Mark E. Boulware, MD

• Instructor of Medicine
• Division of Cardiology
• University of North Carolina School of Medicine
• Chapel Hill, North Carolina

In a long bone hiv infection rate minnesota order medex mastercard, bone tissue begins to replace hyaline cartilage in the center of the diaphysis symptoms of hiv infection in early stage generic medex 1mg fast delivery. This region is called the primary ossification center hiv infection rates male female purchase medex 1 mg line, and bone develops from it toward the ends of the cartilaginous structure antiviral drugs youtube medex 1mg with mastercard. Meanwhile hiv infection inflammation immunosenescence and aging purchase medex 1mg on-line, osteoblasts from the periosteum deposit compact bone around the primary ossification center hiv infection epidemiology pathogenesis treatment and prevention purchase medex 1mg free shipping. Later, secondary ossification centers appear in the epiphyses, and spongy bone forms in all directions from them. Sheets of embryonic connective tissue (mesenchyme) appear at the sites of future bones. Blood vessels and differentiating osteoblasts from the periosteum invade the disintegrating tissue. The cartilaginous cells of the epiphyseal plate form four layers, each of which may be several cells thick, as shown in figure 7. The first layer, or zone of resting cartilage, is closest to the end of the epiphysis. The second layer of the epiphyseal plate, or zone of proliferating cartilage, includes rows of many young cells undergoing mitosis. As new cells appear and as extracellular matrix forms around them, the cartilaginous plate thickens. The rows of older cells, left behind when new cells appear, form the third layer, or zone of hypertrophic cartilage, enlarging and thickening the epiphyseal plate still more. At the same time, invading osteoblasts, which secrete calcium salts, accumulate in the extracellular matrix adjacent to the oldest cartilage cells, and as the extracellular matrix calcifies, the cartilage cells begin to die. In an (f) adult, when bone growth ceases, an epiphyseal line is what remains of the epiphyseal plate. In time, large, multinucleated cells called osteoclasts (oste-oklasts) break down the calcified matrix. These large cells originate from the fusion of single-nucleated white blood cells called monocytes (see chapter 14, p. Osteoclasts secrete an acid that dissolves the inorganic component of the calcified matrix, and their lysosomal enzymes digest the organic components. After osteoclasts remove the extracellular matrix, bone-building osteoblasts invade the region and deposit bone tissue in place of the calcified cartilage. A long bone continues to lengthen while the cartilaginous cells of the epiphyseal plates are active. However, once the ossification centers of the diaphysis and epiphyses meet and the epiphyseal plates ossify, lengthening is no longer possible in that end of the bone. A developing bone thickens as compact bone is deposited on the outside, just beneath the periosteum. As this compact bone forms on the surface, osteoclasts erode other bone tissue on the inside (fig. The resulting space becomes the medullary cavity of the diaphysis, which later fills with marrow. The bone in the central regions of the epiphyses and diaphysis remains spongy, and hyaline cartilage on the ends of the epiphyses persists throughout life as articular cartilage. If an epiphyseal plate is damaged as a result of a fracture before it ossifies, elongation of that long bone may prematurely cease, or if growth continues, it may be uneven. Surgery may be used on an epiphysis to equalize growth of bones developing at very different rates. Homeostasis of Bone Tissue After the intramembranous and endochondral bones form, the actions of osteoclasts and osteoblasts continually remodel them. Bone remodeling occurs throughout life as osteoclasts resorb bone tissue and osteoblasts replace the bone. These opposing processes of resorption and deposition occur on the surfaces of the endosteum and periosteum. Age 15 to 18 years (females) 17 to 20 years (males) 16 to 21 years (females) 18 to 23 years (males) 21 to 23 years (females) 23 to 25 years (males) By 23 years (females) By 25 years (males) Occurrence Bones of the upper limbs and scapulae completely ossified. Emergency medical technicians immobilized the leg and took Jacob to the emergency department at the nearest hospital, where an X ray indicated a broken tibia. He spent the next six weeks with his leg in a cast, and the bone continued to heal over several months. For example, a break due to injury is a traumatic fracture, whereas one resulting from disease is a spontaneous, or pathologic, fracture. It has the added danger of infection, because microorganisms can enter through the broken skin. A greenstick fracture is incomplete, and the break occurs on the convex surface of the bend in the bone. Repair of a Fracture When a bone breaks, blood vessels in it also break, and the periosteum is likely to tear. Blood from the broken vessels spreads through the damaged area A transverse fracture is An oblique fracture A spiral fracture is and soon forms a hematoma, which is a localized colcomplete, and the break occurs at an angle caused by excessive occurs at a right angle to other than a right angle twisting of a bone. The total mass of bone tissue in an adult skeleton normally remains nearly constant because of the tight regulation of bone remodeling. Factors Affecting Bone Development, growth, and Repair A number of factors influence bone development, growth, and repair. These include nutrition, exposure to sunlight, hormonal 208 uNiT 2 secretions, and physical exercise. For example, vitamin D is necessary for proper absorption of dietary calcium in the small intestine. Without this vitamin, dietary calcium is poorly absorbed and the inorganic salt portion of bone matrix will lack calcium, softening and thereby deforming bones. In children, this condition is called rickets, and in adults, it is called osteomalacia. Vitamin D is scarce in natural foods, except for eggs, but it is readily available in milk and other dairy products fortified with vitamin D. An inactive form of vitamin D also forms when dehydrocholesterol, produced by skin cells or obtained in the diet and carried by the blood to the skin, is exposed to ultraviolet light. If the ends of a broken bone are close together, healing is faster than if they are far apart. Compact bone Medullary cavity (filled with yellow marrow) Hematoma Periosteum Fibrocartilage forming the soft callus Spongy bone New blood vessels (a) Blood escapes from ruptured blood vessels and forms a hematoma. Compact bone Medullary cavity (filled