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Beyond this point generic 1 mg finasteride free shipping hair loss black book, there is no addi- membrane but discount finasteride 5mg without a prescription hair loss in men 1 symptoms, unlike N2O, CO has a strong affinity for tional transfer of oxygen. As the red cell moves through the pulmonary gen transfer is more like that of N2O and is limited prima- capillary, CO rapidly diffuses across the alveolar-capillary rily by blood flow in the capillary (perfusion-limited). When Hence, an increase in cardiac output will increase oxygen a trace amount of CO is breathed, most is chemically uptake. Not only does cardiac output increase capillary bound in the blood, resulting in low partial pressure (PCO). The latter increases the surface area for diffusion by illary membrane is never reached, and the transfer of CO to opening up more capillary beds by recruitment. Ordinarily this process takes only about erage alveolar-capillary PO2 difference during a normal one third of the available time, leaving a wide safety mar- transit time is 14 mm Hg, then the DL for oxygen is 18 gin to ensure that the end-capillary PO2 is equilibrated with mL/min per mm Hg. With vigorous exercise, the transit time may difference for oxygen cannot be measured and can only be be reduced to one third of a second (see Fig. Thus, estimated, CO is used to determine the lung diffusing ca- with vigorous exercise, there is still time to fully oxygenate pacity in patients. Pulmonary end-capillary PO2 still equals alveo- uring DL: lar PO2 and rarely falls with vigorous exercise. In this case, there is measurable difference between carbon monoxide to remain essentially zero in the pul- alveolar and end-capillary PO2. To measure the diffusing capacity in a patient with CO, the equation is. DIFFUSING CAPACITY DL VCO (3) In practice, direct measurements of As, T, and D in intact Paco lungs are impossible to make. The most common technique for making this measure- ment is called the single-breath test. The patient inhales Diffusing Capacity Is a Determinant of the a single breath of a dilute mixture of CO and holds his or Rate of Gas Transfer her breath for about 10 sec. By determining the percent- age of CO in the alveolar gas at the beginning and the end The diffusing capacity provides a measure of the rate of gas of 10 sec and by measuring lung volume, one can calculate. The normal ample, if 250 mL of O2 per minute are taken up and the av- resting value for DLCO depends on age, sex, and body size. DLCO ranges from 20 to 30 mL/min per mm Hg and decreases with pulmonary edema or a loss of alveolar membrane (e. Hemoglobin and Capillary Blood Volume • AS Affect Lung Diffusing Capacity Vgas D (P1 P2) T Diffusing capacity does not depend solely on the diffusion properties of the lungs; it is also affected by blood hematocrit and pulmonary capillary blood volume. Both the hematocrit and capillary blood volume affect DL in the same direction (i. For example, if two individuals have the same the pul- monary diffusion properties but one is anemic (reduced hematocrit), the anemic individual will have a decreased lung • diffusing capacity. An abnormally low cardiac output lowers Vgas DL (P1 P2) the pulmonary capillary blood volume, which decreases the alveolar capillary surface area and will, in turn, decrease the diffusing capacity in otherwise normal lungs. GAS TRANSPORT BY THE BLOOD • Vgas The transport of O and CO by the blood, often referred DL 2 2 (P1 P2) to as gas transport, is an important step in the overall gas exchange process and is one of the important functions of FIGURE 21. These properties are combined into one term, lung diffusing capacity Oxygen Is Transported in Two Forms (DL), which can be measured in a human subject. DL is equal to the volume of gas transferred/min (gas) divided by the mean par- Oxygen is transported to the tissues in two forms: com- tial pressure gradient for the gas. Approximately 98% of the oxygen blood and oxygen capacity is 20 mL O2/dL blood, then the is carried by hemoglobin and the remaining 2% is carried blood is 80% saturated. The relation- ship between PO2, oxygen saturation, and oxygen content Dissolved O2 (mL/dL) is illustrated by the oxyhemoglobin equilibrium curve,an 0. The shape of the oxyhemoglobin equilibrium curve re- Binding Affinity of Hemoglobin for Oxygen. The globin molecule consists of four oxygen-binding heme sites plateau region of the curve is the loading phase, in which and a globular protein chain.
