Deputy Director, Geisinger Commonwealth School of Medicine
In Second Half of Proximal Tubule In second half of proximal tubule gastritis diet xtreme discount zantac 150mg overnight delivery, Na+ reabsorption is mainly associated with Cl- reabsorption via transcellular and paracellular pathway gastritis diet ginger zantac 150 mg sale. In the later part of proximal tubule gastritis symptoms dizziness order 150mg zantac with amex, Na+ reabsorption is coupled with the Cl- rather than bicarbonate or organic solutes because of two reasons gastritis low carb diet order line zantac. Also, presence of more chlorideanion antiporter in the distal part of the proximal tubule facilitates transport of Cl- into the cell. The Cl- leaves the cell by means of K+-Cl- symporter located on the basolateral membrane. Thus, Na+ and Cl- are reabsorbed from tubular fluid into the interstitial fluid via tubular cells. Increased concentration Na+ in lateral-interstitial space creates an electrical gradient for Cl- ions also to move through the paracellular pathway. This is because the tight junctions between the tubular cells at their apical margin contain leaky channels that transport Cl- along its electrical concentration gradient from the tubular fluid into the interstitial space. This paracellular pathway of solute reabsorption constitutes about 25% of NaCl reabsorption in the proximal tubule. Transfer of organic and inorganic solutes from tubular fluid into the interstitial space creates the osmotic gradient for the reabsorption of water in the proximal tubule. Na+K+ antiport located on the apical membrane contributes considerably for transfer of Na+ from tubular fluid into the cell. The carrier protein that transports Na+ also cotrans ports glucose, amino acids, phosphates, etc. Therefore, reabsorption of these solutes is considered as secondary active transport (for details, see below). Na+ is also transported from tubular fluid by antiport, especially by Na+H+ exchanger which reabsorbs Na+ into the cell in exchange for secretion of H+ into the luminal fluid. Normally, Na+-H+ exchanger is the primary mechanism of entry of Na+ into the epithelial cells, which accounts for about 60% of the total Na+ entry. However, process of anion absorption along with Na+ is different in first and second half of proximal tubule. About 25% of Na+ is reabsorbed in thick ascending limb of loop of Henle that occurs via Na+2ClK+ cotransporter. The driving force for water reabsorption is the trans cellular osmotic gradient, which is established by absorption of Na+ and accompanying solutes. Transcellular and paracellular reabsorption of NaCl and other solutes from tubular fluid into the lateral intercellular and interstitial spaces increases the osmolality of fluid in these spaces. Water passes through the epithelial cells via water channels (aquaporin 1) present in the cell membranes and also through the water channels present in the paracellular route (in tight junctions between the cells). Note, water reabsorption is efficient inspite of small difference between osmolality of tubular and interstitial fluids. Therefore, even a smaller osmotic gradient (osmolality of interstitial fluid of about 293 mosm/L against osmolality of tubular fluid of about 285 mosm/L) result in adequate movement of water. Thus, water flows along the osmotic gradient via the transcellular and paracel lular pathways. Hence, reabsorption of water is coupled with the reabsorption of solutes, especially with that of Na+ and Cl- (as NaCl is osmotically most active). The transfer of large amount (bulk flow) of water helps in transport of ions like K+ and Ca++ that are carried along with water. Moreover, the hydrostatic pressure is also less in peritubular capillaries as blood has passed through the upstream resistance vessels before entering these capillaries. Thus, high oncotic and low hydrostatic pressures favor uptake of water from the interstitial tissue space surrounding tubules. This transfer of water from peritubular space into peritubular capillaries maintains the gradient for water reabsorption from tubular lumen. Glucose Reabsorption Glucose is reabsorbed completely from tubular fluid in the proximal tubule. Na+ is pumped out of the tubular cells by Na+-K+ pump located on the basolateral membrane. This decreases intracellular Na+ concentration and creates gradient for Na+ entry into the cell from the tubular fluid. The carrier protein that transports Na+ also reabsorbs glucose (sodiumglucose cotransporter). Thus, reabsorption of glucose from the luminal membrane is secondary transport to the active process located on the basolateral membrane of the cells and, therefore, is a typical example of secondary active transport. Role of Peritubular Capillaries the peritubular capillaries play and important role in absorption of solutes and water from the tubule. Peritubular capillaries are derived from efferent arteriole and therefore receive blood from the glomerulus. As the blood draining from glomerulus has already been filtered in the glomerular capillary and protein has not been filtered through the filtration barrier in the renal corpuscle, blood in peritubular capillary has high oncotic pressure. This helps in reabsorption of glucose along with Na+, when Na+ is reabsorbed into the tubular cell from the tubular fluid. However, almost all the filtered glucose is reabsorbed in the proximal tubule, so that in normal condition, urine is essentially glucose free. The rate of reabsorption of glucose is proportional to the amount of glucose filtered. Therefore, plasma glucose level determines the transport maximum for glucose (TmG). Therefore, when the graph of TmG is plotted, the actual curve deviates from the ideal curve. The splay is due to two reasons: - TmG is not same in all the tubules, and - Amount of glucose removed from each tubule is not complete even when the amount filtered is below the TmG.
