By I. Marius. Pine Manor College. 2018.
The place to start this study of the nervous system is the beginning of the individual human life suhagra 100mg amex, within the womb discount suhagra 100 mg mastercard. The embryonic development of the nervous system allows for a simple framework on which progressively more complicated structures can be built suhagra 100mg overnight delivery. Starting from an embryologic perspective allows you to understand more easily how the parts relate to each other. The embryonic nervous system begins as a very simple structure—essentially just a straight line, which then gets increasingly complex. Looking at the development of the nervous system with a couple of early snapshots makes it easier to understand the whole complex system. Many structures that appear to be adjacent in the adult brain are not connected, and the connections that exist may seem arbitrary. By following the developmental pattern, it is possible to learn what the major regions of the nervous system are. The fertilized egg cell, or zygote, starts dividing to generate the cells that make up an entire organism. Sixteen days after fertilization, the developing embryo’s cells belong to one of three germ layers that give rise to the different tissues in the body. The endoderm, or inner tissue, is responsible for generating the lining tissues of various spaces within the body, such as the mucosae of the digestive and respiratory systems. Finally the ectoderm, or outer tissue, develops into the integumentary system (the skin) and the nervous system. It is probably not difficult to see that the outer tissue of the embryo becomes the outer covering of the body. As the embryo develops, a portion of the ectoderm differentiates into a specialized region of neuroectoderm, which is the precursor for the tissue of the nervous system. Molecular signals induce cells in this region to differentiate into the neuroepithelium, forming a neural plate. As the neural folds come together and converge, the underlying structure forms into a tube just beneath the ectoderm called the neural tube. Cells from the neural folds then separate from the ectoderm to form a cluster of cells referred to as the neural crest, which runs lateral to the neural tube. Many tissues that are not part of the nervous system also arise from the neural crest, such as craniofacial cartilage and bone, and melanocytes. As the two sides of the neural groove converge, they form the neural tube, which lies beneath the ectoderm. The anterior end of the neural tube will develop into the brain, and the posterior portion will become the spinal cord. Beginning at 25 days, the anterior end develops into the brain, and the posterior portion becomes the spinal cord. This is the most basic arrangement of tissue in the nervous system, and it gives rise to the more complex structures by the fourth week of development. Primary Vesicles As the anterior end of the neural tube starts to develop into the brain, it undergoes a couple of enlargements; the result is the production of sac-like vesicles. These vesicles are given names that are based on Greek words, the main root word being enkephalon, which means “brain” (en- = “inside”; kephalon = “head”). The prefix to each generally corresponds to its position along the length of the developing nervous system. The prosencephalon (pros- = “in front”) is the forward-most vesicle, and the term can be loosely translated to mean forebrain. The first part of this word is also the root of the word rhombus, which is a geometrical figure with four sides of equal length (a square is a rhombus with 90° angles). Whereas prosencephalon and mesencephalon translate into the English words forebrain and midbrain, there is not a word for “four-sided-figure-brain. One way of thinking about how the brain is arranged is to use these three regions—forebrain, midbrain, and hindbrain—which are based on the primary vesicle stage of development (Figure 13. Secondary Vesicles The brain continues to develop, and the vesicles differentiate further (see Figure 13. The diencephalon gives rise to several adult structures; two that will be important are the thalamus and the hypothalamus. In the embryonic diencephalon, a structure known as the eye cup develops, which will eventually become the retina, the nervous tissue of the eye called the retina. The midbrain is an established region of the brain at the primary vesicle stage of development and remains that way. Dividing the brain into forebrain, midbrain, and hindbrain is useful in considering its developmental pattern, but the midbrain is a small proportion of the entire brain, relatively speaking. The metencephalon corresponds to the adult structure known as the pons and also gives rise to the cerebellum. The cerebellum (from the Latin meaning “little brain”) accounts for about 10 percent of the mass of the brain and is an important structure in itself. The most significant connection between the cerebellum and the rest of the brain is at the pons, because the pons and cerebellum develop out of the same vesicle. The structures that come from the mesencephalon and rhombencephalon, except for the cerebellum, are collectively considered the brain stem, 552 Chapter 13 | Anatomy of the Nervous System which specifically includes the midbrain, pons, and medulla. As the anterior end of the neural tube develops, it enlarges into the primary vesicles that establish the forebrain, midbrain, and hindbrain. Those structures continue to develop throughout the rest of embryonic development and into adolescence. How would you describe the difference in the relative sizes of the three regions of the brain when comparing the early (25th embryonic day) brain and the adult brain? Spinal Cord Development While the brain is developing from the anterior neural tube, the spinal cord is developing from the posterior neural tube.