The special senses are taste 1 mg finasteride with visa hair loss in men 15, smell order 1 mg finasteride hair loss during pregnancy, sight, cerebral cortex travel through nerve fibers composing sensory, or hearing, and balance. Clusters of neuron cell bodies, called nuclei, are The senses can also be classified as somatic or visceral ac- synaptic sites along sensory tracts within the CNS. Somatic senses are that sensory impulses pass through before reaching the cerebral those in which the receptors are localized within the body wall. Through the use of scientific instruments,it is known that the senses act as energy filters that allow perception of only a nar- row range of energy. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Chapter 15 Sensory Organs 489 TABLE 15. Visceral senses are those in which Exteroceptors the receptors are located within visceral organs. Senses are also classified according to the location of the • rod and cone cells in the retina of the eye— receptors and the types of stimuli to which they respond. There photoreceptors; are three basic kinds of receptors: exteroceptors, visceroceptors (en- • hair cells in the spiral organ (organ of Corti) within the teroceptors), and proprioceptors. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 490 Unit 5 Integration and Coordination • taste receptors on the tongue—chemoreceptors; and • skin receptors within the dermis—tactile receptors for touch, Knowledge Check mechanoreceptors for pressure, thermoreceptors for tempera- 4. Pain receptors are located throughout SOMATIC SENSES the body,but only those located within the skin are classified as The somatic senses arise in cutaneous receptors and propriocep- exteroceptors. The perception of somatic sensations is determined by the density of the receptors in the stimulated receptive field and the Visceroceptors intensity of the sensation. Special- ized visceroceptors located within the circulatory system are sen- Objective 6 Explain the purpose of pain and describe the sitive to changes in blood pressure; these are called baroreceptors. Objective 7 Explain what is meant by referred pain and phantom pain and give examples of each. Proprioceptors Proprioceptors are sensory nerve cells that relay information The somatic senses, or somesthetic senses, arise in cutaneous about body position, equilibrium, and movement. Cutaneous sensations include cated in the inner ear, in and around joints, and between ten- touch, tickle, pressure, cold, heat, and pain. Proprioceptors are especially abundant in postural muscles such as the trapezius, which maintains the vertical position of your head on the atlas vertebra. When your head starts to nod for- ward, such as when you are falling asleep during a boring lecture, Tactile and Pressure Receptors proprioceptors are activated in the stretched muscles, and impulses are immediately sent to the cerebellum where motor units involving Both tactile receptors and pressure receptors are sensitive to me- the trapezius muscles are activated. This homeostatic feedback chanical forces that distort or displace the tissue in which they mechanism causes your head to suddenly jerk back before your are located. Tactile receptors respond to fine, or light, touch and nodding head hits the desk. It also awakens you so that you are con- are located primarily in the dermis and hypodermis of the skin. Pressure receptors respond to pressure, vibration, and stretch Receptors may also be classified on the basis of sensory and are commonly found in the hypodermis of the skin and in adaptation (accommodation). The tactile and pressure re- burst of activity when a stimulus is first applied, but then quickly ceptors are summarized in table 15. Receptors with this response pattern are Corpuscles of Touch called phasic receptors. Receptors that produce a relatively con- A corpuscle of touch (Meissner’s corpuscle) is an oval receptor stant rate of firing as long as the stimulus is maintained are composed of a mass of dendritic endings from two or three nerve known as tonic receptors. These corpuscles are Phasic receptors alert us to changes in sensory stimuli and are numerous in the hairless portions of the body, such as the eye- in part responsible for the fact that we can cease paying atten- lids, lips, tip of the tongue, fingertips, palms of the hands, soles of tion to constant stimuli. Corpuscles of touch lie and touch, for example, adapt rapidly; bathwater feels hotter when within the papillary layer of the dermis, where they are especially we first enter it. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Chapter 15 Sensory Organs 491 (see chapter 5). Sensations of fine or light touch are perceived as heat receptors and the latter cold receptors. The bulbs of Krause respond to light touches an object to determine its texture.