with yellow marrow) Periosteum Hard (bony) callus (c) A hard (bony) callus replaces the fibrocartilage. This inactive form of vitamin D is then processed in the liver and kidneys to become the active form of vitamin D. Vitamin A is necessary for osteoblast and osteoclast activity during normal development. Osteoblasts cannot produce enough collagen in the extracellular matrix of the bone tissue, and as a result, bones are abnormally slender and fragile. The pituitary gland secretes growth hormone, which stimulates division of cartilage cells in the epiphyseal plates. If too little growth hormone is secreted, the long bones of the limbs fail to develop normally, and the child has pituitary dwarfism. If excess growth hormone is released before the epiphyseal plates ossify, height may exceed 8 feet-a condition called pituitary gigantism. In an adult, secretion of excess growth hormone causes acromegaly, in which the hands, feet, and jaw enlarge (see chapter 13, p. The thyroid hormone thyroxine stimulates replacement of cartilage in the epiphyseal plates of long bones with bone tissue. This hormone increases cellular metabolism, including stimulating osteoblast activity. In contrast to the bone-forming activity of thyroid hormone, parathyroid hormone stimulates an increase in the number and activity of osteoclasts, which break down bone (see chapter 13, pp. Support, Protection, and Movement Bones give shape to structures such as the head, face, thorax, and limbs. Bones of the rib cage and shoulder girdle protect the heart and lungs, whereas bones of the pelvic girdle protect the lower abdominal and internal reproductive organs. Both male and female sex hormones (called testosterone and estrogens, respectively) from the testes and ovaries promote formation of bone tissue. Beginning at puberty, these hormones are abundant, causing the long bones to grow considerably (see chapter 22, pp. However, sex hormones also stimulate ossification of the epiphyseal plates, and consequently they stop bone lengthening at a relatively early age. The effect of estrogens on the epiphyseal plates is somewhat stronger than that of testosterone. For this reason, females typically reach their maximum heights earlier than males. For example, when skeletal muscles contract, they pull at their attachments on bones, and the resulting stress stimulates the bone tissue to thicken and strengthen (hypertrophy). Conversely, with lack of exercise, the same bone tissue becomes thinner and weaker. This condition, called atrophy, is why the bones of athletes are usually stronger and heavier than those of nonathletes (fig. Blood Cell Formation the process of blood cell formation, called hematopoiesis (hemah-to-poi-esis), or hemopoiesis, begins in the yolk sac, which lies outside the embryo (see chapter 23, p. Later in development, blood cells are manufactured in the liver and spleen, and still later, they form in bone marrow. Marrow is a soft, netlike mass of connective tissue in the medullary cavities of long bones, in the irregular spaces of spongy bone, and in the larger central canals of compact bone tissue. In red marrow, red blood cells (erythrocytes), white blood cells (leukocytes), and blood platelets form. The color comes from the red, oxygen-carrying pigment hemoglobin in red blood cells. In an infant, the cavities of most bones house red marrow, but with time, yellow marrow replaces much of it. In an adult, red marrow is primarily found in the spongy bone of the skull, ribs, sternum, clavicles, vertebrae, and hip bones. Bone marrow transplants have been used for more than half a century to enable people with certain cancers to tolerate high levels of chemotherapy drugs. Stem cells from the umbilical cord of a newborn can be used in place of bone marrow and are less likely to stimulate an immune response in the recipient. If all goes well, the donor cells travel to the spaces within bones that red marrow normally occupies, where they replenish the blood supply with healthy cells. Safer than a bone marrow transplant for some conditions is an autologous ("self") stem cell transplant. The details of the homeostatic mechanism that controls calcium levels in the blood are in chapter 13, pp. In addition to storing calcium and phosphorus (as calcium phosphate), bone tissue contains smaller amounts of magnesium, sodium, potassium, and carbonate ions. Bones also accumulate certain harmful metallic elements such as lead, radium, and strontium, which are not normally present in the body but are sometimes accidentally ingested. The salts account for about 70% of the extracellular matrix by weight and are mostly small crystals of a type of calcium phosphate called hydroxyapatite. The human body requires calcium for a number of vital metabolic processes, including muscle cell contraction, nerve cell conduction, and blood clot formation. When the blood is low in calcium, parathyroid hormone stimulates osteoclasts to break down bone tissue, releasing calcium salts from the extracellular matrix into the blood. Very high blood calcium inhibits osteoclast activity, and calcitonin from the thyroid gland stimulates osteoblasts to form bone tissue, storing excess calcium in the extracellular matrix (fig. Hormonal regulation of bone calcium Q What three components of a homeostatic mechanism (see fig. Before age thirty, cells that form new bone counter cells that degrade it, so that living bone is in a constant state of remodeling. Fragility fractures occur in more than 2 million people in the united States each year, yet despite this warning sign, only onefourth to one-third of them are followed up with bone scans and treatment to build new bone tissue. Screening is advised for all individuals over age sixty-five, as well as for those with risk factors. Divisions of the Skeleton For purposes of study, it is convenient to divide the skeleton into two major portions-an axial skeleton and an appendicular skeleton (fig. The axial skeleton consists of the bony and cartilaginous parts that support and protect the organs of the head, neck, and trunk. The hyoid (hioid) bone is located in the neck between the lower jaw and the larynx (fig. It does not articulate with any other bones but is fixed in position by muscles and ligaments. The hyoid bone supports the tongue and is an attachment for certain muscles that help move the tongue during swallowing. The vertebral column, or spinal column, consists of many vertebrae separated by cartilaginous intervertebral discs. For example, the flat bones of the skull usually grow together and tightly join along irregular lines called sutures. In some people, extra bones called sutural bones (wormian bones) develop in these sutures (fig.

