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The rear of the retina is supplied with blood from the choroid buy discount calan 80mg on-line, while the front is supplied by the central artery and vein that enter the eye- ball with the optic nerve 240mg calan with visa, the fiber bundle that connects the retina with structures in the brain. The vascular supply to the front of the retina, which ramifies and spreads over the retinal surface, is visible through the lens and affords a direct view of the microcirculation; this window is useful for diagnostic purposes, even for conditions not directly re- lated to ocular function. At the optical center of the retina, where the image falls when one is looking straight ahead (i. During fixation macula is the fovea centralis, a depressed region about 0. With the lens flattened, parallel rays from a distant object are Slightly off to the nasal side of the retina is the optic disc, brought to a sharp focus. B, Lens curvature increases with accom- where the optic nerve leaves the retina. CHAPTER 4 Sensory Physiology 73 in the form of external lenses (reading glasses), is required The iris, which has both sympathetic and parasympa- for distinct near vision. They can be capable of a 30-fold change in area and in the amount of corrected with external lenses (eyeglasses or contact light admitted to the eye. Farsightedness or hyperopia is caused by an eyeball flex control, and bright light entering just one eye will that is physically too short to focus on distant objects. In effect, the converging power of the eye is too great; close Eye Movements. The extraocular muscles move the vision is clear, but the eye cannot focus on distant objects. These six muscles, which originate on the bone of the A negative (diverging) lens corrects this defect. If the cur- orbit (the eye socket) and insert on the sclera, are arranged vature of the cornea is not symmetric, astigmatism results. They are under visually Objects with different orientations in the field of view will compensated feedback control and produce several types have different focal positions. Vertical lines may appear of movement: sharp, while horizontal structures are blurred. This condi- • Continuous activation of a small number of motor units tion is corrected with the use of a cylindrical lens, which produces a small tremor at a rate of 30 to 80 cycles per has different radii of curvature at the proper orientations second. Especially in older adults, there may be a progressive and large, slow movements, used in following moving increase in its opacity, to the extent that vision is obscured. This condition, called a cataract, is treated by surgical re- Organized movements of the eyes include: moval of the defective lens. An artificial lens may be im- • Fixation, the training of the eyes on a stationary object planted in its place, or eyeglasses may be used to replace • Tracking movements, used to follow the course of a the refractive power of the lens. The peak spectral sensitivity ward to fix on near objects for the red-sensitive pigment is 560 nm; for the green-sen- • Nystagmus, a series of slow and saccadic movements sitive pigment, it is about 530 nm; and for the blue-sensi- (part of a vestibular reflex) that serves to keep the retinal tive pigment, it is about 420 nm. At wavelengths away from the optimum, the receives a slightly different image of the same object. Be- property, binocular vision, along with information about cause of the interplay between light intensity and wave- the different positions of the two eyes, allows stereoscopic length, a retina with only one class of cones would not be vision and its associated depth perception, abilities that are able to detect colors unambiguously. Many ab- of the three pigments in each cone removes this uncer- normalities of eye movement are types of strabismus tainty. Colorblind individuals, who have a genetic lack of (“squinting”), in which the two eyes do not work together one or more of the pigments or lack an associated trans- properly. Other defects include diplopia (double vision), duction mechanism, cannot distinguish between the af- when the convergence mechanisms are impaired, and am- blyopia, when one eye assumes improper dominance over the other. Failure to correct this latter condition can lead to loss of visual function in the subordinate eye. The retina is a multi- B layered structure containing the photoreceptor cells and a complex web of several types of nerve cells (Fig. There are 10 layers in the retina, but this discussion em- ploys a simpler four-layer scheme: pigment epithelium, photoreceptor layer, neural network layer, and ganglion cell layer. These four layers are discussed in order, begin- ning with the deepest layer (pigment epithelium) and mov- ing toward the layer nearest to the inner surface of the eye C (ganglion cell layer). Note that this is the direction in which visual signal processing takes place, but it is opposite to the path taken by the light entering the retina.