The diencephalon is primarily meant for relay of information to cortex gastritis diet щдч buy cheap zantac 300mg on-line, and control of autonomic and endocrine functions gastritis symptoms on dogs 300mg zantac with mastercard. Midbrain contains central pattern generator for locomotion and nuclei for righting reflexes gastritis diet эротика discount zantac 300mg with mastercard. Rhombencephalon this is the hindbrain gastritis diet узбек buy cheap zantac on-line, which consists of metencephalon (the pons and the cerebellum) and myelencephalon (the medulla oblongata). The main functions of brainstem are control of cardiovascular and respiratory functions, motor activities, sleep-wakefulness and visceral functions. Spinal Cord Spinal cord starts from the base of the skull as the extension of medulla and continues till the body of first lumbar vertebra. The space at the end of spinal cord, especially between L1 and L2 vertebral segments is used in tapping cerebrospinal fluid during lumbar puncture. The nerve roots combine to form the 31 bilaterally symmetrical pairs of spinal nerves. The main function of spinal cord is to receive sensory inputs from peripheral structures via somatic nerves and transmit them to the brain, and convey the signals originating from brain motor and autonomic areas to the target structures. The neural regulation is the major controlling mechanism of many functions and processes of the body. Nervous system achieves its objectives through neurons that are designed for rapid transmission of information from one body part to the other. Neuroglias support and protect the neurons and maintain homeostasis of fluids that bath the neurons. The receptors transduce environmental energy into the action potentials in the sensory neurons. This becomes possible due to the presence of different modalities of receptors in the body that detect changes in their environment. The forms of stimuli that are detected by receptors include mechanical, chemical, photic (light), auditory (sound), thermal (temperature), and electrical. Glial Cells Glial cells neither conduct action potential nor form functional synapse with other cells. Though glial cells generally provide support for neurons, their functions are complex and not completely understood. The action potential (sensory signal) transmitted is first relayed in the thalamus and then processed in sensory cortex. The processed signal is then transformed into other signals in sensory networks in the brain. Integration of the processed signals into appropriate command signals through detailed planning and programming mechanisms. Transmission of the command signal to the effector organs for implementation of the plan. Learning based on sensory inputs and then storage of learned information in memory for future utilization of the knowledge (described in detail in the higher functions). Processes of astrocytes surround the neurons and their axons, and often terminate on the wall of blood vessels. Thus, astrocytes electrically insulate synapses and separate them from one another. Responses Responses consist of movement of body parts (motor activities), change in visceral functions (autonomic responses) or even the change in behavior of the individual. Thus, the responses may be an internal change such as alteration in cognition, behavior, etc. Oligodendrocytes Oligodendrocytes are found close to the myelinated axons in the brain and spinal cord. The processes of oligodendrocytes wrap many times around an axon to form the myelin sheath. This sheath not only insulates axons from one another, but also limits current flow across the axon membrane (axolemma). Note, processes of astrocyte terminate on blood vessel and axon, processes of oligodendrocyte form myelin sheath of myelinated axon, and microglia contains phagocytic vesicle. Because of this myelination, action potential is conducted in a saltatory fashion in myelinated fibers, which is much faster than the transmission of impulse in unmyelinated fibers. If the nervous tissue is damaged or infected, these cells enlarge and become mononuclear phagocytes to eliminate debris and organisms. Following brain injury, neuralgia multiply to fill the space formerly occupied by neurons. Structure of a Neuron A neuron consists of a cell body (soma), dendrites, and the axon. Chapter 115: Functional Organization of Nervous System 979 Soma the soma or the cell body consists of nucleus and cytoplasm. Cytoplasm contains many organelles like endoplasmic reticulum, a prominent Golgi apparatus, many mitochondria and cytoskeletal elements that include microfilaments (neurofilaments) and microtubules. The special granules present in the cytoplasm are Nissl bodies that are modified rough endoplasmic reticulum and act as biosynthetic apparatus for synthesis of proteins in the neurons. Dendrites these are tapering processes of variable complexity that arise from the soma.