In figure on right hiv infection rates japan order medex no prescription, a later stage in the growth of the secondary follicle is shown xl dol antiviral generic 5mg medex otc. The two larger hiv infection rate japan order medex from india, more advanced follicles do not display the remains of a zona pellucida antiviral innate immunity purchase medex 1 mg free shipping, but they do display other features of follicular atresia hiv infection rate in south africa order medex 5 mg overnight delivery. In atresia of a more advanced follicle early hiv symptoms chest infection discount 5mg medex mastercard, the follicular cells tend to degenerate more rapidly than the cells of the theca interna, and the basement membrane separating the two becomes thickened to form a hyalinized membrane, the glassy membrane. Thus, the glassy membrane (arrows) separates an outer layer of remaining theca interna cells from the degenerating inner follicular cells. Note that even though the atresia in these follicles is well-advanced, some of the cells external to one of the glassy membranes still retain their epithelioid character (arrowhead). The cells of the corpus luteum, luteal cells, rapidly increase in size and become filled with lipid droplets. A lipid-soluble pigment in the cytoplasm of the cells, lipochrome, gives them their yellow appearance in fresh tissue. Electron micrographs of the luteal cells demonstrate that they have features typical of steroid-secreting cells, namely, abundant smooth endoplasmic reticulum and mitochondria with tubular cristae. Two types of luteal cells are identified: Large, centrally located granulosa lutein cells are derived from the granulosa cells; smaller, peripherally located theca lutein cells are derived from the theca interna. A rich vascular network is established in the corpus luteum into which progesterone and estrogen are secreted by the lutein cells. These hormones stimulate growth and differentiation of the uterine endometrium to prepare it for implantation of a fertilized ovum. The plication of the membrana granulosa begins just before ovulation and continues as the corpus luteum develops. As the corpus luteum becomes more plicated, the former follicular cavity becomes reduced in size. Cells of the theca interna follow the blood vessels into the outermost depressions of the plicated structure. These theca interna cells become transformed into cells of the corpus luteum called theca lutein cells. Keep in mind that the theca interna was derived from the connective tissue stroma of the ovary. The same arrangement of cells is shown in figure on the right at much higher magnification. The cytoplasm contains yellow pigment (usually not evident in routine H&E sections), hence the name, corpus luteum. Thus, when identifying the two cell types, aside from location, note that the nuclei of adjacent theca lutein cells generally appear to be closer to each other than nuclei of adjacent granulosa lutein cells. The changes whereby the ruptured ovarian follicle is transformed into a corpus luteum occur under the influence of pituitary luteinizing hormone. In turn, the corpus luteum itself secretes progesterone, which has a profound effect on the estrogen-primed uterus. If pregnancy occurs, the corpus luteum remains functional; if pregnancy does not occur, the corpus luteum regresses after having reached a point of peak development, roughly 2 weeks after ovulation. The regressing cellular components of the corpus luteum are replaced by fibrous connective tissue, and the structure is then called a corpus albicans. The oviduct undergoes cyclical changes along with those of the uterus, but these are not nearly as pronounced. The epithelial cells increase in height during the middle of the cycle, just about the time the ovum will be passing through the tube, and become reduced during the premenstrual period. Not only does the number of ciliated cells increase during the follicular phase of the ovarian cycle but also removal of the ovaries leads to atrophy of the epithelium and loss of ciliated cells. The mucosal folds are evident in its distal portion, the infundibulum, as it nears the open end. The infundibulum leads proximally to the ampulla, which constitutes about two-thirds of the length of the oviduct, has the most numerous and complex mucosal folds, and is the site of fertilization. Mucosal folds are least numerous at the proximal end of the oviduct, near the uterus, where the tube is narrow and referred to as the isthmus. A uterine or intramural portion measures about 1 cm in length and passes through the uterine wall to empty into the uterine cavity. For the first several days of development, as it navigates the complex pathway created by the mucosal folds, the embryo is transported proximally by the beating of the cilia of the ciliated epithelial cells and by peristaltic contractions of the well-developed muscularis layer that underlies the mucosa. Many mucosal folds project into the lumen (L), and the complicated nature of the folds is evident by the variety of profiles that is seen. In addition to the mucosa (Muc), the remainder of the wall consists of a muscularis (Mus) and connective tissue. The muscularis consists of smooth muscle that forms a relatively thick layer of circular fibers and a thinner outer layer of longitudinal fibers. The area enclosed by the rectangle in figure above is shown here at higher magnification. The ciliated cells are readily identified by the presence of well-formed cilia (C). The character of the connective tissue is essentially the same from the epithelium to the muscularis, and for this reason, no submucosa is described. The uterine wall is composed of a mucosa, referred to as the endometrium; a muscularis, referred to as a myometrium; and, externally, a serosal cover, the perimetrium. The myometrium consists of smooth muscle and connective tissue and contains the large blood vessels that give rise to the vessels that supply the endometrium. The uterus undergoes cyclical changes that are largely manifested by changes that occur in the endometrium. If implantation of an ovum does not occur after preparation for this event, the state of readiness is not maintained, and much of the endometrium degenerates and is sloughed off, constituting the menstrual flow. The part of the endometrium that is lost is referred to as the stratum functionale; the part that is retained is called the stratum basale. The stratum basale is the deeper part of the endometrium and adjoins the myometrium. In the nonpregnant uterus, the smooth muscle cells are about 50 m in length; during pregnancy, they undergo enormous hypertrophy, often reaching more than 500 m in length. In addition, new muscle fibers develop after division of existing muscle cells and division and differentiation of undifferentiated mesenchymal cells. Fibroblasts increase by division and secrete additional collagen and elastic fibers. Collagen secreted during pregnancy is digested by the very cells that secreted it, the fibroblasts. Similar, but less pronounced, proliferation and degeneration of fibroblasts and collagen occur