bills establishing them have been introduced in Congress and some state legislatures (37). Most proposals contemplate dividing a state into a handful of judicial dis- tricts with dedicated, expert trial judges. Proponents argue that these courts would do better than the current decentralized system at man- aging caseloads, ensuring high-quality evidence, and reaching consis- tent decisions about liability and damages. On the other hand, specialized courts run risks of becoming politicized, especially in states where judges are elected rather than appointed and in areas where well-financed groups have clearly defined, unvarying interests in a court’s outcomes. As Struve observes, one reason the court of appeals for the federal circuit functions well when hearing patent law disputes is that powerful corporations appear as both plaintiffs and defendants. In contrast, in malpractice cases, medical providers and malpractice insurers will always want a specialized court to constrain liability, not expand it. Another caution is that some expertise-based arguments are merely subterfuges for changing the composition of juries. For example, in Pennsylvania the principal effect of the medi- cal courts proposal currently under consideration would be to redis- trict the eastern part of the state so that jurors from Philadelphia—who historically favor plaintiffs with respect to both liability and dam- ages—would be mixed with jurors from surrounding counties. Wide variation in jury behavior is an important issue, but it should be addressed openly. In sum, the malpractice system could benefit from enhanced exper- tise, but the source of the problem and best reform approach may differ from those commonly cited. Some malpractice claims, especially larger ones, turn on delicate clinical judgments; however, many do not. The mismatch between legal claims and actual negligence has major public policy significance, but claims, findings of liability, and assessments 266 Sage of damages are not random (25). Health care providers are far more likely to be held liable when they provide negligent care than when they provide competent care (38). Detailed facts about medical treatment also reside primarily with defendants. In part because of poor informa- tion, most instances of malpractice do not give rise to claims, and many patients go to lawyers because they have not received explanations of their outcomes from health care providers. These considerations argue for educating judges and juries and facilitating their work rather than abandoning them, at least if the goal is to preserve fault-based adjudi- cation of malpractice claims. Alternatives to Litigation For decades, proposals have been circulating that would replace mal- practice litigation with a faster, cheaper, less adversarial system that could potentially compensate a greater number of injured patients (39,40). Various forms of alternative dispute resolution (ADR) are already in widespread use, although mostly on a voluntary rather than mandatory basis. ADR is intended to eliminate frivolous claims, expe- dite claims resolution, and reduce litigation expense. Arbitration is a private form of ADR that uses an impartial third party who is usually an expert in the area of controversy. To reduce litigation delay and costs, incentives must exist for the parties in a large percentage of cases to substitute the informal arbitration process for more costly trial proce- dures. Mediation involves the use of a third party who does not have decision-making authority and does not typically express a direct opin- ion on the merit of the case but who attempts to facilitate negotiation (41,42). The Bush Administration supports early offer approaches in combination with caps on damages (44). Comprehensive reforms that would remove malpractice litigation from the courts entirely also come in various flavors. A pure no-fault approach would compensate for injuries caused by health care regard- less of whether conduct by medical providers fell short of optimal. No-fault accident compensation systems for medical injuries exist in New Zealand and Scandinavia but not in the United States. In other proposals, a no-fault approach would be limited to specific types of harm (e. Florida and Virginia have adopted no-fault birth injury compensation funds but continue to experience high rates of litigation (45). A neo-no-fault scheme, which can be imple- Chapter 17 / New Directions in Liability Reform 267 mented either by legislation or by private contract, builds on early offer proposals by prohibiting lawsuits against health care providers who acknowledge liability and promptly pay economic damages (46). One might also establish a fault-based state administrative system that would replace the courts in adjudicating medical malpractice claims but retain fault as a basis for liability (32). Finally, accelerated compensation events (ACEs) proposals mix fault and no-fault principles by requiring health care providers to pay prompt compensation upon the occurrence of designated injuries or injury triggers that have been validated by physician experts as typically associated with negligence (47). ACEs are also designed to help health care providers identify areas in which improvement will prevent future injuries and claims.
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