A few days later discount suhagra 100 mg line, a cluster of eight cases was reported in New York City order suhagra 100 mg with amex, also involving young patients buy suhagra 100mg without prescription, this time exhibiting a rare form of skin cancer known as Kaposi’s sarcoma. This cancer of the cells that line the blood and lymphatic vessels was previously observed as a relatively innocuous disease of the elderly. The disease that doctors saw in 1981 was frighteningly more severe, with multiple, fast-growing lesions that spread to all parts of the body, including the trunk and face. Indeed, when they were tested, they exhibited extremely low numbers of a specific type of white blood cell in their bloodstreams, indicating that they had somehow lost a major part of the immune system. The lymphatic system, for most people, is associated with the immune system to such a degree that the two systems are virtually indistinguishable. The lymphatic system is the system of vessels, cells, and organs that carries excess fluids to the bloodstream and filters pathogens from the blood. The swelling of lymph nodes during an infection and the transport of lymphocytes via the lymphatic vessels are but two examples of the many connections between these critical organ systems. Functions of the Lymphatic System A major function of the lymphatic system is to drain body fluids and return them to the bloodstream. Blood pressure causes leakage of fluid from the capillaries, resulting in the accumulation of fluid in the interstitial space—that is, spaces between This OpenStax book is available for free at http://cnx. In humans, 20 liters of plasma is released into the interstitial space of the tissues each day due to capillary filtration. Once this filtrate is out of the bloodstream and in the tissue spaces, it is referred to as interstitial fluid. It drains the excess fluid and empties it back into the bloodstream via a series of vessels, trunks, and ducts. When the lymphatic system is damaged in some way, such as by being blocked by cancer cells or destroyed by injury, protein-rich interstitial fluid accumulates (sometimes “backs up” from the lymph vessels) in the tissue spaces. This inappropriate accumulation of fluid referred to as lymphedema may lead to serious medical consequences. As the vertebrate immune system evolved, the network of lymphatic vessels became convenient avenues for transporting the cells of the immune system. Additionally, the transport of dietary lipids and fat-soluble vitamins absorbed in the gut uses this system. Cells of the immune system not only use lymphatic vessels to make their way from interstitial spaces back into the circulation, but they also use lymph nodes as major staging areas for the development of critical immune responses. Structure of the Lymphatic System The lymphatic vessels begin as open-ended capillaries, which feed into larger and larger lymphatic vessels, and eventually empty into the bloodstream by a series of ducts. Along the way, the lymph travels through the lymph nodes, which are commonly found near the groin, armpits, neck, chest, and abdomen. A major distinction between the lymphatic and cardiovascular systems in humans is that lymph is not actively pumped by the heart, but is forced through the vessels by the movements of the body, the contraction of skeletal muscles during body movements, and breathing. Lymph flows from the lymphatic capillaries, through lymphatic vessels, and then is dumped into the circulatory system via the lymphatic ducts located at the junction of the jugular and subclavian veins in the neck. Lymphatic Capillaries Lymphatic capillaries, also called the terminal lymphatics, are vessels where interstitial fluid enters the lymphatic system to become lymph fluid. Located in almost every tissue in the body, these vessels are interlaced among the arterioles and venules of the circulatory system in the soft connective tissues