in each menstrual cycle. The area inscribed in the upper small rectangle is shown at higher magnification in the inset on the right. The endometrium is relatively thin at this phase and over half of it consists of the stratum basale. The area inscribed by the lower small rectangle, located in the region of the stratum basale, is shown at higher magnification in the inset in figure below. The glandular epithelium of the deep portion of the glands is similar to that of the endometrial surface. Under the influence of estrogen, the various components of the endometrium proliferate (proliferative phase), so that the total thickness of the endometrium is increased. This hormone brings the endometrium to a state of readiness for implantation, and as a consequence of its actions, the thickness of the endometrium increases further. There are conspicuous changes in the glands, primarily in the stratum functionale, where the glands take on a more pronounced corkscrew shape and secrete mucus that accumulates in sacculations along their length. The vasculature of the endometrium also proliferates and degenerates in each menstrual cycle. Radial arteries enter the stratum basale of the endometrium from the myometrium and give rise to small, straight arteries that supply the stratum basale and continue into the endometrium to become the highly coiled spiral arteries. The distal portion of the spiral arteries and the arterioles are sloughed with the stratum functionale during menstruation. Alternating contraction and relaxation of the basal portions of the spiral arteries prevent excessive blood loss during menstruation. The uterine glands have been cut in a plane that is close to their long axes, and one gland (arrow) is seen opening at the uterine surface. Except for a few glands near the center of the figure that resemble those of the proliferative phase, most of the glands (Gl) in this figure, including those that are labeled, show numerous shallow sacculations that give the profile of the glandular epithelium a serrated appearance. It is seen most advantageously in areas where the plane of section is close to the long axis of the gland. In contrast to the characteristic sinuous course of the glands in the stratum functionale, glands of the stratum basale more closely resemble those in the proliferative phase. They are not oriented in any noticeable relationship to the uterine surface, and many of their long profiles are even parallel to the plane of the surface. This slightly higher magnification view of the stratum functionale shows essentially the same characteristics of the endometrial glands (Gl) described above; it also shows other modifications that occur during the secretory phase. The increase in endometrial thickness because of edema is reflected by the presence of empty spaces between cells and other formed elements. Thus, many areas of this figure, especially the area within and near the rectangle, show histologic signs of edema. In addition, in this phase, the glandular epithelial cells begin to secrete a mucoid fluid that is rich in glycogen. Typically, the glands of the secretory endometrium are more dilated than those of the proliferative endometrium. The rectangle in this figure highlights two glands that are shown at higher magnification in the inset. The mucoid character of the substance within one of the glands can be surmised from its blue staining. Although not evident in routine H&E paraffin sections, the epithelial cells also contain glycogen during the secretory phase and as mentioned above, this becomes part of the secretion. The arrowheads indicate stromal cells; some of these cells undergo enlargement late in the secretory phase. The cervical canal traverses the cervix and provides a channel connecting the vagina and the uterine cavity. The structure of the cervix resembles the rest of the uterus in that it consists of a mucosa (endometrium) and a myometrium. The endometrium of the cervix does not undergo the cyclical growth and loss of tissue that is characteristic of the body and fundus of the uterus. Rather, the amount and character of the mucus secretion of its simple columnar epithelium vary at different times in the uterine cycle under the influence of the ovarian hormones. At midcycle, there is a 10-fold increase in the amount of mucus produced; this mucus is less viscous and provides a favorable environment for sperm migration. At other times in the cycle, the mucus restricts the passage of sperm into the uterus. It consists of interweaving bundles of smooth muscle cells in an extensive, continuous network of fibrous connective tissue. The portion of the cervix that projects into the vagina, the vaginal part or ectocervix, is represented by the upper two-thirds of top figure. The plane of section in both figures passes through the long axis of the cervical canal, which is narrowed and cone shaped at its two ends. The upper end, the internal os, communicates with the uterine cavity, and the lower end, the external os (Os), communicates with the vagina. The two rectangles in upper figure delineate representative areas of the mucosa that are shown at higher magnification in upper right and middle right figures, respectively. They secrete a mucus substance into the cervical canal that serves to lubricate the vagina. In other respects, the epithelium has the same general features as the vaginal epithelium. Another similarity is that the epithelial surface of the ectocervix undergoes cyclical changes similar to those of the vagina in response to ovarian hormones. The lower rectangle in top left figure marks this site, known as the transformation zone, which is shown at higher magnification here. Note the abrupt change in the epithelium at the transformation zone as well as the large number of lymphocytes present in this region. This figure shows, at high magnification, portions of the cervical gland identified in the rectangle in figure on left. Note the tall epithelial cells and the lightly staining supranuclear cytoplasm, a reflection of the mucin dissolved out of the cell during tissue preparation. The crowding and the change in shape of the nuclei (asterisk) seen at the upper part of one of the glands in this figure are due to a tangential cut through the wall of the gland as it passed out of the plane of section. After birth, the placenta separates from the wall of the uterus and is discharged along with the contiguous membranes of the amniotic cavity. It contains two arteries that carry blood from the fetus to the placenta and a vein that returns blood from the placenta to the fetus. These are arranged as two layers, an inner longitudinal layer and an outer circular layer. Elastic lamellae are poorly developed in these vessels and, indeed, may be absent. The umbilical vein is similar to the arteries, also having a thick muscular wall arranged as an inner longitudinal and an outer circular layer. A section extending from the amniotic surface into the substance of the placenta is shown here. The amnion consists of a layer of simple cuboidal epithelium and an underlying layer of connective tissue.

