By C. Kaffu. The College of Saint Thomas More. 2018.
The compression (or rarefaction) of air molecules in auditory system allow encoding of most of this wide range one region causes a similar compression in adjacent re- into biologically useful information generic ampicillin 500 mg with mastercard. Continuation of this process causes the disturbance Sinusoidal sound waves contain all of their energy at (the sound wave) to spread away from the source order 500 mg ampicillin with mastercard. Complex The speed at which the sound wave travels is deter- sound waves, such as those in speech or music, consist of mined by the elasticity of the air (the tendency of the mol- the addition of several simpler waveforms of different fre- ecules to spring back to their original positions). The human ear is capable of hear- the sound source is moving back and forth at a constant rate ing sounds over the range of 20 to 16,000 Hz, although the of alternation (i. Auditory sensitivity varies compression wave will pass a given point once for every cy- with the frequency of the sound; we hear sounds most read- cle of the source. Because the propagation speed is constant ily in the range of 1,000 to 4,000 Hz and at a sound pres- in a given medium, the compression waves are closer to- sure level of around 60 dB. Not surprisingly, this is the fre- gether at higher frequencies; that is, more of them pass the quency and intensity range of human vocalization. A tone of 1,000 cycles per second, travel- by the masking sound, which would reduce the number of ing through the air, has a wavelength of approximately available receptor cells. The pinna, the visible portion of the outer water are greater than those in air, the speed of sound in ear, is not critical to hearing in humans, although it does water is about 4 times as great, and the wavelength is cor- respondingly increased. Since the wavelength depends on the elasticity of the medium (which varies according to temperature and pressure), it is more convenient to TABLE 4. Sound fre- Common Sounds quency is usually expressed in units of Hertz (Hz or cy- Sound cles per second). Pressure Pressure Relative Another fundamental characteristic of a sound wave is 2 (dynes/cm ) Level (dB) Sound Source Pressure its intensity or amplitude. This may be thought of as the relative amount of compression or rarefaction present as 0. Be- 200 120 Loud thunder 1,000,000 cause the human ear is sensitive to sounds over a million- 2,000 140 Pain and damage 10,000,000 fold range of sound pressure levels, it is convenient to ex- press the intensity of sound as the logarithm of a ratio Modified from Gulick WL, Gescheider GA, Frisina RD.
Genotyping is a (B) Addison’s disease zona glomerulosa valuable diagnostic complement to (C) Defects in ACTH secretion 7 order 500mg ampicillin otc. The rate-limiting step in the synthesis neonatal screening for congenital adre- (D) Defects in corticosteroid-binding of cortisol is catalyzed by nal hyperplasia due to steroid 21-hy- globulin (A) 21-Hydroxylase droxylase deficiency order 250mg ampicillin with mastercard. J Clin Endocrinol (E) Cushing’s disease (B) 3 -Hydroxysteroid dehydrogenase Metab 1999;84:1505–1509. Catecholamines In: Wilson JD, Foster DW, Kronen- How do glucocorticoids influence and the adrenal medulla. Integrating permis- JD, Foster DW, Kronenberg Textbook of Endocrinology. Effects of glucagon on carbohydrate, lipid, and protein me- within each islet of Langerhans shows a distinctive pattern tabolism occur primarily in the liver and are catabolic in and suggests that there may be some paracrine regulation nature. Plasma glucose is the primary physiological regulator of beta cells, whereas type 2 diabetes often results from a insulin and glucagon secretion, but amino acids, fatty lack of responsiveness to circulating insulin. Insulin has anabolic effects on carbohydrate, lipid, and pro- such as ketoacidosis, and chronic secondary complica- tein metabolism in its target tissues, where it promotes the tions, such as peripheral vascular disease, neuropathy, and storage of nutrients. The islets Tamounts of metabolic fuel was an important adaptation contain specific types of cells responsible for the secretion in the evolution of complex organisms. Se- volved in the digestion, storage, and use of fuels require a cretion of these hormones is regulated by a variety of cir- high degree of regulation and coordination. Cells of the exocrine pancreas produce and secrete di- The Islets of Langerhans Are the Functional gestive enzymes and fluids into the upper part of the small Units of the Endocrine Pancreas intestine. The endocrine pancreas, an anatomically small The islets of Langerhans contain from a few hundred to sev- portion of the pancreas (1 to 2% of the total mass), pro- eral thousand hormone-secreting endocrine cells. The human pancreas contains, docrine portions of the pancreas are usually discussed sep- on average, about 1 million islets, which vary in size from 50 arately. Each islet is separated from the sur- of the endocrine pancreas, the overall function of the pan- rounding acinar tissue by a connective tissue sheath. Immunofluorescent staining SYNTHESIS AND SECRETION OF THE techniques have shown that the four cell types are arranged ISLET HORMONES in each islet in a pattern suggesting a highly organized cel- lular community, in which paracrine influences may play an The endocrine pancreas consists of numerous discrete important role in determining hormone secretion rates clusters of cells, known as the islets of Langerhans, which (Fig. Further evidence that cell-to-cell communica- 623 624 PART IX ENDOCRINE PHYSIOLOGY Therefore, islet hormones arrive in high concentrations in some areas of the exocrine pancreas before reaching pe- ripheral tissues.