Therefore gastritis symptoms how long do they last 150 mg zantac free shipping, alteration in cardiovascular and respiratory functions is an integral part of autonomic responses gastritis diet 80 zantac 150mg cheap. However diet by gastritis purchase zantac with paypal, sexual behavior is poorly under stood for its complex integrating mechanisms gastritis xq se produce zantac 150 mg with mastercard. Though, this is an instinctive behavior controlled mainly by limbic system, in human beings the higher cortical centers override limbic influences and refine the behavior. Copulatory responses can be activated in animals by stimulating parts of the hypothalamus, olfactory sys tem, and other limbic areas, that results in mounting behaviors in males and lordosis (arching the back and raising the tail) in females. Therefore, the most effective drugs used in treating psy chiatric disorders are agents that alter monoaminergic transmission. However, bilateral lesion of limbic system confined to pyriform cor tex overlying amygdala and destruction of amygdala result in intense sexual activity (hypersexuality). Acute treatment of mania is the use of drugs that block dopamine receptors and long-term treatment for mania is lithium. Lithium inhibits regeneration of the second messenger phosphatidylinositol in neuronal membranes by blocking the hydrolysis of inositol1phosphate. In humans, cingulate gyrus is believed to play an important role in emotion as it interacts with neocortex. Stimulation of cingulate cortex during neurosurgery has been reported to evoke normal pleasure or fear responses and cingulectomy produced for psychotic or neurotic patients is reported to produce diminished emotional responses. Schizophrenia Schizophrenia refers to a group of closely related psy chotic disorders characterized by a particular type of dis ordered thinking, affect and behavior. The usual features are thought disorder, inappropriate emotional response, and auditory hallucinations. Though the biochemical dis crepancy resulting in schizophrenia is not properly known, neuroleptic drugs that block dopamine receptors in the limbic system are known to ameliorate the features of schizophrenia. Defense Response Defense response is the response for a natural attack or responses to prevent from an attack. In experimental animals, the defense response is elicited by stimulation of hypothalamic areas that in cat elicits hissing, arching of the back, piloerection and dilation of the pupil. This is associated with autonomic cardiovascular responses consisting of a increased heart rate and blood pressure, and a large increase in skeletal muscle blood flow. Physiology of Emotions Emotion is a state of feeling that manifests mentally and physically through cardiovascular and other autonomic changes. Emotional activation and responses occur in three phases: stimulus recognition and evaluation, emo tional responses and emotional experience. Conditioned Response this is the emotional response attached to a conditioned stimulus. Most of our emotional responses are condi tioned emotional responses as they are usually evoked by a conditioned stimulus. The subsequent emotional reactions to the similar stimuli mostly depend on the knowledge of the previous experiences. Stimulus Recognition and Evaluation First, the stimulus should be perceived, which is called recognition or the awareness of sensation. Then, the next step is the stimulus evaluation, the process by which the output is compared with stored information. The inherited infor mation also helps in emotional integration, for example inherent fear in monkeys for snakes. Control of Emotional Responses Though the emotional responses are profoundly influ enced by external factors like social and cultural influ ences, they are mainly mediated by neural and hormonal mechanisms. The neural control mechanisms for emotion are divided into peripheral and central mechanisms. Emotional Responses Emotional response has three components: affect, cona tion and physical changes. However, emotional manifestations mainly depend on the type of emotional response. Emotional response may be a natural response, a defense response and a conditional response. Peripheral Control of Emotion the main output pathway for emotional responses is the autonomic nervous system. The emotion of fear and rage closely resembles the effects of injection of norepinephrine. Thus, it is clear that emotional responses of fear and anger are mediated by sympathetic activation. Central Control of Emotion Emotional responses have been experimentally seen to occur in the absence of cortex. Hypothalamus and other limbic structures are important for expression of emo tion. As suggested by Papez, for emotional expression and experience, the sensory information from environment passes through the thalamus to the hypothalamus. Natural Response Natural emotional response is the normal response of fear, anxiety or pleasure encountered in daily life. Though, the natural stimulus for emotion involves the neocortical perceivecognitive mechanisms like the nonemotional sensory processes, the natural emotion is associated Chapter 137: Limbic System 1133 Ascending Output: the ascending output reaches anterior thalamus via mammillothalamic tract and from there it projects to cingulate cortex. Descending Output: the descending output of the hypothalamus is directed to the brainstem and spinal cord centers from where autonomic fibers originate. Endogenous fear, anxiety, depression and euphoria Role of Limbic System Limbic system receives both exteroceptive and interocep tive sensory inputs. Exteroceptive inputs reach limbic system via two ways; first, through collaterals arising from ascending sensory projections before the fibers reach cortical areas, and second, form sensory cortex. Interoceptive inputs reach hypothalamic and amyg dalar nuclei of limbic system from brainstem especially from the nucleus tractus solitarius.
