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Each time an airway branches purchase 50mg sildenafil with mastercard erectile dysfunction brands, Pulmonary vessels protect the body against thrombi the arterial tree branches so that the two parallel each other (blood clots) and emboli (fat globules or air bubbles) from (Fig buy discount sildenafil 75 mg line erectile dysfunction doctor melbourne. More than 40% of lung weight is comprised of entering important vessels in other organs. The total blood vol- emboli often occur after surgery or injury and enter the sys- ume of the pulmonary circulation (main pulmonary artery temic venous blood. Small pulmonary arterial vessels and to left atrium) is approximately 500 mL or 10% of the total capillaries trap the thrombi and emboli and prevent them circulating blood volume (5,000 mL). The pulmonary veins from obstructing the vital coronary, cerebral, and renal ves- contain more blood (270 mL) than the arteries (150 mL). Endothelial cells lining the pulmonary vessels release The blood volume in the pulmonary capillaries is approxi- fibrinolytic substances that help dissolve thrombi. Emboli, 337 338 PART V RESPIRATORY PHYSIOLOGY A Lung The lungs serve as a blood reservoir. Approximately 500 mL or 10% of the total circulating blood volume is in the Bronchus pulmonary circulation. During hemorrhagic shock, some of Pleura this blood can be mobilized to improve the cardiac output. Pulmonary artery The Pulmonary Circulation Has Pulmonary Unique Hemodynamic Features vein In contrast to the systemic circulation, the pulmonary cir- culation is a high-flow, low-pressure, low-resistance sys- B tem. The pulmonary artery and its branches have much Pulmonary arteriole thinner walls than the aorta and are more compliant. The Muscle strand pulmonary artery is much shorter and contains less elastin Alveolus and smooth muscle in its walls. The pulmonary arterioles Pulmonary venule are thin-walled and contain little smooth muscle and, con- sequently, have less ability to constrict than the thick- walled, highly muscular systemic arterioles. The pulmonary veins are also thin-walled, highly compliant, and contain little smooth muscle compared with their counterparts in Respiratory bronchiole the systemic circulation. Unlike the Alveolar capillary systemic capillaries, which are often arranged as a network of tubular vessels with some interconnections, the pulmonary capillaries mesh together in the alveolar wall so that blood flows as a thin sheet. It is, therefore, misleading to refer to pulmonary capillaries as a capillary network; they comprise a Parallel structure of the vascular and air- dense capillary bed. A, Systemic venous blood flows ceedingly thin, and a whole capillary bed can collapse if lo- through the pulmonary arteries into the alveolar capillaries and cal alveolar pressure exceeds capillary pressure. B, A mesh of capillaries surrounds each alve- ingly in their pressure profiles (Fig. As the blood passes through the capillaries, it gives up car- arterial pressure is 15 mm Hg, compared with 93 mm Hg in bon dioxide and takes up oxygen. The driving pressure (10 mm Hg) for pulmonary flow is the difference between the mean pressure in the pul- especially air emboli, are absorbed through the pulmonary monary artery (15 mm Hg) and the pressure in the left capillary walls. These pulmonary pressures are meas- monary vessel, gas exchange can be severely impaired and ured using a Swan-Ganz catheter, a thin, flexible tube with can cause death. A similar situation occurs if emboli are ex- an inflatable rubber balloon surrounding the distal end. The tremely numerous and lodge all over the pulmonary arterial balloon is inflated by injecting a small amount of air tree (see Clinical Focus Box 20. Although the Swan-Ganz Vasoactive hormones are metabolized in the pulmonary catheter is used for several pressure measurements, most circulation. One such hormone is angiotensin I, which is useful is the pulmonary wedge pressure (Fig. To activated and converted to angiotensin II in the lungs by measure wedge pressure, the catheter tip with balloon in- angiotensin-converting enzyme (ACE) located on the sur- flated is “wedged” into a small branch of the pulmonary ar- face of the pulmonary capillary endothelial cells. When the inflated balloon interrupts blood flow, the tion is extremely rapid; 80% of angiotensin I (AI) can be tip of the catheter measures downstream pressure. The converted to angiotensin II (AII) during a single passage downstream pressure in the occluded arterial branch repre- through the pulmonary circulation. In addition to being a sents pulmonary venous pressure, which, in turn, reflects potent vasoconstrictor, AII has other important actions in left atrial pressure. Metabolism of vasoactive hor- atrial pressures have a profound effect on gas exchange, and mones by the pulmonary circulation appears to be rather pulmonary wedge pressure provides an indirect measure of selective.

