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Medical Instructor, Michigan State University College of Human Medicine
The lens receives all its nutrition from the aqueous humor which is secreted continuously into the posterior chamber by the ciliary epithelium arrhythmia journal purchase atenolol 50mg overnight delivery. The aqueous humor enters the anterior chamber through the pupil and diffuses posteriorly into the vitreous chamber of the eye arrhythmia 29 years old purchase atenolol american express. The aqueous humor supplies nutrients to the transparent media of the eye and is responsible for maintaining the correct intraocular pressure hypertension meds generic 50 mg atenolol with visa. Stationary refraction occurs through the transparent cornea blood pressure chart in pregnancy generic 100mg atenolol free shipping, in contrast to variable refraction that occurs in the lens as it changes shape to focus near or far objects on the retina during eye accommodation. The lens is held in place by zonule fibers that extend from surrounding ciliary processes and focuses an inverted, real image on the retina. The convexity and thickness of the lens are controlled by the ciliary muscle acting through the ciliary processes and zonule fibers. If the ciliary muscle contracts, the ciliary body and choroid are pulled centrally and forward, releasing tension on the zonule fibers; this allows the lens to become thicker and more convex, enabling the eye to focus on near objects. When the ciliary muscle relaxes, the ciliary body slides posteriorly and peripherally, increasing the tension on the zonule fibers and making the lens thinner and less convex to focus on far objects. The iris is continuous with the ciliary body at the periphery and divides the space between the cornea and lens into anterior and posterior chambers. The chambers communicate via the pupil, an aperture in the iris through which light passes into the lens and vitreous chamber. The dilator of the pupil consists of a single layer of radially arranged myoepithelial cells along the posterior surface of the iris. The sphincter of the iris consists of smooth muscle arranged around the margin of the iris that acts as a diaphragm to modify the amount of light entering the eye and permits vision under a variety of light conditions. The rods and cones of the retina are the photoreceptors that collect visual impressions (light patterns) and translate them into nerve impulses. This action closes cation channels, hyperpolarizes the photoreceptor, and slows glutamate release at the synaptic terminal. In this way, the photoreceptor cells detects light and passes on a generated electrical potential that is transferred to dendrites of associated bipolar cells. Rods have a lower threshold to light intensity than cones and are important in dark and light discrimination and in night vision. Light absorption and generation of an electrical impulse in cones follow a sequence similar to that in rods. Cones serve for color perception and visual acuity, responding to light of relatively high intensity. The central region of the fovea centralis consists only of cones and is in direct line with the visual axis of the eye. Here the inner layers of the retina that are beyond the outer nuclear layer are displaced laterally, allowing light almost a free pathway to the photoreceptors; in this portion of the retina vision is most acute. The pigment epithelium of the retina absorbs light after it has passed through the neural retina and prevents reflection within the eye; melanocytes in the choroid, iris, and other regions of the eye serve a similar purpose. The cells of the pigment epithelium phagocytize the membranous sacs as they are shed from the tips of the outer cone and rod segments. Some components of the digested membranes are carried back to the photoreceptor cells to be reused. The pigment epithelium is a storage site for vitamin A, a precursor of rhodopsin, which is recycled to the membranes of the outer rod segments. Apical tight junctions between cells of the pigment epithelium form a barrier to prevent unwanted materials from entering the neural retina. The neurons are nourished by diffusion from capillaries in the choriocapillary layer of the choroid. Basically, the retina represents a three-neuron chain of receptors (rods and cones), bipolar neurons, and ganglion cells equivalent to the threeneuron sensory chains of the peripheral nervous system. Rod and cones can be equated with any other sensory receptors, bipolar neurons with craniospinal ganglia, and retinal ganglion cells with internuncial neurons in the spinal cord and brainstem. Thus, the arrangement of nervous elements in the sensory chain of the retina is similar to that of other sensory pathways. The retina represents an extension of the brain, modified to form a special receptor. Other neurons, horizontal cells, amacrine cells, and interplexiform cells in the retina serve as association neurons.
