Associate Professor, California Health Sciences University
For clarity skin care 2013 generic noitron 10 mg otc, the cochlea has been turned slightly and the middle ear muscles have been omitted acne vulgaris definition buy cheap noitron 5 mg on line. The locations of auditory muscles attached to the middle ear ossicles are indicated skin care zahra order noitron 5 mg. There is no communication between the spaces filled with endolymph and those filled with perilymph skin care clinique order noitron visa. The cochlear portion of the labyrinth is a coiled tube that, in humans, is 35-mm long and makes approximately 2. The upper scala vestibuli and the lower scala tympani contain perilymph and communicate with each other at the apex of the cochlea via a small opening (helicotrema). At the base of the cochlea, the scala vestibuli ends at the oval window, which is closed by the footplate of the stapes. The scala tympani end at the round window, a foramen on the medial wall of the middle ear that is closed by the flexible secondary tympanic membrane. The scala media is continuous with the membranous labyrinth and does not communicate with the other two scalae. The hair cells are arranged in four rows: three rows of outer hair cells lateral to the tunnel formed by the rods of Corti, and one row of inner hair cells medial to the tunnel. Covering the rows of hair cells is the tectorial membrane in which the tips of the hairs of the outer cells are embedded. The cell bodies of the sensory neurons are located in the spiral ganglion within the modiolus; ~95% of these sensory neurons innervate inner hair cells, ~5% innervate outer hair cells, and each sensory neuron innervates several outer hair cells. By contrast, most efferent fibers in the auditory nerve terminate on the outer hair cells. The axons of afferent neurons that innervate hair cells form the auditory (cochlear) division of the eighth cranial nerve. The membranous labyrinth is suspended in perilymph and filled with K+-rich endolymph that bathes the receptors. Hair cells (darkened for emphasis) are in different arrays characteristic of the receptor organs. The semicircular canals are sensitive to angular acceleration that deflects the gelatinous cupula and associated hair cells. In the cochlea, hair cells spiral along the basilar membrane in the organ of Corti. Airborne sounds set the eardrum in motion, which is conveyed to the cochlea by bones of the middle ear. The otolithic organs (saccule and utricle) are sensitive to linear acceleration in vertical and horizontal planes. Each is embedded in an epithelium made up of supporting cells, with the basal end in close contact with afferent neurons. Except in the cochlea, one of these, the kinocilium, is a true but nonmotile cilium with nine pairs of microtubules around its circumference and a central pair of microtubules. The kinocilium is lost from the hair cells of the cochlea in adults; however, the other processes (stereocilia) are found in all hair cells. They have cores composed of parallel filaments of actin that is coated with isoforms of myosin. Along an axis toward the kinocilium, the stereocilia increase progressively in height; along the perpendicular axis, all stereocilia are the same height. Bottom: Structure of the organ of Corti, as it appears in the basal turn of the cochlea. A receptor structure (crista ampullaris) is located in the expanded end (ampulla) of each of the membranous canals. The processes of the hair cells are embedded in the cupula, and the bases of the hair cells contact the afferent fibers of the vestibular division of the eighth cranial nerve. The nerve fibers from the hair cells join those from the cristae in the vestibular division of the eighth cranial nerve. The hair processes provide a mechanism to generate changes in membrane potential proportional to the direction and distance the hair moves. When the bundle of processes is pushed in the opposite direction, the cell is hyperpolarized. Displacing the processes in a direction perpendicular to this axis provides no change in membrane potential, and displacing the processes in directions that are intermediate between these two directions produces depolarization or hyperpolarization that is proportionate to the degree to which the direction is toward or away from the kinocilium. If shorter stereocilia are pushed toward higher ones, the open time of the channels increases. A molecular motor in the higher neighbor then may move the channel toward the base, releasing tension in the tip link. Depolarization of hair cells causes them to release a neurotransmitter that initiates depolarization of neighboring afferent neurons.