of the body (Figure 21. Exceptions are the central nervous system, bone marrow, bones, teeth, and the cornea of the eye, which do not contain lymph vessels. Interstitial fluid slips through spaces between the overlapping endothelial cells that compose the lymphatic capillary. Lymphatic capillaries are formed by a one cell-thick layer of endothelial cells and represent the open end of the system, allowing interstitial fluid to flow into them via overlapping cells (see Figure 21. Entry of fluid into lymphatic capillaries is also enabled by the collagen filaments that anchor the capillaries to surrounding structures. As interstitial pressure increases, the filaments pull on the endothelial cell flaps, opening up them even further to allow easy entry of fluid. In the small intestine, lymphatic capillaries called lacteals are critical for the transport of dietary lipids and lipid-soluble vitamins to the bloodstream. In the small intestine, dietary triglycerides combine with other lipids and proteins, and enter the lacteals to form a milky fluid called chyle. Larger Lymphatic Vessels, Trunks, and Ducts The lymphatic capillaries empty into larger lymphatic vessels, which are similar to veins in terms of their three-tunic structure and the presence of valves. These one-way valves are located fairly close to one another, and each one causes a bulge in the lymphatic vessel, giving the vessels a beaded appearance (see Figure 21. The superficial and deep lymphatics eventually merge to form larger lymphatic vessels known as lymphatic trunks. On the right side of the body, the right sides of the head, thorax, and right upper limb drain lymph fluid into the right subclavian vein via the right lymphatic duct (Figure 21. On the left side of the body, the remaining portions of the body drain into the larger thoracic duct, which drains into the left subclavian vein. The thoracic duct itself begins just beneath the diaphragm in the cisterna chyli, a sac-like chamber that receives lymph from the lower abdomen, pelvis, and lower limbs by way of the left and right lumbar trunks and the intestinal trunk. The lymph from the rest of the body enters the bloodstream through the thoracic duct via all the remaining lymphatic trunks. In general, lymphatic vessels of the subcutaneous tissues of the skin, that is, the superficial lymphatics, follow the same routes as veins, whereas the deep lymphatic vessels of the viscera generally follow the paths of arteries. The Organization of Immune Function The immune system is a collection of barriers, cells, and soluble proteins that interact and communicate with each other in extraordinarily complex ways. The modern model of immune function is organized into three phases based on the timing of their effects.
Patient may also present classical symptoms like polyuria buy suhagra 100 mg free shipping, polydypsia buy discount suhagra 100mg on-line, and polyphasia order suhagra 100mg overnight delivery, accompanied by loss of weight. Since hypoglycemia is a serious possibility in these patients, they are protected by giving orally more than 1000gms of glucose/day. Carboxy peptidase B, trypsin like peptidase in the lysosomes of α-cells, hydrolyze it to produce active glucagon and some inactive peptides. Effect on mineral metabolism: • It increases potassium, and calcitonin release which in turn causes calcium lowering effect. A large part (70%) of iodine in thyroglobulin exists as inactive monoiodotyrosine, diiodotyrosine and rest is in the form of T3, T4. Synthesis of Thyroglobulin: * The acinar cells of thyroid synthesize and store thyroglobulin as colloid in follicles. The iodine pool in acinar cells exists as exchangeable iodide in blood and unused iodine as iodotyrosine. Mechanism of action of thyroid hormone: Targets are liver, kidneys, adipose, cardiac, neurons, and lymphocytes. Thus in hypothyroidism, there is accumulation carotene in blood which is responsible