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Therefore antiviral pills discount medex 5 mg without a prescription, the concentrations of these substances in body fluids are of special importance hiv infection in zimbabwe order genuine medex. Hydrogen ion concentration can be measured in grams of ions per liter of solution hiv infection rate colombia discount medex 5mg with visa. However anti viral hand sanitizer purchase medex line, because hydrogen ion concentration can vary over a wide range (gastric juice has 0 hiv infection cold symptoms cheap 1 mg medex with amex. This system tracks the number of decimal places in a hydrogen ion concentration without writing them out antiviral yify buy generic medex online. Each whole number on the pH scale, which extends from 0 to 14, represents a tenfold difference in hydrogen ion concentration. For example, Many bases are present in body fluids, but because of the way bases react in water, the concentration of hydroxide ions is a good estimate of the total base concentration. The concentrations of hydrogen ions and hydroxide ions in body fluids are always in balance such that if one increases, the other decreases, and vice versa. Solutions with fewer hydrogen ions than hydroxide ions are basic (alkaline); they have pH values greater than 7. Because the pH of blood is normally slightly alkaline, we need terms other than acidic and alkaline to refer to abnormal blood pH. This can be caused by breathing rapidly at high altitudes, taking too many antacids, high fever, anxiety, or mild to moderate vomiting that rids the body of stomach acid. This condition can result from severe vomiting that empties the alkaline small intestinal contents, diabetes, brain damage, impaired breathing, and lung and kidney disease. They combine with hydrogen ions when these ions are in excess, or they donate hydrogen ions when these ions are depleted. Many organic compounds dissolve in water, but most dissolve in organic liquids such as ether or alcohol. Most organic compounds that dissolve in water do not release ions and are therefore called nonelectrolytes. Inorganic Substances Common inorganic substances in cells include water, oxygen, carbon dioxide, and inorganic salts. Water Water (H2O) is the most abundant compound in living material and accounts for about two-thirds of the weight of an adult human. It is the major component of blood and other body fluids, including fluids in cells. When substances dissolve in water, the polar water molecules separate molecules of the substance, or even dissociate them into ions. Blood, which is mostly water, carries oxygen, sugars, salts, vitamins, and other vital substances from organs of the digestive and respiratory systems to cells. Blood also carries waste materials, such as carbon dioxide and urea, from cells to the lungs and kidneys, respectively, which remove them from the blood and release them outside the body. Blood brings heat released from muscle cells during exercise from deeper parts of the body to the surface. At the body surface, skin cells secrete water as part of sweat that can release heat by evaporation. The body regularly gains and loses water, but it must be present in the correct concentration in the extracellular fluid, to maintain homeostasis. A continuing supply of oxygen is necessary for cell survival and, ultimately, for the survival of the organism. It is a waste product of the release of energy during certain metabolic reactions. There, the chemical reactions reverse, and carbon dioxide gas is produced and is then exhaled. Co is a colorless, odorless, gas that is deadly when it leaks from home heating systems or exhaust pipes in closed garages. Co functions in the spleen, which recycles old red blood cells, and in the parts of the brain that control memory, smell, and vital functions. These ions play important roles in metabolism, helping to maintain proper water concentrations in body fluids, controlling pH, blood clotting, bone development, energy transfer in cells, and muscle and nerve functions. The body regularly gains and loses these electrolytes, but they must be present in certain concentrations, in the extracellular fluid, to maintain homeostasis. Such a condition, where gains and losses are equal, is called electrolyte balance. They also supply materials to build certain cell structures and they often are stored as reserve energy supplies. Carbohydrates are water-soluble molecules that include atoms of carbon, hydrogen, and oxygen. Most of these molecules have twice as many hydrogen as oxygen atoms, which is the ratio of hydrogen to oxygen in water molecules (H2O). This ratio is easy to see in the molecular formulas of the carbohydrates glucose (C6H12O6) and sucrose (C12H22O11). Monosaccharides include the five-carbon sugars ribose and deoxyribose, as well as the six-carbon sugars glucose, dextrose (a form of glucose), fructose, and galactose (fig. It is considered to be dietary fiber, passing through the gastrointestinal tract without being broken down and absorbed into the bloodstream. Starch molecules consist of highly branched chains of glucose molecules connected differently than in cellulose. Humans synthesize a polysaccharide similar to starch called glycogen, which is stored in the liver and skeletal muscles. Its molecules also are branched chains of sugar units; each branch consists of up to a dozen glucose units. Lipids include a number of compounds, such as fats, phospholipids, and steroids, that have vital functions in cells and are important constituents of cell membranes (see chapter 3, p. The most abundant lipids are the fats, primarily used to supply energy for cellular activities. Fat molecules can supply more energy gram for gram than can carbohydrate molecules. Like carbohydrates, fat molecules are composed of carbon, hydrogen, and oxygen atoms. The formula for the fat tristearin, C57H110O6, illustrates these characteristic proportions. The building blocks of fat molecules are fatty acids (fate asidz) and glycerol (gliser-ol). Although the glycerol portion of every fat molecule is the same, there are many types of fatty acids and, therefore, many types of fats. Fatty acids differ in the lengths of their carbon atom chains, which usually have an even number of carbon