In positive-pressure ventilation (inset B) skin care advice cheap noitron 40mg otc, the lungs must push against the diaphragm and rib cage to move them skin care 85037 discount noitron uk. The outermost alveoli might be more compressed than those located more interiorly acne 8 year old boy quality 20 mg noitron. However skin care blog order noitron 5mg line, careful analysis has shown that the pressure at the pleural surface is transmitted through the alveolar walls to more centrally located alveoli and small airways. The muscles of inspiration include the diaphragm, the external intercostal muscles, and the accessory muscles of inspiration. The diaphragm is a large (about 250 cm2 in surface area), domeshaped muscle that separates the thorax from the abdominal cavity. When a person is in the supine position, the diaphragm is responsible for about two thirds of the air that enters the lungs during normal quiet breathing (which is called eupnea). When a person is standing or seated in an upright posture, the diaphragm may be responsible for only about one third to one half of the tidal volume. It is innervated by the two phrenic nerves, which are motor nerves that leave the spinal cord at the third to the fifth cervical segments. The muscle fibers of the diaphragm are inserted into the sternum and the six lower ribs and into the vertebral column by the two crura. These small downward movements of the diaphragm are possible because the abdominal viscera can push out against the relatively compliant abdominal wall. With such a deep inspiration, the limit of the abdominal wall to expand is reached, abdominal pressure increases, and the indistensible central tendon becomes fixed against the abdominal contents. After this point, contraction of the diaphragm against the fixed central tendon elevates the lower ribs as shown in the figure. Contraction of the external intercostal, parasternal intercostal, and scalene muscles raises and enlarges the rib cage. These muscles are innervated by nerves leaving the spinal cord at the 1st to the 11th thoracic segments. During inspiration, the diaphragm and inspiratory rib cage muscles contract simultaneously. If the diaphragm contracted alone, the rib cage muscles would be pulled inward (this is called retraction). If the inspiratory muscles of the rib cage contracted alone, the diaphragm would be pulled upward into the thorax. The accessory muscles of inspiration are not involved during normal quiet breathing but may be called into play during exercise, during the inspiratory phase of coughing or sneezing, or in a pathologic state, such as asthma. Dyspnea, the feeling that breathing is difficult, is probably often related to fatigue of the inspiratory muscles. As the inspiratory muscles relax, the increased elastic recoil of the distended alveoli is sufficient to decrease the alveolar volume and raise alveolar pressure above atmospheric pressure, establishing the pressure gradient for airflow from the lung. Although the diaphragm is usually considered to be completely relaxed during expiration, it is likely that some diaphragmatic muscle tone is maintained, especially when one is in the horizontal position. Active expiration occurs during exercise, speech, singing, the expiratory phase of coughing or sneezing, and in pathologic states such as chronic bronchitis. The main muscles of expiration are the muscles of the abdominal wall and the internal intercostal muscles. When the abdominal muscles contract, they increase abdominal pressure and push the abdominal contents against the relaxed diaphragm, forcing it upward into the thoracic cavity. They also help depress the lower ribs and pull down the anterior part of the lower chest. Contraction of the internal intercostal muscles depresses the rib cage downward in a manner opposite to the actions of the external intercostals. Active expiration compresses the thorax and causes positive intrapleural pressure. This has important effects on the respiratory system, which will be discussed later in this chapter, and on pulmonary blood flow, which will be discussed in Chapter 34. For the purpose of clarity, inspiration and expiration are considered to be of equal duration, although during normal quiet breathing, the expiratory phase is longer than the inspiratory phase. Initially, alveolar pressure equals atmospheric pressure, so no air flows into the lung. Contraction of the inspiratory muscles causes intrapleural pressure to become more negative as the lungs are pulled open and the alveoli are distended. As the alveoli are distended, the pressure inside them decreases below atmospheric pressure and air flows into the alveoli, as seen in the tidal volume panel. As the air flows into the alveoli, alveolar pressure returns to 0 cm H2O and airflow into the lung ceases. At the vertical line, the inspiratory effort ceases and the inspiratory muscles relax. Alveoli expand (according to their individual compliance curves) in response to the increased transmural pressure gradient. Alveolar pressure falls below atmospheric pressure as the alveolar volume increases, thus establishing a pressure gradient for airflow 9. Air flows into the alveoli until alveolar pressure equilibrates with atmospheric pressure Expiration (passive) 1. Thoracic volume decreases, causing intrapleural pressure to become less negative and decreasing the alveolar transmural pressure gradientb 4.
