By J. Carlos. Oberlin College. 2019.
The lower group of chordate animals do not have a developed organ like brain and therefore their functions are autonomous cheap norvasc uk. The brain rests securely inside the skull and is covered by three membranes to protect against friction order norvasc 5mg. It extends right from the centre of the brain to the spinal cord order norvasc 2.5 mg on-line, as well as in the outer membranes of the brain and spinal cord buy norvasc from india. F range from assisting the metabolism of the brain to the prevention of friction: As the cells of the brain perform complex functions, they need extra nourishment and oxygen. If the supply of blood and oxygen to the cortex stops completely for more than five minutes, the cortex stops functioning permanently, resulting in death. Cerebellum is located in the posterior region of the skull and is divided into two - left and right - parts. The brain stem, which joins the two sides of the brain, consists of mid-brain, pons and medulla oblongata, which truncate into the spinal cord. The frontal lobe is basically responsible for the movements of the limbs, the personality and the behavior of an individual. The temporal lobe and the limbic system are associated with memory as well as basic instincts, and according to some it can be the seat of special powers like the sixth sense, etc. The left side of the brain of a right handed person (who uses his right hand for writing, eating, throwing etc. However, others believe that the mana may exist either in the temporal lobe, in the limbic circuit, or in the pineal gland of the brain. It is actually a complex biochemical and electromagnetic process and it is the limitation of our science and brain that we do not have the proper understanding of this subject. Similarly, Hypothalamus is an important centre and is the final control point of the sympathetic and the parasympathetic nervous system. It is associated with functions of our involuntary muscles, as well as physical processes like stress. This type of nervous system autonomously controls the extremely important functions of the heart, intestines, eyeballs, blood pressure, respiration etc. We have thus studied the anatomy of the brain, but brain has some amazingly unique features also, which make man superior to all living beings. There is a kind of electrical impulse emanating from the cells of the brain, which is rhythmic and constant. This electrical impulse travels chemically across one nerve cell to the other through neurotransmitters and receptors which form an amazing network and can transmit information from one part to another in a 1000th fraction of a second. Transmission of messages from one person’s minds to the other, as in telepathy can be called an electronic process. Moreover, the human brain is endowed with developed features like thinking, intelligence, the power to differentiate between good and bad, memory, creativity, etc. Though anatomically the heart is situated in the chest, the way poets have described the emotional heart it appears that in fact they are referring to the mind. The amazing thing is that we ourselves can think about our own brain, analyze it; but the one, who has created us, has discreetly left us in the dark about him. The electrical impulse generated by the posterior part of the brain during waking with eyes closed is known as alpha wave. In the past few decades, mental maladies have come to be recognized as problems of the brain, and antidotes have emerged as the treatment of choice. Regardless of how one feels about the biological basis of psychiatry today, two facts must be acknowledged. The essence of who we are is encoded in our brain, and brain changes account for the alterations of thought, mood, and behavior that occur in mental illness. It is instead the nature of the neural changes that underlie mental problems, and the manner in which treatment should proceed. These sections provide a broad framework of the basic concepts and terms necessary to understand the fundamental processes underlying brain function. Basic unit - a neuron & neural organisation As mentioned earlier, the Nervous System comprises of the brain, the spinal cord, the nerves emanating from them and their innervations of muscle fibres (i. Although that extraordinary number is of the same order of magnitude as the number of stars in the Milky Way, it alone cannot account for the complexity of the brain. A major part of the complexity arises from the rich diversity of nerve cells, or neurons, which the famous neuroanatomist Ramon y Cajal described as “the mysterious butterflies of the soul”. A neuron has three main parts - a cell body containing the nucleus, dendrites which are specialized branches for receiving information from other neurons, and axons which are specialized branches for sending out information to other neurons. A neuron that has been excited conveys information to other neurons by generating electrical impulse known as action potentials. These signals propagate like waves down the length of the cell’s single axon and are converted to chemical signals at synapses, the