I. Nafalem. University of Minnesota-Crookston.
In certain reactions order 60 mg alli mastercard weight loss pills pregnancy, fuels are oxidized by transfer of electrons to NADP to ~P intermediates form NADPH discount alli 60 mg with mastercard weight loss 33. For example, glucose 6-P dehydrogenase, in the pentose phosphate pathway, transfers electrons from glucose 6-P to NADP instead of NAD. Consequently, the Pyruvate Lactate energy in its reduction potential is usually used in energy-requiring reactions with- out first being converted to ATP currency. Anaerobic Glycolysis is transferred from high-energy intermediates of the pathway to ADP. Because NADH from Not all ATP is generated by fuel oxidation. In anaerobic glycolysis, glucose is the pathway is reoxidized by reduction of degraded in reactions that form high-energy phosphorylated intermediates of the pyruvate to lactate, no oxygen is required. These activated high-energy intermediates provide the energy for the generation of ATP from ADP without involving electron transfer to O2. Therefore, this pathway is called anaerobic glycolysis, and ATP is generated from substrate level phosphorylation rather than oxidative phosphorylation (see Chapter Oxidases 22). Anaerobic glycolysis is a critical source of ATP for cells that have a decreased O + 4e–, 4H+ 2H O 2 2 O2 supply, either because they are physiologically designed that way (e. OXYGENASES AND OXIDASES NOT INVOLVED IN 2 ATP GENERATION H2O + Electron + S OH donor–X Approximately 90 to 95% of the oxygen we consume is used by the terminal oxi- dase in the electron transport chain for ATP generation via oxidative phosphoryla- Dioxygenases tion. The remainder of the O2 is used directly by oxygenases and other oxidases, enzymes that oxidize a compound in the body by transferring electrons directly to S + O2 SO2 O2 (Fig. The large positive reduction potential of O2 makes all of these reac- Fig. The tions extremely favorable thermodynamically, but the electronic structure of O2 fate of O2 is shown in blue. S represents an slows the speed of electron transfer. These enzymes, therefore, contain a metal ion organic substrate. CHAPTER 19 / CELLULAR BIOENERGETICS: ATP AND O2 355 A. Oxidases In palmitate and other fatty acids, most carbons are more reduced Oxidases transfer electrons from the substrate to O2, which is reduced to water than those in glucose or ethanol (H2O) or to hydrogen peroxide (H2O2). The terminal protein complex in the elec- (more of the carbons have electrons in car- tron transport chain, called cytochrome oxidase, is an oxidase because it accepts bon–hydrogen bonds). Therefore, fatty acids electrons donated to the chain by NADH and FAD(2H) and uses these to reduce O2 have the greatest caloric content/gram, 9 to water. Most of the other oxidases in the cell form hydrogen peroxide (H O ), kcal. In glucose, the carbons have already 2 2 instead of H O, and are called peroxidases. Peroxidases are generally confined to formed bonds with oxygen, and fewer elec- 2 trons in C-H bonds are available to generate peroxisomes to protect DNA and other cellular components from toxic free radicals energy. Thus, the complete oxidation of glu- (compounds containing single electrons in an outer orbital) generated by hydrogen cose gives roughly 4 kcal/g. Oxygenases dation state is intermediate between glucose and fatty acids, and ethanol thus has 7 Oxygenases, in contrast to oxidases, incorporate one or both of the atoms of oxy- kcal/g. Monooxygenases, enzymes that incorporate one atom of oxygen into the substrate and the other into H2O, are often named hydroxylases (e. Monooxygenases NADPH require an electron donor-substrate, such as NADPH, a coenzyme such as FAD, + H+ NADP+ which can transfer single electrons, and a metal or similar compound that can form a reactive oxygen complex (Fig. They are usually found in the endoplasmic reticulum, and occasionally in mitochondria. Dioxygenases, enzymes that incorpo- FAD FMN rate both atoms of oxygen into the substrate, are used in the pathways for convert- ing arachidonate into prostaglandins, thromboxanes, and leukotrienes. ENERGY BALANCE Our total energy expenditure is equivalent to our oxygen consumption (Fig. The resting metabolic rate (energy expenditure of a person at rest, at Fig.