atoms. This type of fatty acid is called a saturated fatty acid; that is, each carbon atom binds as many hydrogen atoms as possible and is thus saturated with them. In contrast, the chains of unsaturated fatty acids have one or more double bonds between carbon atoms. Fatty acids with one double bond are called monounsaturated fatty acids, and those with two or more double bonds are polyunsaturated fatty acids (fig. A glycerol molecule combines with three fatty acid molecules to form a single fat molecule, or triglyceride (figs. The fatty acids of a triglyceride may have different lengths and degrees of saturation, making the fats very diverse. Fat molecules that have only saturated fatty acids are called saturated fats (satu-rated fatz), and those that have unsaturated fatty acids are called unsaturated fats (unsatu-rated fatz). Unsaturated fats are in foods that are liquid at room temperature, such as soft margarine and seed oils (corn, grape, sesame, soybean, sunflower, and peanut). Coconut and palm kernel oils are unusual in that they are high in saturated fats but are liquids at room temperature. Manufacturers add hydrogen atoms to certain vegetable oils to make them harder and easier to use. The fact that phospholipids are both attracted to and repelled by water allows them to form biological membranes, discussed in chapter 3 (pp. Steroid molecules are complex structures that include connected rings of carbon atoms (fig. Among the more important steroids are: cholesterol, found in all body cells and used to synthesize other steroids; sex hormones, such as estrogen, progesterone, and testosterone; and several hormones from the adrenal glands. Some are structural materials, energy sources, and chemical messengers (hormones). Other proteins combine with carbohydrates (forming glycoproteins) and function as receptors on cell surfaces, allowing cells to respond to specific types of molecules that bind to them. Antibody proteins recognize and destroy substances foreign to the body, such as certain molecules on the surfaces of infecting bacteria. Proteins such as hemoglobin and myoglobin carry oxygen in the blood and muscles, A phospholipid molecule is similar to a fat molecule in that it includes a glycerol and fatty acid chains. The phospholipid, however, has only two fatty acid chains and, in place of the third, has a portion containing a phosphate group (fig. The "R group", or the "rest of the molecule," varies and is what makes each type of amino acid unique. Many proteins play vital roles in metabolism as enzymes (enzi mz), which are catalysts in living systems. This central carbon is bonded to a hydrogen atom and to another group of atoms called a side chain or R group ("R" may be thought of as the "Rest of the molecule"). The composition of the R group distinguishes one type of amino acid from another (fig. Proteins have complex three-dimensional shapes, called conformations, yet they are assembled from simple chains of amino acids connected by peptide bonds. These are covalent bonds that link the amino end of one amino acid with the carboxyl end of another. Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. The primary structure may range from fewer than 100 to more than 5,000 amino acids. Hemoglobin, actin, and an antibody protein have very different amino acid sequences. Three-dimensional folding (d) Quaternary structure-Two or more proteins, often different, may combine to form a single, larger protein molecule. Recall that polar molecules result when electrons are not shared equally in certain covalent bonds. In amino acids, this unequal sharing results in slightly negative oxygen and nitrogen atoms and slightly positive hydrogen atoms. Hydrogen bonding between oxygen and hydrogen atoms in different parts of the polypeptide chain determines the secondary structure. Depending on the sequence of amino acids, a single very long polypeptide may include helices, sheets, and less common shapes with such colorful names as zippers, hairpins, loops, and fingers. Hydrogen bonding and even covalent bonding between atoms in different parts of a polypeptide can impart another, larger level of folding, the tertiary structure (fig. The points of attachment in the tertiary structure are farther apart along the amino acid sequence than are the attachments that form the secondary structure. Some proteins are long and fibrous, such as the keratins that form hair and the threads of fibrin that knit a blood clot. For some proteins, slight reversible changes in conformation are part of their normal functions. For example, some of the proteins that interact to contract muscle exert a pulling force as a result of such a shape change, leading to movement. Because the primary structure (amino acid sequence) remains, sometimes the protein can regain its shape when normal conditions return. High temperature, radiation, pH changes, and certain chemicals (such as urea) can denature proteins. A familiar example of irreversible protein denaturation is the response of the protein albumin to heat. The chemicals first break apart the tertiary structure formed when sulfur-containing amino acids attract each other within keratin molecules. When the chemicals are washed out of the set hair, the sulfur bonds reform, but in different places. Chapter 21 describes the homeostatic mechanisms for maintaining the pH of the internal environment. In some proteins, several polypeptide chains are connected in a fourth level, or quaternary structure, to form a very large molecule (fig. The amino acid sequence and interactions among the amino acids in a protein determine the conformation. Thus, it is the amino acid sequence of a protein that determines its function in the body. Nucleic acids (nu-kleik asidz) carry the instructions, in the form of genes (see chapter 4, p. Nucleic acids the very large and complex nucleic acids include atoms of carbon, hydrogen, oxygen, nitrogen, and phosphorus, which form building blocks called nucleotides (nukle-o-ti dz). Each nucleotide consists of a 5-carbon sugar (ribose or deoxyribose), a phosphate group, and one of several nitrogen-containing organic bases, called nitrogenous bases (fig. Dna chains are held together by hydrogen bonds (dotted lines) and they twist, forming a double helix.