contact point between neurons. When the impulse reaches the axon terminals of the presynaptic neuron, it induces the release of neurotransmitter molecules. Such binding leads to the opening of ion channels and often, in turn, to the generation of action potentials in the postsynaptic neuron. Many different kinds of neurotransmitters have been identified in the brain, and this variety has enormous implications for brain function. This level of analysis at the synaptic level is particularly relevant for psychiatric and neurological disorders that shed light on the workings of the mind. Further insight into the chemical basis of thinking and behavior depends on obtaining more precise data at multiple levels of neural organization - from the mind all the way down to molecules. The power of the molecule-to-mind approach is evident in many recent advances in the pharmacologic treatment of many debilitating mental disorders such as schizophrenia, anxiety, amnesia, etc. For instance a change in the personality of a patient may either be due to depression or brain tumor (frontal or corpus callosal region). At times head injuries in cases of road accidents, falling from a height, or injury due to an instrument, demand immediate emergency treatment. In such cases it is essential that the patient is immediately shifted to a hospital without wasting any time, and given emergency treatment by a neurosurgeon. After this basic information about the brain, we will now try to understand the various diseases of the brain in detail, in the subsequent chapters. I would like to clarity that above mentioned psychiatric disorders being out of context, they are not discussed here. Finally, a most important point - It has been observed from experience that, though timely, correct diagnosis and proper medications are important for curing a patient, there are other equally important factors to bring a patient to a state of total healing & health which are unfortunately not being given proper importance in modern medicine. It is important for the patient to have faith in his doctor and have will power, a desire to live, a positive attitude and a disciplined and simple lifestyle, for a quick and complete recovery. This apart, the sympathy of the doctor towards his patient, his honest dedication towards his profession as well as his skill and high character are vital. All these points are worth taking into consideration and due emphasis should be given to each of them, in the management of a patient. In short, the aim should be healing of a patient and not merely eradication of the disease - symptoms. Many a times when it becomes necessary to know the location, extent and damage caused by a disease lying inside the body, radiology- neuroradiology becomes helpful and and necessary. X-Ray : The “miraculous rays” X-Rays which could look-make structures inside the body were discovered in 1895 by a German scientist Mr: Roentegen. Radio and television waves do not have much energy and so though they are present all around us in innumerable numbers, they cannot harm us and we are still alive. The energy from the X-Rays is 10,000 to 15,000 times more powerful than light and therefore can penetrate through objects. An amazing fact of nature is that the human eye can perceive only the sun rays and the rest of the rays are invisible to us. The common X-Rays only give a rough picture of the skull or a one dimensional picture, but the depth of any feature cannot be judged, e. However, since we are now discussing about the diseases of the brain, it is necessary to know how X-Rays are helpful in this context. In the previous chapter we learned that the brain is well protected in the skull and therefore X- Rays are only able to give us the information of the skull. If there is a tumor in the brain, its depth and position can be determined by dividing the brain into imaginary parts like slices of bread, and each part is X-Rayed from various angles. The computer then calculates and creates a three- dimensional picture, which determines the depth and the size of the tumor very accurately.
You know from this and earlier study sessions that breastfeeding is critical for promoting healthy growth in infants buy cheap norvasc, helping prevent disease and encourage bonding between the mother and baby norvasc 10 mg without a prescription. You will therefore need to communicate with the different frontline workers in sectors such as education and agriculture order generic norvasc on-line. Working collaboratively will help to ensure the essential nutrition actions are shared as widely as possible and help to build understanding of their importance purchase 2.5mg norvasc mastercard. Therefore, promotion of food-based approaches are important for you to use within your own community. The intensiﬁcation of horticultural activities needs to be supported by nutrition education and one of the things you can do as Health Extension Practitioner is to provide practical demonstrations for people in your community and encourage women to cultivate vegetable gardens as a source of nutritious food for their families (see Figure 11. Cultural