There are two theories of color vision: Retinal (Young-Helmholtz) theory and Neural (Opponent) theory gastritis diet рбк discount zantac 150 mg overnight delivery. Name the theories of color vision gastritis foods 300 mg zantac, What are the types and causes of color blindness diet for hemorrhagic gastritis order zantac online, What are the tests of color blindness gastritis uptodate purchase cheap zantac on line. Give the names, innervation, functions and effects of paralysis of extraocular muscles. They are lateral rectus, medial rectus, superior oblique, inferior oblique, superior rectus, and inferior rectus. When the eyeball is placed tempo rally (abducted position), the superior rectus causes elevation and the inferior rectus causes depression of the eyeball. When the eyeball moves nasally (adducted position), the superior and inferior oblique elevate and depress it respectively. In the midposition of the eye ball, the lateral and medial recti cause lateral and medial movement of the eyeball respectively. Cardinal Movements the vertical and horizontal movements of the eyeball made from the midposition of the gaze are called cardinal movement. Saccades and pursuit movements are commonly expe rienced while looking out of the window of a moving train. As one looks at an object, initially, pursuit movement follows the object and the eyeball rotates sideways till its maximum. When the object cannot be viewed anymore, the eyeball rapidly moves to the earlier position to fix the gaze on a new object. Types of Ocular Movements Various types of movements occur in the eyeball that helps to visualize the object clearly by controlling the extra ocular muscles. There are four types of eye movements: saccades, smooth pursuit movements, vergence and vestibular movements. Vergence these movements occur when an object comes near or moves far from the eye. For example, if an object comes near in the midline, both the eyeballs turn medially (convergence), and if it goes away, both eyeballs rotate laterally (divergence). So, for a single eyeball, when an object moves closer in the nasal field of vision, conver gence occurs; and when it moves closer in the temporal field of vision, divergence occurs. Saccades these are rapid, jerky movements that occur when the gaze shifts from one object to the other. Their function is to keep the new object in focus by changing the orientation of the eyeball. Thus, they prevent the adaptation of neurons in the visual pathway and reduce the strain on the extraocular muscles by bringing out the change. When the gaze is fixed on an object for longer period, the extraocular muscles remain contracted to maintain the position of the eyeball and this may lead to muscle fatigue. Vestibular Movements When the head moves, to keep the object in focus, the eyeball moves in response to stimuli arriving from the semicircular canals. Nystagmus the involuntary, rhythmical, oscillatory movement of the eyeball is known as nystagmus. Smooth Pursuit Movements these are the tracking movements of the eyes as they follow moving objects. When the gaze is fixed on a stationary object, there occur continuous contractions of a few muscle fibers 1200 Section 12: Special Senses producing minute oscillations at a rate of 3080 cycles per second. Due to these small tremorlike movements, the image constantly moves over a small area of the retina. As the same neuron does not get stimulated continu ously, the adaptation of neurons in the visual pathway is prevented. Though the stimulus first activates the photorecep tors, it is the neurons that get adapted earlier than the photoreceptors. If the image falls on the same spot of the retina, the neural discharge gradually decreases and the object disappears from view. Thus, the physiological nystagmus helps the eyes to see the object clearly for a longer duration. As the oscillations help to fix the gaze on an object, they are also called fixation movements. The eyes slowly follow the object and then quickly come back to the initial position of gaze by a rapid saccade. Recording of electrical activities of the retina by stimulating it with a flash of light is called electroretinography. With fully dilated pupil and following application of local anesthetic, it is performed by placing contact lens electrode (recording electrode) on the cornea, reference electrode on the skin of the forehead, and reference electrode over the earlobe. The awave originates from the retinal photorecep tors; the bwave originates from the bipolar cells and the cwave originates from the pigment epithe lium. It gives information about the rods located at the periph ery of the retina and their connections. It is helpful in the diagnosis of retinal detachment, retinal dystrophy, vitamin A deficiency, etc. Pathological Nystagmus In some pathological conditions, these oscillatory move ments become noticeable. Nystagmus can be due to disor ders of vestibular system or lesion of the neural pathways controlling the ocular movements. Abnormalities of Eye Movements Abnormalities of eye movements are summarized in Table 148.