These signals may result in contraction ( ) or relaxation ( ) of the digestive tract musculature effective 240 mg calan. Afferents calan 120 mg on line, Second-Order Interneurons, and Efferent Neurons A reflex circuit known as the vago-vagal reflex underlies moment-to-moment adjustments required for optimal di- ronal cell bodies in the dorsal motor nucleus in the medulla gestive function in the upper digestive tract (see Clinical oblongata project in the vagus nerves, and those in the Focus Box 26. The afferent side of the reflex arc consists sacral region of the spinal cord project in the pelvic nerves of vagal afferent neurons connected with a variety of sen- to the large intestine. Efferent fibers in the pelvic nerves sory receptors specialized for the detection and signaling of make synaptic contact with neurons in ganglia located on mechanical parameters, such as muscle tension and mucosal the serosal surface of the colon and in ganglia of the ENS brushing, or luminal chemical parameters, including glu- deeper within the large intestinal wall. Cell bodies of the synapse with neurons of the ENS in the esophagus, stom- vagal afferents are in the nodose ganglia. The afferent neu- ach, small intestine, and colon, as well as in the gallbladder rons are synaptically connected with neurons in the dorsal and pancreas. The nucleus of the tractus solitarius, which lies vation of the GI musculature to control digestive processes directly above the dorsal motor nucleus of the vagus (see both in anticipation of food intake and following a meal. A synaptic meshwork ior in the stomach as a result of activation of the enteric cir- formed by processes from neurons in both nuclei tightly cuits that control excitatory or inhibitory motor neurons, re- links the two into an integrative center. Parasympathetic efferents to the small and large neurons are second- or third-order neurons representing intestinal musculature are predominantly stimulatory as a re- the efferent arm of the reflex circuit. They are the final sult of their input to the enteric microcircuits that control the common pathways out of the brain to the enteric circuits activity of excitatory motor neurons. The dorsal vagal complex consists of the dorsal motor Efferent vagal fibers form synapses with neurons in the nucleus of the vagus, nucleus tractus solitarius, area ENS to activate circuits that ultimately drive the outflow of postrema, and nucleus ambiguus; it is the central vagal in- signals in motor neurons to the effector systems. This center in the brain is more effector system is the musculature, its innervation consists directly involved in the control of the specialized digestive of both inhibitory and excitatory motor neurons that par- functions of the esophagus, stomach, and the functional ticipate in reciprocal control. If the effector systems are cluster of duodenum, gallbladder, and pancreas than the gastric glands or digestive glands, the secretomotor neu- distal small intestine and large intestine. The circuits in the rons are excitatory and stimulate secretory behavior. The generalized Abdominal Early satiety symptoms of both disorders overlap (Fig. Surgical Heartburn Pallor vagotomy results in a rapid emptying of liquids and a de- Anorexia Rapid pulse layed emptying of solids. As mentioned earlier, vagotomy Weight loss Perspiration impairs adaptive relaxation and results in increased con- Syncope tractile tone in the reservoir (see Fig. Increased pressure in the gastric reservoir more forcefully presses liquids into the antral pump. Paralysis with a loss of Delayed Rapid propulsive motility in the antrum occurs after a vagotomy. A Symptoms of disordered gastric empty- layed emptying of solids after a vagotomy. Some of the symptoms of delayed vagotomy is performed as a treatment for peptic ulcer dis- and rapid gastric emptying overlap. Delayed gastric emptying with no demonstrable un- absence of inhibitory motor neurons and the failure of derlying condition is common. Up to 80% of patients the circular muscles to relax account for the obstructive with anorexia nervosa have delayed gastric emptying of stenosis. Another such condition is idiopathic gastric Rapid gastric emptying often occurs in patients who stasis, in which no evidence of an underlying condition have had both vagotomy and gastric antrectomy for the can be found. These individuals have are used successfully in treating these patients. The pathological ef- dren, hypertrophic pyloric stenosis impedes gastric fects are referred to as the dumping syndrome, which re- emptying. This is a thickening of the muscles of the py- sults from the “dumping” of large osmotic loads into the loric canal associated with a loss of enteric neurons. Memory, the processing of incoming information ercise and stressful environmental change, coinciding with from outside the body, and the integration of propriocep- the suppression of digestive functions, including motility tive information are ongoing functions of higher brain cen- and secretion.