malpractice and beliefs in child feeding and weaning (complementary feeding process, exposure of children to sunlight, addressing issues relating to food faddism and food prejudices). Growth monitoring refers to the regular assessment of the growth of children under two years old to detect deviation from normal growth and the application of appropriate interventions. In the following section you will learn how you can counsel mothers and caregivers about the growth and nutritional status of their children. To measure individual health and to instigate effective action in response to growth faltering (slowing down). Teach mothers, families and health workers how diet and illness can affect child growth and thereby stimulate individual initiative and improved nutrition and healthcare practices. Poor linear growth (underweight and stunting) usually occurs in the ﬁrst 24 months of life. If the child is not optimally fed during this time, they could lose 11cm from the potential height that they would have reached as an adult. By the time a child is two or three years old, catch-up growth is less likely to occur; such children have probably failed to grow and are potentially stunted for the rest of their lives. You learned how to assess whether a child is stunted in Study Session 4 of this Module. Age of malnourished child Determinant factors Birth Maternal factors (including nutrition), gestational age Four-six months Infant feeding practices, maternal ability to care for the child Six months to two years Complementary feeding practices, exposure to infections, disease and poor household food as the child gets older Two-ﬁve years Inadequate access to household food; infections and social deprivation In Ethiopia we use underweight for monitoring growth, as it indicates acute changes in the nutritional status of the child. If you determine that the child is malnourished (underweight), you should be able to analyse the causes, identify resources, suggest alternative solutions and arrive at decisions together with the mother or caregiver as to what should be done about the child. This process of assessment analysis and action is known as the ‘triple A’ cycle which is described below. Assess This stage involves weighing a child on a regular basis, and comparing the child’s growth with the standard and with their previous weight. This helps to identify any nutritional problems and will help you reﬂect on and review the child’s situation with the mother or caregiver. Analyse This requires exploration of any nutritional problem of the child in order to understand the root causes of any difﬁculties. You should identify gaps in feeding or care practices and think about different alternative solutions and resources that you can suggest to the mother or caregiver. Action This stage involves counselling the mother or caregiver about relevant actions. It involves decision making and resource identiﬁcation as well as deciding on individual and collective doable actions. After thorough discussion with the mother or caregiver, you should be able to decide on the speciﬁc actions they need to do. Ideally these actions are feasible and can realistically be done by the caregiver and the household. Each time the child is weighed again, re- assessment is done, followed by new analysis and new action as necessary. The most important issue in growth monitoring is not the position of the child ThetripleAcyclemeasuresthe on the growth curve at one particular time, but the direction of his or her direction of the child’s growth. A single point on the line of growth could be reached from different directions (that is, the child’s weight could go down to the single point or could move up to that point on the chart). Normally the child’s measurements are expected to fall between the lines indicated on the graph by -2 and +2 Z-scores (see the right hand side of the graph). It gives you information you need to be able to advise the mother and caregiver what they need to do for their child. You need to ﬁnd out the problem together with the mother or caregiver and counsel them on what to do. So you should encourage the mother to continue feeding the child in the way she has been doing. Knowing the rate and direction of growth will help you when you are counselling the mother or caregiver. You should always employ nutrition counselling as a tool to help you achieve this objective. Nutrition counselling is a process of ﬁnding the solution to the child’s nutritional problem together with their mother or caregiver. Unlike nutrition education, nutrition counselling is a two-way process during which the mother is actively involved in describing the child’s problems as well as participating in analysing the causes and identifying the available resources and solutions. Working together in this way with the mother or caregiver will help them reach a decision about the doable actions. Analysing causes and identifying 156 Study Session 11 Nutrition Education and Counselling actions are an important part of the overall process. Once you weigh the child and determine their nutritional status you need to share this