for the yellowish tint of the skin. Hyperthyroidism is treated with radioactive isotope like 131 I or anti thyroid drugs improve the condition of the patient. There is increased level of hyaluronic acid and chondroitin sulfate bound to protein, which forms excessive tissue gel in the interstitial spaces. Catecholamines Synthesis: Epinephrine is synthesized, stored in adrenal medulla while nor- epinephrine is synthesized in sympathetic nervous system. Urinary metabolites of epinephrine and nor-epinephrine are estimated for the conformation of diagnosis. Thus failure of feed- back inhibition of anterior pituitary by thyroid hormone is the pathological basis of the patient’s condition. Following a normal overnight fast and a cup of black coffee, a diabetic woman feels slightly nauseous and decides to skip breakfast. Insulin should be given only when blood glucose level can be maintained by dietary or stored glycogen. When blood glucose is low, if insulin is given, severe hypoglycemia might result, further it can lead to insulin shock. The sugar – phosphate linkages form the backbone of the polymer to which the variable bases are attached. The sequence of the polymer is written in the 5’ to 3’ direction with abbreviations to different bases e. The bases of one strand pairs with the bases of the other strand of the same plane such that adenine always pairs with thymine with two bonds. The negatively charged phosphate group and the sugar units expose themselves to the outside of the chain. The purine, pyrimidine bases are on the inside of the helix, the phosphate and deoxyribose groups are on the outside. Ribonucleotide differs from deoxyribonucleotide in that ribonucleotide contains “O” in the carbon 2’ sugar ribose. Site Nucleus, mitochondria Nucleus, ribosome, cytosol, but never in cytosol Nucleolus, mitochondria 4. According to their sedimentation rates, the subunits are referred as 30S, & 50S, together they form 70S unit. Since uric acid has a precipitation character, excess uric acid in kidney causes kidney stone and in joints causes gout. In prokaryotic cell the primer length is about 10 - ribonucleotides, but in Eukaryotic cell it is about ’ 30. This occurs by addition of 7 - methyl Guanine to the 5’ end and may be associated by further methylation of the adjacent sugar moiety of the next nucleotides. Similarly erythromycin inhibits translocation Diphtheria toxin: Corny bacterium diphtheria produce lethal protein toxin. The sequence of amino acids in the polypeptide chain, from the amino terminus to carboxyl end corresponds to the base sequence of a gene (from 5’ to 3’end). When protein is synthesized we see the translation of genetic information into the universal language called protein. Allosteric regulation The regulation of enzymes by small molecules that bind to a site distinct from the active site, changing the conformation and catalytic activity of the enzyme. Amphipathic A molecule that has both hydrophobic and hydrophilic regions Antibody A protein produced by B-lymphocytes that binds to a foreign molecules Antigen A molecule against which the antibody is directed. Chitin a polymer of N-acetylglucosamine residue that is the principal component of fungal cell walls and exoskeleton of insects. Codon The basic unit of genetic code; one of the 64 nucleotide triplets that code for an amino acid or stop sequence. A small lipid –soluble molecule that carries electrons between protein complexes in the mitochondrial electron transport chain. Low molecular-weight organic molecules that work together with enzymes to catalyze biological reactions Collagen The major structural protein of the extracellular matrix. Cytochrome oxidase A protein complex in the electron transport chain that accepts electrons from cytochrome c and transfer them to O2. Peptide bond The bond joining amino acids in a polypeptide Phagocytosis The uptake of large particles such as bacteria by a cell.