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There are three cell types: olfactory sensory neurons skin care 9 order cheapest noitron, supporting cells skin care 45 years old buy cheap noitron 40 mg on-line, and basal stem cells at the base of the epithelium acne xenia gel buy noitron cheap online. Odorants bind to specific odorant receptors on the cilia and initiate a cascade of events leading to generation of action potentials in the sensory axon acne queloide purchase noitron 20mg fast delivery. Information is transmitted from the olfactory bulb by axons of mitral and tufted relay neurons in the lateral olfactory tract. Mitral cells project to five regions of the olfactory cortex: anterior olfactory nucleus, olfactory tubercle, piriform cortex, and parts of the amygdala and entorhinal cortex. Tufted cells project to anterior olfactory nucleus and olfactory tubercle; mitral cells in the accessory olfactory bulb project only to the amygdala. Conscious discrimination of odor depends on the neocortex (orbitofrontal and frontal cortices). Emotive aspects of olfaction derive from limbic projections (amygdala and hypothalamus). In rodents and some mammals, a well-developed vomeronasal organ is concerned with perception of odors that act as pheromones; its receptors project to the accessory olfactory bulb. The mucus bathes the odorant receptors on the cilia and provides the appropriate molecular and ionic environment for odor detection. Odor-producing molecules are usually small, containing from 3 to 20 carbon atoms, and molecules with the same number of carbon atoms but different structural configurations have different odors. Relatively high water and lipid solubility are characteristic of substances with strong odors. Anosmia (inability to smell) and hyposmia or hypesthesia (diminished olfactory sensitivity) can result from simple nasal congestion or from damage to the olfactory nerves due to fractures of the cribriform plate, neuroblastomas or meningiomas, or infections (such as abscesses). Aging is also associated with abnormalities in smell sensation; more than 75% of humans over the age of 80 have an impaired ability to identify odors. The genes that code for about 1,000 different types of odorant receptors make up the largest gene family so far described in mammals. The amino acid sequences of odorant receptors are diverse, but all the odorant receptors are coupled to heterotrimeric G proteins. This produces the graded receptor potential, which then leads to an action potential in the olfactory nerve. Although there are millions of olfactory sensory neurons, each expresses only 1 of the 1,000 different odorant receptors. This provides a distinct two-dimensional map in the olfactory bulb that is unique to the odorant. The mitral cells with their glomeruli project to different parts of the olfactory cortex. The olfactory glomeruli demonstrate lateral inhibition mediated by periglomerular and granule cells. In addition, the extracellular field potential in each glomerulus oscillates, and the granule cells can regulate the frequency of the oscillation. The exact function of the oscillation is unknown, but it may also help to focus the olfactory signals reaching the cortex. The apical ends of taste cells have microvilli that project into the taste pore, a small opening on the dorsal surface of the tongue where taste cells are exposed to the oral contents. Each taste bud is innervated by about 50 nerve fibers, and conversely, each nerve fiber receives input from an average of five taste buds. They differentiate into new taste cells, and the old cells are replaced with a half-time of about 10 days. If the sensory nerve is cut, the taste buds it innervates degenerate and eventually disappear. The fungiform papillae are rounded structures most numerous near the tip of the tongue; the circumvallate papillae are prominent structures arranged in a V on the back of the tongue; the foliate papillae are on the posterior edge of the tongue. Each fungiform papilla has up to 5 taste buds, mostly located at the top of the papilla; each vallate and foliate papilla contains up to 100 taste buds, mostly located along the sides of the papillae. From there, axons of second-order neurons ascend in the ipsilateral medial lemniscus to pass directly to the ventral posteromedial nucleus of the thalamus, from which fibers project to the anterior insula and frontal operculum in the ipsilateral cerebral cortex. This region is rostral to the face area of the postcentral gyrus, which may be the area that mediates conscious perception of taste and taste discrimination. A protein that binds taste-producing molecules is produced by the Ebner gland that secretes mucus into the cleft around vallate papillae. Ageusia (absence of the sense of taste) and hypogeusia (diminished taste sensitivity) can be caused by damage to the lingual or glossopharyngeal nerve. A) Taste buds on the anterior two thirds of the tongue are innervated by the chorda tympani branch of the facial nerve; those on the posterior one third of the tongue are innervated by the lingual branch of the glossopharyngeal nerve. B) the three major types of papillae (circumvallate, foliate, and fungiform) are located on specific parts of the tongue. C) Taste buds are composed of basal stem cells and three types of taste cells (dark, light, and intermediate). Taste cells extend from the base of the taste bud to the taste pore, where microvilli contact tastants dissolved in saliva and mucus.