information with the mother and negotiate with her what actions she can take. Follow-up is also very important and you should always recommend to the mother that she makes an appointment so you can see whether she has carried the agreed actions or whether she has had some problems with these. Counselling is an important skill, and as you have seen, a key element of the triple A cycle. Knowledge is not sufﬁcient because at least three contacts are needed to change behaviour or practice. These messages are communicated at the six health contacts and through other contacts outside the health sector. Write your answers on your study diary and discuss them with your Tutor at the next study support meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of the module. Depending on the degree of malnutrition, nutrition care can be given at home or at the out-patient or in- patient level. Learning Outcomes for Study Session 12 When you have studied this session, you should be able to: 12. Poor nutrition increases the body’s vulnerability to infections, and infections in their turn make poor nutrition even worse. Inadequate dietary intake lowers immune system functioning and reduces the body’s ability to ﬁght infections. Poor nutrition is therefore likely to increase the incidence, severity and length of infections. Symptoms that accompany infections such as loss of appetite, diarrhoea and fever lead to further reduced food intake, poor nutrient absorption, nutrient loss and altered metabolism. All of these contribute to weight loss and growth faltering, which in turn further weaken the immune system. Vitamin and mineral deﬁciencies may occur at a time when a person actually has increased nutritional needs because of infections, viral replication and poor nutrient absorption. The whole body develops reduced immune functioning and increased susceptibility to opportunistic infections. The disease itself may make the absorption of energy and other nutrients less efﬁcient. Possible increase in the need for other nutrients because of symptoms such as anaemia. You will be able to give nutritional care both at health post level and during home-based care. This gives you the opportunity to help them maintain their health for as long as possible. If you see that a person is losing weight, you can suggest ways of increasing their nutrition intake so they do not have nutrition deﬁciencies which can lead to a weak immune system.
If you are finding it difficult to comply with the regulations generic norvasc 10mg without a prescription, please let us know discount norvasc 5 mg with mastercard. It is assumed you will be present and the attending on service will cover issues during the lecture effective norvasc 2.5mg. There will be times when the attending will do the procedures and times when a more senior resident will do the procedure cheap norvasc 2.5mg on line. As a general rule, lines on infants or hemodynamically unstable patients will be done by the attending. It has been developed by a collaboration of Peds intensivists around the country and is used to tailor our educational objectives. Even if you aren’t a neurologist, you will likely notice something really bad that we should know about). Double Pages and Code 99 A "double page" is a page indicating the emergency need for the house officer named to respond immediately. Occurs due to an absolute or relative insulin deficiency along with an excess of counter regulatory hormones (e. Fatty acids are oxidized in liver resulting in elevated levels of circulating ketone bodies (beta-hydroxybutyrate and acetoacetate) 3. Counter regulatory hormones stimulate hepatic ketogenesis as well as gluconeogenesis and glycogenolysis resulting in excess glucose production and hyperglycemia 4. Careful history: vomiting, abdominal pain, polyuria, polydipsia, nocturia, weakness, heavy breathing or shortness of breath, symptoms of intercurrent illness, mental status changes, sweet odor to breath, weight loss 2. Physical exam: dehydration (dry mucous membranes, poor skin turgor, poor perfusion), tachycardia, hypotension, Kussmaul respirations, somnolence, hypothermia, impaired consciousness 3. Correction for psuedo/dilutional hyponatremia: Na+ (corrected) = Na+ (measured) + [(serum glucose – 100)/100] x 1. Correct fluid deficits - calculate fluid deficit (may assume 5-10% dehydration) - i. Correct electrolyte deficiencies - consider normal saline or 1/2 normal saline - potassium shifts extracellularly due to acidosis- therefore despite normal - serum potassium levels a total body deficit usually exists - if serum K < 5, replace with 40 mEq potassium in fluids initially. Correct metabolic acidosis by interrupting ketone production - begin with continuous insulin drip 0. A deficiency of vasopressin is caused by destruction of the posterior pituitary gland by tumors or trauma 4. Nephrogenic diabetes arises from end-organ resistance to vasopressin, either from a receptor defect or medications that interfere with aquaporin transport of water Epidemiology: 1. Incidence of diabetes insipidus in the general population is 3 in 100,000 slightly higher incidence