Both seem to have jumped the species barrier form non-human primates to humans in th Africa during the 20 century cheap suhagra 100 mg on-line. About 1% of Caucasian populations are homozygous buy suhagra 100 mg with amex, while the haplotype is far less common in African and Asian populations cheap 100mg suhagra. Other routes of infection are by contaminated needles or blood transfusions and from an infected mother to her child before or during childbirth or by breast feeding. Some of its proteins are synthesized as polyprotein precursors that are subsequently cleaved to their final form by viral protease. After all components have been produced in sufficient quantities, they are packaged by self- assembly and leave the cell by budding. When this number falls below a critical threshold of 200, adaptive immunity is so weak that the patient starts to suffer from opportunistic infections with, e. A range of protease inhibitors is used; a virus strain may develop resistance by point mutations in its protease gene. The drug cocktail is effective but frequently causes unwanted side effects including mitochondrial dysfunction resulting in myopathy or pancreatitis or lipodystrophy (esthetically displeasing changes in the distribution of subcutaneous fat). This is not a question of popping two pills a day; therapy protocol is complex, requiring the patient to take medications at exact time points distributed over the entire day. If this is paired with intermittent selective pressure by therapy, resistant strains will emerge rapidly. The countries needing these medications most, especially in sub-Saharan Africa, are the ones least able to pay for them. Despite some programs to equip these countries at reduced prices, this discrepancy remains largely unsolved. By this process of "co-evolution", many pathogens developed strategies to elude host defense mechanisms. The difference between these types is mainly in capsular antigens, represented by polysaccharide patterns and branch points. Antibodies against one serotype are of no use against another serotype, although it is always the same organism, coming in a different disguise. A shift in outer appearance to evade immune mechanisms is even better exemplified by the influenza virus. Via the first, hemagglutinin (H), it binds to human cells; the second, neuraminidase (N), is required for the release of new virus particles from a producing cell and possibly also to enter a cell. There are at least 18 different variants of H and 9 of N, which are used to name different isolates, together with location and time of isolation. As soon as these mutations interfere with antibody binding, the slightly altered virus variant has a selective advantage over its peers and quickly spreads in a previously protected human population, causing a new wave of infections. The H-N-type is maintained: for example, isolate A/Syndey/1977/H3N2 drifts to reinvent itself as A/Moscow/1999/H3N2. At the first influenza infection, a child produces antibodies against all antigenic domains of this specific virus subtype. In the event of later infections, efficient antibody responses are only induced against domains that were already part of the first virus. The probable reason is that memory cells stemming from the first encounter with influenza are activated so quickly that the immune system is not able –or does not need to— activate new naive cells. In addition, influenza A viruses are not restricted to humans, but also infect pigs and fowl (chickens, ducks, swans, etc. Some subtypes of influenza A virus circulate mainly in humans, but many others are best adapted to fowl. The danger is a coinfection, be it in a human or a bird, with two influenza virus subtypes that leads to an exchange of genetic material. If that happens, a novel, human-adapted subtype may emerge against which nobody has any useful antibodies, leading to one of the dreaded pandemics. Such a pandemic during the period 1918-1920 took the lives of approximately 30 million people (out of a world population of 1. During the last ten years, the biggest perceived threat was the fowl-adapted influenza A subtype H5N1. First in Hong Kong in 1997, and several times later on in other places, it infected singular human individuals. A H5N1 epidemic in birds spread and reached western Europe in 2005, exposing more and more humans to the virus. Infected individuals contracted H5N1 from massive contact with infected fowl, and in all but a handful of cases did not transmit the virus to other humans. However, the latest pandemic was unexpectedly caused by a different virus which started to spread from Mexico in 2009. Here, the antigen shift mechanism had reassorted genome segments of swine-adapted influenza virus strains with human-adapted segments. The virus was of the H1N1-Type, yet the specific variants of H1 and N1 differed from those which had been around previously. In these young adults, the 1918 H1N1 caused an especially strong inflammatory response; lung alveoli quickly filled with exsudate, causing respiratory failure). Herpes simplex virus first replicates in the epithelial cells of the oral cavity, then infects the afferent neurons of the trigeminal nerve. Cytotoxic T cells quickly eliminate infected epithelial cells in a painful immune reaction, but some viruses go into hiding in the cell bodies of neurons in the trigeminal ganglion. In response to certain changes in exterior conditions, like exposure to sunlight, other infections or hormonal changes, the virus is reactivated by insufficiently understood mechanisms and reinfects the oral epithelium in the form of cold sores.
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