The epithelial layer contains glands edematous buy calan 120 mg cheap, and the spiral arteries become tortuous (see that penetrate the stromal layer buy discount calan 80mg line. Peak secretory activity, edema formation, and secretory columnar epithelium. The pro- to 8 after ovulation in preparation for implantation of the liferative phase coincides with the midfollicular to late fol- blastocyst. Progesterone antagonizes the effect of estrogen licular phase of the menstrual cycle. Under the influence of on the myometrium and reduces spontaneous myometrial the rising plasma estradiol concentration, the stromal and contractions. The endometrial glands elongate and are lined with the declining levels of progesterone and estradiol caused by columnar epithelium. Necrotic changes and ized, and more spiral arteries, a rich blood supply to this re- abundant apoptosis occur in the secretory epithelium as it gion, develop. The arteries constrict, reducing the blood supply progesterone receptors and increases myometrial excitabil- to the superficial endometrium. Leukocytes persist in large numbers coincides with the early to midluteal phase of the menstrual throughout menstruation, providing resistance against in- cycle. The endometrium contains numerous progesterone fection to the denuded endometrial surface. Ovulation Proliferative phase Secretory phase Days 0 4 8 12 16 20 24 28 32 Progesterone Estradiol 99 Basal body temperature 98 97 100 Vaginal cornification and 50 pyknotic index 0 3 Cervical mucus 2 ferning 1 0 Glycogen vacuoles 4 Gland Endometrium Cyclic changes in the uterus, 3 FIGURE 38. It is se- layer of the endometrium occurs during the menstrual creted in significant amounts during the luteal phase of the phase (menses). The reduction in steroids destabilizes cretes progesterone throughout the first trimester, and the lysosomal membranes in endometrial cells, resulting in the placenta continues progesterone production until parturi- liberation of proteolytic enzymes and increased production tion. Small amounts of 17-hydroxyprogesterone are se- of vasoconstrictor prostaglandins (e. Progesterone binds prostaglandins induce vasospasm of the spiral arteries, and equally to albumin and to a plasma protein called corticos- the proteolytic enzymes digest the tissue. Progesterone is me- blood vessels rupture and blood is released, together with tabolized in the liver to pregnanediol and, subsequently, cellular debris. The endometrial tissue is expelled through excreted in the urine as a glucuronide conjugate. The menstrual flow lasts 4 to 5 days and averages 30 to ovaries and adrenals and from peripheral conversion. It does not clot because of the presence drostenedione and dehydroepiandrosterone (DHEA) orig- of fibrinolysin, but the spiral arteries constrict, resulting in inate from the adrenal cortex (see Chapter 34), and ovarian a reduction in bleeding. Peripheral conversion from an- Changes in the properties of the cervical mucus promote drostenedione provides an additional source of testos- the survival and transport of sperm and, thus, can be im- terone. Testosterone can also be converted in peripheral portant for normal fertility. The cervical mucus undergoes tissues to dihydrotestosterone (DHT) by 5 -reductase. During the fol- However, the primary biologically active androgen in licular phase, estrogen increases the quantity, alkalinity, women is testosterone. Androgens bind primarily to SHBG viscosity, and elasticity of the mucus. Androgens are relax, and the epithelium becomes secretory in response to also metabolized to water-soluble forms by oxidation, sul- estrogen. By the time of ovulation, elasticity of the mucus fation, or glucuronidation and excreted in the urine. With progesterone rising either after ovulation, during pregnancy, or with low-dose progestogen administration during the cycle, the quantity PUBERTY and elasticity of the mucus decline; it becomes thicker (low During the prepubertal period, the hypothalamic-pituitary- spinnbarkeit) and does not form a ferning pattern when ovarian axis becomes activated—an event known as go- dried on a microscope slide. With these conditions, the nadarche—and gonadotropins increase in the circulation mucus provides better protection against infections and and stimulate ovarian estrogen secretion. The vaginal epithelium proliferates under the influence Factors stimulating the secretion of GnRH include gluta- of estrogen. Basophilic cells predominate early in the fol- mate, norepinephrine, and neuropeptide Y emanating from licular phase.