in males (60%) 2. Clinical history: poor feeding, failure to thrive, irritability, soaking of diapers in infants; polyuria, polydipsia, nocturia, large volume of water; growth retardation, seizures 2. Physical examination: irritability, signs of dehydration (decreased tearing, depressed fontanelle, sunken eyes, mottled or poor skin turgor), signs of shock (hypotension, weak pulses) 3. Diagnostic tests: - water deprivation test (perform only w/close monitoring and involvement of endocrine team) - a rise in plasma osmolality >10mOsm/kg over baseline with specific gravity remaining <1. Treat dehydration with oral repletion or if necessary, parental rehydration if severely dehydrated. A life-threatening medical emergency defined as frequent or prolonged epileptic seizures 2. Many definitions including a continuous seizure lasting longer than 30 minutes or repeating convulsions lasting 30 minutes or longer without recovery of consciousness between them. A common neurologic medical emergency, affecting 65,000 to 150,000 persons in the United States yearly 2. Many possible etiologies as listed below: Causes of Status Epilepticus Background of Epilepsy •Poor compliance with medication •Recent change in treatment •Barbiturate or benzodiazepine withdrawal •Alcohol or drug abuse •Pseudostatus epilepticus •Underlying infection/fever - 15 - Presenting de novo •Recent stroke •Meningo-encephalitis, meningitis, encephalitis •Acute head injury •Cerebral neoplasm •Demyelinating disorder •Metabolic disorders (e. Last resort may need to induce pentobarb or general anesthesia (propofol) coma after airway secured 7. Watch for potential complications including hypothermia, acidosis, hypotension, rhabdomyolysis, renal failure, infection and cerebral edema 8. Increased intracranial pressure results when the volume of one of the cranial contents (brain parenchyma, cerebrospinal fluid, or blood) increases and adaptive measures are unable to compensate 2. Brain injury occurs in 2 phases: (1) the primary injury that occurs at the moment of impact and results from a transfer of kinetic energy to the brain and (2) the secondary injury that is a biochemical and cellular response to the initial trauma 5. The primary injury causes direct cellular damage; we cannot do anything to reverse the primary injury as neurons do not regenerate 6. In pediatric trauma patients, head injuries occur in more than 70-80% of those children who require hospitalization and death occurs in 20-40% of those patients 2. Clinical history: -h/o trauma, symptoms including headache, vomiting, depressed level of consciousness i. Physical exam: abnormal posturing, abnormal breathing pattern, abnormal cranial nerve findings, papilledema, hypertension with bradycardia or tachycardia, bulging fontanelle 3. Breathing- ensure adequate oxygenation and avoid hypercapnia (mild hyperventilation is appropriate) 3. Evaluate and treat possible complications: hyperthermia, glucose abnormalities, seizures 7. Intracranial pressure monitoring (intraventricular drain, intraparenchymal catheter (Camino), subarachnoid bolt). Mechanical ventilation: sats >95%, avoid hypercapnia, consider short- term hyperventilation 12. Mannitol- decreases blood viscosity by lowering hematocrit, may reduce brain water content in the uninjured portion) Æ give rapidly, “chronic” dose is 0. Other: barbiturates-controversial, steroids- will help reduce vasogenic edema (around tumors), no effect on cytotoxic brain edema or in the management of head trauma 15. Reversible, diffuse lower-airway obstruction caused by airway inflammation and edema, bronchial smooth muscle spasm and mucous plugging 2. Exam: level of consciousness, breath sounds (distant or absent is ominous),central cyanosis, accessory muscle use 2. Arterial blood gas: - Early phase Æ hypoxemia, hypocarbia - Impending respiratory failure Æ hypercabia Treatment: 1. High flow supplemental oxygen (Non-rebreather if necessary, use blender if possible to avoid 100 % FiO2) 5. Mechanical ventilation is also difficult and should be managed by an experienced pediatric intensivist. Support modes of ventilation (pressure support and volume support) are used frequently. Beta agonists- tachycardia, arrhythmia, hypertension or hypotension, agitation/tremulousness, hyperactivity 5. Magnesium- hypotension, respiratory depression, heart block, flushing, nausea, somnolence 7. Acute Respiratory Distress Syndrome Definition: Acute respiratory distress characterized by acute lung injury, noncardiogenic pulmonary edema and severe hypoxia. The clinical and pathological features closely resembled those seen in infants with respiratory distress and to conditions in congestive atelectasis and postperfusion lung. Pulmonary artery wedge pressure < or = to 18mm or absence of evidence of left atrial hypertension 4. Pao2/Fio2 ratio < or = to 200 *[Pao2/Fio2 ratio < or = to 300 is defined as Acute Lung Injury] -American-European Consensus Conference Statement, 1994 Risk Factors: Pulmonary Extra-pulmonary Bacterial pneumonia Sepsis Viral pneumonia Trauma Aspiration Multiple transfusion Inhalation injury Cardiopulmonary bypass Fat emboli Pancreatitis Near Drowning Peritonitis Anything really bad - 21 - Pathophysiology: 1. Endothelial and epithelial cell damage leads to increased permeability and the influx of fluid into the alveolar space. Ventilatory support- ensures “adequate” oxygenation/ventilation while minimizing ventilator induced lung injury. Drugs sometimes used include steroids (late phase), NitricOxide (no proven survival benefit), 4. If on <60%, Sat goal should be ~92, if not able to maintain 92 on <60%, tolerate 85%. Monitor trends closely—absolute numbers are not usually important, trends in numbers are often extremely important. Remember that cardio-pulmonary interactions occur, and ventilator maneuvers may affect hemodynamics.
