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APPENDIX A Answers to Review Questions the action of either adenylyl or guanylyl cyclase on ATP or GTP order 375mg keftab with amex, respectively purchase keftab 750 mg mastercard. For example, cAMP Chapter 1 can activate protein kinase A, which will phosphory- 1. In a steady state, the amount or con- late its substrates; cGMP activates protein kinase G, centration of a substance in a compartment does not which phosphorylates a different set of substrates. Although there may be though signal transduction in sensory tissues involves considerable movements into and out of the compart- both cAMP and cGMP, cGMP has a more important ment, there is no net gain or loss. Phospholipase body often do not represent an equilibrium condition, C activation is coupled to the activation of a G protein but they are displaced from equilibrium by the con- (Gq), not to cAMP or cGMP. The increase in plasma insulin lowers scriptional regulators found in the cytoplasm or in the the plasma glucose concentration back to normal and nucleus. These receptors are activated by the binding is an example of negative feedback. Negative feedback of steroid ligands that diffuse through lipid bilayers opposes change and results in stability. Activated steroid receptors me- back would produce a further increase in plasma glu- diate their effects by direct interaction with gene reg- cose concentration. Chemical equilibrium indicates a ulatory elements and do not activate G proteins or condition in which the rates of reactions in forward cause binding of IP3 to the IP3-gated calcium release and backward directions are equal. Steroid hor- bition occurs when the products of a chemical reaction mone receptors do not have tyrosine kinase activity slow the reaction (for example, by inhibiting an en- and do not cause the phosphorylation of tyrosine zyme) that produces them. Steroid hormone receptors volves a command signal and does not directly sense are not linked to activation of the MAP kinase path- the regulated variable (plasma glucose concentration). The EGF receptor is a tryosine kinase of cells; upon binding of estrogen, they move to the receptor; therefore, an inhibitor of tyrosine kinases nucleus to bind to estrogen response elements to acti- should have the desired effect. Cardiac muscle cells have many gap crease intracellular levels of cAMP, but this is not the junctions that allow the rapid transmission of electrical second messenger problem here.
The outermost muscle layer purchase keftab 500 mg on-line, which is relatively thin buy 125mg keftab with mastercard, cle, which allows it to remain contracted for long periods runs along the length of the intestine. The inner muscle with little energy consumption, and the small size of its layer, thicker and more powerful, has a circular arrange- cells, which allows precise control of very small structures, ment. Coordinated alternating contractions and relaxations such as blood vessels. Most smooth muscles are not discrete of these two layers propel the contents of the intestine, al- organs (like individual skeletal muscles) but are intimate though most of the motive power is provided by circular components of larger organs. The most complex arrangement of smooth muscle is found in organs such as the urinary bladder and uterus. Numerous layers and orien- Structural Arrangements Equip tations of muscle fibers are present and the effect of their Smooth Muscle for Its Special Roles contraction is an overall reduction of the volume of the or- While there are major differences among the organs and gan. Even with such a complex arrangement of fibers, co- systems in which smooth muscle plays a major part, the ordinated and organized contractions take place. The re- structure of smooth muscle is quite consistent at the tissue lengthening force, in the case of these hollow organs, is level and even more similar at the cellular level. In the typical arrangements of smooth muscle occur in a variety urinary bladder, for example, the muscle is gradually of locations. The variety of smooth muscle tasks—regulating and In a few instances, smooth muscles are structurally simi- promoting movement of fluids, expelling the contents of lar to skeletal muscles in their arrangement. Some of the organs, moving visceral structures—is accomplished by a structures supporting the uterus, for example, are called lig- few basic types of tissue structures. All of these structures aments; however, they contain large amounts of smooth are subject, like skeletal muscle, to the requirement for an- muscle and are capable of considerable shortening. Pilo- tagonistic actions: If smooth muscle contracts, an external motor muscles, the small cutaneous muscles that erect the force must lengthen it again. The structures described be- hairs, are also discrete structures whose shortening is basi- low provide these restoring forces in a variety of ways. Certain areas of mesentery also con- tain regions of linearly oriented smooth muscle fibers. The simplest smooth muscle arrangement is found in the arteries and Small Cell Size Facilitates Precise Control veins of the circulatory system.
Such training may be included in response of the eye called nystagmus hearing aid orientation and/or special pro- (involuntary horizontal eye movement) generic 125mg keftab overnight delivery. Eye Surgical Procedures movement may be monitored visually or Surgical procedures may be performed with electronystagmography buy generic keftab 125 mg line, a procedure in to eliminate pathological conditions and which electrodes are placed near the eye to restore or improve hearing. Myringotomy TREATMENT OF HEARING LOSS When the middle ear is infected, as in AND DEAFNESS otitis media, or when there is a ﬂuid build- up in the middle ear, surgical intervention Both medical and nonmedical interven- may be necessary to drain pus or ﬂuid, tions may be used in the treatment of thus relieving pressure and preventing hearing loss. Medical interventions may in- rupture of the eardrum (tympanic mem- volve surgery or medications, and nonmed- brane). A myringotomy is a procedure in ical interventions may include use of hearing which an incision is made into the aids or other assistive listening devices and eardrum for this purpose. Treatment in cedure is performed under controlled most cases involves a variety of profession- conditions, it seldom leaves enough scar als. An otolaryngologist (a physician who tissue to have a negative effect on hearing. Myringoplasty is a speciﬁc type of not remove ﬂuid that has invaded the tympanoplasty in which the damaged mastoid air cell system, however, and addi- eardrum is repaired. Other types of tym- tional intervention may be necessary if the panoplasty may be performed for the sur- mastoid system is to be rendered dry. A gical repair or reconstruction of the ossicles common procedure performed during of the middle ear. Repairing or recon- myringotomy is placing ventilation- or pres- structing the conductive mechanisms of sure-equalizing tubes in the tympanic mem- the middle ear may improve or restore the brane. The pressure-equalizing tubes act as conductive component of individuals’ an artiﬁcial eustachian tube, equalizing hearing. Abnormal eustachian tube function is the most common cause Stapedectomy of middle ear problems. The ventilation tubes usually extrude on their own with- The most common surgical treatment in 3 to 18 months with few complications.