The position of the zonula adherens blood pressure 4060 discount atenolol online american express, forming a contractile ring around the circumference of the cell heart attack 9gag cheap atenolol 50mg online, coupled with the contractile nature of the actin microfilament bundles is ideal for regulating morphogenetic changes blood pressure medication classes buy atenolol toronto. Desmosomes (answers b and e) are involved in resisting shear forces and are not directly involved in this process blood pressure medication liver disease purchase 100 mg atenolol mastercard. See table in answer for question 83 for detailed summary of function of components of the junctional complex. The action potential is transmitted from cell to cell through the heart, providing the rhythmic contraction of the heartbeat. Abnormalities in the spatial distribution of gap junctions or the proteins (connexins) that compose the connexons will lead to arrhythmias and play a role in obstructive coronary heart disease. Such mutations may also play a role in the racial differences seen in the outcome following myocardial infarction and cardiac disease. For example, alterations in connexin density or distribution 164 Anatomy, Histology, and Cell Biology may be differentially affected during the development of hypertrophy, thereby increasing the risk of reentrant or nonsustained ventricular tachycardia seen in African-American males. In the freeze-fracture micrograph, the connexons are seen in circular arrangements on the P face of the membrane. Rapid nerve conduction in some systems uses gap junctions to avoid the chemical synapse, which requires the release of neurotransmitter. Mutations in connexins would slow down normal nerve impulse conduction (answer a). Normal peristalsis (answer b) requires normal gap junctions between smooth muscle in the small intestine and would be slowed down in the absence of normal gap junctions. Innervated and noninnervated hepatocytes are connected by gap junctions, which allows for a more coordinated effect of norepinephrine on hepatocytes to facilitate release of blood glucose from stored glycogen in hepatocytes (answer d). Adherence of epithelial cells to the basement membrane (answer e) is dependent on integrins and hemidesmosomes, not gap junctions. In most epithelia, the basement membrane prevents penetration from the underlying lamina propria into the epithelium. Basement membranes are a pathway for migrating cells during development and repair processes. In the kidney, the basement membrane of the renal glomerulus forms a selective barrier for the filtration of the plasma. Contractility and excitability (answers b and c) are characteristics that are associated with muscle and nerve, respectively, not with the basement membrane. Active ion transport and modification of secretory proteins (answers d and e) are characteristics of the epithelia that are positioned on the basement membrane, not of the basement membrane itself. The split occurs through the lamina lucida of the basal lamina, which contains primarily laminin and its connections with the integrins. At the light microscopic level, a uniform basement membrane is visible under epithelia. Ultrastructurally, basement membranes are composed of one or two electron-lucent areas (laminae rarae) that contain laminin, proteoglycans, and adhesive proteins. The third layer is the reticular layer that is formed by the underlying connective tissue. This reticular lamina is composed of collagen fibrils formed by the connective tissue below the epithelium (basement membrane = basal lamina + reticular lamina. Exocytosis and endocytosis (answers b and c) may occur across both apical and basolateral membranes, as does ion transport. The apical surface of cells is covered by a glycocalyx (answer e) that consists of oligosaccharides linked to glycoproteins and glycolipids 166 Anatomy, Histology, and Cell Biology and proteoglycans. The presence of those sugars results in a negative (polyanionic) charge on the luminal surface. Polarity of the epithelial cell is based on these apical and basolateral specializations of the cell membrane and is maintained by the zonula occludens of the junctional complex. These deep infoldings of the basal plasma membrane increase surface area and compartmentalize numerous mitochondria that provide energy for ionic and water transport. The primary (isotonic) saliva (answer d) is formed by acinar cells and modified by the striated duct cells which resorb Na+ and excrete K+.
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Pathogens can be found in various compartments of the body arrhythmia potassium purchase atenolol 100 mg without a prescription, where they must be combated by different host defense mechanisms blood pressure medication od buy atenolol with mastercard. Virtually all pathogens have an extracellular phase where they are vulnerable to antibody-mediated effector mechanisms blood pressure medication used to treat acne best 50mg atenolol. However blood pressure goes up when standing buy atenolol australia, intracellular phases are not accessible to antibody, and these are attacked by T cells. The mechanisms of damage, representative infectious agents, and the common names of the diseases associated with each are shown. Exotoxins are released by microorganisms and act at the surface of host cells, for example, by binding to receptors. Endotoxins, which are intrinsic components of microbial structure, trigger phagocytes to release cytokines that produce local or systemic symptoms. Finally, adaptive immune response to the pathogen can generate antigen:antibody complexes that can activate neutrophils and macrophages, antibodies that can cross-react with host tissues, or T cells that kill infected cells. In addition, neutrophils, the most abundant cells early in infection, release many proteins and small-molecule inflammatory mediators that both control infection and cause tissue damage (not shown). The mammalian body is susceptible to infection by many pathogens, which must first make contact with the host and then establish a focus of infection in order to cause infectious disease. To establish an infection, the pathogen must first colonize the skin or the internal mucosal surfaces of the respiratory, gastrointestinal, or urogenital tracts and then overcome or bypass the innate immune defenses associated with the epithelia and underlying tissues. If it succeeds in doing this, it will provoke an adaptive immune response that will take effect after several days and will usually clear the infection. Pathogens differ greatly in their lifestyles and means