If transportation is not available discount alli 60mg line weight loss supplements xenadrine, a manual wheelchair is required cheap 60 mg alli otc weight loss vacations. Wheelchairs for individuals who are func- tional household or minimal community ambulators should have crutch holders added if they use crutches. These holders allow children to carry the crutches on the wheelchair for circumstances when they need to get out of the wheelchair, such as for use of wheelchair-inaccessible bathrooms. Children Who Are Exercise Ambulators and Transfer Standers Childhood Needs Children whose function is limited to exercise ambulation or standing trans- fers usually have their first mobility and seating system ordered at age 2 to 3 years when they enter the school system. Depending on these children’s upper extremity function, a stroller base or a large wheelchair base may be ordered (see Figure 6. The stroller base may seat the children higher and make functional activities, such as feeding the children, easier for parents 6. If children have the upper extremity functional ability, cog- nitive ability, and behavioral stability, the self-propelled wheelchair should be ordered. The footrests can be solid or swing-away, based on the perceived ability of these children to come to standing from the wheelchair. Power mo- bility should be considered when children enter middle childhood, usually at age 7 to 9 years, as the second or third wheelchair is required. The decision of power mobility is based on children’s upper extremity function and gen- eral cognitive function. The seating system for these children needs to include good chest lateral support and usually anterior trunk support. The need for a supported head- rest in this group is variable, and has to be assessed on an individual basis. A lap tray should always be ordered for use when children are sitting in the chair and engaged in upper extremity activities. The lap tray is also an im- portant assist for postural control to prevent forward slouching. Especially for young children, the work surface to do upper extremity activities is al- Figure 6. The lap tray is very important most never at the right height unless a lap tray is routinely used. This lap tray and should not be forgotten as part of the allows children to have the ideal level and most functional work area for fine wheelchair. It is an important aspect of po- motor skills activity development (Figure 6. Usually, these trays are at- sitioning to prevent the child from leaning tached to adjustable armrests so they can be raised or lowered to the correct forward. It is a work and feeding area for the child, and if the tray is made of clear mate- height for the individual child. Adolescent Needs There is a group of adolescents with fair upper extremity function who can propel themselves in the community. However, it is much more common for adolescents who require a wheelchair for all community ambulation to have so little upper extremity function that self-propelling a wheelchair is not pos- sible. If these individuals are otherwise appropriate, a power mobility system is preferred. At this age, it is very important to have flip-up or swing-away footrests as the caretakers now depend much more on standing transfers. Usually, the seating system must continue to have a similar construction, as described earlier. Again, some of these adolescents can use crutches for short household ambulation, and in these cases, the wheelchair should be fitted with crutch holders. Children Who Are Dependent in All Transfers Childhood Needs Children who are fully dependent for all their transfer needs usually require sig- nificant supportive seating by age 12 months, and the first special seating and mobility system is typically obtained between the ages of 12 and 24 months. Usually, this first chair is a tilt-in-space stroller base with solid footrests. The seating system requires full chest laterals, anterior trunk support, and a head- rest to assist with head control.