Onset is sudden; the patient complains of an excru- tradural) space for the blood to enter cheap finasteride 1 mg without a prescription hair loss control. These lesions are frequently ciating headache and may remain conscious generic finasteride 5mg visa hair loss in men jordans, become lethargic and dis- large, lens (lenticular) shaped, may appear loculated, and are “short oriented, or may be comatose. Treatment of an aneurysm is to surgi- and thick” compared to subdural hematomas (see Fig. The patient may lapse into a coma and, if the lesion is left un- development of vasospasm. In some cases, the patient may initially be arachnoid space and cisterns may be removed. These tumors grow Tearing of bridging veins (veins passing from the brain outward slowly (symptoms may develop almost imperceptibly over years), are through the arachnoid and dura), usually the result of trauma, is a com- histologically benign, may result in hyperostosis of the overlying skull, mon cause of subdural hematoma. In decreasing order, menin- misnomer because the extravasated blood actually dissects through a giomas are found in the following locations: parasagittal area falx specialized, yet structurally weak, cell layer at the dura-arachnoid in- (together 29%), convexity 15%, sella 13%, sphenoid ridge 12%, and terface; this is the dural border cell layer. Treatment is primarily by surgical removal, al- dural space” in the normal brain. Acute subdural hematomas, more though some meningiomas are treated by radiotherapy. The Meninges, Cisterns, and Meningeal and Cisternal Hemorrhages 47 Superior sagittal sinus Arachnoid villus Skull Lateral lacunae Cerebrum Dura mater Arachnoid mater Arachnoid trabeculae Pia mater Transverse sinus Falx cerebri Tentorium cerebelli Cerebellum Cistern Skull Dura mater Subarachnoid space Arachnoid mater Cerebral vessel and branch Pia mater Arachnoid trabeculae Vertebrae Spinal nerves Spinal vessel Dura mater Dura mater Intervertebral ligament Epidural space Conus medullaris Vertebra Cauda equina Lumbar cistern Arachnoid mater Filum terminale (interum) Denticulate ligament Pia mater Coccygeal ligament (filum terminale externum) Coccyx 2-47 Semidiagrammatic representation of the central nervous sys- fourth ventricles. It circulates through the ventricular system (small ar- tem and its associated meninges. The details show the relationships of rows) and enters the subarachnoid space via the medial foramen of Ma- the meninges in the area of the superior sagittal sinus, on the lateral as- gendie and the two lateral foramen of Luschka. In the living situation pect of the cerebral hemisphere, and around the spinal cord. There is no brospinal ﬂuid is produced by the choroid plexi of lateral, third, and actual or potential subdural space. Note the lenticular middle arrow where fresher blood has entered the lesion. Note the ex- shape of the epidural lesions (A, B), their loculated appearance, and tent of this lesion on the surface of the cortex and its narrowness com- their location external to the substance of the brain. The patient in D also has small hemorrhages acute subdural lesion (C) is quite thin and extends over a longer dis- into the substance of the brain, the larger of these in the region of the tance on the cortex. For additional com- In D, the subdural hematoma has both chronic and subacute phases. The chronic phase is indicated by the upper two and lower two arrows The Meninges, Cisterns, and Meningeal and Cisternal Hemorrhages 49 A C Blood in frontal lobe Blood in third Temporal horn ventricle Blood in cerebral aqueduct 2-49 Examples of hemorrhages into the substance of the brain that, Blood in the substance of the brain and in the ventricular system may in some cases, have also resulted in blood in the ventricular system. In this example (C), blood is seen in the The large hemorrhages into the hemisphere (A, B) have resulted in en- frontal lobe and in the third ventricle and cerebral aqueduct. The en- largement of the ventricles, a midline shift, and, in the case of A, a larged temporal horns (C) of the lateral ventricles are consistent with small amount of blood in the posterior horn of the lateral ventricle. In the interruption of CSF ﬂow through the cerebral aqueduct (noncom- these examples, the lesion is most likely a result of hemorrhage from municating hydrocephalus). Axial views of the midbrain (B, T1-weighted), pons (C, continuous one with the other. In addition, the subarachnoid space T2-weighted), and medulla (D, T2-weighted) represent the corre- around the brain is continuous with that around the spinal cord. The Meninges, Cisterns, and Meningeal and Cisternal Hemorrhages 51 A B Subdural Lamina terminalis hemorrhage cistern Supraoptic recess Sylvian Interpeduncular cistern cistern Crural cistern Temporal horn Blood on insular cortex Midbrain Ambient Quadrigeminal cistern cistern C Lamina terminalis Third cistern ventricle Sylvian Blood on cistern insula Interpeduncular cistern Crural cistern Cerebellum Ambient cistern Blood on tentorium Rostral part cerebelli of fourth ventricle 2-51 Blood in the subarachnoid space and cisterns. In C, the blood is located around the amples, blood occupies the subarachnoid space and cisterns, outlining midbrain (crural and ambient cisterns), extends into the Sylvian cis- these areas in white. Consequently, the shape of the cisterns is indi- tern, and into the cistern of the lamina terminalis. The sharp interface cated by the conﬁguration of the white area, the white area represent- between the lamina terminalis cistern (containing blood) and the third ing blood. In D, blood is located in cisterns around the pons but avoids related to the midbrain, the supraoptic recess which is devoid of blood, the rostral part of the fourth ventricle. Compare these images with the and blood extending laterally into the Sylvian cistern. In some cases locations of some of the comparable cisterns as seen in Figure 2-50 on (B), subdural hemorrhage may penetrate the arachnoid membrane and the facing page.
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