But with all of these achievements purchase sildenafil 75mg overnight delivery erectile dysfunction ed treatment, the brain still remains largely Objective 1 Describe the divisions of the nervous system effective 75 mg sildenafil erectile dysfunction yahoo. Neurology, the study of the nervous system, has been re- Objective 2 Define neurology; define neuron. Basic ques- tions concerning the functioning of the nervous system remain Objective 3 List the functions of the nervous system. The immensely complex brain and its myriad of connecting path- ways constitute the nervous system. The peripheral nervous system (PNS) consists of cranial nerves and spinal nerves. Also part of the PNS are the plexuses and additional nerves that arise from the cranial and spinal nerves. The autonomic nervous system (ANS) is a functional subdivision of the nervous system. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 345 TABLE 11. Meninges (singular, meninx) Group of three fibrous membranes covering the CNS, composed of the dura mater, arachnoid, and pia mater Cerebrospinal fluid (CSF) Clear, watery medium that buoys and maintains homeostasis in the brain and spinal cord Neuron Structural and functional cell of the nervous system; also called a nerve cell Motor (afferent) neuron Nerve cell that transmits action potentials from the CNS to an effector organ, such as a muscle or gland Sensory (efferent) neuron Nerve cell that transmits action potentials from an effector organ to the CNS Nerve Bundle of nerve fibers (elongated portions of neurons) Nerve plexus Convergence or network of nerves Somatic motor nerve Nerve that innervates skeletal muscle; conveys impulses causing muscle contraction Autonomic motor nerve Nerve that innervates smooth muscle, cardiac muscle, and glands; conveys impulses causing contraction (or inhibiting contraction) of smooth muscle and cardiac muscle and secretion of glands Ganglion Cluster of neuron cell bodies outside the CNS Nucleus Cluster of neuron cell bodies within the CNS Tract Bundle of nerve fibers interconnecting regions of the CNS What are the roles of the many chemical compounds within the ory) and to establish patterns of response on the basis of prior brain? The controlling centers of the Thus, broadly speaking, the nervous system has sensory, integra- ANS are located within the brain and are considered part of the tive, and motor functions, all of which work together to maintain CNS; the peripheral portions of the ANS are subdivided into the the internal constancy, or homeostasis, of the body. An instinct also may be called a fixed action pattern; typically, it is genetically specified with little environmental modification. It Functions of the Nervous System is triggered only by a specific stimulus. Some of the basic instincts in humans include survival, feeding, drinking, voiding, and specific vocal- The nervous system is specialized for perceiving and respond- ization. Some ethologists (scientists who study animal behavior) believe ing to events in our internal and external environments. The nervous system functions throughout the body in conjunction with the endocrine system 1. What are the sub- (see chapter 14) to closely coordinate the activities of the divisions of the peripheral portions of the ANS? Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Developmental Exposition plate (exhibit I), differentiates and eventually gives rise to all of the The Brain neurons and to most of the neuroglia that support the neurons. As development progresses, the midline of the neural plate invaginates to become the neural groove. At the same time, there is a prolifera- EXPLANATION tion of cells along the lateral margins of the neural plate, which be- The first indication of nervous tissue development occurs about 17 come the thickened neural folds. The neural groove continues to days following conception, when a thickening appears along the en- deepen as the neural folds elevate. This thickening, called the neural met and fused at the midline, and the neural groove has become a EXHIBIT I The early development of the nervous system from embryonic ectoderm. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 neural tube. For a short time, the neural tube is open both cranially The brain begins its embryonic development as and caudally. These openings, called neuropores, close during the the cephalic end of the neural tube starts to grow rapidly and fourth week. Once formed, the neural tube separates from the sur- differentiate (exhibit II). By the middle of the fourth week, face ectoderm and eventually develops into the central nervous sys- three distinct swellings are evident: the prosencephalon tem (brain and spinal cord). Further development the peripheral nervous system (cranial and spinal nerves) forms during the fifth week results in the formation of five specific re- from the neural crest. The telencephalon and the diencephalon (di'en-sef-a¯-lon) main tissue mass and migrate to other locations, where they differ- derive from the forebrain, the mesencephalon remains un- entiate into motor nerve cells of the sympathetic nervous system or changed, and the metencephalon and myelencephalon form into neurolemmocytes (Schwann cells), which are a type of neu- from the hindbrain. The caudal portion of the myelencephalon roglial cell important in the peripheral nervous system.