The cardioaccelerator regions stimulate activity via sympathetic stimulation of the cardioaccelerator nerves order norvasc 2.5 mg fast delivery, and the cardioinhibitory centers decrease heart activity via parasympathetic stimulation as one component of the vagus nerve norvasc 5mg lowest price, cranial nerve X norvasc 10 mg with visa. Both sympathetic and parasympathetic stimulations flow through a paired complex network of nerve fibers known as the 868 Chapter 19 | The Cardiovascular System: The Heart cardiac plexus near the base of the heart purchase norvasc without a prescription. It opens chemical- or ligand-gated sodium and calcium ion channels, allowing an influx of positively charged ions. They innervate the heart via sympathetic cardiac nerves that increase cardiac activity and vagus (parasympathetic) nerves that slow cardiac activity. Parasympathetic stimulation originates from the cardioinhibitory region with impulses traveling via the vagus nerve (cranial nerve X). To speed up, one need merely remove one’s foot from the break and let the engine This OpenStax book is available for free at http://cnx. Input to the Cardiovascular Center The cardiovascular center receives input from a series of visceral receptors with impulses traveling through visceral sensory fibers within the vagus and sympathetic nerves via the cardiac plexus. Among these receptors are various proprioreceptors, baroreceptors, and chemoreceptors, plus stimuli from the limbic system. Collectively, these inputs normally enable the cardiovascular centers to regulate heart function precisely, a process known as cardiac reflexes. Increased physical activity results in increased rates of firing by various proprioreceptors located in muscles, joint capsules, and tendons. The cardiac centers monitor these increased rates of firing, and suppress parasympathetic stimulation and increase sympathetic stimulation as needed in order to increase blood flow. Similarly, baroreceptors are stretch receptors located in the aortic sinus, carotid bodies, the venae cavae, and other locations, including pulmonary vessels and the right side of the heart itself. Rates of firing from the baroreceptors represent blood pressure, level of physical activity, and the relative distribution of blood. The cardiac centers monitor baroreceptor firing to maintain cardiac homeostasis, a mechanism called the baroreceptor reflex. With increased pressure and stretch, the rate of baroreceptor firing increases, and the cardiac centers decrease sympathetic stimulation and increase parasympathetic 870 Chapter 19 | The Cardiovascular System: The Heart stimulation. As pressure and stretch decrease, the rate of baroreceptor firing decreases, and the cardiac centers increase sympathetic stimulation and decrease parasympathetic stimulation. There is a similar reflex, called the atrial reflex or Bainbridge reflex, associated with varying rates of blood flow to the atria. Increased metabolic byproducts associated with increased activity, such as carbon dioxide, hydrogen ions, and lactic acid, plus falling oxygen levels, are detected by a suite of chemoreceptors innervated by the glossopharyngeal and vagus nerves. These chemoreceptors provide feedback to the cardiovascular centers about the need for increased or decreased blood flow, based on the relative levels of these substances. Individuals experiencing extreme anxiety may manifest panic attacks with symptoms that resemble those of heart attacks. Heart: Broken Heart Syndrome Extreme stress from such life events as the death of a loved one, an emotional break up, loss of income, or foreclosure of a home may lead to a condition commonly referred to as broken heart syndrome. This condition may also be called Takotsubo cardiomyopathy, transient apical ballooning syndrome, apical ballooning cardiomyopathy, stress-induced cardiomyopathy, Gebrochenes-Herz syndrome, and stress cardiomyopathy. The recognized effects on the heart include congestive heart failure due to a profound weakening of the myocardium not related to lack of oxygen. The exact etiology is not known, but several factors have been suggested, including transient vasospasm, dysfunction of the cardiac capillaries, or thickening of the myocardium—particularly in the left ventricle—that may lead to the critical circulation of blood to this region. While many patients survive the initial acute event with treatment to restore normal