The nervous system produces at least 100 different types of neurotransmitters in the brain alone hiv infection of dendritic cells generic 5mg medex otc. Calcium ions diffuse into synaptic knobs in response to action potentials naproxen antiviral purchase medex 1 mg amex, releasing neurotransmitters hiv infection rates caribbean medex 5mg with visa. A neuron is facilitated when it receives subthreshold stimuli and becomes more excitable antiviral foods list order medex 5mg. Divergence allows a single neuron reaching threshold to have potentially widespread effects hiv infection rate oral buy medex 1mg. Why are rapidly growing cancers that originate in nervous tissue more likely to be composed of neuroglia than of neurons When motor nerve fibers in the spinal cord are severed quercetin antiviral order medex, the muscles they control become permanently paralyzed. From this information, suggest a neurotransmitter imbalance that lies behind alzheimer disease. In tay-Sachs disease, an infant rapidly loses nervous system functions as neurons in the brain become covered in too much myelin. People who inherit familial periodic paralysis often develop very low blood potassium concentrations. How would you explain that the paralysis may disappear quickly when potassium ions are administered intravenously When motor nerve fibers in the leg are severed, the muscles they innervate become paralyzed; however, in time, control over the muscles often returns. Connect Integrated Activity Can you assist a neurology patient in understanding the actions of drugs that alter neuron function and impulse conduction Anatomy & Physiology revealed go more in depth into the functioning of the human body by viewing animations on synapses and action potentials. Yet, the nervous system can process a wide variety of information from the external environment, including sight, sounds, and touch on the surface of the skin. The nervous system can also interpret information from receptors that sense changes in the internal environment and can activate effectors to correct those changes. Among the most fascinating aspects of nervous system function are the abilities of the brain to store memories and to process conscious thought. All of these things are accomplished by neurons working in much the same way, but serving different functions within the brain, the spinal cord, or the peripheral nerves. This is the chapter in which your brain gets to learn about itself and the other parts of the nervous system! It oversees many aspects of physiology, such as sensation and perception, movement, and thinking. The brain includes the two cerebral hemispheres, the diencephalon, the brainstem, and the cerebellum, all described in detail in section 11. The brain contains about one hundred billion (1011) multipolar neurons as well as countless branches of the axons by which these neurons communicate with each other and with neurons elsewhere in the nervous system. In the brain, the outer layers of the cerebral hemispheres and cerebellum are largely gray matter. White matter, representing interconnecting axons, is found deeper, with islands of gray matter located throughout. In the spinal cord, in contrast, gray matter (the cell bodies of neurons) is found more centrally, with white matter more peripheral and consisting of axons extending up to the brain or down from the brain. The brain lies in the cranial cavity of the skull, and the spinal cord occupies the vertebral canal in the vertebral column. Beneath these bony coverings, membranes called meninges, located between the bone and the soft tissues of the nervous system, protect the brain and spinal cord (fig. It attaches to the inside of the cranial cavity and forms the internal periosteum of the surrounding skull bones (see reference plate 13, p. In some regions, the dura mater extends inward between lobes of the brain and forms supportive and protective partitions (table 11. In other areas, the dura mater splits into two layers, forming channels called dural sinuses, shown in figure 11. Venous blood flows through these channels as it returns from the brain to vessels leading to the heart. The dura mater continues into the vertebral canal as a strong, tubular sheath that surrounds the spinal cord. It is attached to the cord at regular intervals by a band of pia mater (denticulate ligaments) that extends the length of the spinal cord on either side. The dural sheath terminates as a blind sac at the level of the second sacral vertebra, below the end of the spinal cord. The sheath around the spinal cord is not attached directly to the vertebrae but is separated by an epidural space, which lies between the dural sheath and the bony walls (fig. This space contains blood vessels, loose connective tissue, and adipose tissue that pad the spinal cord. A blow to the head may rupture some blood vessels associated with the brain, and the escaping blood may collect beneath the dura mater. This condition, called subdural hematoma, can increase pressure between the rigid bones of the skull and the soft tissues of the brain. Unless the accumulating blood is promptly evacuated, compression of the brain may lead to functional losses or even death. The arachnoid mater is a thin, weblike membrane that does not have blood vessels and is located between the dura and pia maters. It spreads over the brain and spinal cord but generally does not dip into the grooves and depressions on their surfaces. The fluid protects the brain and spinal cord by absorbing forces that might otherwise jar and damage their delicate tissues. The pia mater is thin and contains many nerves, as well as blood vessels that nourish the underlying cells of the brain and spinal cord. The pia mater is attached to the surfaces of these organs and follows their irregular contours, passing over the high areas and dipping into the depressions. A visit from an occupational therapist greatly improved both his independence and his spirit. The occupational therapist showed the man how to continue to use a bathroom sink by supporting his weight on his arms, and how to use mirrors to compensate for his neck stiffness. The therapist was comforting and practical as he showed the man how to repurpose metal salad tongs to hold toilet paper to care for his bathroom needs. An occupational therapist helps a person maintain normal activities while struggling with a disease, injury, disability, or other limitation. The therapist may also instruct family members and caregivers on how to assist the patient. More than 5 million people have such injuries, which are classified as mild, mild repetitive, or severe. Its effects are more psychological than neurological, and it does not appear to cause lasting damage. Symptoms include disturbed sleep, ringing in the ears, memory lapse, balance problems, irritability, and sensitivity to light and sound. The first report of the condition in a medical journal appeared in 2005, regarding a player for the National Football League, but in the 1980s cThe was recognized in boxers