A family history of breast cancer discount sildenafil 25 mg without a prescription impotence 22 year old, particularly under age 45 years sildenafil 100mg mastercard erectile dysfunction at the age of 19, imparts increased risk to the patient. All suspicious masses should be biopsied, regardless of the mammogram interpretation. The diagnosis of cervical cancer is an important consideration in the evaluation of intravaginal bleeding. Pelvic sonography in the postmeno- pausal patient may be done to assess the thickness of the endometrium. Again, the patient’s history is often telling and may lead to a diagnosis of cancer when the appropriate evaluations are performed. The other major area of liability for this specialty is prenatal care and delivery. Prenatal diagnostic ultrasonographic evaluation of the fetus is an increasing area of litigation. It is essential that the respon- sible Ob/Gyn clarify for the patient what fetal anatomy can or cannot be seen and what diagnoses can or cannot be made. Limitations of equipment, the impact of fetal position and number, and maternal size should be emphasized. For example, only one-third of major fetal anatomic abnormalities are defined at second-trimester scans. Even when a consultant provides the interpretation of the study, the primary Ob/Gyn should review the implications of the findings with the patient and family. Additionally, genetic counseling is now so complex that only a certified counselor should do it. Fetal death imparts a responsibility on the part of the delivering phy- sician for documentation of the gross anatomy of the baby, the umbilical cord, and the placenta. Such descriptors are far more meaningful than those following examination by the pathologist hours to days later. The bulk of suits for wrongful fetal death arise when the death is unexplained, although up to 75% of fetal deaths can be under- stood after thorough gross, microscopic, and genetic analyses (6). The obstetric department should define a protocol to assess all fetal deaths. Much potential litigation can be prevented by the responsible Ob/Gyn discussing all findings with the patient and her family. This review should take place prior to discharge from the hospital and again at the postpartum visit. Under no circumstances should the patient be left with unanswered questions or concerns as these only drive attempts to get explanations from an attorney. Complications of induction of labor, although not very common, do occur and have associated risks to mother and, more commonly, baby. Informed consent should be obtained according to ACOG Practice Bulletin regarding induction of labor (7). Elements of the consent include the indication for the induction, the agents and methods of labor stimulation, the risks attendant to the use of these agents, meth- ods and alternatives (typically expectant management or Cesarean section [C-section]), and the associated risk for mother and baby. It is noteworthy that the bulletin states, “A physician capable of perform- ing a Cesarean delivery should be readily available. It is rec- ommended that all patients undergoing labor induction have electronic fetal heart rhythm and uterine contraction monitoring although its utility is problematic except in the high-risk pregnancy. Electronic fetal heart rate (FHR) monitoring is a classic example of a procedure becoming codified as the standard of care without proof of effectiveness. In fact, the prevalence of cerebral palsy has not been altered by this modality (8). The physician must be certain that he or she and the nurses are using the same terminology in describing the FHR tracing. For example, quantification of variability is subjective, and there is no such terminology as late variables—indeed variable decelerations are so named in part because the timing of the decelera- tion to the uterine contraction varies in its onset, including occurring late. Just as important, the physician should review the nurses’ notes with special attention to the terminology used, contact times, informa- tion given to the physician, and the physician’s responses. Particular emphasis should be placed on the review of the initial, admission FHR tracing to ascertain whether or not the tracing should be characterized as reassuring. The previously damaged fetus, now Chapter 11 / Obstetrics and Gynecology 145 with recovered acid–base status, may demonstrate a reassuring trac- ing. A nonreassuring tracing, particularly with little or no baseline variability, does highly correlate with a neurologically injured fetus.