Hepatocytes conduct the majority of the metabolic functions of the liver and produce the initial biliary secretion acne 7-day detox order noitron 5 mg amex. Kupffer cells line the sinusoids and cleanse the blood of particulates skin care 35 discount 30 mg noitron with visa, such as bacteria acne gel prescription cheap 5mg noitron fast delivery. The endothelial cells of the liver have large fenestrations that allow small proteins and other molecules to leave the circulation acne cleanser order noitron 30 mg on line, but retain blood cells and intact chylomicrons. Liver failure due to damage to the liver cells or to the biliary system, or blockade of biliary drainage, results in a host of systemic problems. In a patient with end-stage liver disease, which of the following combinations of findings would be expected in the plasma Albumin A) B) C) D) E) Increased Decreased Increased Decreased Decreased Glucose Increased Decreased Decreased Increased Decreased Ammonia Increased Decreased Increased Decreased Increased 2. A 60-year-old man comes to his physician complaining of a progressive increase in girth over several months, despite attempts to diet. He is suffering from jaundice (yellowing of the skin and sclera) and also complains of nausea and malaise. When a large needle is inserted into his abdomen, several liters of tan fluid drain out. An increase in which of the following does not account for this accumulation of fluid The liver is responsible for removing the small numbers of bacteria that enter the portal circulation from the intestines. A) sinusoidal epithelial cells B) cholangiocytes C) hepatocytes D) Kupffer cells E) stellate cells 4. A gallstone lodged in which of the following sites will result in increased bile acid flux through the hepatocytes making up only the left side of the liver A) cystic duct B) common hepatic duct C) right hepatic duct D) left hepatic duct E) common bile duct 5. What structure in the liver permits protein-bound metabolic products to access the basolateral membranes of hepatocytes A) canaliculi B) sinusoidal fenestrae C) Kupffer cells D) bile ducts E) tight junctions Bile Formation, Secretion, and Storage Kim E. Barrett 56 C H A P T E R O B J E C T I V E S Understand the physiologic functions of bile as a route for excretion and in aiding in the digestion and absorption of dietary lipids. Understand how bile acids are formed from cholesterol, how they are modified during gut passage, and their role in driving bile secretion. Describe the major biliary lipids and how they are transported into the canaliculus. Describe how the composition of bile is modified as the bile moves through the biliary ductules. Understand the role of the gallbladder in concentrating bile and coordinating its secretion with ingestion of a meal, and how contraction of the gallbladder is regulated. Explain why the gallbladder is vulnerable to the formation of cholesterol gallstones. Bile consists of a micellar solution in which bile acids, cholesterol metabolites produced by hepatocytes, form mixed micelles with phosphatidylcholine. These mixed micelles solubilize molecules that would otherwise have minimal aqueous solubility, such as cholesterol itself and a variety of xenobiotics. Bile also plays an important role in the digestion and absorption of dietary lipids. While bile acids are not essential for the uptake of most fatty acids, which have appreciable aqueous solubility, they do markedly increase the efficiency of this process. On the other hand, insoluble dietary lipids, such as saturated long-chain fatty acids and fat-soluble vitamins, are almost entirely dependent on micellar solubilization for absorption. In this section, we will consider how bile acids are synthesized, and subsequent modifications to their structure that promote their role as biological detergents. The term amphipathic refers to the fact that bile acids have both a hydrophobic and a hydrophilic face, and form micelles. Changes to both the steroid nucleus of cholesterol and its alkyl side chain are required to convert the highly insoluble cholesterol to the water-soluble bile acid product. The initial, and rate-limiting, step in bile acid formation is the hydroxylation of cholesterol at the 7 position of 565 Ch56 565-574. Trace amounts of a third secondary bile acid, ursodeoxycholic acid (so called because it is a prominent bile acid in bears), are also generated in humans by epimerization of the 7-hydroxyl group. Although only very little ursodeoxycholic acid is formed in humans, it is important to know about this compound because it is used therapeutically. Lithocholic acid, in particular, is cytotoxic if present at high concentrations, and physiologic mechanisms have developed to limit its toxicity. Note that cholesterol already contains a hydroxyl group at the 3 position, and this is retained in all of the bile acids. However, the 3-hydroxyl group in cholesterol is in the -orientation, and this is converted to the -position by a process known as epimerization. After these initial reactions, downstream pathways diverge to yield the two primary bile acids of humans, chenodeoxycholic acid and cholic acid. Note that all of the hydroxyl groups in the mature bile acids are in the form of -epimers, and are thus oriented to the same face of the molecule.