and wrestlers, in whom it was called "punch-drunk syndrome" and "dementia pugilistica. They include depression, impulsive and erratic behavior, headaches, dizziness, memory loss, dementia, and loss of executive function (ability to process information and make decisions). These difficulties stem from mechanical trauma to the cortex, hematomas (bleeding) in the subcortex, vasospasm, ischemia, and sudden movement of the skull, which tears axons. The brains of people who have died with cThe show changes characteristic of Alzheimer disease. Studies of cThe in football players who wear helmets with sensors to record the forces applied to their brains show that a college football player receives on average 950 hits to the head in a season (fig. The brain is initially jolted forward at a force exceeding 1,600 feet per second, and then is hit again as air in the cranium rushes forward. A problem in treating blast-related brain injury is recognizing it swiftly, because symptoms may not appear until hours after the violent event. Whereas one soldier immediately after the blast might be blind or deaf or unable to move or speak, another soldier who has suffered similar injuries to the soft tissue of the brain might not show such effects until later. Studies on veterans of the Vietnam War indicate injury-related cognitive decline years after the injury. The first ventricle is in the left cerebral hemisphere and the second ventricle is in the right cerebral hemisphere. This ventricle communicates with the lateral ventricles through openings (interventricular foramina) in its anterior end. Lateral ventricle Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle To central canal of spinal cord (a) Interventricular foramen Lateral ventricle Third ventricle Cerebral aqueduct Ventricles in the brain. Most of the fluid circulates through the ventricles and enters the subarachnoid space, and is reabsorbed into the blood of the dural sinuses through arachnoid granulations. This ventricle is continuous with the central canal of the spinal cord and has openings in its roof that lead into the subarachnoid space of the meninges. Choroid plexuses are tiny, reddish, cauliflower-like masses of specialized capillaries from the pia mater, covered by a single layer of specialized ependymal cells (see chapter 10, pp. The wall of the anterior portion of the forebrain gives rise to the cerebrum and basal nuclei, whereas the posterior portion forms a section of the brain called the diencephalon. The region the midbrain produces continues to be called the midbrain in the adult structure, and the hindbrain gives rise to the cerebellum, pons, and medulla oblongata (fig. Together, the midbrain, pons, and medulla oblongata comprise the brainstem (branstem), which attaches the brain to the spinal cord. In the embryo and fetus, the brain overgrows, and then apoptosis (programmed cell death) destroys excess cells. Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain) Neural tube (a) 11. It issues motor commands to skeletal muscles and carries on higher mental functions, such as memory and reasoning. The brain also contains neural centers and pathways that coordinate muscular movements, and others that regulate visceral activities. In addition to overseeing the function of the entire body, the brain is responsible for characteristics such as personality. Telencephalon Diencephalon Mesencephalon Metencephalon the term "muscle fi ber" refers to an entire skeletal muscle cell, as discussed in chapter 9 (p. The term "fiber" is also used in discussing the nervous system, but here it does not refer to an entire cell. Myelencephalon Neural tube (b) Brain Development the basic structure of the brain reflects the way it forms during early (embryonic) development. The portion that becomes the brain has three major cavities, or vesicles, at one end-the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon) (fig. Later, the forebrain divides into anterior and posterior portions (telencephalon and diencephalon, respectively), and the hindbrain partially divides into two parts (metencephalon and myelencephalon). The resulting five cavities persist in the mature brain as the fluid-filled ventricles and the tubes that connect them. Cells of the tissue surrounding the spaces differentiate into the structural and functional regions of the brain. A physician inserts a fine, hollow needle into the subarachnoid space between the third and fourth or between the fourth and fifth lumbar vertebrae-below the end of the spinal cord (fig. An instrument called a manometer measures the pressure of the fluid, which is usually about 130 millimeters of water (10 millimeters of mercury). A temporary drain inserted into the subarachnoid space between the fourth and fifth lumbar vertebrae can relieve pressure. In a fetus or infant whose cranial sutures have not yet united, increasing IcP may enlarge the cranium, causing hydrocephalus, or "water on the brain" (fig. A shunt to relieve hydrocephalus drains fluid away from the cranial cavity and into the digestive tract, where it is either reabsorbed into the blood or excreted. It is bordered posteriorly by a central sulcus (fissure of Rolando), which passes out from the longitudinal fissure at a right angle, and inferiorly by a lateral sulcus (fissure of Sylvius), which exits the undersurface of the brain along its sides. The parietal lobe is posterior to the frontal lobe and is separated from it by the central sulcus. The temporal lobe lies inferior to the frontal and parietal lobes and is separated from them by the lateral sulcus. The occipital lobe forms the posterior portion of each cerebral hemisphere and is separated from the cerebellum by a shelflike extension of dura mater called the tentorium cerebelli. The insula (island of Reil) is a lobe deep within the lateral sulcus and is so named because it is covered by parts of the frontal, parietal, and temporal lobes. The cerebral cortex contains nearly 75% of all the neuron cell bodies in the nervous system. Just beneath the cerebral cortex is a mass of white matter that makes up the bulk of the cerebrum. This mass contains bundles of myelinated axons that connect neuron cell bodies of the cortex with other parts of the nervous system. Some of these fibers pass from one cerebral hemisphere to the other by way of the corpus callosum, and others carry sensory or motor impulses from the cortex to areas of gray matter deeper in the brain or to the spinal cord. Lateral ventricles Third ventricle cerebrum Basal nuclei Thalamus Hypothalamus Posterior pituitary gland Pineal gland Midbrain Midbrain (mesencephalon) Hindbrain (rhombencephalon) Anterior portion (metencephalon) Posterior portion (myelencephalon) cerebral aqueduct Fourth ventricle Fourth ventricle cerebellum, pons Medulla oblongata other (fig. A broad, flat bundle of axons called the corpus callosum connects the cerebral hemispheres. The pattern of these elevations and depressions is complex, but, despite individual variations, is similar in all normal brains.