The rate of biosynthesis of cortisol and other adrenal steroids is dependent on stimulation of the adrenal cortical cells by adrenocorti- cotropic hormone (ACTH) order alli 60mg on line weight loss tips for men. Synthesis of Aldosterone The synthesis of the potent mineralocorticoid aldosterone in the zona glomeru- losa of the adrenal cortex also begins with the conversion of cholesterol to prog- esterone (see Figs 60mg alli for sale weight loss pills in pakistan. Progesterone is then hydroxylated at C21, CHAPTER 34 / CHOLESTEROL ABSORPTION, SYNTHESIS, METABOLISM, AND FATE 647 a reaction catalyzed by P450C21, to yield DOC. The P450C11 enzyme system then Hyperplasia or tumors of the adrenal catalyzes the reactions that convert DOC to corticosterone. The terminal steps in cortex that produce excess aldos- aldosterone synthesis, catalyzed by the P450 aldosterone system, involve the oxi- terone result in a condition known as dation of corticosterone to 18-hydroxycorticosterone, which is oxidized to primary aldosteronism, which is characterized by enhanced sodium and water retention, result- aldosterone. The primary stimulus for aldosterone production is the octapeptide angiotensin II, although hyperkalemia (greater than normal levels of potassium in the blood) or hyponatremia (less than normal levels of sodium in the blood) may directly stimu- late aldosterone synthesis as well. ACTH has a permissive action in aldosterone pro- Although aldosterone is the major duction. It allows cells to respond optimally to their primary stimulus, angiotensin II. Synthesis of the Adrenal Androgens with a deficiency of the 11-hydroxylase (the Adrenal androgen biosynthesis proceeds from cleavage of the 2-carbon side chain of P450C11 enzyme), may lead to clinical signs 17-hydroxypregnenolone at C17 to form the 19-carbon adrenal androgen dehy- and symptoms of mineralocorticoid excess droepiandrosterone (DHEA) and its sulfate derivative (DHEAS) in the zona reticu- even though aldosterone secretion is sup- losum of the adrenal cortex (see Fig. These compounds, which are weak pressed in these patients. Androstenedione, another weak adrenal androgen, is produced when the 2-car- bon side chain is cleaved from 17 -hydroxyprogesterone by the C17-C20 lyase Androstenedione can be purchased at health food stores under the name activity of P450C17. This androgen is converted to testosterone primarily in extra- Andros. Although the adrenal cortex makes very little estrogen, the weak letic performance through its ability to be con- adrenal androgens may be converted to estrogens in the peripheral tissues, particu- verted to testosterone. Its use has been banned larly in adipose tissue (Fig. Synthesis of Testosterone year, the drug received a lot of publicity, as the supplement had been used by a player who Luteinizing hormone (LH) from the anterior pituitary stimulates the synthesis of broke the major league home run record. In many ways, the pathways leading to androgen synthesis in the testicle are similar to those described for the adrenal cortex. In the human testicle, the predominant pathway leading to testosterone synthesis is through pregnenolone to 17- - hydroxypregnenolone to DHEA (the ∆5 pathway), and then from DHEA to androstenedione, and from androstenedione to testosterone (see Fig. As for all steroids, the rate-limiting step in testosterone production is the conversion of cholesterol to pregnenolone. LH controls the rate of side-chain cleavage from cholesterol at carbon 21 to form pregnenolone, and thus regulates the rate of Congenital adrenal hyperplasia (CAH) is a group of diseases caused by a geneti- cally determined deficiency in a variety of enzymes required for cortisol synthe- sis. The most common deficiency is that of 21- hydroxylase, the activity of Adrenal which is necessary to convert progesterone to 11-deoxycorticosterone and 17- hydroxy O O progesterone to 11-deoxycortisol. Thus, this deficiency reduces both aldosterone and corti- sol production, without affecting androgen production. If the enzyme deficiency is severe, the precursors for aldosterone and cortisol production are shunted to androgen synthesis, producing an overabundance of androgens, which leads to prenatal masculinization in OH O females and postnatal virilization of males. Another enzyme deficiency in this group of dis- Dehydroepi- Androstenedione eases is that of 11- hydroxylase, which results in the accumulation of 11-deoxycorticos- androsterone terone. An excess of this mineralocorticoid leads to hypertension (through binding of 11- deoxycorticosterone to the aldosterone receptor). In this form of CAH, 11-deoxycortisol Adipose Extra-adrenal also accumulates, but its biologic activity is minimal, and no specific clinical signs and tissue tissues symptoms result. The androgen pathway is unaffected, and the increased ACTH levels may Estrogens Testosterone increase the levels of adrenal androgens in the blood. A third possible enzyme deficiency is that of 17- hydroxylase. A defect in 17- hydroxylase leads to aldosterone excess and Fig. These weak hypertension; however, because adrenal androgen synthesis requires this enzyme, no viril- androgens are converted to testosterone or ization occurs in these patients. In its target cells, the double bond in ring A of testosterone ing androgen is testosterone.