Remember that responsibility for the patient has been transferred to you buy calan 120 mg on-line. Temporary Admission (Holding) Orders Many emergency physicians feel uncomfortable writing temporary admission orders generic calan 80mg overnight delivery. The official policy statement of the American College of Emergency Physicians (ACEP) states that emergency physicians should not be compelled to write such orders and should do so only when they feel comfortable. You do bear some responsibility for the patient so long as your orders are in effect and until the admitting physician has seen the patient. Although this is an area of potential liability, temporary admis- sion orders may be appropriate, and can be done in a manner that minimizes liability to you and danger to the patient. However, sev- eral things must be ensured and must be clearly understood by all parties involved: 1. Chapter 9 / Emergency Medicine 107 Communication is crucial—between you and the floor nurses, between you and the admitting physician, and between the floor nurses and the admitting physician. Orders should clearly specify (a) which doctor is responsible for the patient after admission and (b) whom to call, when to call, and for what reasons. For example, these orders might be necessary if ques- tions or problems or breach of vital sign limits occur, or if the patient has not been seen by a specified time. The temporary holding orders are necessarily based on data that has a life span and you won’t be around if the data change. An example of temporary admitting orders might include the following: • Admit to Dr. X if pulse less than 60 or greater than 100, or if blood pressure less than 110 systolic or 60 diastolic. Emergency Medical Treatment and Active Labor Act The federal Emergency Medical Treatment and Active Labor Act (EMTALA) is the official name for the law governing the transfer or discharge of patients from EDs. It is sometimes referred to by the aptly abbreviated acronym COBRA, a reference to the original Con- gressional legislation of which it was a section (the Consolidated Omnibus Budget Reconciliation Act of 1986). First, a medical screening examination must be performed prior to inquiring about financial matters. However, this does not have to be performed by a physician, although that is the practice in many EDs. If a nurse performs the initial screening exam, he or she should be certified by the hospital to do so in accordance with a formal hospital protocol. Second, the patient must be stabilized prior to transfer using the hospital’s capabilities and must not be in active labor. Unfortunately, despite periodic federal guideline revisions, the word stabilization has never been clearly defined. And different regional jurisdictions have ruled differently on this matter. Fourth, EMTALA governs discharge from the ED, regardless of destination. Fifth, patients may be transferred even if unstable, if they are trans- ferred for medical reasons to a higher level of care facility. This might include cardiac patients transferred for catheterization or trauma pa- tients sent to a trauma center. However, prior to transfer, the patient must be stabilized as much as possible. Sixth, emergency physicians may be exempt from liability if forced to transfer an unstable patient. Thanks to the efforts of the ACEP, EMTALA excuses emergency physicians forced to transfer unstable patients because they cannot obtain an appropriate admitting physi- cian or because the hospital refuses to admit the patient. However, the emergency physician must clearly state the reason and should identify the specialty physician who refused the admission, especially if that physician is formally on call to the ED. In such cases, however, the emergency physician must do what he or she can to stabilize the patient, such as starting intravenous fluids and antibiotics in a severely dehydrated, septic child or relieving the tension pneumothorax in a trauma patient. The patient may have suffered no harm, yet an EMTALA violation may have occurred. Patients can be transferred from a private to a county hospital if they have no insurance or from a hospital that does not contract with their insurer to one that does.