Hypothalamic thermoreceptors play a crucial role in conditions in which rate of heat production and dissipa tion changes dramatically as happens during exercise gastritis medical definition effective 150mg zantac. Failure on the part of hypothalamus to detect such changes and mediate such responses leads to rapid alteration in core temperature resulting in grievous consequences gastritis with fever proven 150 mg zantac. In hypothalamus gastritis diet сландо cheap zantac 300mg with amex, unlike that in the skin diet to help gastritis buy zantac on line amex, warmth receptors greatly outnumber cold receptors. Hypothalamic Temperature Regulating Neurons Hypothalamic neurons that are involved in regulation of body temperature are broadly divided into three categories: sensor neurons, heatloss neurons and heat produc tion neurons. Sensor Neurons these are hypothalamic thermoreceptors that are located in anterior hypothalamus. As described above, warmth sensitive cells are more than the cold sensitive cells. They collect information about temperature from both peri pheral and central thermoreceptors. Reflex responses occur mostly to cutaneous receptor stimu lation and feedback responses occur mostly to change in core temperature. Heat-loss Neurons Neurons that on activation induce loss of heat are located in anterior hypothalamus. On stimulation, this center produces vasodilation and sweating that promote heat loss. These are the reflex responses to change in skin tem perature, which may be anticipatory in nature. These anticipatory responses to the stimulation of skin receptors are important components of an effective Chapter 156: Regulation of Body Temperature and Acclimatization to Hot and Cold Environments Flowchart 156. Responses that promote heat loss Cutaneous vasodilation Sweating Increased respiration or panting 2. Responses that reduce heat production Decreased appetite Decreased physical activity B. Responses that promote heat gain Shivering (shivering thermogenesis) Increased physical activity Increased secretion of catecholamines (nonshivering ther mogenesis) Increased appetite 2. Feedback Responses Thermoregulatory responses to changes in internal body temperature, as occur during exercise, are mainly negative feedback in nature. These effects modify the rate of heat transfer that restores the core temperature to normal level. The feedback responses are also essential compo nents of an effective thermoregulatory system as they minimize change in core temperature and consequent changes in metabolic activity. Thermal error signal influences hypothalamic integra tion centers to generate appropriate thermal effector signals (Flowchart 156. Responses Responses activated by thermal effector signals are mediated by various autonomic, somatic and endocrine mechanisms. The target effector organs mainly include cutaneous blood vessels, sweat glands and skeletal mus cles. These responses may be broadly grouped into two categories: responses activated by heat and responses activated by cold (Table 156. Mechanism of Hypothalamic Integration the major effector mechanisms for temperature regula tion are located in hypothalamus. The set point is set with a narrow range of tempera ture with average set temperature of 98. However, the so called "set point temperature" has no physioanatomical basis though it reflects the effec tive integrated response of the regulatory system. Any deviation from this set temperature is received by the thermostat as an error signal. The hypothalamic integration center receives and interprets the change in the firing rate from either cutaneous or hypothalamic cold or warmth receptors as an error signal that would otherwise lead to body heating or cooling, if appropriate responses are not activated. Responses Activated by Heat On exposure to hot environment, body temperature increases. Body tries to reduce its temperature by activat ing the mechanisms that promote heat loss and the mechanisms that reduce heat production. Responses that Promote Heat Loss Three major responses promote heat loss from the body: cutaneous vasodilation, sweating and increased breath ing. Cutaneous Vasodilation On exposure to heat, the major mechanism activated for heat dissipation is cutaneous vasodilation: 1. By increasing flow of blood from deeper parts of the body to the skin (the body surface), core heat is transferred to the surface. Heat flow to the skin is the primary mechanism of heat dissipation to the environment. Thus, by adjusting the caliber of cutaneous arterioles, body facilitates blood flow, and therefore heat flow, from the core to the skin surface, the principal site of heat dissipation. Sweating In moderate heat load, the primary mechanism of heat transfer is by increasing cutaneous blood flow. When heat load is adequately large, the autonomic response activates the eccrine sweat glands to secrete sweat onto the skin surface. The secretory segment of the sweat gland is inner vated by cholinergic sympathetic fibers. The activity of sympathetic fibers to sweat gland is increased by hypothalamic drive.
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