of pathogenesis, requiring an equally diverse set of defensive responses from the host immune system. It is not known how many infections are dealt with solely by the nonadaptive mechanisms of innate immunity discussed in Chapter 2; this is because such infections are eliminated early and produce little in the way of symptoms or pathology. Moreover, deficiencies in nonadaptive defenses are rare, so it has seldom been possible to study their consequences. Innate immunity does, however, appear to be essential for effective host defense, as shown by the progression of infection in mice that lack components of innate immunity but have an intact adaptive immune system. Adaptive immunity is also essential, as shown by the immunodeficiency syndromes associated with failure of one or the other arm of the adaptive immune response (see Chapter 11). Adaptive immunity is triggered when an infection eludes the innate defense mechanisms and generates a threshold dose of antigen (see. This antigen then initiates an adaptive immune response, which becomes effective only after several days, the time required for antigen- specific T cells and B cells to locate their specific foreign antigen, to proliferate, and to differentiate into armed effector cells. In the earlier chapters of this book, we discussed the cells and molecules that mediate the adaptive immune response, and the interactions between them. We are now ready to see how each cell type is recruited in turn in the course of a primary adaptive immune response to a pathogen, and how the effector lymphocytes and antibodies that are generated in response to antigen are dispersed to their sites of action. A primary adaptive response also establishes a state of long-lasting protective immunity that is ultimately mediated by long-lived resting memory cells, to which we will return in the last part of this chapter. The green curve shows the course of infection in mice and humans that have innate immunity but have no T or B lymphocytes and so lack adaptive immunity. The yellow curve shows the normal course of an infection in immunocompetent mice or humans. The nonspecific responses of innate immunity are necessary for an adaptive immune response to be initiated. The establishment of a focus of infection in tissues and the response of the innate immune system to it produce changes in the immediate environment of the infection. In a bacterial infection, the first thing that usually happens is that the infected tissue becomes inflamed (see. The cytokines cause the release of Weibel-Palade bodies from within the endothelial cells, which deliver P-selectin to the endothelial cell surface. Macrophages encountering bacteria in the tissues are triggered to release cytokines that increase the permeability of blood vessels, allowing fluid and proteins to pass into the tissues. They also produce chemokines that direct the migration of neutrophils to the site of infection. Later in an immune response, activated lymphocytes may also contribute to inflammation. The electron micrograph shows a neutrophil extravasating between endothelial cells.
The surgical removal of the tumor will often relieve those headaches; and post-operative headaches often go away after a short period of time hypertension kidney group 08755 generic 50 mg atenolol. If headaches return hypertension images buy atenolol 100mg without prescription, it could be a sign of recurrent edema or a new tumor and should be addressed by your treatment team blood pressure z score buy atenolol with mastercard. It can cause a range of reactions prehypertension kidney disease cheap atenolol 50 mg with mastercard, from muscle contractions, to staring, to loss of consciousness. Some people only experience one seizure while others suffer from reoccurring seizures, or epilepsy. Seizures are common with slow-growing gliomas, meningiomas, and metastatic brain tumors. A patient may be aware of his or her surroundings but unable to speak, or may feel confused and hallucinate (imagining sights, odors, and sounds). They begin with a sudden loss of physical control with flailing arms and legs, unconsciousness, twitching muscles, and incontinence, or shallow breathing. A patient may be put on an antiepileptic or antiseizure drug if he or she experiences a seizure or to prevent seizures. The type and amount of medication is based on the level of seizure control needed and how well you react to the medication. Try to remove or cushion harmful objects to prevent injury, and do not put anything in their mouth. Call for emergency help if the seizure lasts longer than five minutes, if a second seizure immediately follows, or if the person has trouble breathing or is injured. Patients who suffer from multiple seizures can keep a journal of when and for how long the seizures occur. If anemia becomes severe, it can be treated with medications or with a blood transfusion. Chemotherapy can decrease the production of these cells, and when they fall too low we are at risk for spontaneous bleeding. Thrombosis is the formation of blood clots as a result of increased clotting factors in the blood. With deep vein thrombosis blood clots form in the legs, and disrupt the flow of blood, causing pain or swelling in the calf, behind the knee, or in the thigh. Compression stockings and medication to thin the blood are also used for prevention. It is caused by many things, from tumor treatments to the tumor itself, to the healing process, to poor sleep, stress, or anemia. The goal is to conserve energy so you can focus on doing the things that are important to you. Patients may experience difficulties with their communication, concentration, memory, and their personality may change. Medication may be prescribed to reduce problems with cognitive and behavioral changes, and counseling may help a patient recognize when they are experiencing cognitive problems. Cognitive Rehabilitation Cognitive rehabilitation is designed to help people regain as much of their mental, physical and emotional abilities as possible. It is important that a caregiver has help or compensation strategies that he/she can use to maintain the high level of patience that is required. When full recovery is not possible, treatment includes compensation techniques like learning to live with memory loss by keeping calendars, reminder systems, and organizers. Neuropsychologists are cognitive experts that can help identify compensation solutions or offer medications to enhance mental functioning (for example, Ritalin). Sticky notes, lists, and always putting your keys in the same place help take the burden off your memory systems.