It is postulated that overactivity of the STN leads to excessive excitatory drive to the medial pallidum buy 60mg alli weight loss hacks. The occurrence of cognitive deﬁcits reported with thalamotomy and pallidotomy has driven the interest in trying to ﬁnd alternative targets to lesion alli 60mg with visa weight loss pills 753, especially for patients who require bilateral procedures and who are not suitable for DBS. The most recent development in lesion surgery is the Copyright 2003 by Marcel Dekker, Inc. In contrast, it has been shown that excitotoxic (117) or thermocoagulation (118) lesions of the pathological STN in MPTP-treated primates can alleviate parkinsonism. It should be realized that these thermocoagulation lesions involved the internal capsule, ansa lenticularis, and globus pallidus (118,119), and so the clinical beneﬁt in these cases may not have been solely due to deactivation of the STN. Early studies of deactivation of the subthalamic area by lesioning cannot be used to provide good quality evidence by today’s standards because the lesions in this eloquent region of the brain were not anatomically well deﬁned (120). Indeed, as mentioned above, ‘‘subthalamic’’ lesions usually purposefully avoided the STN proper in an attempt to prevent hemiballism. When the STN became a logical target in the surgical treatment of PD, concern over the possibility of introducing chorea led neurosurgeons to apply DBS rather than electrocoagulation to this site, since the former can be successful and yet is more reversible (39,121). However, the relatively high technological demands and costs of DBS have recently encouraged some groups to attempt subthalamic nucleotomy in patients with PD. Data on the safety and efﬁcacy of this approach are very limited. There have been only three open-label, nonrandomized reports of the use of unilateral subthalamic nucleotomy in PD. The target in one study was the sensorimotor region of the dorsal STN, deﬁned by semimicrorecordings and stimulation (20). These authors showed a sustained reduction in off motor UPDRS by 50% in 10 of 11 patients, and this effect was maintained in 4 of 11 patients for 2 years. UPDRS on scores and ADL scores also improved ‘‘drastically. Axial scores for gait and postural instability showed marked and sustained improvements. Dyskinesias were seen in the contralateral limbs of 5 patients during lesioning and lasted up to 12 hours before abating spontaneously. Another patient developed a post-operative infarction affecting the area of the lesioned STN, zona incerta, and ventral thalamus. This resulted in severe contralateral dyskinesia that persisted despite cessation of all levodopa and eventually required treatment with a pallidotomy on the same side as the ‘‘subthalamotomy. In the second series, the target was the central area of the subthalamus in nine patients and lesioning was guided by macrostimulation (21). Efﬁcacy results were not reported, but only one patient developed chorea post- operatively, which initially required medical treatment but then subsided spontaneously to only mild movements. In the series of Gill and Heywood, ﬁve patients had unilateral and ﬁve had bilateral small subthalamotomies with improved parkinsonism, and only one case had mild dyskinesia (122). These early studies showed that the risk of signiﬁcant chorea after unilateral ‘‘subthalamotomy’’ is about 10% and that medication doses may not be signiﬁcantly reduced, possibly because the ipsilateral side is minimally affected by the lesion. The precise location of lesions in the subthalamic area needs further conﬁrmation of exactly where the optimal target should be placed. It could be hypothesized, for example, that discrete small lesions conﬁned to the nucleus (i. Therefore, the exact location and role of unilateral lesions of the subthalamic region remains unclear in clinical practice. BILATERAL ‘‘SUBTHALAMOTOMY’’ The effects of bilateral subthalamic nucleotomy were reported earlier than unilateral ‘‘subthalamotomy. Both patients were reported to have no complications and to have medication withdrawn. This group later reported in abstract that bilateral ‘‘subthalamotomy’’ had been accomplished safely in ﬁve subjects (122).
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