function, there is a strong correlation with death. Careful statistical analysis by the Cass Business School, a prestigious institution located in London, published in 2008, revealed that within one year of the death of a loved one, women are more than twice as likely to die and males are six times as likely to die as would otherwise be expected. After reading this section, the importance of maintaining homeostasis should become even more apparent. Major Factors Increasing Heart Rate and Force of Contraction Factor Effect Cardioaccelerator Release of norepinephrine by cardioaccelerator nerves nerves Proprioreceptors Increased firing rates of proprioreceptors (e. The rate of depolarization is increased by this additional influx of positively charged ions, so the threshold is reached more quickly and the period of repolarization is shortened. However, massive releases of these hormones coupled with sympathetic stimulation may actually lead to arrhythmias. The physiologically active form of thyroid hormone, T3 or triiodothyronine, has been shown to directly enter cardiomyocytes and alter activity at the level of the genome. Although it is the world’s most widely consumed psychoactive drug, caffeine is legal and not regulated. While precise quantities have not been established, “normal” consumption is not considered harmful to most people, although it may cause disruptions to sleep and acts as a diuretic. Its consumption by pregnant women is cautioned against, although no evidence of negative effects has been confirmed. Tolerance and even physical and mental addiction to the drug result in individuals who routinely consume the substance. While legal and nonregulated, concerns about nicotine’s safety and documented links to respiratory and cardiac disease have resulted in warning labels on cigarette packages. Initially, both hyponatremia (low sodium levels) and hypernatremia (high sodium levels) may lead to tachycardia. Hypokalemia (low potassium levels) also leads to arrhythmias, whereas hyperkalemia (high potassium levels) causes the heart to become weak and flaccid, and ultimately to fail. Acidosis is a condition in which excess hydrogen ions are present, and the patient’s blood expresses a low pH value. Alkalosis is a condition in which there are too few hydrogen ions, and the patient’s blood has an elevated pH. Recall that enzymes are the regulators or catalysts of virtually all biochemical reactions; they are sensitive to pH and will change shape slightly with values outside their normal range. Elevated body temperature is called hyperthermia, and suppressed body temperature is called hypothermia. This distinct slowing of the heart is one component of the larger diving reflex that diverts blood to essential organs while submerged. If sufficiently chilled, the heart will stop beating, a technique that may be employed during open heart surgery. In this case, the patient’s blood is normally diverted to an artificial heart-lung machine to maintain the body’s blood supply and gas exchange until the surgery is complete, and sinus rhythm can be restored. Excessive hyperthermia and hypothermia will both result in death, as enzymes drive the body systems to cease normal function, beginning with the central nervous system. The three primary factors to consider are preload, or the stretch on the ventricles prior to contraction; the contractility, or the force or strength of the contraction itself; This OpenStax book is available for free at http://cnx. One of the primary factors to consider is filling time, or the duration of ventricular diastole during which filling occurs. With increased ventricular filling, the ventricular muscle is increasingly stretched and the sarcomere length increases. If this process were to continue and the sarcomeres stretched beyond their optimal lengths, the force of contraction would decrease. However, due to the physical constraints of the location of the heart, this excessive stretch is not a concern. The relationship between ventricular stretch and contraction has been stated in the well-known Frank-Starling mechanism or simply Starling’s Law of the Heart. This principle states that, within physiological limits, the force of heart contraction is directly proportional to the initial length of the muscle fiber. Otto Frank (1865–1944) was a German physiologist; among his many published works are detailed studies of this important heart relationship. Although they worked largely independently, their combined efforts and similar conclusions have been recognized in the name “Frank-Starling mechanism. While much of the ventricular filling occurs while both atria and ventricles are in diastole, the contraction of the atria, the atrial kick, plays a crucial role by providing the last 20–30 percent of ventricular filling. Factors that increase contractility are described as positive inotropic factors, and those that decrease contractility are described as negative inotropic factors (ino- = “fiber;” -tropic = “turning toward”). Not surprisingly, sympathetic stimulation is a positive inotrope, whereas parasympathetic stimulation is a negative inotrope.